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Science Library!

DESCRIPTIVE MINERALOGY

DESCRIPTIVE
MINERALOGY

WILLIAM SHIRLEY BAYLEY, Ph.D.

FBOFBSSOB OP OEOLOOT, UNIVBR8ITT OF ILLINOIS
AUTHOR OF "ELEMENTABT CRT8TALLOOBAPHT "

WITH TWO HUNDBED AND SIXTY-EIGHT ILLUSTRATIONS

D. APPLETON AND COMPANY
NEW YORK AND LONDON

1917

PRINTED IN THE UNITED STATES OF AMERICA

TO
MY HELPER

MY WIFE

THIS BOOK IS
DEDICATED

PREFACE

The following pages are presented with the purpose of affording
students a comprehensive view of modern mineralogy rather than a
detailed knowledge of many minerals. The minerals selected for
description are not necessarily those that are most common nor those
that occur in greatest quantity. The list includes those that are of
scientific interest or of economic importance, and, in addition, those
that illustrate some principle employed in the classification of minerals.
The volume is not a reference book. It is offered solely as a textbook.
It does not pretend to furnish a complete discussion of the mineral
kingdom, nor a means of determining the nature of any mineral that
may be met with. The chapters devoted to the processes of deter-
minative mineralogy are brief, and the familiar " key to the determina-
tion of species " is omitted. In place of the latter is a simple guide
to the descriptions of minerals to be found in the body of the text.
For more complete determinative tables the reader is referred to one
of the many good books that are devoted entirely to this phase of the
subject. In the descriptions of the characteristic crystals of minerals
both the Naumann and the Miller systems of notation are employed,
the former because of its almost general use in the more important refer-
ence books and the latter because of its almost universal use in modern
crystallographic investigations. The student must be familiar with
both notations. It is thought that this familiarity can be best acquired
by employing the two notations side by side.

In preparing the descriptive matter the author has made extensive
use of Hintze's Handbuch der Mineralogie. The figures illustrating
crystal forms are taken from many sources. A few illustrations have

viii PREFACE

been made especially for this volume. Figures copied to illustrate
special features are accredited to their authors. The statistics are
mainly from the Mineral Resources of the United States. They are
given for the year 191 2 because this was a more nearly normal year in
trade than any that has followed.

The author is under obligation to the McGraw-Hill Book Company
for permission to reproduce a number of illustrations originally published
in his Elements of Crystallography, and also for the use of the original
engravings in making the plates for Figures 11, $$t 71, 90, no, 114, 115,
118, 160, 191, 194, 224, 240, and 248.

W. S. Bayley.

CONTENTS

PART I
GENERAL CHEMICAL MINERALOGY

CHAPTER PAGE

I. The Composition and Classification of Minerals i

II. The Formation of Minerals and Their Alterations 17

PART II
DESCRIPTIVE MINERALOGY

III. Introduction — The Elements 36

IV. The Sulphides, Tellurides, Selentdes, Arsenides, and

Antimonides 68

V. The Sulpho-salts and Sulpho-ferrites 116

VI. The Chlorides, Bromides, Iodides, and Fluorides 134

VII. The Oxtdes 146

VIII. The Hydroxides 179

IX. The Aluminates, Ferrites, Chromites and Manganttes ... 195

X. The Nitrates and Borates 205

XI. The Carbonates 212

XII. The Sulphates 236

XIII. The Chromates, Tungstates and Molybdates 253

XIV. The Phosphates, Arsenates and Vanadates 261

XV. The Columbates, Tantalates and Uranates 293

XVI. The Silicates: The Anhydrous Orthosilicates 300

XVII. The Silicates: The Anhydrous Metasilicates 359

XVIII. The Silicates: The Anhydrous Trimetasilicates 408

XIX. The Silicates: The Anhydrous Polysilicates 426

XX. The Silicates: The Hydrated Silicates 441

XXI. The Silicates: The Titanates and Titanosilicates 461

PART III

DETERMINATIVE MINERALOGY

XXII. General Principles of Blowpipe Analysis 467

XXIII. Characteristic Reactions of the More Important Elements

and Acid Radicals 483

CONTENTS

APPENDICES

CHAPTER PAGE

I. Guide to the Descriptions of Minerals 495

II. List of the More Important Minerals Arranged Accord-

ing to Their Principal Constituents 513

III. List of Minerals Arranged According to their Crys-

tallization 521

IV. List of Reference Books 527

Index 529

LIST OF ILLUSTRATIONS

FIGURE PAGE

i. Sodium fluosilicate crystals 14

2. Potassium fluosilicate crystals 14

3. Cross-section of symmetrical vein 21

4. Cross-section of vein in green porphyry 24

5. Diorite dike cutting granite gneiss 26

6. Vein in Griffith mine 27

7. Vein forming original ore-body, Butte, Mont 27

8. Druse of Smithsonite 28

9. Geodes containing calcite 29

10. Alteration of olivine into serpentine 31

11. Etch figures in cubic face of diamond 38

12. Crystal of diamond with rounded edges and faces 38

13. Octahedron of diamond 38

14. Principal "cuts" of diamonds 42

15. Premier diamond mines in South Africa 43

16. The Cullinan diamond 43

17. Gems cut from Cullinan diamond 44

18. The Tiffany diamond 44

19. Sulphur crystals 47

20. Distorted crystal of sulphur 47

21. Copper crystal '. 53

22. Crystal of copper from Keweenaw Point 53

23. Plate of silver from Coniagas Mine, Cobalt 57

24. Octahedral skeleton crystal of gold with etched faces 58

25. Iron meteorite , 65

26. Widmanstatten figures on etched surface of meteorite 66

27. Realgar crystal 70

28. Stibnite crystal 72

29. Galena crystal 81

30. Galena crystals 82

31. Chalcocite crystal 85

32. Complex chalcocite twin 85

33. Tetrahedral crystal of sphalerite 88

34. Sphalerite crystal 88

35. Sphalerite octahedron 88

36. Greenockite crystal 91

37. Pyrrhotite crystal 92

xii LIST OF ILLUSTRATIONS

FIGURE PAGE

38. Cinnabar crystals 98

39. Group of pyrite crystals in which the cube predominates

40. Pyrite crystals on which 0(1 1 1) predominates

41. Pyrite crystal

42. Group of pyrite crystals

43. Pyrite interpenetration twin

44. Marcasite crystal

45. Marcasite crystal with forms as indicated in Fig. 44

46. Twin of marcasite

47. Spearhead group of marcasite

48. Arsenopyrite crystals

49. Crystal of pyrargyrite

50. Crystal of proustite

51 . Bournonite crystal

52. Bournonite fourling twinned

53. Enargite crystal

54. Stephanite crystal

55. Tetrahedrite crystal

56. Chalcopyrite crystal

57. Chalcopyrite

58. Chalcopyrite twin :

59. Hopper-shaped cube of halite

60. Group of fluorite crystals from Weardale Co

61. Crystal of fluorite

62. Interpenetration cubes of fluorite, twin

63. Photographs of snow crystals

64. Zincite crystal

65. Hematite crystals

66. Corundum crystal

67. Corundum crystal

68. Corundum crystal

69. Quartz crystal exhibiting rhombohedral symmetry

70. Ideal (A) and distorted (B) quartz crystals

71. Etch figures on two quartz crystals of the same form

7 2. Group of quartz crystals

73. Tapering quartz crystal

74. Quartz crystal

75. Supplementary twins of quartz

76. Quartz twinned

77. Cassiterite crystal

78. Cassiterite crystal

79. Cassiterite twinned

80. Rutile crystals

81. Rutile eightling twinned

02
02
02

03
10

19
21

21
23

39
40

47
SO

53
56
56
56
59

59
60

63
69
69

LIST OF ILLUSTRATIONS xiii

FIGURE PACE

82. Rutile twinned 172

83. Rutile cyclic sixling twinned 173

84. Rutile twinned 173

85. Anatase crystal 177

86. Anatase crystal 177

87. Brookite crystals 178

88. Brucite crystal 182

89. Limonite stalactites in Silverbow mine 184

90. Botryoidal limonite 184

91. Pisolitic bauxite from near Rock Run 187

92. Diaspore crystals 190

93. Manganite crystal 192

94. Group of prismatic manganite crystals 192

95. Manganite crystal twinned 193

96. Spinel twin , 196

97. Spinel crystal r . 196

98. Magnetite crystal 198

99. Chrysoberyl crystal 203

00. Chrysoberyl twinned 203

01. Chrysoberyl pseudohexagonal sixling 203

02. Hausmannite 204

03. Borax crystal 207

04. Colemanite crystals 209

05. Boracite crystal 211

06. Calcite crystal. * 214

07. Calcite crystals 214

08. Calcite crystals 214

09. Calcite 214

10. Prismatic crystals of calcite 215

11. Calcite 215

12. Calcite: twin and polysynthetic trilling. 215

13. Calcite 216

14. Artificial twin of calcite 216

15. Thin section of marble viewed by polarized light.. 216

16. Aragonite crystal 224

17. Aragonite twin 224

18. Trilling of aragonite 224

19. Witherite twinned 226

20. Cerussite crystal 227

21. Cerussite trilling twinned 227

22. Cerussite trilling twinned 227

23. Radiate groups of cerussite on galena 228

24. Dolomite crystal 229

25. Group of dolomite crystals 230

XIV

LIST OF ILLUSTRATIONS

FIGURE PAGE

26. Malachite crystal 232

27. Azurite crystals 233

28. Trona crystal 235

29. Gaylussite crystal 235

[30. Glauberite crystal 237

[31. Thenardite crystal 237

[32. Thenardite twinned 237

[33. Barite crystals 239

[34. Barite crystals. 240

[35. Celestite crystals 241

:36. Anglesite crystal * 243

[37. Anglesite crystal 243

[38. Anglesite crystal 243

[39. Gypsum crystals 247

:4c Gypsum twinned 247

[41. Gypsum twinned 248

[42. Epsomite crystal 250

[43. Hanksite crystal 252

[44. Crocoite crystals 253

[45. Scheelite crystal 255

[46. Scheelite crystal 255

47. Wulfenite crystal 257

[48. Wulfenite crystal 257

[49. Wolframite crystal 259

50. Monazite crystal 264

51. Xenotime crystals 265

52. Apatite crystal 267

53. Apatite crystal 267

54. Vanadinite crystal ; 262

55. Skeleton crystal of vanadinite 272

56. Amblygonite crystal 275

57. Lazulite crystals 276

58. Olivenite crystal 277

59. Skorodite crystal 286

:6o. Radiate wavellite on a rock surface 287

:6i. Columbite crystals 294

:62. Samarskite crystals 297

:63. Olivine crystals 303

[64. Wiilemite crystal 307

•65. Phenacite crystal 308

[66. Garnet crystal (natural size) 310

[67. Garnet crystals 310

:68. Garnet crystal 310

69. Nepheline crystal 314

LIST OF ILLUSTRATIONS

FIGURE

PAGE

70. Zircon crystals 317

7 1 . Zircon twinned 317

72. Thorite crystal 319

73. Andalusite crystals 320

74. Topaz crystals 323

75. Topaz crystal 323

76. Topaz crystal 324

77. Danburite crystal 325

78. Zoisite crystal 327

70. Epidote crystal 328

:8o. Epidote crystals , 328

[81. Chondrodite crystal. . . . : 333

:82. Datolite crystal 334

[83. Staurolite crystal 337

84. Staurolite crystal twinned 337

[85. Staurolite crystal twinned. . .• 337

[86. Sodalite interpenetration twin of two dodecahedrons 340

[87. Prehnite crystal 344

:88. Axinite crystal 346

:8q. Axinite crystal 346

:go. Dioptase crystal 347

91. Percussion figure 348

92. Biotite crystal 349

93. Biotite twinned about a plane 349

94. Etch figures 356

95. Muscovite crystal 356

96. Beryl crystals 360

97. Beryl crystals 360

[98. Cross-section of pyroxene 363

[99. Enstatite crystal 366

200. Wollastonite crystal 368

201. Augite crystal 371

202. Augite twinned 371

203. Interpenetration twin of augite 371

204. Diopside crystals 372

205. Hedenbergite crystal 373

206. Acmite crystal 376

207. Spodumene crystal 379

208. Rhodonite crystals 380

209. Ampibole crystals 384

210. Kyanite crystals 394

211. Bladed kyanite crystals in a micaceous quartz schist 395

212. Calamine crystals 39^

213. Orthoclase crystals 4*o

xvi LIST OF ILLUSTRATIONS

FIGURE PAG8

214. Orthoclase crystals > 410

215. Carlsbad interpenet ration twins of orthoclase 410

216. Contact twin of orthoclase according to the Carlsbad law 410

217. Baveno twins of orthoclase 411

218. Manebach twin of orthoclase 411

219. Section of mirocline viewed between crossed nicols 414

220. Adularia crystal 414

221. Albite crystals 419

222. Albite twinned 419

223. Albite twinned 419

224. Twinning st nations on cleavage piece of oligoclase 420

225. Albite twins with the crystal axis 420

226. Position of "rhombic sections" in albite 420

227. Diagram of crystal of triclinic feldspar 420

228. Potash-oligoclase crystal 422

229. Scapolite crystals 424

230. Clintonite twinned according to the mica law 427

231. Clinochlore crystal 430

232. Clinochlore twinned according to mica law 430

233. Clinochlore with same forms as in Fig. 232 430

234. Clinochlore trilling twinned according to mica law 430

235. Penninite crystal 430

236. Penninite crystal twinned 430

237. Vesuvianite crystals 433

238. Tourmaline crystals 436

239. Tourmaline crystals 436

240. Cooling crystal of tourmaline 436

241. Cordierite crystal 439

242. Apophyllite crystals 444

243. Heulandite crystal 447

244. Heulandite, var. beaumontite 447

245. Phillipsite interpenetration twin 448

246. Phillipsite 448

247. Harmotome fourling twinned like phillipsite 449

248. Sheaf -like aggregates of stilbite 450

249. Laumontite crystal 452

250. Divergent groups of scolecite crystals 453

251. Scolecite crystal 453

252. Natrolite crystals 454

253. Thomsonite crystal 456

254. Chabazite crystal 457

255. Chabazite interpenetration twin 457

256. Phacolite with same form as in Fig. 254 457

257. Analcite crystal 459

LIST OF ILLUSTRATIONS xvii

FIGURE PAGE

258. Analcite crystal 459

259. Ilmenite crystal 463

260. Titanite crystal 464

261. Titanite crystal 464

262. Titanite crystal 464

263. Simple blowpipes 468

264. Bellows for use with blowpipe 468

265. Candle flame showing three mantles 470

266. Reducing flame 471

267. Oxidizing flame 471

268. Props and position of charcoal 473

DESCRIPTIVE MINERALOGY

PART I
GENERAL CHEMICAL MINERALOGY

CHAPTER I
THE COMPOSITION AND CLASSIFICATION OF MINERALS

Definition of Mineral. — A mineral is a definite inorganic, chem-
ical compound that occurs as a part of the earth's crust. It possesses
characters which are functions of its composition and its structure.
Most minerals are crystallized, but a few have been found only in an
amorphous, colloidal condition. These are regarded as gels, or solid
colloids.

The most essential feature of a mineral is its chemical composition,
since upon this are believed to be dependent all its other properties.

Chemical Substances Occurring as Minerals. — The chemical
substances found native as minerals may be classed as elements and
compounds. The latter comprise chlorides, fluorides, sulphides, oxides,
hydroxides, the salts of carbonic, sulphuric, phosphorus, arsenic, anti-
mony and silicic acids, a large series of complicated compounds known
as the sulpho-salts, a few derivatives of certain metallic acids — the
aluminates and the ferrites — besides other salts of rarer occurrence,
some simple and others exceedingly complicated, and possibly many
solid solutions of gels or of a gel and a crystalloid. In some of these
classes all the compounds are anhydrous. In others, some groups are
anhydrous while the members of other groups contain one or more
molecules of water of crystallization.

The sulphides, chlorides and fluorides are derivatives of H2S, HC1,
and H2F2, respectively. They may be regarded as having been pro-
duced from these compounds by the replacement of the hydrogen by
metals. Illustrations: CU2S, CuS, NaCl, CaF2.

2 GENERAL CHEMICAL MINERALOGY

The hydroxides and the oxides may be looked upon as derivatives of
water, the hydroxides through the replacement of one atom of hydrogen
by a metal, and the oxides through the replacement of both hydrogen

/OH

atoms. The mineral, brucite, according to this view is Mg<Q ,

x)H

derived from rr/rkxrv by replacement of two hydrogen atoms in two

H(0H) Cu\

molecules of water by one atom of Mg. Cuprite is yO, and tenoriU

CuO, the former derived by replacement of each atom of hydrogen in
one molecule of water by an atom of Cu, and the latter by replacement
of the two hydrogens by a single Cu.

The salts of carbonic acid (H2CO3) are the carbonates, those of sul-
phuric acid (H2SO4) the sulphates, those of orthophosphoric acid
(H3PO4) the phosphates, those of orthoarsenic acid (H3ASO4) the arsen-
ates, those of orthoantimonic acid (HaSbO-O the antimonates and those
of the silicic acids, the silicates. There are, in addition, a few arsenites
and antimonites that are salts of arsenious (H3ASO3) and antimonous
(HaSbOs) acids.

The principal silicic acids whose salts occur as minerals are normal
silicic acid (H4Si04), metasilicic acid (H2Si03), and trisilicic acid
(I^SiaOs). The metasilicic and the trisilicic acids may be regarded
as normal silicic acid from which water has been abstracted, in the same
way that pyrosulphuric acid is ordinary sulphuric acid less H2O, thus:
2H2SO4- H20 = H2S2O7.

(HO)4Si— H20 = H2Si03, metasilicic acid
3(HO)4Si— 4H20=H4Si308, trisilicic acid.

Fayalite is Fe2Si04, wollastonite, CaSi03, and orthoclase, KAlSiaOs.

The aluminates and f errites may be regarded as salts of the hypothet-
ical acids AIO(OH) and FeO(OH), both of which exist as minerals,
the first under the name diaspore and the second under the name

-AlO

goethite. Spinel is the magnesium aluminate, Mg<^ ,(MgAl204),

X)— AlO

and magnoferrite the corresponding ferrate MgFe204. The very com-

/O— FeO

mon mineral magnetite is the iron ferrate Fe<^ , or Fe304. In

N>- FeO

this compound the iron is partly in the ferrous and partly in the ferric
state.

COMPOSITION AND CLASSIFICATION 3

There are other minerals that differ from those of the classes above
mentioned in containing more or less water of crystallization. These
are usually separated from those in which there is no water of crystal-
lization under the name of hydrous salts.

Besides the classes of minerals considered there are others which
appear to be double salts, in which two substances that may exist
independently occur combined to form a third substance with prop-
erties different from those of its components. Cryolite, 3NaF#AlF3
or Na^AlFe, is an example. The sulphosalts furnish many other
examples.

Further, a large number of minerals are apparently isomorphous
mixtures of several compounds. These are homogeneous mixtures
of two or more substances that crystallize with the same sym-
metry, and, consequently, that may crystallize together. Their
physical properties are continuous functions of their chemical com-
positions. Other minerals are apparently solid solutions in one an-
other of simple crystallizable salts, of gels, of gels and salts, and of
gels and adsorbed substances. Among these are some of the commoner
silicates.

Determination of Mineral Composition. — Since the properties
of minerals are functions of their chemical compositions, it is important
that their compositions be known as accurately as possible. It is
necessary in the first place that pure material may be secured for study.
Pure material is most easily secured by making use of the differences
in density exhibited by different compounds. The mineral to be studied
is pounded to a powder, sifted through a bolting cloth sieve and shaken
up with one of the heavy solutions employed in determining specific
gravities. When the solution is brought to the same density as that
of the mineral under investigation all material of a higher specific gravity
will sink. The material with a density lower than that of the solu-
tion will rise to the surface. Material with a specific gravity identical
with that of the solution will be suspended in it. If the mixing is done
in a separating funnel of the proper type, the materials may be drawn
off into beakers in the order of their densities, and thus the pure mineral
may be separated from the impurities that were originally incorporated
with it. After the purity of the substance is assured by examination
under the microscope, it is ready for analysis.

The composition of the purified material is determined by the
ordinary methods of chemistry known as analysis and synthesis.

In analysis the compound is broken into its constituent parts and
these are weighed; or it is decomposed and its constituents are trans-

4 GENERAL CHEMICAL MINERALOGY

formed into known compounds which axe weighed. From the weights
thus obtained the proportions of the components in the original sub-
stance may be easily calculated if the .weight of the original substance
be known.

In synthesis the compound is built up from known elements or
compounds.

If the mineral calcite (CaCOs) is decomposed by heat into lime
(CaO) and carbonic acid gas (CO2), or if its components are trans-
formed into the known compounds CaS04 and K2CO3, the process is
analysis. If the known substance CO2 is allowed to act upon the
known substance CaO and the resulting product is a substance possess-
ing all the properties of calcite, the process is synthesis.

Analytical Methods. — The analytical methods made use of in
mineralogy are: (1) the ordinary wet methods of chemical analysis,
(2) the dry methods of blowpipe analysis, in which the mineral is
treated before the blowpipe without the use of liquid reagents except
to a very subordinate degree, and (3) microchemical methods, per-
formed on the stage of a compound microscope.

Blowpipe and microchemical analyses are made use of principally
for the identification of minerals. By their aid the nature of the atoms
in a compound may easily be learned, but the proportions in which
these atoms are combined is determined only with the greatest difficulty.
The methods are mainly qualitative.

Wet Analysis. — For exact determinations of composition the wet
methods of chemistry are usually employed, since these are the most
accurate ones. They are identical with the methods described in
manuals of quantitative analysis, and therefore require no detailed
discussion here. They are well illustrated by Prof. Tschermak as
follows: If 734 mg. of the mineral goethite (in which qualitative tests
show the presence of iron oxide and water) are roasted in a glass tube,
water is given off. This when caught and condensed in a second tube
containing dry calcium chloride increases the weight of this second
tube by 75 mg. The residue of the mineral left in the first tube now
weighs about 660 mg. An examination of this residue shows it to con-
sist exclusively of the iron oxide (Fe20s). Since only iron oxide and
water are present in goethite the sum of these two constituents ought to
equal the original weight of the mineral before roasting. But 660+75
= 735, whereas the original weight was 734. The difference 1 mg. is
due to unavoidable errors of manipulation. As it is very small it may
be neglected in our calculations.

The results of the analysis are generally expressed in percentages,

COMPOSITION AND CLASSIFICATION S

which are obtained by dividing the weights of the different constituents
by the weight of the original substance.

Thus: 660-5-734=89.92 per cent Fe2Q3

75-5-734=10.22 per centlfeO

Total 100.14

The usual methods of analysis are, however, more indirect than this,
the components of the substance to be analyzed being first transformed
into known compounds and then weighed. For instance, common salt
is known by qualitative tests to contain only Na and CI. If 345 mg.
of the pure salt be dissolved in water and the solution be treated with
silver nitrate under proper conditions a precipitate of silver chloride
is formed so long as any sodium chloride remains in the solution. The
silver chloride is separated from the solution by nitration. It contains
all the chloride present in the 345 mg. of salt. After drying, its weight
is determined to be 840 mg. The solution from which the silver chloride
was separated contains all the sodium that was originally present in
the salt, but now it is in combination with nitric acid. It contains
also any excess of silver nitrate that was added to precipitate the chlorine.

NaCl + AgN03 = AgCl + NaN03

salt reagent precipitate filtrate

The nitrate is now treated with hydrochloric acid to precipitate
the excess silver. The silver chloride precipitate is removed by filtra-
tion, leaving a solution containing sodium salts of nitric and hydro-
chloric acids besides some free acid of each kind. Sulphuric acid is
now added and the whole solution is evaporated to dryness. The free
acids are driven off by the heat and the sodium salts are transformed
into the sulphate, Na2S04. The residue consisting exclusively of Na2SC>4
is now found to weigh 419 mg.

The 345 mg. of salt have yielded 840 mg. of AgCl and 419 mg. of
Na2S04. The silver chloride is known to contain 24.74 per cent of
chlorine and the sodium sulphate 32.39 per cent of sodium. The 840
mg. of AgCl contain 207.8 mg. of chlorine, and the 419 mg. of Na2S04
contain 135.7 m8- °f sodium. Hence 345 mg. of salt yield

207.8 mg. or 60.23 per cent CI,
and 135.7 mg- or 39-34 per cent Na

343.5 mg. 99.57 per cent

GENERAL CHEMICAL MINERALOGY

Records of Analyses. — The composition of minerals like that of
other chemical compounds is determined in percentages of their com-
ponents and is recorded as parts per ioo by weight. A weighed quantity
of the mineral is analyzed, the products of the analysis are weighed and the
percentage of each constituent present is found by dividing its weight
by the weight of the original substance, as has already been indicated.

In chemical treatises the results of the analyses are usually recorded
in percentages of the elements present. In mineralogical works it is
more common to write the percentage composition in terms of the
oxides of the elements, partly because the old analyses are recorded in
this way and partly because certain relations between the mineral
components can be better exhibited by comparison of the oxides than
by comparison of the elements present in them.

The record of the analysis of a magnesik may be given as:

28.35 per cent,

.34 per cent,

14.25 per cent,

56.98 per cent,

Total =99.92 per cent.

- or as

MgO=47.25 per cent,
FeO= .43 per cent,
C02= 52.24 per cent,

Total =99.92 per cent.

Calculation of Formulas. — After the determination of the per*
centage composition of a mineral, the next step is to represent this
composition by a chemical formula — a symbol which indicates the
relative number of elementary atoms in the mineral's molecule, instead
of the number of parts of its constituents in 100 parts of its sub-
stance.

The construction of a formula from the analytical results is simple
enough in principle, but in practice it is often made difficult by the
fact that many apparently pure substances are in reality composed of
several distinct compounds so intimately intercrystallized that it is
impossible to separate them. In the simplest cases the formula is
derived directly from the results of the analyses by a mere process of
division.

The atomic weights of the chemical elements are the relative weights
of the smallest quantities that may enter into chemical combination with
one another, measured in terms of the atomic weight of hydrogen which
is taken as unity, or of oxygen taken as 16. Thus the atomic weights
of nitrogen and oxygen are approximately 14 and 16 respectively, i.e.,
the smallest quantities of nitrogen and oxygen that can enter into com-
bination with each other and with hydrogen are in the ratio of the

COMPOSITION AND CLASSIFICATION

TABLE OF ATOMIC WEIGHTS

Element Symbol

Aluminium Al

Antimony Sb

Argon A

Arsenic As

Barium Ba

Bismuth Bi

Boron B

Bromine Br

Cadmium Cd

Caesium Cs

Calcium Ca

Carbon C

Cerium Ce

Chlorine CI

Chromium Cr

Cobalt Co

Columbium Cb

Copper Cu

Dysprosium Dy

Erbium Er

Europium Eu

Fluorine F

Gadolinium Gd

Gallium Ga

Germanium Ge

Glucinum Gl

Gold Au

Helium He

Holmium Ho

Hydrogen H

Indium In

Iodine I

Iridium, v Ir

Iron Fe

Krypton Kr

Lanthanum La

Lead Pb

Lithium Li

Lutecium Lu

Magnesium Mg

Manganese Mn

Mcjcury Bg

At. Weight

27.1

120.2

39.88

7406

137.37
208.0

11. o

70.02
112.40

132-81 '

40.07

12.005

140.25

35.46
52.0

58.97

93 5

63 57
162.5
167.7
1520

19.0

157.3
69.9

72.5
01
197.2
4.00

1635
1.008

114. 8

126.92

193. 1

5585
82.92

139.0

207 . 20

6.94

I75-0
24.32

5493
200.6

Element Symbol

Molybdenum Mo

Neodymium Nd

Neon Ne

Nickel Ni

Niton Nt

Nitrogen N

Osmium Os

Oxygen O

Palladium Pd

Phosphorus P

Platinum Pt

Potassium K

Praseodymium Pr

Radium Ra

Rhodium Rh

Rubidium Rb

Ruthenium Ru

Samarium Sa

Scandium Sc

Selenium Se

Silicon Si

Silver Ag

Sodium Na

Strontium Sr

Sulphur S

Tantalum Ta

Tellurium Te

Terbium Tb

Thallium Tl

Thorium Th

Thulium Tm

Tin.

Titanium Ti

Tungsten W

Uranium U

Vanadium V

Xenon Xe

Ytterbium (Neoytterbium) . . Yb

Yttrium Y

Zinc Zn

Zirconium Zr

At. Weight

96.0

144 3
20.2

58.68
222.4

14 01
190.9

16.0
106.7

3104
195 2

39 10
140.9
226.0
102.9

8545
101.7

1504

441

792

28.3
107.88

230

8763
3206
181. 5

1275
1592
204.0
232.4
168.5
118. 7

48.1
184.0
238.2

5106
1302

173-5
88.7

6537
90.6

8 GENERAL CHEMICAL MINERALOGY

values 14 : 16 : i.1 The quantities that possess these relative weights
are known as atoms. Often the apparent ratios of the elements in
combination are different from the ratios between their atomic weights,
but this is always due to the fact that one or the other of the elements
is present in more than its smallest possible quantity, i.e., in a greater
amount than is represented by a single atom. For instance, there are
several compounds of oxygen and nitrogen known, in which the weight
relations between the two elements may be represented by the follow-
ing figures: 14 : 8; 14 : 16; 14 : 24; 14 : 32, and 14 : 40. If the
second of these compounds consists of one atom each of nitrogen and
oxygen, and these are the smallest quantities of the elements that
can exist in combination, the several compounds must be made up thus:

14 : 8 14 : 16 14 : 24 14 : 32 14 : 40

N20 NO N2O3 N02 N2O5

for N can exist only in quantities that weigh 14, 28, 42 times as much
as the smallest quantity of hydrogen present in any compound, i.e.,
the single atom, and O in quantities of 16, 32, 48, etc., times the weight
of the single hydrogen atom. In order that even multiples of 14 and
16 shall exist in the ratios given above, their terms must be multi-
plied by quantities that will yield the following results;

28 : 16 14 : 16 28 : 48 14 : 32 28 : 80

which are the weights respectively of the numbers of atoms represented
in the above formulas.

If, then, the elements combine in the ratio of their atomic weights,
or in some multiple of this ratio, the figures obtained by analysis must
be in one of these ratios, and consequently they furnish the data from
which the formula of the substance analyzed may be deduced. In
gold chloride, for example, analysis shows the presence of 64.87 per cent
Au and 35.13 per cent CI, i.e., the gold and the chlorine are united in

the ratio of 64.87 ; 35.13 or . The combining ratio of single

00" o

atoms of gold and of chlorine is, however, 196.7 : 35.5, or . Evi-

35-5
dently in gold chloride the ratio of gold to chlorine is only one-third

as great as is the ratio between the atomic weights of these elements,

or the ratio of the chlorine to the gold three times as great. Hence

1 The atomic weight of hydrogen is more accurately 1.008, when that of oxygen
is taken as 16.

COMPOSITION AND CLASSIFICATION

there must be three times as much chlorine in gold chloride as would
be represented by a single atom of chlorine, or there must be three
atoms of chlorine in the compound, for we cannot imagine a quantity
of gold present which is equivalent to one-third of an atom of gold.
Gold chloride is therefore AuCU.

We can now prove our conclusion by calculation. One atom of
gold and three atoms of chlorine ought to combine in the ratio of
196.7 : 106.5 (i.e., 35.5X3). If our conclusion is correct, and the
gold chloride analyzed is AuCfe, then the quantities of gold and of
chlorine yielded by the analysis should be in this ratio. The figures
obtained are in the ratio of 64.87 : 35.13. Multiplying both terms of
this ratio by 3.031 we obtain 196.62 : 106.5, which is approximately
the ratio expected.

In practice, the same result as that outlined above is reached by
dividing the results of analyses by the atomic weights of the various
elements or groups of elements concerned. The quotients represent the
proportional numbers of the elements or groups present. If the small-
est quotient is assumed as unity, the ratios existing between this and
the other quotients indicate the number of atoms or groups of
atoms represented by the latter.

Illustrations;

Gold Chloride Result of Analysis Atomic Weights Quotients

Au = 64.87 per cent -5- 196.7 = 329&
CI - 3S-J3 ■*■ 35-5 = 9896

Ratios
I

3-00+

Tin Chloride

Sn = 45.26 per cent -s- 117. 4 — .384
CI = 54- 74 -*- 355 - i-54*

4.04

The formula of the gold chloride is AuCk, and of the tin chloride,
SnCU.

Magnesium carbonate on analysis may yield : C = 14. 26 ; Mg =28.37;
Fe=.34; O— 57.03; or, if recorded in the form of oxides: 002=52.24;
MgO= 47.25; FeO=.43- From either of these results the formula is
easily obtained by the method described.

0=14.26-5-11.97 = 1.188=1.009;
Mg= 28.37-^23.94= 1.186= 1.000;
Fe= .34-*- 55.88= .006= .006;
O-57.03-s-15.96-3.573-3.012; -

or,

MgC03, if we neglect the small
quantity of iron present.

GENERAL CHEMICAL MINERALOGY

From the second set of figures we have:

C02= 52.244-43.89= 1.19=1;

MgO=47-2S-5"39-90= 1.184=1;
FeO= .434-71.84= .006;

or.

MgO-C02, which is the same as
MgC03, written in a different way.

All formulas are derived by methods like these, but in many cases
the processes are made more difficult by the impossibility of deciding
positively whether those substances that are present in small quantities
are present as impurities or whether they exist as essential parts of
the compound.

Formulas of Substances Containing Two or More Metallic
Elements or Acid Groups. — In the illustration given above the com-
pounds consist of but one kind of metallic element combined with one
kind of acid. Often in the case of minerals there are present two or
more metallic elements, and less commonly several acid groups. When
two metals are present in definite atomic proportions the formula is
written in the usual manner, as CaMg(C03)2 for the mineral dolomite,
in which calcium and magnesium are present in the ratio of one atom
of each to two parts of the acid group CO3. Very often, and perhaps in
the majority of cases, when two or more metallic elements are present
in different specimens of a mineral they are not found always in the
same proportion — the mineral may consist of isomorphic mixtures
of several substances. For instance, many calcium-magnesium car-
bonates are known in which the ratio of calcium to magnesium present
is not as 1 atom to 1 atom, but in which this ratio is as 2 atoms
to 1 atom, 3 atoms to 2 atoms, or a ratio which would have to be
represented by irrational figures like 2.7236 atoms to 1.5973 atoms.
Each one of these compounds properly requires a separate formula,
as 2CaC03+MgC03, 3CaC03+2MgC03, etc., but practically the entire
series of compounds is represented by a single symbol, thus: (Ca • Mg)C03,
indicating that in the series we have to do with mixtures of carbonates
of calcium and magnesium, or with complex molecules containing in
different instances different proportions of the two carbonates. For
greater definiteness the symbol of the characteristic element of the
substance which is in largest quantity in the compound is usually written
first, as (Ca-Mg)CC>3, when calcium carbonate is in excess, or
(Mg- Ca)CC>3 when magnesium carbonate predominates. If still greater
definiteness is desired small figures are placed below the symbols of the
elements concerned, as (Ca2*Mgi)C03 or (Ca3 • Mg2)CC>3, to indicate
the respective proportions present. (Ca2-Mgi)C03 signifies that the

COMPOSITION AND CLASSIFICATION 11

mineral thus represented contains calcium and magnesium in the
ratio of 2 atoms of the former to 1 of the latter.

Compounds Containing Water. — Often salts that separate from
aqueous solutions combine with certain definite proportions of water.
Sometimes this water combines with the anhydrous portion of the com-
pound to form a double salt, as MgS04+7HaO, or MgSO-i-ylfeO.
At other times a portion of the water, in the form of the group (OH),
called the hydroxyl group, occupies the place usually occupied by
a metallic element, and, occasionally, that usually occupied by an
acid group, or by oxygen, as in Mg(OH)2.

Water of Crystallization. — Double salts composed of an anhydrous
portion combined with water are usually well crystallized. Although
the water appears in many cases to be but loosely combined with the
remainder of the compound it is an essential part of its crystal particle,
for by the loss of even a portion of it the crystal system of the compound
is often changed. Water in this form is known as water of crystalliza-
tion, and the compounds are designated hydrates.

The magnesium sulphate MgS04 • 7H2O forms orthorhombic crystals.
By evaporation of a hot solution of this substance the sulphate
MgSO* - 6H2O separates as monoclinic crystals.

Gypsum is CaS04 • 2H2O. Its crystallization is monoclinic. When
heated to 2000 it passes into the anhydrous orthorhombic mineral
anhydrite, CaS04.

Water of crystallization may frequently be driven from the com-
pound in which it exists by continued heating at a comparatively low
temperature. It is usually given off gradually — an increase in the tem-
perature causing an increase in the quantity of water released until
finally the last trace disappears. In many instances such a very high
temperature is required to drive off the last traces of the water that it
would appear that some of it is held in combination in a different
manner from that in which the remainder is held. Indeed, it is not at
all certain that double salts containing water of crystallization are
different in any essential respect from ordinary atomic molecules in
which hydrogen and oxygen are present in atomic form.

Combined Water. — Water of crystallization is thought of as
existing in the compound as water because of the ease with which it
can be driven off. Compounds in which the hydroxyl group is present
yield water only upon being heated to comparatively high temperatures.
In them the elements of water are present, but not united as water.
When freed from their combinations with the other constituents of the
compound by heat they unite to form water. Because its elements

12 GENERAL CHEMICAL MINERALOGY

are thought of as closely combined with the other elements in the
molecule, this kind of water is often distinguished from water of crystal-
lization by the term combined water.

Brucile (Mg(OH)2) and malachite (Cu2(OH)2CC>3) are minerals
containing the elements of water. When heated they yield water
according to the reactions Mg(OH)2=MgO+H20 and Cu2(OH)2COs
= CuO+CuC03+H20.

Combined water is not only more difficult to separate from its com-
bination than is water of crystallization, but when the combination
is broken the chemical character of the original substance is radically
changed, as may be seen from the reactions above indicated. More-
over, combined water is given off suddenly, at a certain minimum
temperature, and not gradually as in the case of water of crystal-
lization.

Blowpipe Analysis. — Although blowpipe analysis serves merely to
identify the chemical components of minerals, it is a most important
aid to mineralogists in their practical work.

Nearly all minerals may be recognized with a close degree of accu-
racy by their morphological and physical properties. To distinguish
between several minerals that are nearly alike in these characteristics,
however, the determination of composition is often important. In
cases of this kind a single test made with the blowpipe will frequently
give the desired information as to the nature of some one or more of
the chemical elements present, and thus in a few moments the mineral
may be identified beyond mistake.

The apparatus necessary to perform blowpipe analysis is very
simple and the number of pieces few. These, together with all the
reagents in sufficient quantity to determine the composition of hundreds
of minerals, may be packed into a box no larger than a common lunch
box. (See pp. 467-470.)

For more refined work than the mere testing of minerals a larger
collection of both apparatus and reagents is necessary, but in no case
is the quantity of material consumed in blowpipe analysis as great as
when wet methods of analysis are used.

Principles Underlying Blowpipe Analysis.— The principal phe-
nomena that are the basis of blowpipe work are the simple ones known
in chemistry as volatilization, reduction, oxidation, and solution.

For volatilization experiments charcoal sticks and glass tubes are
used. A blowpipe serves to direct a hot blast upon the assay. The
volatilized products collect on the cool parts of the charcoal which
they coat with a characteristic color, or upon the cooler portions of

COMPOSITION AND CLASSIFICATION 13

the glass tubes. The sublimates that collect in the tubes may be tested
with reagents or examined under the microscope.

Some volatile substances impart a distinct and characteristic color
to an otherwise colorless flame. These may be tested in the direct flame
of the blowpipe.

Oxidation and reduction experiments are usually performed either
on charcoal or in glass tubes. Oxidations are effected in open tubes
and reductions in those closed at one end. The products of the oxida-
tion or of the reduction are studied and from their characteristics the
nature of the original substance is inferred.

The solution of bodies to be tested is often made in the usual man-
ner, i.e., by treating them with liquid reagents, but more frequently
it is accomplished by fusion of a small quantity of the body with borax
(Na2B407 • 10H2O) or miopcosmic salt ((NH^NaHPO^-tffeO). The
molten reagent dissolves a portion of the substance to be tested and in
many cases forms with it a colored mass. From the color of the mass
the nature of the coloring matter may be learned.

Although the underlying principles of blowpipe analysis are simple
the reactions that take place between the reagents and the assay are
often very complex.

More explicit details of the operations of qualitative blowpipe
analysis are given in Part III.

Microchemical Analysis. — The processes of microchemical analysis
are limited in their application to the detection of a single element or,
at most, of a very few elements in small quantities of minerals. They
are employed mainly in deciding upon the composition of a substance
whose nature is suspected.

The principle at the basis of all microchemical methods is the manu-
facture of crystallized precipitates by treatment of the mineral under
investigation with some reagent, and the identification of these pre-
cipitates through their optical and morphological properties.

In practice, a small particle of the mineral the nature of which it
is desired to know is placed on a small glass plate, which may be covered
with a thin film of Canada balsam to prevent corrosion, and is
moistened with a drop or two of some reagent that will decompose
it. The solution thus formed is slowly evaporated by exposure to the
air. The plate is then placed beneath the objective of a microscope
and the crystals formed during the evaporation are investigated. Or,
after a solution of the assay is obtained there is added a small quantity
of some reagent and the resulting precipitate is studied under the
microscope. By their shapes and optical properties the nature of the

GENERAL CHEMICAL MINERALOGY

Fie. i. — Sodium Fluosilicate Crystals. Magnified 73

(After Rascnbusch.)

—Potassium Fluosilicate Crystals. Magnified 140 diam. (After Roienbusck.)

COMPOSITION AND CLASSIFICATION 15

crystals produced is determined, and in this way the nature of the con-
stituehts they have obtained from the mineral particles is discovered.

A large number of reagents have been used in microchemical tests
each of which is best suited to some particular condition. The most
generally useful one is hydrofluosilicic acid (H2SiFo). If small frag-
ments of albite and of orthoclase are placed on separate glass slips, such
as are used for mounting microscopic objects, and each is treated with
a drop of this reagent and then allowed to remain in contact with the
air for a few minutes until the solutions begin to evaporate, those
portions of the solutions remaining will be discovered to be filled with
little crystals. The crystals in the solution surrounding the albite are
hexagonal in habit (Fig. i), while those in the solution surrounding
the orthoclase are cubes, octahedrons or combinations of forms belonging
to the isometric system (Fig. 2). The former are crystals of sodium
fluosilicate and the latter crystals of the corresponding potassium salt.
The albite, consequently, is a sodium compound and the orthoclase a
compound of potassium. In similar manner, by means of this or of
other reagents the constituents of many minerals may be easily detected.
The method, however, is made use of only in special cases, when for
some reason or other analytical methods are not applicable.

Synthesis. — Synthesis is the opposite of analysis. By the analytical
processes compounds are torn apart, or broken down, whereas by syn-
thetical operations they are put together or built up. Synthetic methods
are employed principally in the study of the constitution of minerals
and of their mode of formation, and in the investigation of the condi-
tions that determine the different crystal habits of the same mineral.
The products of synthetic reactions are often spoken of as artificial
minerals because made through man's agency. In many instances
these artificial minerals are identical in every sense with natural minerals.
Consequently, they may often serve as material for study, when the
quantity of the natural mineral obtainable is too small for the purpose.

Classification of Minerals. — Classification is the grouping of
objects or phenomena in such a manner as will bring together those
that are related or that are similar in many respects and will separate
those that are different.

Since minerals are chemical compounds whose properties depend upon
their compositions, their most logical classification must be based upon
chemical relationships. But their morphological and physical properties
are their most noticeable features, and hence these should also be taken
into account in any classification that may be adopted. Probably
the most satisfactory method of classifying minerals is to group them,

16 GENERAL CHEMICAL MINERALOGY

first, in accordance with their chemical relationships and, second, in
accordance with their morphological and physical properties.

The first division is into the great chemical groups, as, for instance,
the elements, the chlorides, the sulphides, etc. The second division
is the separation of these great groups into smaller ones comprising
minerals possessing the same general morphological features. These
smaller groups may contain only a single mineral or they may contain
a large number of closely allied ones. If the basis of the subgrouping
is manner of crystallization, it follows that the members of subgroups
containing more than one member are usually isomorphous compounds.
Thus the subdivisions of the great chemical groups are single minerals
and small or large isomorphous groups of minerals, arranged in the
order in which their metallic elements are usually discussed in treatises
on chemistry. For example, the great group of carbonates embraces
all minerals that are salts of carbonic acid (H2CQ3). This great group
is divided into smaller groups along chemical lines, as for instance, the
normal carbonates, the hydrous carbonates, the basic carbonates, etc.
These smaller groups are finally divided into subgroups according to
their morphological properties — the normal salts, for example, being
divided into the two isomorphous groups known as the calcite and the
aragonite groups, and a third group comprising but a single mineral.

In certain specific cases some other classification than the one
outlined above may be desirable. For instance, in books written for
mining students it is often found that a classification based upon the
nature of the metallic constituent is of more interest than the more
strictly scientific one outlined above, because such a classification
emphasizes those components of the minerals with which the mining
student is most concerned. In books written for the student of rocks,
on the other hand, the most important determinative features of minerals
are their morphological characters, hence in these the classification
may be based primarily on manner of crystallization.

In the present volume the classification first outlined is used, but
because such a small proportion of the known minerals are discussed
the beauties of the classification are not as apparent as they would be
were all described.

CHAPTER II

THE FORMATION OF MINERALS AND THEIR ALTERATIONS

The Origin of Minerals. — Minerals, like other terrestrial chemical
compounds, are the result of reactions between chemical substances
existing upon the earth. When they are the direct result of the action
of elements or compounds not already existing as minerals they are said
to be primary products; when formed by the action of chemical agents
upon minerals already existing they are often spoken of as secondary,
though this distinction of terms is not always applied.

Quartz (SiC>2), formed by the cooling of a molten magma, is primary;
when formed by the action of water upon the siliceous constituents of
rocks it is secondary.

The Formation of Primary Minerals. — Minerals are produced in a
great variety of ways under a great variety of conditions. Even the
same mineral may be produced by many different methods. The more
common methods by which primary minerals are formed are: precipita-
tion from a gas or a mixture of gases, precipitation from solution, the
cooling of a molten magma, and abstraction from water or air by plants
and animals.

Deposits from Gases. — Emanations of gases are common in vol-
canic districts. The gases escaping from volcanic vents are mainly
water vapor, hydrochloric acid, sulphur dioxide, sulphuretted hydro-
gen, ammonia salts and carbon dioxide, besides small quantities of other
gases and the vapors of various metallic compounds. By the reactions
of these with one another or with the oxygen of the air, sulphur, salam-
moniac (NH4CI) and other substances may be formed, and by their
reaction upon the rocks in the neighborhood halite (NaCl), ferric chlo-
ride (FeCla), hematite (Fe203) and many other compounds may be
produced.

The production of minerals through the reactions set up between
various gases and vapors is known as pneutnatolysis. Their separation
from the gaseous condition is known as sublimation. Minerals formed
by sublimation are usually deposited as small, brilliant crystals on the
surfaces of rocks or upon the walls of cavities and crevices in them.

18 GENERAL CHEMICAL MINERALOGY

The reactions by which they are produced are often quite simple. Thus
the reaction between sulphuretted hydrogen and sulphur dioxide yields
sulphur (2H2S+S02=3S+2H20), as does also the reaction between the
first named gas and the oxygen of the atmosphere (H2S+0=H20+S).
Ferric chloride may be produced by the action of hot hydrochloric
acid upon some iron-bearing material deep within the earth's in-
terior. This being volatile at high temperatures escapes to the air
as a gas. Here it may react with water vapor, with the resulting for-
mation of hematite (2FeCl3+3H20=Fe203+6HCl). By the action
of carbonic acid gas upon volatile oxides, carbonates are formed,
(Fe203+2C02=2FeCC>3+0). In other cases, however, the reactions
are very complicated.

Precipitation from Solution. — Nearly all substances are soluble
to an appreciable degree in pure water. An increase in temperature
usually increases the quantity of the substance that can be dissolved,
as does also an increase of pressure. Moreover, the solubility of a
salt is increased on the addition of another salt containing no common
ion, and, conversely, is diminished in the presence of another having a
common ion. Thus, gypsum (CaS04*2H20) is sparingly soluble in
water, but it becomes much more soluble upon the addition of salt
(NaCl). On the other hand, salt (NaCl) is much less soluble in water
containing a little magnesium chloride (MgCb) than it is in pure water.

When a solvent contains a maximum amount of any substance that
it may hold under a given set of conditions the solution is said to be
saturated. From a saturated solution under ordinary conditions
precipitation results: Upon the evaporation of the solvent; the lowering
of its temperature or of the pressure under which it exists; or the addi-
tion to the solution of a substance containing an ion already in the
solution. Of course, the addition of a substance which will react with
the solution and produce a compound insoluble in it will also cause
precipitation.

The following table contains the results of various experiments on
the solubility of some common minerals:

Solubility of Various Compounds in 100 Parts Pure Water

(The results are given in parts by weight)

Halite (NaCl), at 70 35.68 Calcite (CaC02), in the

Fluorite (CaFj), at 15 J° 0037 c°ld 002

Gypsum (CaS04*2H20), at 150 .250 Strontianite (SrC03) in

Anhydrite (CaS04), in the cold .00025 the cold °o555

Celestite (SrS04), at 140 015 Magnetite (F3e04) 00035

FORMATION OF MINERALS 19

Percentages of Various Minerals Soluble in Water at 80°

(When treated 30 to 32 days)

Galena (PbS) 1 . 79 Chalcopyrite (CuFeSi) 1669

Stibnite (SbA) 5 .01 Bournonite ((Pb -Cu)SbSa). . . 2 .075

Pyrite (FeSj) 2 . 99 Arsenopyrite (FeAsS) 1.5

Sphalerite (ZnS) 025

So many substances that are usually regarded as insoluble are known
to be dissolved under conditions of high temperature and pressure that
no substance is believed to be entirely insoluble.

Powdered apophyllite ((HK)2Ca(Si03)2-H20), which is a silicate
that is generally regarded as insoluble in water, is dissolved sufficiently
in this solvent at a temperature of i8o°-i90° and under a pressure of
10-12 atmospheres to yield crystals of the same substance upon cooling.

Water containing gases or traces of salts is usually a more efficient
dissolving agent than pure water. When the gases are lost, or the
salts are decomposed by reactions with other compounds, precipitation
may ensue.

Parts of Various Minerals Dissolved in 10,000 Parts of Various

Solutions

Gold loses 1.23 per cent of its weight when treated with 10 per cent soda
solution at 2000.

One part gypsum (CaSO^HjO) dissolves in 199 parts of saturated NaCl
solution. Only .4 part dissolves in 200 parts pure water.

Pyrite (FeSa) loses 10.6 per cent of its mass upon boiling for a long time
with a solution of Na*S. Under the same circumstances galena loses 2.3
per cent.

One of the commonest of the gases found in water on the earth's
surface is carbon dioxide. This is an active agent in decomposing sili-
cates and in dissolving carbonates, so that water in which it is dissolved
is usually a more powerful solvent than pure water. Its dissolving
power increases with the pressure, as in the case of pure water, but
diminishes with increasing temperature. The action of carbonated
water on silicates is due to the replacement of the silicic acid by carbonic
acid and the production of bicarbonates, which are usually more soluble
than the corresponding carbonates. The greater solubility of carbon-
ates, like calcite, in carbonated water is also due to the formation of
bicarbonates. For example, the action of carbonated water upon cal-
cite (CaCOs) is as follows:

CaC03+H20+C02= CaH2(C03)2.

20 GENERAL CHEMICAL MINERALOGY

Carbonated water is more effective as a solvent under pressure
because of the inability of the CO2 to escape under this condition. When
pressure is removed the CO2 escapes, or evaporation takes place, and the
reverse reaction occurs, as:

CaH2(C03)2 = CaC03+H20+C02.

The dissolving effect of carbonated water upon various carbonates
and other minerals and the influence of pressure and temperature upon
the solution of a carbonate are indicated in the three tables following:

Solubility of Certain Carbonates in 10,000 Parts of Carbonated

Water

(The results are given in parts by weight)

Calcite (CaCO,), at io° 10. o Siderite (FeCOs) at 180 7.2

Dolomite (CaMg(COa)a) at 180. 3 . 1 Witherite (BaCO,) at io° 17.0

Magnesite (MgCO»), at 50. . . . 13. 1 Strontianite (SrCOs), at io°. . 12.0

Percentages of Various Minerals Soluble in Carbonated Water

(When treated 7 weeks)

Adularia (KAlSi,Og) 328 Apatite (Ca»(F- CI) (P04)a).. . 1.821

Oligoclase Apatite (Ca»(F • CI) (PO<),) ... 2.018

(NaAlSi,08+CaAl(SiO)4). . . .533 Olivine ((Mg.Fe)2Si04) 2 . in

Hornblende (complex silicate) 1.536 Magnetite (Fe304). . . .307 to 1 .821

Serpentine (HiMgaSijO*) 1 . 211

Influence of Temperature and Pressure upon the Solution of
Magnesium Carbonate (MgCOi) in Carbonated Water
(The results are given in parts per 10,000 by weight)
1 atmos. at 190 . . 2 . 579 parts Temp. 13 .4° under 1 atmos. . 2 .845 parts
32 3-730 29.3 2.195

5.6 4.620 62.0 1 .035

75 5120 82.0 .490

9.0 5659 100. 0 .000

Precipitation from Atmospheric Water. — Rain is an active agent
in dissolving mineral matter. Since it absorbs small quantities of carbon
dioxide, sulphur gases and other substances as it passes through the
atmosphere it may act upon many compounds, dissolving some, decom-
posing others and forming soluble compounds from those that would
otherwise be practically insoluble. Moreover, it transports the dissolved
materials from one portion of the crust to some other portion, where,
under favorable conditions, they may be precipitated. The rain water
that penetrates the earth's crust, dissolving and precipitating in its

FORMATION OF MINERALS 21

course through the crust, is known as vadose water. It is an important
agent in ore-formation, since it may collect mineral matter from a great
mass of rocks and precipitate it in some favorable place, thus making
ore bodies.

Deposits of Springs. — Springs are the openings at which under-
ground water escapes to the earth's surface. Much of the water flowing
from springs is the meteoric water which has circulated through the
crust and is again seeking the surface. In its course through the crust it
dissolves certain materials. Where it reaches the surface some of this
material may be dropped in consequence of (i) evaporation of the water,
or (2) the escape of carbon dioxide, or (3) the oxidation of some of its
constituents through the action of the air, or (4) the cooling of the water
in the case of warm or hot springs.

The deposits thus formed may occur as thin coatings on the rocks
over which the spring water passes, or as layers in the bottom of the
spring and the stream issuing from it. Among the commonest minerals
thus deposited are calcite (CaCOa), aragonite (CaCCb), siderite (FeCOa)
and other carbonates, gypsum (CaSO^zHaO), pyrite (FeSs), sulphur
(S), and limonite (Fe403(OH)e). The carbonates are deposited largely
in consequence of the escape of CO2 from the water, gypsum in conse-
quence of cooling, and limonite and sulphur through oxidation. If the
water contains H2S, this reacts
with the oxygen and a deposit .4 j
of sulphur ensues (compare -'-^^-'. : ^,- '■■

When the precipitation oc- .'"^A'
curs in cracks or fissures in the "■ V'v. V"-_.

rocks the precipitated matter l.-T_-
may partially or completely fill _"-_" V
the fissure, producing a vein; or, ". ^'

the precipitated matter may fill "J " - "
an irregular cavern forming a '.. - x-„ ■

bonanza. It sometimes covers "

the walls of cavities or the sur- Fie. 3.— Cross-section of Symmetrical Veto,
faces of minerals already exist- (After Le Nine Foster.)

ing, giving rise to a druse. In (a) De™™c™«i ™*. W Galena,

other cases precipitation may

occur while the solution is dripping from an overhanging surface,
making a stalactite, or the precipitate may fill the tiny crevices between
grains of sand cementing the loose mass into a compact rock,

Minerals produced by precipitation are often beautifully crystallized.

22 GENERAL CHEMICAL MINERALOGY

At other times they form groups of needles yielding globular and other
imitative shapes, while in still other instances they occur as pulverulent
or amorphous masses. The fillings of veins are often arranged sym-
metrically, similar materials occurring on opposite sides of their central
planes in bands, as shown in the figure (Fig. 3). Some important ores
have been concentrated and deposited in this way.

Deposits from Hot Springs. — The water of hot springs deposits a
greater variety of minerals than that of cold springs. Practically all
minerals that are soluble in hot water or in hot solutions of salts are
among them. Among those of economic value may be mentioned
cinnabar (HgS) and stibnite (Sb2S3).

Deposits from the Ocean and Lakes. — The water of the ocean and
of many lakes is rich in dissolved salts. That of lakes, however, is often
saturated or nearly so, while that of the ocean is not near the saturation
point. Consequently, while many lakes may deposit mineral sub-
stances, the ocean does not do so except under peculiar conditions. When
a portion of the ocean is separated from the main body of water, it may
evaporate and leave all of its mineral matter behind. Lakes may also
completely evaporate with a similar result. In each case the deposits
form layers or beds at the bottom of the basin in which the water was
collected.

In other instances the water brought to the ocean or a lake may
contain substances which will react with some of the materials already
present and produce an insoluble compound which will be precipi-
tated.

Of course, the nature of the beds thus formed will depend upon the
character and proportions of the substances that were in the water.
The ocean will yield practically the same kinds of compounds all over
the world and the beds deposited by the evaporation of ocean water
will be formed in nearly the same succession everywhere. In the case
of enclosed bodies of water — like lakes or seas — in which the composi-
tion of the water may differ, the deposits formed may also differ.

Many of the deposits formed in bodies of water are of great eco-
nomic importance and, consequently, are extensively worked. Prob-
ably the most important are the beds of salt (NaCl) and of gypsum
(CaSO^EfeO), although borax (Na2B407 • 10H2O) was formerly
obtained in large quantity from the deposits of some of the lakes in
the desert portions of the United States.

In the following table are given the results of analyses of water of
the ocean and of Great Salt Lake, in Utah, calculated on the assump-
tion that the elements are combined in the manner indicated in the

FORMATION OF MINERALS

column on the left. The results of the analyses of the waters of a few
noted lakes are given in the succeeding table.

Composition of Salts Contained in Water of the Ocean and Great

Salt Lake

(Parts in iooo of Water)

I II HI

NaCl 27.3726 8.1163 118.628

KC1 5921 .1339

MgClj 33625 .6115 14.908

CaS04 1 .3229 .9004 .858

MgS04 2.2437 3o85S

Na2S04 9-321

K2S04 5363

RbCla .0190 .0034

MgBr3 0547 .0081 tr

Ca«(P04)i 0156 .0021

CaCOi 0434 .0780

FeCOi 0019 .0011

SiOt 0149 .0024

35-°433

12.9427

149.078

I. Water of N. Atlantic off Norwegian Coast. Analyst, C. Schmidt.
II. Average of Five Analyses, Caspian Sea at depths of from 1 m. to 640 m.

Analyst, C. Schmidt.
III. Great Salt Lake, Utah. Analyst, O. D. Allen.

Percentage Composition of the Residues of a Few Lake Waters

Dead Sea

Lake Beisk, Siberia

Goodenough Lake, B. C.
Borax Lake, Cal

Br
1.45

SO4

CO3

3.24

SiO,.

etc.

64.49

.45

15.75

4.09

10.53

22.70

42.32

.61

31.32 1.01

.07

1.86

.02

7.64

7.08

41.41

36.17

6.65

.02

.04

.99

32.27

.04

.13

22.47

38.10

1.52

.03

.35

.02

Total Solida

(per 1000

of Water).

220.3
104.7
103.47
76.56

Deposits from Magmatic Water. — Equally important in depositing
mineral matter is the water that escapes from cooling lavas and other
molten magmas — designated as juvenile water. All molten magmas
existing under pressure, i.e., at some distance beneath the crust, contain
the components of water, which escape as the magma cools or when the
pressure diminishes, whether the diminution of the pressure is due to

24 GENERAL CHEMICAL MINERALOGY

the escape of the lava to the surface or to the cracking of the crust.
In its passage to the surface the hot water carrying dissolved salts pene-
trates all the cracks and cavities in the rocks through which it passes
in its ascent and deposits its burden of material, forming veins and other
types of deposits. Or, its components may decompose the materials
with which it comes in contact, replacing them wholly or in part by the
substances which it is carrying or by the products of decomposition.

FlO. 4. — Croas-section of Vein in Green Porphyry. The vein filling is chalcedony.
The white splotches are feldspar crystals. The [airly uniform character of the
rock where not affected by the vein is seen on the right side of the picture. The
rude banding parallel to the vein is due to changes that have proceeded out-
ward from tbe vein-mass into the rock.

Since in many cases magmatic water contains corrosive gases, such as
fluorine, its action on the rocks which it traverses is profound. A tiny
crack in the rocks may be gradually widened and the material on both
sides of it be replaced by new material, thus producing a vein which
is sometimes difficult to distinguish from a vein made in other ways
(Fig. 4). This process is known as metasomatism, which is one kind of
metamorpkism. It is an important means of producing pseudomorphs
and bodies of mineral matter sufficiently rich in metallic contents to
constitute ore-bodies.

FORMATION OF MINERALS 25

Solidification from Molten Magmas. — A molten magma, such as a
liquid lava, is probably a solution of various substances — mainly sili-
cates— in one another, or in a hot solvent. Upon cooling or upon change
of conditions, such as may arise from loss of gas or water or from reduc-
tion of pressure, this hot solution gradually deposits some of its con-
stituents as definite chemical compounds. Upon further cooling other
compounds solidify and so on, until finally, if the rate of cooling has been
slow, the entire mass may separate as an aggregate of minerals — such
as constitute many of the rocks, as granite for instance, and many of the
lavas. If the cooling has been rapid, some of the material may separate
as definite minerals while the remainder solidifies as a homogeneous
glass, as in the case of most lavas. Sometimes the minerals thus formed
are bounded by crystal planes, but usually their growth has been so
interfered with that it is only by their optical properties that they can
be recognized as crystalline substances. The nature of the minerals
that separate depends upon a great variety of conditions, the most
important of which is the chemical composition of the magma.

In some cases the minerals separating from a magma tend to segre-
gate in some limited portion of its mass and thus produce an accumula-
tion that may be of economic value, i.e., the magma differentiates.
Magnetite (FeaO^, ilmenite ((Fe-Ti)203), pyrite (FeS2) and a few other
minerals are sometimes segregated in this way in very large masses.

Metamorphic Minerals. — Many minerals are characteristic of rocks
that are in contact with others that were once molten. They were
formed by the gases and hot waters given off from the magmas before they
cooled. The hot solutions with their charges of gas and salts penetrated
the pores of the surrounding rock and deposited in them some of their
material. They reacted with some of the rock's components, producing
new compounds, and extracted others, leaving pores into which new
supplies of gas and water might enter. In some cases the entire body
of the surrounding rock has been replaced by new material for some
distance from the contact. Beyond this belt of most profound meta-
morphism are other belts in which the rock is less altered, until finally in
the outer belt is the unchanged original rock. Into the outer contact
belt perhaps only gas penetrated and the changes here may be entirely
pneumatolytic. Near the contact the changes may be metasomatic.
Minerals formed by these processes near the contact of igneous masses
are frequently referred to collectively as contact minerals.

In other cases new minerals may be produced in rocks in consequence
of crushing attended by heat. Hot water under high pressure
greatly facilitates chemical changes. A part of the materials of the

* .#

26 GENERAL CHEMICAL MINERALOGY

crushed rock dissolves, reactions are set up and new compounds may
be formed. The new minerals produced are more stable than the
original ones and have in general a greater density and consequently
a smaller volume. The type of metamorphism that produces these
effects is known as dynamic metamorpkism.

Organic Secretions. — The transfer of mineral substances from a
state of solution to the solid condition is often produced through the aid
of organisms. Mollusca, like the oyster, clam, etc., crustaceans, like
the lobster or crab, the microscopic animals and plants known as pro-

Fig. 5. — Diorite Dike Cutting Granite Gneiss, Pelican Tunnel, Georgetown, Colo.

(After Spun and Carry.)

tozoans and algae and many other animals and vegetables abstract
mineral matter from the water in which they live and build up for them-
selves hard parts. These hard parts, usually in the form of external
shells, are composed of calcium carbonate (CaCOa), either as calcite or
aragonite, of silica (SiOz) or of calcium phosphate Ca3(PO.j)2. Although
not commonly regarded as minerals these substances are identical
with corresponding substances produced by inorganic agencies.1

Paragenesis. — -It is evident that minerals produced in the same

1 Plants and animals upon decaying yield organic acids which may attack minerals

already existing and thus give rise to solutions which may deposit pyrite (FeSj),

limonite (a hydrated iron oxide) or some other metallic compound. This process,

however, is property simply a phase of deposition from solutions.

FORMATION OF MINERALS 27

way will generally be found together. A certain association of minerals
will thus characterize deposits from magmas, another association

Fig. 6.— Vein in Griffith Mine, Georgetown, Colo., Showing Two Periods of Vein

Deposition. (After Sfiurr and Carry.)

(T\ - wall rock. b =- sphalerite. c - chalcopynto.

q - comb quarts. P — pyrite. g — galena.

Balance of vein-filling is a mixture of manganese-iron carbonates.

Fig. 7. Vein Forming Original Ore-Body, Butte, Mont. (After W. H. Weed.)

(0 P«ult breccia; (2) ore; (3) altered granite; (4) firsl-dasa ore; (5) crushed quarti and
wrntte; (6) fault clay; (7) solid pyrite and bornite; (S) crushed quartz and pyrite; (9) solid

those precipitated from water, another those produced by contact
action, etc. This association of minerals of a similar origin is known

28 GENERAL CHEMICAL MINERALOGY

as their paragenesis. From a study of their relations to one another the
order of their deposition may usually be determined.

Occurrence. — The manner of occurrence of mineral substance is
extremely varied, as may be judged from the consideration of the vari-
ous ways in which they are formed. Deposits laid down in water occur
in beds or in the cement uniting grains of sand, etc., such as the beds
of salt (NaCl) or gypsum (CaS04 ■ 2H2Q) found in many regions. Those
produced by the cooling of magmas may form great masses of rock
such as granite, which when it occurs as the filling of cracks in other
rocks is said to have the form of a dike (Fig. 5)- Deposits made by
water, whether meteoric or mag-
matic may give rise to veins, which
may be straight-walled or branch-
ing, like the veins of quartz (SKfe)
that are so frequently seen cutting
various siliceous rocks. When the
veins are filled by meteoric water
they often have a comb-structure —
the filling consisting of several sub-
stances arranged in definite layers
following the vein walls (see p. 21).
If the composition of the depositing
solution, whether meteoric or mag-
matic, has remained constant for a
long time the vein may be filled
with a single substance. If its com-
position changed during the time
the filling was in progress the layers
are of different kinds. Further, it
Fig. 8.— Druse of Smithsonite (ZnCft) deposUioncontmueduninterruptedly
on Massive Smithsonite. the layers may match on opposite

sides of the vein and the succession
may be the same from walls to center. If, however, after the partial
or complete filling of the crack it was reopened and the new crack was
filled, the new vein when filled would be unsymmetrical if the new crack
occurred to one side of the center of the original vein (Fig. 6). Repeated
reopening may give rise to a vein that is so lacking in symmetry that
it is difficult to trace the succession of events by which it was produced
(Fig- 7)- Veins filled by inagmatic water are frequently more homo-
geneous.

Druses (Fig. 8) arise when deposits simply coat the walls of fissures.

FORMATION OF MINERALS 29

In many cases they may be regarded as veins, the development of which
has been arrested and never completed. When the deposits coat the
walls of hollows within rocks they are known as geodes (Fig. o). Geodes
are common in limestones and other easily soluble rocks in which
cavities may be dissolved.

Gases and water under great pressure may penetrate the micro-
scopic pores existing in all rocks and there deposit material which may
fill the pores and cement the rocks. If the deposited material is metallic
the rocks may be transformed into masses sufficiently rich in metallic
matter to become ore-bodies. A body of this kind is known as an
impregnation. It is well represented by some of the low grade gold
ores, such as those in the Black Hills.

When rocks are decomposed by the weather they are broken up.

Fig. q.— Geodes Containing Calcite (CaCOi) Crystals.

The rains wash the disintegrated substance into streams. In its course
downward to lakes or the ocean, the heavier fragments, such as metallic
particles, may settle while the lighter portions are carried along.
Thus the heavy parts may accumulate in the stream bottoms. These
materials, consisting of gold, magnetite, garnet, pyrite and other min-
erals of high specific gravity, form a loose deposit in the stream bed
which is known as a placer. Gold is often found in placer deposits.
The lighter portions may be carried to the lake or sea into which the
streams enter and may accumulate as sand on beaches and on the
bottom near the shores as gravel, sand, silt, etc. Most sand consists
principally of quartz, but many sands contain also grains of feldspar
and other silicates, and sometimes other compounds.

30 GENERAL CHEMICAL MINERALOGY

Alteration of Minerals. — Minerals, like living things, are constantly
subject to change. Circulating waters may dissolve them in part,
or completely, and transport their material to a distant place, there
depositing it either in the form it originally possessed or in some new
form. On the other hand, the mineral substance may be decomposed
into several compounds some of which may be carried off, while others
are left behind. Again, the material remaining behind may com-
bine with other matter held in the water causing the decomposition,
and may form with it a new mineral or a number of different minerals
occupying the place of the original one. This is in part metasomatism.

The atmosphere may also act as a decomposer of minerals. Through
the agency of its oxygen it may cause their oxidation, or it may cause
them to break up into several oxidized compounds. Through the agency
of its moisture, it may dissolve some of these secondary substances or
it may form with them hydrated compounds. The substances thus
formed may be dissolved in water and carried off, or they may remain
to mark the place of the mineral from which they were derived.

Water, containing traces of salts, or gases in solution are exceedingly
active agents in effecting changes in minerals. Many examples of the
alteration of practically insoluble minerals under the influence of dilute
solutions are known. Calcite (CaCOa), for instance, when acted upon
by a solution of magnesium chloride (MgCb) takes up magnesium and
loses some ©f its calcium. Monticellite (CaMgSi04) when acted upon
by solutions of alkaline carbonates breaks up into a magnesium silicate
and calcium carbonate. Dilute solutions of various salts are constantly
circulating through the earth's crust and are there effecting trans-
formations in the minerals with which they come in contact. On, or
near, the surface the transformations are taking place more rapidly
than elsewhere because here the solutions are aided in their decompos-
ing action by the gases of the atmosphere.

The effect of the air in causing alteration is seen in the green coat-
ing of malachite ((CuOH^COs) that covers surfaces of copper or of
copper compounds exposed to its action. In this particular case the
coating is due to the action of the carbon dioxide and the moisture of
the atmosphere. Other substances in contact with the air are coated
with their own oxides, sulphides, etc.

Pseudomorphs. — When the alteration of a mineral has proceeded
in such a manner that the new products formed have replaced it particle
by particle a pseudomorph results. Sometimes the newly formed sub-
stance crystallizes as a single homogeneous grain filling the entire
space occupied by the original substance. Usually, however, the alter-

FORMATION OF MINERALS 31

ation begins along the surfaces of cracks or fissures in the body under-
going alteration, or upon its exterior, thus producing the new material
at several places contemporaneously (Fig. 10). When' the replace-
ment takes place in this manner the resulting mass is a network of
fibers of the new substance or an aggregate of grains with the outward
form of the replaced mineral.

With respect to their method of formation chemical pseudomorphs
may be classified as alteration
pseudomorphs and replacement
pseudomorphs.

Alteration Pseudomorphs. —
Pseudomorphs of this class may
be denned as those which retain
some or all of the constituents of
the original minerals from which
they were derived.

Paramorphs. — Pseudomorphs
composed of the material of the

pseudomorphed substance with- Flc. IO_ Alteration of Olivine into Ser-
out addition or subtraction of pentine. The alteration is proceeding
any component are known as from the surface of the crystal and
paramorphs. from surfaces of cracts that traverse

n ,. . .,, , it. The black specks and streaks

Faramorphism is possible only , __.-., . . - ..

r r J represent magnetite formed during the

in the case of dimorphous bodies. ptoeess. (After Tschtrmak.)
It results from the rearrangement

into new bodies of the particles of which the original body was com-
posed.

Illustrations: CalcUe (hexagonal CaCOa) after aragonite (ortho-
rhombic CaCOa); orthorhombic sulphur after the monoclinic variety.

Partial Pseudomorphs. — The great majority of pseudomorphs
retain a portion, but not all, of the material of the original mineral.
They may be formed by the addition of material to the original body;
by the loss of material from it; or by the replacement of a portion of
its material by new material.

Pseudomorphs formed by the addition of substance to that already
existing are rare. The substances most frequently added in the pro-
duction of such pseudomorphs are oxygen, sulphur, the hydroxyl
group (OH) and the carbonic acid group (CO3 and CO2).

Illustrations: Malachite ((CuOH)2C03) after copper, and argentile
(AgzS) after silver.

Pseudomorphs resulting from the loss of material are not common.

32 GENERAL CHEMICAL MINERALOGY

They are caused by the abstraction of one or more of the constituents
of a compound.

Illustration: Native copper after cuprite (CU2O).

The greater number of partial pseudomorphs are formed by the sub-
stitution of some of the components of the original mineral by a new
material.

Illustrations: Limonite (Fe403(OH)e) pseudomorphs after siderite
(FeC03) may be formed by the following reaction:

4FeC03+ 2O+3H2CM 4C02+Fe403(OH)6.
Cerussite (PbC03) may be formed from galena (PbS), thus:
PbS+40+Na2C03 = PbC03+Na2S04.

Replacement Pseudomorphs. — Often the entire substance of a
mineral is replaced by new material, so that no trace of its original
matter remains. In this case the nature of the pseudomorphed min-
eral can be discovered only from the form of the pseudomorph.

Illustrations: Quartz (S1O2) after calcite (CaC03) and gypsum
(CaS04-2H20) after halite (NaCl).

Mechanical Pseudomorphs. — The processes described above as
originating pseudomorphs are chemical, and the resulting pseudomorphs
are sometimes designated chemical pseudomorphs. There is another
class of pseudomorphs, however, in which the substance of a crystal
has not been replaced gradually by the pseudomorphing substance.
In this class the pseudomorphing substance simply fills a mold left by
the solution of some preexisting crystal. Thus, if a sulphur crystal
should become encrusted with a coating of barite (BaS04) and the
temperature should rise until the sulphur melts and escapes, there
would be left a mold of itself constructed of barite. If, now, a solution
of calcium carbonate should penetrate the cavity and fill it with a deposit
of calcite (CaC03), the mass of calcite would have the shape of a crystal
of sulphur. Pseudomorphs of this kind are known as mechanical
pseudomorphs.

Weathering. — The term weathering is applied to the sum of all the
changes produced in minerals by the action of the atmosphere upon
them. Although nearly all minerals show some traces of weathering,
these traces may often be detected only by the slight differences in color
exhibited by surfaces that have been exposed for a long time to the
action of the air when compared with fresh surfaces produced by frac-
ture or cleavage.

FORMATION OF MINERALS 33

The weathering of minerals is often of great economic importance.
Veins of sulphides and a few other compounds may be oxidized where
they outcrop on the surface. Some of the decomposition products thus
formed may be soluble and others insoluble. The insoluble products
may remain near the surface while the soluble ones are carried down-
ward by ground water along the course of the vein. Here a reaction
may ensue between the soluble salts and the undecomposed portion of
the vein with the result that metallic compounds may be precipitated,
thus enriching the original vein matter and causing it to be changed
from a comparatively lean ore to one of great richness.

Pyrite veins on the surface are often marked by accumulations of
limonite derived by the oxidation of the sulphide. With this may be
mixed insoluble carbonates, silicates and other salts of valuable metals
present in the original sulphide. Weathering may extend downward
along the veins for a short distance, replacing their upper portions with
the oxidized decomposition products. This portion of a vein is often
spoken of as the oxidized zone, and this is sometimes the richest portion
of the vein. It may be rich because less valuable substances have
formed soluble salts and have been drained away.

Below the oxidized zone may be another zone less rich in valuable
compounds than the oxidized zone, but much richer than the material
below it. The soluble decomposition products of the upper portion of
the vein may percolate downward, and react with the unchanged vein
matter, precipitating valuable metallic salts. Although the original
vein matter may contain an inconsiderable quantity of the valuable
material, the precipitation in it of additional stores of material of the
same kind may raise the percentage of this constituent to a point where
it is profitable to mine it. This belt of enriched ore is known as the
zone of secondary enrichment.

The oxidized zone extends downward from the surface to a depth at
which the atmosphere and meteoric water become exhausted of their
oxygen — a depth which varies with local conditions. The zone of
secondary enrichment extends from the bottom of the oxidized zone
to a short distance below the level of the ground water, beyond which
solutions will diffuse and thus be carried away from the vein. Below
the zone of enrichment the original vein-filling may reach downward
indefinite distances.

Since many veins exhibit the features described, it follows that the
ore of many mines must grow poorer with depth, and that in many
instances the richest ore is near the surface.

Some of the changes involved in weathering and secondary enrich-

34 GENERAL CHEMICAL MINERALOGY

ment of sulphide veins in limestone are indicated by the following reac-
tions in the case of a vein containing pyrite (FeS2), sphalerite (ZnS),
and galena (PbS).

(i) The first change produced at the surface may be the oxidation
of the sulphides to sulphates.

(a) ZnS+40=ZnS04;

(b) PbS+40=PbS04 (anglesite);

(2) These may react with the limestone as follows:

(smithsonite) (gypsum)

(a) ZnS04+CaC03+2H20=ZnCOs + CaS04-2H20;

(cerussite) (gypsum)

(b) PbS04+CaC03+2H20=PbC03 + CaS04-2H20.

(3) Some of the sulphates and carbonates carried down into the un-
altered sulphides may react with these, yielding:

(galena)

(a) PbS04+FeS2+02=PbS+FeS04+S02;

(galena) (siderite)

(b) PbC03+FeS2+02=PbS + FeC03 + S02;

(galena)

(galena) (smithsonite)

(d) PbC03+ZnS = PbS + ZnCOs.

The PbS replacing the ZnS and deposited in the cracks in the original
mixture of PbS, ZnS and FeS2 increases the percentage of this compound
in the vein and thus enriches it.

There is also an increase in the percentage of ZnS brought about by
the reactions between the zinc salts (1a and 2a), and the pyrite, analogous
to those between the lead salts and pyrite ($a and 36). Thus:

(sphalerite)
ZnS04+FeS2+02 = ZnS + FeS04+S02,

(sphalerite)
ZnC03+FeS2+02 = ZnS + FeC03+S02.

FORMATION OF MINERALS 35

The zinc salts produced in reactions $c and 3<f if carried downward will
also have the opportunity to react with the pyrite in the same way.

If the ZnS is deposited in fissures in the vein matter this will tend to
enrich it with zinc.

The oxidized zone contains (smithsonite) ZnCCfo, (anglesite) PbSO^,
(cerussite) PbCOa and (limonite) Fe2(OH)2. The ZnS04, formed also
in the oxidized zone, is so readily soluble in water that it is leached from
the other oxidized compounds and is carried downward.

PART II
DESCRIPTIVE MINERALOGY

CHAPTER III

INTRODUCTION— THE ELEMENTS

Of the 1,000 or more distinct minerals recognized by mineralogists
only a few (some 250) are common. A few are important because they
constitute ores, others because they are components of rock masses,
and others simply because of their great abundance. Only a few miner-
alogists profess acquaintance with more than 500 or 600 minerals. The
majority are familiar with but 300 or 400, relying for the identification of
the remainder upon the descriptions of them recorded in mineralogical
treatises.

Only the minerals commonly met with and those of economic or of
special scientific importance are described in this book. They should
be studied with specimens before one, in order that the relation between
the descriptions and the objects studied may be forcibly realized. Min-
eralogy cannot be studied successfully from books alone. It is primarily
a study of objects and consequently the objects should be at hand for
inspection.1

Mineral Names. — The names of the great majority of minerals end
in the termination "ite." This is derived from the ancient Greek suffix
"itis" which was always appended to the names of rocks to signify that
they are rocks. The first portion of the name, to which the suffix is
added, either describes some quality or constituent possessed by the
mineral, refers to some common use to which it has been put, indicates
the locality from which it was first obtained, or is the name of some
person intended to be complimented by the mineralogist who first
described the mineral bearing it.

1 Collections of the common minerals in specimens large enough for convenient
study may be secured at small cost from any one of the mineral dealers whose
addresses may be found in any mineralogical journal.

INTRODUCTION— THE ELEMENTS 37

The following examples taken from Dana illustrate some of these
principles. The mineral hematite (Fe203) is so named because of the red
color of its powder, chlorite (a complicated silicate), because of its green
color, siderite (FeCOa), from the Greek word for iron, because it con-
tains this metal, magnetite (Fe304) after Magnesia in Asia, goethite
(FeO(OH)) after the poet Goethe.

The names of a few minerals end in "ine," "ane," "ase," "ote," etc.,
but the present tendency is to have them all end in "ite." Occasionally,
the same mineral may have two names. This may be due to the fact
that it was discovered by two mineralogists working at the same time
in different places, or it may be due to the fact that the mineralogists of
different countries prefer to follow different precedents set by the old
mineralogists of their respective nationalities. For example, the min-
eral (Mg- Fe)2Si04 is called olivine by the Germans and by most English-
speaking mineralogists, and peridot by the French. The Germans follow
the German mineralogist Werner, who first used the name olivine in
1789, while the French follow the French teacher Hatiy, who proposed
the name peridot in 1801.

ELEMENTS

The elements that occur in nature are few in number, and these,
with rare exceptions, do not occur in great abundance. They may be
separated into the following groups: the carbon group, the sulphur
group, the arsenic group, the silver group, and the platinum-iron
group. Some of these comprise only a single mineral, while others
comprise six or seven. Only a portion of these are described.

THE NON-METALS AND METALLOIDS

CARBON GROUP
The carbon group embraces several minerals of which one is dia-
mond, another is an amorphous black substance known as schungite,
and the other two are apparently but different forms of graphite.
The element may thereupon be regarded as trimorphous. Diamond
and graphite are both important.

Isometric (hextetrahedral) Hexagonal (ditrigonal scalenohedral)

Diamond Graphite

Diamond (C)

The diamond is usually found in distinct crystals or in irregular
masses, varying in size from a pin's head to a robin's egg. In some
cases large individual pieces are found but they are exceedingly rare.

DESCRIPTIVE MINERALOGY

Fig. ii.— Etch Figures on
Cubic Face of Diamond
Crystal. (Afttr Ticker-

The largest ever found, known as the Cullinan diamond (Fig. 16),

weighed 3,024! carats or 621 grams, or 1.37 lb.,

and measured 112x64x51 mm- It was cut

into nine fine gems and a number of smaller

I ones (Fig. 17).

I In composition the diamond is pure car-

I bon, but it is a form of carbon that is not
ignited and burned at low temperatures. At
high temperatures, however, especially when
in the presence of oxygen, it burns freely
with the production of COa, and, in the case
of opaque varieties, a little ash.

Its crystallization is isometric (hextetra-
hedral class), and the forms on the crystals often appear to be tetra-
hedrally hemihedral, although the
etch figures on cubic faces suggest
hexoctahedral symmetry (Fig. n).
Octahedrons, tetrahedrons, icositet-
rahedrons and combinations of these
forms are common, and in nearly all
cases the interfacial edges are rounded
and the crystal faces curved. Some-
times this curving is so pronounced
that the individuals are practically
spheres (Fig. 12). Twins are com-
mon with 0(i n) as the twinning
plane (Fig. 13).

The cleavage of diamond is per-
fect parallel to the octahedral face.
This is an important characteristic, as the lapidary makes use of it
in the preparation of stones for cutting. Its
fracture is conchoidal. Its specific gravity is
3.52 and its hardness greater than that of any
other known substance. Most diamonds are
dark and opaque, or, at most, translucent, but
many are found that are transparent and color-
less or nearly so. Gray, brown, green, yellow,
blue and red tinted stones are also known, and,
with the exception of the blue and red diamonds,
these are more common than the colorless, or
so-called white stones. The luster of all diamonds is adamantine, and

2. — Crystal of Diamond with
Rounded Edges and Faces. (Kraals.)

ric. 13.— Octahedron of
Diamond Twinned
about O(iii).

INTRODUCTION— THE ELEMENTS 39

their index of refraction is very high, «= 2.4024 for red rays, 2.4175 for
yellow rays, and 2.4513 for blue rays. In consequence of their strong
dispersion, the reflection of light from the inner surfaces of transparent
stones is very noticeable, causing them to sparkle brilliantly, with a
handsome play of colors. It is this latter fact and the great hardness
of the mineral that make it the most valuable of the gems.- The mineral
is a nonconductor of electricity.

Three varieties of the diamond have received distinct names in
the trade. These are:

Gem diamonds, which are the transparent stones;

Bart, or Bortz, gray or black translucent or opaque rounded masses,
with a rough exterior and the structure of a crystalline aggregate; and

Carbonado, black, opaque or nearly opaque masses possessing a
crystalline structure, but no distinct cleavage.

The only minerals with which diamond is liable to be confused
are much softer, and, consequently, there is little difficulty in dis-
tinguishing between them.

Syntheses. — Small diamonds have been made by fusing in an
electric furnace metallic iron containing a small quantity of carbon and
cooling the mass suddenly in a bath of molten lead. They have also
been made by heating in the electric arc pulverized carbon on a spiral
of iron wire immersed in hydrogen under a pressure of 3,100 atmospheres.
A third method, which resulted in the production of tiny octahedrons,
consisted in melting graphite in olivine, or in a mixture of silicates
having the composition of the South African " blue ground," with
the addition of a little metallic aluminium or magnesium.

Occurrence and Origin. — Diamonds are found (1) in clay, sand
or gravel deposits or in the rocks formed by the consolidation of these
substances, where they are associated with gold, platinum, topaz,
garnet, tourmaline and with other minerals that result from the decom-
position of granitic rocks, (2) in a basic igneous rock containing frag-
ments of shale (a consolidated mud) and (3) small diamonds have been
discovered in meteorites.

The manner of origin of diamonds has been a subject of contro-
versy for many years. The most popular theory ascribes the diamonds
in igneous rocks to the solution of organic matter in the rock magmas
and the crystallization of the carbon upon cooling. Another theory
regards the carbon as an original constituent of the magma. The
diamonds in sand, sandstone, granite, etc., are believed to have been
transported from their original sources and deposited in river channels
or on beaches.

40 DESCRIPTIVE MINERALOGY

Localities. — The principal localities from which diamonds are obtained
are the Madras Presidency in India; the Province of Minas-Geraes in
Brazil; the Island of Borneo; the valleys of the Vaal and Orange
Rivers, and other places in South Africa, and the valley of the Mazaruni
River and its tributaries in British Guiana. Recently diamond fields
have been discovered in New South Wales, Australia, in the valley of
the Kasai River in the Belgian Kongo, in Arkansas, and in the Tula-
meen district, British Columbia.

In the United States a few gem diamonds have been found from
time to time in Franklin and Rutherford counties in North Carolina;
in the gold-bearing gravels of California, and in soils and sands in the
states of Alabama, Virginia, Wisconsin, Indiana, Ohio, Idaho and
Oregon. A stone (the Dewey diamond) found near Richmond, Virginia,
a few years ago is valued at $300 or $400.

The principal source of diamonds and carbonado in Brazil at the
present time is Bahia, where the mineral occurs in a friable sandstone
along river courses. The output of this region has decreased so greatly
in the last few years that although a mass of carbonado weighing 3,073
carats (the largest mass of diamond material ever found) was obtained
in 1895, the price of this impure diamond rose from $10.50 per carat
in 1894 to $36.00 per carat in 1896 and $85.00 per carat for the best
quality in 19 16.

The only diamond field of prominence in the United States is that
which has recently been exploited near Murfreesboro in Arkansas, where
the conditions are similar to those existing in South Africa. The dia-
monds occur in a basic igneous rock (peridotite) that cuts through sand-
stones and quartzites. The peridotite is weathered to a soft earth or
" ground " in which the diamonds are embedded. Up to the end of
1914 over 2,000 diamonds had been found, mostly small stones weighing
in the aggregate 550 carats, valued at about $12,000. One, however,
weighed 8| carats and another 7! carats. The rough unsorted stones
are valued at $10 per carat. Three stones that were cut were found

to be worth from $60 to $175 per carat. The district has not yet been
sufficiently developed to prove its commercial value. The diamonds
in British Columbia occur in the same kind of rock as those in Arkansas.
The few that have thus far been found are too small for any practical
use.

In former times the mines of India and Borneo were very produc-
tive, the famous Golconda district in India for a long period furnishing
most of the gems to commerce.

The African mines were opened in 1867. Since this time they

INTRODUCTION— THE ELEMENTS 41

have been practically the only producers of gem material in the world.
It is estimated that the quantity of uncut diamonds yielded by the
mines near Kimberly alone have amounted in value to the enormous
sum of $900,000,000. The output of the African mines in 19 13 was
sold for about $53,000,000, being over 95 per cent of the world's out-
put of gem material. Of this amount about $9,000,000 worth of stones
were furnished by German Southwest Africa, the balance by the
Union of South Africa. The diamonds are found in a peridotite which
occurs in the form of volcanic necks, or " pipes," cutting carbonaceous
shales. The igneous rock is much weathered to a soft blue earthy mass
known as " blue earth." Near the surface where exposed to the action
of the atmosphere the earth is yellow. The diamonds are scattered
through the weathered material in quantities amounting to between
.3 and .6 carat per cubic yard.

Extraction. — Where the diamond occurs in sand and gravel it is ob-
tained by washing away the lighter substances.

In South Africa and Arkansas the mineral is found in a basic volcanic
rock which weathers rapidly on exposure to the air. The weathered
rock is mined and spread on a prepared ground to weather. When suf-
ficiently disintegrated water is added to the mass and the mud thus
formed is allowed to pass over plates smeared with grease. The dia-
monds and some of the other materials adhere to the grease, but most
of the valueless material is carried off by the water.

Uses. — Transparent diamonds constitute the most valuable gems
in use. Perfectly white stones, or those possessing decided tints of red,
rose, green or blue are the most highly prized. They are sold by
weight, the standard being known as the carat, which, until recently,
was equivalent to 3.168 grains or 205 milligrams. At present the metric
carat is in almost universal use. This has a weight of 200 milligrams.
The price of small stones depends upon their color, brilliancy and size —
a perfectly white, brilliant, cut stone weighing one carat, being valued
at about $175.00. As the size increases the value increases in a much
greater ratio, the price obtained for large stones depending almost solely
upon the caprice of the purchaser.

Nearly all the gem diamonds put upon the market are cut before
being offered for sale. The chief centers of diamond cutting are Ant-
werp and Amsterdam in the Old World and New York in America.
The favorite cuts are the brilliant and the rose. For the former only
octahedral crystals, or those that will yield octahedrons by cleavage,
are used, for the rose cut distorted octahedrons or twinned crystals.
In producing the "brilliant" a portion of the top of an octahedron is cut

DESCRIPTIVE MINERALOGY

W=W

A A

Bom

Grown Back, ox Parllion

Step or Trap

Grown

gido View

ParCHon, or Base

Brilliant

Fig. 14. — Principal " cuts " of Diamonds.

off and a small portion of the bottom. On the remainder are cut three
or four bands of facets running horizontally around the stone (see Fig. 14).
The "rose" has a flat base surmounted by a pyramidal dome consisting
of 24 or more facets. In late years the shapes into which diamonds are
cut have been determined less by the decrees of fashion and more by the

/v— — 7v desire to save as much ma-

>n> vtI mOi /On terial as possible, and, conse-
quently, irregularly shaped cut
diamonds are much more
common than formerly (com-
pare Fig. 17).

Diamonds are employed
also as cutting tools. Small
fragments, or splinters of gem
quality, are used for cutting
and polishing diamonds and
other gems, and small crystals
with crystal edges for cutting
glass. Small cleavage pieces
are utilized in the manufacture of engravers' tools and writing instru-
ments. Recently diamonds with small holes of from .008 to .0006 of an
inch drilled in them, have been employed as wire dies.

Bort is also used as a polishing and cutting material, while carbonado,
nearly all of which comes from Brazil, is used in the manufacture of
boring instruments. Diamond drills consist of hollow cylinders of soft
iron set at their lower edges with 6, 8 or 1 2 black diamonds. By rapid
revolution of this a "core" may be cut from the hardest rocks.

Some Famous Diamonds. — The largest diamond ever found — the Cull-
inan — was picked up at the Premier Mine (Fig. 15) in the Transvaal in
January, 1905, and was presented to King Edward of England as a birth-
day gift in 1908. (Figs. 16 and 17.) It weighed about 3,025 carats (about
1.37 pounds). The next largest was found in June, 1893, at the Jagers-
fontein mine. It is known as the Excelsior. It weighed in its natural
state 971 carats and was 3 inches long in its greatest dimension. It was
valued at $2,000,000. It is said to have been presented by the Presi-
dent of The Orange Free State to Pope Leo XIII. The third largest
stone is the Reitz. It is a 640-carat stone found at the same mine during
the close of 1895. This, though smaller, is said to be handsomer "than the
Excelsior. The most noted diamond in the world is the Kohinoor, which
weighed, before cutting, 186 carats. It is now a brilliant of 106 carats,
belonging to the crown of England. Other famous diamonds are the

INTRODUCTION— THE ELEMENTS

FlC. 15, — Premier Diamond Mines in South Africa. (After WUiiem.)

—The Cullman Diamond. (Natural size.)

DESCRIPTIVE MINERALOGY

Fig. 17. — Gems Cut from the Cullinaii Diamond. [Two-fifths nat. size.)

Orlov, 193 carats, the property of Russia; the Regent or Pitt diamond
of 137 carats belonging to France; the Green diamond of Dresden,
weighing 48 carats, and the Blue
Hope diamond, weighing 44 carats.
The " Star of the South," found in
Brazil, weighed 254 carats before
cutting and 125 afterward. The
Victoria diamond from one of the
Kimberly mines weighed 457 carats
when found. It has been cut to a
perfect brilliant of 180 carats valued
at $1,000,000. The Tiffany dia-
mond (Fig. 18) now owned in New
York is a double brilliant of a
golden yellow color weighing 128J
F.G.l8.-The Tiffany Diamond. (Nat- carats (25.702 grams) and valued at
ural size.) (Kindness of Tijjany &■ Co.) $100,000. When it is remembered
that a five-carat stone is large, tie
enormous proportions of the above-named gems are better appreciated.

Graphite (C)

Graphite, or plumbago, occurs principally in amorphous masses of a
black, clayey appearance, in. radiated masses, in brilliant lead black
scales or plates, and occasionally in crystals with a rhombohedral habit.

Like diamond, graphite consists of carbon. Crystals from Ceylon
yield: C=79.4o; Ash= 15.50; Volatile matter=5.io. The mineral is
often impure from admixture with clay, etc.

INTRODUCTION— THE ELEMENTS 45

Crystals of the material a*e so rare that their symmetry is still in
doubt. Their habit is hexagonal (di trigonal scalenohedral class).
Measurements made on the interfacial angles of crystals from Ticon-
deroga, New York, gave a : c=i : 1.3859. These possess a rhombo-
hedral symmetry. All crystals are tabular and nearly all are so distorted
that the measurements of their interfacial angles cannot be depended
upon for accuracy. They apparently contain the planes R(ioTi);
oP(iooo); 00 P2(ii2o), and 2P2(nIi).

Graphite is black and earthy, or lustrous, according as it is impure
or pure. It is easily cleavable parallel to the basal plane, and the cleav-
age laminae are flexible. It is very soft, its hardness being only 1-2,
its density about 2.25. Its luster is metallic and the mineral is opaque
even in the thinnest flakes. It is a conductor of electricity.

Graphite is infusible and noncombustible even at moderately high
temperatures. Like diamond, however, it may be burned under cer-
tain conditions at very high temperatures (65o°-7oo°). It is unaffected
by the common acids and is not acted upon by the atmosphere.
When, however, it is subjected to the action of strong oxidizing agents,
such as a warm mixture of potassium chlorate (KCIO3) and fuming
nitric acid, it changes to a yellow substance known as graphitic acid
(CiiH40r>). It is thus distinguished from amorphous carbon, like
schungite and anthracite. Moreover, many forms of graphite, when
moistened with fuming nitric acid and heated, swell up and send out
worm-like processes. Those which do not act thus are called graphitite.
Natural graphite is of both types.

Its color, softness and infusibility serve to distinguish graphite from
all other minerals but molybdenite (p. 75). It may be distinguished from
this mineral by the fact that it contains no sulphur.

Syntheses. — Crystalline graphite is made on a commercial scale
by treating anthracite coal or coke containing about 5.75 per cent of
ash in an electric furnace. It also separates when molten iron con-
taining dissolved carbon is cooled.

Occurrence and Origin. — Graphite occurs as thin plates and scales
in certain igneous rocks, in gneisses, schists and limestones, as large
scales in coarse granite dikes (pegmatite) and in crystalline limestones,
and as amorphous masses at the contacts of igneous rocks with carbona-
ceous rocks. The mineral is also found in veins cutting sedimentary
and metamorphic rocks. Crystals are found only in limestone.

The occurrence of graphite in sedimentary and igneous rocks sug-
gests that it may have been formed in several ways. It is thought
that the material in limestone and quartz-schist may represent carbo-

46 DESCRIPTIVE MINERALOGY

naceous material that was deposited with the sediments and which has
since been carbonized by heat and pressure. The material in peg-
matite may be an original constituent of the magma that produced the
rock, and the graphite may be the product of pneumatolytic processes;
i.e., it may have been produced by deposits from vapors that accom-
panied the formation of the pegmatite. If this be true, the mineral
found in metamorphosed limestone and schist may be of contact origin ;
i.e., it may have been produced by the migration of gases and solutions
from igneous rocks into the mass of the surrounding sediments. The
vein deoosits probably had a similar origin, the mineral having been
deposited mainly in cracks traversing metamorphic rocks. On the
other hand, graphite, in some instances, appears to be a direct separa-
tion from a molten magma.

Localities. — The principal foreign source of supply for commercial
graphite is the Island of Ceylon. In the United States the mineral has
been mined on the southeast side of the Adirondacks in New York;
in Chester County, Pennsylvania; near Dillon, Montana; at several
points in Arkansas, Georgia, Alabama and North Carolina; in Wyo-
ming; in Baraga County, Michigan, and to a small extent in Colorado,
Nevada, and Wisconsin. It occurs also abundantly at many other
places. Its chief source in the United States is Graphite, near Lake
George, New York.

Preparation. — Graphite is obtained on a commercial scale by grind-
ing the rock containing it and floating the graphite flakes.

Uses. — Crude graphite, or plumbago, is used in the manufacture of
stove and other polishes, and of black paint for metal surfaces, for both
of which it is especially valuable on account of its noncorroding proper-
ties. The purified mineral is mixed with clay and made into crucibles
for use at high temperatures. It is also ground and used in this form
as a lubricant for heavy machinery, and is compressed into " black lead "
centers for lead pencils.

Production. — The quantity of crude graphite mined in the United
States during 191 2 amounted to 2,445 tons, valued at $207,033, besides
which there were manufactured 6,448 tons, valued at $830,193. The
imports were 25,643 tons, valued at $709,337.

Schungite is a black, amorphous carbon with a hardness of 3-4
and a sp.gr. of 1.981. It is soluble in a mixture of HNO3 and KCIO3
without the production of graphitic acid. It occurs in some crystalline
schists.

INTRODUCTION— THE ELEMENTS 47

SULPHUR GROUP

Sulphur is known in at least six different forms, four of which are
crystalline. The two best known forms crystallize respectively in the
orthorhombic (orthorhombic bipyramidal class) and the monoclinic
(prismatic class) systems. The former separates from solutions of sulphur
in carbon bisulphide and the latter separates from molten masses.
Both the orthorhombic and the monoclinic phases are believed to be
formed by natural processes, but the latter passes over into the former
upon standing, so that its existence as a mineral cannot be definitely
proven. Selenium and tellurium, which are also members of the sul-
phur group, are extremely rare. Tellurium occurs in rhombohedral
crystals and selenium in mixed crystals of doubtful character with
sulphur and tellurium.

Sulphur (S)

Sulphur occurs in nature as a lemon-colored powder, as spherical or
globular masses, as stalactites and in crystals.

Chemically it is pure sulphur, or a mixture of sulphur and clay,

Fia. 19. Fia. 20.

Fig. 19. — Sulphur Crystals with P, in (p)\ 3P, 113 (5); P«, on (»), and oP,

001 (c).

Fig. 20. — Distorted Crystal of Sulphur. (Forms same as in Fig. 19.)

bitumen or other impurities. It sometimes contains traces of tellu-
rium, selenium and arsenic.

Crystals of sulphur are usually well formed combinations of ortho-
rhombic bipyramids and domes, with or without basal terminations.
Their axial ratio =.8108 : 1 : 1.9005. The principal forms observed
are P(ni), P 66 (101), Poo (on), JP(ii3) and oP(ooi) (Figs. 19 and
20). The habit of the crystals is usually pyramidal, though crystals
with a tabular habit are quite common.

Crystals of sulphur are yellow. Their streak is light lemon yellow.

48 DESCRIPTIVE MINERALOGY

The mineral has a resinous luster. Its hardness is only 1.5-2, and
density about 2.04. Its fracture is conchoidal and cleavage imper-
fect. It is transparent or translucent, is brittle and is a non-
conductor of electricity. Its indices of refraction for sodium light
are a= 1.9579, 0= 2.0377, 7= 2.2452.

Massive sulphur varies in color from yellow to yellowish brown
greenish gray, etc., according to the character and amount of impurities
it contains. Its powder is nearly always crystalline. In mass it pos-
sesses a lighter color than the crystals or the massive sulphur.

At a temperature of 1140 sulphur melts, and at 2700 it ignites,
burning with a blue flame and evolving fumes of SO2. At about 97 °
it passes over into the monoclinic phase. It is insoluble in water and
acids, but is soluble in oil of turpentine, carbon bisulphide and chlo-
roform.

There are few minerals that are apt to be mistaken for sulphur.
From all of them it may be distinguished by its brittleness and by the
fact that it melts readily and burns with a nonluminous blue flame.

Syntheses. — Crystals with the form of the mineral are produced by
the evaporation of solutions of sulphur in carbon bisulphide, and also
by sublimation from the fumes of ore roasters.

Occurrence and Origin. — Sulphur occurs most abundantly in regions
of active or extinct volcanoes, and in beds associated with limestone
and gypsum (CaS04-2H20). In volcanic regions it is produced by
reactions between the gases emitted from the volcanoes, or by the reac-
tions of these with the oxygen of the air (seep. 18). The deposits in
gypsum beds may result from reduction of the gypsum by organic
matter. Sulphur is formed also as a decomposition product of sulphides.

In Iceland and other districts of hot springs sulphur is often deposited
in the form of powder as the result of reactions similar to those that
take place between the gases of volcanoes. These hot springs are always
connected with dying volcanoes, being frequently but the closing
stages of their existence.

Localities. — The localities at which sulphur is known to exist are
very numerous. Those of commercial importance are Girgenti in Sicily,
Cadiz in Spain, Japan; and in the United States, at the geysers of the
Napa Valley, Sonoma County, and at Clear Lake, Lake County,
California; at Cove Creek, Millard County, Utah; at the mines of the
Utah Sulphur Company in Beaver County, in the same State; at
Thermopolis, Wyoming, and at various hot springs in Nevada. The
mineral occurs also abundantly in the Yellowstone National Park, but
cannot be placed on the market because of high transportation charges.

INTRODUCTION— THE ELEMENTS 49

Its principal occurrence in the United States is at Lake Charles in
Calcasieu Parish, La., where it impregnates a bed of limestone at
a depth of from 450 to 1,100 feet. It occurs also abundantly in the
coastal districts of Texas. Here it is associated with gypsum.

Extraction. — Sulphur, when mined, is mixed with clay, earth, rock and
other impurities. Until recently it was purified by piling in heaps and
igniting. A portion of the sulphur burned and melted the balance,
which flowed off and was caught. A purer product is obtained by dis-
tillation. "Flowers of Sulphur" are made in this way. At present
much of the sulphur is extracted by treating the impregnated rock in
retorts with steam under a pressure of 60 pounds and at a temperature
of 1440 C. The sulphur melts and flows to the bottom of the retorts
from which it is drawn off.

In Louisiana and Texas, superheated steam is forced downward into
the sulphur-impregnated rocks. This melts the sulphur, which con-
stitutes about 70 per cent of the rock mass. The melted sulphur is
forced to the surface and caught in wooden bins. The crude material
has a guaranteed content of over 99! per cent sulphur.

Uses. — Sulphur, or brimstone, is used in the manufacture of some
kinds of matches, in making gunpowder, and in vulcanizing rubber
to increase its strength and elasticity. It is used extensively in the
manufacture of sulphuric acid, but is rapidly giving way to pyrite
for this purpose. It is also utilized for bleaching straw, in the man-
ufacture of certain pigments, among which is vermilion, and in the
preparation of certain medicinal compounds.

Production. — Most of the domestic product is at present from the
Calcasieu Parish, La., where about 300,000 tons are mined annually.
New mines have been opened near Thermopolis in Wyoming, in Bra-
zoria County, Texas, and at Sulphur Springs, Nevada. The total
amount of the mineral mined in 191 2 was 303,472 tons, valued at $5,256,-
422. Besides, there were imported about 29,927 tons valued at $583,974,
most of which came from Japan. Sicily is the largest producer of the
mineral, extracting about 400,000 tons annually.

ARSENIC GROUP

The arsenic group comprehends metallic arsenic, antimony, bismuth
and (according to some mineralogists), tellurium, besides compounds
of these metals with each other. They all crystallize in the rhombo-
hedral division of the hexagonal system (di trigonal scalenohedral class).
The only members of the group that are at all common are arsenic and
antimony.

60 DESCRIPTIVE MINERALOGY

Arsenic (As)

Arsenic is rarely found in crystals. It usually occurs massive or in
botryoidal or globular forms.

Specimens of the mineral are rarely pure. They usually contain
some antimony, and traces of iron, silver, bismuth, and other metals.

The crystals are cubical in habit, with an axial ratio of i : 1.4025.
The principal forms observed are: oR(oooi), R(ioTi), JR(ioT4),
— JR(oiT2) and —^(0332). Twins are rare, with — JR(oiT2) the
twinning plane.

Arsenic is lead-gray or tin-white on fresh fractures, and dull gray or
nearly black on surfaces that have been exposed for some time to the
atmosphere.

Crystals cleave readily parallel to the base. The fracture of massive
pieces is uneven. The mineral is brittle. Its hardness is 3.5 and its
density 5.6-5.7. Its streak is tin- white tarnishing soon to dark gray.
It is an electrical conductor.

Arsenic may easily be distinguished from nearly all other minerals,
except antimony and some of the rarer metals, by the color of its fresh
surfaces. From these, with the exception of antimony, it is also readily
distinguished by its action on charcoal before the blowpipe, when it
volatilizes completely without fusing, at the same time tingeing the
flame blue and giving rise to dense white fumes of AS2O3, which coat the
charcoal. The fumes of arsenic possess a very disagreeable and oppres-
sive odor, while those of antimony have no distinct odor.

Syntheses. — Arsenic has been obtained in crystals by subliming
arsenic compounds protected from the air. It has also been obtained in
the wet way by heating realgar (AS2S3) with sodium bicarbonate at
3oo°C.

Occurrence and Origin. — Arsenic often accompanies ores of antimony,
silver, lead and other metals in veins in crystalline rocks, especially in
their upper portions, where it was formed by reduction from its com-
pounds.

Localities. — The silver mines at Freiberg and other places in Saxony
afford native arsenic in some quantity. It is found also in the Harz; at
Zmeov in Siberia; in the silver mines of Chile and elsewhere.

Within the boundaries of the United States arsenic occurs only in
small quantity at Haverhill, N. H., at Greenwood, Me., and at a silver
and gold mine near Leadville, Colo.

Uses. — Arsenic is used only in the forms of its compounds. The
native metal occurs too sparingly to be of commercial importance.

INTRODUCTION— THE ELEMENTS 51

Most of the arsenic compounds used in commerce are obtained from
smelter fumes produced by smelting arsenical copper and gold ores.

Antimony (Sb)

Antimony is more common than arsenic, which it resembles in many
respects. It is generally found in lamellar, radial and botryoidal masses,
though rhombohedral crystals are known.

Most antimony contains arsenic and traces of silver, lead, iron and
other metals.

Its crystals are rhombohedral or tabular in habit, and have an axial
ratio of a : c=i : 1.3236. The forms observed on them are the same
as those on arsenic with the addition of ooP2(ii2o), and several
rhombohedrons. Twinning is often repeated. The cleavage is perfect
parallel to oP(oooi).

Antimony exhibits brilliant cleavage surfaces with a tin-white color.
On exposed surfaces the color is dark gray. The mineral differs from
arsenic in its greater density which is 6.65-6.72, and in the fact that it
melts (at 6290) before volatilizing. Its fumes, moreover, are devoid of
the garlic odor of arsenic fumes.

Syntheses. — Crystals of antimony are often obtained from the flues of
furnaces in which antimonial lead is treated. They have also been
made by the reduction of antimony compounds by hydrogen at a high
temperature.

Occurrence and Localities, — Antimony occurs in lamellar concretions
in limestone near Sala, Sweden, and at nearly all of the arsenic localities
mentioned above, especially in veins containing stibnite (Sb2S3) or silver
ores. It is found also in fairly large quantities in veins near Fredericton,
York County, New Brunswick, in California and elsewhere.

Uses. — Although the metal antimony is of considerable importance
from an economic point of view, being used largely in alloys, the native
mineral, on account of its rarity, enters little into commerce. Some of
the antimony used in the arts is produced from its sulphide, stibnite
(see p. 72). Most of the metal, however, is obtained in the form of a
lead-antimony alloy in the smelting of lead ores and the refining of pig
lead.

Bismuth (Bi) is usually in foliated, granular or arborescent forms,
and very rarely in rhombohedral crystals, with a : c= 1 : 1.3036. It is
silver-white with a reddish tinge, is opaque and metallic. Its streak is
white, its hardness 2-2.5 and density 9.8. It fuses at 271 °. On charcoal
it volatilizes and gives a yellow coating. It dissolves in HNO3. When

52 DESCRIPTIVE MINERALOGY

this solution is diluted a white precipitate results. The mineral occurs
in veins with ores of silver, cobalt, lead and zinc. It is of no commercial
importance. Most of the metal is obtained in the refining of lead. In 1913
the United States produced 185,000 lbs. and Bolivia about 606,000 lbs.

Tellurium (Te) usually occurs in prismatic crystals with a tin-white
color and in finely granular masses in veins of gold and silver ores,
especially sulphides and tellurides. Its hardness is 2 and density 6.2.
Before the blowpipe it fuses, colors the flame green, coats the charcoal
with a white sublimate bordered by red, and yields white fumes.

The mineral tellurium is of little value as a source of the metal.
Most of that used in the arts is obtained as a by-product in the elec-
trolytic refining of copper made from ores containing tellurides and
from the flue dust of acid chambers and smelting furnaces. The United
States, in 1913, produced about 10,000 lbs. of tellurium and selenium,
valued at $35,000.

THE METALS

The metallic elements occur as minerals in comparatively small quan-
tity, most of the metals used in the industries being obtained from their
compounds. Iron, the most common of all the metals used in com-
merce, is rare as a mineral, as are also lead and tin. Silver, copper, gold
and platinum are sufficiently important to be included in our list for
study. Gold and platinum are known almost exclusively in the metallic
state. A large portion of the copper produced in this country is also
native, and some of the silver.

Silver, copper, lead, gold, mercury and the alloys of gold and mer-
cury crystallize in distinct crystals belonging to the isometric system
(hexoctohedral class). Platinum, as usually found, is in small plates
and grains. Crystals, however, have been described and they, too, are
isometric. Platinum and iron are separated from the other metals and,
together with the rare alloys of platinum with iridium and osmium, are
placed in a distinct group which is dimorphous. The reason for this is
that platinum, although isometric in crystallization, often contains
notable traces of iridium, which in its alloy with osmium is hexagonal
(rhombohedral). Iridium, thus, is dimorphous, hence platinum which
forms crystals with it and is, therefore, isomorphous with it, must also
be regarded as dimorphous. The various platinum metals thus com-
prise an isodimorphous group. Iron is placed in the same group because
it is so frequently alloyed with platinum. The metals are, therefore,
divisible into two groups, one of which comprises the metals named at

INTRODUCTION— THE ELEMENTS

the beginning of this paragraph and the other consists of the rare metals,
palladium, platinum, iridium, osmium, iron and their alloys. The
metal tin, which is tetragonal in its native condition, constitutes a third
group, but since it is extremely rare it will not be referred to again.

GOLD GROUP

This group embraces the native metals, copper, silver, goli, gold-
amalgam (Au-Hg), silver -amalgam (Ag-Hg), mercury, and leal. All
crystallize in the isometric system (hexoctahedral class), and all form
twins, with O(m) the twinning plane. Copper, silver and gold are
the most important.

Copper (Ctt)

Most of the copper of commerce is obtained from one or the other of

its sulphides. A large portion, however, is

found native. This occurs in tiny grains and

flakes, in groups of crystals and in large

masses of irregular shapes.

In spite of its softness copper is better

crystallized than either gold or silver. It is

true that its crystals are usually flattened and

Otherwise distorted, but, nevertheless, planes

can very frequently be detected upon them.

The principal forms observed arc °o O °o (ioo),

oo O(no), O(ni), and various tctrahexahedra

and kositetrahedra. (Figs. 21 and 22.) Some-
times the crystals are sim-
ple, in other cases they are
twinned parallel to O.
Often they are skeleton
crystals. Groups of crys-
tals are very common.
These possess the arbo-
rescent forms so frequently
seen in specimens from
Keweenaw Point in Mich-
igan, or are groupings of
simple forms extended in
the direction of the cubic
axes.
Copper is very ductile and very malleable. Its hardness is only

Fio. 2i.— Copper Crystal
with » O, no (d) and

aa. — Crystal of Copper from Keweenaw Point,
Mich., with =o0{no) and 202(211).

54 DESCRIPTIVE MINERALOGY

2.5-3 and its density about 8.8. It possesses no cleavage, and its frac-
ture, like that of the other metals, is hackly. In color it is copper-red
by reflected light, often tarnishing to a darker shade of red. In very
thin plates it is translucent with a green color. The metal fuses at
1083 ° and easily dissolves in acids. It is an excellent conductor of elec-
tricity.

Its most characteristic chemical reaction is its solubility in nitric
acid with the evolution of brownish red fumes of nitrous oxide gas.

Copper may easily be distinguished from all other substances except
gold and a few alloys by its malleability and color. It is distinguished
from gold by the color of its borax bead and by its solubility in nitric
acid with the production of a blue solution which takes on an intense
azure color when treated with an excess of ammonia. From the alloys
that resemble it, copper may be distinguished by its greater softness and
the fact that it yields no coatings when heated on charcoal, while at the
same time its solution in nitric acid yields the reaction described above.

Syntheses. — Copper crystals separate upon cooling solutions of the
metal in silicate magmas and upon the electrolysis of the aqueous solu-
tions of its salts.

Occurrence. — The principal modes of occurrence of the metal are, (1)
as fine particles disseminated through sandstones and slates, (2) as solid
masses filling the spaces between the pebbles and boulders making up
the rock known as conglomerate, (3) in the cavities in old volcanic lavas,
known as amygdaloid, (4) as crystals or groups of crystals imbedded in
the calcite of veins, (5) in quartz veins cutting old igneous rocks or
schists, and (6) associated with the carbonates, malachite and azurite,
and with its different sulphur compounds, in the weathered zone of
many veins of copper ores.

The copper that occurs in the upper portions of veins of copper
sulphides is plainly of secondary origin. That which occurs in conglom-
erates and other fragmental rocks and in amygdaloids was evidently
deposited by water, but whether by ascending magmatic water or by
descending meteoric water is a matter of doubt.

Localities. — Native copper is found in Cornwall, England, in Nassau,
Germany, in Bolivia, Peru, Chile and other South American countries,
in the Appalachian region of the United States and in the Lake Superior
region, both on the Canadian and the American sides.

The most important district in the world producing native copper is
on Keweenaw Point, in Michigan. The mineral occurs mainly in a bed
of conglomerate of which it constitutes from 1 to 3 per cent, though it is
found abundantly also in sandstone and in the amygdaloidal cavities

INTRODUCTION— THE ELEMENTS 55

of lavas associated with the conglomerates. Veins of calcite, through
which groups of bright copper crystals are scattered are also very plentiful
in many parts of the district. The copper is nearly always mixed with
silver in visible grains and patches.

Extraction and Refining. — The rock containing the native metal is
crushed and the metal is separated from the useless material by wash-
ing. The concentrates, consisting of the crushed metal mixed with
particles of rock and other impurities are then refined by smelting
methods or by electrolysis.

Uses. — The uses of copper are so many that all of even the important
uses cannot be mentioned in this place. Both as a metal and in the form
of its alloys it has been employed for utensils and war implements since
the earliest times. In recent times one of its principal uses has been for
the making of telegraph, telephone and trolley wires. It is employed
extensively in electroplating by all the great newspapers and publishers,
and is an important constituent of the valuable alloys brass, bronze,
bell metal and German silver. Its compound, blue vitriol (copper sul-
phate), is used in galvanic batteries, and its compounds with arsenic
are utilized as pigments.

Production. — The world's production of copper amounted to 1,126,-
000 tons in 191 2, but a large portion of this was obtained from its car-
bonates and sulphides. The quantity obtained from the native metal is
unknown. The contribution of the United States to this total was
about 621,000 tons, valued at about $206,382,500, of which 115,000 tons
was native copper from the Lake Superior region. The largest single
mass ever found in the Lake Superior region weighed 420 tons.

Silver (Ag)

Silver is usually found in irregular masses, in flat scales, in fibrous
clusters, and in crystal groups with arborescent or acicular forms.
Sometimes the crystals are well developed, more frequently they ex-
hibit only a few distinct faces, but in most cases they are so distorted
that it is difficult to make out their planes.

Pure silver is unknown. The mineral as it is usually obtained con-
tains traces of gold, copper, and often some of the rarer metals, depend-
ing upon its associations.

Ideally developed silver crystals are rare. They usually show
00 O 00 (100), 00 0(i 10), 0(i 11) various tetrahexahedrons and other
more complicated forms. The majority of the crystals are distorted by
curved faces and rounded edges, and many of them by flattening or

56 DESCRIPTIVE MINERALOGY

elongation. The arborescent groups usually branch at angles of 6o°,
one of the characteristic angles for groups of isometric crystals. Twins
are quite common, with O(in) the twinning plane.

Silver is a white, metallic mineral when its surfaces are clean and
fresh. As it usually occurs it possesses a gray, black or bluish black
tarnish which is due to the action of the atmosphere or of solutions.
The tarnish is commonly either the oxide or the sulphide of silver.

The mineral has no cleavage. Its fracture is hackly. It is soft
(hardness 2-3), malleable and ductile, and is an excellent conductor
of heat and electricity. Its density is about 10.5, varying slightly
with the character and abundance of its impurities. It fuses at
9600.

It is readily soluble in nitric acid forming a solution from which
a white curdy precipitate of silver chloride is thrown down on the
addition of any chloride: This precipitate is easily distinguished from
the corresponding lead chloride by its insolubility in hot water.

Synthesis. — Crystals bounded by O(in) and 00 O 00 (100) have been
made by the reduction of silver sulphate solutions, with sulphurous
acid.

Occurrence. — Native silver is found in veins with calcite (CaCOs),
quartz (SiCfe), and other gangues traversing crystalline rocks, like
granite and various lavas, and also in veins cutting conglomerates
and other rocks formed from pebbles and sands. It is also disseminated
in small particles through these rocks. It occurs invisibly disseminated
in small quantities through many minerals, particularly sulphides,
and visibly intermingled with native copper. It is abundant in the upper
weathered zones of many veins of silver-bearing ores, and in the zones
of secondary enrichment in the same veins. It also occurs in small
quantity in placers. In general, its origin is similar to that of gold
(see p. 59).

Localities. — The localities in which silver is found are too numerous
to mention. Andreasberg in the Harz has produced many fine crys-
tallized specimens. The principal deposits now worked are at Cobalt
in Canada, in Peru, in Idaho, at Butte, Montana, in Arizona and at
many places in Colorado. On Keweenaw Point, in Michigan, fine
crystals have been found in the calcite veins cutting the copper-bearing
rocks, and masses of small size in the native copper so abundant in the
district. Indeed some of the copper is so rich in silver that the ore
was in early times mined almost exclusively for its silver content. At
present the silver is recovered from the copper in the refining process.
At Cobalt the mineral occurs in well defined veins one inch to one foot

INTRODUCTION— THE ELEMENTS 57

or more in width, cutting a series of slightly inclined pre-Cambrian
beds of fragmental and igneous rocks. The veins contain native silver,
sulphides and arsenides of cobalt, nickel, iron and copper, calcite and a
little quartz. Many of the veins are so rich (Fig. 23) that Cobalt has
become one of the most important camps producing native silver in
the world.

Extraction and Refining. — Silver is obtained from placers in small
quantity by the methods made use of in obtaining gold (see p. 61),
i.e., by hydraulic mining. When it occurs in quartz veins or in complex
ores such as constitute the oxidized portion of ore-bodies, the mass
may be crushed and then treated with quicksilver, which amalgamates
with the native silver and gold, forming an alloy. Such ores are known

FlG. 33.— Plate of Silver from Conlanas Mine, Cobalt.

ins. Weight 37 lbs. {Photo by C, W. Knight.)

as free milling. The silver is freed from the gold and other metals by
a refining process. It is separated from native copper by electrolytic
methods.

Uses. — Silver Is used in the arts to a very large extent. Jewelry,
ornaments, tableware and other domestic utensils, chemical apparatus
and parts of many physical instruments are made of it. It is used also
in the production of mirrors and in the manufacture of certain compounds
used in surgery and in photography. Its alloy with copper forms the
staple coinage of China, Mexico and most of the South American coun-
tries, and the subsidiary (or small) coinage of most countries. In
the United States it is used in the coinage of silver dollars and of frac-
tions of the dollar as small as the dime. The silver coins of the United
States are nine-tenths silver and one-tenth copper, the latter metal being
added to give hardness. English coins contain 12$ parts silver to one

58 DESCRIPTIVE MINERALOGY

part of copper. In 1912 the world's coinage of silver consumed 161,-
763,415 oz., with a value after coinage of $171,293,000.

Production. — The total production of silver in the United States
during 1912 was over 63,766,000 oz., valued at over $39,197,000, of
which about $100,000 worth came from placers and $325,000 worth
from tie copper mines of Michigan. The balance was obtained by
smelting silver compounds and in the refining of gold, lead, copper and
zinc ores. The world's production of silver during 1912 was 224,488,-
000 oz., valued at over $136,937,000, but most of this was obtained
from the compounds of silver and not from the native metal. The
proportion obtained from the mineral is not definitely known; but the
production of Canada was more than 30,243,000 oz., valued at
$17,672,000 and nearly all of this came from Cobalt, where the ore is
native silver.

Gold (Au)

A large portion of the gold of the world has been obtained in the
form of native metal. The greater portion of the metal is so very finely
disseminated through other minerals that no sign of its presence can be
detected even with high powers of the microscope. Although present
in such minute quantities it is very widely spread, many rocks con-
taining it in appreciable quantities. Its visible grains, as usually found,
are little rounded particles or thin plates or
scales mixed with sand or gravel, or tiny
irregular masses scattered through white vein-
quartz.

Native gold rarely occurs in well formed
crystals. The metal is so soft that its crystals
are battered and distorted by very slight
pressure. Occasionally well developed crys-
tals, bounded by octahedral, dodecahedral
Fie. 14 -Octahedwl Skde- and complicated icositetrahedral and tetra-
ton Crystal of Gold with , , , , , . , ,

Etched Faces hexahedral faces are met with, but usually

the crystals are elongated or flattened. Skele-
ton crystals (Fig. 24) and groups of crystals are more frequently found
than are simple crystals. Twins are common, with 0(m) the twin-
ning plane.

As found in nature, gold is frequently alloyed with silver and it
often contains traces of iron and copper and sometimes small quanti-
ties of the rarer metals.

Gold containing but a trace of silver up to 16 per cent of this metal

INTRODUCTION— THE ELEMENTS 59

is known simply as gold. When the percentage of silver present is
larger it is said to be argentiferous. When the percentage reaches
20 per cent cr above the alloy is called clectrun. Palladium, rhodium
and bismuth gold are alloys of the last-named metal with the rare metals
palladium or rhodium or with the more common bismuth.

The color of the different varieties of the mineral varies from pinkish
silver-white to almost copper-red. Pure gold is golden yellow. With
increase cf silver it becomes lighter in color and with increase in copper,
darker. The rich red-yellow of much of the gold used in the arts is due
to the admixture of copper. In very thin plates or leaves (.001 mm.)
gold is translucent with a blue or green tint.

Gold is soft, malleable and ductile. Its luster is, of course, metallic
and its streak, yellow. When pure its density is 19.43, its hardness
between 2 and 3, and its fusing point 10620. The metal is insoluble in
most acids, but it is readily dissolved in a mixture of nitric and hydro-
chloric acids (aqua regia). It is not acted upon by water or the atmos-
phere. Its negative properties distinguish it from the other substances
which it resembles in appearance. It is a good conductor of electricity.

Syntheses. — Crystals of gold have been obtained by heating a solu-
tion of AuCfe in amy! alcohol, and by treating an acid solution of the
same compound with formaldehyde.

Occurrence. — Native gold is found in the quartz of veins cutting
through granite and schistose rocks, or in the gravels and sands of rivers
whose channels cut through these, and in the sands of beaches bordering
gold-producing districts. It is sometimes found in the compacted
gravels of old river beds, in a rock known as conglomerate, and in sand-
stones. It is also present in small quantities in many volcanic rocks,
and is disseminated through pyrite (FeS2) and some other sulphur com-
pounds and their oxidation products.

The gold in quartz veins occurs as grains and scales scattered through
quartz irregularly, often in such small particles as to be invisible to the
naked eye, or as aggregates of crystals in cavities in the quartz. Pyrite
is nearly always associated with the gold. On surfaces exposed to the
weather the pyrite rusts out and stains the quartz, leaving it cavernous
or cellular.

Most of the world's supply of gold has come from placers. These
are accumulations of sand or gravel in the beds of old river courses.
The sands of modern streams often contain considerable quantities of
gold. Many of the older streams were much larger than the modern
ones draining the same regions and, consequently, their beds contain
more gold. This was originally brought down from the mountains or

60 DESCRIPTIVE MINERALOGY

highlands in which the streams had their sources. The sands and
gravels were rolled along the streams' bottoms and their greater portion
was swept away by the currents into the lowlands. The gold, however,
being much heavier than the sands and pebble grains, merely rolled
along the bottoms, dropping here and there into depressions from which
it could not be removed. As the streams contracted in volume the gold
grains were covered by detritus, or perhaps a lava stream flowing along
the old river channel buried them. These buried river channels with
their stores of sands, gravels and gold constitute the placers. With the
gold are often associated zircon crystals, garnets, diamonds, topazes
and other gem minerals. Alluvial gold is usually in flattened scales or
in aggregates of scales forming nuggets. Some of the nuggets are so
large, 190 pounds or more in weight, that it is thought they may have
been formed by some process of cementation after they were transported
to their present positions.

The gold-quartz veins are usually closely associated with igneous
rocks, but the veins themselves may cut through sedimentary beds or
crystalline schists. The veins are supposed to have been filled from
below by ascending solutions. Metallic gold is also present in the oxi-
dized zones of many veins of gold-bearing sulphides and in the zones of
secondary enrichment. At the surface the iron sulphides are oxidized
into sulphates, leaving part of the gold in the metallic state and dissolv-
ing another part which is carried downward and precipitated.

Principal Localities, — Vein gold occurs in greater or less quantity in
all districts of crystalline rocks. It has been obtained in large quantity
along the eastern flanks of the Ural Mountains, this having been the
most productive region in the world between the years 1819 and 1849.
It has been obtained also from the Altai Mountains in Siberia, from the
mountains in southeastern Brazil, from the highlands of many of the
Central and South American countries, and from the western portion of
the United States, more particularly from the western slopes of the Sierra
Nevada Mountains and the higher portions of the Rocky Mountains.
In recent years auriferous quartz veins have been worked at various
points in Alaska, at Porcupine, Ontario, and other points in Canada.

The great placer mines of the world are in California, Australia and
Alaska. In Australia the principal gold mines are situated in the streams
rising in the mountains of New South Wales and their extension into
Victoria. The valleys of the Yukon and other rivers in Alaska have
lately attracted much attention, and in the past few years the beach
sands off Nome have yielded much of the metal.

The most important production at present is from South Africa

INTRODUCTION— THE ELEMENTS 61

where the metal occurs in an old conglomerate. In the opinion of some
geologists this is an old beach deposit; in the opinion of others the gold
was introduced into the conglomerate long after it had consolidated.

The sands of many streams in Europe and in the eastern United
States have for many years been "panned" or washed for gold. The
South Atlantic States, before the discovery of gold in California, in
1849, yielded annually about a million dollars' worth of the precious
metal. All of it was obtained by working the gravels and sands of small
rivers and rivulets. Many of these streams have been worked over
several times at a profit and the mining continues to the present day.
Small quantities of gold have also been obtained from streams in Maine,
New Hampshire, Maryland and other Atlantic coast states.

Extraction and Refining. — Gold is extracted from alluvial sands
and from placers by washing in pans or troughs. The sand, gravel
and foreign particles are carried away by currents of water and
the gold settles down with other heavy minerals to the bottom of the
shallow pans used in hand washing, or into compartments prepared for
it in troughs when the processes are on a larger scale. It is after-
ward collected by shaking it with mercury or quicksilver, in which it
dissolves. The quicksilver is finally driven off by heat and the gold
left behind. Auriferous beach sands and many lake, swamp and river
sands are dredged and the sand thus raised is treated by similar methods.
Sands containing as low as 15 cents' worth of metal per cubic yard can
be worked profitably under favorable conditions.

Where the gold occurs free (not disseminated through sulphides)
in quartz the rock is crushed to a fine pulp with water and the mixture
allowed to flow over copper plates coated with quicksilver. The gold
unites with the quicksilver and forms an alloy from which the mercury
is driven off by heat. The process of forming alloys of silver or gold
with mercury is known as amalgamation.

When the gold is disseminated through sulphides, these are concen-
trated, i.e., freed from the gangue material by washing, and then
roasted. This liberates the gold which is collected by amalgamation,
or is dissolved by chlorine or cyanide solutions and then precipitated.

Uses. — Gold, like silver, is used in the manufacture of jewelry and or-
naments, in the manufacture of gold leaf for gilding and in the produc-
tion of valuable pigments such as the "purple of Cassius." It also con-
stitutes the principle medium for coinage in nearly all of the most
important countries of the world. The gold coins of the United States
contain 900 parts gold in 1,000. Those of Great Britain contain 916.66
parts, the remaining parts consisting of copper and silver. The total

62 DESCRIPTIVE MINERALOGY

gold coinage of the United States mints from the time of their organi-
zation to the end of the year 191 2 amounted to $2,765,900,000. The
gold coined in the world's mints in 191 2 amounted in value to $360,-
671,382, and that consumed in arts and industries to $174,100,000.
Jewelers estimate the fineness of gold in carats, 24-carat gold being pure.
Eigh teen-carat gold is gold containing 18 parts of pure gold and 6 parts
of some less valuable metal, usually copper. The copper is added to
increase the hardness of the metal and to give it a darker color. The
gold used most in jewelry is 14 or 1 2 carats fine.

Production. — The total value of the gold product of the United
States during 191 2 was $93,451,000. Of this the following states and
territories were the largest producers:

Alaska $17,198,000 Nevada $13,576,000

California 20,008,000 South Dakota 7,823,000

Colorado 18,741,000 Utah 4,312,000

Of the total product, placers yielded gold valued at $23,019,633, and
quartz veins, metal valued at $62,112,000. The balance of the gold was
obtained from ores mined mainly for other metals, and in these it is
probably not in the metallic state. Moreover, some of the ore in quartz
veins is a gold telluride, but by far the greater portion of the product
from the quartz veins and placers was furnished by the native metal.

The world's yield of the precious metal in 191 2 was valued at $466,-
136,100. The principal producing countries and the value of the gold
produced by each were :

South Africa $211,850,600 Mexico $24,450,000

United States 93>45i,5QO India 11,055,700

Australasia 54,509,400 Canada 12,648,800

Russia 22,199,000 Japan 4,467,000

Lead occurs very rarely as octahedral or dodecahedral crystals,
in thin plates and as small nodular masses in districts containing man-
ganese and lead ores and also in a few placers. It usually contains
small quantities of silver and antimony. The native metal has the
same properties as the commercial metal. Its hardness is 1.5 and
density 11.3. It melts at about 33. 5 °.

The mineral is of no commercial importance. The metal is obtained
from galena and other lead compounds.

Mercury occurs as small liquid globules in veins of cinnabar (HgS)
from which it has probably been reduced by organic substances, and ig

INTRODUCTION— THE ELEMENTS 63

the rocks traversed by these veins. The native metal possesses the
same properties as the commercial metal. It solidifies at — 39 °, when
it crystallizes in octahedrons having a cubic cleavage. Its density is
13.6. Its boiling-point is 3500.

The commercial metal is obtained from cinnabar (p. 98).

Amalgam (Ag • Hg) is found in dodecahedral crystals in a few places,
associated with mercury and silver ores. It occurs also as embedded
grains, in dense masses and as coatings on other minerals. It is silver-
white and opaque and gives a distinct silver streak when rubbed on
copper. Its hardness is about 3 and its density 13.9. When heated
in the closed tube it yields a sublimate of mercury and a residue of
silver. On charcoal the mercury volatilizes, leaving a silver globule,
soluble in nitric acid.

PLATINUM-IRON GROUP

The platinum-iron group of minerals may be divided into the plati-
num and the iron subgroups. The latter comprises only iron and nickel-
irony both of which are extremely rare; and the former, the metals
platinum, iridium, osmium, ruthenium, rhodium, and palladium. The
platinum metals probably constitute an isodimorphous group since
they occur together in alloys, some of which are isometric and others
hexagonal (rhombohedral). Platinum is the only member of the group
of economic importance.

Platinum (Pt)

Platinum occurs but rarely in crystals. It is almost universally
found as granular plates associated with gold in the sands of streams
and rivers, and rarely as tiny grains or flakes in certain very basic
igneous rocks.

As found in nature the metal always contains iron, iridium, rhodium,
palladium and often other metals. A specimen from California yielded:

Cu Ir.Os Sand Total
1.40 1. 10 2.95 101.15

Though the metal occurs usually in grains and plates, nevertheless
its crystals are sometimes found. On them cubic faces are the most
prominent ones, though the octahedrons, the dodecahedrons and
tetrahexahedrons have also been identified. Like the crystals of silver
and gold, those of platinum are frequently distorted.

85.50

.80

6-75

1 05

1. 00

.60

64 DESCRIPTIVE MINERALOGY

The color of platinum is a little more gray than that of silver. Its
streak is also gray. Its hardness is 4-4.5 an^ density 14 to 19. Pure
platinum has a density of 21.5. It is malleable and ductile, a good
conductor" of electricity, and it is infusible before the blowpipe except
in very fine wire. It is not dissolved by any single acid, though soluble,
like gold, in aqua regia. Its melting temperature is 17550.

Syntheses. — Crystals have been obtained by cooling siliceous mag-
mas containing the metal, and by dissolving the metal in saltpeter and
cooling the mixture.

Occurrence. — Platinum is found in the sands of rivers or beaches
and in placer deposits in which it occurs in flattened scales or in
small grains. Nuggets of considerable size are sometimes met with,
the largest known weighing about i8f kilos. It is present also in
small quantity in certain very basic igneous rocks, like peridotite.

Localities. — It occurs in nearly all auriferous placer districts and
in small quantities in the sands of many rivers, among them the Ivalo
in Lapland, the Rhine, the rivers of British Columbia, and of the Pacific
States. It is more abundant in the Natoos Mountains in Borneo, on
the east flanks of the Ural Mountains in Siberia, in the placer of an
old river in New South Wales, Australia, and the sands of rivers of
the Pacific side of Colombia. It is nearly always associated with
chromite (p. 200). A recent discovery which may prove to be of con-
siderable importance is near Goodsprings, Nev., where platinum is in
the free state associated with gold in a siliceous ore.

The native metal is probably an original constituent of some peri-
dotites (basic igneous rocks). Its presence in placers is due to the
disintegration of these rocks by atmospheric agencies.

Extraction and Refining. — The metal is separated from the sand
with which it is mixed by washing and hand picking. The metallic
powder is then refined by chemical methods.

Uses. — On account of its infusibility and its power to resist the cor-
rosion of most chemicals the metal is used extensively for crucibles
and other apparatus necessary to the work of the chemist. It is also
used by dentists and by the manufacturers of incandescent electric
lamps. It is an important metal in the manufacture of physical and
certain surgical instruments, and was formerly used by Russia for coin-
age. The most important use of the metal in the industries is in the
manufacture of sulphuric acid. Sulphur dioxide (SO2) and steam when
mixed and passed over the finely divided metal unite and form H2SO4.
: More than half of the acid made at present is manufactured by this
: process.

INTRODUCTION— THE ELEMENTS 65

Production. — Most of the platinum of the world is obtained from
placers in the Urals in Russia. A small quantity is washed from the
sands of gold placers in Colombia, Oregon and California, and an even
smaller quantity is obtained during the refining of copper from the ores
of certain mines. The total production of the world in 191 2 was
314,751 oz. The output for Russia in this year was about 300,000 oz.,
of Colombia about 12,000 oz., and of the United States 721 oz. (equiv-
alent to 505 oz. of the refined metal, valued at $22,750). In addition,
about 1,300 oz. were obtained in the refining of copper bullion imported
from Sudbury, Ont., and in the treatment of concentrates from the
New Rambler Mine, Wyoming. Of this about 500 oz. were produced

Fig. 35. — Iron Meteorite (Siderite) from Canyon Diablo, Arizona. Weight 365

lbs. {Field Columbian Museum.)

from domestic ores. The importations into the United States for the
same year were about 125,000 oz., valued at $4,500,000.

Platinum-iron, or iron-platinum fPt-Fe), contains from 10 per cent
to 19 per cent Fe. It is usually dark gray or black and is magnetic. It
is found with platinum in sands of the rivers in the Urals. Its crystals
are isometric.

Iron (Fe) occurs in small grains and large masses in the basalt at
Ovifak, Disko Island, W. Greenland, and at a few other points in Green-
land, and alloys consisting mainly of iron are found in the sands of some
rivers in New Zealand, Oregon and elsewhere. The native metal always
contains some nickel. The most common occurrence of iron, however, is
in meteorites (Fig. 25). In these bodies also it is alloyed with Ni. When

66 DESCRIPTIVE MINERALOGY

polished and treated with nitric acid, surfaces of meteoric iron exhibit

series of lines (Widmanstatten figures), that are the edges of plates of
different composition (Fig. 26). These are so arranged as to indicate
that the substance crystallizes in the isometric system.

Iridium (Ir-Pt) and pUtin-iridium (Pt-Ir) are alloys of iridium and
platinum found as silver-white grains with a yellowish tinge, associated
with platinum in the sands of rivers in the Urals, Burmah and Brazil.
Their hardness is 6 to 7, and density 22.7. The mineral is isometric

and its fusing point is between 2iso0-225o".

FlC. 16. — WidmanslStten Figures on Etched Surface of Meteorite from Toluca,
Mexico. (One-half natural size.) (Field Columbian Museum.)

Palladium (Pd) is usually alloyed with a little Pb and Ir. It is
found in small octahedrons and cubes and also in radially fibrous grains
in the platinum sands of Brazil, the Urals and a few other places. It is
whitish steel-gray in color, has a hardness of 4 to 5 and a density of
11. 3 to 11. 8. It fuses at about 1549°. Its crystallization is isometric.
About 2,300 oz. of the metal were produced in the United States during
1912, but all of it was obtained during the refining of bullion. The
imports were 4,967 oz., valued at $213,397.

Allopalladium (Pd) is probably a dimorph of palladium. It is found
in six-sided plates that are probably rhombohedral, intimately asso-
ciated with gold, at Tilkerode, Harz.

INTRODUCTION— THE ELEMENTS 67

Osmiridium (Os • Ir) and iridosmine (Ir • Os) are found in crystals and
flattened grains and plates that are apparently rhombohedral. They
consist of Ir and Os in different proportions, often with the addition
of rhodium and ruthenium. Osmiridium is tin-white and iridosmine
steel-gray. Their hardness is 6 to 7 and density 19 to 21. When heated
with KNO3 and KOH, both yield the distinctive chlorine-like odor of
osmium oxide (OSO4) and a green mass, which, when boiled with
water, leaves a residue of blue iridium oxide. Both are insoluble in
concentrated aqua regia. They occur with platinum in the sands of
rivers in Colombia, Brazil, California, the Urals, Borneo, New South
Wales, and a few other places. They are distinguished from platinum
by greater hardness, light color and insolubility in strong aqua regia.

The world's product of refined iridium is about 5,000 oz., of which
the United States furnishes about 500 oz. Its value is $63 per oz.
Imports into the United States during 191 1 were 3,905 oz., valued at
$210,616. The sources of the metal are native iridium, osmiridium,
platinum, copper ore and bullion. The metal is obtained from the last
two sources in the refining process.

CHAPTER IV

THE SULPHIDES, TELLURITES, SELENIDES, ARSENIDES AND

ANTIMONIDES

The sulphides are combinations of the metals, or of elements acting
like bases, with sulphur. They may all be regarded as derivatives of
hydrogen sulphide (H2S) by the replacement of the hydrogen by some
metallic element. The tellurides are the corresponding compounds of
H2Te, and the selenides of H2SC

With the same group are also placed the arsenides and the anti-
monides, derivatives of H3AS and HaSb, because arsenic and antimony
so often replace in part the sulphur of the sulphides, forming with these
isomorphous mixtures.

The minerals described in this volume may be separated into the
following groups and subgroups:

I. The sulphides, tellurides and selenides of the metalloids arsenic,
antimony, bismuth and molybdenum.

II. The sulphides, tellurides, selenides, arsenides and antimonides
of the metals.

(a) The monosulphides, etc. (Derivatives of H2S, EfeSe, H2Te,

H3AS, HsSb.)

(b) The disulphides, etc. (Derivatives of 2H2S, 2H2Te, 2H3AS,

2HaSb.)

All sulphur compounds when mixed with dry sodium carbonate
(Na2C03) and heated to fusion on charcoal yield a mass containing
sodium sulphide (Na2S). If the mass is removed from the charcoal,
placed on a bright piece of silver and moistened with a drop or two of
water or hydrochloric acid, the solution formed will stain the silver a
dark brown or black color (Ag2S), which will not rub off. The sulphides
yield the sulphur reaction when heated with the carbonate on platinum
foil; the sulphates only when charcoal or some other reducing agent is
added to the mixture before fusing. Moreover, the sulphides yield
sulphureted hydrogen when heated with hydrochloric acid, while the
sulphates do not. These tests are extremely delicate. By the aid of

SULPHIDES, TELLURIDES, ETC. 69

the first one the sulphur in any compound may be detected. By the
aid of the others the sulphates may be distinguished from the
sulphides.

The selenides are recognized by the strong odor evolved when heated
before the blowpipe. Selenates and selenites give their odor only after
reduction with Na2C03.

The tellurides, when warmed with concentrated H2SO4, dissolve and
yield a carmine solution from which water precipitates a black gray
powder of tellurium.

All substances containing arsenic and antimony yield dense white
fumes when heated on charcoal in the oxidizing flame. The fumes of
arsenic possess a characteristic odor while those of antimony are odorless.
When heated in the open tube, arsenides and compounds with sulphur
and arsenic yield a very volatile sublimate composed of tiny white crys-
tals (AS2O3). The corresponding sublimate for antimonides and for
compounds with antimony and sulphur is nonvolatile, or difficultly
volatile, and apparently amorphous. It is usually found on the under
side of the tube.

THE SULPHIDES, SELENIDES AND TELLURIDES OF

THE METALLOIDS

The sulphides of the metalloids include compounds of sulphur with
arsenic, antimony, bismuth and molybdenum and a selenide and several
tellurides of bismuth. Only the sulphides are of importance. One,
stibnite (Sb2S3), is utilized as a source of antimony.

Realgar (As2S2)

Realgar occurs as a bright red incrustation on other substances,
as compact and granular masses and as crystals implanted on other
minerals. It is usually associated with the bright yellow orpiment

(p. 7i)-

Absolutely pure realgar should have the following composition:

As, 70.1 per cent, S, 29.9 per cent. The mineral, however, usually

contains a small amount of impurities. It may be looked upon as a

derivative of H2S in which the hydrogen of two molecules is replaced

by two arsenic atoms, thus:

H2S As=S

yielding |
H2S As=S.

DESCRIPTIVE MINERALOGY

(c); PSb, on (q) and P,
In ($).

Crystals of realgar are usually short and prismatic in habit. They
are monoclinic (prismatic class) with an axial ratio a : b : c : =1.44".
1 : .973 and 0=66° 5'. The characteristic prismatic faces are
(w)ooP(no) and (/) 00 P2(2io). These with (b) 00 P So (010) con-
stitute the prismatic zone. The terminations are (r)£Pob(oi2) or
(q) Poo (on) in combination with the basal plane (c) oP(ooi), the
orthodome (x) (Toi), and one or more of several pyramids. (See Fig.

27.) The crystals are usually small and are
striated vertically. Prismatic angle no A 1 "io
= 1050 34'.

The mineral possesses a distinct cleavage
parallel to (b) 00 P 00 and (/) 00 Pi. It is
sectile, soft (H= 1.5-2), resinous in luster and
aurora-red or orange in color. Its streak is a
lighter shade, but with the mineral are fre-
quently intermingled small quantities of orpi-
Fig. 27.— Realgar Crystal, ment which impart to its streak a distinct
ooP,Mo(m);«P2?2io(/); yellow tinge. Its density is 3.56. In thin
oop 5b, 010 («; oP, 001 splinters it is often translucent or trans-
parent, and strongly pleochroic in red and
yellow tints, but in masses it is opaque. Its
indices of refraction are not known with accuracy, but its double re-
fraction is strong (.030). It is a nonconductor of electricity.

When heated on charcoal before the blowpipe realgar catches fire
and burns with a light blue flame, at the same time giving off dense
clouds of arsenic fumes and the odor of burning sulphur (SO2). When
heated in a closed tube it melts, volatilizes and yields a transparent
red sublimate in the cold parts of the tube.

Its bright red color and its reaction for sulphur distinguish realgar
from all other minerals but cinnabar, the sulphide of mercury (p. 98).
It may easily be distinguished from cinnabar by its softness, its low
specific gravity and the arsenic fumes which it yields when heated on
charcoal.

On exposure to the air and to light realgar oxidizes, yielding orpi-
ment (AS2S3) and arsenolite (AS2O3).

Syntheses. — Realgar is often produced in the flues of furnaces in
which ores containing sulphur and arsenic are roasted. Crystals have
also been produced by heating to 1500 a mixture of AsS with an excess
of sulphur in a solution of bicarbonate of soda sealed in a glass tube.

Occurrence Localities and Origin. — Realgar occurs in masses asso
ciated with orpiment and in grains scattered through it at all places

SULPHIDES, TELLURIDES, ETC. 71

where the latter mineral is found. It also occurs associated with silver
and lead ores in many places. It is found in crystals implanted on
quartz and on the walls of cavities in lavas. It is also occasionally
a deposit from hot springs. In the United States it forms seams in a
sandy clay in Iron Co., Utah. Its crystals are found in calcite in San
Bernardino and Trinity Counties, California, and with orpiment it is
deposited as a powder by the hot water of the Norris Geyser basin in the
Yellowstone National Park.

In most cases it is a product of the interaction of arsenic and sul-
phur vapors.

Uses. — The native realgar occurs in too small a quantity to be of
commercial importance. An artificial realgar is employed in tanning
and in the manufacture of " white-fire."

Orpiment (As2S3)

Orpiment, though more abundant than realgar, is not a common
mineral. It is usually found in foliated or columnar masses with a
bright yellow color. Its name — a contraction from the Latin auri-
pigmentum, meaning golden paint — refers to this color.

The pure mineral contains 39 per cent of sulphur and 61 per cent
of arsenic, corresponding to the formula AS2S3. It thus contains
about 9 per cent more sulphur than does realgar.

The monoclinic orpiment crystals have the symmetry of the pris-
matic class. Their axial ratio is .596 : 1 : .665 with £=89° 19'. Though
always small they are distinctly prismatic with an orthorhombic habit.
Their predominant faces are the ortho and clino pinacoids, several
prisms and the orthodome.

The cleavage of orpiment is so perfect parallel to 00 P 00 (010) that
even from large masses of the mineral distinct foliae may be split.
These are flexible but not elastic. The mineral, like many other
flexible minerals, is sectile. Its luster is pearly on cleavage faces,
which are always vertically striated, and is resinous on other surfaces.
The color of pure orpiment is lemon-yellow; it shades into orange
when the mineral is impure through the admixture of realgar. Its
streak is always of some lighter shade than that of the mineral. Its
hardness is 1.5-2 and its density about 3.4. In small pieces orpiment
is translucent and possesses an orange and greenish yellow pleochroism.
When heated to ioo° it becomes red and assumes the pleochroism of
realgar. It, however, resumes its characteristic color and pleochroism
upon cooling. When heated to 1500 the change is permanent. The
mineral is a nonconductor of electricity.

DESCRIPTIVE MINERALOGY

The chemical properties of orpiment are the same as those described
for realgar, except that the sublimate in the closed tube is yellow instead
of red.

Synthesis. — Orpiment is produced in large pleochroic crystals by
treatment of arsenic acid with H2S under high pressure.

Occurrence, Localities and Origin. — Orpiment occurs in the same
forms and in the same places as does realgar. Small specks of it occur
on arsenical iron at Edenville, N. Y. It is also found in the deposits
of Steamboat Springs, Nevada. The origin of orpiment is similar
to that of realgar. It is also formed by the oxidation of this mineral.

Uses. — Native orpiment mixed with water and slaked lime is used
in the East as a wash for removing hair. It is also employed as a pig-
ment in dyeing. Most of the AS2S3 of commerce is a manufactured
product.

STIBNITE GROUP (RaQ8)

The stibnite group of sulphides contains several isomorphous
compounds, of which we shall consider only two, viz., stibnite (Sb2Ss)
and bismuthinite (Bi2S3). The general formula of the group is R2Q3,
in which R stands for Sb or Bi and Q for S or Se. The group is
orthorhombic (bipyramidal class). All the members have a distinct
cleavage parallel to the brachypinacoid which yields flexible laminae.

Stibnite (Sb2S3)

Stibnite is the commonest and the most important ore of anti-
mony. It is found in acicular and prismatic crys-
tals, in radiating groups of crystals and in
fibrous masses.

Chemically, stibnite is the antimony trisul-
phide, Sb2S3, composed of Sb, 71.4 per cent
and S, 28.6 per cent. As found, however, it
usually contains small quantities of iron and often
traces of silver and gold.

Crystals of stibnite are often very compli-
cated. They are orthorhombic with an axial ratio
.9926 : 1 : 1. 01 79 and a columnar or acicular
habit. The most important forms in the pris-
matic zone are 00 P(no) and 00 P 06 (010). The
prisms are often acutely terminated by P(in), ^4(431) and 6P2(36i),
or bluntly terminated by £P(ii3), (Fig. 28). Sometimes the crystals
are rendered very complicated by the great number of their terminal

Fig. 28.— Stibnite Crys-
tal. 00 P, 110 (w);
00 Poo , 010 (6); 2P2,
121 (t>) andP, in (p).

SULPHIDES, TELLURIDES, ETC. 73

planes. Dana figures a crystal from Japan that possesses a termina-
tion of 84 planes, no a 1 10=89° 34'.

Many of the crystals of this mineral, more particularly those with
an acicular habit, are curved, bent or twisted. Nearly all, whether
curved or straight, are longitudinally striated.

The cleavage of stibnite is very perfect parallel to 00 P 06 (010),
leaving striated surfaces. The mineral is soft (H=2) and slightly
sectile. Its density is about 4.5. Its color is lead-gray and its streak
a little darker. In very thin splinters it is translucent in red or yellow
tints. In these the indices of refraction for yellow light have been
determined to be, 0=4.303 and 7 = 3.194. Surfaces that are exposed
to the air are often coated with a black or an iridescent tarnish. The
luster of the mineral is metallic. It is a nonconductor of electricity.

Stibnite fuses very easily, thin splinters being melted even in the
flame of a candle. When heated on charcoal the mineral yields anti-
mony and sulphurous fumes, the former of which coat the charcoal white
in the vicinity of the assay. When heated in the open tube SO2 is
evolved and a white sublimate of SD2O3 is deposited on the cool walls of
the tube. In the closed tube the mineral gives a faint ring of sulphur
and a red coating of antimony oxysulphide. It is soluble in nitric acid
with the precipitation of SD2O5.

Stibnite may easily be distinguished from all minerals but the other
sulphides by the test for sulphur. From the other sulphides it is dis-
tinguished by its cleavage and the fumes it yields when heated on char-
coal. Its closest resemblance is with galena (PbS), which, however,
differs from it in being less fusible and in yielding a lead globule when
fused with sodium carbonate on charcoal. Moreover, galena possesses
a cubic cleavage.

Syntheses. — Stibnite is produced by heating to 2000, a mixture of
sulphur and antimony with water under pressure, and by the reaction of
H2S on antimony oxide heated to redness.

Occurrence, Localities and Origin.— -The mineral is found as crystals
in quartz veins cutting crystalline rocks, and in metalliferous veins asso-
ciated with lead and zinc ores, with cinnabar (HgS) and barite (BaS04).
The finest crystals, some of them 20 inches in length, come from mines
in the Province of Iyo, on the Island of Shikoku, Japan. The mineral
occurs also in York Co., New Brunswick, in Rawdon township, Nova
Scotia, at many points in the eastern United States, in Sevier Co.,
Arkansas, in Garfield Co., Utah, and at many of the mining districts in
the Rocky Mountain States.

In Arkansas stibnite is in quartz veins following the bedding planes

74 DESCRIPTIVE MINERALOGY

of shales and sandstones. With it are found many lead, zinc and
iron compounds and small quantities of rarer substances. In Utah
the mineral occurs in veins unmixed with other minerals, except its
own oxidation products. The veins follow the bedding of sandstones
and conglomerates. Here, as in Arkansas, the stibnite is believed to
have been deposited by magmatic waters.

Uses. — Stibnite was powdered by the ancients and used to color the
eyebrows, eyelashes and hair. At present it is used to a slight extent in
vulcanizing rubber and in the manufacture of safety matches, percussion
caps, certain kinds of fireworks, etc. Its principal value is as an ore of
antimony. Practically all of the metal used in the arts is obtained
from this source. Antimony is chiefly valuable as an alloy with other
metals. With tin and lead it forms type metal. The principal alloys
with tin are britannia metal and pewter. With lead, tin and copper
it constitutes babbit metal, a hard alloy used in the construction of
locomotive and car journals, and with other substances it enters into
the composition of other alloys used for a variety of purposes. The
double tartrate of antimony and potassium is the well known tartar
emetic. The pigment, Naples yellow, is an antimony chromate.

Production. — The total quantity of stibnite mined in the world can-
not be accurately estimated. That mined in the United States is very
small in amount, most of the antimony produced in this country being
obtained in the form of an antimony alloy as a by-product in the smelting
of antimonial lead ores.

Blsmuthinite (Bi2S3)

Bismuthinite is completely isomorphous with stibnite. It rarely,
however, occurs in acicular crystals, but is more frequently in foliated,
fibrous or dense masses.

Its axial ratio is .968 : 1 : .985.

The angle 1 10 A iTo = &&° 8'.

The mineral resembles stibnite in color and streak, but its surface is
often covered with a yellowish iridescent tarnish. Its fusibility and
hardness are the same as those of stibnite but its density is 6.8-7.1. It
is an electrical conductor.

In the open tube the mineral yields SO2 and a white sublimate
which melts into drops that are brown while hot, but change to opaque
yellow when cold. On charcoal it yields a coating of yellow Bi203 which
changes to a bright red BH3 when moistened with potassium iodide.
The mineral dissolves in hot nitric acid, forming a solution, which upon
the addition of water gives a white precipitate of a basic bismuth nitrate.

SULPHIDES, TELLURIDES, ETC. 75

Bismuthinite is distinguished from stibnite by the coating on char-
coal and by its complete solubility in HNO3.

Syntheses. — Crystals have been obtained by cooling a solution of
Bi2Ss in molten bismuth, and by cooling a solu Jon made by heating
IM2S3 in a solution of potassium sulphide in a closed tube at 2000.

Occurrence, Localities and Origin. — Bismuthinite occurs as a constit-
uent of veins associated with quartz, bismuth and chalcopyrite, in which
it was probably formed as a product of pneumatolytic processes. It is
found at Schneeberg and other points in Saxony; at Redruth and
elsewhere in Cornwall; near Beaver City, Utah; in a gold-bearing vein
at Gold Hill, Rowan County, N. C; and in a vein containing beryl,
garnet, etc., in granite at Haddam, Conn.

TETRADYMITE GROUP

This group comprises a series of tellurides and selenides of bismuth
that have not been satisfactorily differentiated because of the lack of
accurate analyses.

Tetradymite, the best known member of the group, is probably an
isomorphous mixture cf bismuth telluride and bismuth sulphide of the
formula Bi2(Te-S)3. It occurs in small rhombohedral crystals with the
axial ratio 1 : 1.587 and 10T1 A 1101 = 98° 58'. Its crystals are bounded
by rhombohedrons (R(ioTi) and 2R(202i)) and the basal plane
(oP(oooi)). Interpenetration fourlings are common with — 5R(oil2),
the twinning plane. The mineral is, however, more frequently found
in foliated and granular masses. Its color is lead-gray. It possesses a
perfect cleavage parallel to the base. Its hardness is 1.5-2 and its
density about 7.4. It is a good electrical conductor. Its best known
occurrences are Zsubkau, Hungary, Whitehall, Va., in Davidson
County, N. C, near Dahlonega, Ga., near Highland, Mont., and at
the Montgomery Mine and at Bradshaw City in Arizona. It occurs in
quartz veins associated with gold in the gold sands of some streams.

The other members of the group appear to be completely isomorphous
with tetradymite. They vary in color from tin-white through gray to
black.

Molybdenite (MoS^ /

This mineral, which is the sulphide of the rare metal molybdenum,
does not occur in large quantity, but it is so widely distributed that it
seems to be quite abundant. It occurs principally in black scales scat-

76 DESCRIPTIVE MINERALOGY

tered through coarse-grained, crystalline, siliceous rocks and granular
limestones and in black or lead-gray foliated masses.

The theoretical composition of molybdenite is 40 per cent sulphur
and 60 per cent molybdenum. Usually, however, the mineral contains
small quantities of iron and occasionally other components.

Crystals of molybdenite are exceedingly rare. Scales and plates
with hexagonal outlines are often met with but they do not usually pos-
sess sufficiently perfect faces to yield accurate measurements. The
measurements that have been obtained appear to indicate a holohedral
hexagonal symmetry with an axial ratio 1 : 1.908.

The cleavage of molybdenite is very perfect parallel to the base.
The laminae are flexible but not elastic. The mineral is sectile and so
soft that it leaves a black mark when drawn across paper. Its density
is 4.7. Its luster is metallic, color lead-black, and streak greenish
black. In very thin flakes the mineral is translucent with a green tinge.
Otherwise it is opaque. It is a poor conductor of electricity at ordi-
nary temperature, but its conductivity increases with the temperature.

In the blowpipe flame molybdenite is infusible. It, however, im-
parts to the edges of the flame a yellowish green color. Naturally, it
fields all the reactions for sulphur, and in the open tube it deposits a
pale yellow crystalline sublimate of M0O3. Molybdenite is decomposed
by nitric acid with the production of a gray powder (M0O3).

By its color, luster and softness molybdenite is easily distinguished
from all minerals but graphite. From this it is distinguished by its
reaction for sulphur. Moreover, a characteristic test for all molyb-
denum compounds is the dark blue coating produced on porcelain when
the pulverized substance is moistened with concentrated sulphuric
acid and then heated until almost dry. Before this test can be applied
to molybdenite, the mineral must first be powdered and then oxi-
dized by roasting in the air for a few minutes or by boiling to dryness
with a few drops of HNO3.

Syntheses. — Crystalline molybdenite has been prepared by the action
of sulphur vapor or H2S upon glowing molybdic acid. It has also been
produced by heating a mixture of molybdates and lime, in a large excess
of a gaseous mixture of HC1 and H2S.

Occurrence, Localities and Origin. — Molybdenite generally occurs
embedded as grains in limestone and in the crystalline silicate rocks,
as, for instance, granite and gneiss, and as masses in quartz veins, at
Arendal, Norway; at Blue Hill Bay, Maine; at Haddam, Conn.; in
Renfrew Co., Ontario, and at many points in the far western states.
It is thought to be of pneumatolytic origin.

SULPHIDES, TELLURIDES, ETC. 77

Uses. — The mineral is the principal ore of the metal molybdenum,
the salts of which are important chemicals employed principally in
analytical work, especially in the detection and estimation of phosphoric
acid. The molybdate of ammonia (NH^MoOi, the principal salt
employed in analytical processes, is easily obtained by roasting a mix-
ture of sand and molybdenite and treating the oxidized product with
ammonia. Other molybdenum salts are used for giving a green color
to porcelain. The metal is used in an alloy (ferro-molybdenum) for
hardening steel, as supports for the lower ends of tungsten filaments in
electric lamps and for making ribbons used in electric furnaces.

Production. — There was no production of molybdenite in North
America during 191 2. The imports of the metal into the United States
aggregated 3.5 tons, valued at $4,670. The value of the imports
of the ore is not known,

THE SULPHIDES, SELENIDES, ETC., OF THE METALS .
THE METALLIC MONO SULPHIDES, ETC.

The metallic monosulphides, monoselenides, etc., are compounds
in which the hydrogen of H2S, H2Se, H2Te, H3AS, and IfcSb are
replaced by metals. Among them are some of the most important
ores.

They may be separated into several groups of which some are
among the best defined of all the mineral groups, while others consist
simply of a number of minerals placed together solely for convenience
of description. In addition, there are a few members of this chemical
group which seem to have no close relationship with any other mem-
bers. These are discussed separately.

The groups described are as follows:

The Dyskrasite Group.
The Galena Group.
The Chalcocite Group.
The Blende Group.
The Millerite Group.
The Cinnabar Group.

DYSKRASITE GROUP

This group includes a number of arsenides and antimonides, some
of which apparently contain an excess of the metal above that neces-
sary to satisfy the formulas H3AS and HaSb. Although their com-

78 DESCRIPTIVE MINERALOGY

position is not understood, they are generally regarded as basic com-
pounds. A few' of I hem are well crystallized, but their composition is
dcubtful, because of the difficulty of obtaining pure material for anal-
yses. Seme of them are probably mixtures. The members of the
group, all of which are cemparatively rare, are whitneyiie (CugAs),
algodonite (CueAs), domeykite (CU3AS), horsjordite (CuoSb) and dyskras-
ite (Ag3Sb). Other minerals are known which may properly be placed
here, but their identity is doubtful. The only two members that need
further discussion are domeykite and dyskrasite.

Domeykite (C113AS) is known only in disseminated particles and
in botryoidal and dense masses and small orthorhombic crystals. It
may be a mixture of several components, which in other proportions
form algodonite. It is tin-white or steel-gray and opaque. It becomes
dull and covered with a yellow or brown iridescent tarnish when ex-
posed to the air. Its hardness is 3-4 and density about 7.3. It is the
most easily fusible of the copper arsenides. Its principal occurrences
are in the silver mines of Copiap6 and Coquimbo in Chile; associated
with native copper at Cerro de Paracabas, Guerrero, Mexico; at Shel-
don, Portage Lake, Michigan, and on Michipicoten Island, in Lake
Superior, Ontario. The last two occurrences are in quartz veins.

Dyskrasite (Ag3Sb) occurs in foliated, granular and structureless
masses and rarely in small orthorhombic crystals with an hexagonal
habit. Their axial ratio is .5775 : 1 : .6718. Twinning is frequent,
yielding star-shaped aggregates. The mineral has a silver-white color
and streak, but its exposed surfaces are often tarnished yellow or black.
It is opaque and sectile. Its hardness is 3.5-4 and density about 9.6.
It is a good electrical conductor. Dyskrasite is soluble in HNO3
leaving a white sediment of SD2O3. It occurs principally in the silver
mines of central Europe, and especially near Wolfach, Baden; St.
Andreasberg, Harz; and at Carrizo, in Copiap6, Chile.

GALENA GROUP

The minerals comprising the galena group number about a dozen
crystallizing in the holohedral division of the regular system (hex-
octahedral class). They possess the general formula RQ in which
R represents silver, lead, copper and gold, and Q sulphur, selenium
and tellurium. The group may be divided into silver compounds and
lead compounds, thus: (A) argentite (Ag2S), hessite (Ag2Te), petzite
((Ag-Au)2Te), naumannite (Ag2Se), aguilarile (Ag2(Se-S)), jalpaite

SULPHIDES, TELLURIDES, ETC. 79

((Ag-Cu)2S) and eukarite ((Ag-Cu)2Se), and (B) galena (PbS), altaite
(PbTe), and clausthalitc (PbSc). Of these only two are of importance,
viz., galena, and argentite. Hessite and petzite are comparatively
unimportant ores of gold.

Argentite (Ag2S)

Argentite, though not very widespread in its occurrence, is an
important ore of silver. It is found in masses, as coatings, and in crys-
tals or arborescent groups of crystals.

Argentite contains 87.1 per cent silver and 12.9 per cent sulphur when
pure. It is usually, however, impure through the admixture of small
quantities of Fe, Pb, Cu, etc.

The forms most frequently observed on argentite crystals are
00 O 00 (100), ooO(no) and O(in), though various f»Ooo (hlo) and
mOtn (Ml) forms are also met with. The crystals are often distorted
and often they are grouped in parallel growths of different shapes.
Twinning is common, with O(ni) the twinning plane. The twins
are usually penetration twins. The habit of most crystals is cubical
or octahedral.

Argentite is lead-gray in color. Its streak is a little darker. The
mineral is opaque. Its luster is metallic, its hardness about 2.25 and
density 7.3. It is sectile, has an imperfect cleavage and is a conductor
of electricity.

When heated on charcoal argentite swells and fuses, yielding sulphur
fumes and a globule of silver. It is soluble in nitric acid.

Argentite is easily recognized by its color, its sectility, the fact that
it yields a silver globule when fused with Na2CC>3 on charcoal and yields
. the sulphur test with a silver coin.

Syntheses. — Crystals of argentite may be obtained by treating red
hot silver with sulphur vapor or dry H2S, and by heating silver and SO2
in a closed tube at 2000.

Occurrence, Localities and Origin. — The mineral is found in the second-
ary enrichment zones of veins associated with silver and other sulphides
in many silver-mining districts. In Nevada it is an important ore at
the Comstock lode and in the Cortez district. It is found also near
Port Arthur on the north shore of Lake Superior, in Ontario, and asso-
ciated with native silver in the copper mines of Michigan. The ores of
Mexico, Chile, Bolivia and Peru are composed largely of this mineral.

Production. — Much of the silver produced in this country is obtained
from argentite, though by no means so great a quantity as is obtained
from other sources.

SiOz

Total

i-35

• • •

■ • •

99.96

•36

•IS

.70

100.01

1.28

.21

.o<?

100.00

80 DESCRIPTIVE MINERALOGY

Hessite (Ag2Te) and Petzite ((Ag*Au)2Te)

These two minerals, though comparatively rare, are prominent
sources of gold and silver in some mining camps. They usually occur
together associated with other sulphides.

Hessite is the nearly pure silver telluride and petzite, an isomorphous
mixture of gold and silver tellurides, as indicated by the following analy-
ses of materials from the Red Cloud Mine, Boulder Co., Colorado.

Te Ag Au Cu Pb

I. 37.86 59.91 .22 .17 .45

II. 34.91 50.66 13.09 .07 .17

III. 32.97 40.80 24.69

The minerals crystallize in all respects like argentite. They are
opaque and lead-gray to iron-black in color, sectile to brittle, have a
hardness between 2 and 3 and a specific gravity of 8.3-9, increasing with
the percentage of gold present. They are good conductors of electricity.

Before the blowpipe, both minerals melt easily to a black globule, at
the same time coloring the reducing flame greenish and giving the odor
of tellurium fumes. When acted upon by the reducing flame, the globule
becomes covered with little crystals of silver. With Na2C03 on charcoal
both minerals yield a globule of silver, but the globule obtained from
hessite dissolves in warm HNO3, while that obtained from petzite
becomes yellow (gold). In the open tube both yield a white sublimate
of TeCfe which melts, when heated, to colorless drops. When heated
with concentrated H2SO4, they give a purple or red solution which, upon
the addition of water, loses its color and precipitates blackish gray,
powdery tellurium. The minerals dissolve in HNO3. From this solu-
tion HCl throws down white silver chloride.

Both the minerals resemble very closely many forms of argentite
and galena, from which, however, they may be distinguished by the
reactions for tellurium. Petzite and hessite may be distinguished from
one another by the test for gold. Moreover a fresh surface of hessite
blackens when treated with a solution of KCN, whereas a surface of
petzite remains unaffected.

Syntheses. — Octahedrons of hessite are obtained by the action of
tellurium vapor upon glowing silver in an atmosphere of nitrogen, and
dodecahedrons of petzite upon similar treatment of gold-silver alloy.

Origin. — Both minerals are believed to be primary deposits orig-
inating in magmatic solutions. They occur in veins with native gold,
quartz, fluorite, dolomite, and various sulphides and other tellurides.

SULPHIDES, TELLURIDES, ETC. 81

Localities. — These tellurides, together with others to be described
later (p. 113), are important sources of silver and gold in the mines at
Nagyag, Transylvania, at Cripple Creek and in Boulder Co., Colo., and
at Kalgoorlic, W. Australia. The quantity of tellurides mined is con-
siderable, but since it is impracticable to separate these two tellurides
from the other compounds of gold and silver mined with them, it is im-
possible to estimate the proportion of the metals obtained from them.

Galena (PbS)

Galena, the most important ore of lead, occurs in great lead-gray
crystalline masses, in large and small crystals, in coarse and fine granular
aggregates, and in other less common forms. Much galena contains
silver, in which case it becomes an important ore of this metal.

Galena rarely approaches the theoretical composition 13.4 per cent
cf sulphur and 86.6 per cent of lead. It usually contains small quanti-
ties of the sulphides cf silver, zinc, cadmium, copper and bismuth and
in some cases native silver and gold. When the percentage of silver
present reaches 3 oz. per ton the mineral is ranked as a silver ore. This
silver is apparently present in some cases as an isomorphous mixture
of silver sulphide and in other cases in distinct
minerals included within the galena.

" Galena crystals usually possess a cubical habit,
though crystals with the octahedral habit are
very common. The principal forms observed are
ooOoo(ioo), O(ni), ooO(no), mO<x>(hlo) and
mOm (hll) (Figs. 29 and 30). Twins are common,
with O the twinning face. FlG- ^.-Galena Crys-

Galena is well characterized by its lead-gray , ' ~ ' /JX

. (0); °°0, no (a)

color, its perfect cleavage parallel to the cubic faces and O, in (0).
and by its great density (8.5). Its luster is me-
tallic and its hardness about 2.6. Its streak is grayish black. It is a
good conductor of electricity.

On charcoal galena fuses, yielding sulphurous fumes and a globule
of metallic lead, which may easily be distinguished from a silver globule
by its softness. The charcoal around the assay is coated with a yellow
sublimate of lead oxide (PbO). The mineral is soluble in HNO3 with
the separation of sulphur.

Its color and luster distinguish galena from nearly all minerals but
5 Unite. From this mineral it is easily distinguished by its more difficult
fusibility, by its cleavage, and by the fact that it does not yield the anti-
mony fumes when heated on charcoal.

82 DESCRIPTIVE MINERALOGY

Galena weathers readily to the sulphate (angieske) and carbonate
(cerussite); consequently it is usually not found in the upper portions
of veins that are exposed to the action of the air.

Syntheses.— Crystals of galena result from heating a mixture of
lead oxide with NH4CI and sulphur, and from treatment of a lead salt
with H2S at a red heat. Small crystals have been produced by heating

Fir.. 30. — Galena Crystals («0™(ioo) and O(iti)) partly covered by Martasilc;
Irom the Joplin Distri-.i, Mo. (Aft,r II'. S. T. Smith ,ind C. E. Submittal.)

in a sealed glass tube at 8o°-oo° pulverized cerussite (PbCOa) in a water
solution of H2S.

Origin. — Veins of galena containing silver (silver-lead) were probably
produced by ascending solutions emanating from bodies of igneous
rocks, while the galena in limestone was probably deposited by ground-
water that dissolved the sulphide from the surrounding sedimentary
rocks. Galena is also in some cases a melamorphic product.

Occurrence. — The mineral occurs very widely spread. It is found
in veins associated with quartz (SiOs), calcite (CaCO-j), barite (BaSOi)
or fluorite (CaF2) and various sulphides, especially the zinc sulphide,
sphalerite; in irregular masses filling clefts and cavities in limestone;

SULPHIDES, TELLURIDES, ETC. 83

in beds, and in stalactites and other forms characteristic of water
deposits.

It occurs also as pseudomorphs after pyromorphite — the lead phos-
phate. The form that occurs in veins is often silver bearing, while that
in limestone is usually free from silver.

Localities. — Galena is mined in Cornwall and in Derbyshire, Eng-
land; in the Moresnet district, Belgium; at various places in Silesia,
Bohemia, Spain and Australia. In the United States it occurs in veins at
Lubec, Me., at Rossie, St. Lawrence Co., N. Y., at Phoenixville, Penn., at
Austin's Mines in Wythe Co., Va., and at many other places. It is
mined for silver in Mexico; at Leadville, Colo.; at various points in
Montana; in the Cceur d'Alene region in Idaho and at many other places
in the Rocky Mountain region.

The most extensive galena deposits in this country are in Missouri;
in the corner made by the states of Wisconsin, Illinois and Iowa; and
in Cherokee Co., Kansas. In these districts the galena, associated
with sphalerite (ZnS), pyrite (FeS2), smithsonite (ZnCOa), calamine
((ZnOH)2Si03), cerussite (PbCOa), calcite (CaCCte) and other minerals,
fills cavities in limestone.

Extraction of Lead and Silver from Galena. — The ore is first crushed
and concentrated by mechanical or electrostatic methods, and the
concentrates are roasted to convert them into oxides and sulphates.
The mass is then heated without access of air, sulphur dioxide being
driven off, leaving metallic lead carrying impurities, cr a mixture of
lead and silver.

The processes employed in refining the impure lead vary with the
nature of the impurities.

Uses. — Galena is employed to some extent in glazing common
stoneware. It is also used in the preparation of white lead and other
pigments. As has alrcr.c!y been stated, it is the most important ore of
lead and a very important ore of silver.

The metal lead finds many uses in the arts. Its most common
use is for piping. Its alloys, type metal, pewter and babbitt metal
have already been referred to (p. 74). Solder is an alloy of tin and lead;
Wood's metal a mixture of lead, bismuth, tin and cadmium. The spe-
cial characteristic of Wood's alloy is its low fusion point (700).

Production. — The total production of galena by the different coun-
tries of the world cannot be given, but the world's production of lead
in 191 2 was 1,277,002 short tons. The total quantity of lead pro-
duced by the United States from domestic ores in the same year was
about 4i5>395 tens, valued zt $37,385,550. Most of this was obtained

g4 DESCRIPTIVE MINERALOGY

from galena. About 171,037 tons were soft lead, smelted from ores
mined mainly for their lead and zinc contents, and the balance from
ores mined partly for their silver. The importance of galena as an ore
of silver may be appreciated from the fact that of the $39,197,000
worth of this metal produced in the United States during 191 2, silver
to the value of about $12,000,000 was obtained from lead ores or from
mixtures of lead and zinc ores.

Altaite (PbTe) and clausthalite (PbSe) both resemble galena in
appearance. Both occur commonly in fine-grained masses, but they
are also found in cubic crystals. Altaite is tin-white, tarnishing to
yellow or bronze, and clausthalite is lead-gijay. Their hardness is 2.5-3
and specific gravity about 8.1. They are associated with silver and lead
compounds principally in the silver mines of Europe and South America.
Altaite is known also from several mines in California, Colorado and
North Carolina. They are distinguished from one another and from
galena by the tests for Te and Se.

CHALCOCITE GROUP

The chalcocite group includes four or five cuprous and argentous
sulphides, selenides and tellurides. They all crystallize in the ortho-
rhombic system (rhombic bipyramidal class) often with an hexagonal
habit, and are isomorphous. The best known members of the group
are chalcocite (CU2S) and stromeyerite (Cu-Ag)2S, but only the first-
named is common. Although these minerals are orthorhombic, never-
theless CU2S is known to exist also in isometric crystals, in which form
it is isomorphous with argentite. Moreover, stromeyerite is an iso-
morphous mixture of Ag2S and CU2S. Therefore, it is inferred that
CU2S and Ag2S are isomorphous dimorphs.

Chalcocite (Cu2S)

Chalcocite (CU2S), the cuprous sulphide, is an important ore of
copper though by no means as widely spread as the iron-copper sul-
phide, chalcopyrite. It is usually found in black masses with a dull
metallic luster and as a black powder, though frequently also in crys-
tals. It is a common constituent of the enrichment zone of many veins
of copper ores.

The best analyses of chalcocite agree closely with the formula
given above, requiring the presence of 20.2 per cent of sulphur and
79.8 per cent of copper. Iron and silver are often present in the mineral
in small quantity.

SULPHIDES, TELLURIDES, ETC. 85

In crystallization chalcocite is orthorhombic (rhombic bipyramidal
class) with the axial ratio .5822 : 1 : .9701. Its crystals contain as
their predominant forms oP(ooi), ooP(no), «Po&(oio), P(ni),

a series of prisms cf the general symbol — P(nA), and several bra-

chydomes. Many cf the crystals are elongated parallel to H, and
others are so developed as to possess an hexagonal habit (Fig. 31).
Twins are common according to several laws. When the twinning plane is
JP (n a) the twins are usually cruciform (Fig. 31). The zone 001— 010
is often striated through oscillatory combinations. iioaiio=6o° 25'.
The cleavage of chalcocite is indistinct, its fracture is conchoidal.
Its hardness is 2.5-3 an^ density about 5.7. Its streak, like its color,

Fie. 31. Fig. 3a.

Fie. 31.— Chalcocite Crystal. oP, 001 (c); °oP«, 010(b); »P, no (m); iPw ,

021 id); JP«,023 («); P. i" (?)andiP, 113 «■

Fio. 31.— Complex Chalcocite Twin, with »P, no (m) and )P, 112 {») the Twinning

Planes.

is nearly black, but exposed surfaces are often tarnished blue or green,
probably through the production of thin films of other sulphides like
covelUte (CuS), chalcopyrite (FeCuSa),etc. The mineral is an excel-
lent conductor of electricity.

In the open tube or on charcoal chalcocite melts and yields sul-
phurous fumes.

When mixed with NazCOs and heated a copper globule is produced.
The mineral dissolves in nitric acid with the production of a solution
that yields the test for copper.

Upon exposure to the air chalcocite changes readily to the oxide,
cuprite (CU2O), and the carbonates, malachite and azurite. In the
presence of silicious solutions it may give rise to the silicate, chrysocolla
(p. 441).

A pseudomorph of chalcocite after galena is known as harrisiU.

86 DESCRIPTIVE MINERALOGY

It occurs at the Canton Mine in Georgia and in the Polk Co. copper
mines in Tennessee. Pseudomorphs after many other copper min-
erals are common.

Chalcocite is recognized by its color and crystallization. Massive
varieties are distinguished from or gentile by greater brittleness and the
reaction for copper; from bornite (CuaFeSa) by the fact that it is not
magnetic after roasting.

Syntheses. — Crystals of chalcocite have been made in many ways,
more particularly by heating the vapors of CuCk and H2S, and by
gently warming CU2O in H2S. Measurable crystals have been observed
on old bronze that has been immersed in the waters of hot springs for
a long time.

Occurrence, Localities and Origin. — The mineral is a common prod-
uct of the alteration of other copper compounds in the zone of secondary
enrichment of sulphide veins. It is therefore present at most localities
of copper minerals. One of the best known occurrences is Butte,
Mont.

Fine crystals of chalcocite occur in veins and beds at Redruth and
at other places in Cornwall, England; at Bristol in Connecticut, and
at Joachimthal in Bohemia. The massive variety is known at many
places. In the United States it occurs in red sandstone at Cheshire
in Connecticut. It is found also in large quantities near Butte City in
Montana, and in Washoe and other counties in Nevada, and indeed
in the veins of most copper producing mines. In Canada it is present
with chalcopyrite and bornite at Acton, Quebec, and at several places
in Ontario north of Lake Superior.

Extraction of Copper. — Chalcocite rarely occurs alone in large
quantity. In ores it is usually mixed with other compounds of copper,
and is treated with them in extracting the metal (see p. 133).

Stromeyerite ((Ag-Cu)2S) is usually massive, but it occurs also in
simple and twinned crystals similar to those of chalcocite. Their axial
ratio is .5822 : 1 : .9668, almost identical with that of chalcocite. The
mineral is opaque and metallic. Its color and streak are dark steel-
gray. Its hardness is 2.5-3 and density about 6.2. It is soluble in
nitric acid. It occurs associated with other sulphides in the ores of
silver and copper mines at Schlangenberg, Altai; Kupferberg, Silesia;
Coquimbo, Copiapo, and other places in Chile, and in a few mines in
California, Arizona, and Colorado.

SULPHIDES, TELLURIDES, ETC. 87

BLENDE GROUP

The blende group of minerals comprises a series of compounds whose
general formula like that of the galena group is RQ. In the blendes R
stands for Zn, Cd, Mn, Ni and Fe and Q for S, Se and Te.

The blendes are all transparent or translucent minerals of a lighter
color than galena. They constitute an isodimorphous group of a dozen
or more members crystallizing in the tetrahedral division of the regular
system (hextetrahedral class), and in hemimorphic holohedral forms of
the hexagonal system (dihexagonal-pyramidal class). The group may
be divided into two subgroups known respectively as the sphalerite
and the wurtzite groups.

SPHALERITE DIVISION

The most important member of this division of the blende group is
the mineral sphalerite. This, like the other less well known members,
crystallizes in the hemihedral division of the regular system with various
tetrahedrons as prominent forms. The other members of the group
are alabandite (MnS), and an isomorphous mixture of FeS and NiS,
pentlandite.

Sphalerite (ZnS)

Sphalerite, one of the very important zinc ores and one of the most
interesting minerals from a crystallographic standpoint, occurs in amor-
phous and crystalline masses and in handsome crystals and crystal groups.
Botryoidal and other imitative masses are common.

Pure white sphalerite consists of 67 per cent of Zn and 23 per cent of
sulphur. The colored varieties usually contain traces of silver, iron,
cadmium, manganese and other metals. Sometimes the proportion of
the impurities is so large that the mineral containing them is regarded as
a distinct variety. Two analyses of American sphalerites are as follows:

S Zn Cd Fe Total

Franklin Furnace, N. J 32 . 22 67 .46 tr ... 99.68

Joplin, Mo 32-93 66.69 ••• -42 100.04

The hemihedral condition of sphalerite is shown in the predominance
of tetrahedrons among its crystal forms and by the symmetry of its

etched figures (Fig. 33). Its most common forms are — - — (321) and

2O lO

other hextetrahedrons, d= — (221), — (331) and other deltoid-dodeca-

2 2

88 DESCRIPTIVE MINERALOGY

hedrons and ±303(311) and other tris tetrahedrons. In addition,
00 O 00 (100) and 00 0(i 10) are quite common (Fig. 34). Twins are
abundant. Their twinning plane is O and their composition face either
0 (Fig. 35), or a plane perpendicular to this. Through twinning, the
crystals often assume a rhombohedral habit.

The cleavage of sphalerite is perfect parallel to 00 O(no). From a
compact mass of the mineral a fairly good dodecahedron may some-
times be split. Its fracture is conchoidal. When pure the mineral is
transparent and colorless. As usually found, however, it is yellow,
translucent and black, brown, or some shade of red. Its streak is
brownish, yellow or white. The yellow masses look very much like

FlO. 33.— Telrahedral Crystal of Sphalerite Bounded by »0»(ioi) and ±0 (11 1
and ill), Illustrating the Fact that Its Octahedral Faces Fall into Two Groups.

Fie. 34.— Sphalerite Crystal: «0, no (rf), and+— ^, 311 (m).

Fig. 35.— Sphalerite Octahedron Twinned about 0(m).

lumps of rosin. The hardness of sphalerite is between 3.5 and 4, and its
density about 4. Its luster is resinous. The mineral is difficultly fusible,
and is a nonconductor of electricity. Its index of refraction («) for
yellow light is 2.369.

Sphalerite when powdered always yields tests for sulphur under
proper treatment. On charcoal it volatilizes slowly, coating the coal
with a yellow sublimate when hot, turning white on cooling. When
moistened with a dilute solution of cobalt nitrate and heated in the
reducing flame, the white coating of ZnO turns green. The mineral dis-
solves in hydrochloric acid, yielding sulphuretted hydrogen.

By oxidation sphalerite changes into the sulphate of zinc, and by
other processes into the silicate of zinc, calamine, or the carbonates,
smithsonite and hydrozincite.

SULPHIDES, TELLURIDES, ETC. 89

Syntheses. — Sphalerite crystals have been made by the action of H2S
upon zinc chloride vapor at a high temperature. They are also often
produced in the flues of furnaces in which ores containing zinc and sul-
phur are roasted.

Occurrence and Origin. — Sphalerite occurs disseminated through lime-
stone, in streaks and irregular masses in the same rock, and in veins cut-
ting crystalline and sedimentary rocks. It is often associated with
galena. The material in the veins is often crystallized. Here it is asso-
ciated with chalcopyrite (CuFeS2), fluorite (CaF2), barite (BaSCU),
siderite (FeCOa), and silver ores. When in veins it is in some cases the
result of ascending hot waters and in other cases the product of down-
ward percolating meteoric water. Much of the disseminated ore is a
metamorphic contact deposit.

Localities. — Crystallized sphalerite is found abundantly at Alston
Moor, Cumberland, England; at various places in Saxony; in the Bin-
nenthal, Switzerland; at Broken Hill, N. S. Wales, and in nearly all
localities for galena. Handsome, transparent, cleavable masses are
brought from Pilos de Europa, Santander, Spain. Stalactites are
abundant near Galena, 111.

The principal deposits of economic importance in America are those
in Iowa, Wisconsin, Missouri and Kansas, where the sphalerite is asso-
ciated with other zinc compounds and with galena forming lodes in
limestone, and at the silver and gold mines of Colorado, Idaho and Mon-
tana,

Extraction of the Metal. — In order to obtain the metal from sphalerite,
the ore is usually first concentrated by flotation or other mechanical
processes. The concentrates are then converted into the oxide by roast-
ing and the impure oxide is mixed with fine coal and placed in clay retorts
opening into a condenser. These are gradually heated. The oxide is
reduced to the metal, which being volatile distils over into the con-
denser, where it is safely caught. Other processes are based on wet
chemical methods.

Uses of Zinc. — Zinc is used extensively in galvanizing iron wire and
sheets. It is also employed in the manufacture of important alloys
such as brass, and in the manufacture of zinc white, which is the oxide
(ZnO), and other pigments. A solution of the chloride is used for pre-
serving timber. Argentiferous zinc is the source of a considerable quan-
tity of silver.

Production. — The figures showing the quantity of sphalerite pro-
duced in the zinc-producing countries are not available. The total
amount of metallic zinc produced in the year 191 2 was 1,070,045 tons,

90 DESCRIPTIVE MINERALOGY

valued at $44,699,166, of which the United States produced from domestic
ores 323,907 tons, and in addition used, in the making of zinc compounds,
about 55,000 tons. Of this aggregate, Missouri produced about 149,560
tons. Most of the metal was obtained from sphalerite, but a large
part came from other ores. The quantity of silver produced in refining
zinc ores was 664,421 oz., valued at $408,619.

Alabandite (MnS) is isomorphous with sphalerite. It usually
occurs, however, in dense granular aggregates of an iron-gray color.
Its streak is dark green. It is opaque and brittle. Its hardness is 3-4
and density 3.9. It is not an electrical conductor. When heated on
charcoal in the reducing flame it changes to the brown oxide of man-
ganese and finally melts to a brown slag. It is soluble in dilute HC1
with the evolution of H2S. Alabandite occurs with other sulphides at
Kapnik, Hungary; at Tarma, Peru; at Puebla, Mexico, and in the
United States at Tombstone, Arizona, and on Snake River, Summit Co.,
Colorado.

Pentlandite ((Fe • Ni)S) may belong to this group. Iron is frequently
found in crystallized sphalerite. Its sulphide, therefore, may be isomor-
phous with sphalerite, in which case pentlandite, which is probably an
isomorphous mixture of NiS and FeS, would also belong in the sphal-
erite group. The mineral occurs in light bronzy yellow, granular masses
with a distinct octahedral cleavage, a hardness of 3.5-5 and a density of
4.6. It is a nonconductor of electricity. Pentlandite occurs with
chalcopyrite (CuFeS2) and pyrrhotite (FeySg), at Sudbury, Ontario,
where it is probably the constituent that furnishes most of the nickel
(see p. 92).

It is distinguished from pyrrhotite, which it resembles in appearance,
by its cleavage and the fact that it is not magnetic. Moreover, it
weathers to a brassy yellow color, while pyrrhotite weathers bronze.

WURTZITE DIVISION

The wurtzite group comprises only two or three members, wurtziie
(ZnS), greenockite (CdS), and possibly pyrrhotite (FenSn+1). All crys-
tallize in the holohedral division of the hexagonal system and the first
two are unquestionably hemimorphic (dihexagonal pyramidal class).
Pyrrhotite is the most common.

Wurtzite (ZnS) is one of the dimorphs of ZnS, sphalerite being the
other. It occurs in brownish black crystals, in masses and in fibers.

SULPHIDES, TELLURIDES, ETC. 91

Its crystals are combinations of ooP(ioTo) with 2P(202i) and
oP(oooi) at one end, and a series of steeper pyramids at the
other. Their axial ratio is i : .8175. The angle 10T1 A 01^1 = 40° 9';

2P(022l) A2P(022l) = 52° 27'.

The mineral is brownish black to brownish yellow and its streak
is brown. Its hardness is between 3 and 4 and its sp. gr. is about 4.
It conducts electricity very poorly. In chemical and physical prop-
erties it resembles sphalerite. Its crystals have been produced by
fusing a mixture of ZnS04, fluorite and barium sulphide. They are
frequently observed as furnace products.

Wurtzite occurs as crystals at the original Butte Mine, Butte,
Montana, and in a mine near Benzberg, Rhenish Prussia, at both
places associated with sphalerite. They also occur with silver ores near
Oruro and Chocaya, Bolivia, and near Quispisiza, Peru.

Greenockite. — Greenockite (CdS) is completely isomorphous with
wurtzite. Its crystals have an axial ratio
1 : .8109. In general habit they are like
those of wurtzite but they contain many more
planes (Fig. 36). The angle io7iaoi^i =
390 58'. Crystals are rare and small. The
mineral usually occurs as a coating on other
minerals, especially sphalerite. Its color is
honey to orange-yellow, its streak orange- Fig. 36.— Greenockite Crys-
yellow, and its luster glassy or resinous. It taL 00 p, ioTo^(m); 2P,
is transparent or translucent and is brittle. 2021 («); P, ion (*), and

Its hardness is 3-3.5 and density about 4.0. ? ' -/f . Y. e orm

0 ° J . J "* * JP, 1012 (i) is often pres-

Its index of refraction 0 = 2.688. When Cnt at the upper end of

heated in the closed tube it becomes carmine, the crystals.)

but it changes to its original color on cooling.

It yields the usual reactions for sulphur and cadmium, and dissolves

in HC1, yielding H2S.

Crystals have been obtained by melting a mixture of CdO, BaS,
and CaF2, and by heating cadmium in an atmosphere of H2S to near
fusing point. The mineral is a common furnace product. Greenockite
crystals occur with prehnite at Bishoptown, Scotland, and as coatings
on sphalerite in the zinc regions of Missouri and Arkansas, and at
Friedensville, Pennsylvania.

92 DESCRIPTIVE MINERALOGY

Pyrrhotite (FenSn+i)

Pyrrhotite, or magnetic pyrite, occupies the anomalous position
of being one of the most important ores of nickel, whereas it is essen-
tially a sulphide of iron. The name is really applied to a series of
compounds whose composition ranges between FesSe and FeieSiy.
The crystallized material is in some cases FerSg, and in others, FenSi2.
It is probably a solid solution of FeS2 or S in the sulphide of iron (FeS).
As usually found, pyrrhotite is in bronze-gray granular masses, that
tarnish rapidly to bronze on exposure to the air. Good crystals of
the mineral are rare.

Analyses of pyrrhotite vary widely. The percentages of Fe and S
corresponding to FeySg are Fe, 60.4; S, 39.6, and those corresponding
to FenSi2 are Fe, 61.6; S, 38.4. Much of the mineral contains in addi-
tion to the iron and sulphur sufficient nickel to render it an ore of this
metal, but it is probable that the nickel is present in pentlandite (see
p. 90) or some other nickel compound embedded in the pyrrhotite.

Analyses of pyrrhotite from various localities are:

S Fe Co Ni Total

Schneeberg, Saxony 39 . 10 61.77 tr IO° • 87

Brewster, N. Y 37 . 98 61 . 84 ... .25 100.07

Sudbury, Ontario 38. 91 56.39 .... 4.66 99 .96

Gap Mine, Penn 38. 59 55 .82 5.59 100.00

The few crystals of pyrrhotite known are distinctly hexagonal in

habit with a : c=i : 1.7402. They are com-
monly tabular or acutely pyramidal, but it
has not been established that they are hemi-
m—* morphic, although the almost universal pres-
ence of FeS in crystals of wurtzite would
Fig. 37.-Pyrrhotite Crystal. ^^^ that the two substances are isomor-
oP, 0001 (c); P, 1011 (5); , „,, . , , . . , ,

P 4041 (u) and 00 p Ph°us' The tabular crystals possess a broad

10T0 (m). ' basal plane, which surmounts hexagonal prisms

ooP(ioTo) and ooP2(ii2o), and a series of
pyramids, of which 2P(202i), iP(ioi2), P(ioTi) and P2(ii22) are the
most frequent. (Fig. 37.) The angle 10T1 AoiTi = 53° n'.

The cleavage of pyrrhotite is not always equally distinct. When
marked it is parallel to 00 P2 (11 20). There is also often a parting
parallel to the base. Its fracture is uneven. The mineral is brittle.
It is opaque, and has a metallic luster. Its color varies between bronze-

SULPHIDES, TELLURIDES, ETC. 93

yellow and copper-red, and its streak is grayish black. Its hardness is
a little less than 4 and its density about 4.5. All specimens are magnetic
but the magnetism varies greatly in intensity, being at a maximum in
the direction of the vertical axis. The mineral is a good conductor of
electricity.

Pyrrhotite gives the usual reactions for iron and sulphur, and some-
times, in addition, the reactions for cobalt and nickel. It is decom-
posed by hydrochloric acid with the evolution of H2S, which may
easily be detected by its odor.

From the many sulphides more or less closely resembling pyrrhotite
in appearance, this mineral may easily be distinguished by its color
and density and by its magnetism.

Syntheses. — Crystals may be obtained by heating iron wire or
Fea04, or dry FeCb to redness in an atmosphere of dry H2S and by
heating Fe in a closed tube with a solution cf f eCfe saturated with
H2S.

Occurrence, Localities and Origin. — Pyrrhotite occurs completely
filling vein fissures, and also as crystals embedded in other minerals
constituting veins. It occurs also as impregnations in various rocks
and as a segregation in the coarse-grained basic rock known as norite,
where it is believed to have separated from the magma producing the
rock. It may also in some cases be a product of metamorphism on the
borders of igneous intrusions.

It is found at Andreasberg, Harz; Bodenmais, Bavaria; Minas
Geraes, Brazil; various points in Norway and Sweden, and on the
lavas of Vesuvius. In North America crystals occur at Standish, Maine;
at Trumbull, Monroe Co., N. Y.; and at Elizabethtown, Ontario.
The mineral has been mined at Ducktown, Tenn.; at Ely, Vermont,
and at Gap Mine, Lancaster Co., Penn.

Its mines at present, however, are at Sudbury, in Ontario, where the
mineral is associated with magnetite, chalcopyrite and pentlandite
((Fe-Ni)S) on the lower border of a great mass of igneous rock (norite).
Besides these there are present also embedded in the pyrrhotite
small quantities of other minerals, so that the ore as mined is very
complex.

Pyrrhotite is sometimes found altered to pyrite, to limonite and to
siderite (FeCOa).

Extraction. — Pyrrhotite is crushed and roasted to drive off the
greater portion of the sulphur. It is then placed in a furnace and
smelted with coke and quartz. The nickel, copper and some of the
iron, together with some of the fused sulphides, collect as a matte in the

94 DESCRIPTIVE MINERALOGY

bottom of the furnace from which it is withdrawn from time to time.
The matte is riext roasted to transform the iron it contains into oxides
and the remaining nickel and copper are separated by patented or secret
methods.

Uses. — The mineral is sometimes worked for the sulphur it con-
tains. Its principal use, however, is as a source for nickel, nearly all of
this metal used in America coming from the nickeliferous variety found
at Sudbury, Ontario.

The metal nickel has come into extensive use in the past few years
in connection with the manufacture of armor plate for warships. The
addition of a few per cent of nickel to steel hardens it and increases
its strength and elasticity.

Nickel is also extensively used in nickel-plating and in the manufac-
ture of alloys. German silver is an alloy of nickel, copper and zinc. The
nickel currency of the United States contains about 25 per cent Ni and
75 per cent Cu. Monel metal is a silver- white alloy containing about
75 per cent Ni, 1 per cent Fe and 29 per cent Cu. It is stronger than
ordinary steel, takes a brilliant finish and is impervious to acids. It is
made directly at Sudbury, Ont., by smelting.

Production. — The production of pyrrhotite and chalcopyrite (CuFeS)
at the Sudbury mines in 191 2 amounted to 737,584 short tons. The
value of the matte produced was $6,303,102, and the value of nickel con-
tained in it was about $16,000,000. About half of the nickel was used
in America; the remainder, amounting to $8,515,000, was exported, after
being refined in the United States. Formerly the United States pro-
duced a considerable quantity of nickel from domestic ores, most of
it from pyrrhotite, but the mines have been closed down within the past
few years. It is, however, produced as a by-product in the refining
of copper ores to the amount of about 325 tons annually, This is worth
about $260,000 (see also p. 400).

MILLERITE GROUP

This group comprises sulphides, arsenides and antimonides of nickel.
It includes the minerals mUlerite (NiS) 9niccolite (NiAs), arite (Ni(Sb- As))
breithauptite (NiSb) and a few others. Of these only milled te and nic-
colite are at all common. The minerals all crystallize in the hexagonal
system, possibly in the rhombohedral division (ditrigonal scalenohedral
class). Well defined crystals are, however, rare and often capillary so
that their symmetry has not been determined with certainty.

SULPHIDES, TELLURIDES, ETC. 95

Millerite (NiS)

Millerite is easily recognized by its brass-yellow color. It occurs
most frequently in slender hair-like needles, often aggregated into tufts
or radial groups, or, woven together like wads of hair, forming coatings
on other minerals.

Pure millerite contains 35.3 per cent sulphur and 64.6 per cent nickel.
It frequently contains also a little Co and Fe.

Crystals are thin, acicular or columnar with prismatic and rhom-
bohedral faces predominating, and an axial ratio of 1 : .330, or of 1 : .9886
if the rhombohedron 311(0331) is taken as the ground form.

The mineral is elastic. Its hardness is 3-3.5 and density about 5.5.
It is opaque and brassy yellow. Its streak is greenish black. It is an
excellent conductor of electricity.

The mineral yields sulphurous fumes in the open tube. After roast-
ing it gives, with borax and microcosmic salt, a violet bead when heated
in the oxidizing flame of the blowpipe. On charcoal with Na2C03 it
yields a magnetic globule.

Synthesis. — Bunches of yellow acicular crystals of NiS have been
formed by treatment of a solution of NiSO* with H2S, under pressure.

Localities. — Millerite occurs as long acicular crystals in cavities in
other minerals at Joachim thai, in Bohemia, and at many places in
Saxony. In the United States it forms radiating groups in cavities in
hematite (Fe20s) at Antwerp, N. Y. At the Gap Mine, Lancaster Co.,
Penn., it forms coatings on other minerals and at St. Louis, Mo. and
at Milwaukee, Wis., it occurs in delicate tangled tufts in geodes in lime-
stone. Nowhere does it occur in sufficient quantity to constitute an ore*

Niccolite (NiAs)

Niccolite usually occurs massive, though crystals are known. It is
of economic importance only in a few localities.

Theoretically, the mineral contains 56.10 per cent As and 43.90 per
cent Ni, but as usually found it contains also Sb, S, Fe and often small
quantities of Co, Cu, Pb and Bi.

Its crystals, which are rare, are hexagonal and hemimorphic (prob-
ably dihexagonal pyramidal class), with 0:1=1: .8194. The prism
ooP(ioTo), and oP(oooi) are the predominant forms, with the
pyramids P(ioTi) and ^(5057) less well developed. The angle

io7i aoi^i==4o° i2'-

The mineral is pale copper-red and opaque. It has a brownish

fl» DESCRIPTIVE MINERALOGY

black streak. Its hardness is about 5 and its density 7.6. The surfaces
of nearly all specimens are tarnished with a grayish coating. The min-
eral is a good conductor of electricity.

In the open tube niccolite yields arsenic fumes and often traces of
SO2. On charcoal with Na2COa it yields a metallic globule of nickel.
It dissolves in HNO3 with the precipitation of AS2O3. The apple-green
solution, thus produced, becomes sapphire-blue on addition of ammonia.

Its peculiar light pink color and its reactions for arsenic and nickel
distinguish niccolite from all other minerals, except, perhaps, breit-
hauptitCy which, however, contains antimony.

Occurrence. — Niccolite occurs principally in veins in crystalline
schists and in metamorphosed sedimentary rocks, associated with silver
and cobalt sulphides and arsenides.

Localities. — The principal locality for niccolite in North America is
Cobalt, Ontario, where it is found with native silver and silver, cobalt,
and other nickel compounds, all of which are thought to have been de-
posited by hot waters emanating from a mass of diabase. In Europe it
is abundant at Joachimsthal in Bohemia, and at a number of other
places in small quantity.

Although rich in nickel, the mineral is not used as an ore at present,
except to a very minor extent, most of the nickel of commerce being
obtained from other compounds (see p. 94).

Breithauptite (NiSb) is rare. It is of a light copper-red color, much
brighter than that of niccolite, and its streak is reddish brown. Its hard-
ness is 5.5 and density about 7.9. Its crystals are hexagonal tables
with an axial ratio 1 : 1.294, and a distinct cleavage parallel to oP(ooi).
It usually occurs in dendritic groups, in foliated and finely granular
aggregates and in dense masses. It is a frequent furnace product, when
ores containing Ni and Sb are smelted. It is found at Andreasberg, Harz ;
at Sarrabus, in Sardinia; at Cobalt, Ont., and at a few other places. It
is distinguished from niccolite by its deeper color and its content of Sb.

Covellite (CuS)

Covellite, or indigo copper, is the cupric sulphide, chalcocite being
the corresponding cuprous salt. It is called indigo copper because of
the deep blue color of its fresh fracture. It is often mixed with other
copper compounds from which it has been derived by alteration. It
usually occurs massive, but crystals are known. It is an unimportant
ore of copper.

SULPHIDES, TELLURIDES, ETC. 97

The theoretical composition of the mineral is 33.56 per cent S,
66.44 Per cent Cu. It usually, however, contains also a little iron and
often traces of lead and silver.

Crystals of. covellite are not common. They are hexagonal with
a : c= 1 : 3.972 and their habit is usually tabular. The forms observed
are oP(oooi), 00 P(ioTo), P(ioTi) and JP(iol4). 10T1 Aoi^i = 77° 42'.

The mineral has one perfect cleavage parallel to oP(oooi). In
thin splinters it is flexible. Its hardness is 1.5-2 and density about
4.6. Its color is dark blue and its streak lead-gray to black. It is
opaque, with a luster that is sometimes nearly metallic, but more
frequently dull. It is a good electrical conductor.

The blowpipe reactions of covellite are like those of chalcocite, with
these exceptions: Covellite burns with a blue flame when heated on
charcoal, and yields a sublimate of sulphur in the closed tube.

Covellite is distinguished from other minerals than chalcocite by
its reactions for Cu and S and the absence of reactions for Fe. It is
distinguished from chalcocite by its color and density and by the fact
that it ignites on charcoal.

Syntheses. — The treatment of green copper carbonate with water
and H2S in a closed tube at 8o°-9o° yields small grains of covellite.
The mineral has also been produced by the action of H2S upon vapor
of Q1Q2, and by treating sphalerite with a solution of copper sulphate
in a sealed glass tube containing CO2 at a temperature of i5o°-i6o°
for two days.

Localities and Origin. — The mineral is comparatively rare. It is
abundant in Chile and Bolivia and at Butte, Mont., and is found in
crystals on the lava of Vesuvius and elsewhere. It usually occurs as
an alteration product of other copper-sulphur compounds, especially in
the zone of secondary enrichment of copper veins.

Uses. — It is mined with other compounds and used as a source
of copper.

CINNABAR GROUP

This group comprises sulphides, selenides and tellurides of mercury.
The group is dimorphous, with its members crystallizing in hemihedrons
of the isometric system (hextetrahedrai class) and in tetartohedrons
of the hexagonal system (trigonal trapezohedral class). The isometric
HgS is known as metacinndbarite and the hexagonal form as cinnabar.
Only the latter is important. In addition to these are known the rare
compounds onofrite (Hg(S-Se)), tiemannite (HgSe) and color adoite
(HgTe), all of which are isometric.

98 DESCRIPTIVE MINERALOGY

Cinnabar (HgS)

Cinnabar is the only compound of mercury that occurs in sufficient
quantity to constitute an important ore. Nearly all of the mercury,
or quicksilver, in the world is obtained from it. The mineral occurs
both crystallized and massive. The ore is a red crystalline mass that
is easily distinguished from all other red minerals by its peculiar shade of
color and its great weight.

Theoretically, it contains 13.8 per cent S and 86.2 per cent Hg.
Massive cinnabar is, however, usually impure through the admixture
of clay, iron oxides or bituminous substances. Occasionally the quan-
tity of organic material present is so large that the mixture is inflam-
mable.

Though cinnabar is usually granular, massive or earthy, it some-
times occurs beautifully crystallized
in small complex and highly modi-
fied hexagonal crystals that exhibit
tetartohedral forms (trigonal trape-
zohedral class). Usually the crys-
tals are rhombohedral or prismatic
in habit. Their axial ratio is
1 : I-I453- Planes belonging to
more than 100 distinct forms have
Fig, 38.-CiniK.bar Crystals wiih - R, been observed, but the crystals on
10I0 (*); (R, 404s (-'); fR, aoi"s wnlcn thcy occur are usually so
(ft; R, toil (r) and oR, 0001 (.-). small that few of them are of im-
portance as distinguishing charac-
teristics. The prismatic crystals, which are the most common in
this country, are often bounded by 00 R, (10T0) and $R, (4045)
(Fig. 38). Others, however, are very complicated. Their cleavage is
perfect parallel to 00 R(ioTo).

The mineral is slightly sectile. It is transparent, translucent or
opaque, is of a cochineal-red color, often inclining to brown, and its
streak is scarlet. Its hardness is only 2-2.5 and *ls density about
8.t. It is circularly polarizing and is a nonconductor of electricity.
Its dimorph, metacinnabarite, on the other hand, is a good conductor.
The indices of refraction of cinnabar are: 01= 2.854, (=3.201.

When heated gently in the open tube cinnabar yields sulphurous
fumes and globules of mercury. On charcoal before the blowpipe it
volatilizes completely.

There are only a few minerals with which cinnabar is likely to be

SULPHIDES, TELLURIDES, ETC. 99

confused, since its color and streak are so characteristic. From all
red minerals but realgar it may easily be distinguished by its sulphur
reaction. From realgar it is distinguished by its great density and its
greater hardness.

Pseudomorphs of cinnabar after stibnite, dolomite ((Ca-Mg)COa),
pyrite and tetrahedrite (a complicated sulpho-salt) have been described.

Synthesis. — Crystals have been made by heating mercury in an aque-
ous solution of H2S.

Occurrence, Localities and Origin. — Cinnabar is usually found in
veins cutting serpentine, limestones, slates, shales and various schists.
It is associated with gold, various sulphides, especially pyrite and mar-
casite (FeS2), calcite (CaCOa), barite (BaSCU), fluorite (CaF2) and
quartz. It is also found impregnating sandstones and other sedimen-
tary rocks, and sometimes as a deposit from hot springs. Its deposi-
tion is thought to be the result of precipitation from ascending hot
water.

Crystallized cinnabar occurs at a number of places in Bohemia,
Hungary, Serbia, Austria, Spain, California, Texas, Nevada, and at
other localities in Europe, Asia and South America.

The principal deposits of economic importance are at Almaden
in Spain, at Idria in the Province of Carniola, Austria, at Bakhmut
in southern Russia, at various points along the Coast Ranges in Cal-
ifornia, in Esmeralda, Humboldt, Nye and Washoe Counties in Nevada,
at many points in Oregon and Utah, and at Terlingua in Texas. The
mineral is also abundant in Peru and in China but in these countries
it has not yet been mined profitably. The California cinnabar district
extends for many miles along the Coast Ranges, but at only about a
duzen places is the mineral mined.

The Spanish mines, near the city of Cordova, have been worked
for many hundreds of years. Much of the ore is an impregnation of
sandstone and quartzite — the mineral sometimes comprising as much
as 20 per cent of the rock mined.

Extraction. — The metallurgy of cinnabar is exceedingly simple. It
consists simply in roasting the ore alone, or mixed with limestone, and
conducting the fumes into a condensing chamber that is kept cool.
The sulphur gases are allowed to escape through the chamber in which
the mercury is collected

Uses of Metal. — Mercury finds many uses in the arts. Its most im-
portant one is in the extraction of gold and silver by the amalgamation
process. It is the essential constituent of the pigment vermilion, which
is a manufactured HgS. In its metallic state it is largely employed in

100 DESCRIPTIVE MINERALOGY

the making of mirrors, of barometers, thermometers and other physical
instruments. Some of the salts are important medicinal preparations
while others are used in the manufacture of percussion caps.

Production. — The world's annual production of quicksilver, all of
which is obtained from cinnabar, is not far from 4,000 metric tons. The
United States produced 940 tons in 1912, valued at $1,053,941. Of this
total California yielded 20,524 flasks of 75 lbs. each, valued at about
$863,034, and Texas and Nevada 4,540 flasks valued at $190,907. To
produce these quantities of metal California mined 139,347 tons of ore
and Texas and Nevada 16,346 tons. The California ore yielded 11 lbs.
of metal per ton and the Nevada and Texas ore 20.8 lbs.

Metacinnabarite (HgS) is generally found as a gray-black massive
mineral with a black streak. It is brittle, has a hardness of 3 and a
density of 7.8. It is associated with cinnabar at some of the mines in
California and Mexico, and at a few places in other countries. It is
exceedingly rare.

THE METALLIC DISULPHIDES, DISELENIDES AND DIARSENIDES

The disulphides, diselenides, ditellurides, diarsenides and dianti-
monides differ from the corresponding monocompounds in that they
contain double the quantity of S, Se, Te and Sb. They are divisible
into two groups, one of which comprises sulphides, arsenides and anti-
monides of iron, manganese, cobalt, nickel and platinum, and the other
the tellurides and selenides of gold and silver,

GLANZ GROUP

The glanz group is an excellent illustration of an isodimorphous grbup.
Its members are characterized by their hardness, opaqueness, light color
and brilliant luster. Hence the name of the group. In composition
the minerals belonging to the group are sulphides, arsenides or anti-
monides of the iron-platinum group of metals, with the general formula
RQ2 in which R is Mn, Fe, Ni, Co, Pt, and Q=S, As and Sb. The com-
position of the more simple members may be represented by the formula

Fe^ I , and of those in which arsenic or antimony replaces a part of the

<As=Asv
\Fe.
S SX

: It is probable, however, that some of the cobalt and nickel arsenides

SULPHIDES, TELLURIDES, ETC.

101

are mixtures and that their indicated compositions are only approximate.
All members of the group are believed to be dimorphous, crystallizing
in the isometric (dyakisdodecahedral class), and in the orthorhombic
systems (orthorhombic bipyramidal class), though not all have as yet
been found in both forms. The most important members of the group, as
at present constituted, are as follows:

Isometric

Orthorhombic

Pyrite

FeS2

Marcasite

Haueriie

MnSs

FeAsS

Arsenopyrite

FeAs2

Ldllingite

Cobaltite

CoAsS

Glancodot

Gersdorfite

(NiFe)AsS

Korynite

(Ni-Fe)(As-Sb-S)2

WolfackUe

UUmanite

NiSbS

Smaltite

C0AS2

Safflorite

CUoanthite

NiAs2

Rammelsbergite

Sperrylite

PtAS2

The group is divided into two subgroups, the regularly crystallizing
minerals forming the pyrite group and the orthorhombic ones the mar-
casite group. The most important members of the former group are
pyrite, cobaltite, smalttte and chloanthite. The most important members
of the marcasite group are marcasite, arsenopyrite and loUingite.

PYRITE DIVISION

The crystallization of the pyrite group is in the parallel hemihedral
division (dyakisdodecahedral class) of the isometric system. The

[20ool
, 210, is so frequently seen on the mineral

occurrence of the form

pyrite that it has received the name pyritoid.

The group is so perfectly isomorphous that a description of the forms
on one member is practically a description of the forms on all.

Pyrite (FeS2)

Pyrite, one of the most common of all minerals, is found under a
great variety of conditions as crystals, as crystalline aggregates and
as crystalline masses. It occurs under practically all conditions and in
all situations. It is easily recognized by its bright yellow color, its
brilliant luster and its hardness.

DESCRIPTIVE MINERALOGY

Pyrite containing, theoretically, 46.6 per cent of iron and 53.4 per
cent of sulphur is usually contaminated with small quantities of nickel,

Fin. 39. — Group of Pyrite Crystals in which the Cube Predominates. The i_rystals
are striated parallel to the edge between =0 O =0 (100) and l~— — I , i"°)-

cobalt, thallium and other elements. An auriferous variety is worked
for gold, yielding in the aggregate a large quantity of the precious

Fig. 40- Fig. 41.

FlC. 40.— Pyrite Crystals on which O (11 1) Predominates. o = 0, lit and e = ™Os

Fig. 41.— Pyrite Crystal with nOi, 210(c) andO, m (a).

metal. Sometimes arsenic is present in small quantity. Analysis of
the crystals from French Creek, Penn., gave:

S = 54.o8, As=o.20, Fe=44-24, Co = i.75, Ni=o.i8, Cu=o.os, =100.50.

SULPHIDES, TELLURIDES, ETC. 103
The number of forms that have been observed on pyrite crystals is
very large. Hintze records 86. The cube and the pyritoid

Fig. 43. — Group oi Pyrite Crystals in which o»02 (jio) Predominates. From
Daly-Judge Mine, neat Part City, Utah. (After J. W. Boutwell.)

(210) arc the most common of these, though the octahedron and the

dodecahedron are not rare. Four distinct types of crystals may be

recognized, viz.: those with the cubic (Fig. 3g),

the octahedral (Fig. 40), and the pyritoid

habits (Figs. 41 and 41), and those that are

interpenetrating twins (Fig. 43). The cubic

and the pyritoid planes are often striated

parallel to the edges between these faces. The

interpenetrating twins are twinned about the

plane O(m).

The cleavage of pyrite is imperfect and
its fracture conchoids!. The mineral is
brittle. Its hardness is 6-6.5 ar>d density
about 5. Its luster is very brilliant and
metallic. Its color is brassy yellow and its
streak greenish or brownish black. With steel it strikes fire, hence its
name from the Greek word meaning fire. It is a good conductor of
electricity and is strongly thermo-electric.

•"ig. 43. — Pyrite Interpene-
Iration Twin. Two Pyri-
tuids ( °° O-i, 216) Twinned
about O, in.

104 DESCRIPTIVE MINERALOGY

In the closed tube pyrite yields a sublimate of sulphur and a residue
that is magnetic. On charcoal sulphur is freed. This burns with the
blue flame characteristic of the substance. The globule remaining after
heating for some time is magnetic. Treated with nitric acid the
mineral dissolves leaving a flocculent residue of sulphur, which when
dried and heated may readily be ignited.

Pyrite in some of its forms so closely resembles gold that it is often
known as fool's gold. There is, of course, no difficulty in distinguishing
between the two metals, since pyrite contains sulphur and is soluble in
nitric acid,, while gold contains no sulphur and is insoluble in all simple
acids.

The mineral is most easily confounded with chalco pyrite (CuFeS2),
though the difference in hardness of the two easily serves to distinguish
them. Chalcopyrite may be readily scratched with a knife blade or a
file, while pyrite resists both. The latter mineral, moreover, contains
no copper.

Syntheses. — Small crystals of pyrite are produced by the action
of H2S on the oxides or the carbonate of iron enclosed in a sealed tube
heated to 8o°-90°; also by the passage of H2S and FeCfe vapors through
a red-hot porcelain tube.

Occurrence and Origin. — Pyrite occurs in veins and as grains or
crystals embedded in all kinds of rocks. In rocks it usually appears as
crystals, but in vein-masses it may appear either as crystals, with other
minerals, or as radiating or structureless masses occupying entirely the
vein fissures. In slates it often occurs in spheroidal nodules and
concretions of various forms, and also as embedded crystals. The
mineral is the product of igneous, metamorphic and aqueous agencies.

Pyrite weathers readily to limonite. In ore bodies near the
surface it is oxidized. A portion of the mineral changes to FeS04
which percolates downward and aids in the concentration of any
valuable metals that may be present in small quantity in the ore.
Another portion of the iron remains near the surface in the form of
limonite. This covering of oxidized material is known as the " gossan "
and it is characteristic of all pyrite deposits.

Localities. — Pyrite crystals are so widely distributed that but very
few of its most important occurrences may be mentioned here. In the
mines of Cornwall, Eng., and in those on the Island of Elba very large
crystals are found. Fine crystals also come from many different places
in Bohemia, Hungary, Saxony, Peru, Norway, and Sweden.

In the United States the finest crystals are at Schoharie and Rossie,
N. Y.; at the French Creek mines in Chester Co., and at Cornwall,

SULPHIDES, TELLURIDES, ETC. 105

Lebanon Co., Penn., and near Greensboro and Guilford Co., N. Carolina.
Massive pyrite occurs in great deposits at the Rio Tinto mines in
Spain; at Rowe, Mass.; in St. Lawrence and Ulster counties, N. Y.;
in Louise Co., Va., and in Paulding Co., Ga. Much of the massive
pyrite in the veins of Colorado, California and of the southern states,
from Virginia to Alabama, is auriferous and much of it is mined for the
gold it contains.

Uses. — Pyrite is used principally in the manufacture of sulphuric
acid. The mineral is burned in furnaces and the SO2 gases thus result-
ing are carried to condensers where they are oxidized by finely divided
platinum or by the oxides of nitrogen. The residue, which consists
largely of Fe203, is sometimes smelted for iron or made into paint.
This residue also contains the gold and other valuable metals that may
have been in the original pyrite.

The sulphuric acid obtained from pyrite enters into many manu-
facturing processes. The greater portion of it is consumed in the
artificial fertilizer industry.

Production. — Pyrite is mined in the United States in Franklin Co.,
Mass., in Alameda and Shasta Counties, California, in Louisa, Pulaski
and Prince William Counties, Va., in Carroll Co., Ga., in St. Lawrence
Co., N. Y., in Clay Co., Alabama, and at the coal mines in Ohio,
Illinois and Indiana where it is a by-product. The total production
of the United States in 191 2, amounting to 350,928 long tons, was
valued at $1,334,259. Virginia is by far the largest producer. In
addition to this quantity the trade consumed 970,785 tons of imported
ore, most of which came from Spain, and utilized the equivalent of
260,000 tons of pyrite in the shape of low grade sulphide copper ores
from Ducktown, Tenn., and zinc sulphide concentrates from the Mis-
sissippi Valley and elsewhere for the manufacture of sulphuric acid.
The total amount of sulphuric acid manufactured in the United States
during 191 2 was 2,340,000 short tons, valued at $18,338,019. The total
world production of pyrite is about 2,000,000 tons annually.

Small quantities of the mineral are also mined for local consumption
in Lumpkin Co., Georgia, and near Hot Springs, Arkansas. Much
auriferous pyrite has also been mined in the southern states and the
Rocky Mountain region for the gold it contains. This metal is sepa-
rated from the pyrite partly by crushing and amalgamation and partly
by smelting or by leaching processes. In the former case the gold
occurs as inclusions of the metal in the pyrite.

106 DESCRIPTIVE MINERALOGY

Cobaltite (CoAsS)

Cobaltite is a silver-white or steel-gray mineral occurring in massive
forms or in distinct crystals exhibiting beautifully their hemihedral
character. It is completely isomorphous with the corresponding nickel
compound, gersdorffite (NiAsS), and consequently mixtures of the
two are common.

Cobaltite usually contains some iron and often a little nickel.
Theoretically, it consists of 19.3 per cent S, 45.2 per cent As and 35.5
Co. The compositions of a massive variety from Siegen, Westphalia,
and that of crystals from Nordmark, Norway, are as follows:

As S Co Fe Ni Total

Siegen 45.31 19.35 33-71 163 100.00

Nordmark 4477 20.23 29.17 4.72 1.68 100.57

The crystallization of cobaltite is perfectly isomorphous with that
of pyrite, though the number of its forms observed is far smaller. The

[2O 00 1
(210).

The cleavage of cobalt is fairly good parallel to 00 O 00 (100). Its
fracture is uneven, its hardness is 5.5 and its density about 6.2. The color
of the mineral, as stated above, varies between silver-white and steel-
gray. Its streak is grayish black. It is a good conductor of electricity.

In the open tube cobaltite reacts for S and As. On charcoal it
yields a magnetic globule which when fused with borax on platinum
wire yields a deep blue bead. It weathers fairly readily to the rose-
colored cobalt arsenate known as erythrite (Co3(As04)2*8H20).

By its crystallization and color cobaltite is distinguished from
nearly all other minerals but those of the same group. From most of
these it is easily distinguished by its blowpipe reactions for sulphur,
arsenic and cobalt.

Occurrence and Origin. — Cobaltite occurs mainly in veins that are
believed to have been filled by upward moving solutions emanating
from igneous rocks. It is associated with compounds of nickel and other
cobalt compounds and with silver and copper ores.

Localities. — Cobaltite is not very widely distributed. Large, hand-
some crystals occur at Tunaberg in Sweden; at Nordmark, Norway;
at Siegen, Westphalia, and near St. Just in Cornwall, England. It is
found also in large quantity at Cobalt, Ontario, associated with silver
ores and nickel compounds.

SULPHIDES, TELLURIDES, ETC. 107

Uses. — Cobaltite is said to be used by jewelers in India in the pro-
duction of a blue enamel on gold ornaments. It is employed also in the
manufacture of blue and green pigments and in the manufacture of com-
pounds used in small quantity in the various arts. Smalt is the most
valuable of the cobalt pigments and is at present the chief commercial
compound of this metal. It is a deep blue glass that differs from
ordinary glass in containing cobalt in place of calcium. Smalt is hiade
from cobaltite and from other cobalt ores by fusion with a mixture of
quartz and potassium carbonate. Certain cobalt compounds are sug-
gested as excellent driers for oils and varnishes. The mineral is also
utilized as an ore of cobalt, which in the form of stellite, an alloy com-
posed of 70 per cent cobalt, 15 per cent chromium and 15 per cent
molybdenum or tungsten, bids fair to acquire a large use as a material
for the manufacture of table cutlery and edged tools. The use of the
metal has also been suggested as a material for coinage in place of
nickel.

Production. — Most of the cobalt of commerce is handled by the
trade in the form of the oxide. It is produced from the various cobalt
minerals, mainly as a by-product in the extraction of nickel, and hence
very little is obtained from cobaltite. The mines at Cobalt, however,
have furnished a large quantity of cobaltite and smaltite within the past
few years and these have gone into the manufacture of the oxide, of
which about 515 tons were produced in 191 2, having a value of
$317*165.

Smaltite (CoAs2)

Smaltite is another important ore of cobalt. It is found in crystals
and masses.

Its theoretical composition is 71.88 per cent As and 28.12 per cent
Co, though it usually contains also S, Ni, Fe and frequently traces of
Bi, Cu and Pb. Since it is isomorphous with the arsenide of nickel
chloanthite (N1AS2), mixed crystals of the two are common. Moreover,
sharply defined crystals have been found to consist of mechanical mix-
tures of several compounds.

Smaltite occurs in small crystals of cubical habit with 00 O 00 (100),
O(in) and various pyritoids predominating.

The mineral is tin-white to steel-gray, and opaque, and has a grayish
black streak. It is often covered with an iridescent or a gray tarnish.
Its cleavage is indistinct, its fracture uneven, its hardness 5-6 and
density 6.3-7. It is a good electrical conductor.

Before the blowpipe on charcoal smaltite yields arsenic fumes and a

108 DESCRIPTIVE MINERALOGY

magnetic globule of metallic cobalt. It is soluble in HNO3, yielding a
rose-colored solution and a precipitate of AS2O3.

The mineral is fairly easily distinguished from most other minerals
by its color and blowpipe reactions. From cobaltite it is distinguished by
the lack of S. From a few others that are not described in this volume
it can be distinguished by its crystallization or by quantitative analysis.

Synthesis. — Smaltite crystals are produced when hydrogen acts at a
high temperature upon a mixture of the chlorides of cobalt and arsenic.

Occurrence and Origin. — Smaltite is found associated with cobaltite
in nearly all of its occurrences. It is especially abundant at Cobalt, Ont.
As in the case of most other cobalt minerals, its presence is indicated by
deposits of rose-colored erythrite which coat its surfaces wherever these
are exposed to moist air. Its methods of occurrence, origin and uses
are the same as for cobaltite (p. 107).

Chloanthite (NiAs2) resembles smaltite in most of its characteris-
tics. The two minerals grade into each other through isomorphous
mixtures. Those mixtures in which the cobalt arsenide is in excess
are known as smaltite, while those in which NiAs predominates are
called chloanthite. The pure chloanthite molecule is Ni= 28.1 per cent,
As =71.9 per cent.

The two minerals can be distinguished when unmixed with one
another by the blowpipe reactions for Co and Ni. In mixed crystals
the predominance of one or the other arsenides can be determined only
by quantitative analysis.

Chloanthite containing much iron is distinguished as chathamite,
from Chatham, Conn., where it occurs with arsenopyrite and niccolite in
a mica-slate.

The mode of occurrence of chloanthite and the localities at which
it is found are the same as in the case of smaltite.

Sperrylite (PtAs2)

Sperrylite is extremely rare. It is referred to here because it is the
only platinum compound occurring as a mineral. Chemically, it is
43.53 per cent As and 56.47 per cent Pt, but it contains also small quan-
tities of Sb, Pd and Fe.

Its crystals are simple. They contain only O(in), 00 O 00 (100),
00 0(i 10) and several pyritoids. Their habit is usually octahedral or
cubical.

The mineral is opaque and tin-white, and its streak black. Its hard-
ness is 6-7 and density 10.6.

SULPHIDES, TELLURIDES, ETC. 109

In the closed glass tube it remains unchanged, but in the open tube
it gives a sublimate of AS2O3. When dropped upon red-hot platinum
foil it immediately melts, giving rise to fumes of AS2O3, and forming
blisters on the foil that are not distinguishable from the original platinum
in color or general character. It is slowly soluble in concentrated HC1
and aqua regia.

Synthesis. — The mineral has been produced by leading arsenic fumes
over red-hot platinum in an atmosphere of hydrogen.

Occurrence and Localities. — Sperrylite occurs as little crystals com-
pletely embedded in the chalcopyrite (CuFeS2) and the gossan of a
nickel mine, and in the chalcopyrite of a gold-quartz vein near Sudbury,
Ontario; in covellite at the Rambler Mine, Encampment, Wyoming;
and as flakes in the sands of streams in the Cowee Valley, Macon Co., Ga.
The flakes resemble very closely native platinum, from which they are
of course, easily distinguished by the test for arsenic.

Uses. — The sperrylite from Sudbury and Wyoming furnish much of
the platinum produced in the United States (see p. 64).

MARCASITE DIVISION

Three members of the marcasite group are important; all are inter-
esting from the fact that they are so alike in their crystallization that a
description of the forms belonging to any one of them might serve as a
description of those belonging to all others. The crystallization of the
group is orthorhombic (rhombic bipyramidal class), with an axial ratio
approximately a : b : c=.y : 1 : 1.2.

Marcasite (FeS2)

Marcasite, the dimorph of pyrite, resembles this mineral so dosely
that in massive specimens it is difficult to distinguish between the two.
They are nearly alike in hardness, in color and in chemical properties.
Marcasite is a little lighter in color than pyrite. Its density is less
(about 4.9), and it possesses a greater tendency to tarnish on exposed
surfaces.

This tarnish indicates that the mineral is more susceptible to altera-
tion than is pyrite. One of the products of this alteration is ferrous sul-
phate, which may often be detected by its taste upon touching the tongue
to specimens of the mineral. In crystallized specimens there is not the
least difficulty in distinguishing between them, since their crystallization
is very different.

Marcasite is orthorhombic (rhombic bipyramidal class), with the

110 DESCRIPTIVE MINERALOGY

axial ratio .7662 : 1 : 1.2342. Its simple crystals often possess a tabular
or a pyramidal habit (Figs. 44 and 45). In the former case oP(ooi) is
the predominant face, and in the latter case the two domes P 66 (101)

Fie. 45.

Fie. 44.— Mucuite Crystal with «P,no(m); oP, 001 (e); PS, ,011 (0 and JPB ,

013 (»).

Fig. 45. — Marcasite Crystal with Forms as Indicated in Fig. 44, and P » , 101 («)

andP, in (s).

and P 06 (on). The other forms observed on most crystals are 00 P(no),
P(iii), and often jP * (013).

Twins are very common, with 00 P(i 10) the twinning plane (Fig. 46).
Sometimes these are aggregated by repeated twinning into serrated
groups known as cockscomb twins or spearhead twins (Fig. 47), because

Fie. 46.

Fig. 46. — Twin of Marcasite about »

of the outlines of their edges. In many instances the crystals are acic-
ular or columnar in habit, forming radiating groups with globular, reni-
form and stalactitk shapes. Concretions are also common. The basal
plane is usually striated parallel to the edge between it and P06 (on).
The cleavage is distinct parallel to 00 P(no). The fracture is uneven

SULPHIDES, TELLURIDES, ETC. Ill

When powdered marcasite is treated with cold nitric acid and
allowed to stand, it decomposes with the separation of sulphur.

Marcasite readily alters to limonite. The fact that pyrite, sphaler-
ite, chalcopyrite, and other minerals form pseudomorphs after it
indicates that, under suitable conditions, it alters also to these com-
pounds. The mineral is in most cases a direct result of precipitation
from hot solutions.

Synthesis. — Marcasite crystals have been prepared by the reduction
of FeS04 by charcoal in an atmosphere of HaS.

Occurrence and Uses. — The mineral, like pyrite, is found embedded
in rocks in the form of crystals and concretions, and also as the
gangue masses of veins. It constitutes nearly the entire filling of some
veins, and forms druses on the walls of cavities in both rocks and miner-
als. It also replaces the organic matter of fossils preserving their shapes
— thus producing true pseudomorphs.

When associated with pyrite it is mined together with this mineral
as a source of sulphur.

Localities. — Crystalline marcasite occurs in such great quantity
near Carlsbad in Bohemia that it is mined. The cockscomb variety is
found in Derbyshire, England, and crystals at Schemnitz in Hungary
and at Andreasberg and other places in the Harz. In the United States
the mineral occurs as crystals at a great number of places, being par-
ticularly abundant in the lead and zinc localities of the Mississippi
Valley, where it sometimes forms stalactites. The stalactites from
Galena, 111., often consist of concentric layers of sphalerite, galena and
crystallized marcasite.

Arsenopyrite (FeAsS)

Arsenopyrite, or mispickel, is the most important ore of arsenic.
It is found in crystals and in compact ar.d granul&r masses. It is a
silver-white metallic mineral resembling very closely cobaltite in its
general appearance.

The formula FeAsS for arsenopyrite is based on analyses like the
following:

As S Fe Total

Specimen from Hohenstein, Saxony .... 45 . 62 19 . 76 34 . 64 100 . 02
Specimen from Mte. Chalanches, France 45 .78 19 . 56 34 .64 99 . 98

Theoretically, the mineral consists of its components in the following
proportions, As 46 per cent, S 19.7 per cent, Fe 34.3 per cent. In many
specimens the iron is replaced in part by cobalt, nickel or manganese.

112

DESCRIPTIVE MINERALOGY

lw m m I

Fig. 48. — Arsenopyrite Crystals with 00 P,
no (m); JP 00 , 014 (m), and P 00 , on (q).

Sometimes the cobalt is present in such large quantity that the mineral
is smelted as an ore of this metal.

The axial ratio of arsenopyrite is .6773 : * : 1-1882. Its crystals are
usually simpler than those of marcasite (Fig. 48), though the number of
planes observed in the species is larger. Most of the untwinned crystals

are a combination of 00 P(no)
with £P 06 (014), or P 06 (on),
or Px>(ioi), and have a pris-
matic habit. Twins are not
rare. The twinning plane is
the same as in marcasite,
and repetition is often met
with. The angle iioai^o=
68° 13'.

The brachydomes are stri-
ated horizontally, and often
the planes ooP(no) are stri-
ated parallel to the edge 00 P(iio)aP* (ioi).

The cleavage of arsenopyrite is quite perfect parallel to ooP(no).
The mineral is brittle and its fracture uneven. Its hardness is 5.5-6
and density about 6.2. Its color is silver- white to steel-gray; its streak
grayish black. It is a good conductor of electricity.

In the closed tube arsenopyrite at first gives a red sublimate of AsS
and then a black mirror of arsenic. On charcoal it gives the usual
reactions for sulphur and arsenic. Cobaltiferous varieties react for
cobalt with borax. The mineral yields sparks when struck with steel
and emits an arsenic smell. It dissolves in nitric acid with the separa-
tion of sulphur.

Arsenopyrite is distinguished from the cobalt sulphides and arsenides
by the absence of Co.

Synthesis. — Crystals of the mineral are produced by heating in a
closed tube at 3000 precipitated FeAsS in a solution of NaHCC>3.

Occurrence. — Arsenopyrite crystals are often found disseminated
through crystalline rocks, and often embedded in the gangue minerals of
veins. Like pyrite and marcasite they frequently fill vein fissures. Its
associates are silver, tin and lead ores, chalcopyrite, pyrite and sphalerite.
Localities. — The mineral is abundant at Freiberg, in Saxony, at
Tunaberg, in Sweden, and at Inquisivi Mt., Sorato, in Bolivia.

It also occurs in fine crystals at Franconia in New Hampshire, at
Blue Hill in Maine, at Chatham in Connecticut, and at St. Francois,
Beauce Co., Quebec. Massive arsenopyrite is found near Keeseville

SULPHIDES, TELLURIDES, ETC. 113

Essex Co., near Edenville, Orange Co., and near Carmel, Putnam Co.,
N. Y., and at Rewald, Floyd Co., Va. In most cases it is apparently
a result of pneumatolysis.

Uses. — Arsenopyrite was formerly the source of nearly all the arsenic
of commerce. The mineral is concentrated by mechanical methods, and
the concentrates are heated in retorts, when the following reaction takes
place: FeAsS = FeS+As. The arsenic being volatile is conducted
into condensing chambers where it is collected. When the mineral con-
tains a reasonable amount of cobalt or of gold these metals are extracted.

Uses of Arsenic. — The metal arsenic has very little use in the arts,
though its compounds find many applications as insecticides, medicines,
pigments, in tanning, etc. The basis of most of these is AS2O3, and
this is produced directly from the fumes of smelters working on arsenical
gold, silver and copper ores. Only a portion of such fumes are saved,
however, as even half of those produced at a single smelter center
(Butte, Montana), would more than supply the entire demand of the
United States for arsenic and its compounds. Under these conditions
the mining of arsenical pyrite as a source of arsenic has ceased so far
as the United States is concerned.

Lollingite (FeAso) is usually massive, though its rare crystals are
isomorphous in every respect with those of arsenopyrite. The pure
mineral is not common. Most specimens are mixtures of ldllingite with
arsenopyrite or other sulphides or arsenides.

The mineral is silver-white or steel-gray. Its streak is grayish black.
Its hardness is 5-5.5 and density about 7.2. It readily fuses to a mag-
netic globule, at the same time evolving arsenic fumes. It is soluble in

HNO3.

It usually occurs in veins associated with other sulphides and arsen-
ides. It is found at Paris, Maine; at Edenville and Monroe, N. Y.;
at various mines in North Carolina, and on Brush Creek, Gunnison
Co., Colo. At the last-named locality the mineral is in star-shaped
crystalline aggregates, in twins and trillings, associated with siderite
and barite.

SYLVANITE GROUP

The sylvanite group includes at least three distinct minerals, all of
which are ditellurides of gold or silver. The group is isodimorphous.
The pure gold telluride is known only in monoclinic crystals, but the
isomorphous mixtures of the gold and silver compounds occur both in
monoclinic and orthorhombic crystals.

114 DESCRIPTIVE MINERALOGY

Orthorhombic bipyramidal Monoclinic prismatic

AuTe2 Calaverite

Krenneriie (Ag • Au)Te2 SylvaniU

All three minerals are utilized as ores of gold. While occurring only
in a few places, they are sufficiently abundant at some to be mined.

Calaverite (AuTe2)

Calaverite is a nearly pure gold chloride. However, it is usually
intermixed with small quantities of the silver telluride. An analysis of a
specimen from Kalgoorlie, Australia, gave: Te = 57.27; Au = 4i.37;
Ag=.s8.

Calaverite crystallizes in the monoclinic system (prismatic class) in
crystals that are elongated parallel to the orthoaxis and deeply striated
in this direction. Their axial ratio is 1.6313 : 1 : 1.1440 with £=90° 13'.

The prominent forms are 00 P 06 (100), 00 P 00 (010), oP(ooi),
— P*(ioi), +Pob(ioT), — 2P«x)(20i), +2P«>(2oT), and P(in).
Twinning is common and the resulting twins are very complicated.
Usually, however, the mineral occurs massive and granular.

Calaverite is opaque, silver-white or bronzy yellow in color and has a
yellow-gray or greenish gray streak. Its surface is frequently covered
with a yellow tarnish. The mineral is brittle and without distinct cleav-
age. Its hardness is 2-3 and density 9.04.

On charcoal before the blowpipe the mineral fuses easily to a yellow
globule of gold, yielding at the same time the fumes of tellurium oxide.
It dissolves in concentrated H2SO4, producing a deep red solution. When
treated with HNO3 it decomposes, leaving a rusty mass of spongy gold.
The solution treated with HC1 usually yields a slight precipitate of silver
chloride.

Calaverite is distinguished from most other minerals by the test for
tellurium. It is distinguished from fetzite (p. 80), by its crystallization
and the fact that it gives a yellow globule when roasted on charcoal,
and from sylvanite by the small amount of silver it contains, its higher
specific gravity, its color and its lack of cleavage. It is distinguished
from krenneriie by its crystallization.

Occurrence. — The mineral occurs in veins with the other tellurides
associated with gold ores in Calaveras Co., Cal., and at the localities
mentioned for petzite (see p. 81). It is believed to have been deposited
by pneumatolytic processes or by ascending magmatic water at com-
paratively low temperatures.

SULPHIDES, TELLURIDES, ETC. 115

Uses. — The mineral is mined with other tellurides in Boulder Co.,
and at Cripple Creek, Colorado, as an ore of gold.

Sylvanite (Ag-Au)Te2

Sylvanite is more common than calaverite. It is an isomorphous
mixture of gold and silver tellurides in the ratio of about i : i. Analyses
follow:

I. Te=62.i6 Au=24.45 Ag—13.39 Total=ioo.oo

II. Te=59.78 Au=26.36 Ag=i3.86 " 100.00

III. Te=58.9i Au=29«35 Ag=ii-74 " 100.00

I." Theoretical for AgTea+AuTe,.
II. and III. Specimens from Boulder Co., Colo.

In crystallization the mineral is isomorphous with calaverite, with
an axial ratio a : b : c— 1.6339 : 1 : 1.1265 and 0=90° 25'. Its crystals
are usually rich in planes, about 75 having been identified. Their habit
is usually tabular parallel to 00 P ob (010), with this plane, — P «> (101),
oP(ooi), 00 P 6b (100) and 2P2(?2i) predominating. The mineral also
occurs in skeleton crystals and in aggregates that are piaty or granular.
Twinning is common, with — P*(ioi) the twinning plane. Many
twinned aggregates form networks suggesting writing, hence the name
" Schrifterz " often applied to the mineral by the Germans.

Sylvanite is silver-white or steel-gray and has a brilliant metallic
luster and a silver-white or yellowish gray streak. Its hardness is
between 1 and 2 and its density 7.9-8.3. Moreover, it possesses a per-
fect cleavage parallel to ooPw (010).

Its chemical properties are the same as those of calaverite, but the
silver precipitate produced by adding HC1 to its solution in HNO3 is
always large. It is best distinguished from the gold telluride by its
cleavage and from fetzite ((Ag.Au)2Te) and hessite (Ag2Te) by its
crystallization, and by the yellow metallic globule produced when the
mineral is roasted on charcoal. It is distinguishable from krennerite by
its crystallization.

Localities and Origin, — Sylvanite occurs with the other tellurides in
veins at Offenbdnya and Nagyag in Transylvania, at Cripple Creek and
in Boulder Co., Colo., near Kalgoorlie, W. Australia, in small quan-
tities near Balmoral in the Black Hills, S.D., and at Moss, near Thunder
Bay, Ontario. Like calaverite it was deposited by magmatic water, or
by hot vapors.

Uses. — It is mined with calaverite as a gold and silver ore at Cripple
Creek and in Boulder Co., Colo.

CHAPTER V
THE SULPHO-SALTS AND SULPHO-FERRITES

The sulpho-salts are salts of acids analogous to arsenic acid, H3ASO4,
and arsenious acid, H3ASO3, and the corresponding antimony acids
H3SDO4 and H3SDO3. The sulpho-acids differ from the arsenic and the
antimony acids in containing sulphur in place of oxygen, thus H3ASS4,
H3ASS3, H3SDS4 and H3SDS3. The mineral enargite may be regarded as
a salt of sulpharsenic acid, thus C113ASS4, copper having replaced the
hydrogen of the acid. Proustite, on the other hand, is AgaAsS3, or a,
salt of sulpharsenious acid. The salts of sulpharsenic acid are called
sulpharsenates, while those derived from sulpharsenious acid are known
as sulpharsenites. The sulpharsenates are not represented among the
commoner minerals, although the copper salt enargite is abundant at a
few places. A number of salts of other sulphur-arsenic acids are known
but they are comparatively rare.

There is another class of compounds with compositions analogous
to those of the sulpho-salts, though their chemical nature is not well
understood. This is the group of the sulpho-ferrites. We know that
certain hydroxides of iron may act as acids under certain conditions.
The sulpho-ferrites may be looked upon as salts of these acids in which,
however, the oxygen has been replaced by sulphur, as in the case of the
sulpho-acids referred to above. Thus by replacement of O by S, in
ferric hydroxide Fe(OH)3 the compound Fe(SH;3 or IfcFeSs results.
The salts of this acid are sulpho-ferrites. This acid, by loss of H2S,
may give rise to other acids in the same way that sulphuric acid (H2SO4),
by loss of H2O, gives rise to pyrosulphuric acid. In the case of the
sulpho-acid we may have H3FeS3— H2S = HFeS2. The copper salt of
this acid is the common mineral chalcopyrite, CuFeS2-

The sulpho-salts are very numerous, but only a few of them are of
sufficient importance to warrant a description in this book.

116

SULPHO-SALTS AND SULPHO-FERRITES 117

THE SULPHARSENITES AND SULPHANTTMONITES

The sulpharsenites and sulphantimonites are derivatives of the
ortho acids H3ASS3 and H3SbS3.

ORTHO SULPHO-SALTS

The ortho salts are compounds in which the hydrogen of the ortho
acids is replaced by metals. They include a large number of minerals,
of which the following are the most important.

Bournonite (Cu2 ■ Pb)3 (SbSs)2 Orthorhombic

Pyrargyrite Ag3SbS3 Hexagonal

ProuslUe Ag3AsS3 Hexagonal

PYRARGYRITE GROUP

Pyrargyrite (Ag3SbSs)

Pyrargyrite, or dark ruby silver, is an important silver ore, especially
in Mexico, Chile and the western United States. The name ruby silver
is given to it because thin splinters transmit deep red light. The mineral
is usually mixed with other ores in compact masses, but it also forms
handsome crystals.

The composition of pyrargyrite is represented by the formula Ag3SbS3
which demands 17.82 per cent S.; 22.21 per cent Sb.; 59.97 per cent Ag.
Many specimens contain also a small quantity of arsenic, through the
admixture of the isomorphous compound proustite. The analyses given
below show the effect of the intermixture of the two molecules.

Total

Andreasberg, Harz . . .

• 1765

22.36

• • • ■

59- 73

99-77

Zacatecas, Mexico

• 1774

22.39

■27

60.04

100.44

Freiberg, Saxony

• 17-95

18.58

2.62

60.63

99.78

The crystals of pyrargyrite are rhombohedral and hemimorphic
(ditrigonal pyramidal class), with an axial ratio 1 : .8038. They are
usually quite complex and are often twinned. The species is very rich
in forms, not less than 150 having been reported. The most prominent
of these are ooP2(ii2o), ooP(ioTo), R(ioTi), — ^R(oil2) and the
scalenohedrons R3(2i3i) and JR3(2I34) (Fig. 49). In the commonest
twinning law the twinning plane is 00 P2 (11 20) and the composition

118

DESCRIPTIVE MINERALOGY

Fig. 49. — Crystal of
Pyrargyritc with
00 P2, 1 120 (a)
and — JR,oil2(«).

face oP(ooi). The c axes in the twinned portions are parallel and the
00 P2 (11 20) planes coincident, so that the twin at a hasty glance looks
like a simple crystal. The angle 10T1 A ^101 = 71° 22'.

The cleavage of pyrargyrite is distinct parallel to R(ioTi). Its frac-
ture is conchoidal or uneven. The mineral is apparently opaque and its

color is grayish black in reflected light, but is trans-
parent or translucent and deep red in transmitted
light. Its streak is purplish red. For lithium
light o>= 3.084, €=2.881. It is not an electrical
conductor.

In the closed tube the mineral fuses easily and
gives a reddish sublimate. When heated with
sodium carbonate on charcoal it is reduced to a
globule of silver, which, when dissolved in nitric
acid, yields a silver chloride precipitate when
treated with a soluble chloride. The mineral dis-
solves in nitric acid with the separation of sulphur
and a white precipitate of antimony oxide. It is also soluble in a
strong solution of KOH. From this solution HC1 precipitates orange
Sb2S3 (compare proustite).

The color and streak of pyrargyrite, together with its translucency,
distinguish it from nearly all other minerals. Its reaction for silver
serves to distinguish it from cuprite, cinna.ar and realgar, which it some-
times resembles. The distinction between this mineral and its iso-
morph, proustite, is based on the streak and the reaction for anti-
mony.

Pyrargyrite occurs as a pseudomorph after native silver. On the
other hand it is occasionally altered to pyrite or argentite, and some-
times to silver.

Syntheses. — Microscopic crystals have been made by heating in a
porcelain tube, metallic silver and antimony chlorides in a current of
H2S, and by the action of the same gas at a red heat on a mixture of
metallic silver and melted antimony oxide.

Occurrence, Localities and Origin. — Pyrargyrite occurs in veins asso-
ciated with other compounds of silver and sometimes with galena and
arsenic. It is most common in the zone of secondary enrichment of
silver veins. The crystallized variety is found at Andreasberg in the
Harz; at Freiberg, in Saxony; at Pribram, in Bohemia; at many places
in Hungary, and at Chafiarcillo, in Chile. The massive variety is worked
as an ore of silver at Guanajuato in Mexico and in several of the western
states, as, for instance, in the Ruby district, Gunnison Co.. and in other

SULPHO-SALTS AND SULPHO-FERRITES 119

mining districts in Colorado, near Washoe and Austin, Nevada, and at
several points in Idaho, New Mexico, Utah and Arizona.

Uses. — The mineral is an important ore of silver in Mexico and in
the western United States. It is usually associated with other sulphur-
bearing ores of silver, the metal being extracted from the mixture by
the processes referred to under argentite.

Proustite (Ag3AsS3)

Proustite, or light ruby silver, is isomorphous with pyrargyrite. It
differs from the latter mineral in containing arsenic in place of antimony.
It occurs both massive and in crystals, and like pyrargyrite is an ore of
silver.

The formula above given demands 1943 per cent S; 15.17 per cent
As; and 65.40 per cent silver.. The analysis of a specimen from Mexico
yields figures that correspond very nearly to these. Crystals from
Chafiarcillo contain a slight admixture of the antimony compound.

Mexico 19 . 52

Chafiarcillo, Chile 19-64

Like pyrargyrite, proustite is rhombohedral. Its crystals are pris-
matic or acute rhombohedral. The forms present on them are much
less numerous than those on the corresponding
antimony compound, the predominant ones being
ooP2(ii2o), JR(ioT4), -JR(oii2), R3(2i3i),
—|R4(3587) and other scalenohedrons (see Fig.
50). Twins are common, the twinning planes
being (1), parallel to }R(iol4) and (2) parallel to

R(ioTi). The angle 10T1 aTici = 72° 12'. FlG- 5o.-Crystal of

mi 1 £ -l j i_ j £ Proustite with 00 P2.

The cleavage, fracture and haidness of prous- - , . #T>1 '

£ t, i_ j II2° W» ~!R » 35S7

tite are the same as for pyrargyrite. Its hard- ^M) and -JR,oii2 (e).

ness is 2 and its density is about 5.6. The mineral

is transparent or translucent. Its color is grayish black by reflected

light arid scarlet in transparent pieces by transmitted light. Under the

long-continued influence of daylight the color deepens until it becomes

darker than that of pyrargyrite. Its streak is cinnabar-red to brownish

black. Its luster is adamantine. It is a nonconductor of electricity.

For sodium light 01=3.0877, €= 2.7924.

In the closed tube proustite fuses easily and gives a slight sublimate

Total

14.98

• • • ■

65-39

99.89

I3-85

I. 41

65.06

99.96

120 DESCRIPTIVE MINERALOGY

of white arsenic oxide. In its other chemical properties it resembles
pyrargyrite except that it gives reactions for arsenic where this mineral
reacts for antimony, and yields only sulphur when dissolved in HNO3.
From its solution in KOH a yellow precipitate of AS2S3 is thrown down
upon the addition of HC1 (compare pyrargyrite).

Proustite differs from pyra.gyite in its color, transparency and
streak, as well as in its arsenic reactions. It is distinguished from
cinnabar and cuprite (CuO) by the arsenic test.

Syntheses. — Crystals of proustite have been produced by reactions
analogous to those that yield pyrargyrite, when arsenic compounds are
employed in place of antimony compounds.

Occurrence. — The mineral occurs under the same conditions and with
the same associates as pyrargyrite and it yields the same alteration
products as pyrargyrite.

Localities and Uses. — Handsome crystals of proustite occur at
Freiberg and other places in Saxony, at Wolfach in Baden, at Markirchen
in Alsace and at Chaftarcillo in Chile. It is associated with pyrargyrite
and with other ores of silver.

In the western United States it is quite abundant, more particularly
in the Ruby district, Colorado, at Poorman lode in Idaho, and in all other
localities where pyrargyrite occurs. In many it is mined as an ore of
silver.

Bournonite ((Pb-Cu2)3(SbS3)2)

Bournonite is a comparatively rare mineral. It occurs either in
compact or granular masses or in well developed crystals of a steel-
gray color. It is not of any economic importance except as it may be
mixed with other copper compounds exploited for copper.

Analyses of bournonite from two localities are given below:

S Sb

I. I9-36 23.57
II. 19.78 23.80

I. Liskeard, Cornwall, England.

II. Felsdbanya, Hungary.

These analyses are by no means accurate, but they show the compo-
sition of the mineral to be approximately Pb, Cu, Sb and S, in which the
elements are combined in the following proportions: S=ig.8 per cent;
Sb= 247 per cent; Pb 42.5 per cent; Cu 13 per cent.

Bournonite crystals are orthorhombic (rhombic bipyramidal class),

Total

•47

41-95

1327

.68

99 30

• • •

42.07

12.82

.20

98.67

SULPHO-SALTS AND SULPHO-FERRITES

121

with alb: £=.9380 : 1 : .8969. They are usually tabular (Fig. 51), or
short, prismatic in habit, and are often in repeated twins (Fig. 52), with
wheel-shaped or cross-like forms. The principal planes observed on
them are oP(ooi), Poo (ioi),Poo (on), £P(ii2), ooP(no), 00 Poo (100)
and 00 P 06 (010), though 00 or more planes are known. The most com-
mon twinning plane is 00 P(no). Angle no A iTo=86° 20'.

The luster of the mineral is brilliant metallic. Its color and streak
are steel-gray. Its cleavage is imperfect, parallel to 00 P 06 (010) and its
fracture conchoidal or uneven. Its hardness is 2.5-3 and density 5.8.
Like most other metallic minerals it is opaque. It is a very poor con-
ductor of electricity.

In the closed tube bournonite decrepitates and yields a dark red sub-
limate. In the open tube, and on charcoal, it gives reactions for Sb, S,
Pb and Cu. When treated with nitric acid it decomposes, producing a

**l

■^

*~^

Fig. 51. Fig. 52.

Fig. 51. — Bournonite Crystal with oP, 001 (r); Poo , 101 (0); JP, 112 (u) and Poo ,

on (»).
Fig. 52. — Bournonite Fourling Twinned about 00 p, no (m). Form c same as in

Fig. 51. 6= 00 P 00 (010) and a— 00 P 65 (100).

blue solution of copper nitrate that turns to an intense azure blue when
an excess of ammonia is added. In this solution is a residue of sulphur
and a white precipitate that contains lead and antimony.

Bournonite is distinguished from most other minerals by its reactions
for both antimony and sulphur. From other sulphantimonites it is
distinguished by its color, hardness and density.

On long exposure to the atmosphere bournonite alters to the car-
bonates of lead (cerussite) and copper (malachite and azurite).

Synthesis, — Crystals of bournonite have been obtained by the action
of gaseous H2S on the chlorides and oxides of Pb, Cu and Sb, at moderate
temperatures.

Occurrence. — The mineral occurs principally in veins with galena,
sphalerite, stibnite, chalcopyrite and tetrahedrite.

Localities. — Good crystals are found in the mines at Neudorf, Harz;
at Pribram, in Bohemia; at Felsobanya, Kapnik and other places
in Hungary, and at various places in Chile. In North America it has

122 DESCRIPTIVE MINERALOGY

been found at the Boggs Mine in Yavapai Co., Ariz., in Montgomery
Co., Ark., and at Marmora, Hastings Co., and Darling, Lanark Co.,
Ontario.

THE SULPHDIARSENITES AND SULPHDIANTIMONITES

A large number of sulpho-salts we apparently salts of acids that
contain two or more atoms of As or Sb in the molecule. These acids
may be regarded as derived from the ortho acids by the abstraction of
H2S, thus: The arsenious acid containing two atoms of As may be
thought of as 2H3ASS3— H2S = H4As2S6. Acids with larger proportions
of arsenic may be regarded as derived in a similar manner from three or
more molecules of the ortho acid. Only a few of these salts are common
as minerals. Among the more common are two that are lead salts of
derivatives of sulpharsenious and sulphantimonous acids.

Jamesonite (Pb2Sb2S5) and Dufrenoysite (Pb2As2S5)

Jamesonite and dufrenoysite are lead salts of the acids H4SD2S5 and
H4AS2S5. Both minerals occur in acicular and columnar orthorhombic
crystals and in fibrous and compact masses of lead-gray color. Their
cleavage is parallel to the base. The minerals are brittle and have an
uneven to conchoidal fracture. Their hardness is 2-3 and density
5.5-6. The streak of jamesonite is grayish black, and of dufreynosite
reddish brown. Both minerals are easily fusible. They are soluble in
HO with the evolution of H2S, giving a solution from which acicular
crystals of PbCk separate on cooling. They are decomposed by HNO3,
with the separation of a white basic lead salt. They are found in veins
with antimony and sulphide ores abroad and at several points in Nevada,
and in the antimony mines in Sevier Co., Arkansas.

THE SULPHARSENATES AND SULPHANTIMONATES

The sulpharsenates are salts of sulpharsenic acid, H3ASS4, and the
sulphantimonates, the salts of the corresponding antimony acid, HaSbS4.
These compounds are much less numerous among the minerals than the
sulpharsenites and sulphantimonites. Moreover, no member of the
former groups is as common as several of the members of the latter.
The most important member is the mineral enargite (C113ASS4) an ortho-
sulpharsenate, which in a few places is wrought as a copper ore.

SULPHO-SALTS AND SULPHO-FERRITES

123

Enargite (Cu3AsS4)

Enargite, though a rare mineral, is so abundant at a few points that
it has been mined as an ore of copper.

Theoretically, the mineral is S = 32.6, As=i9.i, 01=4.83. Most
specimens, however, contain an admixture of the isomorphous anti-
mony compound, famatinite, and consequently show the presence of
antimony. A specimen from the Rams Mine, Butte, Montana, yielded

Ins

Total

3J-44

17.91

1.76

48.67

•33

.10

.11

100.32

Fig. 53. — Enargite Crys-
tal with 00 P, no (m);
oopoo , 100(a); 00 P^,
1 20 (A) and oP, 001 (c).

The mineral crystallizes in the orthorhombic system (bipyramidal
class), in crystals with an axial ratio .8694 : 1 : .8308. Their habit is
usually prismatic, and they are strongly striated
vertically. The crystals are usually highly modi-
fied, with the following forms predominating:
00 P56 (100), ooP(no), ooP2(i2o), ooP3(i3o),
00 P 06 (010), and oP(ooi) (Fig. 53). Stellar trill-
ings, with ooP2(i2o) the twinning plane, have a
pseudohexagonal habit. The mineral occurs also
in columnar and platy masses.

Enargite possesses a perfect prismatic cleavage
and an uneven fracture. It is opaque with a
grayish black color and streak. Its hardness is 3
and density 4.4. It is a poor electrical conductor.

It is easily fusible before the blowpipe. When roasted on charcoal
it gives the reactions for S and As, and thq roasted residue when
moistened with HC1 imparts to the flame the azure-blue color char-
acteristic of copper. In the closed tube it decrepitates and gives a
sublimate of S. When heated to fusion it yields a sublimate of arsenic
sulphide. The mineral is soluble in aqua regia.

Enargite is easily recognized by its crystallization and blowpipe
reactions.

Occuf fence. Tr-Eneirgite is associated with other copper ores in veins
filled by magmatic water at intermediate depths and in a few replace-
ment deposits.

Localities. — Although not widely distributed, enargite occurs in large
quantities in the copper mines near Morococha, Peru; Copiapo, Chile;
in the province of La Rioja, Argentine; on Luzon, Philippine Islands,

124 DESCRIPTIVE MINERALOGY

and in the United States, at Butte, Montana; in the San Juan Moun-
tains, Colorado, and in the Tintic District, Utah.

Uses. — It is smelted as an ore of copper. At the Butte smelter it
furnishes the arsenic that is separated from the smelter fumes and placed
upon the market as arsenic oxide (see p. 113).

THE BASIC SULPHO-SALTS

The basic sulpho-salts are compounds in which there is a greater
percentage of the basic elements (metals, etc.), present than is
necessary to replace all the hydrogen of the ortho acids. Thus, the
copper orthosulpharsenate, enargite, is CU3ASS4 The mineral steph-
anite is AgsSbS4 and the pure silver polybasite AggSbSo.

Since three atoms of Ag are sufficient to replace all the hydrogen
atoms in the normal acid containing one atom of antimony and the
quantities of silver present in stephanite and polybasite are in excess
of this requirement, the two minerals are described as basic. The
exact relations of the atoms to one another in the molecules are
not known.

Although the number of basic sulpho-salts occurring as minerals is
large only four arc common. These are:

StepJtanite AgoSbS4 Orthorhombic

Polybasite (Ag-Cu)9SbSo Monoclinic

Tetrahedrite (R")4Sb2S7 Isometric

Tennantite (R")4As2S7 Isometric

Stephanite (Ag5SbS4)

Stephanite, though a comparatively rare mineral, is an important ore
of silver in some camps. It occurs massive, in disseminated grains and
as aggregates of small crystals. Analyses indicate a composition very
close to the requirements of the formula AgsSbS4.

S Sb Ag AsandCu Total

Theoretical 16.28 15.22 68.50 .... 100.00

Crystals, Chaiiarcillo, Chile 16.02 15.22 68 . 65 tr 99 . 89

Stephanite crystallizes in hemimorphic orthorhombic crystals (rhom-
bic pyramidal class), with an axial ratio .6291 : 1 : .6851. The crystals
are highly modified, 125 forms having been identified upon them. They
have usually the habit of hexagonal prisms, their predominant planes

SULPHO-SALTS AND SULPHO-FERRITES 125

being ooP(no) and ooP 06(010), terminated by oP(ooi), P(in) and
2 P 06 (021) at one or the other end of the c axis (Fig. 54). Twins are
common, with 00 P(no) and oP(ooi) the twinning planes.

The mineral is black and opaque and its streak is black. Its hard-
ness is 2 and density =6. 2 — 6.3. It cleaves
parallel to 00 P 06 (010) has an uneven frac-
ture, and is a poor conductor of electricity.

On charcoal stephanite fuses very easily
to a dark gray globule, at the same time
yielding the white fumes of antimony oxide Fig. 54.— Stephanite Crystal
and the pungent odor of SO2. Under the with oP, 001 (c); 00 p«,

reducing flame the globule is reduced to OI° )** °°- S1IC ,i\ '

.. 332 (P), 2P00 , 021 (d).

metallic silver. The mineral dissolves in

dilute nitric acid and this solution gives a white precipitate with HC1.

Stephanite is easily distinguished from other black minerals by its
easy fusibility, its crystallization, and its reactions for Ag, Sb and S.

Localities. — The mineral is associated with ether silver ores in the
zone of secondary enrichment of veins at Freiberg, Saxony; Joachimsthal
and Pribram, Bohemia; the Comstock Lode and other mines in the
Rocky Mountain region and at many points in Mexico and Peru.

Uses. — It is mined together with other compounds as an ore of silver^
It is particularly abundant in the ores of the Comstock Lode, Nev., and
of the Las Chispas Mine, Sonora, Mex.

Polybasite ((Ag-Cu)9SbS6)

Polybasite is the name usually applied to the mixture of basic sulph-
antimonites and suipharsenites of the general formula R'9(Sb.As)Se, in
which R' = Ag and Cu. More properly the name is applied to the anti-
monite, and the corresponding arsenite is designated as pearceiie. Sev-
eral typical analyses follow:

Fe Pb Ins Total

.... ... ... 99 ' "9

I.05 ... .42 99.85

.... ... ... 1UO . V/U

76 ... 100.18

I. Pearceite, Veta Rica Mine, Sierra Mojada, Mexico.
II. Crystals of pearceite, Drumlummon Mine, Marysville, Montana.

III. Polybasite, Santa Lucia Mine, Guanajuato, Mexico.

IV. Polybasite, Quespisiza, Chile.

Sb Ag

17.46

7-56

59-22

1565

II.

17.71

7-39

55.17

18. n

III.

15.43

■50

10.64 68.39

5i3

IV.

16.37

388

515 67.95

6.07

126 DESCRIPTIVE MINERALOGY

The crystallization of the two minerals, which are completely isomor-
phous, is monoclinic (prismatic class). Their axial ratios are:

Pearceite, a : b : c= 1.7309 : 1 : 1.6199 £=90° 9'
Polybasite, =17309 : 1 : 1.5796 £=90°

The crystals are commonly tabular or prismatic, with a distinct
hexagonal habit. The prominent forms are oP(ooi), P(in) and
2P 06 (20T). Contact twinning is common, with 00 P(no) the twinning
plane, and oP(ooT) the composition plane.

Both minerals are nearly opaque. Except in very thin splinters
they are steel-gray to iron-black in color. Very thin plates are trans-
lucent and cherry-red. Their streaks are black. Their cleavage is
perfect parallel to oP(ooi) and their fracture uneven. Their hardness
is 2-3, and density 6-6.2.

Both minerals are easily fusible. They usually exhibit the reactions
for Ag, Sb, As and S.

They are readily distinguished from all other minerals but silver
sulpho-salts by their blowpipe reactions. From these they are distin-
guished by their crystallization. Pearceite and polybasite are distin-
guished from one another by the relative quantities of As and Sb they
contain.

Occurrence. — Both minerals occur in the zone of secondary enrich-
ment in veins of silver sulphides.

Localities. — Polybasite was an important ore of silver in the Comstock
Lode, Nevada. It is at present mined with other silver ores at Ouray,
Colorado, at Marysville, Montana, at Guanajuato, Mexico, and at
various points in Chile. Good crystals occur at Freiberg* Saxony, at
Joachimsthal, Bohemia, and in the mines in Colorado, Mexico and Chile.

TETRAHEDRITE GROUP

The name tetrahedrite is given to a mixture of basic sulphanti-
monites and sulpharsenites crystallizing together in isometric forms with
a distinct tetrahedral habit (hextetrahedral class). The isomorphism
is so complete that all gradations between the various members of the
group are frequently met with. The arsenic-bearing member of the
series is known as tennantite and the corresponding antimony member as
tetrahedrite. The latter is the more common.

The following six analyses of tetrahedrite will give some idea of the
great range in composition observed in the species.

SULPHO-SALTS AND SULPHO-FERRITES 127

S Sb As Cu Fe Zn Ag Hg Pb Total

I. 27.60 25.87 tr 35.85 2.665.15 2.30 99.43

II. 23.51 17.21 7.67 42.00 8.28 .49 .55 99.71

III. 24.44 27.60 .... 27.41 4.27 2.31 14.54 IOOS7

IV. 24.8930.18 tr 32.80 5.85 07 5.57 99.36

V. 21.67 24.72 .... 33.53 .56 1.80 16.23 98.51

I. Newburyport, Mass.
II. Cajabamba, Peru.

III. Star City, Nev.

IV. Pontes, Hungary.
V. Arizona.

Upon examination these are found to correspond approximately to
the formula R"4Sb2S7, in which the R" is CU2, Pb, Fe, Zn, Hg, Ag2 and
sometimes Co and Ni. When R is replaced entirely by copper, the
formula (CugSbaSz) demands 23.1 per cent S, 24.8 per cent Sb and 52.1
per cent Cu.

Analyses of tennantite yield analogous results that may be repre-
sented by the formula CU8AS2S7 which demands 26.6 per cent S, 20.76
per cent As and 52.64 per cent Cu.

Analyses of even the best crystallized specimens rarely yield As or
Sb alone. Moreover, nearly all show the presence of Zn in notable
quantity. The great variation noted in the composition of different
specimens which appear to be pure crystals has led to the proposal of
other formulas than those given above — some being simpler and others
more complex. It is possible that the variation may be explained as
due, in part, to some kind of solid solution, rather than as the result
solely of isomorphous replacement. It is more probable, however, that
it is due to the intergrowth of notable quantities of various sulphides
with the sulpho-salts.

There is still considerable confusion in the proper naming of the mem-
bers of the series, but generally the forms composed predominantly of
Cu, Sb and S with or without Zn are known as tetrahedrite and those
containing As in place of Sb as tennantite, although several authors
confine the use of the latter term to arsenical tetrahedrites containing a
notable quantity of iron.

Since the members of the tetrahedrite series often contain a large

quantity of metals other than Cu and Zn the group has been so sub-
divided as to indicate this fact. Thus, there are argentiferous, mercurial
and plumbiferous varieties of tetrahedrite. Some of these varieties are
utilized as ores of the metals that replace the copper and zinc in the more

Total

.11

• • • •

100.15

• • •

• • • B

99.21

• • •

I. 20

101.07

128 DESCRIPTIVE MINERALOGY

common varieties. The relations of the ordinary (II) and the bis-
muthif erous tennantites (III) to tetrahedrite (I) are shown by the fol-
lowing three analyses:

S As Sb Bi Cu Fe Ag

I. 24.48 tr 28.85 45-39 I-32

II. 26.61 19.03 51.62 1.95

III. 29.10 11.44 2.19 13.07 37.52 6.51 .04

I. Fresney d'Oisans, France.
II. Cornwall, England.
III. Cremenz, Switzerland.

The crystals of both tetrahedrite and tennantite are tetrahedral in

habit, the principal forms on them consisting of the simple tetrahedron

2O2 |0 _

and complex tetrahedrons such as (211), (332) together with

2 2

the dodecahedron, ooO(no) and the cube, 00 O 00 (100). (Fig. 55.)

Twins are common with O(ni) the twinning

plane. These are sometimes contact twins

and sometimes interpenetration twins. Some

crystals are very complicated, because of the

presence on them of a great number of forms.

The total number of distinct forms that have

been identified is about 90. The mineral

_, occurs also in granular, dense and earthy
Fig. <«>. — Tetrahedrite Crys-

0 masses,

tal with - in (0); 00 o, The fracture of the tetrahedrites is uneven,
no (d) and sO, 332 (»). Their hardness varies between 3 and 4.5 and

their density between 4.4 and 5.1. Their color
is between dark gray and iron-black, except in thin splinters, which
sometimes exhibit a cherry-red translucency. Their streak is like their
color. All tetrahedrites are thermo-electric.

The chemical properties of the different varieties of tetrahedrites
vary with the constituents present. All give tests for sulphur and for
either antimony or arsenic, and all show the presence of copper in a
borax bead. The reactions of other metals that may be present may
be learned by consulting pages 483-494.

The crystals of tetrahedrite are so characteristic that there is little
danger of confusing the crystallized mineral with other minerals of the
same color. The massive forms resemble most clearly arsenopyrite,
coba'tiU, bournonite and chalcociie. From these the tetrahedrites are

SULPHO-SALTS AND SULPHO-FERRITES 129

best distinguished by their hardness, together with their blowpipe reac-
tions.

Tetrahedrite appears to suffer alteration quite readily, since pseudo-
morpbs of several carbonates and sulphides after tetrahedrite crystals
are well known.

Syntheses. — Crystals of the tetrahedrites have been made by passing
the vapors of the chlorides of the metals and the chlorides of arsenic or
antimony and H2S through red-hot porcelain tubes. They have also
been observed in Roman coins that had lain for a long time in the hot
springs of Bourbonne-les-Bains, Haute-Marne, France.

Occurrence. — The tetrahedrites are very common in the zone of
secondary enrichment of sulphide veins and in impregnations. They
occur associated with chalcopyrite, pyrite, sphalerite, galena and other
silver, lead and copper ores in nearly all regions where the sulphide ores
of these metals are found. They occur also as primary constituents of
veins of silver ores, where they were deposited by magmatic waters.

Localities. — In the United States tetrahedrite occurs at the Kellogg
Mines, ten miles north of Little Rock, Arkansas; near Central City and
at Georgetown, Colorado; in the Ruby and other mining districts in
the same State; at the De Soto Mine in Humboldt Co., Nevada, and
at several places in Montana, Utah and Arizona. It is found also in
British Columbia and in Mexico, and at Broken Hill, New South Wales.

The arsenical tetrahedrites are not quite as common as is the anti-
monial variety. Excellent crystals occur in the Cornish Mines, at
Freiberg in Saxony, at Skutterud in Norway, and at Capelton,
Quebec.

Uses. — The mineral is used to some extent as an ore of silver or of
copper, the separation of the metals being effected in the same way as
in the case of the sulphides of these substances.

THE SULPHO-FERRITES

Only two sulpho-ferrites are sufficiently important to merit descrip-
tion here. Both of these are copper compounds and both are used as
ores of this metal, one — chalcopyrite — being one of the most important
ores of the metal at present worked.

The first of these minerals discussed, bornite, is a basic salt of
the acid HaFeSa; the second is the salt of the derived acid HFeS2,
which may be regarded as the normal acid from which one molecule of
H2S has been abstracted (see p. 116).

130 DESCRIPTIVE MINERALOGY

Bornite (Cu5FeS4)

Bornite, known also as horseflesh ore because of its peculiar purplish-
red color, is found usually massive. In Montana and in Chile it con-
stitutes an important ore of copper.

Bornite is probably a basic sulpho-ferrite, though analyses yield
results that vary quite widely, especially in the case of massive varieties.
This variation is due to the greater or less admixture of copper sulphides,
mainly chalcocite, with the bornite. The theoretical composition of the
mineral is 25.55 S, 63.27 Cu, and 1 1.18 Fe. The analyses of a crystallized
variety from Bristol, Conn., and of a massive variety from the Bruce
Mines, Ontario, follow:

S Cu Fe Ins Total

Bristol, Conn 25.54 63.24 11.20 ... 99.98

Bruce Mines, Ont 2S-39 62.78 11.28 .30 99.75

The crystallization of bornite is isometric (hexoctahedral class), in
combinations of 00 O 00 (ico), 00 0(no),0(in), and sometimes 202(211).
Crystals often form interpenetration twins, with O the twinning plane.

The fracture of the mineral is conchoidal, its hardness 3 and density
about 5. On fresh fracture the color varies from a copper-red to a pur-
plish brown. Upon exposure alteration rapidly takes place covering
the mineral with an iridescent purple tarnish. Its streak is grayish
black. It is a good conductor of electricity.

Chemically, the mineral possesses no characteristics other than those
to be expected from a compound of iron, copper and sulphur. It dis-
solves in nitric acid with the separation of sulphur.

It is easily recognized by its purplish brown color on fresh fractures
and its purple tarnish.

Bornite alters to chalcopyrite, chalcocite, covellite, cuprite (CU2O),
chrysocolla (CuSi03 • 2H2O) and the carbonates, malachite and azurite.
On the other hand, bornite pseudomorphs after chalcopyrite and chal-
cocite are not uncommon.

Syntheses. — Roman copper coins found immersed in the water of
warm springs in France have been partly changed to bornite. Crystals
have been formed by the action of H2S at a comparatively low tempera-
ture (ioo°-2oo° C), upon a mixture of CU2O, CuO and Fe203

Occurrence and Origin. — Bornite is usually associated with other
copper ores in veins and lodes, where it is in some cases a primary min-
eral deposited by magmatic waters and in others a secondary mineral
produced in the zone of enrichment of sulphide veins. It also sometimes

SULPHO-SALTS AND SULPHO-FERRITES 131

impregnates sedimentary rocks, where its origin is part due to contact
action.

Localities. — The crystallized mineral occurs near Redruth, Cornwall,
Eng., and at Bristol, Conn. The massive mineral is found at many
places in Norway and Sweden. It is the principal ore of some of the
Bolivian, Chilian, Peruvian and Mexican mines and of the Canadian
mines near Quebec. In the United States it has been mined at
Bristol, Conn., and at Butte, Montana,

Uses. — Bornite is mined with chalcopyrite and other copper com-
pounds as an ore of this metal.

Chalcopyrite (CuFeS2)

From an economic point of view this mineral is the most important
of the sulpho-salts, as it is one of the most important ores of copper

Fig. 56. Fig. 5;.

Fig. 56.— Chalcopyrite Crystal with P, 111 (J>); -P,
Fig. 57.— Chalcopyrite Crystal with — , 772 (*) and

sometimes approaches w I'(iio) and x approach!

Fig. 58.— Chalcopyrite Twinned about P(m}.

known. It occurs both massive and crystallized. From its similarity
to pynte in appearance it is often known as copper pyrites.

Crystallized specimens of chalcopyrite contain 35 per cent S, 34.5
per cent Cu and 30.5 per cent Fe, corresponding to the formula CuFeSa,
i.e., a copper salt of the acid HFeSj. The mineral often contains small
quantities of intermixed pyrite. It also contains in some instances
selenium, thallium, gold and silver.

The crystallization of chalcopyrite is in the sphenoidal, hemihedral
division of the tetragonal system (tetragonal scalenohedron class).

132 DESCRIPTIVE MINERALOGY

The crystals are usually sphenoidal in habit with the sphenoids -(in),

2
|P

and — (332) the predominant forms (Figs. 56 and 57). In addition to
2

these there are often present also 00 P 00 (100), 00 P(no), 2P 00 (201),

xp
and a very acute sphenoid that is approximately —(772), supposed to be

due to the oscillation of 00 P(no) and —(in) (Fig. 57). Twins are quite

common, with the twinning plane parallel to P (Fig. 58). The plus
faces of the sphenoid are often rough and striated, while the minus faces
are smooth and even.

The fracture of the mineral is uneven. Its hardness is 3.5-4 and
density about 4.2. Its luster is metallic and color brass-yellow. Old
fracture surfaces are often tarnished with an iridescent coating. Its
streak is greenish black. It is an excellent conductor of electricity.

On charcoal the mineral melts to a magnetic globule. When mixed
with Na2C03 and fused on charcoal, a copper globule containing iron
results. When treated with nitric acid it dissolves, forming a green
solution in which float spongy masses of sulphur. The addition of
ammonia to the solution changes it to a deep blue color and at the same
time causes a precipitate of red ferric hydroxide.

From the few brassy colored minerals that resemble it, chalcopyrite
is distinguished by its hardness and streak.

W"hen subjected to the action of the atmosphere or to percolating
atmospheric water chalcopyrite loses its iron component and changes
to covellite and chalcocite. The iron passes into limonite. Bornite,
copper and pyrite are also frequent products of its alteration. In the
oxidation zone of veins it yields limonite, the carbonates, malachite and
azurite, and cuprite (CU2O). When exposed to the leaching action of
water, limonite alone may remain to mark the outcrop of veins, the
copper being carried downward in solution to enrich the lower portions
of the vein. The deposit of limonite on the surface is known as
" gossan."

Syntheses. — Crystals of chalcopyrite have been produced by the
action of H2S upon a moderately heated mixture of CuO and Fe203
enclosed in a glass tube. The mineral has also been made by the action
of warm spring waters upon ancient copper coins. It is also a fairly
common product of roasting-oven operations. '

Occurrence and Origin. — Chalcopyrite is widely disseminated as a
primary vein mineral, and is often found in nests in crystalline rocks.

SULPHO-SALTS AND SULPHO-FERRITES 133

It also impregnates slates and other sedimentary rocks, schists and
altered igneous rocks where, in some cases, it is a contact deposit
and in others is original. It is also formed by secondary processes caus-
ing enrichment of copper sulphide veins. Its most common associ-
ates are galena, sphalerite and pyrite» It is the principal copper ore
in the Cornwall mines, where it is associated with cassiterite (SnCfe),
galena and other sulphides. It is also the important copper ore of
the deposits of Falun, Sweden, of Namaqualand in South Africa,
those near Copiap6 in Chile, those of Mansfeld, Germany, of the Rio
Tinto district in Spain, of Butte and other places in Montana, and of
the great copper-producing districts in Arizona, Utah and Nevada.

Crystals occur near Rossie, Wurtzboro and Edenville, N. Y., at the
French Creek Mines, Chester Co., Perm., near Finksburg, Md., and at
many other places.

Extraction. — The mineral is concentrated by mechanical methods.
The concentrates are roasted at a moderately high temperature, the iron
being transformed into oxides and the copper partly into oxide and
partly into sulphide. Upon further heating with a flux the iron oxide
unites with this to form a slag and the copper sulphide melts, and collects
at the bottom of the furnace as " matte," which consists of mixed copper
and copper sulphide. This is roasted in a current of air to free it from
sulphur. By this process all of the copper is transformed into the oxide,
which may be converted into the metal by reduction. The metal is
finally refined by electrical processes. Much of the copper obtained
from chalcopyrite contains silver or gold, or both, which may be recov-
ered by any one of several processes.

Uses. — A large portion of the ccpper produced in the world is obtained
by the smelting of chalcopyrite and the ores associated with it.

Production. — The world's total product of copper has been referred
to in another place (p. 55). Of this total (2,251,300,000 lb.) the United
States supplied, in 191 2, 1,243,300,000 lb., of which about 1,000,000,000
lb. were obtained from sulphide ores. Arizona and Montana produced
the greater portion of this large quantity, the former contributing about
359,000,000 lb. to the aggregate, and the latter 308,800,000 lb. Out-
side of the United States the most important copper-producing countries
are Mexico, Japan, Spain and Portugal, Australia, Chile, Canada,
Russia, Peru and Germany, in the order named. Practically all of this
copper, except that from Japan and Mexico, is extracted from sulphide
ores.

CHAPTER VI

THE CHLORIDES. BROMIDES, IODIDES AND FLUORIDES

The salts belonging to this group are compounds of metals with
hydrochloric (HC1), hydrobromic (HBr), hydriodic (HI) and hydro-
fluoric (HF) acids. Only a few are of importance. Of these some are
simple chlorides, others are simple fluorides, others are double chlorides
or fluorides (i.e. cryolite, AlF3+3NaF), and others are double hydrox-
ides and chlorides (atacamite).

THE CHLORIDES

The simple chlorides crystallize in the isometric system, but in differ-
ent classes in this system. They comprise salts of the alkalies, K, Na
and NH4, and of silver. Of these only three minerals are of importance,
viz.: sylvite, halite and cerargyrite.

Halite (NaCl)

Halite, or common salt, is the best known and most abundant of the
native chlorides. It is a colorless, transparent mineral occurring in
crystals, and in granular and compact masses.

Pure halite consists of 39.4 per cent CI and 60.6 per cent Na. The
mineral usually contains as impurities clay, sulphates and organic
substances. The several analyses quoted below indicate the nature of
the commonest impurities and their abundance in typical specimens.

NaCl CaCl MgCl CaS04 Na2S04 Mg2S04 Clay H20

23 3°

2.00 .70

■33

*•' 97 • 35 .... ....

I. Ol

•43

II. 90 . 3 .... ....

S°°

2.00

III. 98.88 tr tr

•79

• . • •

I. Stassfurt, Germany.

II. Vic, France.

III. Petit Arise, La.

.... •*..

The crystallization of halite is isometric (hexoctahedral class), the
principal forms being 00 O 00 (100), O(in) and ooO(no). Often the

134

CHLORIDES, FLUORIDES, ETC. 135

faces of the forms are hollowed or depressed giving rise to what are called
" hopper crystals " (Fig. 59). The mineral occurs also in coarse, gran-
ular aggregates, in lamellar and fibrous masses and in stalactites.

Its cleavage is perfect parallel to 00 O 00 (100). Its fracture is con-
choidal. Its hardness is 2-2.5 and density about 2.17. Halite, when
pure, is colorless, but the impurities present often color it red, gray,
yellow or blue. The bright blue mottlings observed in
many specimens are thought to be due to the presence
of colloidal sodium. The mineral is transparent or
translucent and its luster is vitreous. Its streak is
colorless. Its saline taste is well known. It is
diathermous and is a nonconductor of electricity. pIG SQ.— Hopper-
The mineral is plastic under pressure; and its plasticity Shaped Cube of
increases with the temperature. Its index of refraction Halite,
for sodium light, n— 1.5442.

In the closed tube halite fuses and often it decrepitates. When
heated before the blowpipe it fuses (at 7760) and colors the flame yellow.
The chlorine reaction is easily obtained by adding a small particle of the
mineral to a microcosmic salt bead that has been saturated with copper
oxide. This, when heated before the blowpipe, colors the flame a bril-
liant blue. The mineral easily dissolves in water, and its solution yields
an abundant white precipitate with silver nitrate.

The solubility of halite is accountable for a large number of
pseudomorphs. The crystals embedded in clays are gradually dissolved,
leaving a mold that may be filled by other substances, which thus
become pseudomorphs.

Syntheses. — Crystals of halite have been produced by sublimation
from the gases of furnaces, and by crystallization from solution contain-
ing sodium chloride.

Occurrence and Origin. — Salt occurs most abundantly in the water of
the ocean, of certain salt lakes, of brines buried deep within the rocks in
some places, and as beds interstratified with sedimentary rocks. In the
latter case it is associated with sylvite (KC1), anhydrite (CaS04), gypsum
(CaS04-2H20), etc., which, like the halite, are believed to have been
formed by the drying up of salt lakes or of portions of the ocean that
were cut off from the main body of water, since the order of occurrence
of the various beds is the same as the order. of deposition of the corre-
sponding salts when precipitated by the evaporation of sea water at
varying temperatures. (Comp. pp. 22, 23.)

Below are given figures showing the composition of the salts in the
water of the ocean, of Great Salt Lake, and of the Syracuse, N. Y., and

136 DESCRIPTIVE MINERALOGY

Michigan artificial brines (produced by forcing water to the buried rock
salt).

NaCl CaCl2 MgCl2 NaBr KC1 Na2S04 K2S04 CaS04 MgS04

I. 77.07 .... 7.86 1.30 3.89 4.63 5.29

II. 7957 .... 10.00 6.25 3.60 .58

III. 9597 .90 .69 2 54

IV. 91.95 3 .19 2 48 2*39

I. Atlantic Ocean.
II. Great Salt Lake.

III. New York brines.

IV. Michigan brines.

Localities. — The principal mines of halite, or rock salt, are at Wie-
lic2ka, Poland; Hall, Tyrol; Stassfurt, Germany, where fine crystals
are found; the Valley of Cardova, Spain; in Cheshire, England and in
the Punjab region of India. At Petit Anse in Louisiana, in the vicinity
of Syracuse, N. Y., and in the lower peninsula of Michigan thick beds
of the salt are buried in the rocks far beneath the surface. Much of the
salt is comparatively pure and needs only to be crushed to become usable.
In most cases, however, it is contaminated with clay and other sub-
stances. In these cases it must be dissolved in water and recrystallized
before it is sufficiently pure for commercial uses.

The best known deposits are at Stassfurt where there is a great thick-
ness of alternating layers of halite, sylvite (KC1), anhydrite, gypsum,
kieserite (MgS04-H20) and various double chlorides and sulphates of
potassium and magnesium. Although the halite is in far greater quan-
tity than the other salts, nevertheless, the deposit owes most of its value
to the latter, especially the potassium salts (comp. pp. 137, 142).

Uses. — Besides its use in curing meat and fish, salt is employed in
glazing pottery, in enameling, in metallurgical processes, for clearing
oleomargarine, making butter and in the more familiar household oper-
ations. It is also the chief source of sodium compounds.

Production. — Most of the salt produced in the United States is ob-
tained directly from rock salt layers by mining or by a process of solu-
tion, in which water is forced down into the buried deposit and then to
the surface as brine, which is later evaporated by solar or by artificial
heat. In the district of Syracuse, N. Y., salt occurs in thick lenses
interbedded with soft shales. In eastern Michigan and in Kansas salt
is obtained from buried beds of rock salt, and in Louisiana from great
dome-like plugs covered by sand, clay and gravel. Some of the masses
in this State are 1,756 ft. thick.

CHLORIDES, FLUORIDES, ETC. 137

The salt production of the United States for 191 2 amounted to 33,-
324,000 barrels of 280 lb. each, valued at $9,402,772. Of this quantity
7,091,000 barrels were rock salt.

The imports of all grades of salt during the same time were about
1,000,000 barrels and the exports about 440,000 barrels.

Sylvite (KC1)

Sylvite is isometric, like halite, but the etched figures that may be
produced on the faces of its crystals indicate a gyroidal symmetry (pen-
tagonal icositetrahedral class). The habit of the crystals is cubic with
0(i 11) and 00 O 00 (100) predominating.

Pure sylvite contains 47.6 per cent CI and 52.4 per cent K, but the
mineral usually contains some NaCl and often some of the alkaline sul-
phates.

The physical properties of sylvite are like those of halite, except that
its hardness is 2 and the density 1.99. Its melting temperatuie is 7380
and n for sodium light = 1.4903.

When heated before the blowpipe the mineral imparts a violet tinge
to the flame, which can be detected when masked by the yellow flame of
sodium by viewing it through blue glass. Otherwise sylvite and halite
react similarly.

Halite and sylvite are distinguished from other soluble minerals by
the reaction with the bead saturated with copper oxide, and from one
another by the color imparted to the blowpipe flame.

Synthesis. — Sylvite crystals have been made by methods analogous
to those employed in syntheses of halite crystals.

Occurrence. — Sylvite occurs associated with halite, but in distinct
beds, at Stassfurt, Germany, and at Kalusz. Galicia. It has also been
found, together with the sodium compound, incrusting the lavas of
Vesuvius.

Uses. — Sylvite is an important source of potassium salts, large quan-
tities of which are used in the manufacture of fertilizers.

CERARGYRITE GROUP

The cerargyrite group comprises the chloride, bromide and iodide of
silver. The first two exist as the minerals cerargyrite and bromargyrite,
both of which crystallize in the isometric system. The isometric Agl
exists only above 1460; below this temperature the iodide is hexagonal.
The jexhagonal modification occurs as the mineral iodyrite, which, of
course, is not regarded as a member of the cerargyrite group.

138 DESCRIPTIVE MINERALOGY

Cerargyrite (AgCl)

Cerargyrite, or horn silver, is an important silver ore. It is usually
associated with other silver compounds, the mixture being mined and
smelted without separation of the components. It is usually recog-
nizable by its waxy, massive character.

Silver chloride consists of 24.7 per cent chlorine and 75.3 per cent
silver, but cerargyrite often contains, in addition to its essential con-
stituents, some mercury, bromine and occasionally some iodine. Crystals
are rare. They are isometric (hexoctahedral class), with a cubical habit,
their predominant forms being 00 O 00 (100), 00 O(no), O(in), 20(221)
and 202(211). Twins sometimes occur with O(in) the twinning face.
The mineral is sometimes found massive, embedded among other min-
erals, but is more frequently in crusts covering other substances.

The fracture of cerargyrite is conchoidal. The mineral is sectile.
Its hardness is 1-1.5 an^ density about 5.5. Its color is grayish, white
or yellow, sometimes colorless. On exposure to light it turns violet-
brown. It is transparent to translucent and its streak is white. It is a
very poor conductor of electricity. Like halite it is diathermous. n for
sodium light = 2.071.

In the closed tube cerargyrite fuses without decomposition. On
charcoal it yields a metallic globule of silver, and when heated with oxide
of copper in the blowpipe flame it gives the chlorine reaction. The min-
eral is insoluble in water and in nitric acid but is soluble in ammonia, and
potassium cyanide. When a particle of the mineral is placed on a
sheet of zinc and moistened with a drop of water, it swells, turns black
and is finally reduced to metallic silver, which, when rubbed by a knife
blade, exhibits the white luster of the metal.

Cerargyrite is easily distinguished from all other minerals, except
the comparatively rare bromide and iodide, by its physical properties and
by the metallic globule which it yields on charcoal.

Syntheses. — Crystals of cerargyrite have been obtained by the rapid
evaporation of ammoniacal solutions of silver chloride, and by the cooling
of solutions of the chloride in molten silver iodide.

Occurrence. — The mineral occurs in the upper (oxidized) portions of
veins of argentiferous minerals, where it is associated with native silver
and oxidized products of various kinds.

Localities. — The most important localities of cerargyrite are in Peru,
Chile, Honduras and Mexico, where it is associated with native silver.
It is also found near Leadville, Colo,; near Austin, in the Comstock
lode, Nev., and at the Poorman Mine, and in other mines in Idaho

CHLORIDES, FLUORIDES, ETC. 139

and at several places in Utah. Good crystals occur in the Poorman

Extraction. — When a silver ore consists essentially of cerargyrite the
metal may be extracted by amalgamation. Ores containing compara-
tively small quantities of cerargyrite are smelted.

Production. — The quantity of cerargyrite mined cannot be safely
estimated. As has been stated, it is usually wrought with other silver
ores.

THE FLUORIDES

The fluorides are salts of hydrofluoric acid. There are several
known to occur as minerals, but only two, the fluoride of calcium and

Pig to.— Group of Fluorite Crystals from Wear dale, Co., Durham, England. (Foots
Mineral Company.)

the double fluorides of sodium and aluminium are of sufficient impor-
tance to merit description here.

Fluorite (CaF2)
Fluorite, or fluorspar, is the principal source of fluorine. It is usually
a transparent mineral that is characterized by its fine color and its hand-

140

DESCRIPTIVE MINERALOGY

some crystals (Fig. 60). Perhaps there is no other mineral known that
can approach it in the beauty of its crystal groups. The uncrystallized
fluorite may be massive, granular or fibrous.

Fluorite is a compound of Ca and F in the proportion of 48.9 per cent
F and 51.1 per cent Ca. Chlorine is occasionally present in minute
quantities, and Si02, AI2O3 and Fe2<I>3 are always present. A sample of
commercially prepared fluorite from Marion, Ky., gave:

CaF2

Si02

Al203+Fe203

CaC03

MgO

94.72

1 .22

.98

1.82

.68

The crystallization is isometric (hexoctrahedral class), and inter-
penetration twins are frequent. The principal forms observed are

Fig. 61.

Fig. 62.

Fig. 61. — Crystal of Fluorite witji °o O «> , 100 (a) and °o O2, 210 (e).
Fig. 62. — Intcrpenetration Cubes of Fluorite, Twinned about O(iu).

O(iii), ooOoo(ioo), 0002(210) and 402(421) (Fig. 61), but some crys-
tals are highly modified, as many as 58 forms having been identified upon
the species. The twins, with O(in) the twinning plane, are usually
interpenetration cubes, or cubes modified on the corners by the octa-
hedrons (Fig. 62). The mineral occurs also in granular, fibrous and
earthy masses.

The cleavage of fluorite is perfect parallel toO(in). The mineral
is brittle, its fracture is uneven or conchoidal, its hardness is 4 and its
density about 3.2. It melts at 13870. Its color is some shade of yel-
low, white, red, green, blue cr purple, its luster vitreous, and its streak
is white. Many specimens are transparent, some are only translucent.
Most specimens phosphoresce upon heating. A variety that exhibits a
green phosphoresence is known as chlorophane. The index of refraction
for sodium light is 1.43385 at 200. The mineral is a nonconductor of
electricity.

The color of the brightly tinted varieties was formerly thought to be
due to the presence of minute traces of organic substance since it is lost

CHLORIDES, FLUORIDES, ETC. 141

or changed when the mineral is heated, but recent observations of the
effect of radium emanations upon light-colored specimens indicate a
deepening of their color by an increase in the depth of the blue tints.
This suggests that the coloring matter is combined with the CaF2. It
may be a colloidal substance.

In the closed tube fluorite decrepitates and phosphoresces. When
heated on charcoal it fuses, colors the flame yellowish red and yields an
enamel-like residue which reacts alkaline to litmus paper. Its powder
treated with sulphuric acid yields hydrofluoric acid gas which etches
glass. The same effect is produced when the powdered mineral is fused
with four times its volume of acid potassium sulphate (HKSO4) in a
glass tube. The walls of the tube near the mixture become etched as
though acted upon by a sand blast.

Fluorite is easily distinguished by its cleavage and hardness from
most other minerals. It is also characterized by the possession of
fluorine for which it gives clear reactions.

Syntheses. — Crystals are produced upon the cooling of a molten mix-
ture of CaF2 and the chlorides of the alkalies, and by heating amorphous
CaF2 with an alkaline carbonate and a little HC1 in a closed tube at 250°.
Occurrence, Localities and Origin. — The mineral occurs in beds, in
veins, often as the gangue of metallic ores and as crystals on the walls
of cavities in certain rocks. It is the gangue of the lead veins of northern
England and elsewhere. Handsome crystallized specimens come from
Cumberland and Derbyshire, England; Kongsberg, Norway; Cornwall,
Wales, and from the mines of Saxony. In the United States the mineral
forms veins on Long Island; in Blue Hill Bay, Maine; at Putney, in
Vermont; at Plymouth, Conn.; at Lockport and Macomb, in New
York; at Amelia Court House, Va., and abundantly in southeastern
Illinois and the neighboring portion of Kentucky, where it occurs asso-
ciated with zinc and lead ores. These last-named localities, the neigh-
borhood of Mabon Harbor, Nova Scotia, and Thunder Bay, Lake
Superior, afford excellent crystal groups. In nature fluorite has been
apparently produced both by .crystallization from solutions and by
pneumatolytic processes.

Since fluorite is soluble in alkaline waters, its place in the rocks is often
occupied by calcite, quartz or other minerals that pseudomorph it.

Uses. — The mineral is used extensively as a flux in smelting iron and
other ores, in the manufacture of opalescent glass, and of the enamel
coating used on cooking utensils, etc. It is also used in the manufacture
of hydrofluoric acid, which, in turn, is employed in etching glass. The
brighter colored varieties are employed as material for vases and the

142 DESCRIPTIVE MINERALOGY

transparent, colorless kinds are ground into lenses for optical instruments.
The mineral is also cut into cheap gems, known according to color, as
false topaz, false amethyst, etc. Except when used for making lenses or
as a precious stone, fluorite is prepared for shipment by crushing, wash-
ing and screening. A portion is ground.

Production. — The fluorite produced in the United States is obtained
mainly from Illinois and Kentucky, though small quantities are mined
in Colorado, New Mexico and New Hampshire. The production in
1912 amounted to 116,545 tons, valued at $769,163. Of this, 114,410
tons came from Illinois and Kentucky. The imports were 26,176 tons,
valued at $71,616.

THE DOUBLE CHLORIDES AND DOUBLE FLUORIDES

These double salts are apparently molecular compounds, in which
usually two chlorides or two fluorides combine, as in AlF3+3NaF.
Moreover, one of the members of the combination of chlorides is nearly
always either the sodium or the potassium chloride. The law of this
combination is expressed by Professor Remsen in these words: " The
number of molecules of potassium or sodium chloride which combine
with another chloride is limited by the number of chlorine atoms con-
tained in the other chloride." Thus, if NaCl makes double salts with
MCI2, in which M represents any bivalent element, only two are possible,
viz: MCb+NaCl and MCl2+2NaCl. With MCI3 three double salts
with sodium may be formed, etc. These double salts are not regarded
as true molecular compounds, but they are looked upon as compounds
in which CI and F are bivalent like oxygen.

Carnallite (KMgCk 6H20)

Carnallite may be regarded as a hydrated double chloride of the
composition MgCfe • KC1 • 6H2O with 14.1 per cent K, 8.7 per cent Mg,
38.3 per cent CI and 39.0 per cent H2O. It occurs in distinct crys-
tals but more frequently in massive granular aggregates.

Its crystallization is orthorhombic (bipyramidal class), but the habit
of its crystals is usually hexagonal because of the nearly equal develop-
ment of pyramids and brachy domes. Its axial ratio is .5891 : 1 : 1.3759.
Crystals are commonly bounded by 00 P(no), P(in), ^P(ii2), $P(ii3),
00 P 06 (010), 2P 06 (021), P 06 (on), I P 06 (023), oP(ooi), and P 00 (101).
The angle noAi^o=6i° 2o§'.

Carnallite is colorless lo milky white, transparent or translucent,
and has a fatty luster. Many varieties appear red in the hand specimens

CHLORIDES, FLUORIDES, ETC. 143

because of the inclusion of numerous small plates of hematite or goethite,
or yellow because of inclusions of yellow liquids or tiny crystals. The
mineral has a hardness of 1-3, and a density of 1.60. It possesses no
cleavage but has a conchoidal fracture. It is not an electrical conductor.
It is deliquescent and has a bitter taste. Its indices of refraction for
sodium light are a= 1.467, 0= 1.475, T= I-494«

Before the blowpipe carnallite fuses easily. In the closed tube it
becomes turbid and gives off much water, which is frequently accom-
panied by the odor of chlorine. It melts in its own water of crystalliza-
tion. When evaporated to dryness and heated by the blowpipe flame
a white mass results which is strongly alkaline. The mineral dissolves
in water, forming a solution which reacts for Mg, K and CI.

Carnallite is easily recognized by its solubility, its bitter taste and the
reaction for chlorine.

Synthesis. — The mineral separates in measurable crystals from a solu-
tion of MgCl2 and KC1.

Occurrence and Origin. — Carnallite occurs in beds associated with
sylvite, halite, kieserite (p. 246), and other salts that have been pre-
cipitated by the evaporation of sea water or the water of salt lakes.

Localities. — It is found in large quantity at Stassfuxt, Germany; at
Kalusz, in Galicia and near Maman, in Persia.

Uses. — Carnallite is used as a fertilizer and as a source of potash
salts.

Cryolite (NasAlF*)

Cryolite usually occurs as a fine-grained granular white mass in
which are often embedded crystals of light brown iron carbonate (sider-
ite). The formula given above demands 54.4 per cent F, 12.8 per cent
Al and 32.8 per cent Na. Analyses of pure white specimens correspond
veiy closely to this.

The mineral is monoclinic (prismatic class), but crystals are exceed-
ingly rare and when found they have a cubical habit. Their axial ratio
is a : b : ^=.9662 : 1 : 1.3882. £=89° 49'. The principal forms are
ooP(no), oP(ooi), Poo(oTo), —Poo (010) and Poo (100), thus re-
sembling the combination of the cube and octahedron. Twins are com-
mon, with 00 P(no) the twinning plane.

The cleavage of cryolite is perfect parallel to oP(coi). Its fractuie
is uneven. Hardness is 2.5 and density about 3. Its color is snow-white
inclining to red and brown. Its luster is vitreous or greasy and the
mineral is translucent to transparent. Because of its low index of
refraction, massive specimens suggest masses of wet snow. The re-

144 DESCRIPTIVE MINERALOGY

fractive index 0 f or sodium light is 1.364. It is a nonconductor of
electricity.

Cryolite is very easily fusible, small pieces melting even at the low
temperature of a candle flame. The mineral is soluble in sulphuric acid
with the evolution of HF. When fused in the closed tube with KHSO4
it yields hydrofluoric acid, and when fused on charcoal fluorine is evolved.
The residue treated with Co(N(>3)2 and heated gives the color reaction
forAl.

By the aid of its reactions with sulphuric acid, its fusibility and its
physical properties cryolite is easily distinguished from fluorite, .which it
most resembles, and from all other minerals.

Occurrence, Localities and Origin. — The occurrences of cryolite are
very few. It has been found in smaM quantities near Miask in the
Ilmen Mts., Russia; near Pike's Peak, Colo., and in the Yellowstone
National Park. Its principal occurrence is in a great pegmatitic vein
cutting granite near Ivigtut, Greenland, whence all the mineral used
in the arts is obtained. The associates of the cryolite at this place are
siderite, galena, chalcopyrite, p>rite, fluorite, topaz and a few rare
minerals. The vein is said to be intrusive into the granite. It is
believed to be a magmatic concentration.

Uses. — Cryolite was formerly employed principally in the manufac-
ture of alum and of salts of sodium. At present it is used as a flux in
the electrolytic production of aluminium, and is employed in the man-
ufacture of white porcelain-like glass, and in the process of enameling
iron. The mineral is quarried in Greenland and imported into the
United States to the extent of about 2,500 tons annually. Its value is
about $25 per ton.

THE OXYCHLORIDES

The oxychlorides are combinations of hydroxides and chlorides.

Some of them are " double salts " in the sense in which this word is

explained above. Atacamite is a combination of the oxychloride

HO\
Cu(OH)Cl with the hydroxide Cu(OH)2, or >Cu-Cu(OH)2.

Atacamite (Cu(OH)ClCu(OH)2)

Atacamite is especially abundant in South America. The mineral
is usually found in crystalline, fibrous or granular aggregates of a bright
green color.

Analyses of specimens from Australia and from Atacama, Chile, yield:

CuO

H20

Total

14.67

56.64

12.02

99-77

14.16

SS- 70

14-31

100.00

CHLORIDES, FLUORIDES, ETC. 146

Australia 16.44

Atacama, Chile *5«83

The formula requires 16.6 per cent CI, 14.9 per cent Cu, 55.8 per cent
CuO and 12.7 per cent H2O.

The crystallization of atacamite is orthorhombic (bipyramidal class),
with a: b: ^=.6613 : 1 : .7529. Its crystals are usually slender prisms
bounded by ooP(no), <»P2(i2o), 00 P 06 (010), Poo (on), oP(ooi)
and P(ni), or tabular forms flattened in the plane of the macropinacoid
00 Poo (100). Twins are common, with the twinning plane ooP(no).
The cleavage of atacamite is perfect parallel to 00 P 06 (010). Its
fracture is conchoidal. Its hardness is 3-3.5 and density about 3.76.
Pure atacamite is of some shade of green, varying between bright shades
and emerald. Its aggregates often contain red or brown streaks or
grains due to the admixture of copper oxides. It is transparent to trans-
lucent. The streak of the mineral is apple-green. It is a nonconductor
of electricity. Its indices of refraction for green light are: 0=1.831,
0= 1.861,7= 1.880.

In the closed tube atacamite gives off much water with an acid reac-
tion, and yields a gray sublimate. In the oxidizing flame it fuses and
tinges the flame azure blue (reaction for copper chloride). It is easily
reduced to a globule of copper on charcoal and is easily soluble in acids.
Atacamite is readily distinguished from garnierite, malachite and
other green minerals by its solubility in acids without effervescence and
by the azure blue color it imparts to the flame.

Synthesis. — Crystals have been produced by heating cuprous oxide
(CU2O) with a solution of FeCl3, in a closed tube at 2500.

Occurrence, Localities and Origin. — The mineral is most abundant
along the west side of the Andes Mountains in Chile and Bolivia. It
occurs also in South Australia; in India; at Ambriz, on the west coast of
Africa; in southern Spain; in Cornwall, where it forms stalactite tubes;
in southern California, and near Jerome, Arizona. It is formed as the
result of the alteration of other copper compounds, and is found most
abundantly in the upper portions of copper veins. Atacamite changes
on exposure to the weather into the carbonate, malachite, and the sili-
cate, chrysocolla.

Uses. — The mineral is an important ore of copper, but it is mined
with other compounds and consequently no records of the quantity
obtained are available.

CHAPTER VII

THE OXIDES

The oxides (except water) and the hydroxides may be regarded as
derivatives of water, the hydrogen being replaced wholly or in part
by a metal. When only part of the hydrogen is replaced an hydroxide
results; when all of the hydrogen is replaced an oxide results. Thus,
sodium hydroxide, NaHO, may be looked upon as H2O, in which Na has
replaced one atom of H, and sodium oxide, Na2<3, as H2O in which both
hydrogen atoms have been replaced by this element. Ferric oxide and
ferric hydroxide bear these relations to water:

H-O— H O

H-— 0 — H, Fe — 0 — Fe, ferric oxide, H — O — Fe, ferric hydroxide.

,/ Fe203 H-o/ Fe(OH)3

H— O— H O

The oxides constitute a very important, though not a large, class of
minerals. Some of them are among the most abundant of all minerals.
They are separated into the following groups: Monoxides, sesqui-
oxides, dioxides and higher oxides.

THE MONOXIDES

Ice (H20)

The properties of ice are so well known that they need no special
description in this place. The mineral is never pure, since it contains,
in all cases, admixtures of various soluble salts. Its crystallization is
hexagonal and probably trigonal and hemimorphic (di trigonal pyram-
idal class). Crystals are often prismatic, as when ice .forms the cover-
ing of water surfaces, or the bodies known as hailstones. In the form
of snow the crystals are often stellate, or skeleton crystals, and sometimes

146

OXIDES 147

hollow prisms. The principal forms observed on ice crystals are oP(oooi)
ooP(ioTo), iPCioTa), P(ioTi) and-jPUo+O (Fig. 63).

The hardness of ice is about 1.5 and its density .9181. It is trans-
parent and colorless except in large masses when it appears bluish. Its
fracture is conchoidal. It possesses no distinct cleavage. Its fusing

Fig. 63. — Photographs of Snow Crystals, Magnified about 15 Diameters. (After

BtnUey and Perkins^

point is o" and boiling point ico°. It is a poor conductor of electricity.
Its indices of refraction for sodium light at 8° are: «™ 1.3090, «™ 1-3133.

COPPER OXIDES

There are two oxides of copper, the red cuprous oxide (Cu;0) and
the black cupric oxide (CuO). Both are used as ores, the former being
much more important a source of the metal than the latter.

Cuprite (C113O)

Cuprite occurs in crystals, in granular and earthy aggregates and
massive. The mineral is usually reddish brown or red and thus is easily
distinguished from most other minerals. Its composition when pure is
88.8 per cent Cu and n. 2 per cent O.

In crystallization the mineral is isometric, in the gyroidal hemihedral
division of the system (pentagonal icositetrahedral class). Its pre-

148 DESCRIPTIVE MINERALOGY

dominant forms are ooO°o(ioo), O(in), ooO(no), 0002(210),
202(211), 20(221) and 30$(32i)> sometimes lengthened out into
capillary crystals, producing fibrous varieties (var. chalcotriekite).

The cleavage of cuprite is fairly distinct parallel to O(in). Its frac-
ture is uneven or conchoidal. Its hardness is 3.5-4 and density about 6.
The mineral is in some cases opaque; oftener it is translucent or even
transparent in very thin pieces. By reflected light its color is red,
brown and occasionally black. By transmitted light it is crimson. When
gently heated transparent varieties turn dark and become opaque, but
they reassume their original appearance upon cooling. Its streak is
brownish red and has a brilliant luster. When rubbed it becomes yellow
and finally green. The luster of the mineral varies between earthy and
almost vitreous. It is a poor conductor of electricity, but its con-
ductivity increases rapidly with rising temperature. Its refractive index
for yellow light= 2.705.

In the blowpipe flame cuprite fuses and colors the mantle of the
flame green. If moistened with hydrochloric acid before heating the
flame becomes a brilliant azure blue. On charcoal the mineral first
fuses and then is reduced to a globule of metallic copper. It dissolves in
strong hydrochloric acid, forming a solution which, when cooled and
diluted with cold water, yields a white precipitate of cuprous chloride

(Cu2Cl2).

Cuprite may easily be distinguished from other minerals possessing
a red streak by the reaction for copper — such as the production of a
metal globule on charcoal, and the formation of cuprous chloride in con-
centrated hydrochloric acid solutions by the addition of water. More-
over, the mineral is softer than hematite and harder than reaglar, cin-
nabar and proustite.

Cuprite suffers alteration very readily. It may be reduced to native
copper, in which case the copper pseudomorphs the cuprite, or, on ex-
posure to the air it may be changed into the carbonate, malachite,
pseudomorphs of which after cuprite are common.

Syntheses. — Crystals of cuprite have frequently been observed on
copper utensils and coins that had been buried for long periods of time.
Crystals have also been obtained by long-continued action of NH3 upon
a mixture of solutions of the sulphates of iron and copper, and by heating
a solution of copper sulphate and ammonia with iron wire in a closed tube.

Occurrence, Origin and Localities. — Cuprite often occurs as well
defined crystals embedded in certain sedimentary rocks in the upper,
oxidized portions of copper veins, and in masses in the midst of other
copper ores, from which it was produced by oxidation processes. It is

OXIDES 149

found as crystals in Thuringia, in Tuscany, on the island of Elba, in
Cornwall, Eng., at Chessy, France; and near Coquimb6, in Chile.
In Chile, in Peru, and in Bolivia it exists in great masses.

In the United States it occurs at Cornwall, Lebanon Co., Penn. It
is also found associated with the native copper on Keweenaw Point,
Mich.; at the copper mines in St. Genevieve Co., Mo.; at Bisbee and
at other places in Arizona. The fibrous variety known as chalcolrichite
is beautifully developed at Morenci in the same State.

Uses. — Cuprite is mined with other copper compounds as an ore of
copper.

Melaconite, or Tenorite (CuO)

Melaconite, or tenorite, is less common than cuprite. It usually
occurs in massive forms or in earthy masses. Crystals are rare. Its
composition is 79.8 per cent Cu and 20.2 per cent O.

In crystallization melaconite is triclinic with a monoclinic habit.
Its axial ratio is a : b : c— 1.4902 : 1 : 1.3604 and /9=99° 32'. The
angles a and 7 are both 900, but the optical properties of the crystals
proclaim their triclinic symmetry.

The mineral possesses an easy cleavage parallel to oP(ooi). Its frac-
ture is conchoidal and uneven, its hardness 3 to 4 and density about 6.
When it occurs in thin scales its color is yellowish brown or iron gray.
When massive or pulverulent it is dull black. Its streak is black, chang-
ing to green when rubbed. Its refractive index for red light is 2.63.
It is a nonconductor of electricity.

The chemical reactions of melaconite are precisely like those of cu-
prite, with the exception that the mineral is infusible.

Melaconite is distinguished from the black minerals that contain no
copper by its reaction for this metal. It is distinguished from covellite
and other dark-colored sulphides containing copper by its failure to give
the sulphur reaction.

Syntheses. — Crystals of melaconite have been found in the flues of
furnaces in which copper compounds and moist NaCl are being treated.
They have also been obtained by the decomposition of CuCb by water
vapor.

Occurrence, Localities and Origin. — The mineral usually occurs associ-
ated with other ores of copper, from which it has been formed, in part
at least, by decomposition. It is mined with these as an ore. Thin
scales are found on the lava of Vesuvius, where it must have been formed
by sublimation. Masses occur at the copper mines of Ducktown, Tenn.

150 DESCRIPTIVE MINERALOGY

Zincite (ZnO)

Zincite is the only oxide of the zinc group of elements known. It is
rarely found in crystals. It usually occurs in massive forms associated
with other zinc compounds.

Pure zincite is a compound containing 80.3 per cent Zn and 19.7 per
cent O. Since, however, the mineral is frequently admixed with man-
ganese compounds it often contains also some manganese and a little
A iron. A specimen from Sterling Hill, N. J.,

jm\ gave 98.28 per cent ZnO, 6.50 per cent MnO

//I uV and .44 per cent Fe203.

//I \\\ Natural crystals of zincite are very rare.

// pi \\p\ From a study of artificial crystals it is known
/ / J P \\\ ^at ^e mhieral is hexagonal and hemimorphic
x| j T \ *>| (dihexagonal pyramidal class). The principal

I J^^f ^-X™] forms observed are ooP(ioTo), ooP2(n5o),

*^-*-^l w» g. \^s> oP(oooi), P(ioTi), P2(ii22) and various other

Fig. 64.— Zincite Crystal pyramids of the 1st and 2d orders. Their habit

with 00P, 10T0 (m); js hemimorphic with P(ion) and oP(oooi) at

P, ion (p) and oP, the oppOSite en(k 0f a short columnar crystal

OOOI (c). /T?. , V

(Fig. 64).

The cleavage of zincite is perfect parallel to oP(oooi). Its fracture
is conchoidal, its hardness 4-4.5 and density about 5.8. Although color-
less varieties are known, the mineral is nearly always deep red or orange-
yellow, due most probably to the manganese present in it. The streak
of the red varieties is orange- yellow. Its indices of refraction are
about 2. The mineral is a conductor of electricity.

When heated in the closed tube the common variety of zincite
blackens, but it resumes its original color on cooling. With the borax
bead it gives the manganese reaction. Heated on charcoal it coats the
coal with a white film, which, when moistened with cobalt solution and
heated again with the oxidizing flame of the blowpipe, turns green. The
mineral dissolves in acids.

When exposed to the atmosphere zincite undergoes slow decomposi-
tion to zinc carbonate.

Syntheses. — Zinc oxide crystals are frequent products of the roasting
of zinc ores in ovens. They have also been produced by the action of
zinc chloride vapor upon lime and by the action of water upon zinc
chloride at a red heat.

Occurrence and Localities. — The mineral occurs only in a few places.
It is found with other zinc and manganese minerals near Ogdensburg,

OXIDES 151

and at Franklin Furnace, in Sussex Co., N. J., in the form of great
layers in marble, that are bent into troughs. The layers are probably
veins that were filled from below by emanations from a great underground
reservoir of igneous rock.

Uses. — Most of the zincite produced in the United States is used in
the manufacture of zinc oxide. The ore, which consists of a mixture of
zincite, franklinite (see p. 199), and willemite (see p. 306), is crushed
and separated into its component parts by mechanical processes. The
separated zincite is then mixed with coal and roasted. The zinc oxide
is volatilized and is caught in tubes composed of bagging. The willemite
and franklinite are smelted to metallic zinc and the residues are used in
the manufacture of spiegeleisen.

Production. — Formerly this mineral, together with the silicate found
associated with it in New Jersey, constituted the most important source
of zinc in this country. At present most of the metal is obtained from
sphalerite. Of the 380,000 tons of zinc in spelter and zinc compounds
produced in the United States during 191 2 about 69,760 tons were
made from zincite and the ores associated with it. This had an esti-
mated value of $9,626,991.

THE SESQUIOXIDES

The sesquioxides (R2O3) include a few compounds of the nonmetals
that are comparatively rare and a group of metallic compounds that
includes two minerals of great economic importance. One of these,
hematite (Fe203), is the most valuable of the iron ores.

ARSENOLITE— CLAUDETITE GROUP

The only group of the nonmetallic sesquioxides that need be referred
to in this place comprises those of arsenic and antimony. This is an
isodimorphous group including four minerals.

Isometric

Monoclinic

Arsenolite

AS2O3

Claudetite

Senarmontite

Sb203

Valentinite

All the minerals of the group are comparatively rare. The isometric
forms occur in. well developed octahedrons and in crusts covering other
minerals. They are also found in earthy masses. It is probable that at
high temperatures the isometric forms pass over into the monoclinic
modifications, as some of the latter have been observed to consist of
aggregates of tiny octahedrons. Crystals of claudetite are distinctly

152 DESCRIPTIVE MINERALOGY

monoclinic, but they are so twinned as to possess an orthorhombic
habit. Valentinite crystals, on the contrary, appear to be plainly
orthorhombic, but their apparent orthorhombic symmetry may be
due to submicroscopic twinning of the same character as that in
claudetite, but which in the latter mineral is macroscopic.

All four minerals occur as weathered products of compounds contain-
ing As or Sb. They give the usual blowpipe reactions for As or Sb.
In the closed tube they melt and sublime.

Arsenolite (AS2O3) is colorless or white. Its specific gravity is 3.7
and refractive index for sodium light = 1.755. It usually occurs in octa-
hedrons; or in combinations of O(iu) and ooO(no), but these when
viewed in polarized light are often seen to be anisotropic. The mineral is
found also in aggregates of hair-like crystals with a hardness of 1.2. It is
soluble in hot water, yielding a solution with a sweetish taste.

Senarmonite (Sb203) is gray or white. Its density is 5.2 and
n= 2.087 f°r yellow light. Its octahedral crystals are also often aniso-
tropic; its hardness =2. It is soluble in hot HC1 but is only very
slightly soluble in water. When heated it turns yellow; but becomes
white again upon cooling.

Claudetite (AS2O3) is monoclinic prismatic, with a : b : c = .4040 : 1

: .3445 and 0=86° 03'. Its white crystals are usually tabular parallel

to 00 P 00 (010) and are twinned, with 00 P «> (100) the twinning plane.

Their cleavage is parallel to 00 Pod (010) and their density is 4.15.

H=2.5. The mineral is an electrical nonconductor.

Valentinite (Sb20s) is apparently orthorhombic bipyramidal (pos-
sibly monoclinic prismatic) with a : b : £=.3914 : 1 : .3367. Its crystals
are tabular or columnar in habit and are very complex. The mineral is
found also in radial groups of acicular crystals and in granular and
dense masses. Its color is white, pink, gray or brown, and streak
white. Its density is 5.77 and hardness 2.5-3. It *s insoluble in HC1.
It is a nonconductor of electricity.

CORUNDUM GROUP

The sesquioxides of aluminium and iron constitute an isomorphous
group crystallizing in the rhombohedral division of the hexagonal sys-
tem (ditrigonal scalenohedral class). Both the aluminium and iron
compounds, corundum and hematite, are of great economic importance.

OXIDES 163

Hematite (Fe20a)

Hematite is one of the most important minerals, if not the most
important one, from the economic standpoint, since it is the most val-
uable of all the iron ores. It is known by its dark color and its red
powder. It occurs in black, glistening crystals, in yellow, brown or red
earthy masses, in granular and micaceous aggregates and in botryoidal
and stalactitic forms.

Chemically, the mineral is Fe20s corresponding to 30 per cent O and
70 per cent Fe. In addition to these constituents, hematite often con-
tains some magnesium and some titanium. By increase in the latter
element it passes into a mineral which has not been distinguished from
ilmenite (see p. 462).

The habit of hematite crystals is nearly always rhombohedral.

Fig. 6$. — Hematite Crystals with R, 10T1 (r); |p2f 2243 (*); JR 10T4 (u); 00 P2,

1 1 20 (a) and oR, 0001 (c).

Their axial ratio is a: c=i : 1.3658, and the predominant forms are
R(ioTi), iR(iol4), |P2(2243), the prisms ooP(ioTo)and <x>P2(ii2o)
and often the basal plane (Fig. 65). In addition, about no other forms
have been identified. The crystals are often tabular, and sometimes
are grouped into aggregates resembling rosettes. In many cases the
terminal faces are rounded. A parting is often observed parallel to
the basal plane, due to the occunence of the mineral in aggregates in
which each crystal is tabular.

Hematite has no well defined cleavage. Its fracture is conchoidal or
earthy. Its crystals are black, glistening and opaque, except in very
small splinters. These are red and transparent or translucent. Earthy
varieties are red. The streak of all varieties is brownish red or cherry-
red. The hardness of the crystallized hematite is 5.5-6.5 and its density
about 5.2. It is a good conductor of electricity. Its refractive indices
are: (0=3.22, €=2.94 for yellow light.

The mineral is infusible before the blowpipe. In the reducing flame
on charcoal it becomes magnetic, and when heated with soda it is reduced
to a magnetic metallic powder. It is soluble in strong hydrochloric acid.

154 DESCRIPTIVE MINERALOGY

The crystalline and earthy aggregates of hematite to which distinct
names have been given are:

Specular, when the aggregate consists of grains with a glistening,
metallic luster, like the luster of the crystals. When the grains are thin
tabular the aggregate is said to be micaceous.

Columnar or fibrous, when in fibrous masses. The color is usually
brownish red and the luster dull. The botryoidal, stalactic and various
imitative forms belong here. Red hematite is a compact red variety in
which the fibrous structure is not very pronounced.

Red ocher is a red earthy hematite mixed with more or less clay and
other impurities.

Clay ironstone is a hard brownish or reddish variety with a dull luster.
It is usually a mixture of hematite with sand or clay.

Oolitic ore is a red variety composed of compacted spherical or nearly
spherical grains that have a concentric structure.

Fossil ore differs from oolitic ere mainly in the fact that there are
present in it small shells and fragments of shells that are now composed
entirely of hematite.

Mar tile is a pseudomorph of hematite after magnetite.

Hematite is distinguished from all other minerals by its red powder
and its magnetism after roasting.

Syntheses. — Crystals of hematite are obtained by the action of steam
on ferric chloride at red heat; by heating ferric hydroxide with water
containing a trace of NH4F to 2500 in a closed tube, and by cooling a
solution of Fe2<33 in molten borax or halite.

Occurrence and Origin. — Hematite is found in beds with rocks of
nearly all ages. It occurs also as a deposit on the bottoms of marshy
ponds, and in small grains in the rocks around volcanic vents. The
crystallized variety is often deposited on the sides of clefts in rocks near
volcanoes and on the sides of certain veins. It is produced by sublima-
tion, by sedimentation and by metasomatic processes.

Localities. — Handsome crystals occur on the island of Elba; near
Limoges in France; in and on the lavas of Vesuvius and Etna; at many
places in Switzerland, Sweden, etc., and at many in the United States.

Beds of great economic importance occur in the Gogebic, Menominee
and Marquette districts in Michigan; in the Mesabe and Vermilion
districts in Minnesota; in the Pilot Knob and Iron Mountain districts
in Missouri, and in the southern Appalachians, especially in Alabama.

Uses. — In addition to its use as an ore the fibrous variety of hematite
is sometimes cut into balls and cubes to be worn as jewelry. The earthy
varieties are ground and employed in the manufacture of a dark red

OXIDES 155

paint such as is used on freight cars, and the powder of some of the mass-
ive forms is used as a polishing powder.

Production. — Most of the iron ore produced in the United States is
hematite, and by far the greater proportion of it comes from the Lake
Superior region. The statistics for 191 2 follow:

Quantity (in Long Tons) of Iron Ore Mined in the Several Lead-
ing States During 1912

Hematite Other Iron Ores Total

Minnesota 34,431,000 34431,000

Michigan 11,191,000 11,191,000

Alabama 3,814,000 749,ooo 4,563,000

New York 106,327 1,110,000 1,216,327

Wisconsin 860,000 860,000

Tennessee 246,000 171,000 417,000

Total in U. S 51,345,782 3,804,365 55,i5o,i47

The total production in 191 2 was valued at about $104,000,000.

Corundum (AI2O3)

Corundum is the hardest mineral known, with the exception of dia-
mond. In consequence of its great hardness an impure variety is used
as an abrading agent under the name of emery. It is also one of the
most valuable of the gem minerals. It occurs as crystals and in granular
masses.

The mineral is nearly always a practically pure oxide of aluminium of
the composition AI2O3, in which there are 52.9 per cent Al and 47.1 per
cent O. The impure varieties usually contain some iron, mainly as an
admixture in the form of magnetite.

The axial ratio of corundum crystals is 1 : 1.36. The forms are
usually simple pyramids, among which ^2(2243) an^ 1^2(4483)
are the most common (Fig. 66), and the prism 00 P2(ii2o). The basal
plane is also common (Fig. 67). Many crystals consist of a series of
steep prisms and the basal plane, with a habit that may be described as
barrel-shaped (Fig. 68). The crystals are often rough with rounded
edges. The prismatic and pyramidal faces are usually striated hori-
zontally, and the basal plane by lines radiating from the center.

All corundum crystals are characterized by a parting parallel to the
basal plane, and often by a cleavage parallel to the rhombohedron, due
to the presence of lamellae twinned parallel to R(ioTi). The fracture
of the mineral is conchoidal or uneven. Its density is about 4 and its

156

DESCRIPTIVE MINERALOGY

hardness 9. The mineral possesses a vitreous to adamantine luster. It
is transparent or translucent. Its streak is uncolored. Its color varies
from white, through gray to various shades of red, yellow, or blue.
The blue varieties are pleochroic in blue and greenish blue shades. The
mineral is a nonconductor of electricity. Its refractive indices for
yellow light are: «= 1.7690, *= 1.7598.

Three varieties of corundum are recognized in the arts: Sapphire,
corundum and emery.

Sapphire is the generic name for the finely colored, transparent or
translucent varieties that are used as gems, watch jewels, meter bearings,
etc. The sapphires are divided by the jewelers into sapphires, possessing

Fig. 66.

Fig. 67.

Fig. 68.

Fig. 66. — Corundum Crystal with jP2, 4483 (v).

Fig. 67. — Corundum Crystal with R, 10T1 (r); 00 P2, 1120 (a), and oR, 0001 (c).

Fig. 68.— Corundum Crystal. Form a, v and c as in previous figures. Also {P2,

2243 (») and — 2R, 0221 (j).

a blue color, rubies, possessing a red shade, Oriental topazes, Oriental
emeralds and Oriental amethysts having respectively yellow, green and
purple tints.

Corundum is the name given to dull colored varieties that are ground
and used as polishing and cutting materials.

Emery is an impure granular corundum, or a mixture of corundum
with magnetite (Fe304) and other dark colored minerals. Emery, like
corundum, is used, as an abrasive. It is less valuable than corundum
powder because it contains a large proportion of comparatively soft
material.

Powdered corundum when heated for a long time with a few drops of
cobalt nitrate solution assumes a blue color. The mineral gives no
definite reaction with the beads It is infusible and insoluble. It is

OXIDES 157

most easily recognized by its hardness. The mineral alters to spinel
(p. 196) and to fibrous and platy aluminous silicates.

Syntheses. — Corundum crystals have been produced artificially in
many different ways, but only recently has the manufacture of the gem
variety been accomplished on a commercial scale. Amorphous AI2C3
dissolves in melted sodium sulphide and crystallizes from the glowing
mass at a red heat. By melting AI2Q3 in a mass of some fluoride and
potassium carbonate containing a little chromium, and using compara-
tively large quantities of material, violet and blue rubies were obtained
by Fremy and Verneuil. Rubies are also produced by melting AI2O3
and a little Cr203 for several minutes at a temperature of 22500 C. in
an electric oven.

In recent years reconstructed rubies have become a recognized article
of commerce. These are crystalline drops of ruby material made by
melting tiny splinters and crystals of the mineral in an electric arc.

Alundum is an artificial corundum made by subjecting the aluminium
hydroxide, bauxite, to an intense heat (5ooo°-6ooo°) in an electric
furnace.

Occurrence and Origin. — Corundum usually occupies veins in crys-
talline rocks or is embedded in basic intrusive rocks and in granular
limestone. The sapphire varieties are also often found as partially
rounded crystals in the sands of brook beds. The varieties found in
igneous rocks are primary crystallizations from the magmas producing
the rocks. The varieties in limestones are the result of metamorphic
processes.

Localities. — Sapphires are obtained mainly from the limestone of
Upper Burma. They are known also to occur in Afghanistan, in Kash-
mir and in Ceylon. They are occasionally found in the diamond-bearing
gravels of New South Wales and in the bed of the Missouri River, near
Helena, Montana. In the United States sapphire is mined near the
Judith River in Fergus Co., and in Rock Creek in Granite Co., Mont.,
where it occurs in a dike of the dark igneous rock known as monchiquite,
and is washed from the placers of three streams in the same State. The
only southern mines that have produced gem material are at Franklin
and Culsagee, N. C, and from these not any great quantity of stones of
gem quality have been taken.

The largest sapphire crystal ever found was taken, however, from
one of them. It weighs 312 lb., is blue, but opaque. From one of
these mines, also, came the finest specimen cf green sapphire (Oriental
emerald) ever found.

Corundum in commercial quantities occurs on the coast of Malabar,

158 DESCRIPTIVE MINERALOGY

in Siam, near Canton, China, and in southeastern Ontario, Canada.
Emery is obtained from several of the Grecian Islands, more particularly
Naxos, and from Asia Minor. It is mined in the United States at Chester,
Mass., and at Peekskill, N. Y. Crystallized corundum occurs near
Litchfield, Conn.; at Greenwood, Maine; at Warwick and Amity, N. Y. ;
at Mineral Hill, Penn.; in Patrick Co., Va.; at Corundum Hill and at
Laurel Creek, Macon Co., N. C, and at various points in Georgia, at
ail of which places it has been mined. In all the localities within the
United States the corundum occurs on the peripheries of masses of
peridotite (olivine rocks).

Uses. — Corundum, emery and alundum, after crushing and washing,
are used as abrasives and in the manufacture of cutting wheels.

Production. — The amount of sapphire produced in the United States
in 191 2 was valued at $195,505. Most of it was used for mechanical
purposes, but 384,000 carats were used as gem material.

Most of the corundum used in the United States is imported from
Canada, where it occurs in Haliburton, Renfrew and neighboring coun-
ties in Ontario, as crystals scattered through the coarse-grained crys-
talline rocks known as syenite, nepheline syenite and anorthosite.

Most of the emery is also imported. Only 992 tons with a value
of $6,652 were mined in 191 2. The imports of corundum and emery
were valued at $501,725, but the importation of these substances is
gradually diminishing because of the rapid increase in the amounts
of alundum and carborundum manufactured. In 191 2 the production
of alundum reached 13,300.000 lb. valued at $796,000,

THE DIOXIDES

THE NONMETALLIC DIOXIDES

There are but few dioxides of the nonmetals that occur as minerals,
and only one of these, quartz, is abundant.

SILICA GROUP

Silica (Si02) occurs in nature in four or five important modifica-
tions as follows:

a Quartz, trigonal-trapezohedral class, below 5750.

j8 Quartz, hexagonal-trapezohedral class, above 575 ° and below 8700.

Tridymite, rhombic bipyramidal, pseudohexagonal habit. Hex-
agonal above 1170.

Cristobalite, tetragonal system, pseudocubic habit. Isometric above
1400.

OXIDES

159

Chalcedony is regarded by many mineralogists as a form of quartz,
but its index of refraction for red light is »= 1.537, which is noticeably
lower than that of either ray in quartz, which is u= 1.5390, €=1.5480
for the same color. Its hardness also is a little less than that of quartz.
Some mineralogists believe that all of these properties may be explained
on the assumption that the mineral is a mass of fine quartz fibers, perhaps
mixed with other substances, but those who have investigated it by
high temperature methods are inclined to regard it as a distinct mineral.

Quartz (Si02)

Quartz vies with calcite for the commanding position among the
minerals. It is very abundant, and appears under a great variety of

Fig. 69.

Fig. 70.

Fig. 69.— Quartz Crystal Exhibiting Rhombohedral Symmetry. R, ion (r); — R,

01T1 (2) and °°R, 10T0 (m). "»

Fig. 70. — Ideal (A) and Distorted (B) Quartz Crystals Bounded by same Forms as

in Fig. 69.

forms. Often it occurs in distinct crystals. At other times it appears
as grains without distinct crystal forms, and again it constitutes great
massive deposits.

Pure quartz consists of 46.7 per cent Si and 53.3 per cent O. Mass-
ive varieties often contain, in addition, some opal (Si(OH)4), and traces
of iron, calcite (CaCOs), clay, and other impurities.

The crystallization of quartz is in the trapezohedral tetartohedral
division of the hexagonal system (trigonal-trapezohedral class), at tem-
peratures below 5750. When formed above this temperature its sym-
metry is hexagonal trapezohedral (hemihedral). The former is known as
a quartz, and the latter as 0 quartz. They readily pass one into the
other at the stated temperature. The axial ratio is 1 : i.x. The prin-

- - - 2P2 _
cipal forms observed are +R(ioii), — R(oni), 00 R(ioio), (1121),

160 DESCRIPTIVE MINERALOGY

6P(

— -=<5i5i) (Fig- 74) and a series of steep rhombohedrons and trapezo-

hedrons. Although these may all be tetartohedral since ibe geometrical

Fig. 71. — Etch Figures on Two Quartz Crystals of the Same Form, Illustrating Dif-
ferences in Symmetry. A. Right- Hand Crystal. B. Left -Hand Crystal.
(Afltr Ptnfidd.)

Fie. 72. — Group of Quartz Crystals with Distorted Rhombohedral Faces. {Foote
Mineral Company.)

forms of the first four are not distinguishable from the corresponding
hemihedral ones, the crystals possess a rhombohedral symmetry (Fig.
69). The angle 10T1 a ^toi = 85° 46'.

OXIDES

161

. Often the +R and the — R faces are equally developed so that they
appear to belong to the hexagonal pyramid P (Fig. 70A). Their true
character, however, is clearly brought out by etching, when figures are
produced on the +R and the — R that are differently situated with
respect to the edges of the faces (Fig. 71). On the other hand, on many
crystals some of the R faces are very much enlarged at the expense of
the others (Fig. 7a).

The crystals are commonly prismatic. Often they are so dis-

Fig. 73.

Fig. ;

Fig. 73. — Taperini; Quartz Crystal with Rhombohcdral Symmetry. A Combination

of f , e, m and Two Steep Rhombohedrons. B. Cross-section near Top.
Fig. 74.— Quartz Crystals Containing °oR, 10T0 (m); R, 10T1 (r); -R, 01T1 (i);

on B.

1 (f);

torted that it is difficult to detect the position of the c axis (Fig.
70B). The striations on 00 R{ioTo) are, however, always parallel to
the edges between R and 00 R. When these are sharply marked the
position of the vertical axis is easily recognized. Many crystals
taper sharply toward the ends of the c axis. This tapering is due to
oscillatory combination of the prism 00 R with rhombohedrons
(Fig. 73).

The habits of the crystals vary with the crystallization of the quartz.
On crystals of the 0 phase the +R and — R faces are equally developed
and trigonal trapezohedrons are absent. The crystals are hexagonal in

162

DESCRIPTIVE MINERALOGY

habit. Crystals of the a phase usually exhibit marked differences in

the size and character of the rhombohedral planes; and trigonal trape-

zohedrons may be present on them. Such crystals are usually trigonal

in habit and prismatic.

2P2 _

The small (n 21) faces on all types of crystals (Fig. 74) are

always striated parallel to the edge between this plane and +R. By

their aid the +R can always be distinguished from the — R. This is a

matter of some practical importance since plates cut from quartz crystals

possess the power of rotating a ray of polarized light. The plates cut

Fig. 75. — Supplementary Twins of Quartz.

C is a combination of A and B in Fig. 74 twinned about 00 P2(ii2o). This is
known as the Brazil law.

D is a combination of two crystals like B twinned about c as the twinning axis.
One is revolved 6o° with reference to the others, thus causing the r and z faces to
fall together. Swiss law. E is a twin like D, showing portions of planes belonging
to each individual. It contains also the form s.

from some crystals turn the ray to the right; those cut from others turn

it to the left. Crystals that produce plates of the first kind are known

as right-handed crystals; those that produce plates of the second kind as

left-handed crystals. Since this property of quartz plates is employed

in the construction of optical instruments for use in the detection of

sugars and certain other substances in solution it is important to be

able to distinguish those crystals that will yield right-handed plates from

those that will yield left-handed ones. Observation has shown that

2P2 _

when the (n 21) faces are in the upper right-hand corner of the 00 R

plane immediately beneath +R the crystal is right-handed. When

these faces are in the upper left-hand corner of this 00 R plane the crystal

I nterpenet ration twins of quartz are so common that few crystals
can be observed that do not exhibit some evidence of twinning (Fig. 75).
The twinning plane is « R, so that the c axes in the twinned individuals
are parallel and, indeed, often coincident. The R faces and the 00 R
faces practically coincide in the twinned parts so that the crystals
resemble untwinned ones. The twinning is exhibited by dull areas of
— R on bright areas of +R faces and by breaks in the continuity of the
striations on 00 R.

Other twinning laws have also been observed in quartz, but their
discussion as well as the more complete discussion of the mineral's
crystallization must be left for larger treatises. In the most common of
these other laws the individuals are twinned about
Pa(n«). See Fig. 76.

The fracture of quartz is conchoidal. Its hard-
ness is 7 and density 2.65. Its luster is vitreous, or
sometimes greasy. Pure specimens are transparent
or colorless, but most varieties are colored by the
addition of pigments or impurities. When the
coloring matter is opaque it may be present in

sufficient quantity to render the mineral also opaque. _ , _

7. , , . . . , , Fie. ;6.— Quart).

The streak is colorless in pure varieties, and of some jwinne^ about
pale shade in colored varieties. The mineral is pyro- Pi(u5j).
electric and circularly polarizing as described above.
It is an electric insulator at ordinary temperatures. Its refractive
indices for yellow light are: w= 1.5443. *= 1-5534-

Quartz resists most of the chemical agents except the alkalies. It
dissolves in fused sodium carbonate and in solutions of the caustic
alkalies. It is also soluble in HF and to a very slight degree in water,
especially in water containing small quantities of certain salts. When
heated to 575° the a variety passes into the 0 variety; at 8700 both
varieties pass into tridymite, and at 14700 the tridymite passes over into
cristobalite. Gradual fusion occurs just below 1470°.

The varieties of quartz have received many different names depend-
ing largely upon their color and the uses to which they are put. They
may be grouped for convenience into crystallized and crystalline vari-
eties.

The principal crystallized varieties are:

164 DESCRIPTIVE MINERALOGY

Rock crystal, the colorless, transparent variety, that often forms
distinct crystals. This is the variety that is used in optical instruments.
It includes the Lake George diamonds, rhinestones and Brazilian peb-
bles.

Amethyst, the violet-colored transparent variety.

Rose quartz, the rose-colored transparent variety.

Citrine ox false topaz, a yellow and pellucid kind.

Smoky quartz or Cairngorm stone, a smoky yellow or smoky brown
variety that is often transparent or translucent, but sometimes almost
opaque.

The last four varieties are used as gems, the Cairngorm stone being a
popular stone for mourning jewelry.

Milky quartz is the white, translucent or opaque variety such as so
commonly forms the gangue in mineral veins and the material of " quartz
veins."

Sagenite is rock crystal including acicular crystals of rutile (Ti02).

Aventurine is rock crystal spangled with scales of some micaceous
mineral.

The principal crystalline varieties are:

Chalcedony, a very finely fibrous, transparent or translucent waxy-
looking quartz that forms mamillary or botryoidal masses. Its color is
white, gray, blue or some other delicate shade. The water that is always
present in it is believed to be held between the minute fibers, and not to
be combined with the silica (see also p. 159).

Carnelian is the name given to a clear red or brown chalcedony.

Chrysoprase is an apple-green chalcedony.

Prase is a dull leek- green variety that is translucent.

Plasma differs from prase in having a brighter green color and in
being translucent.

Heliotrope, or bloodstone, is a plasma dotted with red spots of jasper.

All of the colored chalcedonies are used as gems or as ornamental
stones.

Agate is a chalcedony, or a mixture of quartz and chalcedony, varie-
gated in color. The commonest agates have the colors arranged in
bands, but there are others, like " fortification agate " in which the
colors are irregularly distributed, and still others in which the variation
in color is due to visible inclusions, as in " moss-agates.' ' The different
bands in banded agates often differ in porosity. This property is taken
advantage of to intensify the contrast in their colors. The agate is
soaked in oil, or in some other substance, and is then treated with chem-
icals that act upon the material absorbed by it. Those bands which

OXIDES 165

have absorbed the greater quantity of this material become darker in
color than those that have absorbed less.

Onyx is a very evenly banded agate in which there is a marked con-
trast in colors. Cameos are onyxes in one band of which figures are cut,
leaving another band to form a background.

Sardonyx is an onyx in which some of the bands consist of carnelian.
It is usually red and white.

Flint, jasper, hornstone and touchstone are very fine grained crystalline
aggregates of gray, red or nearly black mixture of opal, chalcedony and
quartz. They are more properly rocks than minerals. Chert is an im-
pure flint.

Sandstone is a rock composed of sand grains, most of which are
quartz, cemented by clay, calcite or some other substance. When the
cement is quartz the rock is a quartzite. Oilstones, honestones and some
whetstones are cryptocrystalline aggregates of quartz, very dense and
homogeneous, except for tiny rhombohedral cavities that are thought to
have resulted from the solution of crystals of calcite. They are gener-
ally believed to be beds of metamorphosed chert.

Syntheses.— Crystallized quartz has been made in a number of ways
both from superheated aqueous solutions and from molten magmas.
Crystals have been produced by the action of water containing am-
monium fluoride upon powdered glass and upon amorphous Si02, and
by heating water in a closed glass tube to high temperatures. The
separation of crystals from molten magmas is facilitated by the addition
of small quantities of a fluoride or of tungsten compounds.

Occurrence and Origin. — Quartz occurs as an essential constituent of
many crystalline rocks such as granite, gneiss, etc., and as the almost sole
component of certain sandstones. It constitutes the greater portion of
most sands and the material of many veins. It also occurs as pseudo-
morphs after shells and other organic bodies embedded in rocks, having
replaced the original substance of which these bodies were composed.
It is also one of the decomposition products of many silicates. It may
thus be primary or secondary in origin. It may result from igneous or
aqueous processes, or it may be a sublimation product.

Localities. — Quartz is so widely spread in its distribution that only a
very few of its most interesting localities can be referred to in this place.

The finest specimens of rock crystals come from Dauphin6, France;
Carrara, in Tuscany; the Piedmont district, in Italy; and in the United
States from Middleville, and Little Falls, N. Y.; the Hot Springs,
Ark., and from several places in Alexander Co., N. C. Smoky quartz
is found in good crystals in Scotland; at Paris, Me.; in Alexander

166 DESCRIPTIVE MINERALOGY

♦

Co., N. C, and in the Pike's Peak region of Colorado. The handsomest
amethysts come from Ceylon, Persia, Brazil, Nova Scotia and the
country around Lake Superior. Rose quartz occurs in large quantity
at Hebron, Paris, Albany and Georgetown, Me.

Fine agates and carnelians are brought from Arabia, India and Brazil.
They are abundant in the gravels of Agate Bay and of other bays and
coves on the north shore of Lake Superior.

Chalcedony is abundant in the rocks of Iceland and the Faroe Islands,
in those on the northwest side of Lake Superior, and in the gravels of
the Columbia, the Mississippi and other western rivers.

The other valuable varieties of the mineral occur largely in the Far
East.

Agatized, or silicified, wood of great beauty exists in enormous quan-
tity in an old petrified forest near Corrizo, Aiiz. It is also found in
the Yellowstone Park; near Florissant, Colo., and in other places in the
Far West. This wood has had all of its organic matter replaced mole-
cule for molecule by quartz in such a manner that its original structure
has been perfectly preserved.

Uses. — Rock crystal is used more or less extensively in the construc-
tion of optical instruments and in the manufacture of cheap jewelry.
Smoky quartz, amethyst, onyx, carnelian and heliotrope stones are
used as gems, and agate, prase, chrysoprase and rose quartz as orna-
mental stones.

Milky quartz, ground to coarse powder, is employed in the manu-
facture of sandpaper. Its most extensive use, however, is in the man-
ufacture of glass and pottery. Earthenware, porcelain and some other
varieties of potter's ware are vitrified mixtures of clay and ground
quartz, technically known as "flint." Ordinary glass is a silicate of
calcium or lead and the alkalies, sodium or potash. It is made by
melting together soda, potash, lime or lead oxide and ground quartz or
quartz sand, and coloring with some metallic salt. A pure quartz glass
is now being made for chemical uses by melting pure quartz sand.

Quartz is sometimes used as a flux in smelting operations. In the
form of sandstone, it is used as a building stone, and in the form of sand
it is employed in various building operations. Bricks cut from dense
quartzites (very hard and compact sandstones) are often employed
for lining furnaces.

The uses of honestones, oilstones, and whetstones are indicated by
their names.

Production. — Many varieties of quartz are produced in the United
States to serve various uses. Vein quartz is crushed and employed

OXIDES 167

in the manufacture of wood filler, paints, pottery, scouring soaps, sand-
paper and abrasives. It is also used in making ferro-silicon, chemical
ware, pottery, sand-lime brick, quartz glass, etc. The total quantity
produced for these purposes in 191 2 was 97,874 tons, valued at
$191,685.

The largest quantity of quartz produced is in the form of sand, of
which 38,600,000 tons were marketed in 1912 at a valuation of $15,300,-
000. Sandstone, valued at $6,900,000, was quarried for building and
paving purposes. Oilstones, grindstones, millstones, etc., which are
made from special varieties of sandstone, were produced to the value of
$1,220,000.

Gem quartz obtained in 191 2 was valued at about $22,000. This
comprised petrified wood, chrysoprase, agate, amethyst, rock crystal,
smoky quartz, rose quartz, and gold quartz (white quartz containing
particles of gold).

THE METALLIC DIOXIDES

The metallic dioxides include the oxides of tin, titanium, manganese
and lead. Of these the manganese dioxide may be dimorphous, and the
titanium dioxide is trimorphous. A dioxide of zirconium is also known,
badddeyite, but it is extremely rare. The mineral zircon (ZrSiOO is
often regarded as being isomorphous with cassUerite (Sn02) and rutile
(Ti02) because of the similarity in the crystallization of the three min-
erals. The three, therefore, are placed in the same group, in which
case all must be regarded as salts of metallic acids, thus: Ti02 = TiTiO*,
Sn02=SnSn04, zircon =ZrSi04. Other authorities regard zircon as an
isomorphous mixture of Ti02 and Si02. In this book zircon is placed
with the silicates and the other minerals are considered as oxides.

The two manganese dioxides are polianUe and pyrolusite. The former
is tetragonal and the latter orthorhombic. It is possible, however, that
the crystals of pyrolusite are pseudomorphs and that the substance is a
mixture of polianite and some hydroxide, as it nearly always contains
about 2 per cent H2O.

The three titanium oxides are rutile, which is tetragonal; brookite,
which is orthorhombic, and analase or octahedrite, which is tetragonal.
Although rutile and anatase crystallize in the same system, their axial
ratios are different, as are also their crystal habits and their physical
properties. A few of these differences are indicated below:

Rutile a : c=i : .6439; Sp. Gr. =4.283; 00^=2.6158; em— 2.9029.
Anatase =1:1.7771; Sp. Gr. =3.9 ; a>,,a=2.56i8; €«*= 2.4886.

168 DESCRIPTIVE MINERALOGY

Of the three modifications of titanium dioxide, anatase may be
made at a comparatively low temperature. Brookite requires a higher
temperature for its production, but rutile is producible at both high
and low temperatures. Under the conditions of nature both brookite
and anatase pass readily into rutile.

Of the seven dioxides discussed, four are members of a single group.

RUTILE GROUP

The rutile group consists of four minerals apparently completely
isomorphous, though no mixed crystals of any two have been discovered.1
All crystallize in the tetragonal system (ditetragonal bipyramidal class),
with the same forms and with closely corresponding axial ratios. The
names of the members of the group and their axial ratios follow:

Cassiterile (Sn02) ale = i : .6726

Rutile (Ti02) = 1 : .6439

Polianite (Mn02) =1 • .6647

PlattnerUe (PbOa) - 1 : .6764

Cassiterite (S11O2)

Cassiterite, or tinstone, is the only worked ore of tin. It occurs as
rolled pebbles of a dark brown color in the beds of streams, as fibrous
aggregates, and as glistening black crystals associated with other min-
erals in veins.

The analyses of cassiterite indicate it to be essentially an oxide of
tin, or, possibly, a stanyl stannate ((SnO)Sn03), with the composition,
Sn=78.6 per cent; 0=21.4 per cent. The mineral nearly always con-
tains some iron oxide and often oxides of tantalum, of zinc or of arsenic.
The presence of iron and tantalum is so general that most crystals of
cassiterite may be regarded as isomorphous mixtures of (SnO)(Sn03),
Fe(SnOs) and Fe(Ta03)2. Thus, a crystal from the Etta Mine in the
Black Hills, S. D., gave Sn02=9436; FeO=i.62; Ta205=2.42 and
Si02=i.oo, indicating a mixture of 5 pts. of Fe(Ta03)2, 18 pts. of
Fe(Sn03) and 303.5 pts. of (SnO)(Sn03).

The crystals of cassiterite have an axial ratio of 1 : .6726. They are
usually short prisms in habit. They often consist of the simple com-
bination P(ni) and P 00(101) (Fig. 77), or of these forms, together
with 3PI (321) and various prisms (Fig. 78). Twins are common, the

1 An isomorphous mixture of the rutile and cassiterite molecules has recently
been described from Greifenstein, Austria, but its existence has not yet been con-
firmed.

OXIDES 169

twinning plane being P oo (101). When the individuals twinned have
small prismatic faces the resulting combination is often called a visor
twin (Fig. 79), because of its supposed resemblance to the visor of a
helmet. By repetition of the twinning very complex groupings are
produced. The angle m A * ■' ™ 5&° i*)'-

Fio. 77.
Fio. 77.— Cassiterite Crystal with P,
Fio. 7S. — Cassiterite Crystal with s, t and « P, 1 1

Fig. 78.
(1) and P « , 101 («).

k>W; JP|,3«M.

(m)

The cleavage of cassiterite is imperfect parallel to on p 00 (100) and
P(m). Its fracture is uneven. The color of the massive mineral is
some dark shade of brown by reflected light, and of the crystals black.
By transmitted light, the mineral is brown or black. Its luster is very
brilliant, and its streak is white, gray or brown. The purest specimens

Fig. 79. — Cassiterite Twinned about P

Visor Twin.

are nearly transparent, though the ordinary varieties are opaque. Their
hardness is about 6.5 and density about 7. The mineral is a noncon-
ductor of electricity. Its refractive indices for yellow light are: «= 1.9965,
(=2.0931.

Three varieties of cassiterite are recognized, distinguished by physical
characteristics. The ordinary variety known as tinstone is crystallized

170 DESCRIPTIVE MINERALOGY

or massive. Wood tin is a botryoidal or reniform variety, concentric in
structure and composed of radiating fibers. The third variety is stream
tin. This consists of water-worn pebbles found in the beds of streams
that flow over cassiterite-bearing rocks.

Cassiterite is only slightly acted upon by acids. It may be reduced
to a metallic globule of tin only with difficulty, even when mixed
with sodium carbonate and heated intensely on charcoal. With
borax it yields slight reactions for iron, manganese or other impurities.
When placed in dilute hydrochloric acid with pieces of granulated zinc,
fragments of cassiterite become covered with a dull gray coating of
metallic tin which can be burnished by rubbing with a cloth or the hand.
When rubbed by the hand the odor of tin in contact with flesh is easily
detected.

The mineral is most easily distinguished from other compounds that
resemble it in appearance by its high density and its inertness when
treated with reagents or before the blowpipe.

Syntheses. — Crystals of cassiterite have been obtained by passing
steam and vapor of tin chloride or tin fluoride through red-hot porcelain
tubes, and by the action of tin chloride vapor upon lime.

Occurrence and Origin. — Tinstone is found as a primary mineral in
coarse granite veins with topaz, tourmaline, fluorite, apatite and a great
number of other minerals. It also occurs impregnating rocks, sometimes
replacing the minerals of which they originally consisted. In these
cases it is the product of pneumatolytic processes. In many places it
constitutes a large proportion of the gravel in the beds of streams.

Localities and Production. — The crystallized mineral occurs at many
places in Bohemia and in Saxony, at Limoges in France and sparingly
in a few places in the United States, especially near El Paso, Texas,
in Cherokee Co., N. C, in Lincoln Co., S. C, and near Hill City, S. D.
Massive tinstone and stream tin occur in laige enough quantities to be
mined in Cornwall, England; on the Malay Peninsula and on the islands
lying off its extremity; in Tasmania; in New South Wales, Victoria
and Queensland, Australia; in the gold regions of Bolivia; at Durango
in Mexico, and at various points in Alaska, at some of which there
are 400 lb. of cassiterite in a cubic yard of gravel.

The principal tin ore-producing regions of the world are the Straits
district, including the Malay Peninsula and the islands of the Malay
Archipelago; Australia; Cornwall, England; the Dutch East Indies, and
Bolivia. Of the total output of 122,752 tons of tin produced in 1911,
61,712 tons were made from the Straits ore, 25,312 tons from the ore
produced in Bolivia and 16,800 tons from Banka ore. Of the total

OXIDES 171

quantity of tin produced about 78 per cent is said to come from stream
tin and 22 per cent from ore obtained from veins. The quantity
obtained from ore mined in the United States in 191 1 included 61 tons
from Alaskan stream tin and two tons from the tinstone mined in the
Franklin Mountains near El Paso, Texas. Mines have been opened in
San Bernardino Co., California, and in the Black Hills, South Dakota,
but they have not proved successful. The mines at El Paso, Texas, are
not yet fully developed, although they promise to be profitable in the
near future. The crystals are scattered through quartz veins and
through a pink granite near the contacts with the veins. The average
composition of the ore is 2 per cent. This is concentrated to a 60 per
cent ore before being smelted. The production during 1912 was 130
tons of stream tin from Buck Creek, Alaska. This was valued at
$124,800. In the following year 3 tons of cassiterite were shipped from
Gaffney, S. C. The imports of tin into the United States during 191 1
were 53,527 tons valued at more than $43,300,000.

Extraction. — The tin is extracted from the concentrated ore by the
simple process of reduction. Alternate layers of the ore and charcoal
are heated together in a furnace, when the metal results. This collects
in the bottom of the furnace and is ladled or run out. The crude metal is
refined by remelting in special refining furnaces.

Uses of the Metal, — The metal tin is employed principally for coating
other metals, either to prevent rusting or to prevent the action upon
them of chemical reagents. Tmplate is thin sheet iron covered with
tin. Copper for culinary purposes is also often covered with this metal.
It is used also extensively in forming alloys wifj^fnpppi^ antjn)^pyj
bismuth and lead. Among the most important of these alloys are
bronze, bell metal, babbitt metal, gun metal, britannia, pewter and soft
solder. Its alloy, or amalgam,, with mercury is used in coating mirrors.
Several of its compounds also find uses in the arts. Tin oxide is an im-
portant constituent of certain enamels. The chlorides are used exten-
sively in dyeing calicoes, and the bisulphide constitutes " bronze
powder " or " mosaic gold," a powder employed for bronzing plaster,
wood and metals.

Ruffle (Ti02)

Rutile is one of the oxides of the comparatively rare element titanium.
It occurs commonly in dark brown opaque cleavable masses and in bril-
liant black crystals.

Pure rutile consists of 40 per cent O and 60 per cent Ti. Nearly all
specimens, however, contain in addition some iron, occasionally as much

172

DESCRIPTIVE MINERALOGY

as 9 per cent or 10 per cent, which is probably due to the admixture of
Fe203 and FeTiOa in solid solution.

Rutile is peifectly isomorphous with cassiterite. Its axial ratio is
i : .6439. The principal planes observed on its crystals are practically
the same as those observed on cassiterite (Fig, 80). Twins are common,
with Poo (roi) the twinning plane. (Fig. 81.) This twinning is often
repeated, producing elbow-shaped groups (Fig. 8a), or by further repe-

Fig. 80.— Rutile Crystals with «*P, ito(m); »P», 100(0); P«
« P3, 310 (0; P3, 313 CO wd 3PI. 3» W-

Fig. 8c— Rutile Eightling Twinned about P °o (101).
Fig. 81.— Rutile Twinned about P« (101). Elbow Twin.

tition wheel-shaped aggregates (Fig. 83). In another common law the
twinning plane is 3P 00 (301) (Fig. 84). The angle 111 ^ili = $6" 52J'.
The crystals are prismatic and even sometimes acicular in habit. Their
prismatic planes are vertically striated.

The cleavage of rutile is quite distinct parallel to 00 P(no) and less
so parallel to 00 P 00 (100).

The mineral is reddish brown, yellowish brown, black or bluish
brown by reflected light and sometimes deep red by transmitted light.
Many specimens are opaque but some are translucent to transparent.

OXIDES

173

The latter are often pleochroic in tints varying between yellow and
blood-red. The streak is pale brown. The hardness of the mineral is
6 to 6.5 and its density about 4.2. It is an electric nonconductor at
ordinary temperatures. Its refractive indices for yellow light are:
40=2.6030, €=2.8894.

Rutile is infusible and insoluble. Its reactions with beads of borax
and microcosmic salt are usually obscured by the iron present. When
this metal is present only in small quantities the microcosmic salt bead
is colorless while hot, but violet when cold, if it has been heated for some
time in the reducing flame of the blowpipe.

The most characteristic chemical reaction of rutile is obtained upon
fusing it with sodium carbonate on charcoal, dissolving the fused mass in

Fig. 83. Fig. 84.

Fig. 83.— Rutile Cyclic Sixling Twinned about P «> (101).

Fig, 84. — Rutile Twinned about 3P <*> (301). Elbow Twin. Forms: °o P2, 210 (A),

and Poo| 101 (<?).

an excess of hydrochloric acid and adding to the solution small scraps of
tin. Upon heating for some little time, the solution assumes a violet
color. This is a universal test for the metal titanium.

Some of the dark red and reddish brown massive varieties of rutile
may be confounded with some varieties of garnet, which, however, are
much harder. Its density, its infusibility and the reaction for titanium
serve to characterize the mineral perfectly.

Pseudomorphs of rutile after hematite and after brookite and ana-
tase have been described. It often changes into ilmenite and sphene.

Syntheses. — By the reaction between TiCU and water vapcr in a red-
hot porcelain tube, crystals of rutile are formed. Twins are produced
by submitting precipitated titanic acid in a mass of molten sodium tung-
state to a temperature of 10000 for several weeks.

Occurrence and Origin. — Rutile is often found as crystals embedded
in limestone and in the quartz or feldspar of granite and other igneous

174 DESCRIPTIVE MINERALOGY

rocks, as long acicular crystals in slates, and as grains in the rock known
as nelsonite. It occurs also as fine hair-like needles penetrating quartz,
forming the ornamental stone " fteches d'amour," and as grains in the
gold-bearing sand regions. When primary it is probably always a
product of magmatic processes, either crystallizing from a molten magma
or being the result of pneumatolysis.

Localities. — Handsome crystals of the mineral occur at Arendal, in
Norway; in Tyrol, and at St. Gothard and in the Binnenthal, Switzer-
land. In the United States large crystals have been obtained at Barre,
Mass.; at Sudbury, Chester Co., Penn.; at Stony Point, Alexander Co.,
N. C; at Graves Mt., in Georgia; at Magnet Cove, in Arkansas, and
in Nelson Co., Va. In the latter place it occurs in large quantity as
crystals disseminated through a coarse granite rock. The rock con-
taining about 10 per cent of rutile is mined as an ore. It constitutes the
principal source of the mineral in the United States. A second type
of occurrence in the same locality is a dike-like rock, nelsonite, composed
of ilmenite and apatite, in which the ilmenite is in places almost
completely replaced by rutile.

Uses. — The mineral is not of great economic importance. It is used
in small quantity to impart a yellow color to porcelain and to give an
ivory tint to artificial teeth. It is also used in the manufacture of the
alloy ferro-titanium which is added to steel to increase its strength.
Recently the use of titaniferous electrodes in arc lights, and the use of
titanium for filaments in incandescent lamps have been proposed. Some
of the salts of titanium are used as dyes and others as mordants. Most
of the ferro-titanium made in the United States is manufactured from
titaniferous magnetite.

Production. — The only rutile mined in the United States during 19 13
came from Roseland, Nelson Co., Virginia. It amounted to 305 tons of
concentrates containing about 82 per cent Ti02. At the same time there
were separated about 250 tons of ilmenite (see p. 462)

Polianite (MnC>2) is usually in groups of tiny parallel crystals and
as crusts of crystals enveloping crystals of manganite (MnO • OH). Their
axial ratio is 1 : .6647. The color of the mineral is iron-gray. Its streak
is black, its hardness 6-6.5 and density 4.99. It dissolves in HC1 evolv-
ing chlorine. It is distinguished from pyrdusile by its greater hardness
and its lack of water. The mineral is extremely rare, being found in
measurable crystals only at Platten in Bohemia. It occurs in pseudo-
morphs after manganite at a number of other points in- Europe and at a
few points elsewhere, but in most cases it has not been clearly distin-

OXIDES 175

guished from pyrolusite. The rarity of its crystals is regarded by some
mineralogists as being due to the fact that in most of its occurrences
polianite is colloidal (a gel).

Plattnerite (Pb02) is usually massive, but it occurs in prismatic
crystals near Mullan in Idaho. Their axial ratio is i : .6764. They are
usually bounded by 00 P 00 (100), 3P 00 (301), P 00 (101), oP (001) and
often fP(332). The mineral is found also in crusts. Its color is
iron-black and its streak chestnut-brown. Its hardness is 5-5.5 and
its density 8.6. It is brittle and is easily fusible before the blow-
pipe, giving off oxygen and coloring the flame blue. It yields a lead
bead. It is difficultly soluble in HNO3, but easily soluble in HC1 with
evolution of chlorine. Plattnerite is found at Leadhills and at Wanlock-
head, Scotland, and at the " As You Like " Mine near Mullan, Idaho.

Pyrolusite (Mn02)

Pyrolusite is often the result of the alteration of the hydroxide, man-
ganite, or of polianite. The few measurable crystals that have been
studied seem to indicate that their form is pseudomorphic after the
hydroxide. The change by which manganite may pass over into pyro-
lusite is represented by the reaction 2MnO(OH)+0=2Mn02+H20.
Pyrolusite may be, however, only a slightly hydrated form of polianite.

An analysis of a specimen from Negaunee, Mich., gave:

MnO

CaO

BaO

Si02

Limonite

H2O

Total

79.46

17.48

.18

■38

.18

•31

I.94

99*93

Pyrolusite, as usually found, is in granular or columnar masses, or in
masses of radiating fibers. It is a soft, black mineral with a hardness of
only 2 or 2.5 and a density of about 4.8. Its luster is metallic and its
streak black. It is a fairly good conductor of electricity.

The reactions of this mineral are practically the same as those of
polianite and manganite (see p. 191), except that only a small quantity
of water is obtained from it by heating. Upon strong heating it yields
oxygen, according to the equation 3Mn02=Mn3+302.

The manganese minerals are easily distinguished from other minerals
by the violet color they give to the borax bead and by the green product
obtained when they are fused with sodium carbonate. Pyrolusite is
distinguished from manganite by its physical properties, and from poli-
anite by its softness.

176 DESCRIPTIVE MINERALOGY

Localities. — Pyrolusite is worked at Elgersberg, near Iimenau in
Thuringia; at Vorder Ehrensdorf in Moravia; at Platten in Bohemia;
at Cartersville, Ga.; at Batesville, Ark., and in the Valley of Virginia.
A manganiferous silver ore containing considerable quantities of pyro-
lusite is mined in the Leadville district, Colorado, and large quan-
tities of manganiferous iron ores are obtained in the Lake Superior
region.

Uses. — Pyrolusite, together with the other manganese ores with
which it is mixed, is the source of nearly all the manganese compounds
employed in the arts. Some of the ores, moreover, are argentiferous
and others contain zinc. From these silver and zinc are extracted. The
most important use of the mineral is in the iron industry. In this indus-
try, however, much of the manganese employed is obtained from man-
ganiferous iron ores. The alloys spiegeleisen and ferro-manganese are
employed very largely in the production of an iron used in casting car
wheels. It is extremely hard and tough. The manganese minerals are
also used in glass factories to neutralize the green color imparted to glass
by the ferruginous impurities in the sands from which the glass is made.
They are also used in giving black, brown and violet colors to pottery
and some of their salts are valuable mordants. Pyrolusite, finally, is the
principal compound by the aid of which chlorine and oxygen are pro-
duced.

Production. — The United States in 191 2 produced about 1,664 tons
of manganese ores, valued at $15,723, and all came from Virginia, South
Carolina and California. In previous years the ores had been mined
also in Arkansas, Tennessee and Utah. Moreover, there were imported
into the country 300,661 tons, valued at $1,769,000. Nearly all of this
was used in the manufacture of spiegeleisen. The domestic product was
used in the chemical industries largely in the manufacture of manganese
brick. Of the manganiferous iron ores about 818,000 tons were produced
in 191 2. These were utilized mainly as ores of iron, though a large por-
tion was used as a flux. The product of manganiferous silver ores aggre-
gated about 48,600 tons, all of which was used as a flux for silver-lead
ores. Nearly all of this came from Colorado. In addition there were
imported iron-manganese alloys valued at $3,935,000.

Anatase and Brookite (Ti02)^

As has already been stated, the compound Ti02 is trimorphous, one
form being orthorhombic and the two others tetragonal. Of the latter,
one has already been described as rutile. The other is anatase, or octa-
hedrite. The orthorhombic form is known as brookite. Anatase and

OXIDES 177

rutile are separated because of the difference in their axial ratios and in
the habits of their crystals. Both are ditetragonal bipyramidal, but
a:c for rutile is i : .6439 and for anatase 1 : 1.7771. Brookite is
orthorhombic bipyramidal with alb: £=.8416 : 1 : .9444.

Both anatase and brookite have the same empirical composition,
which is similar to that of rutile.

Crystals of anatase are usually sharp pyramidal with the form P(in)
predominating (Fig. 85), blunt pyramidal with $P(ii3) or |P(ii7)
predominating (Fig. 86), or tabular parallel to oP(ooi). Twins are
common in some localities, with P 00 (101) the twinning plane. The
angle 111 A iTi = 82° 91'.

The mineral is colorless and transparent, or dark blue, yellow, brown

Fig. 85. Fig. 86.

Fig. 85. — Anatase Crystal with P, ui'(^).
Fig. 86. — Anatase Crystal with JP, 113 (s); P, in (/>); IP, 117 (»); 00 P, no (w);

00 P 00 f 100 (a) and P 00 , 101 (e).

or nearly black and almost opaque. Its streak is colorless to light
yellow. Its cleavage is perfect parallel to P and oP and its fracture
conchoidal. Its hardness is between 5 and 6 and its density is 3.9. This
increases to 4.25 upon heating to a red heat, possibly due to its partial
transformation into rutile. The mineral is insoluble in acids except
hot concentrated H2SO4. It is a nonconductor of electricity. Its
indices of refraction for yellow light are: a>= 2.5618, c= 2.4886.

Brookite crystals are usually tabular parallel to 00 P 66 (100) and
elongated in the direction of the c axis. Nearly all crystals are
striated in the vertical zone. Although many forms have been identi-
fied on them, by far the most common is P2(i22). In some cases this is
the only pyramidal form present, as in the type known as arkansite
(Fig. 87). Twins are rare, with ooP2~(2io) the twinning plane. The
angle in A ili = 64° 17'.

178

DESCRIPTIVE MINERALOGY

Brookite may be opaque, translucent or transparent. Its color
varies from yellowish brown, through brownish red, to black (arkansite).
Its streak is brownish yellow. Its cleavage is imperfect parallel to
oo Poo (101), and its fracture uneven or conchoidal. Its hardness is
5-6 and density about 4. Upon heating its density increases to that of
rutile. Its refractive indices for yellow light are: a= 2.5832, 0= 2.5856,
7= 2.7414. It fuses at about 15600, and is insoluble in acids.

The chemical properties of both brookite and anatase are similar
to those of rutile. They are distinguished from rutile by their physical
properties and their crystallization.

Both brookite and anatase alter to rutile.

Syntheses. — Upon heating TiF4 with water vapor at a temperature

Fio. 87. — Brookite Crystals with 00 P, no (m); JP, 112 (2) and PT, 122 (<?). The

combination m and e is characteristic for Arkansite.

below that of vaporizing cadmium, crystals of anatase are produced.
If the temperature is raised above the point of vaporization of cadmium
and kept below that of zinc, crystals of brookite result.

Occurrence. — Brookite and anatase occur as crystals on the walls of
clefts in crystalline silicate rocks and in weathered phases of volcanic
rocks. They are mainly pneumatolytic products, the production of the
one or the other depending upon the temperature at which the Ti(>2 was
deposited.

Localities. — Fine brookite crystals are found at St. Gothard, in
Switzerland; at Pregrattan, in the Tyrol; near Tremadoc, in Wales;
at Miask, in Russia, and at Magnet Cove, Arkansas.

Anatase crystals are less common than those of brookite but they
occur at many points in Switzerland, especially in the Binnenthal;
near Bourg d'Oisans, France; at many points in the Urals, Russia; in
the diamond fields of Brazil, and at the brookite occurrences in Arkansas.

CHAPTER VIII
THE HYDROXIDES

The hydroxides, as has already been explained, may be looked upon
as derivatives of water, in which only a portion of the hydrogen has been
replaced. The group includes several minerals of economic importance,
among which is the fine gem mineral opal. All the hydroxides yield
water when heated in a glass tube, but they do not yield it as readily as
do salts containing water of crystallization.

A few of the hydroxides may act as acids forming salts with metals.
Diaspore, for instance, is an hydroxide of aluminium AlO-OH, or

/O— H

A1C , which appears to be able to form salts; at least, the chemical

composition of some of the members of an important group of minerals,
the spinels, may be explained by regarding them as salts of this acid
(see p. 195).

Opal (Si02+Aq)

The true position of opal in the classification of minerals is somewhat
doubtful. From the analyses made it appears to be a combination of
amorphous silica and water, or, perhaps, a mixture of silica in some form
and a hydroxide of silicon. The percentage of water present is variable.
In some specimens it is as low as 3 per cent, while in others it is as high
as 13 per cent. The mineral is not known in crystals. It is probably a
colloid, in which the water is, in part at least, mechanically held in a gel
of Si02. It occurs only in massive form, in stalactitic or globular masses
and in an earthy condition.

When pure the mineral is colorless and transparent. Usually, how-
ever, it is colored some shade of yellow, red, green or blue, when it is
translucent or sometimes even opaque. The red and yellow varieties con-
tain iron oxides and the green, pros opal, some nickel compound. The
play of color in gem opal is due to the interference of light rays reflected
from the sides of thin layers of opal material with different densities
from that of the main mass of the mineral they traverse. The hardness
of opal is 5.5-6.5 and its density about 2.1. Its refractive index for
yellow light, »= 1.4401. It is a nonconductor of electricity.

179

180 DESCRIPTIVE MINERALOGY

The principal varieties of opal are:

Precious opal, a transparent variety exhibiting a delicate play of
colors,

Fire opal, a precious opal in which the colors are quite brilliant
shades of red and yellow,

Girasol, a bluish white translucent opal with reddish reflections,

Common opal, a translucent variety without any distinct play of
colors,

Cachalong, an opaque bluish white, porcelain-like variety,

Hyalite, a transparent, colorless variety, usually in globular or
botryoidal masses, and

Siliceous sinter, white, translucent to opaque pulverulent accumula-
tions and hard crusts, deposited from the waters of geysers and other
hot springs.

Tripolite and infusorial earth are pulverulent forms of silica in which
opal is an important constituent. Tripoli is a light porous siliceous
rock, supposed to have resulted from the leaching of calcareous material
from a siliceous limestone. Infusorial earth represents the remains of
certain aquatic forms of microscopic plants known as diatoms.

Flint and Chert are mixtures of opal, chalcedony and quartz.

All varieties of opal are infusible and all become opaque when heated.
When boiled with caustic alkalies some varieties dissolve easily, while
others dissolve very slowly.

Syntheses. — Coatings of material like opal have been noted in glass
flasks containing hydrofluosilicic acid that had not been opened for
several years. Opal has also been obtained by the slow cooling of a
solution of silicic acid in water.

Occurrence. — The mineral occurs as deposits around hot springs.
It also forms veins in volcanic rocks and is embedded in certain lime-
stones and slates, where it is probably the result of the solution of the
siliceous spicules and shells of low forms of life and subsequent deposi-
tion. It also results from the solution of the calcite from limestones
containing finely divided silica.

It is not an uncommon alteration product of silicates. It seems to
have been deposited from both cold and hot water.

Localities. — Precious opal is found near Kashan, in Hungary; at
Zimapan, Quaretaro, in Mexico; in Honduras; in Queensland and
New South Wales, Australia, and in the Faroe Islands. Common opal is
abundant at most of these localities and is found also in Moravia,
Bohemia, Iceland, Scotland and the Hebrides. Hyalite occurs in small
quantity at several places in New York, New Jersey, North Carolina,

HYDROXIDES 181

Georgia and Florida, and common opal, at Cornwall, Penn., and in
Calaveras Co., California. Common opal and varieties exhibiting a little
fire have recently been explored in Humboldt and Lander Counties,
Nevada. Siliceous sinter is deposited at the Steamboat Springs in
Nevada and geyserite (a globular form of the sinter) at the mouths of the
geysers in the Yellowstone National Park.

Uses. — The precious and fire opals are popular and handsome gems.
Opalized wood, i.e., wood that has been changed into opal in such a
manner as to retain its woody structure, is often cut and polished for use
as an ornamental stone. Infusorial earth, a white earthy deposit of
microscopic shells consisting largely of opal material, possesses many
uses. It is employed in the manufacture of soluble glass, polishing
powders, cements, etc., and as the " body," which, saturated with nitro-
glycerine, composes dynamite. Tripoli, a mixture of quartz and opal,
is used as a wood filler, in making paint, as an abrasive and in the
manufacture of filter stones. The principal sources of commercially
valuable opal material in the United States are the opalized forest in
Apache Co., Ariz., the infusorial earth beds at Pope's Creek and Dun-
kirk, Md., various places in Napa Co., Cal., at Virginia City, Nev.,
and at Drakesville, N. J., and the tripoli beds in the neighborhood of
Stella, Mo., and the adjoining portion of Illinois.

Production. — The total quantity of infusorial earth and tripoli mined
during 191 2 was valued at $125,446. The aggregate value of precious
opal obtained in 191 2 was $10,925. This came from California and
Arizona.

Brucite (Mg(OH)2)

Brucite is the hydroxide of magnesium. It is a white, soft mineral
usually occurring in crystals or in foliated masses.

Analyses of the mineral correspond very closely to the formula
Mg(OH)2 which requires 41.38 per cent Mg, 27.62 per cent O and 31.00
per cent H2O, though they usually show the presence of small quantities
of iron and manganese. A specimen from Reading, Perm., yielded:

MgO

Fe203

MnO

H20

Total

67.64

.82

■63

30.92

100.01

The crystallization of brucite is hexagonal (ditrigonal scalenohedral),
a : c=i : 1.5208. The crystals are tabular in habit in consequence of
the broad development of the basal plane oP(oooi). The other forms
present are R(ioTi), — 4R(o44i) and — £R(oil3) (Fig. 88). The angle
ioTiai"ioi = 97°38'.

182 DESCRIPTIVE MINERALOGY

The cleavage of brucite is very perfect parallel to oP(ooi), and folia
that may be split off are flexible. The mineral is sectile. Its hardness
is 2.5 and its density 2.4. Its color is white, inclining to bluish and
greenish tints, and its luster pearly on oP. Brucite is transparent to

translucent. It is pyroelectric and a non-
conductor of electricity. Its refractive indices
for red light are: (0=1.559, €=1.579.

In the closed tube brucite, like other hy-
droxides, yields water. The mineral is infusi-
ble. When intensely heated, it glows. After
Fig. 88. — Brucite Crystal heating, it reacts alkaline. When moistened
with oR, 0001 W; R ^^ cobalt nitIate aoiution and heated, it turns

a^-4R, I* it)!' P^ the characteristic reaction for magnesium.

The pure mineral is soluble in acids.

Brucite resembles in many respects gypsum, talc, diaspore and some
micas. It is distinguished from diaspore and mica by its hardness and
from talc by its solubility in acids. Gypsum is a sulphate, hence the
test for sulphur will sufficiently characterize it.

Synthesis. — Crystals have been made by precipitating a solution of
magnesium chloride with an alcoholic solution of potash, dissolving the
precipitate by heating with an excess of KOH and allowing to cool.

Occurrence and Origin. — Brucite is usually associated with other
magnesium minerals. It is often found in veins cutting the rock known
as serpentine, where it is probably a weathering product, and is some-
times found in masses in limestone, especially near its contact with
igneous rocks.

Localities. — It occurs crystallized in one of the Shetland Islands; at
the Tilly Foster Iron Mine, Brewster, N. Y.; at Woods Mine, Texas,
Penn., and at Fritz Island, near Reading, in the same State.

Gibbsite (Al(OH)s)

Gibbsite, or hydrargillite, is utilized to some extent as an ore of alu-
minium. It occurs as crystals, in granular masses, in stalactites and in
fibrous, radiating aggregates.

Its theoretical composition demands 65.41 per cent AI2O3 and
34.59 per cent H2O. Usually, however, the mineral is mixed with bauxite
(Al20(OH)4) and in addition contains also small quantities of iron,
magnesium, silicon and often calcium.

Crystals are monoclinic with a : b : c= 1.709 : 1 : 1.918 and £=85°
29!'. Their habit is tabular. Besides the basal plane, oP(ooi), the

HYDROXIDES 183

two most prominent forms are ooP* (ioo) and ooP(no). Thus the
plates have hexagonal outlines. They have a perfect cleavage parallel
to the base. Twinning is common, with oP(ooi) the twinning plane.

The mineral has a glassy luster except on the basal plane where its
luster is pearly. It is transparent or translucent, white, pink, green or
gray. Its streak is light, its hardness is 2-3 and specific gravity 2.35.
It is a nonconductor of electricity. Its refractive indices are: a=/3

= i-5347, 7= 1.5577-

When heated before the blowpipe the mineral exfoliates, becomes

white, glows strongly but does not fuse. Upon cooling the heated mass
is hard enough to scratch glass, The mineral dissolves slowly but com-
pletely in hot HC1 and in strong H2SO4, and gives a blue color when
moistened with Co(NOs)2 solution and heated.

Gibbsite resembles most closely bauxite, from which it is distin-
guished principally by its structure. It differs from wavellite (p. 287),
which it also sometimes resembles, in the absence of phosphorus.

Syntheses. — Crystals of gibbsite have been made by heating on a
water bath a saturated solution of Al(OH)3 in dilute ammonia until all
of the ammonia evaporates; and also by gradually precipitating the
hydroxide from a warm alkaline solution by means of a slow stream
of C02. *

Occurrence.^wThe mineral rarely occurs in pure form. It is found in
veins and in cavities in various schistose and igneous rocks. It is prob-
ably a weathering product of aluminous silicates.

Localities. — Gibbsite has been reported as existing in small quantities
at various points in Europe, near Bombay, India, and at several places
in South America and Africa. In the United States it occurs at Rich-
mond, Mass., at Union Vale, Dutchess Co., N. Y., and mixed with
bauxite at several of the occurrences of this mineral (see page 186).

Uses, — It is mined with bauxite as a source of aluminium.

Limonite (Fe403(OH)tt)

Limonite is an earthy or massive reddish brown mineral whose
composition and crystallization are but imperfectly known. It is an
important iron ore called in the trade " brown hematite."

The analyses of limonite. range between wide limits, largely because
of the great quantities of impurities mixed with it. The formula de-
mands 59.8 per cent Fe, 25.7 per cent O and 14.5 per cent water, but the
percentages of these constituents found in different specimens only
approximately correspond to these figures. Many mineralogists regard

DESCRIPTIVE MINERALOGY

Fig. 89.— Limonite Stalactites in Silverbow Mine, Butte, Mont. (After W. H. Weed.}

Fig. 90. — Botryoidal Limonite.

HYDROXIDES 185

limonite as colloidal goethite (FeO-OH) with one molecule or more of
H2O, depending upon temperature. The principal impurities are clay,
sand, phosphates, silica, manganese compounds and organic matter.
The great variety of these is thought to be due to the fact that the
limonite, like other gels, possesses the power of absorbing compounds
from their solution, so that the mineral is in reality a mixture of col-
loidal iron hydroxide and various compounds which differ in different
occurrences.

The mineral occurs in stalactites (Fig. 89), in botiyoidal forms (Fig.
90), in concretionary and clay-like masses and often as pseudomorphs
after other minerals and after the roots, leaves and stems of trees.

Limonite is brown on a fresh fracture, though the surface of many,
specimens is covered with a black coating that is so lustrous as to appear
varnished. Its streak is yellowish brown. Its hardness is a little over
5 and its density about 3.7. The mineral is opaque and its luster is dull,
silky or almost metallic according to the physical conditions of the spec-
imen. Its index of refraction is about 2.5. It is a nonconductor of
electricity.

The varieties recognized are: compact, the stalactitic and other
fibrous forms; ocherous, the brown or yellow earthy, impure variety;
bog iron, the porous variety found in marshes, pseudomorphing leaves,
etc., and brown clay ironstone, the compact, massive or nodular
form.

In its chemical properties limonite resembles goethite, from which it
can be distinguished only with great difficulty except when the latter is
in crystals. From uncrystallized varieties of goethite it can usually be
distinguished only by quantitative analysis, although in pure specimens
the streaks are different.

Occurrence and Origin. — Limonite is the usual result of the decom-
position of other iron-bearing minerals. Consequently, it is often found
in pseudomorphs. In almost all cases where large beds of the ore occur
the material has been deposited from ferriferous water rich in organic
substances. One of the commonest types of occurrence is " gossan."
In the production of this type of ore, those portions of veins carrying
ferruginous minerals are oxidized under the influence of oxygen-bearing
waters, forming a layer composed largely of limonite which covers the
upper portion of the veins and hides the original vein matter. Gossan
ores derived from chalcopyrite and pyrite are common in all regions in
which these minerals occur. Another type of limonitic ore comprises
those found in clays derived from limestones by weathering. In such
deposits the ore occurs as nodules and in pockets in the clay. Ores of

186 DESCRIPTIVE MINERALOGY

this type are common in the valleys within the Appalachian Moun-
tains. Bog iron ores occur in swamps and lakes into which ferruginous
solutions drain. The iron may come from pyrite or iron silicates in the
drainage basins of the lakes or swamps. When carried down it is oxi-
dized by the air and sinks to the bottom.

Localities. — The mineral occurs abundantly and in many different
localities. The most important American occurrences are extensive
beds at Salisbury and Kent, Conn.; at many points in New Jersey,
Pennsylvania, Michigan, Tennessee, Alabama, Ohio, Virginia and
Georgia.

Uses. — Although containing less iron than hematite, on account of
its cheapness, and the ease with which it works in the furnace, brown
hematite is an important ore of this metal. The earthy varieties are
used as cheap paints.

Production. — The yield of the United States " brown hematite "
mines for 191 2 was a little over 1,600,000 tons. Of this amount the
largest yields were:

Alabama .• . 749,242 tons

Virginia 398,833 tons

Tennessee 171,130 tons

The quantity of ocher produced in the United States during the same
year amounted to about 15,269 tons, valued at $149,289. Most of it
came from Georgia. In addition, 8,020 tons were imported. This
had a value of $148,300.

Bauxite (Al20(OH)4)

Bauxite, or beauxite, like limonite, is probably a colloid. At any
rate it is unknown in crystals. Until recently it possessed but little
value. It is now, however, of considerable importance as it is the prin-
cipal source of the aluminium on the market.

The mineral is apparently an hydroxide of aluminium with the for-
mula Al20(OH)4 or A1203-2H20 in which 26.1 per cent is water and
73.9 per cent alumina (AI2O3), but it may be a colloidal mixture of the
gibbsite and diaspore (p. 190) molecules, or of various hydroxides,
since its analyses vary within wide limits. A sample of very pure
material from Georgia gave on analysis:

A1203

Fe203

S1O2

Ti02

H20

62.46

.81

4-72

31.0*

HYDROXIDES 187

Bauxite occurs in concretionary grains (Fig. 91), in earthy, clay-like
forms and massive, usually in pockets or lenses in clay resulting from the
weathering of limestones or of syenite. It is white when pure, but as
usually found is yellow, gray, red or brown in color, is translucent to
opaque and has a colorless or very light streak. Its density is 2.55
and its hardness anywhere between 1 and*3. Its luster is dull. It is
a nonconductor of electricity.

Before the blowpipe bauxite is infusible. In the closed tube it yields

Fig. 91.— Pisolitic Bauxite, from near Rock Run, Cherokee Co., Ala.

water at a high temperature. Its powder when intensely heated with a
few drops of cobalt nitrate solution turns blue. The mineral is with
difficulty soluble in hydrochloric acid.

Occurrence and Origin. — Bauxite in some cases may be a deposit from
hot alkaline waters, but in Arkansas it is a residual weathering product
of the igneous rock, syenite. It occurs in beds associated with corundum,
clay, gibbsite and other aluminium minerals.

Localities. — Large deposits of the ore occur at Baux, near Aries,
France; near Lake Wochein, in Carniola; in Nassau; at Antrim, Ire-
land; in a stretch of country between Jacksonville, Fla., and Carters-

188 DESCRIPTIVE MINERALOGY

ville, Ga.; in Saline and Pulaski Counties, Ark.; in Wilkinson Co., Ga.,
and near Chattanooga, Tenn.

Preparation. — The ore is mined by pick and shovel, crushed and
washed. It is then, in some cases, dried and broken into fine particles.
The fine dust is separated from the coarser material, and the latter,
which comprises most of the ore, is heated to 4000. This changes the
iron compounds to magnetic oxide which is separated electro-mag-
netically. The concentrate contains about 86 per cent of AI2O3. This
is then purified and dissolved in a molten flux, in some cases cryolite,
and is subjected to electrolysis. The quantity of aluminium made in the
United States during 191 2 was over 65,600,000 lb., valued at about
$17,000,000. The value of the aluminium salts produced was about
$3,000,000.

Uses. — Bauxite (or more properly the mixture of bauxite and gibbs-
ite) is practically the only commercial ore of aluminium which, on
account of its lightness and its freedom from tarnish on exposure, has
become a very popular metal for use in various directions. It is em-
ployed in castings where light weight is desired and in the manufacture
of ornaments and of plates for interior metallic decorations. It is also
employed in the steel industry, and, in the form of wire, for the trans-
mission of electricity. The mineral is also used in the manufacture of
aluminium salts, in making alundum (artificial corundum), and bauxite
brick for lining furnaces, and in the manufacture of paints and alloys.

Production. — The bauxite mined in the United States during 191 2
amounted to about 159,865 tons valued at $768,932, the greater portion
coming from Arkansas. This is about two-thirds the value of the pro-
duction of. the entire world.

Psilomelane

Psilomelane is probably a mixture of colloidal oxides and hydroxides
of manganese in various proportions. In most specimens there is a
notable percentage of BaO or K2O present, and in others small quantities
of lithium and thallium. The barium and potassium components are
thought to have been absorbed from their solutions.

The substance occurs in globular, botryoidal, stalactitic, and massive
forms exhibiting, in many instances, an obscure fibrous structure. Its
color is black or brownish black and its streak brownish black and
glistening. Its hardness is 5.5-6 and specific gravity 4.2.

Psilomelane is infusible before the blowpipe, in some cases coloring
the flame green (Ba) and in others violet (K). With fluxes it reacts for

HYDROXIDES 189

manganese. In the closed tube it yields water. It is soluble in HC1
with evolution of chlorine.

It is distinguished from most other manganese oxides and hydroxides
by its greater hardness.

Occurrence. — Psilomelane occurs in veins associated with pyrolusite
and other manganese compounds, as nodules in clay beds, and as coatings
on many manganiferous minerals. In all cases it is probably a product
of weathering.

Localities. — It is found in large quantity at Elgersburg in Thuringia;
at Ilfeld, Harz; and at various places in Saxony. In the United States
it occurs with pyrolusite and other ores of manganese at Brandon, Vt. ;
in the James River Valley, and the Blue Ridge region of Virginia; in
northeastern Tennessee; at Cartersville, Georgia; at Batesville, Arkan-
sas; and in a stretch of country about forty miles southeast of San
Francisco, California. At many of these points it has been mined as an
ore of manganese.

Wad

Wad is a soft, earthy, black or dark brown aggregate of manganese
compounds closely related to psilomelane.

It occurs in globular, botryoidal, stalactitic, flaky and porous
masses, which, in some cases, are so light that they float on water. It
also occurs in fairly compact layers and coats the surfaces of cracks,
often forming branching stains, known as dendrites.

Wad contains more water than psilomelane, of which it appears
often to be a decomposition product. More frequently it results from
the weathering of manganiferous iron carbonate. It is particularly
abundant in the oxidized portions of veins containing manganese car-
bonates and silicates.

Wad is easily distinguished from all other soft black minerals, except
pyrolusite, by the reaction for manganese, and from all other manganese
compounds, except pyrolusite, by its softness. From pyrolusite it is
distinguished by its content of water.

Localities. — It occurs in most of the localities at which other man-
ganese compounds are found.

DIASPORE GROUP

The diaspore group comprises the hydroxides of aluminium, iron
and manganese, possessing the general formula R"'0(OH). They are
regarded as hydroxides in which one of the hydrogens in H2O is replaced
by the group R'"0, thus: H — O — H, water, AlO — O — H, diaspore. These

190

DESCRIPTIVE MINERALOGY

three compounds from a chemical viewpoint, may be looked upon as the
acids whose salts comprise the spinel group of minerals, which includes
among others the three important ore minerals magnetite, chromite and
franklinite. Of the three members of the diaspore group the manganese
and iron compounds are valuable ores. All are orthorhombic, in the
rhombic bipyramidal class.

Diaspore (AIO(OH))

Diaspore is found in colorless or light colored crystals, in foliated
masses and in stalactitic forms.

Its composition is theoretically 85 per cent AI2O3 and 15 per cent

tf^H5v

Fig. 92. — Diaspore Crystals. 00 P 06 , 010 (6); *> P3, 130 (z); 00 P, no (m); 00 P2,
210 (h); P£, on (e), P2, 212 (s); 00 P2, 120 (/); °o P$, 150 (n); |P|,
232 (tf).

H2O, though analyses show it to contain, in addition, usually, some iron
and silicon. A specimen from Pennsylvania yielded:

AI2O3
80.95

H20

14.84

Fe203
3.12

Si02 Total
1.53 100.44

Other specimens approach the theoretical composition very closely.

In crystallization the mineral is orthorhombic (rhombic bipyramidal
class), with a : b : ^=.9372 : 1 : .6039. The crystals are usually pris-
matic, though often tabular parallel to 00 Poo (010). The principal
planes observed on them are 00 Poo (010), a series of prisms as
ooP(no), ooP2(2io), °oP3(i3o), the dome Poo (on) and several
pyramids (Fig. 92). The planes of the prismatic zone are often ver-
tically striated. The angle iioAi^o = 86° 17'.

The cleavage of diaspore is very distinct parallel to the brachy-
pinacoid. Its fracture is conchoidal and the mineral is very brittle.
Its hardness is about 6.5 and density 3.4. The luster of the mineral is
vitreous, except on the cleavage surface, where it is pearly. Its color

HYDROXIDES 191

varies widely, though the tint is always light and the streak colorless.
The predominant shades are bluish white, grayish white, yellowish or
greenish white. The mineral is transparent or translucent. It is a
nonconductor of electricity. Its refractive indices for yellow light are:
a=.i702, 18=1.722, 7 = 1.750.

In the closed tube diaspore decrepitates and gives off water at a high
temperature. It is infusible and insoluble in acids. When moistened
with a solution of cobalt nitrate and heated it turns blue, as do all other
colorless aluminium compounds.

In appearance, diaspore closely resembles bruciie (Mg(OH)2), from
which it may be distinguished by its greater hardness and its aluminium
reaction with cobalt nitrate.

Synthesis. — Crystal plates of diaspore have been made by heating at
a temperature of less than 5000, an excess of amorphous AI2O3 in sodium
hydroxide, enclosed in a steel tube. At a higher temperature corundum
resulted.

Occurrence. — Diaspore occurs as crystals implanted on corundum
and other minerals, and on the walls of rocks in which corundum is
found. It is probably in most cases a decomposition product of other
aluminium compounds.

Localities. — In Ekaterinburg, Russia, it is associated with emery.
At Schemnitz, Hungary, it occurs in veins. It is found also in the
Canton of Tessin, in Switzerland, at various places in Asia Minor, and
on the emery-bearing islands of the Grecian Archipelago. In the
United States it is associated with corundum, at Newlin, Chester Co.,
Penn., with emery at Chester, Mass., at the Culsagee corundum mine,
near Franklin, N. C, and at other corundum mines in the same State.

Manganite (MnO(OH))

Manganite usually occurs in groups of black columnar or prismatic
crystals and in stalactites.

The formula MnO(OH) requires 27.3 per cent O, 62.4 per cent Mn
and 10.3 per cent water, or 89.7 per cent MnO and 10.3 per cent water.
In addition to these constituents, the mineral commonly contains also
some iron, magnesium, calcium and often traces of other metals. An
analysis of a specimen from Langban, in Sweden, yielded:

Mn203 Fe203 MgO CaO H20 Total

88.51 .23 1. 51 .62 9.80 100.67

The orthorhombic crystals of the mineral have an axial ratio a : b : c
= .8441 : 1 : .5448. The crystals are nearly all columnar with a series

192 DESCRIPTIVE MINERALOGY

of prisms, among which are w P4(4io) and °o P(i 10), and the two lateral
pinacoids ooP 06(010) and 8 P 60 (100) terminated by oP(ooi) or by
the domes PS (on), P* (101), and pyramids (Figs. 93 and 04). Cru-
ciform and contact twins, with the twinning plane P 06 (on), are not
uncommon (Fig. 95). The prismatic surfaces are
I vertically striated and the crystals are often in

bundles. The angle 1 10 A tio— 8o° 20'.

Cleavage is well defined parallel to 00 P 06 (010)
and less perfectly developed parallel to qoP(iio).
The fracture is uneven. The luster of the mineral
is brilliant, almost metallic. Its color is iron-black
and its streak reddish brown or nearly black. It
Fig. 93. — Manganite -K usually opaque but in very thin splinters it is
Crystal "1th ™p' sometimes brown by transmitted light. Its hard-
and p"m "ioH") ness ** 4 an<* density about 4-3- The mineral is
a nonconductor of electricity.
Manganite yields water in the closed tube and colors the borax bead
amethyst in the oxidizing flame of the blowpipe. In the reducing flame,
upon long-continued heating, this color disappears. The mineral dis-
solves in hydrochloric acid with the evolution of chlorine. It is dis-

FlO. 94- — Group of Prismatic Manganite Crystals from Ilfeld, Harz.

tinguished from other manganese minerals by its hardness and crystal-
lization.

By loss of water manganite passes readily into pyrolusite (MnOs).
It also readily alters into other manganese compounds.

Synthesis. — Upon heating for six months a mixture of manganese
chloride and clcium caarbonate fine crystals like those of manganite

HYDROXIDES 193

have been obtained. Their composition, however, was that of haus-
mannite, indicating that while manganite was produced, it was changed
to hausmannite during the process.

Occurrence, Localities and Origin, — Man-
ganite occurs in veins in old volcanic rocks,
and also in limestone. It is found at Ilfeld
in the Harz; at Ilmenau in Thuringia, and
at Langban in Sweden, in handsome crys-
tals. In the United States it occurs at the
Jackson and the Lucie iron mines, Negaunee,

Mich., and in Douglas Co., Colo. It is ^ ,, . ^

, , , A . . . XT Fig. 95. — Manganite Crystal

also abundant at various places in New Twhmed about p5(oxi)b

Brunswick and Nova Scotia. In all cases The forms are <»P. no(«);
it is a residual product of the weathering of ooPXiaoCOandPa^iaQ;).
manganese compounds.

Uses. — Manganite is used in the production of manganese compounds.
As mined it is usually mixed with pyrolusite, this being the most im-
portant portion of the mixture.

Goethite (FeO(OH))

This mineral, though occasionally found in blackish brown crystals,
usually occurs in radiated globular and botryoidal masses. Analyses
of specimens from Maryland, and from Lostwithiel, in Cornwall, gave:

FC2O3 Mn203

Maryland 86.32

Lostwithiel 89-55 • J6

The formula FeO(OH) demands 89.9 per cent Fe203 and 10. 1 per cent
H2O or 62.9 per cent Fe, 27.0 per cent O and 10. 1 per cent H2O.

Like diaspore and manganite, goethite is orthorhombic, its axial
ratio being a : b : ^ = .9185 : 1 : .6068. Its crystals are prismatic or
acicular with the prisms plainly striated vertically. The forms observed
are commonly 00 P 66 (010), ooP2~(2io),ooP(no),P66 (on) andP(ni).
The angle no A 1 10=85° 8'.

The cleavage of goethite is perfect parallel to 00 P 06 (010) and its
fracture uneven. Its hardness is 5 and density about 4.4. Its color is
usually yellowish, reddish or blackish brown and its luster almost
metallic. In thin splinters it is often translucent with a blood-red color
and a refractive index of about 2.5. Its streak is brownish yellow. It
is an electric nonconductor.

H20

Si02

Total

10.80

2.88

100.00

10.07

.28

100.06

194 DESCRIPTIVE MINERALOGY

The chemical reactions of the mineral are about the same as those of

hematite, except that it yields water when heated in the closed tube.
By this reaction it is easily distinguished from the fibrous varieties of
hematite, as it is also by its streak.

Synthesis. — Needles of goethite are produced by heating freshly
precipitated iron hydroxide for a long time at ioo°.

Occurrence and Localities. — Goethite is usually associated with other
ores of iron, especially in the upper portion of veins, where it is produced
by weathering. It is found near Siegen in Nassau; near Bristol and
Clifton, England, and in large, fine crystals at Lostwithiel and other
places in Cornwall.

In the United States it occurs in small quantity at the Jackson and
the Lucie hematite mines in Negaunee, Mich.; at Salisbury, Conn.;
at Easton, Penn., and at many other places.

Uses. — Goethite is used as an ore of iron, but in the trade it is classed
with limonite as brown hematite.

CHAPTER DC
THE ALUMINATES, FERRITES, CHROMITES AND MANGANITES

Most of these compounds are salts of the comparatively uncommon
acids HAIO2, HFeCfe and HC1O2, which may be regarded as metaacids
derived from the corresponding normal acids by the abstraction of water,
thus: H3AIO3— H20 = HA102. There are only a few minerals belong-
ing to the group but they are important. One, magnetite, is an ore of
iron; another, chromite, is the principal ore of chromium and two others
are utilized as gems. Most of them are included in the mineral group
known as the spinels. (Compare p. 189.)

That there is a manganese acid corresponding to the metaacids of Al,
Fe and Cr is indicated by the fact that in some of the spinels manganese
replaces some of the ferric iron, as, for example, in franklinite. This
suggests that this mineral is an isomorphous mixture of a metaferrite
and a salt of the corresponding manganese acid (HMnCfe). This may
be regarded as derived from the hydroxide, Mn(OH)3, by abstraction
of H2O, thus: HsMn03— H20=HMn02. But there are other man-
ganous acids. Normal manganous acid is Mn(OH)4, or HUMnC^. If
from this one molecule of water be abstracted, there remains H2Mn03,
the metamanganous acid. The manganous salt of the normal acid,
Mn2Mn04, occurs as the mineral, hausmannite, and the corresponding
salt of the metaacid, MnMnC>3, as the mineral, braunite.

SPINEL GROUP

The spinels are a group of isomorphous compounds that may be
regarded as salts of the acids AIO(OH), MnO(OH), CrO(OH) and
FeO(OH), in which the hydrogen is replaced by Mg, Fe and Cr.

Al— O— Ov

Thus, spinel, Mg- AI2O4 may be regarded as || /Mg; magnetite,

Al— O— (K
Fe— O— (X Cr— O— Ov

Fe304, as || /Fe; cl.romite, FeCr204, as || /Fe; and

Fe-O— (X Cr— O-CX

(Fe • Mn)— 0— <X
frank1 inite, as | | y(Zn-Mn-Fe). Chemical compounds of

(Fe Mn)— O— Cr

195

196

DESCRIPTIVE MINERALOGY

this general type are fairly numerous, but only a few occur as minerals.

The most important are the three important ores mentioned above;

spinel is of some value as a gem stone.

The spinels crystallize in the holohedral divi-
sion of the isometric system (hexoctahedral class),
in well defined crystals that are usually combina-
tions of O(iii) and ooO(no), with the addition on
some of 00O00 (ioo), 303(311), 202(211), 5OK531),
etc. Contact twins are so common with O the
twinning plane, that this type of twinning is often
referred to as the spinel twinning (Fig. 96).

Fig. 96.
Spinel Twin.

The complete list of the known spinels is as follows:

Spinel

Ceylonite (pleonaste)

Chlorspinel

Picotite

Hercynite

Gahnite

Dysluite

Kreittonite

Magnetite

Magnesioferrite

Franklinite

Jacobsite

Chromite

Mg(A102)2
(Mg.Fe)(A102)2

Mg((Al-Fe)02)2

(Mg-Fe)((Al-Fe-Cr)02)2

Fe(A102)2

Zn(A102)2

(Zn-Fe-Mn)((Al-Fe)02)2

(Zn-Fe-Mg) ((Al-Fe)02)2

Fe(Fe02)2

Mg(Fe02)2

(Fe • Zn.Mn) ((Fe • Mn)02)2

(Mn-Mg)((Fe-Mn)02)2

(Fe-Mg)(Cr-Fe)02)2

Spinel (Mg(A102)2)

Ordinary spinel is the magnesian aluminate, which, when pure, con-
tains 28.3 per cent MgO and 71.7 per cent
Al203. Usually, however, there are present
admixtures of the other isomorphs so that
analyses often indicate Fe, Al and Cr.

The mineral usually occurs in isolated
simple crystals, rarely in groups. The forms
observed on them are O(iu), ooO(no) and
303(311), and rarely 00 O 00 (100) (Fig. 97).

The pure magnesium spinel is colorless or FlG*. 97-— Spinel Crystal

some shade of pink or red, brown or blue, and T?N \ x" w> '

v ' ' \d) and 303, 311 (m).

is usually transparent or translucent, though

opaque varieties are not rare. Its streak is white. It possesses a glassy

ALUMINATES, FERRITES, ETC. 197

luster, and a conchoidal fracture, but no distinct cleavage. Its hard-
ness is 8 and its density 3.5-3.6. Its refractive indices vary with the
color: n for yellow light is 1.7150 for red spinel and 1.7201 for the blue
variety.

The mineral is infusible before the blowpipe and is unattacked by
acids. It yields the test for magnesia with cobalt solution.

Spinel is easily distinguished from most other minerals by its crys-
tallization and hardness. It is distinguished from pale-colored garnet
by its blowpipe reactions, especially its infusibility, and its failure to
respond to the test for Si02.

The best known varieties are:

Precious spinel, which is the pure magnesian aluminate. It is trans-
parent and colorless or some light shade of red, blue or green. The
bright red variety is known as ruby spinel and is used as a gem. Its
color is believed to be due to the presence of chromium oxide. It is
easily distinguished from genuine ruby by the fact that it is not doubly
refracting and not pleochroic.

The best ruby spinels come from Ceylon, where they occur loose in
sand associated with zircon, sapphire, garnet, etc.

Common spinel differs from precious spinel in that it is translucent.
It usually contains traces of iron and alumina.

Both these varieties of spinel occur in metamorphosed limestones
and crystalline schists.

Syntheses. — The spinels have been made by heating a mixture of
AI2O3 and MgO with boracic acid until fusion ensues; and by heating
Mg(OH)2 with AICI3 in the presence of water vapor.

Origin. — Spinel has been described as an alteration product of corun-
dum and garnet. It is also a primary component of igneous rocks and
a product of metamorphism in rocks rich in magnesium.

Uses. — Only the transparent ruby spinels have found a use. These
are employed as gems.

Ceylonite, or pleonaste, is a spinel in which a portion of the Mg
has been replaced by Fe, i.e., is an isomorphous mixture of the magne-
sian and iron aluminates; thus ((Mg-Fe)(A102)2). It is usually black
or green and translucent, and has a brownish or dark greenish streak
and a density =3.5-3.6.

The analysis of a sample separated from an igneous rock in Madison
Co., Mont., gave,

AI2O3 FeO MgO Cr203 Fe203 MnO CaO SiCfe Total
62.09 17.56 15.61 2.62 2.10 tr .16 .55 100.69

198 DESCRIPTIVE MINERALOGY

Ceylonite occurs in igneous rocks in the Lake Laach region,
Germany, and in the Piedmont district, Italy and elsewhere; in meta-
morphosed limestones at Warwick and Amity, N. Y. ; in the limestone
blocks enclosed in the lava of Vesuvius; and in dolomite metamor-
phosed by contact action at Monzoni, Tyrol.

Picotite, or chrome spinel, is a variety intermediate between spinel
proper and chromite. Its composition may be represented by the
formula (Mg-Fe)((Al-Fe- 0)02)2. It occurs only in small crystals in
basic igneous rocks and in a few crystalline schists. Density =4.1.

Magnetite (Fe(Fe02)2)

Magnetite, the ferrous ferrite, the empirical formula of which is
FesOi, is a heavy, black, magnetic mineral which is utilized as one of
the ores of iron.

The pure mineral consists of 72.4 per cent Fe and 27.6 per cent O.
Most specimens, however, contain also some Mg and many contain small
quantities of Mn or Ti. A selected sample of magnetite from the Eliza-
beth Mine, Mt. Hope, New Jersey, analyzed as follows:

Fe203 FeO Si02
65 . 26 30 . 20 1 . 38

Magnetite occurs in crystals that are usually octahedrons or dodeca-
hedrons, or combinations of the two. Other forms are rare. Twins
are common. The mineral occurs also as sand
and in granular and structureless masses. When
the dodecahedron is present, its faces are fre-
quently striated parallel to the edge between
ooO(no) and O(in) (Fig. 98).

Magnetite is black and opaque and its streak Fig. 98. — Magnetite
is black. It has an uneven or a conchoidal frac- Crystal, with » o
ture, but no distinct cleavage. Its hardness is ("<>) and O (in),

5.5-6 and density 4.9-5.2. It is strongly attracted p^rljlef J Edge' 1 10
by a magnet and in many instances it exhibits aiMi lllm
polar magnetism.

The mineral is infusible before the blowpipe. Its powder dissolves
slowly in HC1, and the solution reacts for ferrous and ferric iron.

Magnetite is easily recognized by its color, magnetism, and hardness.

The mineral weathers to limonite and hematite and occasionally to
the carbonate, siderite.

Ti02

AI2O3

MgO

CaO

Other

Total

1.09

•55

.10

.68

•73

99-99

ALUMINATES, FERRITES, ETC. 199

Syntheses. — Crystals have been made by cooling iron-bearing silicate
solutions; treating heated ferric hydroxide with HC1; and by fusing
iron oxide and borax with a reducing flame.

Occurrence end Origin. — The mineral occurs as a constituent of
many igneous rocks and crystalline schists, and in lenses embedded in
rocks of many kinds. It also constitutes veins cuttinjg these rocks
and as irregular masses produced by the dehydration and deoxidation
of hematite and limonite under the influence of metamorphic processes.
It occurs also as little grains among the decomposition products of
iron-bearing silicates, such as olivine and hornblende.

The larger masses are either segregations from igneous magmas or
deposits from hot solutions and gases emanating from them.

Localities. — The localities at which magnetite has been found are so
numerous that only those of the greatest economic importance may be
mentioned here. In Norway and Sweden great segregated deposits are
worked as the principal sources of iron in these countries. In the
United States large lenses occur in the limestones and siliceous crys-
talline schists in the Adirondacks, New York, and in the schists and
granitic rocks of the Highlands in New Jersey. Great bodies are mined
also at Cornwall, and smaller bodies at Cranberry, and in the Far
West.

Extraction. — The magnetite is separated from the rock with which it
occurs by crushing and exposing to the action of an electro-magnet.

Production. — The total amount of the mineral mined in the United
States during 191 2 was 2,179,500 tons, of which 1,110,345 tons came
from New York, 476,153 tons from Pennsylvania, and 364,673 tons
from New Jersey.

Franklinite ((Fe-Zn-Mn)((Fe-Mn)02)2)

Franklinite resembles magnetite in its general appearance. It is an
ore of manganese and zinc.

It differs from magnetite in containing Mn in place of some of the
ferric iron in this mineral and Mn and Zn in place of some of its ferrous
iron. Since it is an isomorphous mixture of the iron, zinc and manganese
salts of the iron and manganese acids of the general formula R'"0(OH),
its composition varies within wide limits. The franklinite from Mine
Hill, N. J., contains from 39 per cent to 47 per cent Fe, 10 per cent to
19 per cent Mn and 6 per cent to 18 per cent Zn. A specimen from
Franklin Furnace, N. J., contained,

Fe203 MnO ZnO MgO CaO SiCfe H20 Total
66.58 9.96 20.77 .34 .43 .72 .71 99.51

200 DESCRIPTIVE MINERALOGY

Its crystals are usually octahedrons, sometimes modified by the do-
decahedron and occasionally by other forms. The mineral occurs also
in rounded grains, in granular and in structureless masses.

It is black and lustrous and has a dark brown streak. Its fracture
and cleavage are the same as for magnetite. It is only very slightly
magnetic. It has a hardness of 6 and a density of 5.15.

The mineral is infusible before the blowpipe. When heated on
charcoal it becomes magnetic. When fused with Na2CC>3 in the oxidizing
flame it gives the bluish green bead characteristic of manganese. Its
fine powder mixed with Na2COa and heated on charcoal yields the white
coating of zinc oxide which turns green when moistened with Co(N03)2
solution and again heated.

Franklinite is distinguished from most minerals by its color and crys-
tallization and from magnetite and clromite by its brown streak and
by its reactions for Mn and Zn. It is also characterized by its associa-
tion with red zincite and green or pink willemite (p. 306).

Synthesis. — Crystals of franklinite have been made by heating a
mixture of FeCk, ZnCk and CaO (lime).

Occurrence and Origin. — Franklinite occurs at only a few places. Its
most noted localities are Franklin Furnace and Sterling Hill, N. J., where
it is associated in a white crystalline limestone with zincite, willemite
and other zinc and manganese compounds. The deposit is supposed
to have been produced by the replacement of the limestone through the
action of magmatic waters and vapors.

Uses. — The mineral is utilized as an ore of manganese and zinc.
The ore as mined is crushed and separated into parts, one of which
consists largely of franklinite. This is roasted with coal, when the zinc
is driven off as zinc oxide. The residue is smelted in a furnace producing
spiegeleisen, which is an alloy of iron and manganese used in the man-
ufacture of certain grades of steel.

Production. — The quantity of this residuum produced in 191 2 was
104,670 tons, valued at $314,010.

Chromite (Fe(Cr02)2)

Chromite, or chrome-iron, is the principal ore of chromium. It
resembles magnetite and franklinite in appearance. It occurs in iso-
lated crystals, in granular aggregates, and in structureless masses.

Chemically, it is a ferrous salt of metachromous acid, of the theoret-
ical composition CT2O3 = 68 per cent and FeO =32 per cent, but it usually
contains also small quantities of AI2O3, CaO and MgO. An analysis of

ALUMINATES, FERRITES, ETC. 201

a specimen from Chorro Creek, California, after making corrections for
the presence of some serpentine, yielded:

Cr203

AI2O3

Fe203

FeO

MgO

MnO

Total

56.96

12.32

381

12.73

14.02

.16

100.00

Its crystals are usually simple octahedrons, but they are not as
common as those of the other spinels.

Its color is brownish black and its streak brown. It has a conchoidal
or uneven fracture and no distinct cleavage. It is usually nonmag-
netic, but some specimens show slight magnetism because of the ad-
mixture of the isomorphous magnetite molecule. Its hardness is 5.5
and its density 4.5 to 4.8.

The mineral is infusible before the blowpipe. It gives the chromium
reaction with the beads. If its powder is fused with niter and the fusion
treated with water, a yellow solution of K.2Cr04 results. When fused
with Na2COa on charcoal it yields a magnetic residue.

Chromite is easily distinguished from all other minerals but pico-
tite by its crystallization and its reaction for chromium. It is distin-
guished from picotite by its inferior hardness and its higher specific
gravity.

Synthesis. — Crystals have been made by fusing the proper constit-
uents with boric acid and after fusion distilling off the boric acid.

Occurrence and Origin. — Chromite occurs principally in olivine rocks
and in their alteration product — serpentine. The mineral is found not
only as crystals embedded in the rock mass, but also as nodules in it
and as veins traversing it. It is probably in all cases a segregation from
the magma producing the rock. In a few places the mineral occurs
in the form of sand on beaches.

Localities. — It is widely spread through serpentine rocks at many
places, notably in Brussa, Asia Minor; at Banat and elsewhere in
Norway; at Solnkive, in Rhodesia; in the northern portion of New
Caledonia; at various points in Macedonia; in the Urals, Russia; in
Beluchistan and Mysore, India.

In the United States the mineral is known at several points in a belt
of serpentine on the east side of the Appalachian Mountains, and at
many points in the Rocky Mountains, the Sierra Nevada and the Coast
Ranges. It has been mined at Bare Hills, Maryland; in Siskiyou,
Tehama and Shasta Counties, Colorado; in Converse County, Wyoming;
and in Chester and Delaware Counties, Pennsylvania; and; in 1914,
some was washed from chrome sand at Baltimore, Maryland.

202 DESCRIPTIVE MINERALOGY

Metallurgy. — The mineral is mined by the usual methods and con-
centrated, or, if in large fragments, is crushed. It is then fused with
certain oxidizing chemicals and the soluble chromates are produced.
Or the ore is reduced with carbon yielding an alloy with iron. The
metal is produced by reduction of its oxide by metallic aluminium or by
electrolysis of its salts.

Uses. — Chromite is the sole source of the metal chromium, which is
the chrome-iron alloy employed in the manufacture of special grades
of steel. Chromium salts are used in tanning and as pigments. The
crude ore, mixed with coal-tar, kaolin, bauxite, or some other ingredient,
is molded into bricks and burned, after which the bricks are used as
linings in metallurgical furnaces. These bricks stand rapid changes of
temperature and are not attacked by molten metals.

Production. — The annual production of chromite in the world is
now about 100,000 tons, of which Rhodesia produces about J, New
Caledonia about J and Russia and Turkey about fc each. The produc-
tion of the United States in 191 2 was 201 tons, valued at $2,753. All
came from California. The imports in the same year were 53,929 tons,
worth $499,818.

Chrysoberyl (BeAl204)

Chrysoberyl is a beryllium aluminate, the composition of which is
analogous to that of the spinels. It may be written Be02(A10)2. Al-
though theoretically it should contain 19.8 per cent BeO and 80.2 per
cent AI2O3, analyses of nearly all specimens show the presence also of
iron and magnesium.

The mineral differs from spinel in crystallizing in the orthorhombic
system (bipyramidal class). Its axial ratio is .4707 : 1 : .5823. The
principal forms observed on crystals are: P(in), 00 P 66 ( 1 00) ,
00 P 66 (010), P 06 (on), 00 P2(i2o) and 2P2(i2i) (Fig. 99). The crystals
are often twins (Fig. 100), trillings or sixlings, with 3Po6(o3i) the
twinning plane, forming pseudohexagonal groupings (Fig. 101). Sim-
ple crystals are usually tabular parallel to 00 P 06 (100), which is striated
vertically. Consequently, in twins this face exhibits striatums arranged
feather-like. The angle no A iTo=50° 21'.

The cleavage of chrysoberyl is distinct parallel to Poo (on), and
indistinct parallel to 00 P 06 (010) and 00 P 65 (100). Its fracture is
uneven or conchoidal. Its color is some shade of light green or yellow
by reflected light. It is transparent or translucent and in some cases is
distinctly red by transmitted light. It is strongly pleochroic in orange,

ALUMINATES, FERRITES, ETC. 203

green and red tints. The mineral is brittle, has a hardness of 8.5 and a
density of about 3.6. Its refractive indices are: « = 1.7470, (3=1.7484,

T= I-7565-

Four distinct varieties are recognized:

Ordinary, pale green, translucent.

Gem, yellow and transparent.

Alexandrite, emerald-green in color, but red by transmitted light,
transparent, usually in twins. Used as a gem.

Cat's-eye, a greenish variety exhibiting a play of colors (chatoyancy).

Before the blowpipe the mineral is infusible. It yields the Al reac-
tion with Co(N03)2, but otherwise is only slightly affected by the flame.
It is insoluble in acids.

Chrysoberyl is characterized by its crystallization and great hard-

Fig. 99. I-'k;. 100. Fie

Fig. oo.—Chrysolicryl Crystal with « 1*« , 100 («); « I* w ,010 (*); «P!,i2o(s);

aP», 121 Mi P, in (•) and PS, mi (fl.

Flu. 100.— Chrysoberyl Twinned about jp 5 (0.11)-

Fig. 101. — Chrysoberyl Pscudohexagona] Sibling Twinned about 3P w {031).

ness. It most closely resembles the beryllium silicate, beryl, in appear-
ance, but is easily distinguished from this by its crystallization.

Synthesis. — Crystals have been made by fusing BeO and AI2O3
with boric acid and then distilling off the boric acid.

Occurrence and Origin. — Chrysoberyl is found principally in granites
and crystalline schists and as grains in the sands produced by the erosion
of these rocks. In its original position the mineral is a separation
from the magma that produced the rocks.

Localities. — Its best known localities are in Minas Geraes, Brazil;
near Ekaterinburg, Ural; in the Moume Mrs., Ireland; at Haddam,
Conn.; at Greenfield, N. Y.; at Orange Summit, N. Hamp.; and at
Norway and Stoneham, Me. The alexandrite comes from Ceylon, where
it occurs as pebbles, and from the Urals.

204

DESCRIPTIVE MINERALOGY

Braunite (MnMnOs) occurs massive and in crystals. The latter
are tetragonal (ditetragonal bipyramidal class), with a : c=i : .9922.
They are usually simple bipyramids P(ni). Because of the nearly
equal value of a and c all crystals are isometric in habit. The angle
iiiAi^i • 700 7'. Twins are common, with P 00(101) the twinning
plane. Cleavage is perfect parallel to P(ni).

The mineral is brownish black to steel-gray in color and in streak.
Its luster is submetallic. Its hardness is 6-6.5 and density 4.7. It is
infusible before the blowpipe. With fluxes it gives the usual reactions
for manganese. It is soluble in HC1 yielding chlorine.

It occurs in veins with manganese and other ores in Piedmont, Italy,
and at Pajsberg and various other places in Sweden, where its origin
is secondary.

Hausmannite (Mn2Mn04) crystallizes like braunite, but a : c—
1 : 1. 1573 and its crystals are, therefore, distinctly tetragonal in habit.
They are usually simply P(ni) or combinations of P(in) and JP(ii3),
though much more complicated crystals are known. The angle
in A iTi=6o° 1'. Twins and fourlings (Fig. 102) are common, with

A B

Fig. 102. — Hausmannite. (A) Simple Crystal, P, in (p) and oP, 001 (c).

Fiveling Twinned about P °o (101).

(B)

P 00(101) the twinning plane. The cleavage is imperfect parallel to
oP(ooi). The mineral also occurs in granular masses.

Hausmannite is brownish black. Its streak is chestnut brown.
Its hardness is 5-5.5 and density 4.8. Its reactions are the same as
those of braunite.

Hausmannite occurs as crystals at Ilmenau, Thiiringia; Ilfeld,
Harz, and as granular masses in dolomite at Nordmark and several
other points in Sweden. Like braunite it is probably a decomposition
product of other manganese minerals.

CHAPTER X
THE NITRATES AND BORATES

THE NITRATES

The nitrates are salts of nitric acid. Only two are of importance
to us, saltpeter (KNO3) and chile saltpeter (NaNCfe). Both are color-
less, or white, crystalline bodies, both are soluble in water and both pro-
duce a cooling taste when applied to the tongue. The potassium com-
pound is distinguished from the sodium compound by the flame test.
Both minerals when heated in the closed tube with KHSO4 yield red
vapors of nitrogen peroxide (NO2).

Soda Niter (NaN03)

Soda niter, or chile saltpeter, is usually in incrustations on mineral
surfaces or in massive forms. It consists of 63.5 per cent N2O5 and
36.5 per cent Na20.

Its crystals are in the ditrigonal scalenohedral class of the hexagonal
system with an axial ratio of a : e= 1 : .8297. They are usually rhom-
bohedrous R(ioTi) in some cases modified by oR(oooi). Apparently
the mineral is completely isomorphous with calcite (CaCOs).

Its cleavage is perfect parallel to the rhombohedron. Its hardness
is under 2, its density about 2.27 and its melting point about 31 20.
Its luster is vitreous; color white, or brown, gray or yellow. The min-
eral is transparent. Its refractive indices for yellow light are: to = 1 .5854,
€=1.3369.

Soda niter deflagrates when heated on charcoal and colors the flame
yellow. When exposed to the air it attracts moisture and finally lique-
fies. It is completely soluble in three times its own weight of water.

Occurrence and Localities. — The principal occurrences of the mineral
are in the district of Tarapaca, northern Chile, where, mixed
with the iodate and other salts of sodium and potassium, under the
name calichey it comprises beds several feet thick on the surface of rain-
less pampas, and in Bolivia at Arane under the same conditions. It is
associated with gypsum, salt and other soluble minerals. Smaller

205

206 DESCRIPTIVE MINERALOGY

deposits are found in Humboldt Co., Nevada, in San Bernardino Co.,
Cal., and in southern New Mexico.

The material is thought to result from the action of microorganisms
upon organic matter decomposing in the presence of abundant air.

Uses. — Soda niter is used in the production of nitric acid, and in the
manufacture of fertilizers and gunpowder. About 480,000 tons are
imported into the United States annually at a cost of $15,430,000.
Most of it comes from Chile.

Since soda niter usually contains sodium iodate as an impurity, the
mineral is an important source of iodine.

Niter (KNO3)

Niter, or saltpeter, resembles soda niter in appearance. It gener-
ally occurs in crusts, in silky tufts and in groups of acicular crystals.
Its crystals are orthorhombic with a : b : £=.5910 : 1 : .7011. Their
habit is hexagonal. The principal forms observed on them are 00 P(i 10),
00 Poo (100), 00 P 66 (010), oP(ooi), P(in), and a series of brachy-
domes. In many respects the mineral is apparently isomorphous with
aragonite which is the orthorhombic dimorph of calcite. At 1260 it
passes over into an hexagonal (trigonal) form. Its cleavage is perfect
parallel to P 66 (on). Its fracture is uneven; its hardness 2 and den-
sity 2.1. Its medium refractive index for yellow light, /3= 1.5056.

Niter deflagrates more violently than soda niter and detonates with
combustible substances. It fuses at about 335 °. It colors the blowpipe
flame violet. It is soluble in water.

Occurrence and Localities. — The mineral forms abundantly in dry
soils in Spain, Egypt, Persia, Ceylon and India, where it is produced
by a ferment, and on the bottoms of caves in the limestones of Madison
Co., Ky., of Tennessee, of the valley of Virginia and of the Mississippi
Valley.

Production. — Most of the niter used in the arts is manufactured, but
some is obtained from the deposits in Ceylon and in India. The
amount imported in 191 2 aggregated 6,976,000 lb., valued at $226,851.

THE BORATES

The borates are salts of boric acid, H3BO3, metaboric acid, HBO2,
tetraboric acid, H2B4O7, hexaboric acid, H4B6O11, and various poly-
boric acids in which boron is present in still larger proportion. The
metaacid is obtained from the orthoacid by heating at ioo°, at which

NITRATES AND BORATES

207

temperature the former loses one molecule of water, thus: H3BO3 —
H20=HB02, and the tetraacid by heating the same compound to 1600
at which temperature 5 molecules of water are lost from 4 molecules of
the acid, thus: 4H3BO3— 5H2O =1128407. Hexaboric acid may be
regarded as the orthoacid less 1$ molecules of water, thus: 6H3BO3
-7H2O=H4B0Oii.

Only three of the borates are important enough to be discussed
here. These are borax, a sodium tetraborate (Na2B407*ioH20), cole-
manite, a hexaborate (Ca2BeOn-5H20) and boracite, a magnesium
chloro-polyborate (Mg5(MgCl)2Bi603o). Borax and colemanite are
commercial substances that are produced in large quantities.

All borates and many other compounds containing boron when
pulverized and moistened with H2SO4 impart an intense yellow-green
color to the flame. If boron compounds are dissolved in hydrochloric
acid, the solution will turn turmeric paper reddish brown after drying
at ioo°. The color changes to black when the stain is treated with
ammonia.

Borax (Na2B407 10H2O)

Borax occurs as crystals and as a crystalline cement between sand
grains around salt lakes, as an incrustation on the surfaces of marshes
and on the sands in desert regions, and dissolved
in the water of certain lakes in deserts. It
occurs also as bedded deposits interlayered with
sedimentary rocks.

The composition of borax is 16.2 per cent
Na20, 36.6 per cent B2O3 and 47.2 per cent H2O.

Crystals are monoclinic (prismatic class), with
alb: c= 1.0995 : x : 5629, and £=73° 25'.
They are prismatic in habit and in general form
resemble very closely crystals of pyroxene.
The principal planes occurring on them are
ooPoo(ioo), ooP(no), oP(ooi), — P(m) and
— 2P(22i) (Fig. 103). Their cleavage is perfect
parallel to 00 P 00 (100), and their fracture conchoidal. The angle

iioaiTo=93°-

The mineral has a white, grayish or bluish color and a white streak.

It is brittle, vitreous, resinous or earthy; is translucent or opaque; has

a hardness of 2-2.5, a density of 1. 69-1. 72, and a sweetish alkaline taste.

On exposure to the air the mineral loses water and tends to become white

Fig. 103. — Borax Crystal
with 00 P, no (m);
00 P 00 , 100 (a); 00 P 5b ,
010 (b); oP, 001 (c);
P, In (0) and 2P, 221

W-

208 DESCRIPTIVE MINERALOGY

and opaque, whatever its color in the fresh condition. Its medium
refractive index for yellow light, 0= 1.4686.

Before the blowpipe borax puffs up and fuses to a transparent
globule. Fused with fluorite and potassium bisulphate it colors
the flame green. It is soluble in water, yielding a weakly alkaline
solution.

Occurrence. — The principal method of occurrence of the mineral is
as a deposit from salt lakes in arid regions, and as incrustations on the
surfaces of alkaline marshes overlying buried borax deposits. The
original beds were deposited by the evaporation to dryness of ancient
salt lakes, and the incrustations were produced by the solution of these
deposits by ground water, and the rise of the solutions to the surface by
capillarity.

Localities. — Borax occurs in the water of salt lakes in Tibet; of
several small lakes in Lake County, and of Borax Lake in San Bernardino
County in California, and in the mud and marshes around their borders.
It occurs also in the sands of Death Valley in the same State, and in
various marshes in Esmeralda County, Nevada. Other large deposits
are found in Chile and Peru.

Uses. — Borax is used as an antiseptic, in medicine, in the arts for
soldering brass and welding mqf als, and in the manufacture of cosmetics.

Boric acid obtained from borax and colemanite is employed in the
manufacture of colored glazes, in making enamels and glass, as an
antiseptic and a preservative. Some of the borates are used as pig-
ments.

Production. — Borax was formerly obtained in the United States,
especially in California, Oregon and Nevada, by the evaporation of
the water of borax lakes, by washing the crystals from the mud on their
bottoms and by the leaching of the mineral from marsh soil. At pres-
ent, however, nearly all the borax of commerce is manufactured from
colemanite.

Colemanite (Ca2B60n 5H2O)

Colemanite occurs in crystals and in granular and compact masses.
It is the source of all the borax now manufactured in the United States.

The formula ascribed to the mineral corresponds to 27.2 per cent
CaO, 50.9 per cent B2O3 and 21.9 per cent H2O. As usually found,
however, it contains a little MgO and SK>2. A crystal from Death
Valley, California, yielded:

8203 = 50.70; CaO=27.3i; MgO=.io; H20=2i.87. Total = 99-98.

NITRATES AND BORATES

209

The mineral crystallizes in the monoclinic system (prismatic class),
in short, prismatic crystals (Fig. 104), with the axial constants a : b : c
= .7769 : 1 : .5416 and £=69° 43'. The crystals are usually rich in
forms. Their cleavage is perfect parallel to 00 O 00 (010), and less
perfect parallel to oP(ooi). Their fracture is uneven. The angle
110A 110=72° 4'.

Colemanite is colorless, milky white, yellowish white or gray. It
is transparent or translucent, has a vitreous or adamantine luster, a
hardness of 4 to 4.5 and a specific
gravity of 2.4. Its index of refrac-
tion for yellow light, 0= 1.5920.

Before the blowpipe it decrep-
itates, exfoliates, and partially
fuses, at the same time coloring
the flame yellowish green. It is
soluble in hot HC1, but from the
solution upon cooling a volumi-
nous mass of boric acid separates
as a white gelatinous precipitate. Fig. 104. — Colemanite Crystals with « p,

It is easily distinguished from IIO(m>; 3P * , 301 (w); « P « , 100 (a);

ooPjp,,oio (6); oP, 001 (c)\ — P, in
(0); 2P«,o2i(a); Pob,oii(*c); co P2,
210 (/); 2P06, 201 (A); 2P, 221 (*) and
P, I" (y).

other white translucent minerals,
except those containing boron,
by the flame test. It is distin-
guished from borax by its insolu-
bility in water and from boracite by its inferior hardness and crystal-
lization.

Synthesis. — Colemanite has been prepared by treating ulexite
(NaCaB509 • 8H2O) with a saturated solution of NaCl at 700.

Occurrence and Origin. — The mineral occurs as indefinite layers
interstratified with shale and limestones that are associated with basalt.
The rocks contain layers and nodules of colemanite. Gypsum is often
associated with the borate and in some places is in excess. The cole-
manite is believed to be the result of the action of emanations from
the basalt upon the limestone.

Localities. — Colemanite occurs in Death Valley, California, near
Daggett, San Bernardino County, and near Lang Station, Los Angeles
County, and at other points in the same State, and in western Nevada,
near Death Valley. A snow-white, chalky variety (priceite) has been
found in Curry County, Oregon, and a compact nodular variety (pander-
mite) at the Sea of Marmora, and at various points in Asia Minor.

Preparation. — Colemanite is at the present time the principal source

210 DESCRIPTIVE MINERALOGY

of borax. The crude material as mined contains from 5 per cent to 35
per cent of anhydrous boric acid (B2O3). This is crushed and roasted.
The colemanite breaks into a white powder which is separated from
pieces of rock and other impurities by screening, and then is bagged and
shipped to the refineries where it is manufactured into borax and boracic
acid.

Production. — The principal mines producing the mineral in 191 2
were situated in the Death Valley section of Inyo County, near Lang
Station in Los Angeles County, California, and in Ventura County in
the same State. The total production during the year was 42,315
tons of crude ore, valued at $1,127,813. The imports of crude ore,
refined borax and boric acid during the same year were valued at $11,200.
The production of the United States in boron acid compounds is
about half that of the entire world, with Chile producing nearly all
the rest.

Boracite (Mg5(MgCl)2Bi603o)

Boracite is interesting as a mineral, the form and internal structure
of which do not correspond, that is, do not possess the same symmetry.
Its crystals have the well marked hextetrahedral symmetry of the iso-
metric system, but their internal structure, as revealed by their optical
properties is orthorhombic. This is due to the fact that the substance
is dimorphous. Above 265 ° it is isometric and below that temperature
orthorhombic. Crystals formed at temperatures above 265° assume
the isometric shapes. As the temperature falls the substance changes
to its orthorhombic form, and there results a pseudomorph of ortho-
rhombic boracite after its isometric dimorph.

It is a salt of the acid which may be regarded as related to boric
acid as follows: 8H3BO3— gl^C^HeBgOis. Ten atoms of hydrogen
in two molecules of the acid are replaced by Mgs and the other two by
2(MgCl). The resulting combination is: 31.4 per cent MgO; 7.9 per
cent CI and 62.5 per cent B203=ioi.8(0=C1=i.9). The mineral
alters slowly, taking up water, so that some specimens yield water on
analysis and in the closed tube (stassfurti'.e and parasite).

The forms usually found on the crystals are -(in), ooO(no),

• 2

00 O 00 (100), (1T1) (Fig. 105). Usually the positive and negative

tetrahedrons may be distinguished by their luster, the faces of the posi-
tive form being brilliant and those of the negative form dull. The
crystals are isolated, or embedded, and rarely in groups. They are

NITRATES AND BORATES

211

Fig. 105. — Boracite
Crystal with 00 O 00 ,
100 (a); 00 O, no (rf);

O O

+-, in (0) and --,

ill (Oi).

strongly pyroelectric with the analogue pole in the negative tetrahedrons.
The mineral is also found massive.

Boracite is transparent or translucent and is gray, yellow, or green.
Its streak is white. Its luster is vitreous. Its cleavage is indistinct
parallel to O(ni) and its fracture is conchoidal.
The mineral is brittle. Its hardness is 7 and
its density 3. Its refractive index 0, for yellow
light, =1.667.

Boracite fuses easily before the blowpipe
with intumescence to a white pearly mass, at
the same time coloring the flame green. With
copper oxides it colors the flame azure-blue.
When moistened with Co(NC>3)2 it gives the
pink reaction for magnesium. Some massive
forms yield water in the closed tube, in conse-
quence of weathering. The mineral is soluble
in HC1.

Boracite is distinguished from other boron salts by its crystallization,
its lack of cleavage and its much greater hardness. The massive vari-
eties which resemble fine-grained white marble can be distinguished
from this by the flame coloration, hardness and reaction with HC1.

Syntheses. — Crystals have been formed by heating borax, MgCb
and a little water at 2750, and by fusing borax with a mixture of NaCl
and MgCb-

Occurrence. — Boracite occurs in beds with anhydrite, gypsum and
salt, and as crystals in metamorphosed limestones.

Localities. — It is found as crystals in gypsum and anhydrite at
Ltineburg, Hanover, and Segeberg, Holstein; in carnallite at Stassfurt,
Prussia; and in radiating nodules (stassfurtite) and in massive layers
associated with salt beds at the last-named locality. It is rare in the
United States.

Uses and Production. — Boracite is utilized in Europe as a source of
boron compounds. Turkey produces annually about 12,000 tons.

CHAPTER XI
THE CARBONATES

The carbonates constitute an important, though not a very large,
group of minerals, though one of them, calcite, is among the most com-
mon of all minerals. They are all salts of carbonic acid (H2CO3). Those
in which all the hydrogen has been replaced by metal are normal salts,
those in which the replacement has been by a metal and a hydroxyl
group are basic salts. Both groups are represented by common minerals.

The normal salts include both anhydrous salts and salts combined
with water of crystallization. Illustrations of the three classes of car-
bonates are: CaCC>3, calcite, normal salt; Na2C03 • 10H2O, soda,
hydrous salt and (Cu '011)2003, malachite, basic salt. All carbonates
effervesce in hot acids. The basic salts yield water at a high tempera-
ture only; the hydrous ones at a low temperature.

The carbonates are all transparent or translucent, and all are poor
conductors of electricity. Most of them are practically nonconductors.

ANHYDROUS CARBONATES

NORMAL CARBONATES

The anhydrous normal carbonates comprise the most important
carbonates that occur as minerals. Most of them are included in a
single large group whose members are dimorphous, crystallizing in the
ditrigonal scalenohedral class of the hexagonal system and in the holo-
hedral division (rhombic bipyramidal class) of the orthorhombic sys-
tem. The calcium carbonate exists in three forms but only two are
known to occur as minerals.

CALCITE-ARAGONITE GROUP

The relation of the dimorphs of this group to one another has been
subjected to much study, especially with reference to the two forms of
CaC03. The orthorhombic form, aragonite, passes into the hexagonal
form, calcite, upon heating to about 4000. At all temperatures below
9700, calcite is the stable form. Moreover, while calcite crystallizes
from a dilute solution of CaC03 in water containing CP2 at a low tem-

212

CARBONATES 213

perature, aragonite separates at a temperature approaching that of
boiling water — the more freely, the less CO2 in the solution. Arag-
onite crystals will also separate from a solution of calcium carbonate,
if, at the same time, it contains a grain of an orthorhombic carbonate,
or a small quantity of a soluble sulphate. Some of the other carbon-
ates, for instance, strontianite (the orthorhombic SrCOs), pass over
into an hexagonal form like that of calcite at 700°, but again change
to the orthorhombic form upon cooling. For convenience the group
is divided for discussion into the calcite division and the aragonite
division.

CALCITE DIVISION

The calcite division of carbonates includes nine or more distinct
compounds and a number of well defined varieties of these. Six of the
compounds are common minerals. All crystallize in the ditrigonal
scalenohedral class of the hexagonal system and are thus isomorphous.
Their most common crystals have a rhombohedral habit. The names of
the six common members with their axial ratios are:

Calcite CaCCto 0 : c= 1 : .8543

Magnesite MgCC>3 =1 : .8095

Siderite FeCC>3 =1 : .§191

Rhodochrosite MnCC>3 =1 • 8259

Smit'.iSonitc ZnCCfe =1 : .8062

There is usually also included in the group the mineral dolomite, which
is a calcium magnesium carbonate in which CaCCfe and MgCC>3 are
present in the molecular proportions, thus: MgCCb-CaCOs, or
MgCa(C03)2. Its crystals are similar to those of calcite and its physical
properties are intermediate between those of calcite and magnesite.
Its symmetry, however, as revealed by etching is tetartohedral (rhom-
bohedral class).

The close relationship existing between the members of the group
(including dolomite) will be appreciated upon comparing the data in
the following table:

Calcite 3.

Dolomite 3-5~4

Magnesite 3-5~4-5

Siderite 3-5"4

Rhodochrosite.. 3.5-4.5

Smithsonite. ... 5.

Ref. Indices

Sp. Gr.

a : c

ion Aon

I (1)

2-73

■8543

74° 55'

1-6585

1.4863

2.85

.8322

73° 45'

I. 6817

1 . 5026

3-°4

.8095

72° 36'

1. 717

I-5I5

3-88

.8191

73° 0'

1.8724

16338

3 55

•8259

73 0

1.820

1 5973

4-45

.8062

720 20'

i.8i8±

1. 6177

214

DESCRIPTIVE MINERALUGY

Calcite (CaC03)

Calcite is one of the most beautifully jcrystallized minerals known.
Its crystals are very common, and sometimes very large. They are
usually colorless, though sometimes colored, and are nearly always
transparent. Besides occurring in crystals the mineral is often found
massive, in granular aggregates, in stalactites, in pulverulent masses,

Fig. 106.

Fig. 108.

Fig. 107. Fig. 109.

Fig. 106.— Calcite Crystal with — JR, 01T2 (<?) and 00 R; 10T0 (m). Nail-head Spar.

Fig. 107. — Calcite Crystal with m and e. Prismatic Type.

Fig. 108.— Calcite Crystals with m; R3, 2 131 (v) and R, 10T1 (r). Dog-tooth Spar.

Fig. 109. — Calcite with r, v; 4R, 4041 (M) and R*, 3251 (y).

in radial groupings, in fibrous masses and in a variety of other forms. As
calcite is soluble in water containing CO2, it has often been found pseu-
domorphing other minerals.

Theoretically, calcite contains 56 per cent CaO and 44 per cent CO2,
but practically the mineral contains also small quantities of Mg, Fe,
Mn, Zn and Pb, metals whose carbonates are isomorphous with
CaC03.

The forms that have been observed on calcite crystals are arranged

CARBONATES

215

in such a manner as to produce three distinct types of habit, as fol-
lows: (i) the rhombohedral type, bounded by the flat rhombohedrons,
R(ioTi), — JR(oiTa) and often blunt scale-
nohedrons, like R3(2ili) and ^(3145)
in which the rhombohedrons predominate
(Fig. 106); (2) the prismatic type, with
the prism 00 P(ioTo) predominating, and
— jR(oiia) as the principal termination
(Fig. 107), and (3) dog-tooth spar, contain-
ing the same scalenohedrons as on the first
type mentioned above with other steeper
ones and small steep rhombohedral planes
(Fig. 108, 109, no). Nail-head spar con-
tains the flat rhombohedron — JR(oiTa)
with the prism 00 P(ioTo) (Fig. 106).

Some of the crystals are very compli-
cated, belonging to no one of the distinct

types described above, but forming barrel-shaped or almost round
bodies. Over 300 well established forms have been identified on them.

Twins are common. The principal laws are: (1) twinning plane
oP(oooi), with the vertical axis common to the twinned parts (Fig.
in), (2) twinning plane — §R(otl2), with the two vertical axes inclined

Fie. 1 10.— Prismatic Crystals
of Calrite Terminated by
Scalenohedrons and Rhom -
bohedrons, from Cumber-
laud, England.

Fic. in. — Calcite, R* (.3131) Twinned about oP (0001).
— Calcite: Twin and Per/synthetic Trilling of R (10T1) about — )R (01

at an angle of about 525° (Fig. 112) and (3) twinning plane R(ioTi),
with the vertical axes inclined 8o° 14' (Fig. 113).

Twins of the second class can easily be produced artificially on cleav-
age rhombs by pressing a dull knife edge on the obtuse rhombohedral
edge with sufficient force to move a portion of the mass (Fig. 114).
The change of position of a portion of the calcite does not destroy its

DESCRIPTIVE MINERALOGY

transparency in the least. Repeated twinning of this kind is frequently
seen in marble (Fig. 115), where it gives rise to parallel lamellae.

The cleavage of calcite is so perfect parallel to R that crystals when

Fig.

Fig. 113. F10. 114.

Fig. 113— Calcite with m, c and e, Twinned about R (ioii).
14.— Artificial Twin of Calcite, with — JR (011a) the Twinning Plane.

shattered by a hammer blow usually break into perfect little rhombo-
hedrons. Its hardness is about 3 and its density 2.713. Pure calcite
is colorless and transparent, but most specimens are white or some pale
shade of red, green, gray,
blue, yellow, or even brown
or black when very impure,
and are translucent or opaque.
The mineral is very strongly
doubly refracting, (see p. 213).
It is a very poor conductor of
electricity.

The principal varieties of
the mineral to which distinct
names have been given are:

Iceland spar, the trans-
parent variety used in the
manufacture of optical instru-
ments.

Salin spar, a fine, fibrous
variety with a satiny luster.

Limestone, granular ag-
gregates occurring as rock
masses.
Marble, a crystalline limestone, showing when broken the cleavage
faces of the individual crystals.

Lithographic stone. 1 very fine and even-grained limestone.

Fig. 115. — Thin Section of Marble Viewed by
Polarized Light. The dark bars are poly-
synthetic twinning lamellae. Magnified 5
diameters.

CARBONATES 217

Stalactites, cylinders or cones of calcite that hang from the roofs of
caves. They are formed by the evaporation of dripping water.

Stalagmites, corresponding cones on the floors of caves beneath the
stalactites.

Mexican onyx, banded crystalline calcite, often transparent.
Usually portions of stalactites.

Travertine, a deposit of white or yellow porous calcite produced
in springs or rivers, often around organic material like the blades
or roots of grass.

Chalk, a fine-grained, pulverulent mass of calcite, occurring in
large beds.

In the closed tube calcite often decrepitates. Before the blowpipe it
is infusible. It colors the flame reddish yellow and after heating reacts
alkaline toward moistened litmus paper. The mineral dissolves with
evolution of CO2 in cold hydrochloric acid. Its dissociation tempera-
ture l is 8980, though it begins to lose CO2 at a much lower temperature.

The reaction with HC1, together with the alkalinity of the mineral
after heating, its softness and its easy cleavage, distinguish calcite from
all other minerals. In massive forms it has been thought that it could
be distinguished from aragonite by heating its powder with a little
Co(NOa)2 solution. Aragonite was thought to become violet-colored
in a few minutes while calcite remained unchanged, but recent work
proves that this test cannot be relied upon.

Syntheses. — Calcite crystals are obtained by allowing a solution
of CaCOa in dilute carbonic acid to evaporate slowly in contact with the
air at ordinary temperatures. If evaporated at from 8o° to ioo°
ordinary temperatures, or in the presence of a little sulphate, the ortho-
rhombic aragonite will form. Calcite is also formed by heating arag-
onite to 400-4700.

Occurrence and Origin. — The mineral is widely distributed in beds,
in veins and as loose deposits on the bottoms of springs, lakes and rivers.
Its principal methods of origin are precipitation from solutions, the
weathering of calcareous minerals, and secretion by organisms.

Calcite is the most important of all pseudomorphing agencies. It
forms pseudomorphs after many different minerals and the hard parts
of animals.

Localities. — The most noted localities of crystallized calcite are:
Andreasberg in the Harz; Freiberg, Schneeberg and other places in
Saxony; Kapnik, in Hungary; Traverselia, in Piedmont; Alston Moor

1 The dissociation temperature of a carbonate is that temperature at which the
pressure of the released CO? equals one atmosphere.

218 DESCRIPTIVE MINERALOGY

and Egremont, in Cumberland, Matlock, in Derbyshire, and the mines
of Cornwall, England; Guanajuato, Mexico; Lockport, N. Y.; Ke-
weenaw Point, Mich.; the zinc regions of Illinois, Wisconsin and
Missouri; Nova Scotia, etc.

Iceland spar is obtained in the Eskefjord and the Breitifjord in
Iceland. Travertine is deposited from the waters of the Mammoth
Hot Springs, Yellowstone National Park. It occurs also along the
River Arno, near Tivoli, Rome.

Uses. — Calcite has many important uses. In the form of Iceland
spar, on account of its strong double refraction, it is employed in optical
instruments for the production of polarized light. Calcite rocks are
used as building and ornamental stones. They are employed also as
fluxes in smelting operations, as one of the ingredients in glass-making
and in the manufacture of lime, cement, whiting, and in certain printing
operations. Limestone is also used as a fertilizer.

Production. — The calcite rock marketed in the United States during
191 2 was valued at about $44,500,000. It was used as follows: In
concrete, $5,634,000; in road and railroad making, $12,000,000; as a
flux, $10,000,000; as building and monumental stone, $12,800,000;
in sugar factories, $335,000; as riprap, $1,183,000, for paving, $279,000,
and for other uses, $2,400,000. Moreover, the value of the Portland
cement manufactured during the year amounted to $67,017,000, the
quantity of lime made to $13,970,000, the value of the hydrated
lime to $1,830,000, and of sand-lime brick to $1,170,884. The quantity
of limestone required for these manufactures is not known, but it was
very great.

Magnesite (MgC03)

Magnesite usually occurs in fine-grained white masses. Crystals
are rare. Pure magnesite consists of 52.4 per cent CO2 and 47.6 per
cent MgO. It usually, however, contains some iron carbonate.

Magnesite is completely isomorphous with calcite. Its cleavage is

perfect parallel to R(ioTi). Its hardness is about 4 and the density 3.1.

The mineral is transparent or opaque. It varies in color from white

to brown, but always has a white streak. Its dissociation temperature

is 4450.

Magnesite behaves like calcite before the blowpipe. It effervesces
in hot hydrochloric acid and readily yields the reaction for magnesia
with Co(N03)2. It is most easily distinguished from the latter mineral
by its density, by the fact that it does not color the blowpipe flame with
the yellowish red tint of calcium and does not effervesce in cold HC1.

CARBONATES 219

Synthesis. — Magnesite crystals may be obtained by heating MgSOi
in a solution of Na2CC>3 at 1600 in a closed tube.

Occurrence and Origin. — Magnesite usually occurs in veins and masses
associated with serpentine and other magnesium rocks from which it
has been formed by decomposition. It is often accompanied by brucite,
talc, dolomite and other magnesium compounds. It has recently been
described as occurring also in a distinct bed near Mohave, Cal., inter-
stratified with clays and shales. It is thought that in this case it may
have been precipitated from solutions of magnesium salts by Na2C03.

Localities. — The mineral is found abundantly in many foreign local-
ities and at Bolton, Mass.; Bare Hills, near Baltimore, Md., and in
Tulare Co., Cal., and near Texas, Penn. The largest deposits are in
Greece and Hungary.

Uses. — Magnesite is employed very largely in the manufacture of
magnesite bricks used for lining converters in steel works, in the lining
of kilns, etc., in the manufacture of paper from wood pulp, and in mak-
ing artificial marble, tile, etc. From it are also manufactured epsom
salts, magnesia (the medicinal preparation), and other magnesium com-
pounds, and the carbon dioxide used in making soda water.

Production. — All of the magnesite mined in the United States comes
from California, where the yield was 10,512 tons in 191 2, valued at
$105,120. Most of the magnesite used in the United States is imported
from Hungary and Greece. In 191 2, 14,707 tons of crude material
entered the country and 125,000 tons of the calcined product, the total
value of which was $1,370,000.

Siderite (FeC03)

Siderite is an important iron ore, though not as much used as formerly.
It is found crystallized and massive, in botryoidal and globular forms
and in earthy masses.

In composition the mineral is FeCC>3, which is equivalent to 62.1
per cent FeO (48.2 per cent Fe) and 37.9 per cent CO2. Manganese,
calcite and magnesium are also often present in it.

Crystals are more common than those of magnesite. They fre-
quently contain the basal plane and the steep rhombohedrons— 8R(o85i)
and — 58.(0551). R(ioTi) and — £R(oil2) are common. The faces
of the rhombohedron are frequently curved. Compare (Fig. 125.)

The cleavage of siderite is like that of the other minerals of this
group. Its hardness is 3.5-4 and density 3.85. In color the mineral
is sometimes white, but more frequently it is some shade of yellow or
brown. Its streak is white. Most specimens are translucent.

220 DESCRIPTIVE MINERALOGY

In the closed tube siderite decrepitates, blackens and becomes mag-
netic. It is only slowly affected by cold acids but it effervesces briskly
in hot ones.

Siderite is distinguished from the other carbonates by its reaction
for iron.

The mineral changes on exposure into limonite and sometimes into
hematite or even into magnetite.

Synthesis. — Crystals of siderite may be obtained by heating a solu-
tion of FeSC>4 with an excess of CaCC>3 at 2000.

Occurrence and Origin. — The mineral is often found accompanying,
metallic ores in veins. It occurs also as nodules in certain clays and in
the coal measures. In some cases it appears to be a direct deposit from
solutions. In others it is a result of metasomatism and in others is an
ordinary weathering product.

Localities. — The crystallized variety is found at Freiberg, in Saxony;
at Harzgerode, in the Harz; at Alston Moor, and in Cornwall, Eng-
land; and along the Alps, in Styria and Carinthia. Cleavage masses
are present in the cryolite from Greenland.

Workable beds of the ore are present in Columbia Co., and at Rossie,
in St. Lawrence Co., N. Y.; in the coal regions of Pennsylvania and
Ohio, and in clay beds along the Patapsco River, in Maryland. The
massive or nodular ore from clay banks is known as ironstone. The
impure bedded siderite interstratified with the coal shales is known
as black-band ore.

Production. — Only 10,346 tons of siderite were produced in the United
States during 191 2, all of it coming from the bedded deposits in Ohio.
This was valued at $20,000.

Rhodochrosite (MnC03)

This mineral sometimes occurs in distinct crystals of a rose-red
color; but it is usually found in cleavable masses, in a compact form,
or as a granular aggregate. Sometimes it is in incrustations. It is
not of commercial importance in North America.

Pure manganese carbonate containing 61.7 per cent MnO and 38.3
per cent CO2 is rare. The mineral is usually impure through the addi-
tion of the carbonates of iron, calcium, magnesium or zinc.

The most prominent forms on crystals of rhodochrosite are R(io7i),
— £R(oil2), ooP2(ii2o), oR(oooi) and various scalenohedrons.

Its cleavage is perfect parallel to R. The mineral is brittle. Its
hardness is about 4 and its density about 3.55. Its luster is vitreous,
and its color red, brown, or yellowish gray. Its streak is white. When

CARBONATES 221

heated it begins to lose CO2 at about 3200; but its dissociation temper-
ature is 63 2°.

The mineral is infusible, but when heated before the blowpipe it
decrepitates and changes color. When treated in the borax bead it
gives the violet color of manganese, and when fused with soda on char-
coal it yields a bluish green manganate. It dissolves in hot hydro-
chloric acid.

There are bu.t few minerals resembling pure rhodochrosite in appear-
ance. From all of these, except the silicate, rhodonite (p. 380), it is
distinguished by its reaction for manganese. It is distinguished from
rhodonite by its hardness, its cleavage and its .effervescence with acids.
The impure varieties are very like some forms of siderite, from which,
of cqurse, the manganese test will distinguish it.

Synthesis. — Small rhombohedrons of rhodochrosite have been pro-
duced by heating a solution of MnSO* with an excess of CaCCfe at 2000
in a closed tube.

Occurrence and Origin. — Rhodochrosite occurs in veins associated
with ores of silver, lead, copper and other manganese ores and in bedded
deposits. It is the result of hydrothermal or contact metamorphism,
and of weathering of other manganese-bearing minerals.

Localities. — The mineral is found at Schemnitz, in Hungary; at
Nagyag, in Transylvania; at Glendree, County Clare, Ireland, where it
forms a bed beneath a bog; at Washington, Conn., in a pulverulent
form; at Franklin, N. J.; at the John Reed Mine, Aliconte, Lake Co.,
and at Rico, Colo.; at Butte City, Mont.; at Austin, Nev., and on
Placentia Bay, Newfoundland. The Colorado and Montana specimens
are well crystallized.

Uses. — The mineral is mined with other ores of manganese. Occa-
sionally it is employed as a gem stone.

Smithsonite (ZnCOs)

Smithsonite, or " dry-bone ore," is rarely well crystallized. It
appears as druses, botryoidal and stalactitic masses, as granular aggre-
gates and as a friable earth.

In ZnC03 there are 64.8 per cent ZnO and 35.2 per cent CO2. Smith-
sonite usually contains iron and manganese carbonates, often small
quantities of calcium and magnesium carbonates and sometimes traces
of cadmium. A specimen from Marion, Arkansas, gave:

ZnO

CdO FeO

CaO

CuO

C02

CdS

Si02

Total

64.12

.63 .14

.38

tr.

34.68

•25

.06

100.26

222 DESCRIPTIVE MINERALOGY

The mineral is closely isomorphous with calcite, R(ioTi), — JR(oiT2),
4R(404i), oo R2(ii2o), oR(oooi) and R3(2i3i) being present on many
crystals. The R faces are rough or curved.

Its cleavage is parallel to R(ioTi). Its hardness is 5 and its density
about 4.4. The luster of the mineral is vitreous, its streak is white and
its color white, gray, green or brown. It is usually translucent, occa-
sionally transparent. When heated to 3000 for one hour it loses all of
its C02.

When heated in the closed tube CO2 is driven off, leaving ZnO as a
yellow residue while hot, changing to white on cooling. The mineral
is infusible before the blowpipe. If a small fragment be moistened with
cobalt nitrate solution and heated in the oxidizing flame it becomes
green on cooling. When heated on charcoal a dense white vapor is
produced. This forms a yellow coating on the coal, which, when it
cools, turns white. If this be moistened with cobalt nitrate and reheated
in the oxidizing flame it is colored green.

The above reactions for zinc, together with the effervescence of the
mineral in hot hydrochloric acid distinguish smithsonite from all other
compounds.

Smithsonite forms pseudomorphs after sphalerite and calcite and is
pseudomorphed by quartz, limonite, calamine and goethite.

Synthesis. — Microscopic crystals of smithsonite may be produced by
precipitating a zinc sulphate solution with potassium bicarbonate and
allowing the mixture to stand for some time.

Occurrence. — Smithsonite occurs in beds and veins in limestones,
where it is associated with galena and sphalerite and usually with cala-
mine (p. 396). It is especially common in the upper, oxidized zone of
veins of zinc ores and as a residual deposit covering the surface of weath-
ered limestone containing zinc minerals.

Localities. — The mineral is found at Nerchinsk, Siberia; Bleiberg,
in Carinthia; Altenberg, Aachen; Province of Santander, Spain; at
Alston Moor and other places in England; at Donegal, in Ireland; at
Lancaster, Penn.; at Dubuque, Iowa; in Lawrence and Marion Coun-
ties, Arkansas; and in the lead districts of Wisconsin and Missouri (see
galena and sphalerite).

The Wisconsin and Missouri localities are the most important ones
in North America. Here the ore occurs in botryoidal, in stalactitic
and in earthy, compact, cavernous masses of a dull yellow color incrusted
with druses of smithsonite crystals, of calamine and of other minerals,
principally of lead. This is the variety known as " dry bone."

Uses. — The mineral was formerly an important ore of zinc, being "

CARBONATES 223

mined alone for smelting. It is now mined only in connection with
calamine and other zinc ores, and all are worked up together. A trans-
lucent green or greenish blue variety occurring at Laurium, Greece,
and at Kelly, New Mexico," is sometimes employed for ornamental pur-
poses. About $650 worth of the material from New Mexico was utilized
as gem material in 191 2.

ARAGONITE DIVISION

This division of the carbonates includes the orthorhombic (rhombic
bipyramidal) dimorphs of the members of the calcite group which,
together, form a well characterized isodimorphous group. The carbon-
ate of calcium is found well crystallized in both divisions, but the other
carbonates are common to one only. They actually occur in both divi-
sions, but they are found as common members of one and only as
isomorphous mixtures with other more common forms in the other.
Thus, barium carbonate is a common orthorhombic mineral under the
name of uitherite. It occurs also with CaCC>3 hi mixed crystals under
the name baricalcite, or neotypey which is hexagonal. (See also p. 212
and p. 213.)

The common members of the aragonite division are:

Aragonite CaCC>3 Sp. Gr. = 2.936 a : b : c= .6228 : 1

Stroniianite SrC03 = 3 . 706 = . 6090 : 1

Witherite BaC(>3 =4.325 = . 5949 : 1

Cerussite PbC03 =6.574 =.6102:1

.7204
.7266

•7413
.7232

Aragonite (CaCOs)

Aragonite occurs in a great variety of forms. Sometimes it is in
distinct crystals, but more frequently it is in oolitic globular and reni-
form masses, in divergent bundles of fibers or of needle-like forms, in
stalactites and in crusts.

In composition aragonite is like calcite. It often contains small
quantities of the carbonates of strontium, lead or zinc.

Crystals are often acicular with steep domes predominating. Some
of the simplest crystals consist of ooP(no), 00P06 (010), fPoo (032),
P06 (on), 4P(44i), 9P(99i) and ooP2(i2o) (Fig. 116). Twinning is
common. The twinning plane is often ooP(no). By repetition this
gives rise to pseudohexagonal forms, resembling an hexagonal prism and
the basal plane (see Figs. 117 and 118). The angle noAiTo=63° 48'.

The cleavage of aragonite is distinct parallel to 00 P 06 (010) and
indistinct parallel to 00 P(no). Its hardness is 3.5-4 and density about
2.93. Its luster is vitreous and its color white, often tinged with gray,

DESCRIPTIVE MINERALOGY

green or some other light shade. Its streak is white and the mineral is
transparent or translucent. Its indices of refraction for yellow light are:
a= 1.5300, 7= 1.6857. At 4000 it passes over into calcite.

Before the blowpipe aragonite whitens and falls to pieces. Other-
wise its reactions are like those of calcite, from which it can be distio-

^P\

kj>^

/ 1 1 u 1. in a

u m » 1 i m B

Fie. 116.— Aragonite Crystal with =oP,iio(m); »Pw, 010 (S) and P« , on {*).
Fig. 117. — Aragonite Twin and Trilling Twinned about » P (no).

Fie. 118.— Trilling of Aragonite Twinned about »P (no). (/I) Cross-section.
(B) Resulting pseudohexagonal group, resembling an hexagonal prism and

guished by its crystallization, its lack of rhombohedral cleavage and its
density.

Synthesis. — Solutions of OCO3 in dilute H2CO3 form crystals of
aragonite when evaporated at a temperature of about 900. In general,
hot solutions of the carbonate deposit aragonite, while cold solutions
deposit calcite. If the solution contains some sulphate or traces of
strontium or lead carbonates, mixed crystals consisting principally of
the aragonite molecule are formed at ordinary temperature.

Occurrence and Origin. — Aragonite occurs in beds, usually with
gypsum. It is also deposited from hot waters and from cold waters

CARBONATES 225

containing a sulphate (as from sea water). The pearly layer of oyster
shells and the body of the shells of some other mollusca are composed
of calcium carbonate crystallizing like aragonite. Aragonite is often
changed by paramorphism into calcite, pseudomorphs of which after
the former mineral are quite common.

Localities. — The mineral is found at Aragon, Spain; at Bilin, in
Bohemia; in Sicily; at Alston Moor, England; and at a number of
other places in Europe. It occurs in groupings of interlacing slender
columns (flos ferrt) , in the iron mines of Styria. Stalactites are abundant
at Leadhills, Lanarkshire, Scotland, and a silky fibrous variety known as
satins par, at Dayton, England.

In the United States crystallized aragonite occurs at Mine-la-Motte,
Mo., and in the lands of the Creek Nation, Oklahoma. Flos ferri has
been reported from the Organ Mts., New Mexico, and fibrous masses
from Hoboken, N. J., Lockport, Edenville and other towns in New York
and from Warsaw, 111.

Strontianite (SrC03)

In general appearance and in its manner of occurrence strontianite
resembles aragonite. Its crystals are often acicular in habit though
repeated twins are common. The angle noAiTo=62° 41'.

The composition of pure strontianite is SrO=7o.i, ^2=29.9, but
the mineral usually contains an admixture of the barium and calcium
carbonates.

Strontianite is brittle, its hardness is 3.5-4 and its density 3.7.

Before the blowpipe strontianite swells and colors the flame with a
crimson tinge. It dissolves in hydrochloric acid. The solution im-
parts a crimson color to the blowpipe flame. When treated with sul-
phuric acid it yields a precipitate of SrSO*. Its refractive indices for
yellow light are: a =1.5 199, 7=1.668. Its dissociation temperature is

"55°.

Aragonite, witherite (BaCOa) and strontianite are so similar in ap-
pearance and in general properties that they can be distinguished from
one another best by their chemical characteristics. They are all sol-
uble in hydrochloric acid and these solutions impart distinctive colors
to the blowpipe flame (see p. 477).

Syntheses. — Crystals of strontianite are obtained by precipitating
a hot solution of a strontium salt by ammonium carbonate, and by cool-
ing a solution of SrC03 in a molten mixture of NaCl and KC1.

Occurrence. — Strontianite occurs in veins in limestone and as an

226 DESCRIPTIVE MINERALOGY

alteration product of the sulphate (celestite) where this is exposed to the
weather. It is probably in all cases a deposit from water.

Localities. — Strontianite is the most common of all strontiaa-fiem-
goupds. It frequently occurs as the filling of metallic veins. It forms
finely developed crystals at the Wilhelmine Mine near Munster, West-
phalia. At Schoharie, N. Y., it occurs as crystals and as granular masses
in nests in limestone. It is found also at other places in New York, in
Mifflin Co., Penn., and on Mt. Bannell near Austin, Texas.

Uses. — Strontium compounds are little used in the arts. The
hydroxide is employed to some extent in refining beet sugar and the
nitrate in the manufacture of " red fire." Other compounds are used
in medicine. All the strontium salts used in the United States are
imported.

Witherite (BaC03)

Witherite differs very little in appearance or in manner of occurrence
from aragonite. Its crystals are nearly always in repeated twins that

have the habit of hexagonal pyramids' (Fig.
119). The angle 1 10 A 1 To = 62° 46'.

When pure the mineral contains 77.7 per
cent BaO and 22.3 per cent CO2.

It is much heavier than the calcium car-
bonate, its density being 4.3. Its hardness
Fig. 119.— Witherite Twinned is 3 to 4. Its refractive index for yellow
about cop (1 10), thus Imi- Hghtj /3=Ii740. its dissociation tempera-

tating Hexagonal Combina- . 0

tions. m°°

It dissolves readily in dilute hydrochloric

acid with effervescence, and from this solution, even when dilute, sul-
phuric acid precipitates a heavy white precipitate of BaS04, which,
when heated in the blowpipe flame, imparts to it a yellowish green
color.

Witherite is distinguished from the other carbonates by its crys-
tallization, and the color it imparts to the blowpipe flame.

Syntheses. — Crystals are produced by precipitating a hot solution of
a barium salt with ammonium carbonate, and by cooling a molten
magma composed of NaCl and BaC03.

Localities. — Witherite is not a very common mineral in the United
States, but it occurs in large quantity associated with lead minerals in
veins at Alston Moor, in Cumberland and near Hexham, in Northum-
berland, England. Some of the crystals found in these places measure
as much as six inches in length.

CARBONATES

227

Its best known locality in the United States is Lexington, Kentucky,
where the mineral is associated with the sulphate, barite.

Uses. — It is used to some extent as a source of barium compounds.
The importations of the mineral during 1912 aggregate $25,715.

Cerussite (PbC03)

Cemssite generally occurs in crystals and in granular, earthy and
fibrous masses of a white color.

The pure lead carbonate contains COa=i6.5 and PbO=83.5, bui
the mineral usually contains in addition some ZnCOs.

Mi -PS, «©<»);
<*); JP», onto and

—Cerussite Trilling Twinned about °°P(uo).
—Cerussite Trilling Twinned about « P3(l3o).

Its simple crystals are tabular combinations of °oP(no}, 00 Pd6 (010)
ooPob(roo) and various brachydomes (Fig. 120), and these are often
twinned in such a way as to produce six rayed stars (Fig. 121), or other
symmetrical forms (Fig. 122). Groups of interpenetrating crystals
are also common. The angle iioaii°=o2° 46'.

The color of the mineral is usually white, but its surface is frequently
discolored by dark decomposition products. Its luster is adamantine
or vitreous and its hardness is 3-3.5. Itsdensity=6.s. Its refractive
indices for yellow light are: 0 = 1.8037,^=2.0763,7=2.0780.

The mineral is dissolved by nitric acid with effervescence and by
potassium hydroxide. Before the blowpipe it decrepitates, turns yellow
and changes to lead oxide. On charcoal it is reduced to a metallic
globule, and yields a white and yellow coating.

228 DESCRIPTIVE MINERALOGY

Cerussite is not easily confused with other minerals. It is well char-
acterized by its high specific gravity, its reaction (or lead, and is dis-
tinguished from the sulphate (anglestie) by effervescence with hot acids.

Syntheses. — Crystals have been obtained by heating lead formate with
water in a closed tube, and by treatment of a lead salt by a solution of
ammonium carbonate at a temperature of tso°-i8o°.

Occurrence and Origin. — The mineral occurs at all localities at which
other lead compounds are found, since it is often produced from thes?

Fig. 123. — Radiate Groups of Cerussite on Galena from Part City District, Utah.
(After J. M. BoutmB.)

latter by the action of the atmosphere and atmospheric water. It is,
therefore, usually found in the upper portions of veins.

Localities. — Cerussite crystals of great beauty are found in many of
the lead-producing districts of Europe and also at Phoenixville, Penn.;
near Union Bridge, in Maryland; at Austin's Mines, Wythe Co., Vir-
ginia, and occasionally in the lead mines of Wisconsin and Missouri.
In the West it occurs at Leadville, Colo.; at the Flagstaff and other
mines in Utah (Fig. 123), and at several different mines in Arizona.

Uses.— It is mined with other lead compounds as an ore of the metal.

CARBONATES 229

Dolomite (MgCa(C03)2)

Dolomite is apparently isomorphous with calcite but the etch
figures on rhombohedral faces prove it to belong in the trigonal
rhombohedral class. It occurs as crystals and in all the forms charac-
teristic of calcite except the fibrous.

Nearly all calcite contains more or less magnesium carbonate, but
most of the mixtures are isomorphous with calcite and magnesite.
When the ratio between the two carbonates reaches 54.35 per cent
CaC03 : 45.65 per cent MgCC>3, which is equal to the ratio between
the molecular weights of the two substances, or in other words when the
two carbonates are present in the compound in the ratio of one molecule
to one molecule, the mineral is called dolomite. The calculated com-
position of dolomite (MgCa(COs)2) is 30.4 per cent CaO; 21.7 per cent
MgO and 47.8 per cent CO2.

The crystals of dolomite are usually rhombohedral combinations of
the rhombohedron R(ioTi) with the scalenohedron
R3(2i3i) (Fig. 124), and its tetartohedral forms,
and often the prism ooP2(ii2o) and the basal
plane. Its axial ratio is a : c=i : .8322. Twins
are not rare, with oR(oooi) and R(ioTi) the
twinning planes. The R planes are often curved,
frequently with concave surfaces (Fig. 125). The
angle 10T1 A 1101 = 73°. FiG l2 _Dolomite

The cleavage of dolomite is perfect parallel crystal with° R
to R. The mineral is brittle. Its hardness is 40^I (^ an(j 0p'
3.5-4 and density 2.915. Its luster is vitreous or 0001 (c).
pearly and its color white, red, green, gray or
brown. Its streak is always white and the mineral is translucent or
transparent. Its refractive indices for yellow light are: a>=i.68i7,
e= 1.5026. The important varieties recognized are:

Pearlspar, with curved faces having a pearly luster.

Granular or saccharoidal, including many marbles and magnesian
limestones.

Dolomitic limestone, including much hydraulic limestone.

Many dolomites are intermixed with the carbonates of iron, manga-
nese, cobalt or zinc and these are known as ferriferous dolomite, etc.

Dolomite behaves like calcite before the blowpipe and in the closed
tube. It, however, dissolves only slowly, if at all, in cold hydrochloric
acid, except when very finely powdered, though dissolving readily with
effervescence in hot acid.

230 DESCRIPTIVE MINERALOGY

The reaction toward cold acid and its greater hardness easily dis-
tinguish dolomite from catcUe. It is distinguished from magnetite by
the name reaction.

Occurrence and Origin. — Dolomite, like the calcium carbonate, occurs
crystallized in veins, and as granular masses forming great beds of rock.
It is a precipitate from solutions and a metasomatic alteration product
of calcite.

Localities. — Its crystals are present at many places, among them
Bex, in Switzerland; Traversella, in Piedmont; Guanajuato, in Mexico;
Roxbury, in Vermont; Hoboken, N. J.; Niagara Falls, the Quarantine

Fig. 135. — Group of Dolomite Crystals from Joplin, Mo. Flat Rhombobcdrons with
Curved Faces.

Station, and Putnam, N. V.; Joplin, Mo.; and Stony Point, N. C. It
is also very widely spread as beds of dolomitic limestone.

Uses. — Dolomite is used for many of the purposes served by calcite;
indeed, much of the material used as marble, limestone, etc., contains a
large percentage of magnesium carbonate. It is not, however, used as a
flux or in the manufacture of Portland cement, nor as a source of lime.

Ankerite(Ca(Mg-Fe)(C03)2) is a ferruginous dolomite. It is an
isomorphous mixture of the carbonates of calcium, magnesium and iron,
in which the FeC03 replaces a part of the MgCOs in dolomite. It is
usually in rhombohedral crystals, with the angle 10T1 aTioi = 73° 48'.
Its color is white, gray or red and its streak is white. Its hardness
=3.5-4, and its density = 2.98. It also occurs in coarse and fine-grained
granular masses. Ankerite is infusible before the blowpipe. In the

CARBONATES 231

closed tube it darkens and when heated on charcoal it becomes mag-
netic. It occurs in veins, especially those containing iron minerals.
It has been found at Antwerp and other places in northern New York.

CALCIUM-BARIUM CARBONATES

Carbonates of the general composition CaBa(COs)2 occur (i) as a
series of mixed crystals isomorphous with calcite under the name bari-
calcite; (2) as a series of mixed crystals isomorphous with aragonite
known as alstonite or bromlite, and (3) a typical double salt, barytocalcite,
which is monoclinic. Both alstonite and barytocalcite occur in veins
of lead ores and of barite (BaSC>4).

Barytocalcite, CaBa(COs)2 is monoclinic (prismatic class), with
a : b : £=.7717 : 1 : 6255 and $ = 73° 52'. It forms crystals bounded
by 00 P 6b (100), ooP(no), oP(ooi), and a series of clinopyramids, of
which 2P2 (1 2!) and 5P5 (1 5!) are common. It also occurs massive. Its
perfect cleavage is parallel to ooP(no). The mineral is white, gray,
greenish or yellowish. Its streak is white, hardness =4 and sp. gr.=
3.665. It is transparent or translucent. Before the blowpipe frag-
ments fuse on thin edges, and assume a pale green color, due to the
presence of a little manganese. The mineral is soluble in HC1. Its
principal occurrence is Alston Moor, Cumberland, England.

BASIC CARBONATES

The basic carbonates are salts in which all or a portion of the hydro-
gen of carbonic acid is replaced by the hydroxides of metals. There
are only three minerals belonging to the group that need be referred to
here. Two are copper compounds. One is the bright green malachite
and the other the blue azurite. The composition of the former may be

CuOHv
represented by the formula 7CO3, and that of the latter by

CuOH'
CuOHv

Cu=(COs)2. Both are used to some extent as ores of the metal,
CuOH/

though their value for this purpose is not great at the present time.
They may easily be distinguished from all other minerals by their
distinctive colors, by the fact that they yield water in the closed tube
and by their effervescence with acids. The third mineral (hydrozincite)
is a white substance that occurs as earthy or fibrous incrustations on other
zinc compounds. Its composition corresponds to 2ZnC03*3Zn(OH)2.

232

DESCRIPTIVE MINERALOGY

Its hardness = 2-2.5 an^ *ts specific gravity is about 3.7. Only the two
copper compounds are described in detail.

Malachite ((CuOH)2C03)

Malachite usually occurs in fibrous, radiate, stalactitic, granular
or earthy, green masses, or as small drusy crystals covering other copper
compounds. The mineral contains, when pure, 19.9 per cent CO2,
71.9 per cent CuO and 8.2 per cent H2O.

Well defined crystals are usually very small monoclinic prisms (mon-

oclinic prismatic class), with an axial ratio .8809 : 1
: .4012 and 0=6i° 50'. Their predominant forms
are 00 Pco (100), 00 Pod (010), ooP(no), and
oP(ooi). Contact twins are common, with
00 Pco (100) the twinning plane (Fig. 126). The
angle no A 1^0=75° 40'.

The pure mineral is bright green in color and has
a light green streak. It possesses a vitreous luster,
but this becomes silky in fibrous masses and dull
in massive specimens. Crystals are translucent
and massive pieces are opaque. Translucent

Fig. 126. — Malachite
Crystal with 00 P,
no (m); 00 Poo,

100 (o), and oP, pieces are pleochroic in yellowish green and dark
001 (c) Twinned green tmts fne deavage is perfect parallel to

oP(ooi). The hardness of malachite is 3.5-4, and
its density about 3.9. Its refractive index, /?, for yellow light=i.88.

Malachite turns black and fuses before the blowpipe and tinges the
flame green. With Na2C03 on charcoal it yields a copper globule. It is
difficultly soluble in pure water, but is easily dissolved in water con-
taining CO2. It is soluble with effervescence in HC1 and its solution
becomes deep blue on the addition of an excess of ammonia. When
heated in a closed glass tube, it gives an abundance of water. Boiled
with water it turns black and loses its CO2.

Malachite, on account of its characteristic color, may be easily dis-
tinguished from all other minerals but some varieties of turquoise and
a few copper compounds, such as atacamile (p. 144). It may be dis-
tinguished from all of these by its effervescence with acids.

Synthesis. — Malachite crystals have been obtained with the form of
natural crystals by heating a solution of copper carbonate in ammonium
carbonate.

Occurrence and Origin. — Malachite is a frequent decomposition
product of other copper minerals, being formed rapidly in moist places.

CARBONATES 233

It occurs abundantly in the upper oxidized portions of veins of copper
ore, where it is associated with azurite, cuprite, copper, limonite and the
sulphides of iron and copper, often pseudomorphing the copper minerals.
The green stain noticed on exposed copper trimmings of buildings is
composed in part of this substance.

Localities. — The mineral occurs in all copper mines. At Chessy,
France, it forms handsome pseudomorphs after cuprite. In the United
States it has been found in good specimens at Cornwall, Lebanon Co.,
Penn.; at Mineral Point, Wisconsin; at the Copper Queen Mine, Bisbee,
and at the Humming Bird Mine, Morenci, Arizona, and in the Tintic
district, Utah.

Uses. — In addition to its use as an ore of copper the radial and mass-
ive forms of malachite are employed as ornamental stones for inside
decoration. The massive forms are also sawn into slabs and polished
for use as table tops and are turned into vases, etc.

Production. — As malachite is mined with other copper compounds,
the quantity utilized as an ore of the metal is not known. The amount
produced in the United States during 191 2 for ornamental purposes was
valued at $1,085. This, however, included also a mixture of malachite
and azurite.

Azurite (Cu(CuOH)2(C03)2)

Azurite is more often found in crystals than is malachite. It occurs
also as veins and incrustations and in massive, radiated, and earthy

Fig. 127. — Azurite Crystals with oP, 001 (c); — Poo, 101 (<r); 00 Poo, 100 (a);
P, In (*), 00 P, no (w); -2P, 221 (A); JP2, 243 (d) and Poo , on (/).

forms associated with malachite and other copper compounds. Its
most frequent associate is malachite, into which it readily alters.

In composition azurite is 25.6 per cent CO2, 69.2 per cent CuO, and
5.2 per cent H2O. It changes rapidly to malachite, and sometimes is
reduced to copper.

The crystals are tabular, prismatic, or wedge-shaped monoclinic
forms (monoclinic prismatic class), with an axial ratio a : b : £=.8501 :
1 : 1.7611, and £=87° 36'. They are usually highly modified, 58 or

234 DESCRIPTIVE MINERALOGY

more different planes having been identified on them. The predominant
ones are oP(ooi), — P<»(ioi), oo P(no), — 2P(22i) and ooPao(ioo).
(Fig. 127.) The angle noAiTo=8o° 40'.

The mineral is dark blue, vitreous, and translucent or transparent,
and is pleochroic in shades of blue. It is brittle. Its streak is light
blue, its hardness 3.5-4 and density 3.8. Its cleavage is distinct parallel
to Pob (on).

The blowpipe and chemical reactions for azurite are the same as
those for malachite. By them the mineral is easily distinguished from
the few other blue minerals known.

Synthesis. — Crystals have been formed on calcite by allowing frag-
ments of this mineral to lie in a solution of CUNO3 for a year or more.

Occurrence. — The mineral occurs in the oxidized zone of copper veins.
It is an intermediate product in the change of other copper compounds
to malachite.

Localities. — Azurite occurs in beautiful crystals at Cressy, France;
near Redruth, in Cornwall; at Phoenixville, Penn.; at Mineral Point,
Wis.; at the Copper Queen Mine, Bisbee, Ariz.; at the Mammoth
Mine, Tintic district, Utah; at Hughes's Mine, California, and at many
other copper mines in this country and abroad.

From Morenci, Ariz., Mr. Kunz describes specimens consisting of
spherical masses composed of alternating layers of malachite and
azurite, which, when cut across, yield surfaces banded by alternations of
bright and dark blue colors.

Uses. — Azurite is mined with other copper minerals as an ore of cop-
per. It is also used to a slight extent as an ornamental stone (see mal-
achite).

HYDROUS CARBONATES

The hydrous carbonates are salts containing water of crystalliza-
tion. They are carbonates of sodium or of this metal with calcium or
magnesium. Some of them occur in abundance in the waters of salt or
bitter lakes, but very few are known to occur in any large quantity in
solid form. Among the commonest are:

Soda or natron Na2C03 • 10H2O monoclinic

Trona HNa3(C03)2-2H20 monoclinic

Gaylussite Na2Ca(C03)2 • 5H2O monoclinic

HydromagnesUe Mg4(OH)2(C03)3 • 3H2O orthorhombic

These minerals occur either in the muds of lakes or as crusts upon the
mud or upon other minerals.

CARBONATES 235

Natron occurs only in solution and in the dry mud on the borders
of lakes.

Trona, or urao, (HNa3(C03)2 2H2O) is found as crystals in the
mud of Borax Lake, California, as a massive bed in Churchill Co.,
Nevada, and as thin coatings on rocks in other
places. Its crystallization is monoclinic (pris-
matic class), with the axial ratio, 2.8426 : 1 :
2.9494 and 0=76° 31'. Its crystals are usually
bounded by oP(ooi), 00 Poo (ioo), — P(in) and Fig. 128.— Trona Crys-
+P(Tn) (Fig. 128). Fibrous and massive forms tal with oP,ooi (c);
are common. The mineral has a perfect cleavage °° p * ' IO° ^ and
parallel to 00 Pdb (100). It is gray or yellowish \11

and has a colorless streak. It has a vitreous luster, a hardness of
2.5-3, and a density of 2.14. It is soluble in water and has an alkaline
taste. It exhibits the usual reactions for Na and for carbonates.

Gaylussite (Na2Ca(C03)2-5H20) also occurs as crystals in the
muds of certain lakes, especially Soda Lake, near Ragtown, Nevada,
and Merida Lake, Venezuela, and in clays under swamps in Railroad

Valley, in Nevada. Its crystals are monoclinic
(prismatic class) with alb: c— 1.4897 : 1 : 1.4442
and 18=78° 27'. They are usually bounded by
00 P(no), Po> (on), and £P(Ti2) (Fig. 129), or by
these planes and oP(ooi) and 00 P 60 (100). They
are either prismatic because of the predominance
of Poo (on) and oP(ooi), or are octahedral in
habit because of the nearly equal development of
P 00 (on) and 00 P(no). Their cleavage is perfect
Fig. 1 29.- Gaylussite parallel to ooP(no).

t\ W^ ' The mineral is white or yellowish and trans-
no (w); Poo , on J

(e) and iP, 112 (r). lucent. Its hardness is 2-3 and density 1.99.

It is very brittle. When heated in the closed
tube it decrepitates and becomes opaque. It loses its water at ioo0.
In the flame it melts easily to a white enamel and colors the flame yellow.
It is partially soluble in water, leaving a white powdery residue of CaCCfe
and is entirely soluble in acids with effervescence. The mineral occurs
in such large quantity in the clays underlying swamps in Railroad Valley,
Nevada, that its use has been suggested as a source of NagCOs.

CHAPTER XII

THE SULPHATES

The sulphates are salts of sulphuric acid. A large number are
known to occur in nature but many of them are dissolved in the waters
of salt lakes. Of the remaining ones only a few are very common.
These may be divided into an anhydrous normal group, a basic group and
a hydrated group. In addition, there are several minerals that are
sulphates mixed with chlorides or carbonates.

All the sulphates that are soluble in water give the test for sulphuric
acid. When heated with soda on charcoal they are reduced to sulphides.
The mass when placed on a silver coin and moistened with a drop of
water or of hydrochloric acid partly dissolves and stains the silver dark
brown or black.

The sulphates when pure are all white and transparent, and are all
nonconductors of electricity.

ANHYDROUS SULPHATES

NORMAL SULPHATES

The anhydrous normal sulphates have the general formula R'2S04
or R"S04. The most common ones are sulphates of the alkaline earths
and lead. They belong in a single group which is orthorhombic. The
few less common ones are sulphates of the alkalies or of the alkalies
and alkaline earths. Only two of the latter are described.

Glauberite (Na2Ca(S04)2)

Glauberite may be regarded as a double salt of the composition
Na2S04 • CaS04, which requires 51.1 per cent Na2S04 and 48.9 per cent
CaS04. The mineral contains 22.3 per cent Na20, 20.1 per cent CaO
and 57.6 per cent SO3.

It nearly always occurs in monoclinic crystals (prismatic class),
with an axial ratio 1.2209 : 1 : 1.0270 and P=6j° 49'. The most fre-
quent combination is oP(ooi), — P(ni), ooP(no), ooPoo(ioo),
3P3(3iT) and +P(nT), with oP(ooi) prominent (Fig. 130). The
cleavage is perfect parallel to oP(ooi). The angle no A 110=96° 58'.

236

SULPHATES

237

Glauberite is yellow, gray or brick-red in color, is transparent or
translucent and has a white streak, a vitreous luster and a conchoidal
fracture. Its hardness is 2.5-3 and its specific
gravity about 2.8. It is brittle. It is partly
soluble in water, imparting to the solution a
slight saltiness. The red color of many speci-
mens is due to the presence of inclusions.

Before the blowpipe the mineral decrepi-
tates, whitens and fuses easily to a white
enamel, at the same time coloring the flame Fig. 130— Glauberite Crys-
yellow. It is soluble in HC1 and in a large tal with oP, 001, (c); °oP,

i.\L £ t 11 4. 'a. e no (m); oo P oo , ioo (a)

quantity of water. In a small quantity of h -P ()
water it is partially dissolved with loss of
transparency and the production of a deposit of CaS04.
It sometimes alters to calcite.

Occurrence. — Glauberite is associated with rock salt and other de-

posits from bodies of salt water. It is found
at Villa Rubia, in Spain, and elsewhere
in Europe, and in the Rio Verde Valley,
Arizona and at Borax Lake, California.

Fig. 131. — Thenardite Crystal
with 00 P, no (w); P, 11T
(0); iP«, 106 (/) and oP,
oor(c).

Thenardite (Na2S04) occurs as ortho-
rhombic crystals in the vicinity of salt
lakes, and in beds associated with other
lake deposits. Its crystals have an axial ratio .5976 : 1 : 1.2524.
They are commonly prismatic but those
from California are tabular and are bounded
by ooP(no), oP(ooi), P(iiT), JP *> (106),
and 00 P* (100) (Fig. 131). Twins arc
common (Fig. 132).

The mineral is colorless, white or reddish
and has a salty taste. Its hardness is 2-3
and its specific gravity 2.68. Its inter-
mediate refractive index is 1.470. It is
readily soluble in water. It occurs in exten-
sive deposits in the Rio Verde Valley, Ari-
zona, and as crystals at Borax Lake, Cali-
fornia and on the shores of salt lakes in
Central Asia and South America.

Fig. 132. — Thenardite
Twinned about P 06 (on).
Forms same as in Fig. 131
and 00 P « , 100 (a).

238 DESCRIPTIVE MINERALOGY

BARITE GROUP

The barite group includes the sulphates of the alkaline earths and
lead. They are all light colored minerals with a nonmetallic luster.
They all crystallize in the orthorhombic system (bipyramidal class),
and all have a hardness of about 4. The minerals comprising this group,
with their axial ratios, are:

Anhydrite CaSC>4 alb: £=.8932 : 1 : 1.0008

Barite BaSC>4 =.8152 : 1 : 1.3136

Celestite SrSQi =.7790 : 1 : 1.2800

AnglesUe PbS04 =-7852 : 1 : 1.2894

Anhydrite (CaSOj

Calcium sulphate is dimorphous. The natural compound, anhy-
drite, is orthorhombic bipyramidal. In addition to this, there is another
which passes over into anhydrite when shaken for a long time with boiling
water. It is produced by dehydrating gypsum at about ioo°. When
moistened it combines with water and passes back to gypsum. It is
probably triclinic. It is unstable under the conditions prevailing at
the earth's surface and is, therefore, not found as a mineral.

Anhydrite occurs usually in fibrous, granular or massive forms, not
often in crystals. When crystals occur they are commonly prismatic or
tabular in habit.

In composition the mineral is 58.8 per cent SO3 and 41.2 per cent
CaO.

Its crystals are usually bounded by the three pinacoids oP(ooi),
00 Poo (100), 00 Poo (010) and P(ni), 2P2(i2i), 3P3(i3i), P*(ioi)
and P06 (on). The prismatic types are usually elongated parallel to
the macroaxis. The angle noAiTo=83° 41'.

Anhydrite fuses quite easily before the blowpipe and colors the flame
reddish yellow. It is very slightly soluble in water but is completely
dissolved in strong sulphuric acid. It cleaves parallel to the three pin-
acoids yielding rectangular fragments. Its hardness is 3-3.5 and den-
sity about 2.95. Its luster is vitreous in massive pieces and its color
white, often with a distinct tinge of blue, gray or red. In small frag-
ments it is translucent, but in large masses it is opaque. Its refractive
indices for yellow light are: a= 1.5693, 7= 1.6 130.

It is distinguished from the other sulphates by its specific gravity
and the color it imparts to the blowpipe flame.

SULPHATES 239

Synthesis. — Its crystals have been produced by slowly evaporating a
solution of gypsum in H2SO4.

Occurrence. — Anhydrite occurs as crystals implanted on the minerals
of ore veins, as beds of granular masses associated with gypsum, and as
crystalline masses in layers associated with rock salt — the two having
been deposited by the evaporation of salt waters.

Localities. — The mineral is found at the salt mines of Stassfurt, in
Germany; Hall, in Tyrol; Bex, in Switzerland; in the ore veins of
Andreasberg, in Harz; Bleiberg, in Carinthia, and at many other places
in Europe. At Lockport, N. Y., and at Nashville, Tenn., it occurs as
crystals lining geodes in limestone, and at the mouths of the Avon and
St. Croix Rivers in Nova Scotia it forms large beds associated with
gypsum.

Uses. — Finely granular forms of the mineral are used for ornamental
purposes, and as a medium for the use of sculptors. The massive variety
is occasionally employed as a land plaster to enrich cultivated soils.

Barite (BaS04)

Barite, or heavy spar, usually occurs crystallized, though it is also
often found massive and in granular, fibrous and lamellar forms. It is
a common mineral associated with sulphide ores as a gangue.

The mineral is sometimes pure but it is usually intermixed with the
isomorphous calcium and strontium sulphates. The pure mineral con-
tains 34.3 per cent SO3 and 65.7 per cent BaO. As usually mined it
contains SiCfe, CaO, MgO, AI2O3, Fe2(h and in some instances PbS2
(galena).

The simple crystals are usually tabular or prismatic in habit. The
tabular forms are commonly bounded by oP(ooi), ooP(no) and the
domes, P 66 (101), JP w (102), 2P 66 (021), and P 66 (on), and sometimes
P(ni) and 00 Poo (100) (Fig. 133). The prismatic forms are usually
elongated in the direction of
the a axis, and are bounded
by the same planes as the
tabular crystals (Fig. 134). FlG> I33._Barite Crystals with 00 P, no (m);
Complex crystals are also JP5o, 102 (rf); P£,oii (0) and oP, 001 (c).
abundant. They are often

beautifully supplied with planes, the total number known on the
species being about 100. The angle noAiTo=78° 225'.

The cleavage of barite is perfect parallel to oP(ooi) and ooP(no).
It is brittle. Its hardness is about 3 and its density about 4.5. The;

^r^

240 DESCRIPTIVE MINERALOGY

mineral is white, often with a tinge of yellow, brown, blue, or red.

It is transparent or opaque and its streak is white. Its refractive

indices for yellow light are: 0=1.6369, 7=1.6491.

Before the blowpipe barite decrepitates and fuses, at the same time

coloring the flame yel-
lowish green. The fused
mass reacts alkaline to
litmus paper. It is in*
soluble in acids.

The mineral barite is
Fig. i34.-Barite Crystals with m, dt 0 and c as in distinguished from the

pTg'x«3wAlso °°P55' IO° (fl); P' IXI w "d other sulPhates by its

high specific gravity and

the color it imparts to the blowpipe flame.

Syntheses. — Crystals have been made by heating precipitated barium
sulphate with dilute HC1 in a closed tube at 150°, and by cooling a fusion
of the sulphate in the chlorides of the alkalies or alkaline earths.

Occurrence and Origin. — Barite is a common vein-stone. It con-
stitutes the gangue of many ore veins, particularly those of copper,
lead and silver. It is found also as a replacement of limestone, which,
when it weathers, leaves the barite in the form of fragments and nodules
in a residual clay, and as a deposit in hot springs. In all cases it is
believed to be a deposit from solutions.

Localities. — Barite occurs abundantly in England, Scotland, and on
the continent of Europe. Crystals are found at Cheshire, Conn.; at
DeKalb, St. Lawrence Co., N. Y.j at the Phoenix Mine in Cabarrus
Co., N. C, and near Fort Wallace, New Mexico. Massive barite in
pieces large enough to warrant polishing is found on the bank of
Lake Ontario, at Sacketts Harbor, N. Y. It constitutes the filling of
veins at many different places, more particularly in the southern Appa-
lachians and in the Lake Superior region.

Preparation. — Much of the mineral that enters the trade in the
United States is obtained from the deposits in residual clay. The rough
material is washed, hand picked, crushed, ground and treated with
sulphuric acid. The acid dissolves most of the impurities and leaves
•the powdered mineral white.

Uses. — The white varieties of the mineral are ground and the powder
is used in making paints. The mineral is also employed in the manu-
facture of paper, oilcloth, enameled ware, and in the manufacture of
barium salts, the most important of which is the hydroxide, which is
employed in refining sugar.

SULPHATES

241

The colored massive varieties, more especially stalactitic and fibrous
forms, are sawn into slabs, polished and used as ornamental stones.

Production. — The quantity of barite mined in the United States
during 1912 was over 37,000 tons, valued at $153,000. The principal
producing states are Missouri, Tennessee and Virginia. The imports
in the same year were about 26,000 tons of crude material, valued at
$52,467 and 3,679 tons of manufactured material, valued at $26,848.
Besides, there were imported $70,300 worth of artificial barium sul-
phate and about $280,000 worth of other barium salts, exclusive of
witherite.

Celestite (SrS04)

Celestite occurs in tabular prismatic crystals, in fibrous and some-
times in globular masses. Though usually white, it often possesses a
bluish tinge, to which it owes its name.

The theoretical composition of the mineral is 43.6 per cent SO3
and 56.4 per cent SrO, but it often contains small quantities of the
isomorphous Ca and Ba compounds.

Many celestite crystals are very similar in habit to those of barite.

Fig. 135. — Celestite Crystals with <*> P, no (m); JP«o, 102 (d); J Poo, 104 (r);

00 P 00 , 010 (6); P 00 , on (0) and oP, 001 (c).

Tabular forms are perhaps more common (Figs. 135). Occasionally,
pyramidal crystals are bounded by P4(i44), 00 Poo (100), Po6(on)
and oP(ooi). These often have rounded edges and curved faces and
thus come to have a lenticular shape. The angle no A iTo= 75 ° 50'.

The cleavage of the mineral is perfect parallel to oP(ooi) and almost
perfect parallel to ooP(no). Its hardness is about 3 and its specific
gravity 3.95. Its luster and streak are like those of barite. Its color
is often pale blue and sometimes light red, but pure specimens are
white or colorless. Its refractive indices for yellow light are: a= 1.6220,
7=1.6237.

Before the blowpipe celestite reacts like barite except that it tinges
the flame crimson. This crimson color may be obtained more dis-
tinctly by fusing a little powder of the mineral on charcoal in the reduc-

242 DESCRIPTIVE MINERALOGY

ing flame and dissolving the resulting mass in a small quantity of hydro-
chloric acid, then adding some alcohol and igniting the mixture.

Syntheses. — Crystals of celestite are produced in ways analogous
to those in which barite crystals are formed.

Occurrence and Origin. — Celestite occurs in beds with rock salt and
gypsum, as at Bex, Switzerland; associated with sulphur, as at Gir-
genti, Italy; and in crystals and grains scattered through limestone,
as at Strontian Island, Lake Erie, and in Mineral Co., W. Va., or
as crystals lining geodes in the same rock. It is also sometimes found
as a gangue in mineral veins. In some instances it was deposited by
hot waters, in others by cold waters, and in others it was concentrated
by the leaching of strontium-bearing limestones by atmospheric water.

Production and Uses. — Although the mineral occurs in large quan-
tity at a number of places in the United States and Canada it is not
mined. A small quantity of the strontium oxide is annually imported.
Strontium salts, prepared from celestite in part, are used in the manu-
facture of fireworks and medicines and in refining sugar.

Anglesite (PbS04)

Anglesite occurs principally as crystals associated with galena and
other ores of lead, but is found also massive, and in granular, stalactitic
and nodular forms.

The theoretical composition of the mineral demands 73.6 per cent
PbO and 26.4 SO3.

Its orthorhombic crystals are usually prismatic or isometric in habit.
Tabular habits are less common than in barite and celestite. The
principal forms occurring are ooP<x> (100), o°P(no), £P * (102), and
other macrodomes, P 06 (on) and various small pyramids, with oP(ooi),
in addition, on the tabular crystals (Figs. 156, 137, 138). The angle
no A iTo=76° i6|'.

The cleavage of anglesite is distinct parallel to oP(ooi) and 00 P(i 10).
Its fracture is conchoidal. The mineral is white, gray or colorless and
transparent, and is often tarnished with a gray coating. It has an
adamantine or residuous luster, is brittle and has a colorless streak.
Its hardness is 2/5-3 and sp. gr. 6.3-6.4. Impure varieties may be
tinged with yellow, green or blue shades and in some cases may be
opaque. Its refractive indices for yellow light are : a = 1 .877 1 , 7 = 1 .893 7.

Before the blowpipe anglesite decrepitates. It fuses in the flame of
a candle. On charcoal it effervesces when heated with the reducing
flame and yields a button of metallic lead. In the oxidizing flame it

SULPHATES

243

gives the lead sublimate. The mineral dissolves in HNO3 with dif-
ficulty.

The mineral is characterized by its high specific gravity and the

Fig. 136.-
Fig. 137.-

Fig. 136. Fig. 137.

-Anglesite Crystal with <*> P, no (m); 00 P qo , xoo (a); oP, 001 (c);

}P, 112 (r) and PX 122 (y).

-Anglesite Crystal with m, a and y as in Fig. 136. Also 00 Poo,
cio l&}, P 00 , 011 (0); P, in (s) and JP 00 , 102 (d).

reaction for lead. It is distinguished from cerussite by the reaction for
sulphur and the lack of effervescence with HCl.

Syntheses. — Crystals of anglesite have been made by methods anal-
ogous to those used in the preparation of barite crystals.

Occurrence. — The mineral occurs as an alteration product of galena,
mainly in the upper portions of veins of
lead ores. Under the influence of solu-
tions of carbonates it changes to cerus-
site.

Localities. — It is found in Derby-
shire and Cumberland, in England;
near Siegen, in Prussia; in Australia and
in the Sierra Mojada, in Mexico. In the
United States crystals occur at Phoenix-

ville, Penn., in the lead districts of the Mississippi Valley, and at
various points in the Rocky Mountains.

Uses. — It is mined with other lead compounds as an ore of this metal.

BASIC SULPHATES

Although several basic sulphates are known as minerals, only two
are of importance. One, brochantite, is a copper compound found, with
other copper minerals, in the oxidized portions of ore veins, and the
other, alunite, is a double salt of aluminium and potassium. This min-

Fig. 138. — Anglesite Crystal with
m, y, c and d as in Figs. 136 and
137. Also JP 00 , 104 (/) and P4,

144 (x).

244 DESCRIPTIVE MINERALOGY

eral is one of a series of compounds forming an isomorphous group, with
the general formula (R,/,(OH)2)6R/2(S04)4 or (R'"(OH)2)6R"(S04)4,
in which R'" = A1 or Fe, R'2 = K2, Na2 or H2 and R"=Pb.

Alunite ((A1(OH)2)gK2(S04)4)

Alunite, or alumstone, is a comparatively rare mineral, but, because
of its possible utilization as a source of potash, it is of considerable in-
terest. It has long been used abroad as a source of potash alum.

The mineral, when pure, contains 38.6 per cent SO3, 37.0 per cent
A12C>3, 1 1. 4 per cent K20 and 13.0 per cent H20, which corresponds to
the formula given above, or if written in the form of a double salt
3(Al(OH)2)2S04-K2S04. The chemical composition of a crystalline
specimen from Marysville, Utah, is as follows:

SO3 A1203 Fe203 P2O5 K20 Na20 H20+ H20- Si02 Total
38.34 37-x8 tr. .58 10.46 .33 12.90 .09 .22 100.10

Alunite occurs in hexagonal crystals (di trigonal scalenohedral class),
with an axial ratio of 1 : 1.252. The natural crystals are nearly always
simple rhombohedrons, R(ioTi), or R modified by other rhombohedrons
and the basal plane. Because the angle between the rhombohedral
faces is about 900 (900 50'), the habit of the crystals is cubical. The .
mineral also occurs massive, with fibrous, granular or porcelain-like
structure.

Alunite is white, pink, gray or red, and has a white streak. It is
transparent or translucent and has a vitreous or nearly pearly luster.
Its cleavage is distinct parallel to oP(oooi), and it has an uneven, con-
choidal or earthy fracture. Its hardness is 3.5-4 and its density =
2.6-2.75. Its indices of refraction for yellow light are: 6=1.592,
(0=1.572.

Before the blowpipe the mineral decrepitates, but is infusible. In
the closed tube it yields water and at a high temperature sulphurous and
sulphuric oxides. Heated on charcoal with Co(N03)2 it gives the blue
color characteristic of AI22O3. It also gives the sulphur reaction. It is
insoluble in water but is soluble in H2SO4. When ignited it gives off
all its water and three-quarters of its SO4, the other quarter remaining
in K2SO4. When the ignited residue is treated with water, the potas-
sium sulphate dissolves and insoluble AI2O3 is left. It is upon this
latter reaction that the economic utilization of the mineral depends.

The mineral is characterized by its color and hardness together
with the reactions for A1,H20 and sulphuric acid.

SULPHATES 245

Synthesis. — Crystals have been made by heating an excess of alu-
minium sulphate with alum and water at 2300.

Occurrence and Origin. — The mineral occurs in seams or veins in
acid lavas. It is thought to have been formed in some instances by
the action of sulphurous vapors upon the rock forming the vein walls,
in other instances by direct precipitation from ascending magmatic
waters, and in others by the action of descending H2SO4.

Localities. — The principal known occurrences of alunite are at
Tolfa, Italy; at Bulla Delah, New South Wales; on Milo, Grecian
Archipelago, and at Mt. Dore, France.

In the United States it is found with quartz and kaolin in the
Rosita Hills, and the Rico Mts., Colo.; in the ore veins at Silverton
and Cripple Creek, Colo.; as a soft white kaolin-like material in the
ore veins at Goldfield, Nev.; as a crystalline constituent in the rocks
at Goldfield, Nev., and Tres Cerritos, Cal., and in the form of a great
vein of comparatively pure material at Marysville, Utah.

Uses. — In Australia alunite is calcined and then heated with dilute
sulphuric acid. The mixture is then allowed to settle and the clear
solution is drawn off and cooled. Alum crystallizes. The mother liquor
which contains aluminium sulphate, after further treatment with the
calcined mineral, is evaporated and the aluminium salt separated by
crystallization. In the United States it is now (1916) being utilized
as a source of potash and aluminium.

Brochantite ((CuOH)2S04 2Cu(OH)2) occurs in groups of small
prismatic crystals, in fibrous masses and in drusy crusts. Its crystal-
lization is orthorhombic with a : b : c=.yy^g : 1 : .4871 and the angle
iioAiTo=75° 28'. Cleavage is perfect parallel to 00 P 06 (010). The
mineral is emerald-green to blackish green and its streak is light
green. It is transparent or translucent, and its luster is vitreous,
except on cleavage planes where it is slightly pearly. Its hardness is
3.5-4 and density 3.85. In the closed tube it decomposes, yielding
water and, at a high temperature, sulphuric acid. It gives the usual
reactions for copper and sulphuric acid. Brochantite occurs in the
upper portions of copper veins at many places, in some of which it was
formed by the interaction between silicates and solutions of copper
salts. In the United States it has been found at the Monarch Mine,
Chaffee Co., Colorado, at the Mammoth Mine, Tintic District, Utah,
and in the Clifton-Morenci Mines, Arizona,

246 DESCRIPTIVE MINERALOGY

HYDROUS SULPHATES

The hydrous sulphates comprise a number of sulphates combined
with water. Among them are the normal salts mirabUite or glauber
salt (Na2S04- 10H2O), gypsum (CaSO-r 2H2O), the epsomite and melan-
terite groups (R"S04-7H20), chalcanthite (CUSO45H2O), and the
alum group (R'A1(S04)2- 12H2O), kieserite (MgS04*H20), polyhalite
(K.2MgCa2(S04)4-H20), and a number of basic compounds. Several
of them are of considerable economic importance. They are separated
into a normal group and a basic group,

HYDRATED NORMAL SULPHATES

The hydrated normal sulphates occur in crystals, and most of them
are found also in beds interstratified with other compounds that are
known to have been precipitated by the evaporation of sea water or the
water of salt and bitter lakes. All are soluble in water.

Mirabilite, or glauber salt, (Na2S04 • 10H2O) is a white, trans-
parent to opaque substance occurring in monoclinic crystals or as
efflorescent crusts. Its hardness is 1.5-2 and specific gravity 1.48. It
is soluble in water and has a cooling taste. When exposed to the air it
loses water and crumbles to a powder. Mirabilite occurs at the hot
springs at Karlsbad, Bohemia and is obtained from the water of many
of the bitter lakes in California and Nevada. Its crystals are deposited
from a pure solution of Na2S04. If the solution contains NaCl, how-
ever, thenardite (Na2S04) deposits.

Kieserite (MgS04 • H2O) occurs commonly in granular to compact,
massive beds interstratified with halite and other soluble salts at Stass-
furt, Germany, and at other places where ocean water has been evap-
orated. It is believed to have resulted from the partial desiccation of
epsomite (MgS04*7H20), though it may be deposited from a solution
of MgS04 in the presence of MgCb. Kieserite is white, gray, or yellow-
ish, and is transparent or translucent. It forms sharp bipyramidal
monoclinic crystals. Its hardness is 3 and its density 2.57. In the
presence of water it passes over into epsomite and dissolves, yielding a
solution with a bitter taste. Large quantities are utilized in the fer-
tilizer industry.

When exposed to the air it becomes covered with an opaque crust.

SULPHATES

Gypsum (CaS04 aH-O)

Gypsum is the most important of all the hydrous sulphates. It
occurs in massive beds as:sociated with limestone, in crystals, in finely
granular aggregates and in fibrous masses, under a great variety of
conditions.

Theoretically, it consists of 46.6 per cent SO3, 32.5 per cent CaO and
30.9 per cent H2O, but usually it contains also notable quantities of other
components, especially Fe203, AI2O3 and Si02- Clay is a common im-
purity in the massive varieties.

The analyses of two commercial gypsums follow:

CaSO.,

Dillon, Kans 78 . 40

Alabaster, Mich 78.51

H20 Si02 AI2O3 CaC03 MgC03 Total
10.06 .35 .12 .56 .57 99.96
2096 .05 .08 ... .11 9971

The crystals are monoclinic {prismatic class), with a : b : £=.6895 :
1 : .4132 and (J=8i° 02'. They are usually developed with a tabular
habit due to the predominance of °oPm>(oio). The prism «>P(iio),

Fie. 139.
Fio. 139. — Gypsum Crystals with '

Fio. 140.
a (ft); -P, in (0 and

o(«i); =»P
JP 5>, T03 W.
FlC. i40.r~<iypmni Twinned about »P» (1°°). Swallow-tail Twin. Form tn,
/ and b as in Fig. J3y.

and pyramid +P(irT) are also nearly always present {Fig. 139). Often
the +P faces are curved, producing a lens-shaped body. Twinning is
very common, giving rise to two types of twinned crystals. In the most
common of these 00 P 00 {too) is the twinning plane and the resulting
twin has the form of Fig. 140. In the second type — Poo (101) is the
twinning plane {Fig. 141). Forms of this type are frequently bounded
by +PC11T), -P(iii), JP*(7oj), and 00 P do (100). When the side

248

DESCRIPTIVE MINERALOGY

faces are curved the well known arrowhead twins result (Fig. 141).

The angle noAiTo=68° 30'.

The mineral possesses a good cleavage parallel to 00 P 00 (010)

yielding thin inelastic foliae, another parallel to +P(Tn) and a less

perfect one parallel to 00 P * (100).
It is white, colorless and transpar-
ent when pure; gray, red, yellow,
blue or black when impure. Its
hardness is 1.5-2 and sp. gr.= 2.32.
The luster of crystals is pearly on
00 P ob (010) and on other surfaces
vitreous. Massive varieties are often
dull. The refractive indices for yel-
low light are: a= 1.5205, 0= 1.5226,

Fig. 141. — Gypsum Twinned about '" '^ '

-P «(ioi). Forms: °° P ao , 100 In tne closed tube the mineral
(a); -P, in (/); P, 11T («) and gives off water and falls into a white
JPq6,To3(*). Arrow head Twin, powder (see p. 238). It colors the

flame yellowish red and yields the sul-
phur test on a silver coin. It is soluble in about 450 pts. of water and
is readily soluble in HC1. When heated to between 2220 F. and 4000 F.
it loses water and disintegrates into powder, which, when ground,
becomes " plaster of Paris." This, when moistened with water, again
combines with it and forms gypsum. The crystallization of the mass
into an aggregate of interlocking crystals constitutes the " set."

Gypsum is distinguished from other easily cleavable, colorless min-
erals by its softness and the reactions for S and H2O.

The varieties of gypsum generally recognized are:

Selenite, the transparent crystallized variety;

Satins par, a finely fibrous variety;

Alabaster, a fine-grained granular variety, and

Rock-gypsum, a massive, structureless, often impure and colored
variety.

Gypsite is gypsum mixed with earth.

Syntheses. — Crystals of gypsum separate from aqueous solutions of
CaS04 at ordinary temperatures, and also from solutions saturated
with NaCl and MgCb. Some of these are twinned.

Occurrence and Origin. — Gypsum forms immense beds interstrati-
fied with limestone, clay and salt deposits where it has been precipitated
by the evaporation of salt lakes. Its crystals occur around volcanic
vents, where they are produced by the action of sulphuric acid on cal-

SULPHATES 249

careous rocks. They are also found isolated in day and sand, and in
limestone, wherever this rock has been acted upon by the sulphuric acid
resulting from the weathering of pyrite. Gypsum also occurs in veins
and is found in New Mexico in the form of hills of wind-blown sand.

Localities. — Crystals are found in the salt beds at Bex, Switzerland;
in the sulphur mines at Girgenti, Sicily, and at Montmartre, France.
In the United States they occur at Lockport, N. Y., in Trumbull Co.,
Ohio, and in Wayne Co., Utah, in limestone; and on the St. Mary's
River, Maryland, in clay.

Extensive beds occur in Iowa, Michigan, New York, Virginia, Ten-
nessee, Oklahoma and smaller deposits in many other states, and wind-
blown sands in Otero Co., New Mexico.

Uses. — Crude gypsum is used in the manufacture of plaster, as a
retarder in Portland cement, and as a fertilizer under the name of land
plaster. The calcined mineral is used as plaster of Paris and in the
manufacture of various wall finishing plasters, and certain kinds of
cements. Small quantities are used in glass factories, and as a white-
wash, a deodorizer, to weight phosphatic fertilizer, as an adulterant in
candy and other foods, and as a medium for sculpture.

Production. — The quantity of gypsum mined in the United States
during 1912 aggregated 2,500,757 tons, valued at $6,563,908 in the form
in which it was sold. Of this amount, 441,600 tons of crude material,
valued at $623,500 were sold ground, and 1,731,674 tons, valued at $5,-
940,409, were calcined. The output of New York was valued at $1,241,-
500, that of Iowa at $845,600 and of Ohio at $812,400.

After the United States the next largest producer is France with a
product in 1910 of 1,760,900 tons, valued at $2,942,600 and Canada with
525,246 tons, valued at $934,446.

EPSOMITE AND VITRIOL GROUPS

These groups comprise minerals with the general formula RSO4 • 7H2O,
in which R=Mg, Zn, Fe, Ni, Co, Mn and Cu. Isomorphous mix-
tures indicate that the compounds are diomorphous, and that the
group is, therefore, an isodimorphous group. The group is separable
into two divisions, of which one, the epsomite group, crystallizes in the
bisphenoidal class of the orthorhombic system with axial ratios approx-
imating 1:1: .565. The other division, the vitriol, or melanterite,
group crystallizes in the prismatic class of the monoclinic system with
axial ratios approximating 1.18 : 1 : 1.53 and 0 approximating 750.
Only the magnesium compound among the pure salts is known to crys-
tallize in both systems. Crystals separated from a saturated solution

250 DESCRIPTIVE MINERALOGY

are orthorhombic, while those separated from a supersaturated solution
are monoclinic. Other salts occur in isomorphous mixtures in both
systems. All members of the group are soluble in water and all occur as
secondary products formed by decomposition of other minerals.

Epsomite (MgS04 7H2O)

Epsomite, or Epsom salt, usually occurs in botryoidal masses and
fibrous crusts coating various rocks over which dilute magnesium sul-
phate solutions trickle, and mingled with earth
in the soils of caves. The solutions result from
the action upon magnesian rocks of sulphuric
acid derived from oxidizing sulphides. Crys-
tals are rare.

The composition corresponding to MgS04 •
I i 7H2O demands 32.5 SO3, 16.3 MgO and 51.2

^7 H2°-

The mineral forms white or colorless bi-
Fig. i42.~Epsomite Crys- sphenoidal, orthorhombic crystals, with an

tal with 00P, no (m) . . . ... . «,. .

p axial ratio alb: c=.oooi : 1 : .5709. Their

and -r, in (s). habit is tetragonal. The angle no A 110=89°

26'. The commonest forms occurring on syn-

P P

thetic crystals are combinations of ooP(no), and — r(in) or —/(in)

2 2

(Fig. 142). Natural crystals contain, in addition 00 Poo (010) and

P 06(101).

The luster of epsomite is vitreous, its hardness 2.0-2.5 and specific
gravity 1.70. Its refractive indices for yellow light are: a= 1.4325,
0= 1.4554 and 7= 1.4608.

The mineral is soluble in water, yielding a solution with a bitter taste.
With a solution of barium chloride it yields a white precipitate of BaS04.

Epsomite is distinguished from other colorless, soluble minerals by
its taste and the reactions for S and Mg.

Synthesis. — Crystals are produced by evaporation of solutions of
MgS04 containing certain other salts. From those containing borax,
crystals of the type indicated above are separated. The production of
right or left crystals may be provoked by inoculation of the solution with
a particle of a crystal of the desired type.

Localities. — Epsomite occurs in mineral waters, as, for instance, at
Seidlitz, Bohemia, on the walls of mines and caves, among the deposits
of bitter lakes, and as crystals in the soil covering the floors of caves.

SULPHATES 251

Melanterite, or copperas (FeS04 7H2O), is usually in fibrous,
stalactitic or pulverulent masses associated with pyrite or other sul-
phides containing iron, from which it was produced by weathering
processes. It is commonly some shade of green. Its streak is colorless.
Its crystals, which are monoclinic (prismatic class), are rare. The
mineral has a hardness of 2 and a density of 1.9. It is soluble in water,
forming a solution which has a sweetish astringent taste.

ALUM GROUP

The alum group includes a large number of isomorphous compounds
with the general formula R'Al(SC>4)2-i2H20. The group crystallizes
in the isometric system (dyakisdodecahedral class), but all of its mem-
bers are so readily soluble in water that they are rarely found in nature.
The commonest alums are kalinite (KAl(S04)2-i2H20) and soda alum
(NaAl(S04)2-i2H20).

DOUBLE SULPHATES WITH CARBONATES OR CHLORIDES

A number of compounds of sulphates with chlorides and carbonates
are known, but of these only one is of any great economic importance.
Two others afford interesting crystals. The commercial compound is
kainite, which is a hydrated combination of MgS04 and KC1, with
the formula MgS04 • KG • 3H2O. The other two best known members
of the group are leadhillite (PbS04-Pb(PbOH)2(C03)2 and hanksite
(2Na2C03 • oNa2S04 • KC1).

Kainite (MgS04 KC1 3H20)

Kainite is found only in beds associated with halite and other deposits
from saline waters. It is rarely crystallized. Crystals are monoclinic
(prismatic class), with a:6:c=i.2i86:i: .5863 and 0=85° 6'. They
possess a pyramidal habit with oP(ooi) and ±P(ni)(iiT) predom-
inating.

The mineral usually forms granular masses which are white, yellow,
gray or red. It is transparent, has a hardness of 2 and sp. gr. 2.13,
and is easily soluble in water. Its refractive indices for sodium light are:
a= 1.4948 and 7 = 1.5203.

When heated in a glass tube it yields water and HC1. It is distin-
guished from other soluble minerals by this reaction, and by the fact
that it yields the test for sulphur, and colors the flame blue when its
powder is mixed with CuO and heated before the blowpipe.

252 DESCRIPTIVE MINERALOGY

Synthesis. — Crystals have been produced by evaporating a solution
of K2SO4 and MgSC>4 containing a great excess of MgCi2.

Occurrence. — Kainite occurs in the salt beds of Stassfurt, Germany,
and of Kalusz in Galicia, and in the deposits of salt lakes and lagoons.
It also occurs as crusts on some of the lavas of Vesuvius.

Uses. — The mineral is utilized as a source of potassium in the manu-
facture of potassium salts and fertilizers. Large quantities are imported
annually into the United States. In 191 2 the imports aggregated
485,132 tons, valued at $2,399,761.

Hanksite (2Na2C03 9Na2S04 KC1) occurs almost exclusively in

hexagonal prisms that are prismatic or tabular,
or in double pyramids suggesting quartz crys-
tals. Their axial ratio is 1 : 1.006. The com-
monest crystals are bounded by oP(oooi),
Fig. 143.— Hanksite Crys- ooP(ioTo), P(ioTi) (Fig. 143) and 2P(202i),
tal with cop, 1010 (m); or ^(4045). Their cleavage is imperfect

P, ion (0) and oP, 0001 hi- t>/ \ <™. • 1 • v-^

/ v parallel to oP(oooi). The mineral is white or

yellow. Its hardness =2 and its specific

gravity =2.56. It is soluble in water. Its refractive indices are:

o)= 1.4807 and €=1.4614. It occurs at Borax Lake and Death valley,

California, in the deposits of salt lakes.

Leadhillite (PbS04Pb(PbOH)2(C03)2) occurs principally as
crystals in the oxidized zones of lead and silver veins. The crys-
tals are monoclinic (prismatic class), and have an hexagonal habit.
Their axial ratio is 1.7515 : 1 : 2.2261. /3=89°32'. The principal
forms observed on them are oP(ooi), ooP(no), 00 Poo (100), P(m)
and §P6o (102). In the most common twins ooP(no) is the twin-
ning plane. The mineral is white or yellow, green or gray, and it is
transparent or translucent. Its streak is colorless. It is sectile, has a
hardness of 2.5 and a specific gravity of 6.35. Before the blowpipe it
intumesces, turns yellow, and fuses easily (1.5). Upon cooling it again
becomes white. It effervesces in HNO3 and leaves a white precipitate
of PbS04. It reacts for sulphur and water. It is found at Leadhills,
Scotland, and Mattock, England, associated with other ores of lead;
at a lead mine near Iglesias, Sardinia, and at several silver-lead mines
in Arizona.

CHAPTER XIII

THE CHROMATES, TUNGSTATES AND MOLYBDATES

THE CHROMATES

The only chromate of importance, among minerals, is the lead salt of
normal chromic acid, H2C1O4. There are several other chromates
known, but they are basic salts and are rare. All are lead compounds.
The normal salt, PbCrCU, is known as crocoite. Chromic acid is un-
known, as it spontaneously breaks down into C1O3 and water when set
free from its salts. Its best known compound is potassium chromate,
K^CrCU.

Crocoite (PbCr04)

Crocoite is well characterized by its hyacinth-red color. It is a lead
chromate with PbO=68.g per cent and 003 = 31.1 per cent.

Its crystallization is monoclinic
(prismatic class) with a : b : c
= .9603 : 1 : .9159 and £=77° 33'.
Its crystals, which are usually im-
planted on the walls of cracks in
rocks, are prismatic or columnar
parallel to ooP(no). Their pre-
dominant forms are oop(no),
— P(iii), and various domes (Fig.
144). Their cleavage is distinct
parallel to ooP(no). The angle
iioAiio=86° 19'. The mineral
also occurs in granular masses.

Crocoite is bright hyacinth-red,
and is translucent. Its streak is
orange-yellow. The mineral is sec-
tile. Its fracture is conchoidal, its
hardness 2.5-3 and density about 6.

Fig. 144. — Crocoite Crystals with 00 Pf
no (m); 00 P2, 120 (/); -P, in (/);
3P*. 301 (*); P«, 101 (*); oP,
001 (c); Pob, on («); 2Pobfo2i (y)
and iPob , 012 (u>).

Its intermediate refractive index

is about 2.42.

In the closed tube it decrepitates, and blackens; but it reassumes its
red color when heated. On charcoal it deflagrates and fuses easily,

253

254 DESCRIPTIVE MINERALOGY

yielding metallic lead and a lead coating. With microcosmic salt it
gives the green bead of chromium.

The mineral is easily recognized by its color and the test for chro-
mium.

Synthesis. — Crystals, like those of crocoite, have been obtained by
heating on the water bath a solution of lead nitrate in nitric acid and
adding a dilute solution of potassium bichromate. '

Occurrence. — Crocoite occurs under conditions which suggest that it
is a product of pneumatolysis.

Localities. — It is found in the Urals; at Rezbanya and Moldawa, in
Hungary; in Tasmania, and in the Vulture Mining district, Maricopa
Co., Arizona.

THE TUNGSTATES AND MOLYBDATES

The tungstates are salts of tungstic acid, H2WO4. They are the
principal sources of the metal tungsten which is beginning to have im-
portant uses. The molybdates are salts of moiybdic acid, H2M0O4.
The two most prominent tungstates are scheelite, CaWCk, and wolf-
ramite (Fe-Mn)W04, and the most prominent molybdate is wulfenite,

PbMo04.

All tungsten compounds give a blue bead with salt of phosphorus in
the reducing flame. When fused with Na2C(>3, dissolved in water
and hydrochloric acid, and treated with metallic zinc (see pp. 482, and
492 for details of test), they also yield a blue solution which rapidly
changes to brown.

The molybdates give with the salt of phosphorus bead in the oxidiz-
ing flame a yellow-green color while hot, changing to colorless when cold.
In the reducing flame the color is clear green.

SCHEELITE GROUP

The scheelite group comprises a series of tungstates and molybdates
of Ca, Cu and Pb. The minerals are tetragonal and hemihedral and
are all well crystallized. The more important members of the group
are scheelite and wulfenite. Cuprotungstite is a copper tungstate (CuWCU)
and stolzite a lead tungstate (PbW04).

Scheelite (CaW04)

The formula of scheelite demands 80.6 per cent WO3, and 19.4 per
cent CaO, but the mineral usually contains a little molybdenum in
place of some of the tungsten. It nearly always contains also a little Fe.

CHROMATES, TUNGSTATES AND MOLYBDATES 255

Scheelite crystallizes in the tetragonal bipyramidal class. Its crys-
tals are usually pyramidal, though often tabular in habit. Their axia!
ratio is i : 1.5268. On the pyramidal types the predominant planes
are pyramids of the first, second (Fig. 145), and third orders and on the
tabular types, in addition, the basal plane. One of the most familiar

combinationsisPtxxO.Poo (loI). ^(3.3) and [^](130 (Fig. 145).

Other forms frequently found on its crystals are £P oo (102) and £P °°
(105). The angle iioaTii = 79° 55 J'.. Twinning is common, both
contact and penetration twins having °o P 00 (100) as the twinning
plane. The mineral also occurs in reniform and granular masses.

Scheelite is white, yellow, brown, greenish or reddish, with a white

Fig. 145. Fig. 146.

Fig. 145. — Scheelite Crystal with P, n 1 \p); Poo , 101 (e) and oP, 001 (c).

Fig. 146. — Scheelite Crystal with P and e as in Fig. 145. Also I 1 , 313 (h) and

f3p3l , n L 2 J

L"TJ» r3x W-

•

streak and vitreous luster. It has a distinct cleavage parallel to P(ooi),
and an uneven fracture. It is brittle, has a hardness of 4.5-5 an(i a
density of about 6, and is transparent or translucent. It is soluble in
HC1 and HNO3 with the production of a yellow powder, tungsten tri-
oxide, which is soluble in ammonia. Its refractive indices are: e= 1.9345,
«= 1.9185 for red light.

Before the blowpipe the mineral fuses to a semitransparent
glass. With borax it forms a transparent glass which becomes opaque
on cooling. With salt of phosphorus it yields the characteristic beads
for tungsten, but specimens containing iron must be heated with tin on
charcoal before the blue color can be developed.

Scheelite is distinguished from limestone, which its massive forms
closely resemble, by its higher specific gravity and the absence of effer-

266 DESCRIPTIVE MINERALOGY

vescence with HC1. From quartz it is distinguished by its softness and
from barite by greater hardness and higher specific gravity.

Syntheses. — Crystals of scheelite have been made by adding a solu-
tion of sodium tungstate to a hot acid solution of CaCk, and by fusing
the two compounds. They have also been produced by fusing wolfram-
ite with CaCl2.

Occurrence and Origin. — Scheelite is found in gold-quartz veins
and in veins cutting acid igneous rocks, where it is associated with
cassiterite, topaz, fluorite, molybdenite, wolframite and many other
metallic compounds, and as a contact metamorphic product in altered
limestone intruded by granite. It is probably in all cases a deposit
from hot solutions.

Localities. — It occurs at Zinnwald, Bohemia; Altenberg, Saxony;
Carrock Fells, Cumberland, England; Pitkaranta, Finland; in New
Zealand; and in the United States at Monroe and Trumbull, Conn.; in
the Atolia District, Kern Co., California; the Mammoth Mining Dis-
trict, Nevada; in Lake County, Colorado; near Gage, New Mexico,
where it occurs with pyrite and galena in a vein cutting limestone,
and in the placer gravels at Nome, Alaska.

Uses of Tungsten. — Tungsten is used principally in the manufacture
of tool steel, electric furnaces and targets for Rontgen rays. It is
employed also as filaments in electric-light bulbs, in the manufacture
of sodium tungstate which is used for fireproofing cloth, as a mordant
in dyeing, and for a number of other minor purposes.

Production. — Scheelite has been mined in small quantity in Idaho,
Alaska, California, Nevada, Arizona, and New Mexico, as a source of
tungsten, but most of this element has heretofore been produced from
other compounds, mainly wolframite. In 191 3 a few hundred tons of
scheelite concentrates were produced in the Atolia district, California,
and the Old Hat district, near Tucson, Ariz. At present (1916) it is
being produced in large quantity near Bishop, Inyo Co., Cal.

Stolzite (PbW04) is completely isomorphous with wulfenite. Its
crystals, which are pyramidal or short columnar, are mainly combina-
tions of ooP(no), P(iii), 2P(22i) and oP(ooi). Their axial ratio is
1 : 1.5606.

The mineral is gray, brown, green or red. It is translucent and
has a white streak. Its hardness is 2.75-3 an(^ *ts SP- 6r- 7-87-8.23.
Its refractive indices for yellow light are: w = 2.2685, € = 2.182.

Before the blowpipe it decrepitates and melts to a lustrous crystal-
line globule. The bead with microcosmic salt in the reducing flame

CHROMATES, TUNGSTATES AND MOLYBDATES 257

is blue when cold; in the oxidizing flame it is colorless. The mineral
is decomposed by HNO3 leaving a yellow residue of WO3. Crystals
have been made by fusing sodium tungstate and lead chloride.

Its principal localities are the tin-bearing veins at Zinnwald, Bo-
hemia; the copper veins in Coquimbo, Chile; and Southampton, Mass.,
where it is associated with other lead compounds.

Wulfenite (PbMoCU)

Wulfenite is the only raolybdate of importance that occurs as a
mineral. Its formula demands 39.3 M0O3 and 60.7 PbO. Calcium
sometimes replaces a part of the Pb and tungsten a part of the Ma

Wulfenite is hemihedral and hemimorphic (tetragonal pyramidal
class). Its crystals are more frequently tabular than those of scheelite,
and they are usually very thin.

The mineral, however, occurs also in pyramidal and prismatic crys-
tals which, in some cases, exhibit distinct hemimorphism. Their axial

<^i

Fig. 147. Fig. 148.

Fig. 147. — Wulfenite Crystal with 00 p 00 , 100 (a) and ^P 00 , 1.0.12 (0).
Fig. 148. — Wulfenite Crystal with oP, 001 (c); JP°ot 102 (w); P«, ioi (e);

P, hi (n) and JP, 113 (5).

ratio is a : c=i : 1.5777. The most common forms found on its crys-
tals are: oP(ooi), P(in), |-^— ^(320), £P(ii3) and P 00(101) (Fig.

147 and 148). The angle 1 1 1 A Ti 1 = 8o° 22'.

The cleavage, parallel to P, is very smooth, and the fracture is con-
choidal. The mineral is brittle. Its hardness is about 3 and specific
gravity about 6.8. Its luster is resinous or adamantine, and its color
orange-yellow, olive-green, gray, brown, bright red or colorless. Its
streak is white and it is transparent. For red light, co= 2.402, €= 2.304.

Before the blowpipe wulfenite decrepitates and fuses readily. With
salt of phosphorus it gives the molybdenum beads. With soda on
charcoal it yields a lead globule. When the powdered mineral is evap-
orated with HC1 molybdic oxide is formed. On moistening this with
water and adding metallic zinc an intense blue color is produced.

Wulfenite is distinguished from lanadinite (p. 271), by crystalliza-
tion, by the test for chlorine (vanadinite) and the test for tungsten.

258 . DESCRIPTIVE MINERALOGY

Synthesis. — Wulfenite crystals have been produced by melting
together sodium molybdate and lead chloride.

Occurrence and Localities. — The mineral occurs in the oxidized zone
of veins of lead ores at some of the principal lead occurrences in Europe,
end in the United States near Phoenixville, Pennsylvania; in the Organ
Mountains, New Mexico; at the mines in Yuma County, Arizona; at
the Mammoth Mine, in Pinal County in the same State, and at many
other of the lead mines in the Rocky Mountain states.

Uses. — Wulfenite is an important source of molybdenum, but,
because of the few uses to which this metal is put, the amount of wulfen-
ite mined annually is very small.

~ * •

WOLFRAMITE GROUP

Wolframite ((Fe Mn)W04)

Wolframite is the name given the isomorphous mixture of the man-
ganese and iron tungstates that occur nearly pure in some varieties
of the minerals hiibnerite and ferberite.

The mixture of the iron and manganese molecules is more common
than either alone, consequently wolframite is the commonest member of
the group. The properties of all three minerals, however, are so nearly
alike that they must be distinguished by chemical analysis.

The name wolframite is usually applied to mixtures of the tungstates
in which the proportion of Fe to Mn varies between 4 : 1 and 2 : 3, or
between 9.5 per cent and 18.9 per cent of FeO and 14 per cent and
4.7 per cent of Mn02.

It has recently been suggested that the name ferberite be limited
to mixtures containing not more than 20 per cent of the hiibnerite mole-
cule and the name hiibnerite to those containing not more than 20 per
cent of the ferberite molecule. This would leave the name wolframite
for mixtures containing more than 20 per cent of both FeW04 and

MnW04.

Analyses of specimens of hiibnerite (I), wolframite (II and III)
and ferberite (IV) follow:

WO3 FeO MnO CaO Other Total

I. Ellsworth, Nye Co., Nev. . . 74.88 .56 23.87 .14 .16 99.61

II. Sierra Cordoba, Argentine . . 74.86 13.45 11.02 ... 1.22 100.55

III. Cabarrus Co., N. C 75-79 19.80 5.35 .32 tr 101.26

IV. Kimbosan, Japan 75-47 24.33 •••■ tr tr 99.80

All members of the group crystallize in the monoclinic system
(prismatic class) with axial ratios as follows:

CHROMATES, TUNGSTATES AND MOLYBDATES 259

Ferberite a :

:b:

^=.8229 :

1 :

.8463.

= 89°

38'

Wolframite

= .8300 :

1 :

.8678.

= 89°

38'

Hiibnerite

= •8315^

1 :

.8651.

= 89°

38'

Fig. 149. — Wolframite Crys-
tal with 00 P, no (m);
00 P2, 210 (/); oop56,
100 (a); -JP06, 102 (0;
P«,on (/); — 2P2, 121
(a); +JP« , 102 (>') and
— P, in (w).

The crystals are prismatic or cubic in habit and are bounded by
ooP(no), 00 Poo (100), and two or more of the following: oP(ooi),

00 P 06 (OIO), 00 P5(2I0), P ob (oil), £P 6b (T02), -£P 56 (102), -P(lll),

— 2P2(i2i) and +2P00 (102) (Fig. 149). The
angle 110A110 for ferberite=78° 51', for wol-
framite 790 23', and for hiibnerite 790 29'.
Twins are fairly common, with 00 P 60 (100)
the twinning plane. Cleavage is perfect
parallel to 00 P ob (010). The minerals also
occur in lamellar and granular masses.

Hiibnerite is* brownish red to black and
translucent, wolframite is black and trans-
lucent only on thin edges, and ferberite is
black and opaque. The streak is yellow to
yellowish brown in hiibnerite and brown or
brownish black in ferberite, with the streak
of wolframite between.

Wolframite is brittle, has a hardness of
5-5.5, a specific gravity of 7.2-7.5, and a submetallic luster. Before
the blowpipe it fuses to a globule which is magnetic. Fused with
soda and niter on platinum it gives the bluish green manganate. The
salt of phosphorus bead is reddish yellow when hot and a paler tint
when cold. In the reducing flame the bead becomes dark red. If
the mineral is treated first on charcoal with tin its bead assumes a
green color on cooling. The mineral dissolves in aqua regia with
the production of the yellow tungsten trioxide. When treated with
concentrated H2SO4 and zinc it yields the blue tungsten reaction.

Crystals of wolframite are easily distinguished from crystallized
columbite (p. 293), samarskite (p. 295), and uraninite (p. 297), by dif-
ferences in crystallization. Massive wolframite is distinguished from
massive forms of the other three minerals by its more perfect cleavage
and by the reactions with the beads. Uraninite, moreover, contains
lead. Wolframite is distinguished from black tourmaline (p. 434) by
the differences in specific gravity.

Occurrence and Origin. — Wolframite usually occurs in veins with tin
ores, and in quartz veins with various sulphides, and in pegmatite.
Its origin is probably pneumatolytic.

260 DESCRIPTIVE MINERALOGY

Localities. — Wolframite is found in all tin-producing districts, espe-
cially at Zinnwald, Schneeberg and Freiberg, in Germany; at Ner-
chinsk, in Siberia; in Cornwall, England; at Oruro, in Bolivia, and at
various points in New South Wales, Australia.

In the United States it occurs at Monroe, Conn.; near Mine La
Motte, Missouri; near Lead, South Dakota, where it impregnates a
sandy dolomite, and at Htil City in the same State in quartz veins,
sometimes containing cassiterite; in Boulder Co., Colorado, in veins
in granite (ferberite); near Butte, Montana, in quartz veins carry-
ing silver ores (hubnerite) ; and the quartz-cassiterite veins near Nome
and on Bonanza Creek, in Alaska; and in quartz veins at various
points in Washington, Idaho, California, Nevada, New Mexico and
Arizona. At some of these localities the mineral is more properly
hubnerite.

One or another of the three has been mined in Colorado, Nevada,
South Dakota, Montana, Washington, California, Arizona, and New
Mexico, but the total production has never been large. Some of the
ore shipped has been obtained from placers along streams that drain
regions containing the mineral in veins, but most of it has been obtained
from vein rock which is crushed and concentrated.

Uses. — These three minerals constitute the principal source of tung-
sten used in the arts. The uses of the metal are referred to under
scheelite.

Production. — The total production of concentrates containing 60
per cent WO3 in the United States during 1913 was 1,525 tons, valued
at $640,500. Of this, 953 tons were ferberite from Boulder Co.,
Colorado. A little hubnerite was produced in the Arivica region, in
southeast California, at Dragoon, Arizona, at Round Mountain, Nevada,
and on Paterson Creek, Idaho. In addition, there were imported
$86,000 worth of tungsten-bearing ores and $143,800 worth of tung-
sten metal and ferro-tungsten. The world's production of tungsten ore
in 1912 was 9,115 tons.

CHAPTER XIV

THE PHOSPHATES, ARSENATES AND VANADATES

The phosphates are salts of phosphoric acid, H3PO4, the arsenates
of the corresponding arsenic acid, H3ASO4, and the vanadates of the
corresponding vanadic acid, H3VO4. The phosphates are by far the
most important as minerals. They are easily distinguished by yielding
phosphine, H3P, upon igniting with metallic magnesium and moistening
the resulting MgaP2 with H20 or HC1 (Mg3P2+6HCl = 3MgCl2+
2PH3). The gas is recognized by its disagreeable odor. The arsenates
are detected by the test for arsenic.

The arsenates, phosphates and vanadates form groups of isomor-
phous compounds, the most important of which is the apatite group.
Those occurring as minerals are divisible into several subgroups, of
which the following six contain common minerals, viz.: (1) anhydrous
(a) normal salts, (b) basic salts and (c) acid salts, and (2) hydrous
(a) normal salts, (b) basic salts and (c) acid salts.

A number of the phosphates and arsenates are of value commercially
either because of the phosphorus they contain; because they are sources
of valuable metallic salts; because they serve to indicate the presence
of other valuable compounds; or because they possess an ornamental
character.

Nearly all the phosphates are transparent or translucent and all are
nonconductors of electricity or are very poor conductors.

ANHYDROUS PHOSPHATES, ARSENATES AND

VANADATES

NORMAL PHOSPHATES, ARSENATES AND VANADATES

The minerals belonging in this class of compounds are not as numer-
ous as the basic salts, but some of them are of great value. The class
includes phosphates of yttrium, the alkalies, beryllium, cerium, mag-
nesium, iron and manganese and a group of isomorphous phosphates,
arsenates and vanadates — the apatite group — in which a haloid radicle
replaces one of the hydrogen atoms of the acids. Apatite, the prin-
cipal member of the group, is an important source of phosphoric acid.

261

262 DESCRIPTIVE MINERALOGY

Triphylite— (Li(Mn Fe)P04)— Lithiophilite

Triphylite is the name usually applied to the isomorphous mixture
of LiFeP04 and LiMnPCU, in which the manganese molecule is present
in small quantity only. The mixture containing a large excess of the
manganese molecule is called lithiophilite.

The pure triphylite molecule contains FeO=45.5 Per cent> Li20
= 9.5 per cent and P20s=45 per cent. The pure lithiophilite molecule
consists of 45.1 per cent MnO, 9.6 per cent Li20 and 45.3 per cent
P205.

Both substances are orthorhombic (bipyramidal class), with an axial
ratio approximating .4348 : 1 : 5265. Crystals are rare and not well
developed. They are usually rough prisms bounded by 00 P 06 (010),
oP(ooi), ooP(no), ooP2(i2o) and 2P06 (021). The minerals usually
occur massive, or in irregular, rounded crystals, with two very dis-
tinct cleavages.

Both minerals are transparent to translucent, both have a white
streak, and both are vitreous to resinous in luster. Their hardness is
about 4.5-5 and sp. gr. about 3.5. Triphylite is greenish gray to blue,
and lithiophilite pink, yellow or brown. The refractive indices for
light brown lithiophilite are: a= 1.676, £=1.679, 7=1.687; those for
blue triphylite are a trifle higher.

When heated in closed tubes both compounds are apt to turn dark.
They fuse at a low temperature (1.5) and color the flame crimson. In
the case of triphylite the crimson streak is bordered by the green of iron.
Lithiophilite gives the reactions for Mn. Most specimens give reac-
tions for all these metals — Fe, Mn and Li. Both minerals are soluble
in HC1.

The two minerals are distinguished from other compounds by their
reactions for phosphorus and lithium, and from each other by the reac-
tions for Fe and Mn.

Occurrence. — They usually occur as primary constituents of coarse
granite veins. They are associated with beryl, tourmaline and other
pneumatolytic minerals and with secondary phosphates, which are
presumably weathering products of the primary phosphates.

Localities. — Both minerals occur at a number of points associated
with other lithium compounds, especially spodumene (p. 378). In this
country triphylite has been found at Peru, Maine; Grafton, New
Hampshire, and Norwich, Massachusetts; lithiophilite at Branchville,
Connecticut, and at Norway, Maine.

Neither of the minerals possesses a commercial value at present.

PHOSPHATES, ARSENATES AND VANADATES 263

Beryllonite (NaBeP04)

Beryllonite is a comparatively rare mineral occurring at only a few
places and always in crystals or in crystalline grains.

Its composition is 24.4 per cent Na20, 19.7 per cent BeO and 55.9
per cent P2O5.

Its crystals are orthorhombic (bipyramidal class), with an axial
ratio .5724 : 1 : .5490. They are short pyramidal or tabular in habit,
often exhibiting a pseudohexagonal symmetry. Most crystals are
highly modified with oP(ooi), ooPw(ioo), 00 P 66 (010), P 66(101)
and 2P2(i2i), the principal forms. Twins are common, with 00 P(no)
the twinning plane. The crystal faces are frequently strongly etched.

The mineral is white to pale yellow. It has a vitreous luster,
except on oP(ooi), where the luster is sometimes pearly. It possesses
four cleavages, of which the most perfect is parallel to oP(ooi). That
parallel to ooPw (100) is distinct, but the others are indistinct. Its
hardness is 5.5-6 and its density 2.845. ^s fracture is conchoidal.
Crystals often contain numerous inclusions of water and liquid CO2
} arranged in lines parallel to c. Its refractive indices for yellow light
are: 0=1.5520,13=1.5579,7=1.5608.

Beryllonite decrepitates and fuses in the blowpipe flame to a cloudy
glass, at the same time imparting to the flame a yellow color. It is
slowly soluble in HC1, and gives the phosphorus reaction with mag-
nesium.

It is distinguished from most other colorless transparent minerals
by the reaction for phosphorus; from other colorless phosphates by its
crystallization and the sodium flame test.

Occurrence and Localities. — The best known occurrence of beryllo-
nite in the United States is Stoneham, Maine, where it is found in the
debris of a pegmatite dike associated with apatite (p. 266), beryl (p. 359),
and other common constituents of pegmatites. It originally existed
implanted on the walls of cavities in the pegmatite and was apparently
the result of pneumatolytic processes.

Use. — The mineral is used to some extent as a gem stone.

Monazite ((Ce Di La)P04)

Monazite is the principal source of certain rare earths that are used
in manufacturing gas mantles. Although it occurs as small grains and
crystals in certain granites it is found in commercial quantities only in
the sands of streams.

264 DESCRIPTIVE MINERALOGY

The mineral is a phosphate of the metals cerium, lanthanum, praseo-
didymium and neodidymium in most cases combined with the silicate of
thorium. Its composition may be represented by the formula

*((Ce • La • Di)P04)+y(ThSi04),

in which the proportion of the second constituent varies from a trace to
an amount yielding 20 per cent ThCfe. Since this is not constant in
quantity it is not to be regarded as an essential portion of the com-
pound. It is probable that in monazite we have to do with a solid
solution of cerium and thorium phosphates, thorium silicate and oxides
of the rare metals.

Monazite is monoclinic with a : b : £=.9693 : 1 : .9255 and j5=
760 20'. Crystals are usually prismatic with the pinacoids 00 P * (100),
00 Poo (010), the prism ooP(no), the two domes — P 60(101) and
+P66(ioT) and the pyramids — P(ni) and +P(nT). They are

often flattened parallel to the orthopinacoid
(Fig. 150). The angle iioAiTo=86° 34'.

Their cleavage is perfect parallel to oP.
The color of the mineral is gray, yellow, red-
dish, brown or green. It is usually transpar-
ent or translucent and sometimes opaque. It
is brittle, has a white streak, and a resinous
luster. Its hardness is 5-5.5 and its sp. gr.
Fig. 150.— Monazite Crys- 4.7-5.3, varying with the proportion of thorium
tal with oop do, 100(a); present> j^ refractive indices for yellow

00P, no (*w); 00 P2, ... 00

' „w ,.v light are: a= 1.7038, 7=1.8452.

120 («); 00 P 00 , 010 (6); ° m §/° ' ' ^D

-Poo, 101 («/)• +P00, The mineral is infusible. Before the blow-
10T (x) and P, nT (v). pipe it turns gray, and when moistened with

H2SO4 it colors the flame bluish green. It is
difficultly soluble in HC1 and HNO3. Most specimens are strongly
radioactive.

Synthesis. — Crystals of monazite have not been prepared, but crys-
tals of cerium phosphate similar to those of monazite have been made
by heating to redness a mixture of cerium phosphate and cerium chloride.
Occurrence and Origin. — Monazite occurs as the constituent of cer-
tain granites and granitic schists in small crystals scattered among the
other components. In this form it is a separation from the granitic
magma. When the granites are broken down to sand by weathering
the monazite is freed and because of its specific gravity it concentrates
in stream channels.

Localities. — Although the mineral is fairly widespread in the rocks,

PHOSPHATES, ARSENATES AND VANADATES 265

it is concentrated into commercial deposits at only a few places. The
most important of these are in southeastern Brazil, in Norway, and in a
belt 20 to 30 miles wide and 150 miles long extending along the east side
of the Appalachian Mountains from North Carolina into South Carolina.

The mineral has also been reported from many points in ten coun-
ties in Idaho. Near Centerville it may be in sufficient quantity to be
of commercial importance.

Preparation. — Monazite is separated from the valueless sand in
which it is found, by washing, and the residues thus resulting are further
concentrated by a magnetic process. The commercial concentrates
produced in this way usually contain from 3 to 9 per cent TI1O2, and
their price varies accordingly.

. Production and Uses. — Monazite is the chief source of thorium oxide
used in the manufacture of incandescent gas mantles. Formerly it was
produced in large quantity in the Carolinas, the production in 1909
amounting to 542,000 lb., valued at $65,032, and in 1905 to
1,352,418 lb., valued at $163,908. All of this was manufactured into
the nitrate of thorium in this country and the amount made was
not sufficient to meet the domestic demand. Consequently, large quan-
tities of the nitrate were imported. In 1910-11 mining of the mineral
in the Carolinas ceased and all the monazite needed has been imported
since then. The imports of thorium nitrate for 191 2 were 117,485 lb.,
valued at $225,386 and of monazite, an amount valued at $47,334.

Xenotime (YP04)

Xenotime, though essentially an yttrium phosphate, usually contains
erbium and in some cases cerium.
It occurs in tetragonal crystals
and in rolled grains. Its axial
ratio is 1 : .6177 and the angle
111A1T1 =55° 30'. Its crystals
are octahedral or prismatic and
are bounded by 00 P(i 10), P(i 11),
and in some cases by 00 P 00 (100)
and 2P 00 (201) (Fig. 151). Their
cleavage is perfect parallel to Fig. 151.— Xenotime Crystals with °op, iXO

■n/ \ »m. • 1 • u (OT)> P- I" W, and 00 Poo; ioo (a).

ooP(no). The mineral is brown, w' ' w

pink, gray or yellow. Its streak is a pale shade of the same color.
It is opaque and brittle. Its luster is vitreous or resinous; its hardness
4-5 and specific gravity 4.5. Its indices of refraction are: e=i.8i,

tt=1.72.

266 DESCRIPTIVE MINERALOGY

Xenotime is infusible, insoluble in acids and with difficulty soluble
in molten microcosmic salt. It is distinguished from zircon by its
cleavage and inferior hardness.

A variety of xenotime containing a small percentage of sulphates is
known as hussakite.

The mineral occurs in pegmatite veins, in granites and in the sands
of streams. It is found in pegmatite veins at Hittero, Moss, and other
places in Norway; at Ytterby, Sweden; in the granites of Minas Geraes,
Brazil, and in the gold washings at Clarksville, Georgia, and many places
in North Carolina, and in pegmatite veins in Alexander County in the
same State.

APATITE GROUP

The apatite group consists of a number of phosphates, arsenates and
vanadates in which fluorine or chlorine takes the place of the hydroxyl
in basic compounds. Thus, jluorapatite is Ca4(CaF)(P04)3 and chlor-
apatite Ca4(CaCl)(P04)3- The group contains a number of important
minerals, of which apatite is by far the most valuable. These minerals
are isomorphous, all crystallizing in the hemihedral division of the hex-
agonal system (hexagonal bipyramidal class). The names, composi-
tions and axial ratios of the most important are as follows:

Fluor apatite Ca4(CaF)(P04)3 a: c=i : .7346

Chlorapatite Ca4(CaCl)(P04)3 a : c=i : .7346+

Pyromorphite Pbi(PbCl)(P04)3 a : c=i : .7293

Mimetite Pbi(PbCl)(As04)3 a : c=i : .7315

Vanadinite Pb4(PbCl)(V04)3 a : c=i : .7122

Apatite (Ca4(Ca(F-Cl))(P04)3)

Although fluorapatite and chlorapatite are distinct compounds with
slightly different properties, nevertheless, because of the difficulty of
discriminating between them without analyses, the name apatite is
commonly applied to both. This is justified because of the fact that the
two compounds are completely isomorphous, and the mineral as it
usually occurs is a mixture of both. The ideal molecules comprising
the two varieties of apatite have the following compositions:

Fluorapatite CaO=55-5, F=3.8, P20s = 42.3
Chlorapatite CaO=53-8, Cl = 6.8, P20s = 4i.o

Apatite is found in well defined crystals, sometimes very large.
These have a holohedral habit, but etch figures on their basal planes

PHOSPHATES, ARSENATES AND VANADATES 267

reveal the grade of symmetry of pyramidal hemihedrism. The min-
eral occurs also massive, in granular and fibrous aggregates and less
commonly in globular forms and as crusts.

The crystals are usually columnar or tabular, with the hexagonal
prism or pyramid well developed. Although in some cases highly
modified, most crystals contain only the oo P(iolo), P(ioTi) and oP(oooi)
planes prominent, though £P(iol2) and 2P2(ii2i) are not uncommon as
small faces (Figs. 152 and 153). Their cleavage is indistinct, and their
fracture often conchoidal.

Apatite may possess almost any color. In a few cases the mineral is
colorless or amethystine and transparent, but in most cases it is trans-
lucent or opaque and white, green, bluish, brown or red. Its streak is

Fig. 152.

Fig. 153.

Fig. 152. — Apatite Crystals with 00 P, 1010 (w); P, 1011 (.r); oP, oooi (c); JP,

1012 (r) and 00 P2, 1120 (a).

Fig. 153. — Apatite Crystal with m, x, r and c as in Fig. 152 and 2P, 2021 (y); 4PJ,
1341 00; 3P}> i23i GO; 2P2, 1121 (5); P2, 1122 (») and 00 p|, 1230 (A).

white and its luster vitreous to resinous. Its hardness is 4.5-5 an^ sp.
gr. between 3.09 and 3.39. The refractive indices of fluorapatite for
yellow light are: «= 1.6335, €=1.6316 and of chlorapatite, o>= 1.6667.
Many specimens are distinctly phosphorescent. Nearly all fluoresce in
yellowish green tints, and all are thermo-electric.

Apatite fuses with difficulty, tinging the flame reddish yellow. The
chlorapatite melts at 15300 and the fluorine variety at 16500. When
moistened with H2SO4 all varieties color the flame pale bluish green,
due to the phosphoric acid. Specimens containing chlorine give the
brilliant blue color to the flame when fused in a bead of microcosmic
salt that has been saturated with copper oxide. Specimens containing
fluorine etch glass when fused with this salt in an open glass tube.
The mineral also yields phosphine when ignited with magnesium, and
it dissolves in HC1 and HNO3.

268 DESCRIPTIVE MINERALOGY

Apatite is much softer than beryl (p. 359), which it closely resembles
in appearance. It is distinguished from calciU by lack of effervescence
with acids and from other compounds by the phosphorus reaction.

The varieties of the mineral recognized by distinct names are:

Ordinary apatite, crystals or granular masses.

Manganapatite, in which manganese partly replaces the Ca of ordi-
nary apatite. This is dark bluish green.

Fibrous, concretionary apatite. Known also as phosphorite.

Osteolite. The earthy variety.

Phosphate rock. A mixture of apatite, phosphorite, several hydrous
carbonates and phosphates of calcium, and fragments of bone and
teeth. It is more properly a rock with a brecciated and concretionary
structure. The composition of typical deposits is represented by the
following analysis of hard rock phosphate from South Carolina:

CaO P2O5 C02 Fe203 AI2O3 MgO Insol. Undet. H20 Moist.
50.08 38.84 .65 .96 3.07 .30 .49 2.46 2.96 .07

Guano is a mixture of various phosphates, both hydrous and an-
hydrous, calcite and a number of other compounds. It is rather a rock
than a mineral, as it has no definite composition.

Syntheses. — Crystals of fluorapatite have been made by fusing
sodium phosphate with CaF2 and by heating calcium phosphate with a
mixture of KF and KC1.

Origin. — The crystallized apatite was formed by direct separation
from igneous rock magmas and by pneumatolytic action upon limestone.
The phosphorite variety and the phosphate in phosphate rock were
probably produced by the solution of calcium phosphate and its later
deposition from solution — the original phosphate having been furnished
in many cases by the shells of mollusca, and by the action of phosphoric
acid produced by the decay of organisms upon limestone. In many
cases phosphorite accumulated as a residual deposit in consequence of
the solution of the calcite and dolomite from phosphatic limestone,
leaving the less soluble phosphate as a mantle on the surface.

Occurrence. — The mineral occurs in microscopic crystals- as a com-
ponent of many rocks, as large crystals in metamorphosed limestones,
as a component of many coarse-grained veins, especially those composed
of coarse granite and those in which cassiterite, magnetite, tourmaline,
and other pneumatolytic minerals are found. At a number of places
aggregates of apatite and magnetite or ilmenite occur in such large
masses as to be worthy of being called rocks. An impure apatite in
concretionary and fibrous forms also occurs in thin beds covering large

PHOSPHATES, ARSENATES AND VANADATES 269

areas. It is often mixed with other phosphates, with the bones and
teeth of animals and with other impurities. This is the well known
phosphate rock or phosphorite.

Localities. — Crystallized apatite is so widely spread that it is useless
to mention its occurrences. It is mined at Kragero and near Bamle,
in Norway; at various points in Ottawa County in Quebec, and in
Frontenac, Lanark and Leeds Counties in Ontario; and at Mineville,
New York. Rock phosphate is found in extensive beds on the west
side of the peninsula of Florida, in South Carolina, North Carolina,
Alabama, Tennessee, Wyoming, Idaho, Utah and Arkansas. A mixture
of apatite and ilmenite {nelsonite) , occurs as dikes in Nelson and
Roanoke Counties, Virginia.

Uses. — The principal use of apatite and phosphate rock is in the
manufacture of fertilizers. The rock (or crushed apatite) is treated
with H2SO4 to make an acid phosphate which is soluble in water. Am-
monia or potash, or both, are added to the mass and the compound is
sold as a superphosphate. The purest varieties are treated with H2SO4
in sufficient quantity to entirely decompose them, CaS04 and H3PO4
being formed. The latter is drawn off and mixed with additional high-
grade rock and the mixture is known as concentrated phosphate. Super-
phosphates are manufactured in large quantities in the United States
and the concentrated phosphates in Europe. Unfortunately, for the
latter use the best grades of apatite or rock phosphate are required, and
consequently the best grades of rock produced in the United States are
exported and thus lost to American farmers.

Production. — The world's production of apatite and phosphate rock
during 191 2 was as follows:

United States 3,020,905 tons, valued at $11,675,774

Tunis 2,050,200 tons, valued at 7,500,000

Christmas Island. . 159,459 tons, valued at 2,024,036

France ... 313,151 tons, valued at 1,169,400

Algeria 207,111 tons, valued at 759,455

Belgium 203,110 tons, valued at 316,703

Other countries 65,000 tons, valued at 280,000

For the United States production of 191 2 the statistics are:

Florida 2,407,000 tons, valued at $9,461,000

Tennessee 423,300 tons, valued at 1,640,500

South Carolina.. . . 131,500 tons, valued at 524,700

Other States 11,600 tons, valued at 49,200

270 DESCRIPTIVE MINERALOGY

The total production was 3,020,905 tons, valued at $11,675,774.00,
of which 1,206,520 tons, valued at $8,996,456.00 were exported. Par-
tially offsetting this, there were imported guano, apatite and other phos-
phates to the value of about $2,000 000.

Pyromorphite (Pb4(PbCl)(P04)3)

In composition pyromorphite is PbO, 82.2 per cent, P2O5, 15.7 per
cent and CI, 2.6 per cent, but there are usually present also CaO and
AS2O5.

The mineral is completely isomorphous with apatite. Its crystals
are smaller and simpler than those of apatite, but they have the same
habit. Their axial ratio is a : c=i : .7293. This increases to 1 : .7354
in varieties containing calcium.

Crystals are often rounded into barrel-shaped forms, and frequently
are mere skeletons. Tapering groups of slender crystals in parallel
growths are also common. Their cleavage is parallel to the 00 P(no)
faces, and their fracture is feebly conchoidal. The mineral also occurs
in globular, granular and fibrous masses.

Pyromorphite is translucent. It is brittle, has a hardness of 3.5-4
and a density of about 7. Its luster is resinous and color usually green,
yellow, brown or orange. Some varieties are gray or milk-white. Its
streak is white. Its refractive indices for yellow light are: «= 2.0614,
€= 2.0494. The mineral is distinctly thermo-electric.

When heated in the closed tube pyromorphite gives a white subli-
mate of lead chloride. It fuses easily, coloring the flame bluish green.
When heated on charcoal it melts to a globule, which crystallizes on
cooling and yields a coating which is yellow (PbO) near the assay and
white (PbCfe), at a greater distance from it. When fused with Na2C03
on charcoal a globule of lead results. The mineral also gives the CI and
P reactions. The mineral is soluble in HNO3.

Pyromorphite is recognized by its form, high specific gravity and its
action when heated on charcoal.

Synthesis. — Crystals have been obtained by fusing sodium phosphate
with PbCl2.

Occurrence. — The mineral occurs principally in veins with other lead
ores, especially in the zone of weathering. It also exists in pseudomorphs
after galena.

Localities. — It is found in all lead-producing regions, especially in
the upper portions of veins. It occurs in particularly good specimens
at Pribram, Bohemia; at Ems, in Nassau; in Cornwall, Devon, Derby-

PHOSPHATES, ARSENATES AND VANADATES 271

shire and Cumberland, England; at Phoenix ville, Pennsylvania, and
at various other points in the Appalachian region.

Uses. — Pyromorphite alone possesses no commercial value, but it
is mined with other compounds of lead as an ore of this metal.

Mimetite (Pb4(PbCl)(As04)3)

Mimetite, or mimetesite, resembles pyromorphite in its crystals and
general appearance, and many of its properties. Its color, however, is
lighter and its density slightly greater. It occurs in crystals, in fila-
ments, and in concretionary masses and crusts. Its axial ratio is
i : .7315 and its refractive indices for yellow light are: £0=2.1443, e
= 2.1286.

The formula for mimetite demands 74.9 per cent PbO, 23.2 per cent
AS2O5 and 2.4 CI. Usually a portion of the lead is replaced by CaO and
a portion of the As by P.

Mimetite fuses more easily than pyromorphite. It differs from this
mineral in yielding arsenical fumes when heated on charcoal. More-
over, when heated in a closed tube with a fragment of charcoal it coats
the walls of the tube with metallic arsenic.

Occurreftce and Localities. — It occurs with other lead minerals in
veins, usually coating them either as crusts or as a series of small crys-
tals. It is found at Phoenix ville, Pennsylvania; in Cornwall, England;
at Johanngeorgenstadt, in Germany; at Nerchinsk, Siberia; at Lang-
ban, in Sweden, and at a number of other places. It is, however, not
as common as the corresponding phosphorus compound.

Uses. — It is mined with other compounds as an ore of lead.

Vanadinite (Pb4(PbCl)(V04))3

Vanadinite is the most widely distributed of all the vanadium min-
erals. It usually occurs in small bright red prismatic crystals implanted
on other minerals, or on the walls of crevices in rocks. It is one of the
sources of vanadium.

Its theoretical composition is as follows: PbO =78.7 per cent,
Vo05=i94 per cent and CI =2.5 per cent, but phosphorus and arsenic
are often also present. When arsenic and vanadium are present in
nearly equal quantities the mineral is known as endlichitc.

Its crystals are hexagonal prisms and pyramids bounded by
ooP(ioTo), oP(oooi), ooP2(ii2o), P(ioTi) and other forms, with an
axial ratio 1 : .7122 (Fig. 154). Often the crystals have hollow faces

272 DESCRIPTIVE MINERALOGY

(Fig, 155)- Frequently they are grouped into pyramids like those of
pyromorphite. The mineral occurs also in globules and crusts.

Vanadinite is brittle, has a hardness of about 3 and a specific gravity
of about 7. Its fracture is conchoidal. Its luster is adamantine or
resinous and its color ruby red, brownish yellow or reddish brown.
Its streak is white or light yellow. The mineral is translucent
or opaque. Its refractive indices for yellow light are: (0=2.354,
4=2.299.

In the closed tube vanadinite decrepitates. It fuses easily on char-
coal to a black lustrous mass which is reduced on being further heated
in the reducing flame to a globule of lead. A white sublimate of PbCfe
also coats the charcoal. The mineral, moreover, gives the flame test

f^\

\^sJJ

—Vanadinite Crystal with °°P, 1010 (in); oP, 1

Fig. 155. — Skeleton Crystal of Vanadinite.

for chlorine with copper. After complete oxidation of the lead by heat-
ing in the oxidizing flame on charcoal the residue gives an emerald-green
bead in the reducing flame with microcosmic salt and this turns to a
light yellow in the oxidizing flame. The mineral is soluble in hydro-
chloric acid. If to the solution a little hydrogen peroxide is added it
will turn brown. The addition of metallic tin to this will cause it to
turn blue, green and lavender in succession, in consequence of the reduc-
tion of the vanadium compounds.

Vanadinite is easily distinguished from most other minerals by its
color. It is distinguished from other compounds of the same color by
its crystallization and by the reactions for vanadium.

Occurrence. — Vanadinite occurs principally in regions of volcanic
rocks. It is probably a result of pneumatolytic processes.

Localities. — Crystals are found at Zimapan, Mexico; Wanlockhead,

PHOSPHATES, ARSENATES AND VANADATES 273

England; Undenas, Sweden; in the Sierra de C6rdoba, Argentine, and in
the mining districts of Arizona and New Mexico.

Uses. — Vanadinite is an important source of vanadium, which is
employed in the manufacture of certain grades of steel and bronze.
Its compounds are, moreover, used as pigments and mordants. Most
of the vanadium compounds produced in this country are obtained from
other vanadium minerals, among them patronite — a mixture, of which
the principal component is a sulphide (VS4) — and carnotite (p. 290),
but vanadinite has been used abroad and also to a small extent in the
United States.

WAGNERITE GROUP

This group, in chemical composition, is analogous to the apatite
group. It includes a number of phosphates and arsenates containing a
fluoride radical. The group is monoclinic (prismatic class), with an
axial ratio which is approximately 1.9 : 1 : 1.5, with £=71° 50'. None
of its members are important. The two most common ones are wag-
nerite (Mg(MgF)P04), and triplite (Fe-Mn) ((Fe-Mn)F)P04.

Wagnerite occurs in massive forms and in large rough crystals, with
imperfect cleavages parallel to 00 P <x> (100) and 00 P(no). Its crystals
have an axial ratio of 1.9145 : 1 : 1.5059 with /3=7i° 53'. They are
often very complex. The mineral is brittle. Its fracture is uneven.
Its hardness is 5.5 and density 3.09. Its color is yellow, gray, pink or
green. It is vitreous, translucent and has a white streak. Its refractive
indices are: a= 1.569, 0= 1.570, 7 = 1.582. It fuses to a greenish gray
glass and gives the usual reactions for fluorine and phosphoric acid. It
is soluble in HC1 and HNO3, and heated with H2SO4 it yields hydro-
fluoric acid. It occurs in good crystals near Werfen, Austria, and in
coarse crystals near Bamle, Norway.

Triplite is an isomorphous mixture of Fe(FeF)PC>4 and Mn(MnF)PC>4.
It usually occurs massive, but is found in a few places in rough crystals.
The mineral is dark brown or nearly black, is translucent to opaque,
and has a yellowish gray or brown streak. It possesses two unequal
cleavages perpendicular to one another and a weakly conchoidal frac-
ture. Its hardness is 4-5.5 and specific gravity about 3.9. Its luster is
resinous. Its intermediate refractive index is 1.660.

Before the blowpipe triplite fuses easily (1.5) to a black magnetic
globule. It reacts for Mn, Fe, F, and P2O5. It is soluble in HC1 and
evolves hydrofluoric acid with H2SO4. It is found in coarse granite

274 DESCRIPTIVE MINERALOGY

veins at Limoges, France; Helsingfors, Finland; Stoneham, Maine;
and Branchville, Connecticut. In all of its occurrences it appears to
be pneumatolytic.

BASIC PHOSPHATES AND ARSENATES

The basic phosphates are those in which there is more metal present
than sufficient to replace the three hydrogen atoms in the normal acid,
H3PO4. This is due to the replacement of one or more of the hydrogen
atoms by a group of atoms consisting of a metal and hydroxyl (OH).
All yield water when heated in the closed tube.

The principal basic phosphates are amblygonite, a source of lithium
compounds, dufrenite and lazulite, neither of which is of economic im-
portance, and libethenite^ a copper compound which occurs in compara-
tively small quantities with other copper ores, and is mined with
them.

Olivenite is a basic copper arsenate corresponding to the phosphate
libethenite.

Amblygonite (Li(Al(F OH))P04)

Amblygonite is an isomorphous mixture of the two compounds
(AlF)LiP04 and (AlOHQLiPQi. It is an important source of lithium.

The composition of the fluorine molecule is Al20a = 34.4 per cent,
Li02=io.i per cent and P20s = 47.9 per cent, making a total of 105.3
per cent from which deducting 5.3 per cent (0= 2F), leaves 100. Nearly
always a portion of the F is replaced by OH and a part of the Li
by Na. The pure Na(A10H)PC>4 is known Sisfremonttie, and the pure
Li(AlOH)P04 as montcbrasite.

The analysis of a specimen from Paia, California, gave:

P«Os

AltOa

FeaOi

MnO

MgO

Li,0

NajO

H.O

0-P Total

48.83

33.70

.12

.09

.31

9.88

.14

595

2.29 =»ioi.3i — .96 — 100.45

The mineral forms large, ill-defined triclinic crystals (Fig. 156), and
compact masses with a columnar cleavage. Crystals are very rare, and
are poorly developed. Their axial ratio is .7334 : 1 : .7633. The
cleavage pieces often show polysynthetic twinning lamellae parallel to
'P' 00 (101) and /Py 00 (Toi).

The cleavage of the mineral is perfect parallel to oP(ooi). Its
fracture is uneven. It is brittle, has a hardness of 6 and a density of
3.03. Its color is white, gray, or a very light tint of blue, pink or
yellow. Its luster is vitreous, except on oP where it is pearly. Its

PHOSPHATES, ARSENATES AND VANADATES 275

ioo (a); oP, ooi (c);
oo 'P, ilo (M);oop],
no (m); oo^, 1 20
(z) ; /P/ 00 , Toi (A)
and a'P 00 , 021 (e).

streak is white and it is translucent. Its refractive indices for yellow
light are: a= 1.579, £=1.593, 7=1.597.

In the closed tube at high temperature it yields water which reacts
acid and corrodes glass. It fuses easily to an
opaque white enamel. It colors the flame red
with a slight fringe of green. When moistened
with H2SO4 it tinges the flame bluish green.
When finely powdered it dissolves readily in
II2SO4 and with dfficulty in HC1.

Amblygonite resembles in appearance many
other minerals, especially spodumene (p. 378),
and some forms of barite, feldspar, dolomite, etc. pIG IS6— Amblygonite
From spodumene it is distinguished by the phos- Crystal with 00 p 56 ,
phorus reaction and the acid water; from the
others by its easy fusibility.

Occurrence. — Amblygonite is found in granite
and in pegmatite veins associated with other
lithium compounds, tourmaline, cassiterite and
other minerals of pneumatolytic origin. In all cases it also is probably
a result of pneumatolytic action associated with the last phases of granite
intrusions.

Localities. — The mineral occurs near Penig, in Saxony; at Arendal,
in Norway; at Montebras, France; at Hebron, Paris and Peru, Maine;
at Branchville, Conn.; at Pala, in California; and near Keystone, in
the Black Hills, South Dakota.

Uses and Production. — The mineral is the principal source of lithium
compounds in the United States. It is used in the manufacture of
LiC03, which is employed as a medicine, in making mineral waters, in
photography and in pyrotechnics.

It has been mined in South Dakota and in California to the extent
of a couple of thousand tons, valued perhaps at $20,000.

Dufrenite (Feo(OH)3P04)

Dufrenite, or kraurite, is a basic iron phosphate containing 62 per
cent Fe2C>3, 27.5 per cent P2O5 and 10.5 per cent water. It may be
regarded as a normal phosphate in which one H atom of H3PO4 has been
replaced by the Fe(0H)2 group and two by the group Fe(OH), thus

HO-Fe=P04-Fe<^'

It forms small orthorhombic crystals with a cubic habit that are rare.
Their axial ratio is .3734 : 1 : .4262. It usually occurs massive, in

276

DESCRIPTIVE MINERALOGY

nodules, or in fibrous radiating aggregates. The same substance is
believed to occur also in the colloidal condition under the name delvauxite.

The color of dufrenite varies from leek-green to dark green, which
alters on exposure to yellow and brown. It is translucent to opaque,
has a light green streak and is strongly pleochroic. Its hardness is
3.5-4 and specific gravity about 3.3.

In the closed tube it yields water and whitens. It fuses easily, color-
ing the flame bluish green and yielding a magnetic globule. It is sol-
uble in HC1 and in dilute H2SOt.

It is recognized by its color and the presence in it of water, phos-
phorus and iron.

Localities and Origin, — The mineral has been observed at several
points in Europe; at Allentown, New Jersey, and in Rockbridge County,
Virginia. It is thought to be ptoduced by the weathering of other fer-
ruginous phosphates.

Lazulite ((Mg-Fe)(A10H)2(P04)2)

Lazulite is essentially an isomorphous mixture of the two com-
pounds Mg(A10H)2(P04)2 and Fe(AiOH)2(PO.i)2. There is also fre-
quently present in it a little calcium.
When the proportion of the two
molecules present is as 2 : 1 the com-
position becomes FeO=7.7; MgO
= 8.5; Al203 = 32.6; P205=454and
H20=5.8.

The mineral occurs in blue pyram-
idal crystals that are monoclinic
(prismatic class), with the axial ratio
= .9750 : 1 : 1.6483 and £=89° 14'.
A u The predominant forms are +P(nT),

Fig. 157.— Lazulite Crystals. A with — P(ni) and — P 00 (ioi)(Fig. 157^).
-P, in (/>); +P, hi Wand P«, The angle in AITI = 79040,. Twins
101 (/). B is the same combination are not common> Those most fre.

twinned about 00 P 06 (100). with oP . . , A . . .

, x #. , quently found are twinned about c

(001) the composition face. M J

as the twinning axis (Fig. 157B).
It is found also massive and in granular aggregates.

The cleavage of lazulite is not distinct. Its fracture is uneven. It
is brittle, has a vitreous luster, is translucent or opaque, has an azure
color and a white streak. Its hardness is 5 or 6 and its specific gravity
about 3.1. Translucent crystals are strongly pleochroic in deep blue
and greenish blue tints — the former when viewed along the vertical

PHOSPHATES, ARSENATES AND VANADATES 277

axis. Their indices of refraction for yellow light are: a= i .603, 0= 1.632,
7=1.639.

In the closed tube lazulite swells, whitens and yields water. When
heated in the blowpipe flame it whitens, falls to pieces and colors the
flame bluish green. The white powder moistened with Co(NQs)2 and
reheated regains its blue color. When moistened with H2SO4 and
heated in the blowpipe flame it imparts to it a green blue color. It is
infusible and is unacted upon by acids.

Lazulite, when massive, closely resembles in appearance massive
forms of some varieties of sodalite, haiiynite and lazurite (p. 333). The
latter, however, are soluble in HC1. Moreover, none of them contains
phosphorus.

Occurrence. — The mineral occurs in quartz veins in sandstones and
slates and is usually a product of metamorphism. It is sometimes, how-
ever, found in serpentine rocks, with corundum, in which case it may be
original.

Localities. — Good crystals occur at Krieglach, in Styria; at Horrs-
joberg, in Sweden, and in the United States at Crowder's Mountain,
North Carolina, and on Graves Mountain in Georgia.

OLIVENITE GROUP

The olivenite group includes a number of basic copper, lead and
zinc compounds of the general formula R"2(OH)R/"04 in which R"
= Cu, Zn, Pb and R"'=As, P, V. The group is
orthorhombic (bipyramidal class), with axial ratios
approximating .95 : 1 : .70. The most important
members of the group are the two copper min-
erals, olivenite, Cu(CuOH) As04 and libethenite,
Cu(CuOH)P04.

Olivenite occurs in fibrous, globular, lamellar,
granular and earthy masses and in prismatic and
acicular crystals bounded by 00 P(i 10), 00 P 6b (100), FlG- J58- — Olivenite
ooP66(oio),P56(oii) andPob(ioi) (Fig. 158). CryStal mth °° P °° '
Their axial ratio is .9396 : 1 : .6726 and the angle
1 10 A 1 To= 86° 26'. Their cleavage is poor.

The mineral is some shade of green, brown,
yellow or grayish white and its streak is olive-green
in greenish varieties. It is transparent to opaque, is brittle, has a
hardness =3, and a specific gravity =4.3. Its refractive indices for

100 (a); 00 P, no
(w); 00 Poo ,010(6);
P 00 , 01 1 (e ) and
P »o , 101 (»).

278 DESCRIPTIVE MINERALOGY

yellow light are about 1.83. Its luster is usually vitreous. Fibrous
varieties are sometimes known as wood-copper.

Olivenite fuses easily (2) to a mass that appears crystalline on cooling.
It gives the usual reactions for H2O, Cu, and As. It is soluble in acids
and in ammonia.

It is associated with other copper compounds in some copper ores.
Its origin is secondary in all cases. It occurs in the Tintic district,
Utah, and in many copper veins in Europe and in South America.

Libethenite occurs in compact or globular masses and in small
crystals that resemble those of olivenite. Their axial ratio is .9605 :
1 : .7019 and no A 110=87° 40'.

The mineral is brittle. Its fracture is indistinctly conchoidal. Its
color is dark olive-green and its streak a lighter shade. It is translucent
or transparent and has a resinous luster. Its hardness =4 and sp. gr.
= 3.7. Its intermediate refractive index for yellow light is 1.743.

When heated in the closed tube it yields water and blackens. It is
easily fusible (2). It yields the usual reaction for Cu and P, and is sol-
uble in acids and in ammonia. It is distinguished from olivenite by the
reaction for phosphorus.

It occurs at many of the localities for olivenite, where, like this min-
eral, it is a decomposition product of other copper compounds.

Herderite (CaBe(OH F)P04)

Herderite is an isomorphous mixture of the two phosphates, CaBeFP04
and CaBe(OH)P04. The latter molecule occurs in nature as hydro-
herderite\ the former occurs only in mixtures. The theoretical compo-
sition of the fluorine (I) and hydroxyl (II) molecules and of transparent
crystals from Stoneham (III), and Paris (IV), Maine, are given below:

BeO

CuO

P2O5

H20

Ins.

Total
(lessO=F)

15-39

3433

4353

11.64

. * • .

• • •

100

II.

IS- 53

34.78

44.10

• • • •

5-59

• B •

100

III.

i5-5i

3367

4374

S-27

3-7°

■ • •

99.67

IV.

16.13

34 04

44 05

5-85

• • • •

■44

100.51

The mineral is found only in crystals, which are monoclinic, with
alb: £=.6301 : 1 : .4274 and 18=89° 54'. Their habit is hexagonal,
pyramidal or short prismatic, elongated in the direction of a.

PHOSPHATES, ARSENATES AND VANADATES 279

Herderite is colorless or light yellow, transparent or translucent.
Its refractive indices are: a= 1.592, 0= 1.612, 7= 1.621.

Its density is about 3, diminishing, as the amount of hydroxyl in-
creases, to 2.952 in the pure hydroherderite.

Before the blowpipe herderite first phosphoresces with an orange-
yellow light, then fuses to a white enamel, colors the flame red and yields
fluorine. In the closed glass tube most specimens yield an acid water,
which, when strongly heated, evolves fluorine that etches the glass.
The mineral also reacts for phosphorus with magnesium ribbon. It is
slowly soluble in HC1.

Occurrence, Origin and Uses. — Herderite occurs in pegmatite dikes
at Stoneham, Hebron, and other places in Maine, and at the tin mines of
Ehrenfriedersdorf, Saxony; in all of these places it is apparently of
pneumatolytic origin. The material from Maine is used to a small
extent as a gem stone.

ACID PHOSPHATES

Acid phosphates are those in which all of the hydrogen atoms of the
acids have not been replaced by metals or by basic radicals. Theoret-
ically, they contain replaceable hydrogen atoms. There are 12 or 15
minerals that are thought to belong to this class, but the composition
of many of them is very obscure. Most of them appear to be hydrated.
The only important mineral that may belong to the class is the popular
gem stone, turquoise. This, according to the best analyses, contains its
components in the proportions indicated by the formula CuO, 3AI2O3,
2P2O5, 9H2O, which may be interpreted as (CuOH)(Al(OH)2)6H5(P04)4.
which is 4(HaP04), in which 6 hydrogen atoms are replaced by 6A1(0H)2
groups and one by the group CuOH.

Turquoise ((CuOH)(Al(OH)2)6H5(P04)4)

Turquoise is apparently a definite compound of the formula indicated
above, which requires 34.12 per cent P2O5, 36.84 per cent AI2O3, 9.57
per cent CuO and 19.47 per cent H2O. Analysis of a crystallized variety
from Lynch, Campbell Co., Virginia, gave:

P205

A1203

Fe203

CuO

H20

Total

34.13

36.50

.21

9.00

20.12

99.96

Most specimens, however, have not as simple a composition as this.
They are probably isomorphous mixtures of unidentified phosphates.

280 DESCRIPTIVE MINERALOGY

The mineral as usually found is apparently an amorphous or cryp-
tocrystalline, translucent or opaque material with a waxy luster and a
sky-blue, green or greenish gray color. Material recently found at
Lynch, Virginia, however, occurs in minute triclinic crystals with an
axial ratio .7910 : 1 : .6051, with 0=87° 02', 0=86° 29', and 7=72° 19'-
Their habit is pyramidal with 00 Poo (100), 00 P 60 (010), oo'P(iTo),
ooP'(no) and Poo (0T1).

The fracture of turquoise is conchoidal. It has a hardness of 5-6
and a specific gravity between 2.61 and 2.89. It is brittle, and has cleav-
ages in two directions. The determined refractive indices of the Vir-
ginia crystals are: a= 1.61, 7= 1.65.

In the closed tube the mineral decrepitates, yields water and turns
black or brown. It is infusible, but it assumes a glassy appearance when
heated before the blowpipe and colors the flame green. When moistened
with HC1 and again heated the flame is tinged with the azure blue of
copper chloride. The mineral reacts for copper and phosphoric acid.
Some specimens dissolve in HC1, but the crystallized material from Vir-
ginia is insoluble until after it is strongly ignited. It partly dissolves
in KOH, with the production of a brown residue of a copper compound.

Occurrence. — Turquoise occurs in thin veins cutting through certain
decomposed volcanic rocks and other rocks in contact with them,
and in grains disseminated through them, in stalactites, globular
masses and crusts. It is probably an alteration product of other com-
pounds.

Localities. — Turquoise is found in narrow veins and irregular masses
in the brecciated portions of acid volcanic rocks and the surrounding clay
slates, near Nishapur, in Persia; in the Megara Valley, Sinai, and near
Samarkand, in Turkestan. In all these places the mineral is of gem
quality and until recently nearly all the gem turquoise came from them.
Within late years gem turquoise has been discovered in the Cerillo Moun-
tains, near Santa F6, New Mexico, where it has been mined in consid-
erable quantity. The locality is the site of an ancient mine which was
worked by the Mexicans. It is also found and mined in the Burro
Mountains, Grant County, in the same State, near Millers, and at other
points in Nevada and near Mineral Park, Mohave County, Arizona,
where also the ancient Mexicans once had mines. At La Jara, Conejos
County, Colorado, old mines have likewise been opened up and are now
yielding gem material.

Uses. — The only use of turquoise is as a gem stone. Though much
of the American mineral is pale or green, some of it is of as fine color as
the Oriental stone. A favorite method of using the stone is in its

PHOSPHATES, ARSENATES AND VANADATES 281

matrix. Small pieces of the rock with its included turquoise are pol-
ished and sold under the name of turquoise matrix.

Production. — The total value of the turquoise and turquoise matrix
produced in the United States during 191 1 was $44,751. This weighed
about 4,363 pounds. In several previous years the production reached
about $150,000, but in 1912 it was valued at only $10,140.

HYDROUS PHOSPHATES AND ARSENATES

HYDRATED NORMAL PHOSPHATES AND ARSENATES

Of the hydrous salts of orthophosphoric and orthoarsenic acids there
are two which are of some importance because they are fairly common,
a third which is utilized in jewelry, and a fourth that is important as an
indicator of the presence of an ore of cobalt. The first two are vivianite
and scorodite, a phosphate and an arsenate of iron, the third is variszite,
an aluminium phosphate, and the fourth is erythrite, an arsenate of
cobalt. A dimorph of variscite, known as lucinite, is rare. All give
water in the closed tube and yield phosphine when fused with magne-
sium and moistened with water.

VIVIANITE GROUP

The only important group of the hydrated orthophosphates and
orthoarsenates is that of which vivianite and erythrite are members.
The general formula of the group is R"3(R'"04)2-8H20 in which R"
= Fe, Co, Ni, Zn and Mg, and R"'=P or As. Although some members
have not been found in measurable crystals, crystals of all have been
made in the laboratory, so that there is little doubt of their isomorphism.
All are monoclinic prismatic with axial ratios of about .75 : 1 : .70 and
P about 740. The group is as follows:

Bobierite, Mg3 (P04)2 • 8H20 Erythrite, C03 (As04)2 • 8H20

Hornesite, Mg3 (As04)2 ■ 8H2O A nnabergite, Nia (As04)2 • 8H20

Vivianite, Fe3 (P04)2 • 8H20 Cabrerite, (Ni • Mg)3 ( As04)2 • 8H20

Symplesite, Fe3(As04)2 • 8H20 Kottigite, Zn3(As04)2 • 8H20

Only vivianite, erythrite and annabergite are described.

Vivianite (Fe3(P04)2-8H20)

Vivianite is a common phosphate of iron. It occurs not only in dis-
tinct crystals but also as bluish green stains on other minerals, and as
an invisible constituent of certain iron ores, thereby diminishing their
value.

282 DESCRIPTIVE MINERALOGY

Its formula indicates the presence of 43 per cent FeO, 28.3 per cent
P2O5 and 28.7 per cent H2O.

Vivianite crystals are monoclinic (prismatic class), usually with a
prismatic habit. Their axial ratio is .7498 : 1 : .7015, and 18=75° 34'.
The principal forms observed on them are 00 P 56 (100), 00 P 00 (010),
oop(no), °oP3(3io), P*(ioi), P(in) and oP(ooi). The angle
110A 110=71° 58'. The mineral also occurs in stellate groups, in glob-
ular, fibrous and earthy masses and as crusts coating other compounds.

Its cleavage is perfect parallel to 00 Pod (010). It is flexible in
thin splinters and sectile. The fresh, pure mineral is colorless and trans-
parent, but specimens usually seen are more or less oxidized and have
a blue or green color. It has a vitreous to pearly luster. Its streak is
white or bluish, changing to indigo-blue or brown on exposure to the air.
Its pleochroism is strong in blue and pale yellow tints. Its hardness
is 1.5-2 and density about 2.6. Its refractive indices for yellow light
are: a= 1. 5818, 0=1.6012, 7=1.6360.

In the closed tube vivianite whitens, exfoliates and yields water at a
low temperature. It fuses easily (2), tingeing the flame bluish green.
Its fusion temperature is n 14°. The fused mass forms a grayish black
magnetic globule. It gives the reaction for iron, and is soluble in HC1.

The mineral is easily recognized by its softness, easy fusibility and
by yielding the test for phosphorus.

Synthesis. — Crystals have been made by heating iron phosphate with
a great excess of sodium phosphate for eight days.

Occurrence and Origin. — Vivianite occurs in veins of copper, tin and
gold ores; disseminated through peat, clay, and limonite; coating the
walls of clefts in feldspars and other minerals of certain igneous rocks,
and partially filling cavities in fossils and partly fossilized bones. It is
usually the result of the decomposition of other minerals.

Localities. — Crystals are found at several points in Cornwall, Eng-
land; at the gold mines at Verespatak, in Transylvania; at Allentown,
Monmouth County, New Jersey, and at many other places. The earthy
variety occurs at Allentown, Mullica Hill and other points in New Jer-
sey, in Stafford County, Virginia, and in swamp deposits at many places.
It is abundant in limonite at Vaudreuil, in Quebec, and in bog iron ores
elsewhere.

Erythrite (Co3(As04)2-8H20)

Erythrite, or cobalt bloom, is not a common mineral, but, because
of its beauty and the fact that it is the usual alteration product of cobalt
ores, it deserves to be described.

PHOSPHATES, ARSENATES AND VANADATES 283

In composition erythrite is 37.5 per cent CoO, 38.4 per cent AS2O5,
and 24.1 per cent H2O. It usually, however, contains some iron, nickel
and calcium.

The mineral is isomorphous with vivianite. Its crystals are mono-
clinic and prismatic or acicular and their axial ratio is .7937 : 1 : .7356
and 0=74° 51'. The prisms are striated vertically. Erythrite occurs
in all the forms in which vivianite is found. Its crystals are usually
bounded by 00 P 00 (010), ooP(no), 00 Poo (100), +P<x>(Toi) and

P(Tn).

The cleavage of erythrite is perfect parallel to 00 P 00 (010). It is

transparent or translucent, has a gray, crimson or peach-red color,

and a white or pink streak. Its hardness varies between 1.5 and 2.5

and its density is 2.95. Its luster is pearly on 00 P 00 (010) and

vitreous on other faces. It is flexible and sectile. Its refractive

indices for yellow light are: a= 1.6263, 0= 1.6614, 7= 1.6986.

In the closed tube erythrite turns blue and yields water at a low tem-
perature. At a high temperature it yields AS2O3, which condenses in
the cold portion of the tube as a dark sublimate. It fuses at 2, and
tinges the flame pale blue. On charcoal it fuses, yields arsenic fumes and
a gray globule which colors the borax bead a deep blue. The mineral
is soluble in HC1, giving rise to a pink solution, which, upon evaporation
to dryness, gives a blue stain.

It is easily recognized by its color and the cobalt reaction. It is
readily distinguished from pink tourma.ine (p. 434), by its hardness
and easy fusibility.

Synthesis. — Crystals have been obtained by carefully mixing to-
gether warm solutions of C0SO4 and HNa2As04 • 7H2O.

Occurrence. — Erythrite occurs in the upper portions of veins con-
taining cobalt minerals, being formed by their weathering.

Localities. — It occurs as scales and crystals at Schneeberg, Saxony,
and as crystals at Modum, Norway. It is found, also, at Lovelock's
Station, Nevada, at several points in California and in large quantities
at Cobalt, Ontario.

Annabergite (Ni3(As04)2-8H20)

Annabergite, or nickel bloom, is isomorphous with erythrite. It
occurs massive, disseminated in tiny grains through certain rocks, as
crusts and stains in globular and earthy masses, and in fibrous crystals,
the axial ratios of which are not known.

The mineral is apple-green in color, and is translucent or opaque.

284 DESCRIPTIVE MINERALOGY

Its streak is light green. Its luster is vitreous; its hardness, 1.5-2.5
and sp. gr. = 3.

Before the blowpipe it melts to a gray globule and gives the arsenic
odor. In the closed glass tube it blackens and yields water. In the
beads it gives the usual reactions for Ni. The mineral dissolves easily
in acids.

Synthesis. — Crystals have been produced by the method employed
in the synthesis of erythrite, using NiSQt, instead of C0SO4.

Occurrence. — It is found as a common alteration product of nickel-
bearing minerals, in the oxidized portions of veins.

Localitus. — Its best known occurrences are in Allemont, Dauphin^;
Annaberg and Schneeberg, Saxony; Cobalt, Ontario, and mines in
Colorado and Nevada.

Variscite (AIPO42H2O)

Variscite is a bright green mineral that has recently come into use as
a gem material. It is apparently an aluminium phosphate with a
theoretical composition as follows: 44.9 per cent P2O5; 32.3 per cent
AI2O3 and 22.8 per cent H2O. A specimen of crystallized material from
Lucin, Utah, gave the following analysis:

P205

A1203

Fe203

Cr03

V2O3

H20

Total

44.73

32-40

.06

.18

•32

22.68

100.37

Recent investigations indicate that the compound A1P04-2H20 is
dimorphous. Both forms are orthorhombic but one, variscite, has the
properties described under this heading. The other, lucinite, is associ-
ated with variscite, near Lucin, Utah. It, however, occurs in crystals
that are octahedral in habit, rather than tabular, and that have an
axial ratio of .8729 : 1 : .9788. In other respects lucinite is very much
like variscite.

An amorphous variety of the same substance is also kaiown. It
occurs as a white, pale brown or pale blue earthy mass with a sp. gr. of
2.135. I* differs from the crystalline varieties in being completely
soluble in warm concentrated H2SO4.

The crystals of variscite are orthorhombic and are bounded by
00 P 60 (010), 00 P(no) and ^P 06 (012), and in a few cases 00 P 60 (100).
Their axial ratio is .8944 : 1 : 1.0919. Nearly all crystals are tabular
parallel to 00 P 60 (010). Twins are common, with ^P 60 (102) the
twinning plane. » Crystals are comparatively rare, the mineral occur-
ring usually in fibrous or finely granular masses and as incrustations.

PHOSPHATES, ARSENATES AND VANADATES 285

Variscite varies in color from a pale to a bright green. It is weakly
pleochroic, has a vitreous luster, a hardness of about 4 and a density of
2.54. Its refractive indices for yellow light are: a= 1.546, 18=1.556,

y= 1-578-

Before the blowpipe the mineral is infusible. It, however, whitens
and colors the flame deep bluish green. It yields water in the closed
tube, and with the loss of its water, it changes color from green to
lavender. The same change in color takes place gradually at temper-
atures between iio°-i6o°. When heated with Co(N03)2, it turns blue
and when fused with magnesium ribbon it gives the test for phosphorus.
It forms a yellowish green glass with borax or microcosmic salt. The
mineral is insoluble in acids before heating.

Variscite resembles in some respects certain varieties of turquoise
and wavelliie (p. 287). It is distinguished from turquoise by the absence
of copper and from wavellite by its insolubility in acids.

Occurrence. — The mineral occurs as a cement in a brecciated, cherty
limestone and a brecciated rhyolite, as nodules in the cherty portions
of the breccias and also as veins traversing these rocks. It is also
found as nests in weathered pegmatites. The crystals occur as coarsely
granular, loosely coherent masses in more compact granular masses.

Localities. — Variscite occurs at Messbach, Saxony; in Montgomery
County, Arkansas; near Lucin, Utah, and at a number of other places
in Tooele and Washington Counties in this State; in Esmeralda County,
Nevada, and in Montgomery County, Arkansas. The colloidal variety
occurs as concretions in slates at Brandberg, near Leoben, Austria.

Uses. — The mixture of variscite and rock is cut, and employed as
sets in necklaces, belt pins, etc., under the names " utahlite " and
" amatrice," but because of the softness of the variscite it cannot be
used with success for all the purposes for which turquoise matrix is
used.

Production. — The production of the material in the United States
during 191 1 was 540 lb., valued at $5,750. In the previous year
5,377 lb. were reported as having been sold for $26,125. In 191 2,
the amount marketed was valued at $8,150.

Skorodite (FeAs(V 2H2O)

Skorodite is more common than vivianite. It occurs in globular
and earthy masses, as incrustations, and in crystals of a green or brown
color. The globular forms are colloidal.

Its formula indicates Fe2C>3 = 34.6 per cent, As203 = 49-8 per cent

286

DESCRIPTIVE MINERALOGY

and HaO= 15.6 per cent. An incrustation on the deposits of the Joseph's
Coat Spring, Yellowstone National Park, consisted of:

As205

Fe203

H20

Si02

SO3

Total

46.48

33 29

15.50

435

.84

100.46

Its crystallization is orthorhombic (bipyramidal class), with a : b : c
= .8658 : 1 : .9541. The crystals, which are commonly bounded by

00 P 56 (lOo), 00 P06 (oio), 00P2(l2o), OOP(HO),

P(iii) and £P(ii2), are either prismatic or octa-
hedral in habit (Fig. 159). The angle 111A1I1

= 65° 20'. Their cleavage is imperfect, parallel to

ooP(no).

The mineral is brittle. It has a vitreous luster,
a leek-green or liver-brown color and a white
streak. It is translucent and has an uneven frac-
ture. Its hardness is 3.5-4 and density about 3.3.

Fig. 150. — Skorodite ^he colloidal phases are somewhat softer than the
Crystal with 00 P 00 , . ... ,

, . ~- crystalline phases.

100 (a); 00 P2, 120 J 11

(d), and P, in (p) *n tne c*osed tube skorodite turns yellow and

yields water. It fuses easily, coloring the flame
bluish. On charcoal it yields white arsenical fumes and gives a black
porous, magnetic button. It is soluble in HC1, forming a brown solution.

It is distinguished from livianite by the arsenic test, and from dufren-
ite by its streak and reaction in the closed tube.

Synthesis. — Skorodite crystals have been made by heating metallic
iron with concentrated arsenic acid solution at i40°-i5o°.

Occurrence. — Skorodite is frequently associated with arsenopyrite,
in the oxidized portions of veins containing iron minerals. It is found
also in a few places as incrustations deposited by hot springs.

Localities. — It occurs in fine crystals at Nerchinsk, Siberia; at
Loelling, in Carinthia; near Edenville, New York; in the Tintic dis-
trict, Utah, and as an incrustation on the siliceous sinter of the geysers
in Yellowstone Park.

HYDRATED BASIC PHOSPHATES AND ARSENATES

The hydrated basic phosphates and arsenates are rather more nu-
merous than the hydrated normal compounds, but most of them are rare.
One, wavellite, however, is a handsome mineral that is fairly common.
Another, pkarmacosiderite, an iron arsenate, is known to occur at a
number of places. The uranite group also belongs here. Its members

PHOSPHATES, ARSENATES AND VANADATES 287

are comparatively rare, but, because of the presence of uranium in them,
they are of considerable interest.

WaveUite ((Al(OH-F)3)(P04)a-5HsO)
Wavellite rarely occurs in crystals. It is usually in acicular aggre-
gates that are either globular or radiating (Fig. 160). The few crystals
that have been seen are orthorhombic (bipyramidal class), with an
axial ratio of .5573 : 1 : .4057.

Its composition varies widely, and frequently a fairly large portion
of the OH is replaced by F, and a portion of the Al by Fe.

The mineral is vitreous in luster and white, green, yellow, brown or
black in color. Its streak is white. It is brittle and translucent, in-

Fig. 160.— Radiate Wavellile on a Rock Surface.

fusible and insoluble in acids. Its hardness is 3.5 and its density 3.41.
Its intermediate refractive index for yellow light is 1.526.

Heated in a dosed glass tube, wavellite yields water, the last traces
of which react acid and often etch the glass. In the blowpipe flame the
mineral swells up and breaks into tiny infusible fragments, at the same
time tingeing the flame green. The mineral is soluble in HC1 and
H2SO4. When heated with H2SO4 many specimens yield hydrofluoric
acid. When heated on charcoal and moistened with Co(N03)2 and
reheated, the mineral turns blue.

Wavellite is distinguished from turquoise, which it sometimes
resembles, by its action in the blowpipe flame, by its inferior hardness
and its manner of occurrence.

Occurrence- — Wavellite occurs as radiating bundles on the walls of

288

DESCRIPTIVE MINERALOGY

cracks in various rocks and as globular masses filling ore veins and the
spaces between the fragments of breccias. It is probably in all cases
the result of weathering.

Localities. — It is found at a great number of places, especially at
Zbirow, in Bohemia; at Minas Geraes, Brazil; at Magnet Cove, Arkan-
sas, and in the slate quarries in York County, Penn.

Pharmacosiderite ((FeOH)3(As04)2 5H2O)

Pharmacosiderite is a hydrated ferric arsenate, the composition of
which is not firmly established. It usually occurs in small isometric
crystals (hextetrahedral class), that are commonly combinations of

00 O 00 (100) and —(in). It is also sometimes found in granular

masses. Its cleavage is parallel to 00 O 00 (100).

The mineral is green, dark brown or yellow. Its streak is a pale
shade of the same color. It has an adamantine luster and is translucent.
Its hardness = 2.5 and sp. gr. = 3. It is sectile and pyroelectric. Its
refractive index, n= 1.676.

Pharmacosiderite reacts like skorodite before the blowpipe and with
reagents.

The mineral occurs in the oxidized portions of ore veins, in Cornwall,
England; at Schneeberg, Saxony; near Schemnitz, Hungary; and in the
Tintic district, Utah.

URANITE GROUP

The uranites are a group of phosphates, arsenates and vanadates
containing uranium in the form of the radical uranyl (UO2) which is
bivalent. The members of the group are either tetragonal, or ortho-
rhombic with a tetragonal habit. They all contain eight molecules of
water of crystallization. Only three members of the group are of
sufficient interest to be discussed here. These are the hydrated cop-
per and calcium uranyl phosphates, torbernite and autunite and the
potassium uranyl vanadate, carnotite.

The entire group so far as its members have been identified is as
follows:

Autunite

Uranospinite

Torbernite

Zeunerite

Uranocircite

Carnotite

Ca(U02)2(P04)2-8H20

Ca(U02)2(As04)2-8H20

Cu(U02)2(P04)2-8H20

Cu(U02)2(As04)2-8H20

Ba(U02)2(P04)2-8H20

(Ca • K2) (U02)2(V04)2 • xHaO

Orthorhombic

Tetragonal

Orthorhombic

PHOSPHATES, ARSENATES AND VANADATES 289

The uranites are of interest because of their content of uranium, an
element which is genetically related to radium.

Autunite (Ca(U02)2(P04)2-8H20)

Autunite occurs in thin tabular crystals with a distinctly tetragonal
habit, and in foliated and micaceous masses.

The percentage composition corresponding to the above formula
is 6.i per cent CaO, 62.7 per cent UO3, 15.5 per cent P2O5 and 15.7 per
cent H2O.

Its crystals are orthorhombic (bipyramidal class), with an axial
ratio, .9875 : 1 : 2.8517, thus possessing interfacial angles that closely
approach those of torbernite. Its crystals are bounded by oP(ooi),
Poo (101), P06 (on), and several less prominent planes. Their cleav-
age is very perfect and the cleavage lamellae are brittle. The luster is
pearly on the base and vitreous on other surfaces.

The mineral is lemon-yellow or sulphur-yellow in color, and its streak
is yellow. It is transparent to translucent. Its hardness is 2-2.5 and
its specific gravity about 3.2. Its refractive indices for yellow light are:

« = i.553> 0=i-575> 7=1.577-

The mineral reacts like torbernite before the blowpipe and with acids,

except that it shows none of the tests for copper. It is recognized by its

color, streak and specific gravity.

Occurrence. — Autunite occurs in pegmatite veins and on the walls
of cracks in rocks near igneous intrusions, especially in association with
other uranium compounds, of which it is a decomposition product.

Localities. — It has been found at Johanngeorgenstadt, Germany;
at Middletown and Branch ville, Conn., in the mica mines of Mitchell
County, North Carolina, and coating cracks in gneiss at Baltimore, Md.

Torbernite (Cu(U02)2(P04)2 -8H20)

Torbernite occurs in small square tables, that may be very thin or
moderately thick, and in foliated and micaceous masses.

The pure mineral contains 61.2 per cent UO3, 8.4 per cent Cu,
15.1 per cent P2O5 and 15.3 per cent H2O, but frequently a part of the P
is replaced by As.

Its crystals are tetragonal (ditetragonal bipyramidal class), with
a : c=i : 2.9361. They are extremely simple, their predominating
forms being oP(ooi) and Poo (101). Less prominent are 00 Poo (100),
2Poo(2oi) and ooP(no). Their cleavage is perfect parallel to oP.
The cleavage lamellae may be almost as thin as those of the micas
but they are brittle.

290 DESCRIPTIVE MINERALOGY

The mineral is bright green in emerald, grass or apple shades, has a
lighter green streak, is translucent or transparent, and has a hardness
of 2.25 and a specific gravity of about 3.5. Its luster is pearly on the
basal plane, but nearly vitreous on other surfaces. It is strongly pleo-
chroic in green and blue.

Torbernite gives reactions for Cu and P and yields water in the
closed tube. The bead reactions for uranium are masked by those of
copper. The mineral is soluble in HNO3.

The mineral is easily recognized by its color and other physical
properties.

Occurrence. — Torbernite is occasionally found as a coating on the
walls of crevices in rocks. It occurs in Cornwall, England; at Schee-
berg, Saxony; at Joachimsthal, Bohemia, and at most places where other
uranium minerals exist. It is probably in all cases a weathering product.

Carnotite ((Ca-K2)(U02)2(V04)2-xH20)

Carnotite, like the other uranites described, is extremely complex
in composition. It may be an impure potassium uranyl vanadate, or a
mixture of several vanadates in which the potassium uranyl compound
is the most prominent. The formula given above indicates its com-
position as well as any simple formula that has been proposed. A
specimen from La Sal Creek, Colorado, shows the mineral to be essen-
tially as follows:

V2O5 U03 CaO BaO K20 H20 at 105 ° H20 above 105 °
18.05 54 -00 I-^° J-86 5 46 3.16 2.21

though there are present in the specimen analyzed, or in other specimens
from the same locality, also As203, P2Os, Si02, Ti02, C02, SO3, M0O3,
Cr203, Fe203, A1203, PbO, CuO, SrO, MgO, Li20 and Na20, and there
are reported in them also small quantities of radium. Radiographs
taken with the aid of carnotite have been published, which are almost
as clear as those taken with pitchblende. The complete analysis of a
specimen from the Copper Prince Claim, Montrose Co., Colo., gave:

v2o5

As205

P205

UO3

M0O3

Fe203

Al20s PbO

18.35

•33

5225

•23

1.77

1.08 .25

CuO

CaO

BaO

K20

H20-

H20+

Ins. Total

.20

2.85

.72

6-73

2-59

3.06

8.34 99.84

Also Ti02 = .io; C02 = 33; S03 = .i2; Cr03 = tr.; MgO=.2o and
Na20=.o9.

PHOSPHATES, ARSENATES AND VANADATES 291

The mineral has been found only in tiny crystalline grains, so that its
physical properties are not well known. It is bright yellow in color, and
is completely soluble in HNO3. If to the nitric acid solution hydro-
gen peroxide be added a brown color will appear. Or if the solution
is filtered, made alkaline by ammonia and through it is passed H2S, a
garnet color will develop. If the mineral be moistened by a drop of
concentrated HC1, a rich brown color will result. The addition of a drop
or two of water will change the color to light green or make it disappear.

Occurrence. — Carnotite occurs as a yellow crystalline powder, some
of which seems to consist of minute crystals with an hexagonal habit,
in the interstices between the grains in sandstones and conglomer-
ates, as nodules or lumps in these rocks, and as coatings on the walls
of cracks in pebbles in the conglomerates and on pieces of silicified
wood embedded in the sandstones. It is limited to very shallow
depths and is apparently a deposit from ground water.

Localities. — Its principal known occurrences are in Montrose, San
Miguel, Mesa and Dolores Counties in southwestern Colorado, especially
in Paradox Valley, and in adjoining portions of New Mexico and Utah,
and in Rio Blanco and Routt Counties in the northwestern portion of
Colorado. At all these places there are large quantities of the impreg-
nated rock but it contains on the average only about 1.5 per cent to
2 per cent of U3O8. The mineral has also been described from Mt.
Pisgah, Mauch Chunk, Pennsylvania, and from Radium Hill, South
Australia.

Uses. — The mineral is one of the main sources of radium and uranium
and is one of the principal sources of vanadium. Although it contains a
notable quantity of uranium, carnotite has little value except as an ore
of radium and vanadium, because of the few uses to which uranium is
put. This metal is used to some extent in making steel alloys and in the
manufacture of iridescent glazes and glass. Its compounds are used in
certain chemical determinations, as medicines, in photography, as por-
celain paint, and as a dye in calico printing. The uses of vanadium have
been referred to on p. 273.

The principal value of carnotite depends upon its content of radium,
which in the form of the chloride is valued at about $40,000 per gram
or $1,500,000 per oz. The importance of radium as a therapeutic agent
has not been established; but that its use is wonderfully helpful in many
diseases is beyond question. Without doubt in the near future carno-
tite will become the principal source of radium in the world. Practically
the only other source is the pitchblende (p. 297), of Gilpin, Colorado,
Cornwall, England and Joachimsthal, Austria,

292 DESCRIPTIVE MINERALOGY

Production. — Carnotite has been mined in San Miguel and Montrose
Counties, Colorado, and at several points in eastern Utah, but mainly
for the vanadium it contains. At present it is being utilized as a source
of radium. From Colorado 8,400 tons of vanadium ore, with a value
of $302,000, were shipped in 19 11 and from New Mexico and Utah about
70 tons, valued at $3,500. Some of this, however, was vanadinite.
Most of it was exported and used as a source of vanadium. However,
the uranium content of the carnotite mined was about 1.1 tons of the
metal. During 191 2 ore containing 26 tons of uranium oxide and 6.7
grams of radium was produced. This would have yielded n.43 grams
of radium bromide, valued at $52,800. The present price of standard
carnotite carrying at least 2 per cent U3O8 and 5 per cent V2O5, is at the
rate of $1.25 per lb. for the former and thirty cents for the latter. In
1914 the selling price of 4,294 tons of carnotite ore containing 87 tons
of U3O8 was $103 per ton. At the present time nothing is paid for the
radium content of the ore, though this is its most valuable component.
One ton of ore containing 1 per cent of U3O8 carries 2.566 milligrams of
radium. The imports of uranium compounds during 191 2 were valued

at $14,357-

HYDRATED ACID PHOSPHATES AND ARSENATES

A number of hydrated acid phosphates and arsenates are known to
constitute an isomorphous group, but only a few of them occur as
minerals. Brushiie is an acid calcium phosphate and pharmacolite is
the corresponding arsenate. Both crystallize in the monoclinic system
(prismatic class). Neither is common.

Pharmacolite (HCaAs04 • 2H2O) occurs principally in silky fibers, in
botryoidal and stalactic masses and rarely in crystals with an axial
ratio .6236 : 1 : .3548 and #=83° 13'. Their cleavage is perfect par-
allel to 00 Poo (010). The mineral is white or gray, tinged with red.
Its streak is white. It is translucent or opaque. Its luster is vitreous,
except on 00 P 00 (dio) where it is slightly pearly. Thin laminae are
flexible. Its hardness is 2-2.5 and density 2.7. Its refractive indices
for yellow light are: a= 1.5825, 18=1.5891, 7=1.5937.

Before the blowpipe pharmacolite swells up and melts to a white
enamel. The mineral gives the usual reactions for As, H2O and Ca. It
usually occurs in the weathered zone of arsenical ores of Fe, Ag and Co,
at Andreasberg, Harz; Joachimsthal, Bohemia, and elsewhere.

CHAPTER XV

THE COLUMBATES, TANTALATES AND URANATES

The rare metals, columbium and tantalum, exist in a few silicates,
but their principal occurrences are as columbates and tantalates which
are salts of columbium and tantalum acids, analogous to the various
acids of sulphur. The commonest compounds are salts of the meta-
acids IfeQ^Oe and H2Ta20e, the relations of which, to the normal acids,
are indicated by the equation 2H3CbC>4— 2H20=H2Cb20e. Other im-
portant minerals are derivatives of the pyroacids corresponding to
H4Ct>207, or 2H3CDO4— H2O. The best known ortho salt is ferguson-
ite, YCb04, but it is rare.

All the columbates yield a blue solution when partially decomposed
in H2SO4 and boiled with HC1 and metallic tin. The tantalates when
fused with KHSO4 and treated with dilute HC1 give a yellow solution
and a heavy white precipitate, which, on treatment with metallic zinc
or tin, assumes a deep blue color. When diluted with water the blue
color of the tantalate solution disappears, while that of the columbate
solution remains.

The uranates are salts of uranic acid, H2UO4. The only mineral
known that may be a uranate is uraninite, and the composition of this
is doubtful.

Columbite ((Fe-Mn)Nb206) and Tantalite ((FeMn)Ta206)

These two minerals are isomorphous mixtures of iron and manganese
columbates and tantalates. The name columbite is applied to the mix-
ture that is composed mainly of the columbates, and tantalite to that
which is principally a mixture of tantalates. When the tantalite is
composed almost exclusively of the manganese molecule, it is known as
manganotantalitei Tin and tungsten are frequently found in both min-
erals.

Their crystals are orthorhombic, with a : b : £=.8285 : 1 : .8898 for
the nearly pure columbium compound, and .8304 : 1 : .8732 for the
nearly pure tantalum compound. Both form short prismatic crystals
containing many faces, among the most prominent being the three
pinacoids; various prisms, notably 00 P(no), 00 P^^o) and 00 P6(i6o),

293

294

DESCRIPTIVE MINERALOGY

and the domes 2P &> {201) and JP 06 (012) (Fig. 161). The most promi-
nent pyramids are P(in) and P3(i33)- Twins are not uncommon,
with 2P00 (201) the twinning plane. The angle 110A1T0 for colum-
bite=79° 17'.

Both minerals are usually opaque, black and lustrous, and occasion-
ally iridescent, though, in some instances, they are translucent and
brown. Their streak is dark red or black. Their cleavage is distinct
parallel to 00 P 66 (100), fracture uneven or conchoidal, their hardness
6 and their specific gravity
between 5.3 and 7.3, in-
creasing with the propor-
tion of the tantalum mole-
cules present. They are
both infusible before the
blowpipe. Some specimens
exhibit weak radioactivity.
When columbite is de-
composed by fusion with
KOH and dissolved in HC1
and H2SO4, the solution
1 turns blue on the addition
of metallic zinc. The min-
eral is also partially decom-
posed when evaporated to
dryness with H2SO4, forming a white compound that changes to yellow.
When this residue is boiled with HCI and metallic zinc a blue solution
results. The mineral also gives reactions for iron and manganese.

Tantalite is decomposed upon fusion with KHSO4 in a platinum
spoon, or on foil. This when heated with dilute HCI yields a yellow
solution and a heavy white powder. Upon addition of metallic zinc, a
blue color results and this disappears on dilution with water. In the
microcosmic salt bead tantalite dissolves slowly, giving reactions for iron
and manganese. When treated with tin on charcoal the bead turns
green.

The two minerals may easily be confused with black tourmaline
(p. 434), ilmenite (p. 462) and wolframite. From tourmaline, they are
distinguished by crystallization, high specific gravity and luster; from
wolframite by their less perfect cleavage and by the reaction with
aqua regia (see p. 259); from ilmenite by the test for titanium,

Occurrence, Origin and Localities. — Both minerals occur in veins of
coarse granite and probably have a pneumatolytic origin.

Fits.

1 .—Columbite Crystals with «P«, 1
«=P«,o.o (6); «.p, iio(m); "Pi.?
°pl . 73° W); »P3, 130 is); iP«=, 1
P, in (o) and P3, 133 («)■

COLUMBATES, TANTALATES AND URANATES 295

Columbite is found in granite veins at Bodenmais, Bavaria; Tam-
mela, in Finland; near Limoges, France, with tantalite; near Miask,
in the Ilmen Mountains, Russia, with samarskite; and at Ivigtut, in
Greenland. In the United States it is found at Standish and Stone-
ham, in Maine; at Acworth, in New Hampshire; at Haddam, in Con-
necticut; at Amelia Court House, Virginia; with samarskite in the mica
mines in Mitchell County, North Carolina; in the Black Hills, South
Dakota, and at a number of other points in New England and the Far
West.

Tantalite is found at many of the localities for columbite and also
at several other places in Finland; near Falun, in Sweden; in Yancy
County, North Carolina, and in Coosa County, Alabama.

Uses. — At the present time columbium and its compounds have no
commercial uses. Tantalum, however, is employed in the manufacture
of filaments for certain types of incandescent lamps. Since, however,
about 20,000 filaments may be made from a single pound of the metal the
market for tantalum ores is very limited.

Samarskite and Yttrotantalite

These two minerals may be regarded as isomorphous mixtures of
salts of pyrocolumbic and pyrotantalic acids,, in which the bases are
yttrium, iron, calcium and uranyl.

Samarskite, according to this view, is approximately

Y2(Ca-Fe.U02)3(Nb207)3

and yttrotantalite the corresponding tantalate. Yttrium and iron are
the principal bases, but there are also often present erbium, cerium,
tungsten and tin.

Analyses made by Rammelsberg and quoted by Dana give some idea
of the complexity of the compounds:

Density

Ta205 Nb205 W03 Sn02 Ti02* Y2O3

Er203

I- 5-4*5

46.25 12.32 2.36 1. 12 10.52

6.71

n. 5.839

14.36 41.07 .16 .56 6.10

10.80

in. 5.672

55 34 .22 1.08 8.80

382

Ce203t

U02 FeO CaO H2O

Total

I. 2.22

1. 61 3.80 5.73 6.31

98-95

II. 2.37

10.90 14.61 ....

100.93

ni. 433

11.94 1430

99 83

1. From Itterby, Sweden. II. From North Carolina. IH. From Miask

. Russia.

Including Si02. t Including Di303 and LajOj.

296 DESCRIPTIVE MINERALOGY

The first of these three minerals has been called yttrotantalite and
the other two samarskite. If the first is weathered, as seems probable
from the presence of over six per cent of water, the three may constitute
members of an isomorphous series with the third representing the nearly
pure columbate (samarskite), the first a compound in which the tantalate
molecule is in excess (yttrotantalite), and the second an intermediate
compound which contains both the tantalum and columbium molecules,
with the latter predominating.

With more accurate analyses the great complexity of these compounds
becomes even more apparent. Hillebrand has given the following report
of his analysis of a samarskite from Devil's Head Mountain, near Pike's
Peak, Colorado, which shows the futility of attempting to represent its
composition by a chemical formula:

Pitch-black Black Weathered

Variety Variety Variety

Tajd 27.03 28.II 19-34

Cb2Oft 27.77 26.16 27.56

WOi 2.25 2.08 5.51

SnO« 95 1.09 .82

ZrOj 2 . 29 2 . 60 3 . 10*

UO» 4.02 4.22

UOj ... 6 . 20

ThO* 3.64 3.60 3.19

Ce808 54 .49 .41

(La,Di)208 1.80 2.12 1.44

Erj02 10.71 10.70 9.82

Y2O3 6.41 5.96 5.64

Fe*0, 8.77 8.72 8.90

FeO 32 .35 .39t

MnO 78 .75 1

ZnO 05 .07 I'77

PbO 72 .80 1.07

CaO 27 .33 1. 61

MgO ... .11

K*° 17 .13 \ ,

(Na,Li),0 24 .17 /'3

H2O 1.58 1.30 3.94

F ? ? ?

Total 100.31 99-75 100.18

Sp.gr 6.18 6.12 5.45

♦With Ti02. t Or 0.74 UO*.

COLUMBATES, TANTALATES AND UEANATES 297

Both samarskite and yttrotantalite are orthorhombic, with an axial
ratio for samarskite of .5456 : 1 : .5178, and for yttrotantalite, .5411 :
1 : 1. 1330. They, however, more commonly occur massive and in
flattened grains embedded in rocks. Their crystals are prismatic in
the direction of the c or the b axis. Their most prominent forms are
00 P* (100), 00 P 66 (010) and P 66(101) (Fig. 162). Less prominent
but fairly common are *>P2(i2o), ooP(no), P(iu) and 3Pf(23i).
The angle 110A1T0 for samarskite is 570 14'
and for yttrotantalite 560 50'.

The cleavage of both minerals is indistinct
parallel to 00 P 06 (010). Their fracture is
conchoidal. Both are brittle. The hardness of
samarskite is 5-6, its density about 5.7, its
luster vitreous, its color velvety black and its
streak reddish brown. Yttrotantalite is a little
softer (5-5.5). Its specific gravity is 5.5-5.9,
its luster submetallic to vitreous, its color black, Fig. 162.— Samarskite Crys-
brown, or yellow, and its streak gray to color- **! with °° P * , 100 (a);
less. Samarskite is opaque and yttrotantalite
opaque or translucent.

The reactions of the minerals vary with
their composition. They always yield the
blue solution test for tantalum or columbium, and most specimens react
for Mn, Fe, Ti and U. The reaction for uranium is an emerald green
bead with microcosmic salt in both reducing and oxidizing flame.

They are distinguished from columbite and tantalite by the form of
their crystals.

Occurrence. — The two minerals, like columbite and tantalite, are
found principally in pegmatite veins and in many of the same localities.
Yttrotantalite occurs mainly at Ytterby and near Falun, in Sweden, and
samarskite, near Miask in the Ilmen Mountains, Russia. In the United
States the last-named mineral is sometimes found in large masses in the
mica pegmatites of Mitchell County, North Carolina.

Uses. — Neither mineral is at present of any commercial value. They
are, however, extremely interesting as the source of many of the rare
elements, and, especially, as a possible source of radium and closely
related substances.

Uraninite

Uraninite, or pitchblende, like the other compounds containing the
element uranium, is of doubtful composition. It contains so many

00 Poo, 010 (b); 00 p,
no (m); 00 P2, 120 (A);
P«, 101 («); P,ni (p);
3Pf, 231 (»).

298 DESCRIPTIVE MINERALOGY

different components that a correct conception of its character is almost
impossible to grasp. The mineral is particularly interesting because it
always contains a trace of radium, of which it is an important com-
mercial source at the present time.

Analyses of crystallized material (I) from Branchville, Conn.,
and from Annerod (II), Norway, gave the following results:

U03 U02 TI1O2 PbO FejjOa CaO H20 He Insol.

I. 21.54 64.72 6.93 4.34 .28 .22 .67 Und. .14

II.30.63 46.13 6.00 9.04 .25 .37 .74 .17 442

with small quantities also of Z1O2, CeCfe, La203, Di203, Y2O3, Er2C>3,
MnO, Alkalies, Si02 and P2O5. These analyses are interpreted as indi-
cating that the mineral is a uranium salt of uranic acid, UQ2(OH)2, or

H2UO4, thus U -^>n , or U3O8, in which Pb replaces the U in

\)>U02
part, and TI1O2 the UO2. Radium is found in most specimens and
helium in nearly all.

Several varieties are recognized, the distinctions being based largely
upon chemical differences.

Broggerite has UO3 to other bases as 1 : 1.

Cleveite and nhenile contain 9 per cent to 10 per cent of the yttria
earths.

Pitchblende is possibly an amorphous uraninite containing a very
little thoria and much water. Its specific gravity is often as low as 6.5,
due probably to partial alteration.

Uraninite crystallizes in the isometric system in octahedrons, and in
combinations of O(in), 00 O(no), and 00 O 00 (100). Crystals are rare,
however, the material usually occurring in crystalline masses and in
botyroidal groups.

The mineral is gray, brown or black and opaque. Its streak is
brownish black, gray or olive green. Its luster is pitch-like or dull. Its
fracture is uneven or conchoidal. It is brittle, its hardness is 5.5 and
density 9-9.7. Like the other uranium minerals it is radioactive.

Before the blowpipe uraninite is infusible. Some specimens color
the flame green with copper. With borax it gives a yellow bead in the
oxidizing flame, turning green in the reducing flame. All specimens give
reactions for lead and many for sulphur and arsenic. The mineral is
soluble in nitric and sulphuric acids, with slight evolutions of helium,

COLUMBATES, TANTALATES AND URANATES 299

the ease of solubility increasing with the increase in the proportion of
rare earths present.

Uraninite is distinguished from wolframite, samarskite, columbite and
tantalite, by lack of cleavage, greater specific gravity, and differences in
crystallization. From all but samarskite it is also distinguished by the
reactions for uranium and, in the case of most specimens, by the reac-
tion for lead. It is especially characterized by its pitch-black luster.

Occurrence and Localities, — Uraninite occurs in pegmatites and in
veins associated with silver, lead, copper and other ores. It is found in
the ore veins in Saxony, Bohemia, and in pegmatites near Moss, Arendal
and other points in Norway.

In the United States it occurs in pegmatites at Middletown and
Branchville, in Connecticut; at the Mitchell County mica mines,
North Carolina; and at Barringer Hill, Llano County, Texas. It is
also found in large quantity near Central City, Gilpin County, Colorado,
where it is associated with gold, galena, tetrahedrite, chalcopyrite and
other ore minerals.

Production. — Uraninite has been mined in small quantity in Colo-
rado, and at Barringer Hill, both as a source of uranium and as a
source of radium. In Cornwall, England, and at Joachimsthal,
Austria, it is mined as a source of radium. (See also p. 292.)

CHAPTER XVI

THE SILICATES

The silicates are salts of various silicon acids, only a few of which
are known uncombined with bases. The silicates include the commonest
minerals and those that occur in largest quantity. They make up the
greater portion of the earth's crust, forming most of the igneous rocks
and a large portion of vein fillings. In number, the silicates exceed all
other mineral compounds, but because of their stability they are of very
little economic importance. A few are used as the sources of valuable
substances, and their aggregates, the silicious rocks, are utilized as
building stones, but, on the whole, they are of little commercial value.
Since, however, they occur in good crystals and their material is trans-
parent in thin sections so that it can easily be studied by optical methods,
they are of great scientific importance. Much of the progress made in
crystallography has been accomplished through the study of these com-
pounds.

Although the salts of the silicic acids are very numerous and most of
them are very stable toward the ordinary reagents of the laboratory,
the acids from which they are derived are only imperfectly known.
The only one that has been prepared in the pure state is the compound
H2Si03. This occurs as a gelatinous (colloidal) white substance which
rapidly loses water upon drying and probably breaks up into a number
of other compounds which are also acids, containing, however, a larger
proportion of silicon in the molecule than that in the original compound.
When the tetrafluoride, or the tetrachloride, of silicon is decomposed by
water, the principal product is the acid referred to above, but in addition
to this there is probably formed also the compound I^SiCU or Si(OH)4,
which is the ortho acid. Some silicates are salts of these acids. Others
are salts of the acids containing a larger proportion of silicon. In most
cases, however, these acids may be regarded as belonging to a series in
which the members are related to one another in the same manner as
are normal sulphuric, common sulphuric and pyrosulphuric acids. Nor-
mal sulphuric acid is HeSOe. By abstraction of 2H2O the compound
H2SO4, or ordinary sulphuric acid, results. If from two molecules of
H2SO4, one molecule of HoO is abstracted, H2S2O7, or pyrosulphuric
acid, is left. In the same manner all of the silicic acids may be regarded

300

SILICATES 301

as being derived from normal silicic acid Si(OH)4 or H4Si04 by the ab-
straction of water, thus:

Orthosilicic acid is RtSiC^,
Metasilicic acid is H4Si04 — H2O or IfcSiOa,
Diorthosilicic acid is 2H4Si()4— H2O or HeSi207,
Dimetasilicic acid is 2H2Si03— H2O or H2S12O5,
Trimetasilicic acid is 3H2Si03— H2O or HiS^Og.

The compounds containing more than one silicon atom in the molecule
are known as polysilicates. The salts of metasilicic acid are meta-
silicates.

Many attempts have been made to discover the chemical structure
of the comparatively simple silicates and several proposals have been
offered to explain the great differences often observed in the properties
of silicates with the same empirical formula; but no explanation of these
differences has thus far proved satisfactory. The silicates are so very
stable under laboratory conditions, and, when they are decomposed,
their decomposition products are so difficult to study, that it has been
impossible to determine their molecular volumes or to understand their
substitution products. We are thus driven to ascribe many of the
anomalies in their composition to solid solutions, to absorption phenom-
ena, and to the isomorphous mixing of compounds, some of which do
not exist independently.

There are many silicates, moreover, which cannot be assigned to any
of the simple acids mentioned above, but which probably must be
regarded as salts of very much more complex acids. Others are pos-
sible salts of aluminosilicic acids in which aluminium functions in the
acid portions. Thus, albite is usually regarded as a trisilicate, NaAlSiaOs,
and anorthite as an orthosilicate, CaAl2(Si04)2. But the two substances
are completely isomorphous, and for this reason it is thought that they
must be salts of the same acid. If we assume an aluminosilicic acid of
the formula HsA^Os, albite may be written (NaSi)AlSi20s, and anor-
thite (CaAl)AlSi208. The two minerals thus become salts of the same
acid and their complete isomorphism is explained. The relations that
exist among many silicates might be better understood on the assump-
tion that they are salts of complex silicic and of aluminosilicic acids
than on the assumption that they are salts of simpler acids, as is now the
case. But, since it has been impossible to isolate the acids and study
them we are not certain as to their character. It is, therefore, believed
best to represent most silicates as salts of the simplest acids possible,
consistent with their empirical compositions as determined by analyses.

302 DESCRIPTIVE MINERALOGY

As in the case of salts of other acids there are silicates that contain
hydrogen and oxygen in such relations to their other components that
when heated they yield water. In some cases this water is driven off at
a comparatively low temperature and the residue of the compound re-
mains unchanged. A compound of this kind is usually called a hydrate
or the compound is said to contain water of crystallization. In other
cases a high temperature is necessary to drive off water, and the com-
pound breaks up into simpler ones. In these instances the water is
said to be combined. The compound is usually basic.

In the descriptions of the silicates the order in which the minerals are
discussed is that of increasing acidity, i.e., increasing proportion of the
SiCfe group present in the molecule. This order, however, is not fol-
lowed rigorously. The members of well defined groups of closely related
minerals are discussed together even if their acidity varies widely.
Nearly all the silicates are transparent or translucent and all are elec-
trical insulators.

THE ANHYDROUS ORTHOSILICATES

NORMAL ORTHOSILICATES— R^SiC^
OLIVINE GROUP (R"flSi04). R" - Mg, Fe, Mn, Zn

The members of the olivine group are normal silicates of the metals
Mg, Fe, Mn and Zn. They constitute an isomorphous series crystalliz-
ing in the holohedral division of the orthorhombic system (rhombic bi-
pyramidal class). The most common member is the magnesium-iron
compound (Mg-Fe)2Si04, olivine, or chrysot.le, from which the group
gets its name. The members with the simplest composition are for-
sterile (Mg2Si04), fayalitc (Fe2Si04) and tephroite (Mn2Si04). The
others are isomorphous mixtures of these, with the exception of three
rare minerals, of which one, monticeUUe, is a calcium magnesium silicate,
another, titanolivine, contains Ti in place of a part of the Si, and the
other, roepperite, contains some Zn2Si04. Most of them are formed
by crystallization from molten magmas.

Crystals of all the members of the group are prismatic and all have
nearly the same habit. They are often flattened parallel to one of the
pinacoids, oo P 06 (010) or 00 P 60 (100). The axial ratios of the com-
moner members are as follows:

Forsterite a : b : £=.4666 : 1 : .5868. The angle no A i7o=5o° 2'

Olivine =.4658 : 1 : .5865. The angle no A 11*0=49 ° 57'

Tephroite =.4600 : 1 : .5939. The angle no A 1^0=49° 24'

Fayalite =4584 : 1 : .5793. The angle noAiio=49° *5'

ANHYDROUS ORTHOSILICATES

303

Crystals of olivine are usually combinations of some or all of the following
forms: oo P 66 (ioo), oo P oo (oio),
oP(ooi), ooP(no), ooP2(i2o),

Poo (oil), 2Poo(o2l), Pob(lOl),

P(iii) and 2P2(i2i) (Fig. 163).
The crystals of fayalite are usually
more tabular than those of olivine,
but forsterite and tephroite crystals
have nearly the same forms. The
cleavage of all is distinct parallel
to 00 P60 (010), less distinct parallel
to 00 P 66 (100) in olivine, and par-
allel to oP(ooi) in fayalite.

The compositions of the pure Mg,
Mn, and Fe molecules are:

Fig. 163. — Olivine Crystals with
00 P, no (m); 00 Poo, 010 (6);
oP, 001 (c); 2P 00 , 021 (k); oo P2 ,
120 (*),P 00 , xoi (d) and P, in (e).

MgO.
MnO.
FeO.
Si02.

Mg2Si04

- 57-x

42.9

Mn2Si04
70.25

29 -75

Fe2Si04

70.6
29.4

All natural crystals, however, contain some of all the metals indicated
and, in addition, many specimens contain also a determinable quantity
of CaO and traces of other elements.

Forsterite, Olivine and Fayalite (Mg2Si04 - (Mg • Fe)2Si04 - Fe2Si04)

The composition of olivine naturally depends upon the proportion
of the forsterite and fayalite molecules present in it. When the propor-
tion of FeO exceeds 24 per cent, the variety is known as hyalosiderite.
A few typical analyses are quoted below:

MgO

FeO

CaO

AI2O3

Si02

Total

Sp. Gr.

I. 51.64

5-oi

1.08

42.30 .

100.45

3.261

II. 50.27

8.54

• a • ■

• • •

41.19

100.00

III. 48.12

n. 18

.12

a • •

40.39

99.81

3-294

IV. 39.68

22.54

a • ■ •

a a •

37.17

99 39

•

I. From masses enclosed in Vesuvian lava.
II. Concretion in basalt near Sasbach, Kaisers tuhl.

III. Grains from glacial debris, Jan Mayen, Greenland.

IV. Grains from coarse-grained rock, near Montreal, Canada.

I. 6319

1.6519

I . 6698

1 . 6674

1 . 6862

1 • 70S3

1.8236

1 . 8642

1.8736

304 DESCRIPTIVE MINERALOGY

In addition, there are often also present small quantities of Ni, Mn,
and Ti.

Forsterite, olivine and fayalite are usually yellow or green in color
and have a vitreous luster. Forsterite is sometimes white and olivine
often brown. All three minerals become brown or black on exposure
to the air. All are transparent or translucent. Their streak is colorless
or yellow. The fracture of olivine is conchoidal. In the other two
minerals it is uneven. Their hardness, density and refractive indices
for yellow light are as follows:

Hardness Sp. Gr.

Forsterite 6-7 3 . 21-3 . 33

Olivine 6.5-7 3-27"3-37

Fayalite 6.5 4.00-4.14

Before the blowpipe most olivines and forsterites whiten but are in-
fusible. Their fusion temperatures are between 13000 and 14500,
decreasing with increase in iron. Fayalite and varieties of olivine rich
in iron fuse to a black magnetic globule. All three minerals are decom-
posed by hydrochloric and sulphuric acids with the separation of gelat-
inous silica; the iron-rich varieties are decomposed more easily than
those poor in iron.

The minerals are characterized by their color and solubility in
acids.

Both fayalite and olivine alter on exposure to the air, the former
changing to an opaque mixture of Fe203 and Si02, or to the fibrous
mineral anthophyllite ((Mg*Fe)Si03), and olivine to a mixture of
iron oxides and fibrous or scaly gray or green serpentine (H4Mg3Si20Q).
In other cases, under metamorphic conditions, the alteration is to a
red lamellar mineral (iddingsite) which may be a form of serpentine,
or to magnesite, or to the silicate, talc. Other kinds of alteration of
this mineral have also been noted but those described are the most
common.

Syntheses. — The members of the olivine series have been produced
by fusing together the proper constituents in the presence of magnesium
and other chlorides. They are, moreover, present in many furnace
slags where they have been made in the process of ore smelting.

Occurrence. — Olivine occurs as an original constituent of basic igneous
rocks and as a metamorphic product in dolomitic limestones. It is
found also in the form of rounded grains in some meteoric irons. Fayalite
occurs in acid igneous rocks, especially where affected by pneumatoiytic

ANHYDROUS ORTHOSILICATES 305

action, and forsterite in dolomitic rocks when they have been meta-
morphosed by the action of igneous rocks.

Localities. — Members of the olivine group occur in the basaltic lavas
of many volcanoes — as those of the Sandwich Islands; in the limestone
inclusions in the lava of Mt. Somma, near Naples; in various basic
rocks in Vermont and New Hampshire and at Webster, N. C. At the
latter place granular aggregates of almost pure olivine constitute great
rock masses known as dunite,

Fayalite is found in the rhyolites of Mexico, the Yellowstone Park
and elsewhere, and in coarse granite at Rockport, Mass., and in the
Mourne Mountains, Ireland.

Forsterite occurs in limestone enclosures in the lava of Mt. Somma
and at limestone contacts with igneous rocks at Bolton, Roxbury, and
Littleton, Mass., and elsewhere.

Uses and Production. — The only member of the group that is of any
economic importance is a pale yellowish green transparent olivine, which
is used as jewelry under the name of " peridot." Gem material is found
at Fort Defiance and Rice, in Arizona, scattered loose in the soil. The
little grains came from a basic volcanic rock. The amount produced in
the United States during 191 2 was valued at about $8,100.

Tephroite (Mn2Si04)

Although tephroite is regarded as the manganese silicate it nearly
always contains some of the forsterite molecule.

Analyses of brown (I), and red (II), varieties from Sterling Hill
gave:

MnO FeO MgO CaO ZnO Loss Si02 Total

I. 52.32 1.52 7.73 1.60 5.93 .28 30.55 99.93

II.47.62 .23 14.03 .54 4.77 .35 31.73 99.27

The mineral is gray, brown or rose-colored and transparent or
translucent. Its streak is nearly colorless. It is rarely found in crys-
tals. Its hardness is about 6 and its density 4.08. It is strongly
pleochroic in reddish, brownish red and greenish blue tints. Its inter-
mediate refractive index for yellow light = about 1.80.

It is fusible with difficulty (fusing temperature =1200°), and is sol-
uble in HC1 with separation of gelatinous silica. It is distinguishable
from other like-appearing minerals by its difficult fusibility and its
reaction with HC1.

Syntheses. — Crystals of the mineral have been made by fusing to-
gether Si02 and Mn02 in the proportion of 1 : 2, and by long-continued

306 DESCRIPTIVE MINERALOGY

heating of MnCk and Si02 in an atmosphere of moist hydrogen or carbon
dioxide.

Localities. — Tephroite occurs at Mine Hill and Sterling Hill, near
Franklin, N. J., where it is associated with franklinite, zincite and
troostite. It is found also at Pajsberg in Sweden with other man-
ganese minerals and magnetite, and at Langban, in Wermland,
Sweden.

Uses. — The mineral is of little commercial value. It is separated
with other manganese minerals from the zinc ore of Franklin, N. J., and
is smelted with these in the production of spiegeleisen.

WILLEMITE GROUP (R,"SiO*). R"=Zn, Mn.

The willemite group comprises the two minerals -willemite (Zn2Si04)
and troostite ((Zn-Mn^SiCU), of which the latter is rare. Willemite
occurs in small quantity only, but troostite is an important source of
zinc at the Franklin locality in New Jersey. Both minerals are found in
crystals.

Willemite and troostite crystallize in the rhombohedral hemihedral
division of the hexagonal system (ditrigonal scalenohedral class), with
the axial ratios

Willemite a : c=i : 0.6698
Troostite = 1 : 0.6698

Willemite and Troostite (Zn2Si04- (Zn Mn)2Si04)

Willemite and troostite occur massive, in grains, and in simple crys-
tals.

The theoretical composition of willemite is Si02= 27.04 and ZnO
= 72.96, but nearly all natural crystals contain traces of other elements.
When a noticeable quantity of manganese is present, the compound
is troostite. Several analyses are quoted below:

SiO*

Willemite from Stolberg, Germany 26 . 00

Willemite from Greenland 27 . 86

White troostite from Franklin, N. J.. . . 27. 20
Dark red troostite from Franklin, N. J. . 27. 14

The crystals of willemite exhibit the forms 00 R(ioTo), 00 P 2(1 120),
oR(oooi), 111(3034) and — £R(oil2)(Fig.i64). Twins, with |P2 (3.3.6. 10)
as the twinning planes, are rare. The crystals of troostite are even
more simple, with ooP2(ii2o) and R(ioTi), usually the only forms

ZnO

MnO

FeO

Total

72.91

• • * •

• 35

100.16

7I-SI

• • • ■

99-74

65.82

6-97

100.22

64.38

6.30

1.24

99.06

ANHYDROUS ORTHOSILICATES

307

present, though — £R(oiT2), — |R(°332) and R3(2i3i) are also occa-
sionally found. The angle 10I1 A 1101 = 63° 59'. The cleavage of
willemite is distinct parallel to oP(oooi), and of troostite distinct
parallel to ooP2(ii2o), and less perfect parallel to R(ioTi) and
oR(oooi).

Willemite is colorless, yellow, brown or blue. Troostite is green,
yellow, brown or gray. The colored varieties of both minerals are
translucent. Colorless willemite is transparent. Both minerals are
vitreous in luster. Their hardness is between
5 and 6 and density between 3.9 and 4.3. The
refractive indices of willemite for yellow light
are: u> =1.6931, €=1.7118.

Both minerals glow when heated before the
blowpipe and are fused with difficulty (about
1484 °), and both gelatinize with HC1. Willem-
ite gives the reaction for zinc with Co(N03)2
on charcoal, and troostite gives, in addition,
the reaction for manganese.

Syntheses. — Willemite crystals have been
made by the action of gaseous hydrofluo-
silicic acid upon zinc, and by the action of
silicon fluoride on zinc oxide at cherry-red temperature.

Localities and Origin. — Willemite occurs in comparatively small quan-
tity at only a few places, associated with other zinc minerals. In
America it is found in colorless and black crvstals at the Merritt
Mine near Socorro, New Mexico, associated with mimetite, wulfenite,
cerussite, barite and quartz.

Troostite occurs only at Sterling Hill and Franklin Furnace, N. J.,
but in such large quantity that it constitutes an important proportion
of the zinc ore for which these localities are noted. It is associated with
franklinite and zincite. Both willemite and troostite are results of
magmatic processes.

Fig. 164. — Willemite Crys-
tal with 00 P2, 1 1 20 (a);
R, ioii (r) and — JR,
01 T2 (e).

Phenacite (Be2SiC>4)

The theoretical composition of the compound Be2Si(>4 is Si04 = 54.47,
BeO= 45.53. Many of the analyses of phenacite show that it ap-
proaches very closely to this. A specimen from Durango, Mexico, for
example, is:

SiO= 54.71, BeO=45-32, MgO+CaO=.i4. Total = 100.17.

308 DESCRIPTIVE MINERALOGY

Phenacite crystallizes in the rhombohedral tetartohedral division of
the hexagonal system with a : c= i : 1.0661. It occurs in crystals pos-
sessing many different types of habit and with many different combina-
tions of forms. Perhaps ooP2(iiIo), ooP(ioTo), R(ioli), R3(2i3i)
and — JR(oii2) are the most common (Fig. 165). Interpenetration

twins are common at some localities. The
cleavage is indistinct parallel to 00 P(io7o).
The angle 10T1 Alioi = 630 24'.

Phenacite is colorless or white or some
light shade of yellow or pink. It is trans-
parent or translucent and has a glassy luster.
Its hardness is 7.5, and density about 3 and
the refractive indices for yellow light are:

Fig. i6S.-Phenacite Crystal »=I-6542, c- 1.6700. It is infusible and
with 00 P2, 1120 (a); « p, insoluble in acids. When heated with a

_ -JP3 little soda before the blowpipe it affords a

/ v 2 ' white enamel. The mineral is phosphores-

cent and pyroelectric.

Colorless phenacite resembles quartz and I.erderiie, and the yellow
variety topaz. It is best distinguished from them by its crystalliza-
tion.

Syntheses. — Small crystals have been made by the fusion of a mix-
ture of SiOa and beryllium oxide and borax, and by melting together
beryllium nitrate, silica and ammonium nitrate.

Localities. — Phenacite occurs at the Emerald Mines near Ekaterin-
burg in the Urals; near Fremont, in the Vogesen; at Reckingen, in
Switzerland; in Durango, Mexico; near Pike's Peak, at Topaz Butte,
and at Mount Antero, in Colorado, and at Greenwood, in Maine. In
all cases the mineral is probably a result of pneumatolysis.

Uses, — The colorless phenacite is used to a slight extent as a gem.

GARNET GROUP
(R",R'",(Si04)s). R"=Ca, Mg, Fe, Mn. R"'=A1, Fe, Cr

The garnet group comprises a large number of isomorphous com-
pounds, some of which are very common. The members nearly all
occur in distinct crystals that are combinations of isometric holohedrons
(hexoctahedral class). Many different names have been given to the
garnets and analyses show that they possess very different compositions.
With the exception of a few rare varieties, they can all, however, be
explained as consisting of one of the six molecules indicated below, or of

ANHYDROUS ORT*HOSILICATES

309

mixtures of them. The six molecules and the names of the garnets
corresponding to them, together with their densities, are:

Ca3Al2(Si04)3 Grossularite or Hessonite Sp. gr. = 3.4-3.6

Mg3Al2(Si04)3 Pyrope =3.7-3.8

MnaAl2(Si04)3 S pes sar tile =4.1-4.3

Fe3Al2(Si04)3 Almandite =4.1-4.3

Ca3Fe2(SiC>4)3 Andradite or Mdanite =3.8-4.1

Ca3Cr2(Si04)3 Uvarovite =3-4

The following table contains the calculated percentage composition
of the several pure garnet molecules and the records of analyses of some
typical varieties of the mineral:

II*

lib

HI*

IIIb
IVa

IVb

Vo
Via
VIb

SiO, Al2Os

40.01 22.69

42.01 17.76

44.78 25.40 ..

40.92 22.45 5
36.30 20.75 ••
36.34 12.63 4
36.15 20.51 43
37.61 22.70 33

35-45 3i

35 . 09 tr. 29

26.36 22

38. 23

36.93 5-68 1

FcaOi CnO, FeO

• •

15
00

• •

• • • •

506

8. 11

MgO

CaO

• • • a a

3730

•13

35 01

29.82

• • • • •

17.85

504

.47 1.49

2.49

29.27

21.84

3.01

1.44

• a • •

3306

• 24

3280

1.25

30.72

• • • •

29.27

i-54

3163

MnO TiO,

• •

42.95
44.20

• • • • •

tr.

■ • • a a

• • • • •

• • a • •
a • a a a

21.56

a a a a a

Total
100.00
100.17
100.00
100.39
100.00

99.70
100.00
100.31
100.00
100.48
101.89
100.00

9958

la. Theoretical composition of the grossularite molecule.

lb. Green and red grossularite from the limestone at Santa Clara, Cal.

Ila- Theoretical composition of the pure pyrope molecule.

lib. Pyrope from a peridotite in Elliot Co., Ky. Also, HjO ■» .10.
Ilia. Theoretical composition of spessartite.
IIIb. Spessartite from Amelia Court House, Va.
IVa. Theoretical composition of almandite.
IVb. Almandite from Salida, Colo.

Va. Theoretical composition of andradite.

Vb. Andradite from East Rock, New Haven, Conn. Also, HjO ** .35.

Vc. Schorlomite from Magnet Cove, Ark.
Via- Theoretical composition of uvarovite.
VIb- Uvarovite from Bissersk, Urals.

The crystals of garnet are usually simple combinations of 00 O(no)
(Fig. 166); 202(211) and often 3OK321) (Figs. 167 and 168), although
all the other holohedrons are also occasionally met with. Their cleavage
which is indistinct is parallel to 00 O(uo).

310 DESCRIPTIVE MINERALOGY

When examined in polarized light many garnets, especially those
occurring in metamorphic rocks, are doubly refracting and, therefore,
have not the molecular structure belonging to isometric crystals. This

Fig. 166.— Garnet Crystal. (Natural size.) Form: °oO (no).

Ficj. 167. Fie. 168.

Fie. 167.— Garnet Crystals with «0, no (d) and 2O2, 211 (n).
Fig. 168.— Garnet Crystal with d and « as in Fig. 16;. Also « O2, 210 (c) and 30|,

131 w.

phenomenon has been explained as due to several causes, the most rea-
sonable explanation ascribing it to strains produced in the crystals upon
cooling.

ANHYDROUS ORTHOSILICATES 311

The garnets vary in color according to their composition, the com-
monest color being reddish brown. Their luster is vitreous, their
streak white, hardness 6-7.5, and density 3.4-4.3. They are transparent
or translucent. Most varieties are easily fusible to a light brown or
black glass, which in the case of the varieties rich in iron is magnetic.
Uvarovite, however, is almost infusible. Some garnets are unattacked
by acids; others are partially decomposed.

Garnets, when in crystals, are easily distinguished from other sim-
ilarly crystallizing substances by their color and hardjiess. Massive
garnet may resemble resuzianilct sphene, zircon or tourmaline. It is
distinguished from zircon by its easier fusibility and from vesuvianite
by its more difficult fusibility; from tourmaline by its higher specific
gravity, and from sphene by the reaction from titanium.

Under the influence of the air and moisture garnets may be partially
or entirely changed to epidote, muscovite, chlorite, serpentine, and oc-
casionally to other substances.

Grossularite, Essonite, Hessonite, or Cinnamon Garnet occurs
principally in crystalline schists and in metamorphosed limestones,
where it is associated with other calcium silicates. It is found also
in quartz veins. The mineral is white, bright yellow, cinnamon-brown
or some pale shade of green or red. The lighter-colored varieties are
transparent or nearly so. Those that are colored are used as gems.
Much of the hyacinth of the jewelers is a red grossularite (see p. 317).
Its hardness is about 7 and its density 3.4-3.6. It is fairly easily
fusible before the blowpipe. The refractive index of colorless vari-
eties for yellow light is, »= 1.7438.

Good crystals of grossularite occur at Phippsburg, Raymond and
Rumford, in Maine, and at many other places both in this country and
abroad. Bright yellow varieties are reported from Canyon City, Colo.

Pyrope is deep red, sometimes nearly black. Its hardness is a little
greater than 7 and its density 3.7. Its refractive index for yellow light
is between 1.74 12 and 1.7504. The pure magnesium garnet is unknown.
All pyropes contain admixtures of iron and calcium molecules. Many
pyropes are transparent. Those with a dark red color are used as gems.
They occur principally in basic igneous rocks.

The principal occurrence of the gem variety in this country is in
Utah, near the Arizona line, .about 100 miles west of Ganado, Ariz.,
where it is found lying loose in wind-blown sand.

Rhodolite is a pale rose-red or purple variety from Macon Co., N. C.
It consists of two parts pyrope and one of almandite,

312 DESCRIPTIVE MINERALOGY

Spessartite is hyacinth or brownish red, with occasionally a tinge
of violet. The purest varieties are yellow, but since there is nearly
always an admixture of one of the iron molecules, the more usual color
is reddish brown. The mineral is usually transparent. Its hardness is
7 or a little greater, and its density 3.77-4.27. Its refractive index for
yellow light is 1.8105. In the blowpipe flame it fuses fairly easily to a
black, nonmagnetic mass, and with borax gives an amethyst bead. It
is found in acid igneous rocks and in various schists.

Its best known occurrences in the United States are in granite, at
Haddam, Conn., in pegmatite, at Amelia Court House, Va., and in
the lithophyse of rhyolites, near Nathrop, in Colorado.

Almandite is deep red, brownish red or black. It is one of the com-
monest of all garnets. It furnishes nearly all the material manufactured
into abrasives. Transparent varieties are also used as gems. The min-
eral has a hardness of 7 and over. Its density is 4.1-4.3, and its refrac-
tive index, n, for yellow light, is about 1.8100. It is slightly decom-
posed by HC1. Before the blowpipe it fuses to a dark gray or black
magnetic mass. It is found in granites and andesites, and also in various
gneisses and schists and in ore veins.

Its best known occurrences in North America are at Yonkers and
at various points in the Adirondacks, N. Y., at Avondale, Pa., and on the
Stickeen River, in Alaska.

Andradite, or melanite, is black, brown, brownish red, green, brown-
ish yellow or topaz-yellow. The purest varieties are topaz-yellow or
light green and transparent. The former constitute the gem iopazolite
and the latter, demantoid. The black variety, melanite, nearly always
contains titanium. It occurs in alkaline igneous rocks, in serpentine,
in crystalline schists and in iron ores. The most titaniferous varieties
are known as schorlomite. The hardness of andradite is about 7 and its
density between 3.3 and 4.1. n for yellow light = 1.8566. It is fusible
before the blowpipe to a black magnetic mass.

The mineral is very widely spread. It occurs at Franklin, N. J., in
metamorphosed limestone; near Franconia, N. H., in quartz veins, and
at many other places. A black titaniferous variety occurs in a meta-
morphosed limestone in southwestern California and near Magnet Cove,
in Arkansas. The variety found at Magnet Cove is schorlomite. It is a
black glassy mineral associated with brookite (TiCfe), nepheline (p. 314),
and thomsonite (p. 455).

Common garnet is a mixture of the grossularite, almandite and

ANHYDROUS ORTHOSILICATES 313

andradite molecules. It occurs in many metamorphosed igneous rocks
and in some slates.

Uvarovite is emerald-green. It is rare, occurring only with chromite
in serpentine at Bissersk and Kyschtim in the Urals and in the chromite
mines at Texas, Penn., and New Idria, Cal. Its hardness is about 7
and density 3.42. Its refractive index for yellow light is 1.8384. It is
infusible before the blowpipe but dissolves in borax, producing a green
bead.

Syntheses. — Garnet crystals have been produced by fusing 9 parts of
nepheline and 1 part of augite (p. 374). The fusion results in a
crystalline mass of nepheline, in which spinel and melanite crystals Are
embedded.

Occurrence. — The members of the garnet group are widely spread in
nature. They occur in schists, slates and other regionally metamor-
phosed rocks, in granite, rhyolite and other igneous rocks, and as con-
tact products in limestones. They are found also in quartz veins, in
pegmatite, and associated with other silicates in ore veins. In some
instances they separated from a cooling magma, in others they are the
products of pneumatolitic process, and in others they are the results of
contact and dynamic metamorphism.

Uses and Production. — The varieties that are transparent are used
as gems. Other varieties are crushed and employed as abrasives. The
value of the gem material produced in the United States in 191 2 was
$860. The production for abrasive purposes was 4,182 short tons, val-
ued at $137,800. All of this was produced in the mountain regions of
New York, New Hampshire and North Carolina. The rock is crushed
and the garnet separated by hand picking, screening, or by jigging.
The crushed material is used largely in the manufacture of garnet paper.

NEPHELINE GROUP

The nepheline group of minerals includes three closely related com-
pounds, of which nepheline is the most common. They are all alumino-
silicates of the alkalies. Nepheline appears to be a solution of Si02,
or of albite, in isomorphous mixtures of the orthosilicates, NaAlSi04
and KAlSi04 in the proportion of 8 molecules of the silicates to one of
Si02, thus:

8(Na- K)AlSi04+Si02= (Na- K)0((Na- K)AlSi03)2Al6(Si04)7

The other two members of the group are eucryptite (LiAlSi04) and
kaliophilite (KAlSi04).

314

DESCRIPTIVE MINERALOGY

The members of the group crystallize in the hexagonal system and
are apparently holohedral, but nepheline is hemihedral and hemi-
morphic (hexagonal pyramidal class). At temperatures above 1,248°
the nepheline molecule crystallizes also in the triclinic system as car-
negieUc (see p. 418).

Nepheline ((Na-K)8Al8Si©034)

Although approximately a potash-soda silicate, nearly all specimens
of nepheline contain more or less CaO and nearly all contain small
quantities of water. All contain an excess of SiC>2. To avoid the
necessity of assuming the existence of this SiC>2 in solution with
(Na* K)AlSiC>4, it has been suggested that the variable composition of
the mineral may be explained by regarding it as a solid solution of
NaAlSiaOs and CaAkSi^s (best known in their triclinic forms as
albite and anorthite) in an isomorphous mixture of the two molecules,
NaAISiCU and KAlSiO*. The average of five analyses of crystals from
Monte Somma, Italy, is shown in I, and the composition of a mass of
the mineral from Litchfield, Maine, in II.

Si02 AI2O3

I.44.08 33.28

II. 43 .74 34 • 48

CaO MgO Na20 K20 H20

1.57 .19 16.00 4.76 .15
tr tr 16.62 4.55 .86

Total
100.03
100.25

When found in crystals, the mineral is apparently holohedral in form
with an axial ratio 1 : .8389. The crystals are nearly always short

columnar in habit and usually consist of very
/<^ c ^>\ simple combinations. The most prominent
NX p A^-il forms are 00 P(ioTo), ooP2(ii2o), oP(oooi),

2P(202l), P(ioll), £P(l0l2) and 2P2(lI2l)

(Fig. 169). Their cleavage is imperfect parallel
to 00 P( 10T0) and oP (0001 ) .

Nepheline is glassy, white or gray and trans-
parent, when occurring as implanted crystals.

xt 1 i- ^ The translucent varietv with a glassy luster
Fig. 169 —Nepheline Crys- . . - * f

tal with oP 0001 U)' ^at occurs m rocks is known as eleohte. This
00 p, 10T0 (w); P, 10T1 variety may be gray, pink, brown, yellowish or
(p) and 00 P2, 1 1 20 (a), greenish. The streak is always white. The

fracture of both forms is conchoidal or uneven;
hardness, 5-6 and density, 2.6. For yellow light, co= 1.5424, 6=1.5375.

ANHYDROUS ORTHOSILICATES 315

Before the blowpipe nepheline melts to a white or colorless blebby
glass. At 1,248° it passes over into carnegieite which melts at 1,526°.
It dissolves in hydrochloric acid. with the production of gelatinous
silica. Its powder before and after roasting reacts alkaline.

The mineral is distinguished from other silicates by its crystalliza-
tion, gelatinization with acids, and hardness. The massive varieties
are often distinguishable by their greasy luster.

Nepheline alters to various hydrated compounds, especially to the
zeolites (p. 445), and to gibbsite, muscovite, cancrinite and sodalite.

Syntheses. — Nepheline has been prepared by fusing together AI2O3,
Si02 and Na2CC>3, and by the treatment of muscovite by potassium
hydroxide.

Occurrence. — The mineral occurs principally as an original constit-
uent of many igneous rocks, both plutonic and volcanic, and also as
crystals on walls of cavities in them.

Localities. — Crystals occur near Eberbach, in Baden; in the inclu-
sions within volcanic rocks at Lake Laach, in Rhenish Prussia; in the
older lavas of Monte Somma, Naples, Italy; at Capo de Bove, near
Rome; in southern Norway; and at various other points in southern
Europe. Massive forms are found in coarse-jjrained rocks near Litch-
field, Maine; Red Hill, N. H.; Magnet Cove, Ark. ; in the Crazy Mts.,
Mont., and at other places.

Cancrinite (He^CaMNaCOa^AlsCSiO^)

Cancrinite is extremely complex in composition. It is nearly allied
to nepheline but contains a notable quantity of CO2. It corresponds
approximately to an hydrated admixture of Na2CC>3 and 3NaAlSi04,
in which some of the Na is replaced by K and Ca. Specimens from
Barkevik (I) in Norway, and from Litchfield (II), in Maine, yield the
following analyses:

Si02 AI2O3 Fe203 CaO Na20 K20 C02 H20 Total
I. 37.01 26.42 .... 7.19 18.36 .... 7.27 3.12 99.37
II. 36.29 30.12 tr. 4.27 19.56 .18 6.96 2.98 100.36

Cancrinite is hexagonal (dihexagonal bipyramidal class).

Crystals are rare, and those that do exist are very simple, prismatic
forms bounded by ooP(ioTo), ooP2(ii2~o), oP(oooi) and P(ioTi).
Their axial ratio is 1 : .4410.

316 DESCRIPTIVE MINERALOGY

The mineral is usually found without crystal planes. It is colorless,
white or some light shade, such as rose, bluish gray or yellow. Its
streak is white, its luster glassy, greasy or pearly and it is translucent.
Its cleavage is perfect parallel to ooP(ioTo) and less perfect parallel
to oo P2 11 20). Its break is uneven; hardness 5 and density 2.45.
For red light: w= 1.5244, €=1.4955.

Before the blowpipe the mineral loses its color, swells and fuses to a
colorless blebby glass. In the closed glass tube it loses CO2 and water,
and becomes opaque. After roasting it is easily attacked by weak
acids with effervescence and the production of gelatinous silica. When
boiled with water Na2CC>3 is extracted in sufficient quantity to give an
alkaline reaction.

Cancrinite is easily distinguished by its effervescence with acids and
the production of gelatinous silica.

Synthesis. — Small colorless, hexagonal crystals with a composition
corresponding to that of cancrinite, have been made by treating mus-
covite with a solution of NaOH and NaoCCb at 5000.

Occurrence. — The mineral occurs principally as an associate of neph-
eline in certain coarse-grained igneous rocks. In some cases it appears
to be an original rock constituent and in others an alteration product of
nepheline. It sometimes alters to natrolite (see p. 454), forming pseu-
domorphs.

Localities. — Cancrinite is found in rocks at Ditro, Hungary; at
Barkevik and other localities in southern Norway, where it occurs in
pegmatite dikes; in the parish of Kuolajarvi, in Finland, and in nepheline
syenite at Litchfield in Maine.

ZIRCON GROUP

The orthosilicates of zirconium, zircon, and of thorium, thorite, con-
stitute a group, the members of which possess forms that are almost
identical with those of rutile, cassiterite and xenotime. Indeed, parallel
growths of zircon and xenotime are not uncommon. Formerly zircon
was grouped with the two oxides.

Zircon and thorite are tetragonal (ditetragonal bipyramidal class),
with approximately the same axial ratios and the same pyramidal angles.
The two minerals are completely isomorphous.

Zircon ZrSi04 a : £=.6301 in A 1^1 = 56° 37',
Thorite ThSi04 =.6402 =56° 40'.

Zircon is fairly common. Thorite is rare.

ANHYDROUS ORTHOSILICATES

317

Zircon (ZrSi04)

Zircon, like rutile, is a fairly common compound of a comparatively
rare metal. It is practically the only ore of the metal zirconium. It is
found mainly in crystals and as gravel.

Although some specimens of zircon contain a large number of ele-
ments, others consist only of zirconium, silicon and oxygen in propor-
tions that correspond to the formula ZrSiCU, which demands 67.2 per
cent ZrO and 32.8 per cent Si02.

Its axial ratio is a : f=i : .6391. Its crystals are usually simple
combinations of 00 P(no) and P(m), with the addition of 00 P 00 (100)

Fig. 170.

Fig. 171.

Fig. 170. — Zircon Crystals with 00 P, no («); 00 Poo, 100 (a); 3P, 331 (*),

P, in (p) and 3P3, 311 (x).
Fig. 171. — Zircon Twinned about P 00 (101). *=2P (221).

and often 3P3(3ii) (Fig. 170). Elbow twins, like those of rutile and
cassiterite, are known (Fig. 171).

The cleavage of zircon is very indistinct. Its fracture is conchoidal.
Its hardness is 7.5 and density about 4.7. The mineral varies in tint
from colorless, through yellowish brown to reddish brown. Its streak
is uncolored and luster adamantine. Most varieties are opaque, but
transparent varieties are not uncommon. The orange, brown and red-
dish transparent kinds constitute the gem known as hyacinth. The
refractive indices for yellow light are: «= 1.9302, c= 1.9832.

Zircon is infusible, though colored varieties often lose their color
when strongly heated. In the borax and other beads the mineral gives
no preceptible reactions. In fine powder it is decomposed by concen-
trated sulphuric acid. When fused with sodium carbonate on platinum
it is likewise decomposed, and the solution formed by dissolving the
fused mixture in dilute hydrochloric acid turns turmeric paper orange.
This is a characteristic test for the zirconium salts.

318 DESCRIPTIVE MINERALOGY

The mineral is easily recognized by its hardness, its resistance toward
reagents and its crystallization.

Syntheses. — Small crystals of zircon are obtained by heating for sev-
eral hours in a steam-tight platinum crucible a mixture of gelatinous
silica and gelatinous zirconium hydroxide. Crystals have also been
made by heating for a month a mixture of ZnCfe and S1O2 with 6 times
their weight of lithium bimolybdate.

Occurrence and Origin. — Zircon is widely spread in tiny crystals as a
primary constituent in many rocks, and in large crystals in a few, notably
in limestone and a granite-like rock known as nepheline syenite. In
limestone it is a product of contact action. It occurs also in sands,
more particularly in those of gold regions, and abundantly in a sand-
stone near Ashland, Va.

Localities. — The principal occurrences of the mineral are Ceylon, the
home of the gem hyacinth; the gold sands of Australia; Arendal,
Hakedal and other places in Norway; Litchfield and other points in
Maine; Diana, in Lewis Co., and a large number of other places in New
York; at Reading, Penn.; Henderson and other Counties, in North
Carolina and Templeton, Ottawa Co., Quebec.

Uses. — Zircon is the principal source of the zirconium oxide employed
in the manufacture of gauze used in incandescent gas lights and in the
manufacture of cylinders for use in procuring a light from the oxyhydro-
gen jet. The mineral has been mined for these purposes in Henderson
Co., North Carolina.

Transparent orange-colored zircons are sometimes used as gems
since they possess a high index of refraction and consequently have
a great deal of " fire." These are the true .hyacinth. The mineral
often called by this name among the jewelers is a yellowish brown
garnet.

Production. — A small quantity of zircon is usually obtained from
Henderson Co., N. C, but it rarely amounts to more than a few hundred
pounds. The mineral occurs in a pegmatite and the soil overlying its
outcrop. It is obtained by crushing the rock and hand picking. Usually
there is a little also separated from the sands in North Carolina and
South Carolina that are washed for monazite. A pegmatite dike, rich
in zircon, is also being prospected in the Wichita Mountains, Okla., but
no mining has yet been attempted.

ANHYDROUS ORTHOSILICATES 319

Thorite (ThSi04)

Thorite occurs in simple crystals bounded by oo P(no) and P(m)
(Fig. 172), and in masses. The mineral is always
more or less hydrated, but this is believed to be
due to partial weathering. It is black or orange-
yellow (orangeite), has a hardness of 5 and a specific
gravity of 4.5-5 for black varieties and 5.2-5.4 for
orange varieties. Its streak is brown or light orange.
Hydrated specimens are soluble in hydrochloric acid
with the production of gelatinous silica. The min- Fig. 172.— Thorite
eral occurs as a constituent of the igneous rock, Crystal with *> p,
augite-syenite, at several points in the neighborhood IIQ '*' an '
of the Langesundf jord, Norway,

BASIC ORTHOSILICATES

ANDALUSITE GROUP

Three compounds with the empirical formula AkSiOs exist as min-
erals, kyanite, or disthene, andalusite and sUlimanile. The first named is
less stable with reference to chemical agents than the other two, but at
high temperatures both kyanite and andalusite are transformed into
sillimanite. Kyanite is regarded as a metasilicate (A10)2SiC>3. The
other two are thought to be orthosilicates (Al(AlO)SiC>4). The latter
are orthorhombic and both possess nearly equal prismatic angles.
They differ markedly, however, in their optical and other physical
properties and, therefore, are different substances. Kyanite is triclinic.
For this reason and because of its different composition it is not re-
garded as a member of the andalusite group. A fourth mineral, topaz,
differs from andalusite in containing fluorine. Often this element is
present in sufficient quantity to replace all of the oxygen in the radical
(AlO). In other specimens the place of some of the fluorine is taken
by hydroxyl (OH). The general formula that represents these varia-
tions is Al(Al(F-OH)2)Si04. The mineral crystallizes in forms that are
very like those of andalusite, and if corresponding pyramids are selected
as groundforms their axial ratios are nearly alike. Unfortunately,
however, different pyramids have been accepted as groundforms, and
therefore the similarity of the crystallization of the two minerals has
been somewhat obscured. Danburite, another mineral that crystallizes
in the orthorhombic system with, a habit like that of topaz is often also
placed in this group, although it is a borosilicate, thus CaB2(Si04)2.

320

DESCRIPTIVE MINERALOGY

If 4P2(24i) be taken as the groundform of andalusite, 3P(33i) as
that of topaz and 3P(33i) as that of danburite, the corresponding axial
ratios would be:

Andalusite a : b : c— .5069 : 1 : 1 .4246
Topaz =.5281 : 1 : 1.4313

Danburite = . 5445 : 1 : 1 . 4402

These, however, are not the accepted ratios, since other and more prom-
inent pyramids have been selected as the groundforms.

Andalusite and Sillimanite (Al(A10)Si04)

Andalusite and sillimanite have the same empirical chemical compo-
sition and crystallize with the same symmetry, which is orthorhombic
holohedral (rhombic bipyramidal class), but they have different physical
properties and different crystal habits, and hence are regarded as dif-
ferent minerals. The theoretical composition of both is:

Si02= 37.02; Al203 = 62.98. Total= 100.00.

Nearly all specimens when analyzed show the presence of small
quantities of Fe, Mg, and Ca, but otherwise they correspond very closely
to the theoretical composition.

Both minerals are characteristic of metamorphosed rocks, but
andalusite occurs principally in those that have been metamorphosed by

contact with igneous intru-
sives, while sillimanite is
especially characteristic of
crystalline schists and, in gen-
eral, of rocks that were dy-
namically metamorphosed. It
also occurs with olivine as in-
clusions in basalt lavas. Silli-

Fig. 173.— Andalusite Crystals with <» p, no manite is more stable at high

jw»;^l(* P»£ii_(j); oops 100 temperatures than andalusite.

/ x r>-OI° ,\ t* 2> "/^v J" t>-' When in contact rocks it is

120 (»); Poo, 101 (r); P, 111 (p) and 2P2,

121 (£). found nearer the intrusive

than andalusite.
Andalusite. — The accepted axial ratio of andalusite is .9861 : 1 : .7024.
Its crystals are columnar in habit and are usually simple combinations

of 00 P GO (lOo), 00 P 06 (OIO), OP(OOI), 00 P(lio), 00 P2(2I0), 00 P2(l20)

P« (101), Poo (on) with sometimes P (in) and 2P2(i2i) (Fig. 173).
The angle no A 110=89° I2'-

ANHYDROUS ORTHOSILICATES 321

The mineral, when fresh, is greenish or reddish and transparent.
Usually, however, it is more or less altered, and is opaque, or, at most,
translucent, and gray, pink of violet. Its cleavage is good parallel to
oo P(no) and its fracture uneven. Its hardness is 7 or a little less and
its density 3.1-3.2. In some specimens pleochroism is marked, their
colors being olive-green for the ray vibrating parallel to a, oil-green for
that vibrating parallel to b and dark red for that vibrating parallel to c.
For yellow light the indices of refraction are: 0=1.6326, 18=1.6390,
7=1.6440.

Before the blowpipe the mineral gradually changes to sillimanite and
is infusible. When moistened with cobalt nitrate and roasted it becomes
blue. It is insoluble in acids.

The mineral is distinguished by its nearly square cross-section, its
hardness, its infusibility, and the reaction for Al, and by its manner of
occurrence in schists and metamorphosed slates.

Some specimens contain as inclusions large quantities of a dark
gray or black material, which may be carbonaceous, arranged in
such a way as to give a cross-like figure in cross-sections of crystals.
Because of the shape of the figure exhibited by these crystals, this
variety was early called chiastolite, and was valued as a sacred
charm. 1

Andalusite alters readily to kaolin (p. 404), muscovite (p. 355), and
sillimanite. It has not been produced artificially.

Occurrence. — Andalusite is found principally in clay slates and schists
that have been metamorphosed by contact with igneous masses, and
to a less extent in gneisses.

Localities. — Its principal occurrences are in Andalusia, Spain; at
Braunsdorf, Saxony; at Gefrees, in the Fichtelgebirge; in Minas
Geraes, Brazil, and in the United States at Standish, Maine; Westford,
Mass., and Litchfield, Conn. Chiastolite occurs at Lancaster and
Sterling, Mass.

Use. — The only use to which andalusite has been put is as a semi-
precious stone, and for this purpose only the chiastolite variety is of any
value.

Sillimanite, or fibrolite, occurs principally in acicular or fibrous
aggregates, on the individuals of which only the prismatic forms
ooP(no) and 00 P|(23o) and the macropinacoid 00 Poo (100) can be
detected. End faces are not sufficiently developed to warrant the
determination of an axial ratio. The relative values of the a and b
axes are .687 : 1. The angle no A 110=69°.

While most of the fibers correspond in composition very closely to the

322 DESCRIPTIVE MINERALOGY

theoretical value demanded by the formula Al(A10)Si04, many contain
small quantities of Fe^, MgO and H2O.

The mineral is yellowish gray, greenish gray, olive-green or brownish.
It has a glassy or greasy luster and when pure is transparent. Most
specimens, however, are translucent, and many of the colored varieties
show a pleochroism in brown or reddish tints. Its cleavage is perfect
parallel to 00P60 (100). Its needles have an uneven fracture trans-
versely to their long directions. Their streak is colorless, hardness
6-7 and density 3.24. The indices of refraction for the lighter colored
varieties are: a= 1.6603, £=1.6612, 7=1.6818 for yellow light.

Sillimanite reacts similarly to andalusite toward reagents and before
the blowpipe. It is distinguished from other minerals by its habit and
manner of occurrence.

This mineral is much more resistant to weathering than is andalusite.
It is, however, occasionally found altered to kaolin. On the other hand,
it is known also in pseudomorphs after corundum.

Synthesis. — It has been produced by cooling fused silicate solutions
rich in aluminium.

Occurrence. — Sillimanite is very widely spread in schistose rocks,
especially those that have been formed from sediments. It is essentially
a product of dynamic metamorphism, but is formed also bv contact
metamorphism, in which case it is found near the intrusive, where the
temperature was high.

Localities. — Its principal occurrences in North America are in quartz
veins cutting gneisses at Chester, Conn., at many points in Delaware
Co., Penn., and at the Culsagee Mine, Macon Co., N. C. At the lAtter
place and at Media in Penn., a fibrous variety occurs in such large

masses as to constitute a schist — known as fibrolite schist. • r-\

{ •

Topaz (Al(Al(F-0H)2)Si04)

Topaz is a common constituent of many ore veins and is often present
on the walls of cracks and cavities in volcanic rocks. It occurs massive
and also in distinct and handsome crystals.

The mineral has a varying composition, which is explained in part
by the fact that it is a mixture of the two- molecules Al(AlF2)Si04 and
Al(Al(OH)2)SiOi. The theoretical composition of the fluorine molecule
is: Si02=32.6, Al203 = 55.4; F= 20.7= 108.7; deduct (0=2F)8.7
s= 100.00. A specimen from Florissant, Colo., gave:

Si02=33-I5; Al2Oa = 57.01; F =16.04 =106.20- 6.75(0 «=F) = 99.45.

ANHYDROUS ORTHOSILICATES

323

Crystals of topaz appear to be orthorhombic (rhombic bipyramidal
class), but the fact that they are pyroelectric and that they frequently
exhibit optical phenomena that are not in accord with the symmetry of
orthorhombic holohedrons suggests that they may possess a lower grade
of symmetry. On the assumption that the mineral crystallizes with the
symmetry of orthorhombic holohedronf the axial ratio of fluorine varie-
ties is .5281 :.i : -477r.1 With the increasing presence of OH, however,
the relative length of a increases and that of c diminishes. The angle
noAiTo=S5° 43'-

The crystals are usually prismatic in habit with w>P(no) and
00 PJ(i2o) predominating. They are notable for the number of forms

f&>\

Fie. 174-
FlG.174.— Topaz Crystals with »P,iio{m); °° 1
4P » , 041 00 and »P«
Fic. 175.— Topaz Crystal with m, I, n and y as

*P«,043(A-)and2P«

Fig. i7S.

r,i»(0; P.iiiMi iP»niM

>.o (6).

1 Fig. 174. Also 2p«,o2i (J);

2OI (d).

that have been observed on them, especially in the prismatic zone and
among the brachypyramids. The number of the latter that have
already been identified is about 45.

The three types of crystals that are most common are shown in
Figs. 174, 175 and 176. Their most prominent forms are oop(no),
■oPa(iao), P»(on), P(ni), |P(233). 4P*(o4i), « P3d3°) and
oP(ooi). Often planes are absent from one end of the vertical axis,
but since the etch figures on the prismatic planes do not indicate hemi-
morphism, the absence of the lacking planes is explained as being due to
unequal growth. The planes of the prismatic zone are usually striated.

The mineral is colorless, honey yellow, yellowish red, rose and rarely
bluish. When exposed to the sunlight the colored varieties fade, and

inly accepted axial ratio is a : b : t= .5^85 :i : .0539, the form

Then

aP(aai) being taken as the groundform.

324

DESCRIPTIVE MINERALOGY

when intensely heated some honey-yellow crystals turn rose-red. Its
cleavage is perfect parallel to oP(ooi) and imperfect parallel to P 06 (on)
and P * (101). The hardness of the mineral is 8 and its density 3. 5-3. 6.
Its refractive indices for yellow light are: a= 1.6072, 0= 1.6104, 7= 1.6 176
for a variety containing very little OH, and a =1.6294, 0=1.6308,

7=1.6375 for a variety rich in
hydroxyl. The indices of refraction
being high, the mineral when cut
exhibits much brilliancy — a feature
which, together with its hardness,
gives it much of its value as a
gem.

Topaz is infusible before the

blowpipe and is insoluble in acids.

Fig. 176.— Topaz Crystal with m, I, y, At a high temperature it loses its

/", d, O and u as in Figs. 174 and 175. fluorine as silicon and aluminium

Also JP, 223 (0; oP, 001 (c) and fluorides. The mineral also ex-

9 4 hibits pyroelectrical properties, but

these are apparently distributed without regularity in different

crystals. Many crystals contain inclusions of fluids containing bubbles,

and sometimes of two immiscible fluids the nature of which has not vet

been determined. It has been thought that the principal fluid present

is liquid carbon-dioxide or some hydrocarbon.

The mineral is distinguished from yellow quartz by its crystalliza-
tion, its greater hardness and its easy cleavage.

Topaz is frequently found coated with a micaceous alteration product
which may be steatite (p. 401), muscovite (p. 355) 01 kaolin (p. 404).

Synthesis. — Crystals have been made by the action of hydrofluosilicic
acid (I^SiFe) upon a mixture of silica and alumina in the presence of
water at a temperature of about 500 °.

Occurrence. — The mineral occurs principally in pegmatites, espe-
cially those containing cassiterite, in gneisses, and in acid volcanic rocks.
In all cases it is probably the result of the escape of fluorine-bearing
gases from cooling igneous magmas.

Localities. — Topaz is found in handsome crystals at Schneckenstein
in Saxony, in a breccia made up of fragments of a tourmaline*quartz
rock cemented by topaz. It occurs also in the pegmatites of the tin
mines in Ehrenfriedersdorf, Marienberg and other places in Saxony,
Bohemia, England, etc.; on the walls of cavities in a coarse granite in
Jekaterinburg and the Ilmengebirge, Russia; in veins of kaolin cutting
a talc schist in Minas Geraes in Brazil; and in the cassiterite-bearing

ANHYDROUS ORTHOSILICATES 325

sands at San Luis Potosi, Durango and other points in Mexico. In the
United States it occurs on the walls of cavities in acid volcanic rocks, at
Nathrop, Colo., in the Thomas Range, Utah, and other places. It occurs
also in veins with muscovite, fluorite, diaspore and other minerals at
Stoneham, Maine, and Trumbull, Conn.

Uses and Production. — Topaz is used as a gem. About 36 lb., valued
at $2,675, was produced in the United States in ion. In the following
year the production was valued at only $375.

Danburite (CaBz(Si04)z)

Danburite, which is a comparatively rare mineral, is a calcium
borosilicate with the following theoretical composition: SK)2=48.84;
Bz03 = 28.39 and CaO= 22.77. Usually, however, there are present in it
small quantities of AI2O3, Fea03, M^Oa and HzO. Thus, crystals from
Russell, New York, contain:

S1O2 BjOa AI2O3, etc. HzO CaO Total

49.70 25.80 1.02 .20 23.26 99.98

The mineral crystallizes in the orthorhombic system (rhombic bipy-
ramidal class), with an axial ratio .5445 : 1 : .4801. Its crystals are
usually prismatic in habit. They contain a great number of forms, of
which wPoo(ioo), ooP66(oio), «P2(i2o), ooPJf^o), and <*>P(no)
among the prisms, 2P4(i42), 2P2(i2i) among
the pyramids and oP(ooi) are the most prom-
inent (Fig. 177). The angle noAiio=
57° 8'.

When fresh and pure the mineral is trans-
parent, colorless or light yellow, but when
more or less impure is pink, honey-yellow or
dark brown. Its streak is white, and luster

vitreous. Its cleavage is imperfect parallel to fic. 177.— Danburite Crys-
oP(ooi) and its fracture uneven or conchoidal. tal with » P, no (m);
Its hardness is about 7 and density 2.95-3.02. *>Pi, j» (/); P», 101
Its refractive indices for yellow light are: <<0; *pM" Wand4P«,
«=r.63i7, (3=1-6337, 7=1-6383- °4' W'

Before the blowpipe the mineral fuses to a colorless glass and colors
the 8ame green. It is only slightly attacked by hydrochloric acid, but
after roasting is decomposed with the formation of gelatinous silica.
It phosphoresces on heating, glowing with a red light.

Origin. — Danburite is probably always a product of pneumatolytic

326 DESCRIPTIVE MINERALOGY

action, as it is found in quartz and pegmatite veins in the vicinity of
igneous rocks and on the walls of hollows within them.

Localities. — Its principal occurrences in this country are at Danbury,
Conn., where it is in a pegmatite, and at Russell, N. Y., on the walls of
rocks and hollows in a granitic rock. Its principal foreign occurrence is
at Piz Valatscha, in Switzerland.

EPIDOTE GROUP (Ca,R'"a(OH)(Si04),)

The epidote group comprises six substances, of which two are di-
morphs with thecomposition Ca2Al3(OH) (Si04)3 = Ca2Al2(A10H) (SiQi)3.
One of these, known as zoisitey crystallizes in the orthorhombic system,
and the other, known as clinozoisite, in the monoclinic system. The
other four are isomorphous with clinozoisite. These are hancockUe,-
epidote, piedtnontite and allanite. The composition and comparative
axial ratios of the four commoner isomorphs are as follows (assuming
$P(Ti2) as the groundform of clinozoisite):

Clinozoisite Ca2Al3(OH)(Si04)3 1-4457 • i • 18057

Epidote Ca2(AlFe)3(0H)(Si04)3 15807 : 1 : 1.8057, $=64° 36'
Piedmontite Ca2(Al • Mn)3(0H)(Si04)3 1.6100 : 1 : 1.8326, £=64° 39'
Allanite Ca2(Al-Ce-Fe)3(OH)(Si04)3 1.5509 : 1 : 1.7691, £=64° 59'

Clinozoisite is rare, though its molecule occurs abundantly in iso-
morphous mixtures with the corresponding iron molecule in epidote.

Zoisite (Ca2Al3(OH)(Si04)3)

Zoisite is a calcium, aluminium orthosilicate containing only a small
quantity of the corresponding iron molecule. The theoretical composi-
tion of the pure Ca molecule is:

SiO=39-52; Al203 = 33i92; CaO= 24.59; H20=i.97. Total = 100.00.

Colored varieties contain a little iron or manganese. Green crystals (I),
from Ducktown, Tenn., and red crystals (thulite) (II), from Kleppan, in
Norway, analyze as follows:

Si02 AI2O3 Fe203 FeO CaO MgO Mn203 Na20 H20 Total

I. 39.61 32.89 .91 .71 24.50 .14 2.12 100.88

II. 42.81 31.14 2.29 ... 18.73 ••■ 1-^3 1&9 .64 99.13

Zoisite crystallizes in the orthorhombic system (orthorhombic bi-
pyramidal class), with the axial ratio .6196 : 1 : .3429. Its crystals are

ANHYDROUS ORTHOSILICATES

327

.-I

usuaUy simple and without end faces. The most frequent forms are
ooP(no), ooP4(i4o), oo P 06(010). P(iii), 2P 06 (021) and 4P 06 (041)
are the commonest terminations (Fig. 178). The crystals are all pris-
matic and are striated longitudinally. Their
cleavage is perfect parallel to 00 P 06 (010).
The angle noAiTo=63° 34'.

The mineral is ash-gray, yellowish gray,
greenish white, green or red in color and has a
white streak. The rose-red variety, contain-
ing manganese, is known as thulite. Very
pure fresh zoisite is transparent, but the ordi-
nary forms of the mineral are translucent.
Its luster is glassy, except on the cleavage
surface, where it is sometimes pearly. Its
fracture is uneven. Its hardness is 6 and
density about 3.3. In specimens from Duck-
town, Term., a= 1.7002, 0= 1.7025, 7=1.7058
for yellow light. A notable fact in connection
with this mineral is that with increase of the
molecule Ca2Fe3(OH)(Si04)3 in the mixture
the plane of its optical axes tends to change
from oP(oio) to 00 P 06 (001).

Zoisite fuses to a clear glass before the blowpipe and gives off water,
which causes a bubbling on the edges of the heated fragments. It is
only slightly affected by acids, but after heating it is decomposed by
hydrochloric acid with the production of gelatinous silica.

Occurrence, — The mineral occurs as a constituent of crystalline
schists, especially those rich in hornblende, or of quartz veins traversing
them. It is also a component of the alteration product known as
saussurite which results from the decomposition of the plagioclase
(p. 418) in certain basic, augitic rocks known as gabbros. It is thus a
product of metamorphism.

Localities, — Good crystals of zoisite are found near Pregratten in
Tyrol; at Kleppan (thulite), Parish Souland, Norway, and in the ore
veins at the copper mines of Ducktown, Tenn., where it is associated with
chalcopyrite, pyrite and quartz.

Epidote (Ca2(Al-Fe)3(OH)(Si04)3)

Epidote, or pistazite, differs from the monoclinic dimorph of zoisite
(clinozoisite) in containing an admixture of the corresponding iron sili-
cate which is unknown as an independent mineral.

Fig. i 78. — Zoisite Crystal
with 00 P, no (m); 00 P 06 ;
010 (6); 00 P4, 140 (/),
2P00, 021 («) and P, in

W-

328

DESCRIPTIVE MINERALOGY

Since it consists of a mixture of an aluminium and an iron compound
its composition necessarily varies. The four lines of figures below give
the calculated composition of mixtures containing 15 per cent, 21 per
cent, 30 per cent and 40 per cent of the iron molecule.

Percent SiCk AI2O3 Fe203 CaO H20 Total

15 38.60 28.80 6.65 24.02 1.93 100.00

21 3823 26.76 9.32 23.78 1. 91 100.00

30 37-67 23.71 13.31 23.43 1.88 100.00

40 37 °4 20.32 17.75 23.04 1.85 100.00

Most specimens contain small quantities of Mg, Fe, Mn, Na or K.

Epidote is isomorphous with clinozoisite, crystallizing in the mono-

Fig. 179. — Epidote Crystals with 00 P 00 , 100 (a); oP, 001 (c); P 00 , 10 1 (r); JP 00 ,

102 (1); P, 11T (») and P 00 , on (0).

Fig. 180. — Epidote Crystals with a, c, r, f, n and 0 as in Fig. 179. Also 00 P,
no(m); 2P60, 2oT(/); -P66, 101 (c); —$P\, 231 (p) and |P2, 423 (/).

clinic system (monoclinic prismatic class), with the axial ratio 1.5787 : 1
: 1.8036. 0=64° 36'. The mineral is remarkable for its handsome
crystals, many of which are extremely rich in forms. The crystals are
usually columnar in consequence of their elongation parallel to the b
axis. The most prominent forms are 00 P 60 (100) , oP(ooi), £P 66 (20T).
Poo (ioT),P(iiT), 00 P(no) and Pob (on) (Fig. 179 and 180). In addi-
tion to these, over 300 other forms have been identified. Twinning
is common, with 00 Poo (100) the twinning plane. The angle no A
iTo= 1090 56'.

Epidote is yellowish green, pistachio green, dark green, brown or,
rarely, red. It is transparent or translucent and strongly pleochroic.
In green varieties the ray vibrating parallel to the b axis is brown, that
vibrating nearly parallel to c, yellow, and that vibrating perpendicular to

ANHYDROUS ORTHOSILICATES 329

the plane of these two is green. Its luster is glassy and its streak gray.
Its cleavage is very perfect parallel to oP(ooi). Its hardness is 6.5 and
density 3.3 to 3.5. The refractive indices for yellow light in a crystal
from Zillerthal are: 0=1.7238, 13=1.7291,7=1.7343. They increase
with the proportion of the iron molecule present, being 1.7336, 1.7593
and 1. 7710 in a specimen containing 27 per cent of the iron epidote.

The varieties that have been given distinct names are:

Bucklandite, a greenish black variety in crystals that are not elon-
gated;

Withamite, a bright red variety containing a little MnO.

Fragments of the mineral when heated before the blowpipe yield
water and fuse to a dark brown or black mass that is often magnetic.
With increase in iron fusion becomes more easy. Before fusion epidote
is practically insoluble in acid. After heating HC1 decomposes it with
the separation of gelatinous silica.

The ordinary forms of the mineral are characterized by their yellow-
ish green color, ready fusibility and crystallization.

Occurrence and Origin. — Epidote occurs in massive veins cutting crys-
talline schists and igneous rocks, as isolated crystals and druses on the
walls of fissures through almost any rock and in any cavities that may
be in them, and as the principal constituent of the rock known as epi-
dosite. It is a common alteration product of the feldspars (p. 408),
pyroxenes (p. 364), garnet, and other calcium and iron-bearing minerals.
Pseudomorphs of epidote after these minerals are well known. The
mineral is a weathering product, but is more commonly a product of
contact and regional metamorphism.

It has not been produced artificially.

Localities. — Epidote crystals are so widely spread that only a few of
the important localities in which they have been found can be mentioned
here. Particularly fine crystals occur in the Sulzbachthal, Salzburg,
Austria; in the Zillerthal, in Tyrol; near Zermatt, in Switzerland; in
the Alathal, Traversella, Italy; at Arendal, Norway; in Japan, at
Prince of Wales Island, Alaska, and at many other points in North
America.

Piedmontite (Ca2(Al-Mn)3(OH)(Si04)3)

Piedmontite is the manganese epidote, differing from the ordinary
epidote in possessing manganese in place of iron. Usually, however,
the iron and the manganese molecules are both present. Typical analy-
ses of crystals from St. Marcel, in Piedmont, Italy (I), Otakisan, Japan
(II), and Pine Mt., near Monterey, Md. (Ill), follow:

330 DESCRIPTIVE MINERALOGY

S1O2 AI2Q3 M112O3 MnO Fe2Q8 MgO CaO H2O Total
I. 35.68 18.93 14.27 3.22 1.34 ... 24.32 2.24 100.00
II. 36.16 22.52 6.43* 9.33 .40 22.05 .3-2° 100.53*

III. 47-37 i8-55 685 x-92 402 .25 15.82 2.08 100.05*
* II. contains also .44 per cent NatO. The MniO* contained also MnO.

III. contains also 2.03 per cent of the oxides of rare earths, .14 per cent PbO,
.11 per cent CuO, .23 per cent Na.O and .68 per cent KsO. The specimen contained
also a little admixed quartz, which was determined with the SiO*.

The axial ratio of piedmontite is 1.6100 : 1 : 1.8326. 0=64° 39'.
Its crystals are similar in habit to those of epidote, but they are .much
simpler. The most prominent forms are 00 P «» (100), oP(ooi), P(Tn),
$P 00(102), 00 Poo (010) and ooP(no). Twins are fairly common,
with 00 P 60 (100) the twinning plane.

The mineral is rose-red, brownish red or reddish black. It is trans-
parent or translucent and strongly pleochroic in yellow and red tints
and has a glassy luster and pink streak. It is brittle, and has a good
cleavage parallel to oP(ooi). Its hardness is 6 and density 3.40. Its
refractive indices are the same as those of epidote.

Before the blowpipe piedmontite melts to a blebby black glass and
gives the manganese reaction in the borax bead. It is unattacked by
acids until after heating, when it decomposes in HC1 with the separation
of gelatinous silica.

It is characterized by its color and hardness and by its manganese
reaction.

Occurrence and Origin. — Piedmontite occurs as an essential constit-
uent of certain schistose rocks that are known as piedmontite schists.
It occurs also in veins and in certain volcanic rocks, where it is probably
an alteration product of feldspar. Its methods of origin are the same
as those of epidote.

Localities. — Good crystals are found in the manganese ore veins at
St. Marcel, Piedmont; on ilmenite in crystalline schists on the Isle of
Groix, off the south coast of Brittany; and at a number of points on the
Island of Shikoku, Japan, in crystalline schists and in ore veins. In
the United States it is so abundant in the acid volcanic rocks of South
Mountain, Penn., as to give them a rose-red color.

Allanite (Ca2(Al-Ce-Fe)3(OH)(Si04)3)

Allanite is a comparatively rare epidote in which there are present
notable quantities of Ce, Y, La, Di, Er and occasionally other of the
rarer elements. Since cerium is present in the largest quantity the

ANHYDROUS ORTHOSILICATES

331

formula of the mineral is usually written as above, with the under-
standing that a portion of the cerium may be replaced by yttrium and
the other elements. Some idea of the complex character of the mineral
may be gained from the two analyses quoted below. The first is of
crystals from Miask, Ural, and the second of a black massive variety
from Douglas Co., Colo.

I
30.81
16.25
6.29

Si02

AI2O3

Fe203

Ce2C>3 10.13

BeO

Di20a 3.43

La20a 6.35

Y2O3 1 . 24

FeO 8.14

MnO 2 . 25

MgO 13

CaO 1043

K20 S3

Na20

H2O 2 . 79

CO2

Total 98.77

3i-i3
11.44

6.24

12.50

.27

10.98

13-59
.61

.16

9-44
tr.

■56

2.78

.21

99.81

Allanite rarely occurs in crystals, but when these are found they are
usually more complex than those of piedmontite but much less compli-
cated than those of epidote. Their axial ratio is 1.5509 : 1 : 1.7691
with 0=64° 59'. Their habit is like that of epidote crystals. Common
forms are 00 P 06(100), oP(ooi), <»P(iio). Twins are like those of
epidote. The mineral usually occurs as massive, granular or columnar
aggregates, or as ill-defined columnar crystals resembling rusty nails.
It sometimes forms parallel intergrowths with epidote.

It is black on a fresh fracture and rusty brown on exposed surfaces,
and has a greenish gray or brown streak. It has a glassy luster and is
translucent in thin splinters, with greenish gray or brownish tints and
is pleochroic in various shades of brown. Its hardness is 5-6 and
density 3-4, both varying with freshness and composition. The cleav-
ages are imperfect and the fracture uneven. Its indices of refraction
are nearly the same as those of epidote.

32 DESCRIPTIVE MINERALOGY

Small fragments of fresh allanite fuse to a blebby black magnetic
glass before the blowpipe and are decomposed by HC1 with the separa-
tion of gelatinous silica.

Allanite is distinguished by its color, manner of occurrence, and the
reaction for water in the closed tube.

The mineral alters readily on exposure to the weather, yielding
among other compounds mica and limonite.

Occurrence. — Allanite occurs as an original constituent in some
granites, and other coarse-grained rocks. It is found also in gneisses,
occasionally in volcanic rocks and rarely as a metamorphic mineral in
crystalline limestones.

Localities. — The best crystals have been found in the druses of a
volcanic rock at Lake Laach, Prussia; in coarse-grained granitic rocks
at several places in the Tyrol; in the limestone at Pargas, Finland; and
at various points in Ural, Russia. Massive allanite occurs in the coarse
granite veins at Hittero, Norway and as the constituents of granites
at many places in the United States. Parallel intergrowths with epidote
are found in granite at Ilchester, Md.

CHONDRODITE GROUP

The chondrocyte group of minerals includes four members of the
general formula (Mg(F • OH^Mg^SiC^)* in which x equals i, 3, 5, 7, and
y, 1, 2, 3, 4. Of these, one (humite) may be orthorhombic. The other
three are monoclinic with the angle £=90°. The four members of the
group with their compositions and axial ratios are:

ProlectiU (Mg(F-OH)2)Mg(Si04) 1.0803 : 1 : 1.8862 £=90°
Chondrodite (Mg(F-OH)2)Mg3(Si04)2 1.0863 : 1 : 3-1445 £=90

b Z
Humite (Mg(F-OH)2)Mg5(Si04)3 1.0802 : 1 : 4.4033

Clinohumite (Mg(F-OH)2)Mg7(Si04)4 1.0803 : 1 : 5.6588 0=90

To show the similarity in the ratios between the lateral axes of the
four minerals, the & axis of humite is written as 1. Chondrodite, humite
and clinohumite frequently occur together. Chondrodite has been
reported at more localities than either humite or clinohumite, but it is
not certain that much of it is not clinohumite. The three minerals
resemble one another very closely. They are relatively unstable under
conditions prevailing at moderate depths in the earth's crust, passing
easily into serpentine, brucite or dolomite. Only chondrodite is de-
scribed.

ANHYDROUS ORTHOSILICATES

333

Chondrodite (Mg3(Mg(FOH)2)(Si04)2)

Chondrodite is a rather uncommon mineral that occurs mainly as a
constituent of metamorphosed limestones that have been penetrated
by gases and water emanating from igneous rocks. It is a characteris-
tic contact mineral.

Its composition varies somewhat in consequence of the fact that OH
and F possess the power to mutually replace one another. The two
analyses below are typical of varieties containing a maximum amount
of F.

Si02

MgO

FeO

H20

I- 33 • 77

57.98

3-96

i-37

H. 35 42

54-22

5-72

• • • •

F F=0 Total

5.14=102.22 — 2.16 100.06
9 . 00= 104 . 36 — 3 . 78 100 . 58

I. Crystals from limestone inclusions in the lava of Vesuvius.
II. Grains separated from the limestone of the Tilly Foster Iron Mine, Brewster,

N. Y.

Chondrodite is monociinic (prismatic class), with an axial ratio
1.0863 : * : 3I445- 0=9OO- The crystals vary widely in habit and
are often complex. The forms oP(ooi),
00 P * (100), 00 P 00 (010) and various unit
and clinobemipyramids of the general sym-
bol xPi are frequently present, but other
forms are also common (Fig. 181). Twin-
ning about oP(ooi) is also common.
Usually, however, the mineral occurs in
little rounded grains, in some instances

showing crystal faces, scattered through Fig. 181.— Chondrodite Crys-
tal with oP, 001 (c); JP 5b ,

012 (0; |F2,l27(fi);fP2,
"5 (*); fP2, 123 (r,);
-2P2, 121 (r4); -P, in
(*); P, In (-»i); JP 00,

103 M; P«, 101 (-*)
and -P5o, 101 («j). The
a axis runs from right to left
and the upper left hand
octant is assumed to be
minus.

limestone.

When fresh, chondrodite has a glassy
luster, is translucent and is white or has a
light or dark yellow, brown or garnet color.
It has a distinct cleavage parallel to oP(ooi),
a conchoidal fracture, a hardness of 6 and
a density of 3.15. Its refractive indices
for yellow light are: a= 1.607, 0=1.619,
7=1.639.

Before the blowpipe chondrodite bleaches
without fusing. With acids it decomposes with the production of
gelatinous silica.

334

DESCRIPTIVE MINERALOGY

It weathers readily to serpentine, chlorite and brucite, and conse-
quently many grains are colored dark green or black.

Occurrence. — Chondrodite, as has been stated, occurs in meta-
morphosed limestones. It also occurs in sulphide ore bodies and in a
few instances in magnetite deposits. It is probably in all cases a pneu-
matolytic or metamorphic product.

Localities. — It is found as crystals in the blocks enclosed in the lavas
of Vesuvius; in the copper mines of Kapveltorp, Sweden; in limestone
in the Parish of Pargas, Finland; and at the Tilly Foster Iron Mine, at
Brewster, N. Y. It occurs as grains in the crystalline limestone of
Sussex Co., N. J., and Orange Co., N. Y.

DATOLITE GROUP

The members of the datolite group are four in number, but
of these only two, viz., datolite (Ca(B'OH)Si04) and gadolinite
(Be2Fe(YO)2(Si0.i)2) are of sufficient importance to be described here.
Both minerals crystallize similarly in the monoclinic system (mono-
clinic prismatic class), with axial ratios that are nearly alike.

Datolite alb: ^=.6345 : 1 : 1.2657 /S = 8o°5i'
Gadolinite alb: £ = .6273 : 1 : 1.3215 /S = 8o°26i'

Datolite (Ca(BOH)Si04)

Datolite, or datholite, is characteristically a vein mineral.

The composition corresponding to the
formula given above is:

^ SiO=37.S4; B20:* = 21.83; CaO=35.oo;

1120=5.63. Total= 100.00

Some specimens contain a little AI2O3 and
Fe203 but, in general, crystals that have
been analyzed give results that are in
close accord with the theoretical com-

Fig. 182 —Datolite Crystal with P°sltl0n-

oop 56, 100 (a); 00 p, no (m); The mineral crystallizes in fine crys-

-P co , 101, (<*>); — JP co , 102 tals that are often very complicated (Fig.

(*); -P, in (»); -P2, 212 !82). About 115 different forms have

(*); P * , on (mz) and JP <2 , been observed on them. Because of the

suppression of some faces by irregular
growth many of the crystals are columnar in habit, others are tabular.
Most crystals, however, are nearly equi-dimensional. The angle

ANHYDROUS ORTHOSILICATES 335

noA 110=64° 40'. The mineral occurs also in globular, radiating,
granular and massive forms.

Datolite is colorless or white, when pure, and transparent. Often,
however, it is greenish, yellow, reddish or violet, and translucent. Its
streak is white and its luster glassy. It has no distinct cleavage. Its
fracture is conchoidal. Its hardness is 5 and its sp. gr. about 3. Some
crystals are pyroelectric. For yellow light, 0=1.6246, 18=1.6527,
7=1.6694.

Before the blowpipe it swells, and finally melts to a clear glass and,
at the same time, it colors the flame green. Its powder before heating
reacts strongly alkaline. After heating this reaction is weaker. The
mineral loses water when strongly heated, and yields gelatinous silica
when treated with hydrochloric acid.

The mineral is characterized by its crystallization, its easy fusibility
and the flame reaction for boron.

Synthesis. — Datolite has not been produced artificially.

Occurrence, Origin and Localities. — It occurs on the walls of clefts
in igneous rocks, in pegmatite veins and associated with metallic com-
pounds in ore veins. It is found in many ore deposits of pneumatolytic
origin, notably at Andreasberg in the Harz Mts.; at Markirch, in
Alsace; in the Seisser Alps, in Tyrol; in the Serra dei Zanchetti in the
Bolognese Apennines; at Arendal, Norway, and at many other places.
In North America it occurs at Deerfield, Mass.; at Tariffville, Conn.;
at Bergen Hill, N. J.; and at several points in the copper districts of
the Lake Superior region.

Gadolinite (Be2Fe(YO)2(Si04)2)

Gadolinite is a rather rare mineral with a composition that is not
well established. Its occurrence is limited to coarse granite veins or
dikes — pegmatites — of which it is sometimes a constituent.

Its theoretical composition is as follows, on the assumption that it is
analogous to that of datolite:

SiO= 25.56; ¥203=48.44; FeO= 15.32; BeO= 10.68. Total=ioo.oo,
but nearly all specimens contain cerium oxides. Others contain nota-
ble quantities of erbium or lanthanum oxides and small quantities of
thorium oxide. Nearly all show the presence of Fe203, AI2O3, CaO and
MgO, and in some helium has been found.

The mineral is found massive and in rough crystals with an axial
ratio alb: £=.6273 : 1 : 1.3215. £=89° 263'. The crystals show
comparatively few forms, of which oop(no), oP(ooi), Poo (on),

336 DESCRIPTIVE MINERALOGY

£P 00(012), P(Tii) and — P(in) are the most common. They are
usually columnar in habit and are rough and coarse. The angle
iioAiTo=64° 12'.

Gadolinite is usually black or greenish black and opaque or trans-
lucent, but very thin splinters of fresh specimens are translucent or
transparent in green tints. Its luster is glassy or resinous, streak
greenish gray and fracture conchoidal. Its hardness is 6-7 and its
density about 4-4.5. Upon heating the density increases. Many crys-
tals appear to be made up of isotropic and anisotropic substance, and
some to consist entirely of isotropic matter. This phenomenon has
been explained in a number of different ways, but no one is entirely satis-
factory. In general, the isotropic material is believed to be an amor-
phous alteration form of the anisotropic variety. It may be changed
into the anisotropic form by heating.

The crystallized gadolinite swells up in the blowpipe flame without
becoming fused and retains its transparency. The amorphous variety
also swells without melting, but yields a grayish green translucent mass.
The mineral phosphoresces when heated to a temperature between that
of melting zinc and silver. After phosphorescing it is unattacked by
hydrochloric acid. Before heating it gelatinizes with the same reagent.
The mineral is weakly radioactive.

Localities and Origin. — Gadolinite occurs in the pegmatites of Ytterby
near Stockholm, and of Fahlun, Sweden; on the Island of Hittero, in
southern Norway; in the Radauthal, in Harz; at Barringer Hill, Llano
Co., Texas, as nodular masses and large rough crystals; and at Devil's
Head, Douglas Co., Colo. In the last locality it occurs in a de-
composed granite as a black isotropic variety with a very complex
composition. Specimens analyzed as follows:

I n

SiC>2 22.13 21.86

ThCfe 89 .81

AI2O3 2.34 .54

Fe203 1 . 13 3-59

Ce203 1 1. 10 6.87

(La-Di)203 21.23 19.10

Y2O3 9-5° 12.63

Er203 12.74 15.80

i n

FeO 10.43 1136

BeO 7.19 5.46

CaO 34 .47

H20 86 .74

Other .60 .79

Total 100.48 100.02

It has apparently in some cases solidified from an igneous magma.
In others it is of pneumatolytic origin.

ANHYDROUS ORTHOSILICATES

337

Staurolite (Fe(A10H)(A10)4(Si04)2)

Staurolite is a mineral that is interesting from the fact that it fre-
quently forms twinned crystals that resemble a cross in shape, and which
consequently, during the Middle Ages, was held in great veneration.
Its composition is not well established. The composition indicated by
the formula above is as shown in the first line below (I). Three analyses
are quoted in the next three lines:

Si02

AI2O3

Fe20s

FeO

MgO

H20

Ti02

Total

26.3

55-9

■ • • *

158

• • • •

2.00

• ■ ■

100.00

II.

27-38

5420

6.83

913

■ • ■ •

i-43

• • •

98.97

III.

3°-23

51.16

• ■ • •

14.66

2-73

1.26

.29

100.33

IV.

27.91

52.92

6.87

• •

7.80

328

i-59

• ■ •

100.37

I. Theoretical composition.
II. From Monte Campione, Switzerland.

III. From Morbihan, France.

IV. From Chesterfield, Mass.

Staurolite crystallizes in the orthorhombic system (bipyramidal
class) in simple crystals with the axial ratio .4734 : 1 : .6828. The indi-

Fic. 183. Fig. 184. Fig. 185.

Fig. 183. — Staurolite Crystal with 00 P, no (tn); wPoo, 100 (6); oP, 001 (c) and

Poo , 101 (r).

Fig. 184. — Staurolite Crystal Twinned about fP 00 (032).

Fig. 185. — Staurolite Crystal Twinned about |P| (232).

vidual crystals are usually bounded by 00 P(i 10), 00 P 60 (001), P 60 (101)
and often oP(ooi), but all their faces are rough (Fig. 183). The angle
1 10 Alio =50° 40'. More common, however, than the simple crystals
are interpenetration twins. The most common of these are of two kinds,
(1) with fP 06 (032) the twinning plane (Fig. 184), and (2) with ^£(232)
the twinning plane (Fig. 185). Both types of twins yield crosses, but
the arms of the first type are perpendicular to one another and those of

338 DESCRIPTIVE MINERALOGY

the second type make angles of about 6o° and 1200. Sometimes the
twinning is repeated, giving rise to trillings.

The mineral is reddish or blackish brown, and has a glassy or greasy
luster. Its streak is white. It is slightly translucent in fresh crystals,
but usually is opaque. In very thin pieces it is pleochroic in hyacinth-
red and golden yellow tints. Its cleavage is distinct parallel to 00 P 06
(010) and indistinct parallel to ooP(no). Its fracture is conchoidal,
its hardness 7 and its density 3.4-3-8. For yellow light, a= 1.736,
18=1.741, 7=1.746.

Before the blowpipe staurolite is infusible, unless it contains man-
ganese, in which case it fuses to a black magnetic glass. It is only
slightly attacked by sulphuric acid.

It is distinguished from other minerals by its crystallization, in-
fusibility and hardness.

Staurolite weathers fairly readily into micaceous minerals, such as
chlorite (p. 428) and muscovite (p. 355).

Synthesis. — It has not been produced in the laboratory.

Occurrence. — The mineral occurs principally in mica schist and other
schistose rocks where it is the result of regional or contact metamor-
phism. Because of its method of occurrence it frequently contains
numerous mineral inclusions, among them garnet and mica.

Localities. — Good crystals of staurolite are found in the schists at
Mte. Campione, Switzerland; in the Zillerthal, Tyrof; at AschafFen-
burg, in Bavaria; at various places in Brittany, France; and in the
United States, at Windham, Maine, at Franconia, N. H., at Chester-
field, Mass., in Patrick Co., Va., and in Fannin Co., N. C.

Uses. — Twins of staurolite are used, to a slight extent, as jewelry.
Specimens from Patrick Co., Virginia, are mounted and worn as charms
under the name of " Fairy Stones."

Dumortierite (Al(A10)7H(BO)(Si0.4)3)

Dumortierite is one of the few blue silicates known. It is a borosili-
cate with a composition approaching the formula indicated above. The
analysis of a sample from Clip, Arizona, gave (I) :

Si02 AI2O3 Fe203 Ti203 MgO B2O3 P2O5 Loss on Ign. Total

I.27.99 64.49 ••• tr 4.95 .20 1.72 99.35

II.28.58 63.31 .21 1.49 5.21 ... 1.53 100.33

Specimens from California (II) contain in addition notable quantities
of Ti02, which is thought to exist as Ti203 replacing a part of the AI2O3.

ANHYDROUS ORTHOSILICATES 339

The mineral crystallizes in the orthorhombic system in aggregates of
fibers, needles or very thin prisms exhibiting only ooP(no) and
oo P 56 (ioo) without end faces. Its axial ratio is a : £=.5317 '• 1, and
the prismatic angle no A 1^0=56°. Its crystals possess a distinct
cleavage parallel to 00 P 60 (100) and a fracture perpendicular to the
long axes of the prisms. Twinning is common, with ooP(no) the
twinning plane.

Dumortierite is commonly some shade of blue, but in some cases is
green, lavender, white, or colorless. It is translucent or transparent
and strongly pleochroic, being colorless and red, purple or blue. Its
streak is light blue. Hardness is 7 and density 3.3. Its refractive indices
for yellow light are: a= 1.678, /3= 1.686, 7= 1.089.

Before the blowpipe the mineral loses its color and is infusible. It is
insoluble in acids.

It is distinguished from other blue silicates by its fibrous or columnar
character and its insolubility in acids.

Its principal alteration products are kaolin and damourite
(pp. 404, 357).

Occurrence and Localities. — Dumortierite occurs only as a constit-
uent of gneisses and pegmatites. It is found in pegmatite near Lyons,
France; near Schmiedeberg, in Silesia; at Harlem, N. Y.; in a granular
quartz, at Clip, Yuma Co., Ariz., and in a dike rock composed of quartz
and dumortierite, near Dehesa, San Diego Co., Cal. It is evidently
a pneumatolytic mineral. Its common associates are kyanite, anda-
lusite or sillimanite.

SODALITE GROUP

The sodalite group includes a series of isometric minerals that may be
regarded as compounds of silicates with a sulphate, a sulphide or a chlor-
ide, or, perhaps better, as silicates in which are present radicals con-
taining CI, SO4 and S. The minerals comprising the group are haiiynite,
nosean, sodalite and lasurite. Of these, sodalite appears to be a mixture
of 3NaAlSi04 and NaCl, in which the CI has combined with one atom of
Al, thus Na4(ClAl)Al2(Si04)3- The other members of the group are
comparable with this on the assumption that the CI atom is replaced by
the radicals NaSC>4, and NaSa. It is possible, however, that all are
molecular compounds as indicated by the second set of formulas given
below. All are essentially sodium salts, except that in typical haiiynite
a portion of the Na is replaced by Ca. The chemical symbols of the
four minerals with the calculated percentages of silica, alumina and
soda corresponding to their formulas are:

340

DESCRIPTIVE MINERALOGY

Si02
37H

AI2O3
31.60

27.03

27.32

26.9

NasO

25 .60

27.26

16.53
27-3

Sodalite Nai(Cl • Al) AWSiQOs, or

3NaAlSi04-NaCl
Noselite Na4(NaS04 • Al) Al2(Si04)3, or 31 . 65

3NaAlSi04 • Na2S04
Hatiynite (Na2Ca)2(NaS04* Al)Al2(SiOi)3, or 31.99

3NaAlSi04 • CaS04
Lasurite Na4(NaS3 • Al)Al2(Si04)3, or 31.7

3NaAlSi04-Na2S-S*

SodaUte (Na4(Cl-Al)Al2(Si04)3)

Sodalite, theoretically, is the pure sodium compound corresponding
to the composition indicated by the formula given above. Natural
crystals, however, usually contain a little potassium in place of some of
the sodium and often some calcium, as indicated by the analyses of
material from Montreal, Canada (I), and Litchfield, Maine (II), quoted
below. Moreover, their content of CI is not constant.

SiCfe AI2O3 Na20 K2OCaO CI C1=0

I- 37-52 31-38 25.15 .78 .35 6.91 = 102.09 -I-S5

II- 37-33 31-87 24.56 .10 ... 6.83 - 101.76* -1.54

* Includes 1.07 per cent H*0.

Total
100.54
100.22

Sodalite occurs massive and in crystals that appear to be holohedral,
but etch figures indicate that they are probably tetrahedrally hemi-

hedral (hextetrahedral class). Most crystals
are dodecahedral in habit, though some are
tetrahexahedral and others octahedral. The
forms usually developed are ooO(no),
00O00 (100), O(iii), 202(112) and 404(114).
Interpenetration twins of two dodecahedrons
are common, with O the twinning plane (Fig.
186). These often possess an hexagonal habit.
The mineral is colorless, white or some
light shade of blue or red, and its streak is
white. Its luster is vitreous. It is trans-
parent, translucent and sometimes opaque.
Its cleavage is perfect parallel to ooO(no)
and its fracture conchoidal. Its hardness is 5-5.6, and its density
2.3. Its refractive index for yellow light, n= 1.4827. Some specimens
are distinctly fluorescent and phosphorescent.

Fig. 186. — Sodalite. Inter-
penetration Twin of Two
Dodecahedrons Elon-
gated in the Direction of
an Octahedral Axis and
Twinned about O(in).

ANHYDROUS ORTHOSILICATES 341

Before the blowpipe, colored varieties bleach and all varieties swell
and fuse readily to a colorless blebby glass. The mineral dissolves com-
pletely in strong acids and yields gelatinous silica, especially after heat-
ing. When dissolved in dilute nitric acid its solution yields a chlorine
precipitate with silver nitrate. Its powder becomes brown on treatment
with AgNOa, in consequence of the production of AgCl.

The mineral is best distinguished from other similarly appearing
minerals by the production of gelatinous silica with acids and the reac-
tion for chlorine.

As a result of weathering sodalite loses CI and Na and gains water.
Its commonest alteration products are zeolites (p. 445), kaolin (p. 440),
and muscovite (p. 355).

Syntheses. — It has been produced artificially by dissolving nepheline
powder in fused sodium chloride, and by decomposing muscovite
with sodium hydroxide and NaCl at a temperature of 5000 C.

Occurrence and Origin. — Sodalite occurs principally as a constituent
of igneous rocks rich in alkalies and as crystals on the walls of pores in
some lavas. It is also known as an alteration product of nepheline.

Localities. — Good crystals are found in nepheline syenite at Ditr6,
in Hungary, in the lavas of Mte. Somma, Italy; in the pegmatites of
southern Norway; and at many other points where nepheline rocks
occur. In North America it is abundant in the rocks at Brome, near
Montreal; in the Crazy Mts., Montana, and at Litchfield, Maine. The
material at the last-named locality is light blue.

Noselite and Haiiynite ((Na.Ca)2(NaS01Al)Al2(Si0.1)3)

Noselite, or nosean, and haiiynite, or haiiyn, consist of isomorphous
mixtures of sodium and calcium molecules of the general formula given
above. Those mixtures containing a small quantity of calcium are
usually called nosean, while those with larger amounts constitute hatiyn.
The theoretical nosean and haiiyn molecules are indicated on p. 340.
The theoretical compositions of the pure nosean molecule (I) and of the
most common hatiyn mixture (II) are as follows:

Si02 AI2O3 Fe203 CaO Na20 Ka20 SO3 H20 Total

27.26 .... 14.06 .... 100.00

9.94 16.53 .... 14.22 .... 100.00

.31 .21 20.91 .... 10.58 1.63 99.61*

10.08 13.26 3.23 12.31 100.08

* Contains also .57 per cent CI.

31-65

27.03

II.

31 99

2732

III.

35-99

29.41

IV.

33.78

27.42

342 DESCRIPTIVE MINERALOGY

In line III is the analysis of a blue nosean from Siderao, Cape Verde,
and in line IV, the analysis of a blue haiiyn from the lava of Monte Vul-
ture, near Melfi, Italy.

Nosean and haiiyn are isomorphous with sodalite. They crystallize
is the isometric system in simple combinations with a dodecahedral
habit. The principal forms observed are ooO(no), ooOoo(ioo)
0002(102), O(ni) and 202(112). Contact and interpenetration twins
are common, with O(in) the twinning plane. The twins are often
columnar.

The minerals have a glassy or greasy luster, are transparent or trans-
lucent, have a distinct cleavage parallel to ooO(no) and an uneven or
conchoidal fracture. Their hardness is 5.6 and density 2.25 to 2.5, the
value increasing with the amount of CaO present. Nosean is generally
gray and haiiyn blue, but both minerals may possess almost any color,
from white through light green and blue tints to black. Red colors are
rare. The streaks of both minerals are colorless, or bluish. For yel-
low, light n= 1.4890 to 1.5038, increasing with increase in the Ca
present. Both minerals are fluorescent and phosphorescent.

Before the blowpipe both minerals fuse with difficulty to a blebby
white glass, the blue haiiyn retaining its color until a high temperature
is reached. In this respect it differs from blue sodalite which bleaches
at comparatively low temperatures. Upon treatment with hot water
both minerals yield Na2S04. They are decomposed with acids yielding
gelatinous silica. The powders of both minerals react alkaline. Both
also give the sulphur reaction with soda on charcoal.

The minerals are easily distinguished from all others by their crys-
tallization, gelatinization with acids and reaction for sulphur.

Both minerals upon weathering yield kaolin or zeolites and
calcite.

Synthesis. — Crystals of noselite have been made by melting together
Na2COa, kaolinite and a large excess of Na2SO*.

Occurrence. — Haiiyn and nosean occur in many rocks containing
nepheline, especially those of volcanic origin and in a few metamorphic
rocks. Haiiyn is so common in some of them as to constitute an essen-
tial component.

Localities. — Both minerals are found in good crystals in metamor-
phosed inclusions in the volcanic rocks of the Lake Laach region, in
Prussia; also in the rocks of the Kaiserstuhl, in Baden; in those of
the Albanian Hills, in Italy, and at S. Antao in Cape Verde. In
America haiiyn has been reported from the nepheline rocks of the
Crazy Mts., Montana.

ANHYDROUS ORTHOSILICATES 343

Lasurite (Na^NaSa- Al)Al2(Si04)3)

Lasurite is better known as lapis lazuli. It is bright blue in color
and was formerly much used as a gem stone. The material utilized for
gem purposes is usually a mixture of different minerals, but its blue
color is given it by a substance with a composition corresponding to the
formula indicated above. Since the artificial ultramarine, which is
ground and used as a pigment, also has this composition, the molecule is
sometimes represented by the shortened symbol US3, or if it contains
but two atoms of S, by the symbol US2. The deep blue lasurite from
Asia contains as its coloring material a substance with a composition
that may be represented by 15.7 molecules of US3, 76.9 molecules of
hatiyn and 7.4 molecules of sodalite, corresponding to the percentages:

SiCb

AI2O3

CaO

Na20 K20

32-52 •

27.61

6.47

19.45 .28

SOa

Total (Less CI = 0)

10.46

2.71

•47

99.97 = 99.42

Lasurite is thus the name given to the blue coloring matter of lapis
lazuli, which is a mixture. It apparently crystallizes in dodecahedrons.
Its streak is blue, its cleavage is dodecahedral, its hardness about 5 and
its specific gravity about 2.4. Before the blowpipe it fuses to a white
glass. Its powder bleaches rapidly in hydrochloric acid, decomposes
with the production of gelatinous silica and yields H2S.

It is distinguished from blue sodalite and hatiyn by the reaction with
HC1, especially by the evolution of H2S.

Occurrence. — Lasurite is principally a contact mineral in limestone.

Localities. — Good lapis lazuli occurs at the end of Lake Baikal, in
Siberia; in the Andes of Ovalle, in Chile; in the limestone inclusions in
the lavas of Vesuvius, and in the Albanian Mts., Italy.

Uses. — Lapis lazuli is used as an ornamental stone in the manufacture
of vases, and various ornaments, in the manufacture of mosaics, and as a
pigment, when ground, under the name ultramarine. Most of the ultra-
marine at present in use, however, is artificially prepared.

ACID ORTHOSILICATES

Prehnite Q^CazAfeCSiO^a)

Prehnite is nearly always found in crystals, though it occurs also in
stalactitic and granular masses.

The theoretical composition of the pure mineral is Si02 = 43.69,

344 DESCRIPTIVE MINERALOGY

Al203 = 24.78, CaO= 27.16, and H20=4-37- Most crystals, however,
contain small quantities of Fe203 and other constituents.

SiO, A1,0, Fe«Oa FeO CaO MgO HaO Total

Jordansmtthl, Silesia 44. 12 26.00 .61 25.26 tr 4.91 100.90

Cornwall, Penn 42.40 20.88 5.54 27.02 tr 4.01 99-85

Chlorastrolite, Isle Royale 3741 24.62 2.21 1.81 22.20 3.46 7.72 99-75*

* Also .32 per cent NajO.

Its crystallization is orthorhombic and hemimorphic (rhombic py-
ramidal class), with a: b: c=. 8420: 1 : 1.1272. The crystals vary
widely in habit, but they contain comparatively few forms. The most
prominent are oP(ooi), ooP(no), 6Poo(o6i), 2P(22i) and 6P(66i)

(Fig. 187). The angle noAiTo=8o°
12'. Because they exhibit pyroelectric
polarity in the direction of the a axis the

, . , crvstals are thought to be twins, with
Fig. 187. — Prehnite Crystal with "t» - / \ .1 A • • 1

' , ,. n - / x 00 P 00 (100) as the twinning plane.

00 P, no (m); 00 poo , 100 (a); v ' & v

iP«, 304 (»); iP*, 308 (») Cleavage is good parallel to oP(ooi).
and oP, 001 (c). The crystals are frequently tabular

parallel to oP(ooi), although other
habits are also common. Isolated individuals are rare, usually many
are grouped together into knotty or warty aggregates.

Prehnite is colorless or light green, and transparent or trans-
lucent, and it has a colorless streak. Its luster is pearly on oP(ooi) but
glassy on other faces. Its fracture is uneven, its hardness 7+ and its
density 2.80-2.95. For yellow light, a= 1.616, 0= 1.626, 7 = 1.649.

Before the blowpipe prehnite exfoliates, bleaches and melts to a
yellowish enamel. At a high temperature it yields water. Its powder is
strongly alkaline. It is partially decomposed by strong hydrochloric
acid with the production of pulverulent silica. After fusion it dissolves
readily in this acid yielding gelatinous silica.

The mineral has not been produced artificially.

Occurrence. — Prehnite occurs as crystals implanted on the walls of
clefts in siliceous rocks, in the gas cavities in lavas, and in the gangue of
certain ores, especially copper ores. It is found also as pseudomorphs
after analcite (p. 458), laumonite (p. 451), and natrolite (p. 454). In
all cases it is probably a secondary product.

Localities. — Fine crystals come from veins at Harzburg, in Thiiringia;
at Striegau and Jordansmiihl, Silesia, and at Fassa and other places in
Tyrol. Good crystals are found also in the Campsie Hills in Scotland.
The mineral is abundant in veins with copper along the north shore of

ANHYDROUS ORTHOSILICATES 345

Lake Superior and on Keweenaw Point, and it occurs also at Farmington,
Conn.; Bergen Hill, N. J. ; and Cornwall, Penn.

Uses. — The mineral known as chlorastrolite is probably an impure
prehnite. It is found on the beaches of Isle Royale and the north shore
of Lake Superior as little pebbles composed of stellar and radial bunches
of bluish green fibers. The pebbles were originally the fillings of gas
cavities in old lavas. They are polished and used, to a slight extent, as
gem-stones. About $2,000 worth were sold in 191 1 and $350 worth in
1912.

Arinite (H(Ca-Fe-Mn)3Al2B(Si04)4)

Axinite is especially noteworthy for its richness in crystal forms.
The mineral is a complicated borosilicate for which the formula given
above is merely suggestive. Analyses of crystals from different localities
vary so widely that no satisfactory simple formula has been proposed
for the mineral. Four recent analyses are quoted below:

Kadauthal Stricgau Oisans Cornwall

SiCfe 39 26 42.02 41 .53 42.10

B2O3 4-91 5.00 4.62 4.64

AI2O3 1446 17-73 *7 °o I7-40

FeoOa 2.62 .93 3.90 3.06

FeO 3.65 6.55 4.02 5.84

MnO 2.80 6.52 3.79 4.63

CaO 29.70 19.21 21.66 2°S3

MgO 2 . 00 .38 .74 .66

H2O 1.22 1.77 2.16 1.80

Total.... 100.62 100. 11 100.32 100.66

Axinite crystallizes in the triclinic system (pinacoidal class), with
a: b : £=.4921 : 1 : .4797 and a=82° 54', 0=91° 52', 7=131° 32'.
The crystals are extremely varied in habit but nearly all are somewhat
tabular parallel to 'P(iii), ooP'(no) or 00 'P(iTo). About 45 forms
have been observed. In addition to the three mentioned, 2'P' 06 (201),
P'(ui), /P(iFi), 2/P' 06 (021), 00 P 06 (010) and 00 P 00 (100) are the most
frequently met with (Figs. 188, 189). The plane 'P(iTi) is usually
striated parallel to its intersection with 00 'P(iTo). The angle 100 A 1T0
= 15° 34'. The cleavage is indistinct parallel to ooP'(no) and the
crystals are strongly pyro electric.

Axinite is brownish, gray, green, bluish or pink, and is strongly pleo-
chroic in pearl-gray, olive-green and cinnamon-brown tints. It is

346

DESCRIPTIVE MINERALOGY

transparent or translucent and has a glassy luster and a colorless streak.
Its fracture is conchoidal or uneven. It is brittle, has a hardness of 6-7
and a density of 3.3. For red light, a= 1.6720, 0= 1.6779, 7 = 1.6810.

Axinite, before the blowpipe, exfoliates and fuses to a dark green
glass which becomes black in the oxidizing flame. It colors the flame
green, especially upon the addition of KHSO4 and CaF2 to its powder.
Its powder reacts alkaline. It is only slightly attacked by acids. After

Fig. 188.

Fig. 189.

Fig. 188. — Axinite Crystal with 00 Poo, 100 (a); 2'P'oo, 201 (5); 00 p/f no (f»);

00 ,'P, 1T0 (M); P', in (*) and 'P, 1T1 (r).
Fig. 189. — Axinite Crystal with M , m, a, r and s as in Fig. 188. Also 00 P 00 ,

010 (b); 2P' » , 021 (y); ,P, In (e); §^3, 132 (<?); 4,P*5, 241 (0); 3JP3, T31 (F);

00 /FX x30 (w); 3'PX 131 (») and 4'Pl, 241 (d).

fusion, however, it dissolves readily with the production of gelatinous
silica.

The mineral is easily characterized by its crystallization and the
green color it imparts to the flame.

It has not been produced artificially.

Pseudormorphs of chlorite after axinite have been found in Dart-
moor, England.

Occurrence. — Axinite crystals occur in cracks in old siliceous rocks.
It is found also in ore veins and. as a component of a contact rock com-
posed mainly of augite, hornblende and quartz, occurring near the
peripheries of granite and diabase masses. It was formed by the aid
of pneumatolytic processes.

Localities. — Excellent crystals of axinite are found at Andreasberg
and other places in the Harz Mts.; near Striegau, in Silesia; near
Poloma, in Hungary; at the Piz Valatscha, in Switzerland; near Vernis
and at other points in Dauphine, France; at Botallak, Cornwall, Eng-
land; at Konigsberg, Norway; Nordmark, Sweden; Lake Onega, and
Miask, Russia; at Wales in Maine and at South Bethlehem, Penn.

ANHYDROUS ORTHOSILICATES 347

Dioptase (H2CuSi04)

Dioptase is especially interesting because of its crystallization, which
is rhombohedral tetartohedral (trigonal rhombohedral class). Its crys-
tals are columnar. Their axial ratio is i : .5342. They are usually

bounded by 00 P2(ii2o), — 2R(o22i) or R(ioii) and — — — - (1341) or

4P4 r - * r

+ (3141) (a rhombohedron of the third order, Fig. 190). Besides

4 J

occurring as crystals the mineral is found also
massive and in crystalline aggregates.

The composition expressed by the formula
given above is Si02=38.i8; CuO= 50.40;
H20= 11.44, which is approached very closely
by some analyses. The same composition may
be expressed by CuSiOa'JfeO. Indeed, recent
work indicates that the mineral is a hydrated
metasilicate and not an acid orthosilicate. Fig. 190.— Dioptase Crys-

Dioptase has an emerald-green or blackish **! with *P2» x«° and

green color, a glassy luster and a green streak. ~~ ' °221 ^'' "^ a
Ta . A A , , . - Rhombohedron o£ the

It is transparent or translucent, is brittle 3rd Qrder Indicated by

and its fracture is uneven or conchoidal. Its striations.

hardness is 5 and its density 3.05. It is weakly

pleochroic and is distinctly pyroelectric. For yellow light, «= 1.6580,

€=1.7079.

Before the blowpipe dioptase turns black and colors the flame green.
On charcoal it turns black in the oxidizing flame and red in the reducing
flame without fusing. It is decomposed by acids with the production of
gelatinous silica.

Synthesis. — Crystals of dioptase have been made by allowing mix-
tures of copper nitrate and potassium silicate to diffuse through a sheet
of parchment paper.

Occurrence and Localities. — The mineral occurs in druses on quartz
in clefts in limestone, and in gold-bearing placers in the Altyn-Tiibe Mt.
near the Altyn Ssu River, in Siberia; in crystals on wulfenite and cala-
mine and embedded in clay near R6zbanya, Hungary; with quartz and
chrysocolla in the Mindonli Mine, French Congo; in copper mines at
Capiapo, Chile; and in Peru; at the Bon Ton Mines, Graham Co.,
Ariz.; and near Riverside, Pinal Co., in the same State. In the Bon
Ton Mines it covers the walls of cavities in the ore, which consists of a
mixture of limonite and copper oxides.

348

DESCRIPTIVE MINERALOGY

MICA GROUP

The mica group comprises a series of silicates that are characterized
by such perfect cleavages that extremely thin lamellae may be split
from them with surfaces that are perfectly smooth. The lamellae are
elastic and in this respect the members of the group are different from
other minerals that possess an almost equally perfect cleavage. Some
of the micas are of great economic importance, but most of them have
found little use in the arts.

The micas may be divided into four subgroups, (i) the magnesium-
iron micas, (2) the calcium micas, (3) the lithium-iron micas, and (4)
the alkali micas. Of the latter there are three subdivisions, (a) the
lithia micas, (b) the potash micas, and (c) the soda micas.

All the micas crystallize in the monoclinic system (monoclinic pris-
matic class), in crystals with an orthorhombic or hexagonal habit.

In composition the micas are complex. The alkali micas are ap-
parently acid orthosilicates of aluminium and an alkali — the potash
mica being KH2Al3(Si04)3. Other alkali micas are more acid, and
some of the magnesium-iron micas are very complex. The members
with the best established compositions are apparently salts of orthosilicic

acid, and, hence, the entire group is placed
with the orthosilicates.

All the micas possess also, in addition to
the very noticeable cleavage which yields
the characteristically thin lamellae that are
so well known, other planes of parting
which are well exhibited by the rays of
the percussion figure (Fig. 191). The
largest ray — known as the characteristic
ray — is always parallel to the clinopinacoid.
In some micas the plane of the optical
axes is the clinopinacoid and in others is
perpendicular thereto. In the latter, known
as micas of the first order, the plane of
the axes is perpendicular to the characteristic ray and in the former,
distinguished as micas of the second order, it is parallel to this ray.

The value of the optical angle varies widely. In the magnesia micas
it is between o° and 150, in the calcium micas between roo° and 1200,
and in the other micas between 550 and 750. When the angle becomes
zero the mineral is apparently uniaxial. But etch figures on all micas
indicate a monoclinic symmetry (compare Fig. 194).

Fig. 191. — Percussion Figure
on Basal Plane of Mica.
The long ray is parallel to
00 P ob (010).

ANHYDROUS ORTHOSILICATES

349

THE MAGNESIUM-IRON MICAS

Biotite ((K-H)2(Mg-Fe)2(Al-Fe)2(Si04)3)

The magnesium-iron micas are usually designated as biotite. This
group includes micas of both orders as follows:

ist Order
Anomite

2d Order
Meroxene
Lepidomelane
Phlogopiie

The crystals of biotite have an axial ratio .5774 : 1 : 3.2904 with
0= 900. They are usually simple combinations of oP(ooi), 00 P 00 (010),
— JP(ii2) and P(Tn) (Fig. 192). Twins are
common, with the twinning plane perpendic-
ular to oP(ooi). The composition face may
be the same as the twinning plane or it may be
oP(ooi) (Fig. 193). The crystals have an
hexagonal habit, the angle In A 010 being
6o° 2 2 J'. The mineral also occurs in flat
scales and in scaly aggregates.

The color of biotites varies from yellow,
through green and brown to black. Pleochroism is strong in sections
perpendicular to the perfect cleavage, i.e., perpendicular to oP(ooi).
The streak of all varieties is white. Their hardness =2.5 and density
2-7~3«I> depending upon composition. The refractive indices for yellow

Fig. 192. — Biotite
with oP, 001 (c)\
010 (b); P, In
-IP, 112 (*).

Crystal
00P00,

(ju) and

\ A \

I - )

Fig. 193. — Biotite Twinned about a Plane Perpendicular to oP (001), and Parallel
to the Edge Between oP(ooi) and — 2P(22i). The composition plane is
oP(ooi). Mica law. A = right hand twin, B and C = left hand twins.

light in a light brown biotite from Vesuvius are: a=i.54i2, 0= 1.5745.
They are higher in darker varieties.

Etch figures are produced by the action of hot concentrated sulphuric
acid.

Varieties and their Localities. — Anomite is rare. It occurs at Green-
wood Furnace, Orange Co., N. Y., and at Lake Baikal, in Siberia.

350 DESCRIPTIVE MINERALOGY

Merozene is the name given to the common biotite of the 2d order.
It occurs in particularly fine crystals in the limestone blocks included
in the lava of Mte. Somma, Naples, Italy; at various points in Switzer-
land, Austria and Hungary; and at many other points abroad and in
this country.

Lepidomelane is a black meroxene characterized by the presence
in it of large quantities of ferric iron. It is essentially a magnesium-free
biotite. It occurs in igneous rocks, especially those rich in alkalies.
Two of its best known occurrences in the United States are in the nephe-
line syenite at Litchfield, Maine, and in a pegmatite in the northern part
of Baltimore, Md.

Phlogopite, or amber mica, is the nearly pure magnesium biotite
which by most mineralogists is regarded as a distinct mineral, partly
because in nearly all cases it contains fluorine. Its color is yellowish
brown, brownish red, brownish yellow, green or white. Its luster is
often pearly, and it frequently exhibits asterism in consequence of the
presence of inclusions of acicular crystals of rutile or tourmaline arranged
along the rays of the pressure figure. Its axial angle is small, increasing
with increase of iron. Its refractive indices are: a= 1.562, 0= 1.606,
7=1.606.

Phlogopite is especially characteristic of metamorphosed limestones.
It occurs abundantly in the metamorphosed limestones around Easton,
Pa.; at Edwards, St. Lawrence Co., N. Y., and at South Burgess,
Ontario, Canada. It is also found as a pyrogenetic mineral in certain
basic igneous rocks.

Typical analyses of the four varieties of biotite follow:

I II in IV

Si02 40.81 35.79 32.35 39.66

Ti02 3-51 tr. .56

AI2O3 16.47 x3-7° *7-47 17.00

Fe2C>3 2.16 4.04 24.22 .27

FeO 5.92 1709 13. n .20

MnO .40 1.20

CaO 1.48

BaO .33 .62

MgO 21.08 9.68 .89 26.49

Na20 1.55 -45 7-°° -6°

ANHYDROUS ORTHOSILICATES 351

I II III IV

K2O 9.01 8.20 6.40 9.97

H20— \ .90 \ .66

H20+ ) 2I9 3^6 I4"67 2.33

F .10 2 . 24

Total

(lessO=F) 99.19 99 .91 100.83 99.66

I. Anomite from Greenwood Furnace, Orange Co., N. Y.
II. Meroxene from granite, Butte, Mont.

III. Lepidomelane from eleolite syenite, Litchfield, Maine.

IV. Brown phlogopite from Burgess, Can.

Before the blowpipe the dark, ferruginous varieties fuse easily to a
black glass; the lighter colored varieties with greater difficulty to a
yellow glass. Their powder reactions are strongly alkaline. The
minerals are not attacked by HC1 but are decomposed by strong
H2SO4. In the closed tube all varieties give a little water.

The biotites are distinguished from all other minerals except the other
micas by perfect cleavage and from other micas by their color, solubility
in strong sulphuric acid and pleochroism.

The commoner alteration products of biotite are a hydrated biotite,
chlorite (p. 428), epidote, sillimanite and magnetite, if the mica is
ferriferous. At the same time there is often a separation of quartz.
Phlogopite alters to a hydrophlogopite and to penninite (p. 429), and
talc (p. 401).

Syntheses. — The biotites are common products of smelting operations.
They have been made by fusing silicates of the proper composition with
sodium and magnesium fluorides.

Occurrences and Origin. — The biotites are common constituents of
igneous and metamorphic rocks and pegmatite dikes. They also are
common alteration products of certain silicates, such as hornblende
and augite. They are present in sedimentary rocks principally as the
products of weathering.

Uses. — Phlogopite is used as an insulator in electrical appliances
and to a less extent for the same purposes as those for which ground
muscovite is employed. No " amber mica " is produced in the
United States. Most of that used in this country is imported from
Canada.

352 DESCRIPTIVE MINERALOGY

THE CALCIUM MICAS

Margarite (Ca(A10)2(A10H)2(Si04)2)

Margarite, the calcium mica, is like biotite in the habit of its crys-
tals, which, however, are not so well formed as these. Usually the min-
eral occurs in tabular plates with hexagonal outlines but without side
planes. It occurs also as scaly aggregates.

Analyses of specimens from Gainsville, Ga. (I), and Peekskill, N. Y.
(II), gave:

Si02

AI2O3

FeO

MgO

CaO

Na20

H20

Total

I. 31.72

50 03

• • m m

.12

"•57

2.26

4.88

100.58

II- 32-73

46.58

512

1. 00

11.04

• • • •

449

100.96

The mineral has a pearly luster on its basal planes, and a glassy luster
on other planes. Its color is white, yellowish, or gray and its streak
white. It is transparent or translucent. Its cleavage is not as perfect
as in the other micas, and its cleavage plates are less elastic. Its hard-
ness varies from 3 to over 4 and its density is 3. It is a mica of the
first order.

Before the blowpipe it swells, but fuses with great difficulty. It
gives water in the closed tube and is attacked by acids.

Occurrence. — Margarite is associated with corundum. It is also
present in some chlorite schists. In all cases it is of metamorphic origin.

Localities. — It occurs in the Zillerthal, Tyrol; at Campo Longo, in
Switzerland; at the emery localities in the Grecian Archipelago; at
the emery mines near 'Chester, Mass.; in schist inclusions in mica
diorite at Peekskill, N. Y.; with corundum at Village Green, Penn.;
at the Cullakenee Mine, in Clay Co., N. C; and at corundum local-
ities in Georgia, Alabama and Virginia.

THE LITHIUM-IRON MICAS

Zinnwaldite ((Li- K Na)3FeAl(Al(F- OH))2Si5Oi6)

The principal lithium-iron mica, zinnwaldite, is a very complex
mixture that occurs in several forms so well characterized that they have
received different names. All of them contain lithium, iron and fluorine,
but in such different proportions that it has not been possible to ascribe
to them any one generally acceptable formula. Some of the most im-
portant of these varieties have compositions corresponding to the fol-
lowing analyses:

ANHYDROUS ORTHOSILICATES 353

i n m iv

Si02 4019 59-25 5*46 45-87

AI2O3 22.79 12.57 16.22 22.50

Fe203 I9-78 2.21 .66

FeO .93 7.66 11. 61

MnO 2.02 .06 1.75

Na20 7 . 63 .95 .42

K20 7.49 5 37 IO-65 10.46

Li20 3.06 904 4-83 3.28

F 3-99 7-32 744 7-94

Total.. 99.32 102. 11 102.71 105.48

—0=F=.. 9764 9905 99.60 102.15

I. Rabenglimmer from Altenberg, Saxony. Greenish black with greenish gray

streak. Sp. gr. =3.146-3.190.
II. Polylithionite from Kangerluarsuk, Greenland. White or light green plates.
Sp. gr. = 2.81.

III. Cryophyllite from Rockport, Mass. Strongly pleochroic green and brown-

ish red crystals. Sp. gr. = 2.000. Contains also .17 MgO and 1.06 HjO.

IV. Zinnwaldite from Zinnwald, Bohemia. Plates, white, yellow or greenish
gray. Sp. gr. = 2.956-2.987. Contains also .91 H20 and .08 PiO*

Zinnwaldite occurs in crystals with an axial ratio very near that
of biotite, and a tabular habit. Twins are like those of biotite with
ooP(no) the twinning plane.

It has a pearly luster, is of many colors, particularly violet, gray,
yellow, brown and dark green and is strongly pleochroic. Its streak is
light, its hardness between 2 and 3 and its density between 2.8 and 3.2.
It is a mica of the second order.

Before the blowpipe it fuses to a dark, weakly magnetic bead. It is
attacked by acids.

Occurrence and Localities. — Zinnwaldite is found in certain ore veins,
in granites containing cassiterite, and in pegmatites. Its origin is as-
cribed to pneumatolytic processes. Its principal occurrences are those
referred to in connection with the analyses.

THE ALKALI MICAS

The alkali micas include those in which the principal metallic con-
stituents besides aluminium are lithium, potassium and sodium. All
these metals are present in each of the recognized varieties of the
alkali micas, but in each variety one of them predominates. That in
which lithium is prominent is known as lepidolite; that in which potas-

354 DESCRIPTIVE MINERALOGY

sium is most abundant is muscovite; and that in which sodium is
most prominent is paragoniie. Muscovite is common. Lepidolite is
abundant in a few places. Paragonite is rare. The first two are im-
portant economically. All are micas of the first order, except a few
lepidolites, and all are light colored.

Another mica, which is usually regarded as a distinct variety of
muscovite, or, at any rate, as being very closely related to the mineral
is roscoelite. In this, about two-thirds of the AI2O3 in muscovite is
replaced by V2O3. It is a rare green mica which is utilized as an ore
of vanadium.

Lepidolite ((Li-K.Na)2((Al-Fe)OH)2(Si03)3)

Lepidolite occurs almost exclusively as aggregates of thin plates
with hexagonal outlines. Crystals are so poorly developed that a satis-
factory axial ratio has not been determined. Its variation in composi-
tion is indicated by the analyses of white and purple varieties from
American localities.

in III IV

Si02 51S2 49-52 51-12 5125

AI2O3 25 . 96 28 . 80 22 . 70 25 . 62

Fe2C>3 .31 40 .80 .12

FeO undet. .24 .00

MnO .20 .07 i-34* 05

MgO .02 .02 .00

CaO 16 .13 tr.

Li20 4.90 3.87 5.12 . 4.31

Na20 1.06 .13 2.28 1.94

K2O 1 1. 01 8.82 10.60 10.65

Rb20 3.73

Cs20 .08

F 5.80 5.18 6.38 7.06

H2O .95 1.72 2.05 1.60

Total

(lessO=F) 99.45 100.53 99 74 99 -63

I. Lilac-purple granular lepidolite from Rumford, Maine.
II. White variety from Norway, Maine.

III. Red-purple variety from Tourmaline Queen Mine, Pala, Cal. Contains

also .04 P2O6.

IV. White variety from Pala, Cal.

* Mn2Os.

■■■«•

ANHYDROUS ORTHOSILICATES 355

The mineral is white, rose or light purple, gray or greenish. The
rose and purple varieties contain a little manganese. The streak
of all lepidolites is white, their luster* pearly, their hardness 2.5-4
and density 2.8-2.9. The refractive indices of a typical variety are:
0=1.5975, 7=1.6047.

Lepidolite fuses easily to a white enamel and at the same time colors
the flame red. It is difficultly attacked by acids, but after heating is
easily decomposed.

Cookeitc from Maine and California is probably a weathered lepido-
lite. Its analyses correspond to the formula, Li (Al (011)2)3 (Si03)2.

Occurrence, — The mineral occurs principally in pegmatites in which
rubellite (p. 435), and other bright-colored tourmalines exist and on
the borders of granite masses and in rocks adjacent to them. It is
often zonally intergrown with muscovite. In all cases it is probably a
pneumatolytic product, or, at least, is produced by the aid of magmatic
emanations.

Localities. — The mineral occurs in nearly all districts producing tin,
and also in those producing gem tourmaline. Its best known foreign
localities are Jekaterinburg, Russia; Rozna, Moravia; Schnittenhofen,
Bohemia; and Penig, Saxony. In the United States it is found in large
quantities at Hebron, Paris, and other points in western Maine; in the
tin mines of the southern Black Hills, South Dakota, and in the tourma-
line localities in the neighborhood of Pala, San Diego Co., Cal.

Uses. — Lepidolite is utilized to a slight extent in the manufacture of
lithium compounds, which are employed in the preparation of lithia
waters, medicinal compounds, salts used in photography and in the
manufacture of fireworks and storage batteries.

Muscovite (H2(K-Na)Al3(Si04)3)

Muscovite is one of the most common, and at the same time the
most important, of the micas. Because of its transparency it is em-
ployed for many purposes for which the darker biotite is not suitable.

While predominantly a potash mica, nearly all muscovite contains
some soda, due to the isomorphous mixture of the paragonite molecule.
Two typical analyses are quoted below:

SiQi AI2O3 Fe»0, FeO MnO MgO CaO Na«0 K20 HtO F Total

I. 44-39 35-70 109 1.07 tr ... .10 2.41 9.77 5.88 .72 101.13

II. 46.54 34-96 1-59 32 ••■ -4i 10.38 5.43 99.63

I. Broad plates of muscovite bordered by lepidolite, Auburn, Maine.
II. Greenish muscovite, Auburn, Maine. Total less O = F is 100.83.

356

DESCRIPTIVE MINERALOGY

The crystals are usually tabular and frequently orthorhombic or
hexagonal in habit, though the etch figures on their basal planes reveal
clearly their monoclinic symmetry (Fig. 194). If orientated to corre-
spond with crystals of biotite their axial constants are: a : b : £=.5774
: 1 : 3.3128, 18=89° 54', and their principal planes oP(ooi), 00 P 00 (010)
|Pob (023), 4P(44i) and -2P(22i) (Fig. 195).

Twins like those of biotite are not uncommon in some localities.

Muscovite is colorless or of some light shade of green, yellow or red.
It has a glassy luster, a perfect cleavage parallel to the base, a hardness
of 2 and a density of 2.76-3.1. Pleochroism is marked in directions
perpendicular and parallel to the cleavage, the color of the crystals,
when viewed in the direction perpendicular to the cleavage being lighter

Fig. 194. Fig. 195.

Fig. 194. — Etch Figures on oP(ooi) of Muscovite, Exhibiting Monoclinic Symmetry.

Fig. 195. — Muscovite Crystal with — 2P, 221 (M); oP, 001 (c); 00 Poo, 010 (6),

and §Pob , 023 (e).

than when viewed parallel to the cleavage. The optical angle is com-
paratively large (s6°-76°), in this respect being very different from that
of biotite which is small (2°-22°). The mineral is a nonconductor
of electricity at ordinary temperatures and a poor conductor of heat.
Its refractive indices vary somewhat with composition. For yellow light
intermediate values are as follows: a= 1.5619, 0= 1.5947, 7= 1.6027.

Before the blowpipe thin flakes of muscovite fuse on their edges to a
gray mass. In the closed tube the mineral yields water which, in some
cases, reacts for fluorine. It is insoluble in acids under ordinary con-
ditions, but is decomposed on fusion with alkaline carbonates.

Muscovite is very stable under surface conditions. Its principal
change is into a partially hydrated substance, which may be called
hydromuscovite. It alters also into scaly chloritic products, into
steatite (p. 401), and serpentine (p. 398).

ANHYDROUS ORTHOSILICATES 357

Damourite is a dense fine-grained aggregate of muscovite, often
forming pseudomorphs after other minerals.

Sericite is a yellowish or greenish muscovite that occurs in thin,
curved plates in some schists.

Fuchsite is a chromiferous variety of an emerald-green color from
Schwarzenstein, Tyrol.

Synthesis. — Crystals of muscovite have been made by fusing anda-
lusite with potassium fluo-silicate and aluminium fluoride.

Occurrence. — Muscovite occurs in large, ill-defined crystals in peg-
matites, and in smaller flakes in granites and other acid igneous rocks,
in some sandstones and slates and in various schists and other meta-
morphic rocks. It is found also in veins. It is in some cases an orig-
inal pyrogenic mineral, in other cases a metamorphic mineral and in
still other cases a secondary mineral resulting from the alteration of
alkaline aluminous silicates.

Localities. — The mineral occurs in all regions where pegmatites and
acid igneous rocks exist. It is mined in North Carolina, South Dakota,
New Hampshire, Virginia and other states. While phlogopite (amber
mica) is produced in some countries all the mica produced in this country
is of the muscovite variety.

Uses. — Muscovite is used in two forms, (i) as sheet mica, and (2)
as ground mica. The sheet mica comprises thin cleavage plates cut
into shapes. It is used in making gas-lamp chimneys, lamp shades, and
windows in stoves. The greater portion is used as insulators in
electrical appliances, though for some forms of electrical apparatus the
amber mica is better. Because of the comparatively high cost of large
mica plates, small plates are sometimes built up into larger ones. The
ground mica consists of small crystals and the waste from the manu-
facture of sheet mica ground very fine. It is used in the manufacture
of wall paper, heavy lubricants and fancy paints. It is also mixed with
shellac and melted into desired forms for electrical insulators.

Production. — The total value of the mica produced in the United
States during 191 2 was $355,804, divided as follows: 1,887,201 lb. sheet
mica, valued at $310,254 and 3,512 tons ground mica, valued at $45,550.
Of this North Carolina produced 454,653 lb. of sheet mica, valued at
$187,501 and 2,347 tons of scrap mica, valued at $29,798, or a total
value for both kinds of mica of $217,299. The imports of sheet mica
during the same year amounted to $502,163, of which 241,124 lb.,
valued at $155,686 was trimmed and the balance untrimmed. The
imports during 191 2 were valued at $748,973, and the domestic produc-
tion at $331,896.

358 DESCRIPTIVE MINERALOGY

Roscoelite may be regarded as a muscovite in which a large portion
of the AI2O3 has been replaced by V2O3. A specimen from Lotus, Eldo-
rado Co., Cal., gave:

S1O2 TiO, A1A VA FeO MgO K,0 H,0- H£>+ Total
45.17 .78 n.54 24.01 1.60 1.64 10.37 .40 4.29 99.80

besides traces of Li20 and Na20.

The mineral occurs as clove-brown or green scales with a specific
gravity of 2.92-2.94. It is translucent and has a pearly luster and a
strong pleochroism. Its refractive indices for sodium light are : a = 1 .6 io,
0= 1.685, 7=1.704.

Before the blowpipe it fuses to a black glass. It gives the usual
reactions for vanadium in the beads and is only slightly affected by
acids. It has been found associated with gold in small veins near Lotus,
Eldorado Co., California, in seams composed of roscoelite and quartz
between the beds of a sandstone in the high plateau region of south-
western Colorado, and as a cement of minute scales between the grains
of the sandstone on both sides of the seams. In all cases it appears to
have been deposited by percolating water, possibly of magmatic origin.

The impregnated sandstone is mined as a source of vanadium. The
material, which contains an average of about 3 per cent of metallic
vanadium is concentrated by chemical processes, and the concentrates
are manufactured into ferro-vanadium. Most of the vanadium pro-
duced in the United States is made from this ore.

Paragonite (H2(Na-K)Al3(Si04)3)

Paragonite, the sodium mica, differs from muscovite mainly in com-
position. Both contain sodium and potassium but in paragonite the
sodium molecule is in excess.

The analysis quoted below is made on a sample from Monte Cam-
pione, in Switzerland.

Si02 AI2O3 Fe203 Na20 K20 H20 Total

47.75 4°i° tr. 6.04 1. 12 4.58 99. 59

It occurs in the same associations as some forms of muscovite but it
is much less common. It apparently occurs most abundantly in certain
fine-grained mica schists to which the name paragonite schists has been
given. It is in all known cases a product of dynamic metamorphism.

CHAPTER XVn
THE SILICATES— Continued

THE ANHYDROUS METASILICATES •

NORMAL METASILICATES

Beryl (BeaAfcCSiC^e)

Beryl is a frequent constituent of coarse-grained granites. It is
important as a gem material, and is particularly interesting because of
the many physical investigations that have been made with the aid of its
crvstals.

Although the mineral is essentially a beryllium aluminometasilicate,
it usually contains also a little Fe20a and MgO, in many cases small
quantities of the alkalies, and in some cases also caesium. Analyses of
a green beryl from North Carolina, an aquamarine from Stoneham, Me.,
and a light-colored crystal from Hebron are given below.

SiCfe AI2O3 Fe203 BeO FeO Na20 LijjO Cs20 H20 Total

14. 11 100.00

13.61 .22 .83 99-54

13.73 ••• -71 2-GI IOO-39

11.36 .38 1. 13 1.60 3.60 2.03 100.30

I. Theoretical.
II. Alexander Co., N. C.

III. Stoneham, Me.; also .06% CaO.

IV. Hebron, Me.

The mineral occurs massive without distinct crystal form and also in
granular and columnar aggregates, but its usual method of occurrence is
in sharp and, in some cases, very large columnar crystals with a distinct
hexagonal habit (dihexagonal bipyramidal class), and an axial ratio
1 : .4989. The forms found on nearly all crystals are 00 P(ioTo),
ooP2(ii2o), oP(oooi), P(ioTi), P2(ii22) and 2P2(ii2i) (Fig. 196).
In addition, there are present on many crystals other prismatic forms
and the pyramids 3PK2131) and 2P(202i). Other crystals are highly

359

I. 66.84

19-05

■ • •

II. 66 . 28

18.60

■ ■ •

III. 65.54

17-75

.21

IV. 62.44

17-74

.40

360

DESCRIPTIVE MINERALOGY

modified (Fig. 197), the total number of forms that have been identified
approximating 50. The angle 10T1 AoiTi = 28° 55'. Some crystals
are very large, measuring 2 to 4 feet in length and 1 ft. in diameter.

Beryl has a glassy luster. It is transparent or translucent. It is
colorless or of some light shade of green, red, or blue. Its streak is
white, hardness 7-8 and density 2.6-2.8. Its cleavage is very imperfect
but there is frequently a parting parallel to the base. Pleochroism is
noticeable in green and blue crystals. Its refractive indices for yellow
light at 200 are: w= 1.5740, €= 1.5690. They become greater with increas-
ing temperature.

Before the blowpipe colorless varieties become milky, but others are

Fig. 196. Fig. 197.

Fig. 196.— Beryl Crystals with 00 P, 10T0 (m); oP. 0001 (c); 00 P2, 11 20 (a); P,

10T1 (p) and 2P2, 1121 (s).

Fig. 197.— Beryl Crystal with tn, c, p and s as in Fig. 196. Also 2P, 2021 Ga) and

3P|, 2131 (v).

unchanged except at very high temperatures when sharp edges are fused
to a porous glass. The mineral is not attacked by acids.

Beryl is distinguished from apatite, which it much resembles, by its
greater hardness.

It alters to mica and kaolin (p. 404).

Syntheses. — Beryl crystals have been formed by long heating of
Si02, AI2O3 and BeO in a melt of the molybdate or vanadate of lithium,
and by precipitating a solution of beryllium and aluminium sulphates
with sodium silicate and heating the dried precipitate with boric acid
in a porcelain oven.

Occurrence, — The mineral occurs as an accessory constituent in peg-
matites and granites, in crystalline schists, especially mica schists and

ANHYDROUS METASILICATES 361

gneisses, in ore veins and sometimes in clay slates and bituminous lime-
stones.

Uses. — The transparent varieties' are utilized as gems, under the
following names:

Emerald is a deep green variety, the color of which is probably

due to O2O3,

Aquamarine, a blue-green variety,

Golden beryl, a topaz-colored variety,

Blue beryl, a blue variety, and

While beryl, a colorless variety.

Localities. — Crystals of ordinary beryl occur at Striegau, Silesia; in
the cassiterite veins near Altenberg, in Saxony; in the granite dikes near
S. Piero, Elba; in the Mourne Mts., at Down, Ireland; at various points
(especially near Jekaterinburg), in Ural, Russia, and in North America,
in the mountain counties of North Carolina; at Mt. Antero, Colo.; at
Peiperville, Perm.; in granite veins at Haddam, Conn., at Acworth,
N. H., and at Norway, Hebron, and other points in western Maine.
Much of the beryl of Maine is the variety containing caesium.

The finest emeralds are found in geodes, and embedded in a clay
slate at the Muso Mine, Colombia, New Grenada; but fine gem mate-
rial occurs also at Zabara, near the Red Sea; Habachthal, Tyrol; Glen,
New South Wales, and in Brazil, Hindustan and Ceylon. The finest
aquamarines come from Siberia.

The most important beryl mines in the United States are in pegma-
tites in Cleveland, Burke and Macon Counties, N. C. Aquamarine,
golden beryl and the more usual varieties occur at Walker Knob, Burke
Co., and on Whiterock Mt. in Macon Co., but those at the first-named
locality are not clear enough to furnish gems. Near Clayton, Ga., a
pegmatite contains large bluish and yellowish green beryls, some of which
yield gem material. The finest aquamarine ever found in the United
States was from Stoneham, Me. Near Shelby, Cleveland Co., and at
Crabtree Mountain, Mitchell Co., in North Carolina, genuine emeralds
occur in a pegmatite that cuts basic rocks. Fine emeralds have also
been mined at Stony Point, N. C, Haddam, Conn., andTopsham, Me.

Production. — The total yield of emerald from North Carolina during
191 2 was about 2,969 carats, valued at $12,875 in the rough. The
average value of the cut stone was $25 per carat, but some especially
fine gems from the Shelby locality were valued at $200 per carat. There
were also produced in the United States during this year other varieties
of beryl, valued at $1,765.

362 DESCRIPTIVE MINERALOGY

Leucite (K2Al2(Si03)4)

Leucite occurs almost exclusively in what are apparently simple
isometric crystals, but which are actually polysynthetic twins of a doubly
refracting substance. At 500 ° and above, leucite substance is isometric.
It separates from molten magmas as isometric crystals, which, upon
further cooling, become twinned. The twinning is revealed by striation
on the crystal faces. The substance is, therefore, dimorphous.

Theoretically, leucite is a potassium aluminium metasilicate, but
most natural crystals contain some soda and many contain small quan-
tities of calcium. The calculated composition of the pure molecule and
the actual composition of two natural crystals are shown below.

Si02 AI2O3 CaO Na20 K20 H20 Total

Calculated 5502 23.40 21.58 100.00

Mt* Vesuvius . . 55.28 24.08 60 20.79 ••• IOO-75

Mt. Vulture. .. . 54. 94 25.10 1.80 1.23 15.18 2.13 100.38

The mineral occurs in icositetrahedrons, 202(211), in some cases
modified by 00 0(i 10) and 00 O 00 (100). Twinning parallel to 00 0(i 10)
is common, but often the twins are polysynthetic and are recognizable
only by striations on the crystal faces. The twinning lamellae are
anisotropic, as shown by their optical properties, but at 5000 the twin-
ning disappears and the crystals become completely isotropic through-
out.

Leucite is glassy in luster and colorless, white or light gray in color.
It is transparent or translucent and has a white streak. Its cleavage is
imperfect parallel to 00 O(no), and its fracture is conchoidal or uneven.
It is brittle. Its hardness is 5-6 and density 2.5. Its indices of refrac-
tion approximate 1.508.

Before the blowpipe leucite is infusible. It is soluble in HC1 with
the production of pulverulent silica. Its powder reacts strongly alka-
line.

It is distinguished from other minerals by its crystallization, by the
violet color it imparts to the flame and its reaction toward HC1. It is
most apt to be confused with analcile (p. 458) and colorless garnet. It
is distinguished from the latter by its inferior hardness and from the
former by its infusibility and failure to yield water when heated in the
glass tube below red heat. Analcite, moreover, fails to give the flame
test for potash.

The mineral alters quite readily into analcite and some other zeolite,
into a mixture of orthoclase and nepheline, or into orthoclase (p. 413)

ANHYDROUS METASILICATES

363

and muscovite, or into orthoclase alone. Its final alteration product is
kaolin.

Syntheses. — Its crystals have been obtained by fusing its constituents,
and also by melting a mixture of SiCte, potassium aluminate and vana-
date, and by fusing a mixture of Si02 and AI2O3 with an excess of KF.

Occurrence. — It occurs only in igneous rocks, especially in lavas low in
silica and high in potash, and in the plutonic rock known as missourite.
In some old rocks it is represented by its alteration products. In all
cases it is a primary mineral.

Localities. — Leucite is an essential constituent of the lavas in the
Kaiserstuhl, Baden; in Rhenish Prussia; near Wiesenthal, Saxony;
in the Siebenburger, Bohemia; at Vesuvius, Italy; in the Leucite Hills,
and other places in Wyoming, and at several places in Montana; at
Magnet Cove, Ark., and near Hamburg, N. J.

Uses. — It is suggested that the large masses of leucite rocks in the
Leucite Hills be used as a source of potash. On the assumption that
the rocks at this place contain 10 per cent of K2O it is estimated that
the total quantity of potash in them amounts to about 200,000,000 tons.

THE AMPHIBOLOIDS

The amphiboloids embrace a large number of minerals, some of
which are extremely important as rock components. Economically,

A'VX"." ■.:::'. y.
yy.- "-VX- • • .•.*.'.".■■ f •

X ;*//<>.,...'...> ■>•:' y;/->y\ilO

tW.v '• :..■■■ y-"sy

100

Fig. 198. — Cross-Sections of Pyroxene (A) and Amphibole (B) Crystals Illustrating

Differences in Intersections of Cleavages.

they have little value. Several are used in the arts, but only to a com-
paratively slight extent. Apparently they crystallize in the orthorhom-
bic, monoclinic and triclinic systems.

The amphiboloids are divisible into two groups, the pyroxenes and
the amphiboles, which differ from one another in the ratio between their

364 DESCRIPTIVE MINERALOGY

a and b axes. In the pyroxenes this ratio is nearly i . i, while in the
amphiboles it is approximately 2:1. The angle between the prismatic
planes («>P, no) on the former is nearly equal (870 and 93 °), and on
the latter very unequal (56°-i24°). Since, moreover, in all members of
both groups there is a distinct cleavage parallel to the unit prism, the
angles of intersection of the cleavage planes in the pyroxenes and in the
hornblendes are also different. This difference in prismatic and cleav-
age angles of the two groups serves readily to distinguish between them

(Fig. 198).

The pyroxenes appear to be the more stable at high temperatures
and the amphiboles under high pressures. Thus pyroxenes are more
common than the amphiboles in lavas and amphiboles more common
than pyroxenes in crystalline schists.

Chemically, the amphiboloids are metasilicates ot Na, Li, Mg, Ca,
Fe, Mn, Zn and Al, or isomorphous mixtures of these metasilicates with
one another and with an orthosilicate of the general composition rep-
resented by (Mg- Fe)((Al- Fe)0)2Si04.

THE PYROXENES
(R'SiO,, R'AI(SiO,)a and R^R^OsSiOj

The pyroxenes occur very widely spread as constituents of igneous
rocks, and in veins that have been filled by igneous processes. Some
members of the group are also common metamorphic products. Although
crystallizing in different systems their crystals possess a certain family
resemblance, expressed best in their horizontal cross-sections, which
have a nearly orthorhombic symmetry, i.e., they are nearly symmetrical
about two planes at right angles to one another, passing through the
a and b axes, which are nearly equal. The most perfect cleavage of all
the pyroxenes is parallel to ooP(no), and consequently their cleavage
angles are nearly equal (Fig. 198A). They approximate 92 ° and 88°,
with the plane of the a and c axes (the plane of symmetry in monoclinic
forms) bisecting the acute angle.

The best known members of the series with their axial ratios are
listed below. In the case of the orthorhombic members it will be noticed
that the shorter of the lateral axes is made 1. This is done to empha-
size the correspondence between the orthorhombic, monoclinic and tri-
clinic forms in their axial ratios. The usual orientation, that which
regards the longer of the lateral axes as b(=i) gives a : b : ^=.9702
: 1 : .5710 for bronzite, and .9713 : 1 : 5700 for hypersthene. By
many authors wollastonite and pectolite are placed in an independent

ANHYDROUS METASILICATES

365

group partly because of the fact that they are much more easily decom-
posed by acids than are the other pyroxenes, and partly because of
their very different crystal habits, and different axial ratios.

Enstatite
Bronzite
Hypersthene

Wollastonite

Pectoliie

Diopside

Sahlite

Hedenbergite

Schejferite

Augite

Acmite
Aegirine

Jadeite
Spodumenc

Rhodonite
Bustamite
Babingtonite
Fowlerite

Orthorhombic (possibly twinned monoclinic).

MgSi08 b:a:c =1.035 : 1 : .587

(MgFe)Si08 = 1.0308 : 1 : .5885

FeSiOa =1.0295 : 1 : .5868

c =1.0523 : 1
= 1.1140 : 1

Monoclinic (monoclinic prismatic class).

CaSi03 a : b

HNaCa*(SiO,)8

(MgCa)Si08

(MgFe)Ca(SiO,),

FeCa(SiOs)2

(Mg.Fe)(CaMn)(SiO,),
r(Mg.Fe)Ca(SiO,)2
\ (Mg.Fe)((Al.Fe)0)2Si04
lNa(Al.Fe)(Si08),

NaFe(SiO,)j

NaFe(SiOa), \

(MgFe)((Al.Fe)0)2Si04j

NaAl(SiO,)a

LiAl(SiOa),

.9649 &
.9864

= 1.0921 : 1 : .5893
=1.000 : 1 : .583

=1.0955 : 1 : -59<H

= 1.0096
= 1.098

.6012
.601

= 1.103 : 1 : .613
= 1.1283 : 1 : .6234

'84° 35'
=84° 40'

74° 11'

74° 10'

74° 14'

= 73° 11'
= 73° 09'

= 72° 45'
=69° 33'

Triclinic (triclinic pinacoidal class).

MnSiOs a : b : c =1.0729 : 1 : .6213 0=io8° 44'

(MnCa)SiOa

(CaFeMn),Fej(Si08)e =1.0807 : 1 : -6237 /3=io8°34'

(MnFeCaZn)SiO,

In addition, there are several comparatively rare monoclinic pyrox-
enes and one triclinic form, that contain zirconium. They occur only
as components of rocks rich in alkalies.

ORTHORHOMBIC PYROXENES

Enstatite MgSi03)—Bronzite— Hypersthene (FeSiQ3)

The orthorhombic pyroxenes are isomorphous mixtures of MgSi03
and FeSi03. The pure magnesium and iron molecules are not known in
nature, though the former has been produced artificially. Nearly all
members of the group contain both magnesium and iron. When the
proportion of the iron present is small (5 per cent FeO), the mixture is
known as enstatite. Mixtures with 5 to 16.8 per cent of FeO (cor-

366

DESCRIPTIVE MINERALOGY

responding to MgO : FeO= 3 : 1), are known as bronzite and mixtures
containing more than 16.8 per cent FeO are known as hypersthene.
The composition of MgSiOs and of some typical members of the group
follow.

Si02

AI2O3

FeO

MgO

I. 60.03

• ■ • a

39-97

II. 58.00

i-35

3.16

3691

HI. 55 50

■ • ■ ■

16.80

27.70

IV. 52.12

1.69

20.94

21.56

CaO H2O

.80

320

Total
100.00
100.22
100.00

9951

I. Calculated composition of MgSiOs.
II. Portion of large crystals of enstatite from Kjorrestad, Norway.

III. Calculated composition of upper limit of bronzite, i.e., in which MgO : FeO

=3 : 1.

IV. Hypersthene powder separated from a gabbro at Mt. Hope, Md.

The three minerals occur in crystals that have a well marked ortho-
rhombic symmetry, but it is believed that this may be a case of pseu-
dosymmetry only, i.e., that the minerals may in reality be monoclinic,
and that their apparently orthorhombic symmetry may be due to
repeated polysynthetic twinning of very thin lamellae. Monoclinic
MgSi03 has been made by fusion of SK>2 and MgO in the presence of

B2O3, but it is not certain that this is identi-
cal with an iron-free enstatite.

The natural crystals of the orthorhombic

pyroxenes are columnar in habit and are

usually bounded by ooP(no), 00 Poo (010),

00 Poo (100), P2(2i2), JP 06 (014), with the

addition on some crystals of ooP2(i2o),

fP 86(034), P(lll), 2P2(2Il), £Po6(oi2)

and other forms (Fig. 199). All cleave per-
fectly parallel to ooP(no) with a cleavage
angle of 88° i6'-2o' and 91 ° 4o'-44'. The
angle noAiio=88° 16' to 88° 20'.

The color and other physical properties of
the orthorhombic pyroxenes vary with the
amount of iron present. Enstatite is light gray, yellow or green.
Hypersthene is black, dark purple or dark green. Bronzite is brown,
or some shade lighter than hypersthene and darker than enstatite.
All colored varieties are pleochroic, the difference in color in different
directions increasing with the increase in iron. Green, red, yellow and
brown tints are most prominent. All varieties have a colorless streak.

Fig. 109. — Enstatite Crys-
tal with 00 P, no (m);
00 P 00 , 100 (a); 00 P 00 ,
010 (6); §P«, 023 (q);
§PX, 012 (A); JP»,
016 (<t>) and JP, 223 (t).

ANHYDROUS METASILICATES 367

Many hypersthenes and bronzites exhibit a metallic shimmer on
oo P 06(010), due to tiny inclusions with their flat sides parallel to
this direction. The hardness of the orthorhombic pyroxenes varies
between 5 and 6 and their density between 3.1 and 3.5 increasing with
the iron present. Their refractive indices for yellow light are:

Enstatite a= 1.665 0=1.669 7=1.674

Hypersthene =1.692 =1.702 =1.705

Before the blowpipe the iron-free members of the series are infusible.
With increase in iron they become more easily fusible, very ferruginous
hypersthene melting easily to a greenish black weakly magnetic glass.
When treated with hydrochloric acid the members near enstatite are
unattacked, while those near hypersthene are slightly decomposed.

Syntheses. — Crystals of these pyroxenes have been made by fusing
the proper components with B2O3, and by heating mixtures of Si(>2 and
MgCfe. They are frequent constituents of slags.

Occurrence. — The rhombic pyroxenes occur in igneous rocks, in crys-
talline schists, in metamorphosed dolomites and in veins that have been
filled by igneous magmas. They are not very stable under the condi-
tions at the earth's surface. They weather to serpentine, hornblende
and rarely to talc. Enstatite occurs also in meteorites.

Localities. — Good crystals of the orthorhombic pyroxenes are found
in the volcanic bombs (inclusions in lava) of the Lake Laach district,
Prussia; in ore. veins at Bodenmais, Bavaria; at Malnas, Hungary;
in the trachyte of Mont Dore*, France; in apatite veins at Snarum,
Norway; and in a glassy andesite on Peel Island, Japan. In the United
States they occur in basic coarse-grained igneous rocks in North Carolina,
Maryland, and the Highlands of New York and New Jersey, in volcanic
rocks in Colorado, and at the Corundum Mines, in Georgia. Espe-
cially fine bi;onzite occurs on Paul's Island, Labrador.

MONOCLINIC PYROXENES

The monoclinic pyroxenes comprise a series of isomorphous mixtures
of monoclinic metasilicates of Na, Li, Ca, Mg, Fe" and Mn and the
silicate R" (R'"0)2 Si04, in which R" is usually Mg, Ca or Fe and R'"
is Al or Fe.

-Although their chemical composition varies quite widely, the crys-
tallization of all the members of the group is practically the same. With
the exception of wollastonite and pectolite the habit of their crystals is
similar and their corresponding interfacial angles have approximately
the same value.

368

DESCRIPTIVE MINERALOGY

The group may be subdivided into four subgroups (i) the wollas-
tonite subgroup, including this mineral and pectolite, with calcium as
the principal metallic component, (2) the magnesium-calcium-iron
pyroxenes, including diopslde, sa\lUey he lender gite and augite, and (3)
the alkali pyroxenes including acm'U^jaleite and spolumene. A fourth
subgroup includes the rare zirconium-bearing pyroxenes. All crystal-
lize in the monoclinic prismatic class.

Wollastonite Subgroup

These minerals, because their axial ratios are somewhat different
from those of the other monoclinic pyroxenes, and because they are
much more easily decomposed by acids, are by some mineralogists re-
garded as constituting an independent group.

Wollastonite (CaSi03)

Wollastonite analyses correspond very closely to the theoretical
composition required by the formula assigned to it. There is, however,
nearly always a little Fe2C>3 present and usually there are present also
small traces of other constituents. A dimorph, pseudowollastonite, or
/3 wollastonite, has been made by melting wollastonite and cooling
slowly, but it has not yet been found in nature. Its crystals are hexag-
agonal or monoclinic with an hexagonal habit.

Si02 FeOMnOCaO MgONa20 H20 Total

Theoretical 51 . 75 ... 48.25 100.00

Bonaparte Lake, N. Y. 50 . 66 .07 47 . 98 .05 .46 .72 99 . 94

The mineral forms tabular or columnar crystals bounded by

00 Pob (100), — P 6b(lOl), OP(OOI), Poo(iol), 00P2(l2o), — P2(l22)

and 00PK540) (Fig. 200). Twins are
sometimes found with 00 P 60 (100) the
twinning plane. The angle 540 A 540 = 790
58'. The mineral occurs also in granular
and fibrous masses. Its cleavage is per-
fect parallel to 00 P do (100) and only a
little less perfect parallel to oP(ooi).

Wollastonite is usually colorless or
white, but in some cases is grayish, yellow-
ish, reddish or brown. It is transparent
or translucent and has a white streak. Its
luster is glassy except on the cleavage face
where it is often pearly. Its hardness is

-a

Fig. 200. — Wollastonite Crys-
tal with oP, 001 (r); 00 P ^ r
100 (a); -Pm, ioi (»);
j-Pco, 101 (0; +JP«,
T02 (a) and ooPf, 54© W.

ANHYDROUS METASILICATES 369

4.5-5 and density 2.8-2.9, and its refractive indices for yellow light
are: <*= 1. 62 1, /3= 1.633, 7=1.636.

Before the blowpipe wollastonite fuses with difficulty to a white
transparent glass. Its fusing point varies between 12400 and 13250,
diminishing with increase in iron. It dissolves in HC1, leaving a residue
of gelatinous silica> and is attacked vigorously by strong solutions of
NaOH. When fused it recrystallizes in hexagonal crystals (pseudo-
wollastonite).

The mineral is distinguished from other white silicates by its crys-
tallization, its cleavage and its solubility in hydrochloric acid. Its prin-
cipal alteration is into apophyllite (p. 443).

Syntheses. — Crystals of wollastonite have been made by fusing Si02
and CaF2, and by dissolving the hexagonal modification (made by fusing
and cooling wollastonite) in molten calcium vanadate at 8oo°-9oo°.

Occurrence. — Wollastonite is characteristically a product of meta-
morphic processes, both contact and regional. It occurs in metamor-
phosed dolomites, in the limestone inclusions in the lava of Vesuvius,
etc., in many gneisses and in some eruptive rocks. It is found also
abundantly in calcareous slags.

Localities. — Crystals of wollastonite are found in the phonolite of the
Kaiserstuhl, near Freiburg, Bavaria; in a contact metamorphosed lime-
stone near Cziklova, Hungary; in the limestone bombs in the lava of
Mt. Somma, Naples, Italy, and of Santorin, Greece; and in limestone
at Diana, N. Y. Granular or fibrous masses occur also at Attleboro,
Penn., at different points in Lewis, Essex and Warren Counties, N.
Y.; and at the Cliff Mine, Keweenaw Pt., Mich.

Pectolite (HNaCa2(Si03)3)

Pectolite was formerly regarded as a partially weathered wollastonite.
Recent analyses, however, indicate that it may have a definite compo-
sition which can be represented by the formula written above, as shown
by the analyses quoted below. The excess of water shown by most
analyses is ascribed to the admixture of some weathered material.

Si02 AI2O3

MgO

CaO

Na20 K20

H20

Total

I- 54.23

• • • a

3372

9-34 ..

2.71

100.00

II. 4S-32

• • • •

3400

9.32

2-55

100.30

III. 53.94 .71

i-43

32.21

8-57 -47

4.09

100.82

I. Theoretical.

IT. Niakornat, Greenland. Contains also

.11 per cent FejOs.

III. Point Barrow, Alaska.

370 DESCRIPTIVE MINERALOGY

The mineral usually occurs in fibrous masses of acicular crystals
elongated in the direction of the orthoaxis, but in a few cases in tabular
forms flattened parallel to oo P 66 (ioo). Its cleavage is distinct parallel
to the same plane.

Pectolite when pure, or nearly pure, is colorless or white or gray, and
transparent or translucent. Its luster is pearly on cleavage surfaces
and satiny on fracture surfaces. Its hardness is about 4.5 and its den-
sity 2.88. When broken in the dark, some specimens phosphoresce.
Its average refractive index for yellow light is 1.61.

Before the blowpipe the mineral fuses to a white enamel. It yields
water when heated in the closed tube and when treated with hot hydro-
chloric acid it decomposes, leaving a residue of flocculent silica.

The principal alteration product of pectolite is talc (p. 401).

Synthesis. — Small, fine needles of pectolite have been produced by
heating to 4000 mixtures of S1O2, AI2Q3, Na20, CaO and H2O, in various
proportions.

Occurrence. — The mineral occurs in druses and as isolated crystals on
the walls of cracks in eruptive rocks, and also in a few instances as vein
fillings, and as a constituent of metamorphic rocks. It is mainly a
secondary mineral.

Localities. — Crystals are found in seams in basalts at Edinburghshire,
Scotland; at Bergen Hill, N. J., in clefts in traprock; and in the eleolite-
syenite at Magnet Cove, Ark. {manganopectolite with about 4 per cent
MnO). At Barrow Point, Alaska, fine-grained fibrous aggregates are
found in abandoned workshops of the Eskimo. Radially fibrous masses
occur in the Thunder Bay region, Lake Superior, at Disco, Greenland,
and at a number of points in the Alps.

Magnesium-Caicium-Iron Pyroxenes
Diopside-Augite

The calcium-magnesium-iron pyroxenes include a number of com-
pounds that have been given distinctive names. They are apparently
isomorphous mixtures of the metasilicates of Mg, Ca, Fe and Mn, or of
these together with the magnesium and iron salts of the basic orthosilicate
of iron and aluminium (Mg- Fe)((Al* Fe)0)2Si04.

The crystals of all members of the group are alike in habit and similar
in their interfacial angles. Their axial ratios are nearly the same and
the angle 0 has nearly the same value in all. It is possible that the
slight differences observed are due to the effect of the varying amounts of
iron present. The crystals are nearly all short columnar in habit, with

ANHYDROUS METASILICATES

371

the vertical zone well developed. The simplest crystals are bounded by
oo P 60(100), ooP(no), 00 Poo (010) and P(Tn), but — P(in),
2P(22i), oP(ooi) and 2Pob(o2i) are also common (Fig. 201). Other
forms to the number of 95 have been observed, but they are compara-
tively rare. Contact and interpenetration twins are fairly common.
In the contact twins the usual twinning plane is 00 P do (100) (Fig. 202).
Polysynthetic twins are twinned parallel to oP(ooi). In the interpene-
tration twins —P 00(101) (Fig. 203) and P2(l22) are the twinning
planes. The cleavage is parallel to 00 P(no), the cleavage angles being
about 930 and 87 °. Partings are also common, parallel to one or the
other of the three pinacoids.

All the pyroxenes of this group have a glassy luster and are trans-
parent or translucent, Their color varies with composition as does also

Fig. 201.

Fig. 202.

Fig. 203.

Fig. 201. — Augite Crystal with *> P, up (m); 00 P 55 , 100 (a); 00 P So , 010 (b) and

P, In (5).

Fig. 202. — Augite Twinned about 00 P 55 (100).

Fig. 203. — Interpenetration Twin of Augite, with — P55 (101) the Twinning Plane.

their hardness and density. The limits of hardness are 5 and 6 and of
density 3.2 and 3.6. The streak of all varieties is white. Pleochroism
has been observed in some occurrences but it is not as noticeable as in
the corresponding amphiboles. In the pyroxenes of this group it is
usually in shades of green, but in the diallage of the Lake Superior region
it is fairly strong in shades of amethyst.

Before the blowpipe the members of the group are fusible, their
fusibility increasing with the quantity of iron present. The fusing
temperature of the pure diopside is 13810 and of hedenbergite 11000-
1 1600. The fusing points of the other pyroxenes of the group lie between
these temperatures. None of the varieties are attacked by acids to any
appreciable degree.

All the pyroxenes are distinguished from other minerals by their
crystallization and their cleavage.

372

DESCRIPTIVE MINERALOGY

Diopside is a mixture of the magnesiumand calcium silicates in which
the two molecules are in the ratio i : i. With the addition of the cor-
responding iron molecule diopside grades into sahlite. The calculated
composition of a mixture of the formula MgCa(SiOs)2 is indicated in
the first line. The compositions of several typical diopsides are quoted
in the following two lines.

Theoretical

Albrechtsberg, Aus. . .
Alathal, Switzerland.

Si02 AI2O3 Fe203 FeO MgO CaO Total

55 55 18.52 25.93 100.00

55.60 .16 ... .5618.34 26.77 101.43

54.28 .51 .98 1. 91 17.30 25.04 100.02

Fig. 204. — Diopside Crystals with » P, no
(m) ; ooPm, 100 (a); 00 P « , 010 (b) ; oP,
001 (c), -P, in («); +2P, 221 (0); 3P3,'
311 (A); +P06, Toi (J>).

Its crystals are usually characterized by the presence of the basal

plane (Fig. 204). The value
of the angle iioAiTo=92°

So'-

Diopside is usually light

green or colorless, yellowish,
dark green or nearly black
and rarely deep blue. The
lighter varieties are transpar-
ent or translucent, the darker
ones opaque; The density of
the pure mineral is 3.25. Its
refractive indices for yellow
lightare:a= 1.6685,0= 1.6755,
7=1.6980. All these values

increase with increase in the iron molecule. Among the varieties that

have been given distinct names may be mentioned:
Malacolite, a pale colored translucent variety, and
Chrome-diopside, a bright green variety containing from one to

several per cent CfoOa.

Diopside occurs in igneous rocks and in metamorphosed limestones.

Hedenbergite is the calcium-iron pyroxene, though it always con-
tains some of the diopside molecule. The calculated compositions of the
type mineral (FeCaS20e) and of a specimen from its best known locality
are:

Si02 AI2O3 Fe203 FeO MgO CaO Total

Theoretical 4839 29 .43 22.18 100.00

Tunaberg, Sweden . . 47.62 1.88 .10 26.29 2.76 21.53 100.18

ANHYDROUS METASILICATES

373

The mineral is black, except varieties that contain Mn which are
grayish green. It occurs in crystals (Fig. 205)
and in lamellar masses. Its density is 3.31, and
refractive indices for yellow light, a =1.73 20,
18=1.7366, 7=1.7506.

Sahlite. — Intermediate between diopside and

hedenbergite are several pyroxenes which are *j jlj

characterized by possessing all three of the \ j»\s,

elements Ca, Mg and Fe in notable amounts. ^ 2^^

Of these the most common is sahlite, which is Fig. 205.— Hedenbergite

grayish, grayish green or black. It occurs in Crystal. Forms at m,

crystals and granular masses. *» c' °> ?> u and \M

a 4. ' 1 1 • c 11 *.i_ • in Fig. 204. Also 2P 00.

A typical analysis follows, the specimen fx , B-

• / xt 1 i 1 - t. 1 °21 W and °°p5» 5">

coming from Valpeleina, Italy: (xy

SiCb

AI2O3

FeO

MgO

CaO

Total

54 02

.20

8.07

13 -52

24.88

100.69

Schefferite is a brown or black pyroxene characterized by the fact
that it contains considerable manganese. It may be regarded as heden-
bergite in which a portion of the iron molecule has been replaced by the
corresponding manganese molecule. A specimen from the best known
locality for the species — Langban, Sweden — gave:

Si02= 52.28, FeO=3-83, MnO=8.32, MgO= 15.17, CaO= 19.62 = 99.22.

It occurs in tabular crystals that are usually elongated in the direction
of the zone ooPob(oio), P(Tn), P<x> (Toi) and in crystalline masses.

The mineral is yellowish brown or black, according to the percentage
of iron present. Its sp. gr. is 3.46-3.55 and its fusing temperature

I200°-I250°.

A fine blue variety, known as violan, from St. Marcel, Italy, is char-
acterized by the presence of about 5 per cent Na20, due possibly to the
admixture of NaMn(SiOs)2. Its sp. gr.=3.2i.

Jeffersonite is a variety containing zinc, occurring at Franklin Fur-
nace, N. J. It is found in large crystals with rounded edges. Its color
is greenish black on fresh fractures and chocolate brown on exposed sur-
faces. An analysis yielded:

Si02

AI2O3

FeO

MnO

ZnO

MgO

CaO

H20

Total

49-01

i-93

i°-53

7.00

4-39

8.18

iS-48

1.20

98.62

374 DESCRIPTIVE MINERALOGY

Augite is the name given to the Ca-Mg-Fe pyroxenes containing
alumina. They are isomorphous mixtures of (Ca, Mg, Fe) Si03 with
the alumino and ferric orthosilicates of the same metals, and often with a
small quantity of the acmite or jadeite molecuje. The varieties of augite
are numerous, their composition and properties differing with the pro-
portions of the various molecules in the compounds. The three most
prominent varieties are:

Fassaite, a pale to dark green richly magnesian variety. Sp. gr. =
2.98.

Ordinary augite, a dark green or brownish black variety, common
in igneous rocks. Specific gravity 3.24. For yellow light, a=i.7i2,
£=1.717,7=1.733.

Diattage, a variety that is characterized by the possession of a
distinct parting and a lamellar structure, usually parallel to 00 P 66
(100).

Omphacite is a bright green sodic variety. Sp. gr. = 3-33. Analyses
of fassaite (I), of three varieties of augite (II, III, IV) and of ompha-
cite (V) follow:

Si02 AI2O3 Fe203 FeO MgO CaO Na20 Loss Total

70 100.10

100.02

99.90

100.32

4.51 .05 100.15

I. Grass green, Fassathal, Tyrol.
II. Yellow, Monte Somma, Italy.

III. Dark green, Monte Somma, Italy.

IV. Black, Monte Somma, Italy.

V. Omphacite from the Eclogite of Otztal, Tyrol. Also .92% K20 and .46% TiO*.

The augites are usually in short prismatic crystals (Figs. 201, 202).
They are common constituents of igneous rocks.

All the pyroxenes of this group are subject to change under the
conditions on the earth's surface. Under the influence of the weather
they alter to chlorite. Under metamorphosing conditions they change
into the corresponding amphiboles, more particularly into the bright
green variety known as uralite. Alteration to serpentine is also
common. Steatite, tremolite, epidote and other minerals are also
frequent alteration products.

41-97

10.63

736

•55

26.60

10.29

II.

50 -4i

6.07

1.09

6.78

12.92

22.75

III.

51.01

4.84

3.5i

3.16

16.58

20.80

IV.

46.95

9-75

447

4.09

16.04

19.02

5421

10.91

3.12

i-33

10.03

14.61

ANHYDROUS METASILICATES 375

Syntheses. — Diopside and augite are common in furnace slags. They
have been made by fusing their constituents in open crucibles, with or
without the addition of a flux. Molten hornblende crystallizes as
monoclinic pyroxene.

Occurrence. — The most common methods of occurrence of the various
pyroxenes have already been mentioned. The magnesium-calcium
varieties such as diopside and sahlite are found principally in metamor-
phic limestones. The green varieties are most common in schists and the
black varieties in igneous rocks, especially the basic ones. Augite often
occurs also in ore veins, especially with magnetite.

Localities. — The occurrences of the various pyroxenes are so numerous
that they cannot be enumerated here. It will be sufficient to state that
good crystals of diopside are found in the Ala Valley, Piedmont; at Zer-
matt, in Switzerland; at Pargas, in Finland; and Nordmark, in Sweden.
Hedenbergite occurs at Tunaberg, Sweden, and Arendal, Norway;
schefferite at Langban, Sweden, and augite at Mt. Monzoni, in the
Fassathal; Traversella, Piedmont; Mt. Vesuvius, Italy; the Sandwich
Islands and the Azores.

In the United States good crystals are found at Raymond and Rum-
ford, Me. (diopside, sahlite) ; at Edenville and Dekalb, N. Y. (diopside) ;
and at Franklin Furnace, N. J. (hedenbergite and jeffersonite).

Alkali Pyroxenes

The alkali pyroxenes are characterized by the presence in them of
alkalis, especially sodium. They may be regarded as isomorphous mix-
tures of the sodium, lithium, iron and aluminium metasilicates, thus
Na2Si03+Fe2(Si03)3=2NaFe(Si03)2, or Na2Si03+Al2(Si03)3=2NaAl
(Si03)2. The three most common alkali pyroxenes are acmite f jadeite
and spodumene. Spodumene is used as a source of lithium. Jadeite
was formerly a favorite material from which to carve sacred emblems.

Acmite — Aegirine

Acmite has a composition corresponding to the formula NaFe(SiC>3)2,
and is rare. More commonly this molecule is mixed with the augite
molecule in the compound known as aegirine or aegirite, or aegirine-
augite, according to the proportion of the augite molecule present.
When the mixture contains about 2.50 per cent Na20 the correspond-
ing mineral is usually known as aegerine-augite. When MgO and CaO
are absent (Na20= 12-13 per cent), it is known as acmite. Between
these limits it is aegirine.

The calculated compositions of the pure acmite molecule and the

376 DESCRIPTIVE MINERALOGY

composition of specimens of acmite, aegirine and aegirine-augite as
found by analyses are:

SiOa AI2O3 FeaOa FeO MgO CaO NaaO K20 Total

I. 51.97 .... 34.60 13.43 100.00

II. 51.66 28.28 5.23 12.46 .43 100.25*

III. 49.31 4.88 16.28 5.65 4.28 9.30 8.68 .68 100.41 f

IV. 50.33 .30 12.37 10.98 22. 01 2.14 -94 99-73t

I. Theoretical acmite.
II. Acmite, Rundemyr, Norway.
HI. Aegirine, Sarna, Daleltarlien.
IV. Aegirine-augite, Laurvik, Norway.

• Contains also .69 per cent MnO, 39 per cent H,Oand 1.11 per cent TiOi.
t Contains also 1.15 per cent TiOi.
t Contains also .66 per cent TiOi.

Acmite crystals are usually more acicular in habit than those of the
ordinary pyroxenes, and their terminations are steeper. P(Tn) and
P^(ioi) are common and 6P(56i) and other
steep pyramids are not uncommon (Fig. 206).

The mineral has a vitreous luster, and is
transparent or translucent. Its color is reddish
brown to brownish black and in some cases
green. Its hardness is 6 and sp. gr. = 3-52. Its
refractive indices for yellow light are: 0=1.7630,
0=1.7990, 7=1.8126.

Aegirine is greenish black. Its streak is
yellowish gray or dark green. Pleochroism is
Fie. 106.— Acmite Crys- strong in green and brown tints. Hardness is 6
tal with » P s , 100 and density 3.52.

(a), =0 =0 010 ( ), Before the blowpipe acmite and aegirine fuse

« P, 110 (m); +P,

In (s)- +iPi in t0 a D'ac'i magnetic globule. The fusing tem-
(5); -|-6P: 56i (o) perature of acmite is from 9700 to 1020 °. Both
and 8P, 881 (ft). O minerals are slightly attacked by acid before and
and G merge. gjter fusing.

Synthesis. — Acmite has been made by the
fusion of a mixture of powdered quartz, Fe203 and Na2C(>3 in the pro-
portions indicated by the formula NaFe(SiC>3)2.

Occurrence. — Both minerals are limited in their occurrence to soda-
rich igneous rocks, in which they are primary.

Localities. — Crystals of acmite occur in a dike of pegmatite near
Eker, Norway, and in a nepheline syenite at Ditro, Hungary.

ANHYDROUS METASILICATES 377

Aegirine crystals are more common. They occur abundantly in the
nepheline syenite dikes in the neighborhood of Langesundf jord, Norway,
in some instances in crystals a foot long. They are found also in can-
crinite syenites at Elfdalen and elsewhere in Sweden; in nepheline
syenite on the Kola Peninsula, Russia; and in the same rock at Hot
Springs, Ark.

Jadeite (NaAl(Si03)2)

Jadeite is not known in measurable crystals, but, because sodium
is almost universally present in the mineral spodumene, where it is ap-
parently in isomorphous mixture with LiAl(SiOs)2, it is assumed that the
molecule NaAl(SiC>3)2 crystallizes in the same way as the spodumene and
the acmite molecules. Most specimens of jadeite are isomorphous mix-
tures of the jadeite and diopside molecules. When in addition to these
there is a notable admixture of the acmite molecule, NaFe(Si03)2,
the mineral is known as chloromelanite.

The mineral is of great ethnological interest because so many orna-
ments were made of a rock composed mainly of jadeite by the ancient
inhabitants of China, Mexico, South America and elsewhere. " Jade "
ornaments, however, are not all made of jadeite, but in all instances their
material resembles this mineral in color, structure and density. Many
of them are made of fibrous amphiboles, some of which correspond to
jadeite in composition.

The theoretical composition of the mineral is given in line I, and the
analyses of specimens from Mexico and China in lines II and III:

Si02 AI2O3 FeO MgO CaO Na20 K20 H20 Total

I. 59.39 25.56

II. 58.18 23.53 l67

III. 58.68 21.56 .94

I. Theoretical.
II. Oaxaca, Mexico.
III. Ornament, China.

Jadeite occurs in fibrous, flaky and dense, finely granular masses
with a glassy luster, inclining to pearly on cleavage surfaces. Its color
is in some cases white or yellowish white, but more frequently bright
green or bluish green. Its streak is white. Its cleavages make angles
of 87 °. Its fracture is tough and splintery. Its hardness is 6.7 and its
density 3.3-3.35. Its intermediate index of refraction, 0= 1.654.

Before the blowpipe jadeite fuses easily to a transparent, blebby glass.
It is unattacked by acids. After fusion, however, it is easily decomposed

• • • •

• • • »

15-35

• • •

■ • •

100.00

1.72

2-35

11. 81

•77

•53

100.56

2.49

3-37

13.09

•49

• • •

100.62

378 DESCRIPTIVE MINERALOGY

by HC1 and sometimes by Na2C(>3. At high temperatures (2250 -
23 50) it is also decomposed by water.

Jadeite alters by metamorphic processes to a white hornblende
(tremolite).

Localities. — Ornaments and instruments made of jadeite, and water-
worn fragments of the mineral are known from many localities in China,
Tibet, Burma, Switzerland, France, Egypt, Italy, Mexico and Central
America. The original sources of the material of the ornaments are
not known. The mineral, however, occurs with albite and nepheline
in a dike at Tawman, Burma, and probably as a constituent in some
metamorphic schists.

Spodumene (LiAl(Si03)2)

Spodumene is essentially the lithium molecule corresponding to the
sodium molecule jadeite. Nearly always, however, the mineral contains
some of the sodium molecule, and a small quantity of helium. Three
typical analyses are quoted below:

Theoretical

Si02 . . .

64.49

AI2O3 . .

27-44

Fe203. . .

Mn203.

FeO. . .

CaO . . .

LJ2O . . .

8.07

Na20 . .

K20...

H20...

Total.

100.00

Colorless,

Yellowish green,

Kunzlte,

Branchville,

Minas Geraes,

S. Diego

Conn.

Brazil

Co., Cul.

64.25

64.32

64.42

27.20

27.79

27.32

.20

.67
•17

•15

7.62

7-45

7.20

•39

•55

•39
•03

.24

.12

99.90 101.07 99 5i

Crystals are usually columnar parallel to 00 P (no) or tabular par-
allel to 00 P 6b (100) (Fig. 207). They are more complex than those of
the members of the diopside-augite group and their habit is different.
The most frequent forms are 00 Poo (100), 00 Poo (010), ooP(iio),
ooP2(i2o), ooP3(i3o), 2Pob(o2i), 2P(22i) and P(Tn). Some of
them are of enormous size. In the Etta Mine, Black Hills, South
Dakota, are many 30 ft. long and 3-4 ft. in diameter. One meas-
ured 47 ft. in length. Most crystals are striated vertically. Twins are

ANHYDROUS METASILICATES

379

Fig. 207. — Spodumene Crys-
tal with «P(», 100 (a);
00 P« # 010 (6); ooP, no
(w); 00P 2, 120 (/<); 00 P3,
130 (»); 2P00, 021 (rf);
+2P, 2_2i_(r); +P, in
(/>); 2P2, 211 (/) and Poo,
101 (p).

fairly common, with ooP(no), the twinning plane. Although crystals
are not uncommon the mineral more frequently occurs as platy or scaly
aggregates. The angle 1 10 A iTo= 93 °.

Spodumene has a glassy luster, which is pearly on cleavage surfaces.
Its color is white, gray, greenish or yellowish
green, or amethystine. It is transparent or
translucent, and its streak is white. Its
fracture is uneven or conchoidal, its hardness
between 6 and 7 and its density 3.2. Dark
green crystals exhibit marked pleochroism.
Refractive indices for yellow light in speci-
mens from North Carolina are: 0=1.651,
/3= 1.669, 7=1.677.

Two varieties have been named and used
as gems. These are:

Hiddenile, a glassy emerald-green variety,
from Alexander Co., N. C.

Kunzite, a pink or lilac variety, from
San Diego Co., California. Under the influ-
ence of radium rays it becomes green. When
heated to 2400 it becomes a darker rose
color, but at 4000 it loses all color.

Before the blowpipe the mineral swells up and fuses to a colorless
glass, at the same time imparting a crimson color to the flame. It is
unattacked by acids. It melts at about 13250. Its powder reacts
alkaline.

It alters readily to albite, muscovite, eucryptite (LiAlSiCU), or mix-
tures of these. One of the commonest mixtures is known as cymatclUe
or cumaiolite. The mixture of albite and eucryptite has been called
0 spodumene.

Spodumene crystals have not been made artificially.

Occurrence and Origin. — The mineral occurs in granites, pegmatites
and crystalline schists, where it was formed by pneumatolytic processes.
It is often associated with cassiterite.

Localities. — Spodumene crystals occur at Huntington, Mass., in a
quartz vein in mica schist; at Branch ville, Conn., in pegmatite; at
Stony Point in Alexander Co., N. C, in cavities in a gneiss; at the Etta
Mine and at other places in the Black Hills, N. D., in a pegmatite; at
the lepidolite localities in California and in Minas Geraes, in Brazil.

Uses. — The ordinary varieties of the mineral are used as a source of
lithium in the manufacture of lithium salts, and the transparent varieties

380

DESCRIPTIVE MINERALOGY

as gems. The total production of kunzite in this country during 191 2
was valued at $18,000, all from California. One specimen found in this
year weighed 47^ oz. Another was a crystal measuring 9X5X1 inches.
The other forms of the mineral were not mined. In recent years a few
tons have been furnished by the mines in the Black Hills.

TRICL1NIC PYROXENES

The triclinic pyroxenes include the four minerals rhodonite, bustamite y
fowlerite and babingtonite. They are completely isomorphous. The
first is the manganese metasilicate, MnSi03, and the others are iso-
morphous mixtures of this molecule with the corresponding silicate of
calcium (bustamite), or of these two with the corresponding iron (babing-
tonite), or with the iron and zinc compounds (fowlerite).

Rhodonite— Fowlerite (R"MnSi03. R = CahFe,Zn)

Rhodonite is the pure manganese silicate with the percentage com-
position shown in I. In II is the result of an analysis of crystals from
Pajsberg, Sweden. An analysis of bustamite from Campiglia, Italy, is
quoted in III and one of fowlerite from Franklin Furnace, N. J., in IV.

Si02 AI2O3 MnO FeO ZnO MgO CaO H20 Total

.... 1 .65

.... I . ol

7-33 J-30

All are triclinic (pinacoidal class), with the axial constants" of

1.0729 : 1 : .6213, a=io3°

i9',/3=io8044',7 = 8i°39'
for rhodonite, and 1.0807 : 1

: .6237 and a=i02° 27',
/3=io8°34,,7=82° 53' for
babingtonite. Their crys-
tals possess many habits, o£
which the cubical, tabular,
and columnar are the most
Fig. 208.— Rhodonite Crystals with 00 'P, 1T0 common. They are usually
(Af); 00 p', no (w); oP, 001 (c); 00 p£, rough with rounded edges.
100 (a); 00P 56, 010(6) ; 2,P, 221 (*) and 2P,, The most frequently oc-

221 (n^' curring forms are oP(ooi),

00 P06 (100), 00 P6b (010), ooP'(no), oo'P(no), P,(nT) and
2/P(22i) (Fig. 208). The angle iooAooi = 72° 37'. Their cleavage

1. 45.85

• • •

54.15

• • • •

II. 45.86

• • ■

4592

III. 49 23

•37

26.99

1 .72

IV. 46.06

• ■ «

3428

3 *>3

• • • *

100.00

6.40

• • ■ •

100.09

18.72

1-54

100.38

7.04

....

99.64

ANHYDROUS METASILICATES 381

is perfect parallel to ooP'(no) and oo 'P(iTo). Although crystals are
fairly common in some places, the minerals are more usually in dense,
structureless or finely granular masses.

All the triclinic pyroxenes have a glassy luster which is somewhat
pearly on cleavage surfaces. They are transparent or translucent and
all except babingtonite have a rose-red color when pure. When mixed
with other substances their color may be yellowish, greenish, brownish
or black. They are pleochroic in rose and yellowish tints. Their streak
is always reddish white. Babingtonite is greenish black and is pleo-
chroic in green and brown tints. All have an uneven fracture. Dense
varieties are tough and their crystals are brittle. Their hardness
= 5-6, and density 3.4-3.7. The intermediate refractive index of rhodo-
nite is 1.73 for yellow light.

Before the blowpipe all become black, swell and fuse to a brown
glass. The fusing temperature of rhodonite is about 12000 and of
bustamite about 13000. They are attacked by acids with loss of color.

When exposed to the weather the members of the group containing
manganese alter to a mixture of which the principal constituents are a
manganese oxide, Mn203, silica and water, or to mixtures of carbon-
ates of manganese, or a mixture of the carbonates of manganese, iron
and calcium.

Syntheses. — Crystals of rhodonite have been prepared by fusing a
mixture of SiC>2 and Mn02 and by passing a current of steam and CO2
over a red-hot mixture of MnCfe and SiCfe. Rhodonite and babington-
ite crystals are also formed in the slags of manganese iron furnaces, and
the latter has been found in cavities in roasted iron ores.

Occurrence. — The members of the group containing manganese occur
in veins of magnetite, copper and other metals, and in contact zones
between limestones, shales and igneous rocks, associated with other
manganese minerals. Under these conditions they may have been pro-
duced by the help of magmatic emanations. Rhodonite occurs also with
rhodochrosite in deposits of manganese ores and in other associations,
where it may be of secondary origin. Babingtonite occurs principally
as a rare component of siliceous rocks.

Localities. — Crystals of rhodonite and bustamite occur in iron ore
deposits in the gneiss of Langban, Sweden. Fine crystals of rhodonite
are found in the iron ore at Pajsberg, Sweden, and crystals of fowlerite
in metamorphosed limestone associated with the zinc ores at Stirling
Hill and Franklin Furnace, N. J. Massive rhodonite is abundant at
Jekaterinburg, Ural, Russia; at Kapnik, Hungary; at Blue Hill Bay,
Maine; and in Jackson Co., N. C, associated with wad. Massive bus-

382

DESCRIPTIVE MINERALOGY

tamite occurs at Rfebanya, Hungary, in veins in limestone, and at Mts.
Civillina and Campiglia, Italy, in fibrous masses. Babingtonite occurs
in a mica schist at Athol, Mass., and in druses in granite at Baveno,
Italy, and in the ore veins at Arendal, Norway.

The principal occurrences of gem rhodonite in this country are in
Siskiyou Co., Cal., and near Butte, Mont. In the former locality the
mineral occurs nine miles north of Happy Camp in a fine-grained
quartz schist. It consists of a mixture of quartz grains cemented by
rhodonite and traversed by veins of pyrolusite. The Montana material
is in radiating groups with quartz, pyrite and brown manganese oxide.
At the Alice Mine it is associated with rhodochrosite.

Uses and Production. — Transparent rhodonite is used as a gem-stone
to a slight extent. The total yield of the material in the United States
during 191 2 was valued at $550.

THE AMPHIBOLES

(R"SiO,, R'Al(Si03), and R//(R/"0)aSi04)

The amphiboles are common alteration products of pyroxenes and
some other silicates. They are also abundant as components of certain
schistose rocks, as for instance, the hornblende schists, and they occur
also as original constituents of igneous rocks. The crystals of all the
amphiboles are similar in habit to those of the pyroxenes (Fig. 209),
but since the ratio between the a and b axes is about .5 to 1, the angles
between their cleavage planes, which, like those of the pyroxenes, are
parallel to 00 P(no), are from 540 to 560 and 1240 to 1260 (see Fig.
198B). The plane of symmetry bisects the obtuse angle.

The members of the group are about as numerous as those of the
pyroxenes, but the common types are much fewer. Moreover, there is
no subgroup corresponding to the wollastonite subgroup of the pyrox-
enes. The best known members of the series, with their axial ratios are:

Anthophyllile
Gedrite

Orthorhombic (possibly twinned monoclinic).

(Mg-Fe)SiOs ) a : b : c = .$2i : 1 : .2=4=

(Mg.Fe)(A10)2Si04 j =.523 : 1 : .217

Monoclinic (monoclinic prismatic class).

Mg,Ca(SiOs)4 a : 6 : £ = .5415 : 1 ' .2886

(Mg-Fe)8Ca(SiO,)4
CummingtonUe (Fe • Mg) Si08

FeSi03

(Mg-Fe)5Ca(Si03)«

(Mg.Fc)((Al-Fe)0)sSiO«

NaAl(SiO,)a

Tremolite
Actinoliie

Griinerite
Hornblende

0 = 74° 49'

.5318: 1 1.2937 0 = 75° 02'

ANHYDROUS METASILICATES

383

Glaucophane

Arfvedsonite
RiebeckUe

CrocidoliU
AemgmaHte

NaAl(SiO,)i
(Fe.Mg)Si03
(Na«.CaFe)SiO,
(CaMg)((Al.Fe)0),SiO
NaFe(SiO,)2
f NaFe(SiO,)t
FeSiO,

»)

*».53 : i : .29

= .5496 : 1 : .2975
- -5475 : 1 : .2925

0~77P

0 = 75° 45'
0» 76*10'

Triclinic (triclinic pinacoidal class).
Na4Fe9(AlFe)2(SiTi)uO» =.6778 : 1 : .3506

ORTHORHOMBIC AM PHI BOLES

0 = 7*°49'

Anthophyllite — Gedrite

The orthorhombic amphiboles are comparatively rare. They are
isomorphous mixtures of MgSiC>3, FeSiOa and the alumino-orthosilicates
(Mg» Fe)(A10)2Si04. The pure MgSiCta has not been found in nature,
but it has been produced in the laboratory. The mixture of the mag-
nesium and iron silicates (Mg* Fe)SiOs, is known as anthophyllite. In
nature it always contains a little of the molecule (Mg*Fe)(A10)2Si04.
Gedrite, which is much less common than anthophyllite, contains more
AI2O3 than does this mineral, which may be regarded as due to a larger
admixture of the molecule (Mg*Fe)(A10)2Si04. The name is thus
applied to aluminous anthophyllites.

The difference in composition of the two minerals is shown by the
following analyses of (I) anthophyllite and (II) gedrite.

Si02 Fe203 AI2O3 MnO FeO MgO CaO Na20 H2O Total

I.57.98 ... .63 .31 10.39 28.69 .20 1.79 99.99

II. 46.18 .44 21.78 ... 2.77 25.05 ...

2-3° I-37 99-89

I. Brown crystals; Franklin, Macon Co., N. C.
II. Colorless prisms; Fiskernas, Greenland.

The orthorhombic amphiboles usually occur in platy or fibrous
aggregates that rarely show traces of end faces, and, consequently the
ratio between c and b is not accurately known. The planes in the pris-
matic zone are, however, 1 sometimes so well developed that they
can be recognized as ooP«(ioo), 00 P 06 (010), and ooP(no).
Cleavage is perfect parallel to 00 P(no) and distinct parallel to 00 P 06
(010). The cleavages intersect at angles 540 2o'-55° 18'.

The minerals have a glassy luster which is slightly pearly on cleavage
surfaces. They are green or brown in color and have a colorless, yellow
white or gray streak and are translucent and pleochroic in colorless,

384

DESCRIPTIVE MINERALOGY

greenish and brownish tints. Their fracture is somewhat conchoidal.
Hardness is 5.5. and density 3.2. The refractive indices for yellow light
in anthophyllite are: 0=1.633, 0s* 1.642, 7=1.657; and in gedrite,
1.623, 1.636, and 1.644.

Synthesis. — Pure magnesium metasilicate has been made in ortho-
rhombic crystals mixed with monoclinic crystals, by rapid cooling of a
magma made by heating Mg salts and silica with water at 375°-475°

Occurrence. — The minerals are found in crystalline schists — more
particularly in hornblende gneisses and hornblende schists, where they
are distinctly metamorphic minerals, having been derived in some cases,
at least, by the alteration of the orthorhombic pyroxenes. They alter
to talc.

Localities. — Anthophyllite occurs in dark brown platy aggregates at
Kongsberg and Modum in Norway, associated with hornblende in mica
schists; on the Shetland Islands, Scotland, associated with serpentine;
and at the Jenks Corundum Mine in Macon Co., N. C.

Gedrite occurs in yellowish gray fibrous aggregates at Bamle, Norway,
in dark brown aggregates associated with magnetite and brown mica, at
Gedres, Hautes-Pyr£n6es, France; and in a mica schist at Fiskernas,
Greenland, associated with a large number of metamorphic minerals.

MONOCLINIC AM PHI BOLES

The monoclinic amphiboles, like the corresponding pyroxenes, com-
prise isomorphous mixtures of the metasilicates of Na, Mg, Ca and Fe

Fig. 209. — Ampibole Crystals with ooP, no (m); oopSb, 010 (b); 00 PJ, 130 («);

P ob , on (r) and — P » , 101 (/).

and the basic orthosilicates of Al and Fe. Recent work seems to indi-
cate that in tremolite there is present also a little H2O. In the amphi-
boles the alumino-silicate is more common than in the pyroxenes and
consequently aluminous amphiboles are more common than aluminous
pyroxenes.

ANHYDROUS METASILICATES 385

All the monoclinic amphiboles crystallize with the same habit in
crystals that are columnar like those of the corresponding pyroxenes,
but on which the terminations are different (Fig. 209). Moreover, all
have a distinct cleavage parallel to ooP(no) with cleavage angles of
about 56°-i24°.

The amphiboles are distinguished from other minerals by their
crystallization and their cleavage.

For convenience, the monoclinic amphiboles may be subdivided into
(1) the magnesium-calcium-iron amphiboles including tremolite, actino-
lite, cummingUmite* grunerite and hornblende, and (2) the alkali amphi-
boles, including arfvedsonite, glaucophane and riebeckite.

Before the blowpipe all the members of the group fuse to a glass which
is colorless, green or black, according to the quantity of iron present.
The varieties rich in iron are attacked by acids.

Magnesium-Calcium-Iron Amphiboles

Tremolite-Hornblende

This group includes the monoclinic amphiboles that are mainly meta-
silicates of magnesium and iron and the mineral hornblende, which is a mix-
ture of these molecules and the orthosilicate (Mg«Fe)((Al*Fe)0)2Si04.
The calcium metasilicate is present in some members as an isomorphous
mixture, but it does not occur alone as an independent member corre-
sponding to wollastonite among the pyroxenes. Hornblende is the only
member of the series that is essentially aluminous.

The crystals of the monoclinic amphiboles are short columnar or
long and acicular. Their axial ratios are nearly alike and their cleavage
angles differ only by a few minutes. The simpler crystals are bounded
by 00 Poo (100), 00 P co (010), ooP(no), oP(ooi), 3P 00(031),
+P6o(Toi), — P 00(101), 2P2(T2i), 2P2(2ii) and Poo (on) (Fig.
209). Contact twins are common, with 00 P 60 (100) the twinning
plane as in the pyroxenes. Polysynthetic twins are rare.

All the amphiboles of this group have a glassy luster and are trans-
parent or translucent. All the members but hornblende are white or
some shade of green, though colorless and brown varieties are not un-
common and yellow and red varieties are known. Hornblende is fre-
quently so dark as to be almost black. Their streak is light, hardness is
5-6 and density 2.9-3.4, depending upon composition.

The cleavage is perfect in all the amphiboles and there is present
often also a parting parallel to 00 P do (100) and P 00 (Toi), the latter due
to gliding. Pleochroism is strong in all the colored varieties in green

386

DESCRIPTIVE MINERALOGY

and yellowish green tones in the green varieties, and brown and yellow-
ish brown tints in the brown varieties.

Tremolite is the calcium magnesium silicate. When there is mixed
with this the corresponding iron molecule the mixture is known as
actinolite if the proportion of the iron molecules present is not great.
The theoretical compositions of the two molecules Mg3Ca(Si03)4 and
Fe3Ca(Si03)4 are given in lines I and II, and analyses of several trem-
olites and actinolites in lines III, IV, V and VI. The almost universal
presence of small quantities of water in tremolite, and the lack of
enough Mg, Ca, Fe and other metallic bases to satisfy all the SiCfe re-
vealed by the analyses has suggested to some mineralogists that the
water is an essential part of the compound, and that its composition is
best represented by MgsCa2H2(Si03)8.

Si02 AI2O3 Fe203 FeO MgO CaO Na20 H20

I- 57 -72

• • •

II. 46.90

■ • *

III. 58.27

•33

IV. 57 40

•38

V. 58.80

• • •

VI. 55 50

■ ■ ■

tr.

28.83 13

42.17 10

25.93 11

25.69

22.23

22.56

1.36

3 05
6.25

13
16

93
90

47
46

1.22
.40

• « • •

1.29

Total
100.00
100.00
99.40*
99.12

i°°-55
99.06

I. Theoretical for MgjCa (SiO?)4.
II. Theoretical for FesCa (SiOa)^

III. Tremolite, East on, Pa.

IV. Tremolite, Gouverneur, N. Y.
V. Asbestus, Bolton, Mass.

VI. Actinolite, Greiner, Zillerthal, Tyrol.

* Also .08 MnO and .42 K20.

Tremolite is white or nearly white, and actinolite is green. The
former occurs in columnar crystals, in plates and occasionally in fibers,
while actinolite is nearly always in long, slender acicular crystals without
terminations. The refractive indices for yellow light in tremolite are:
a= 1.6065, £=1.6233, 7=1.6340. In actinolite, a =1.61 1 6, 0 = 1.6270,
7=1.6387.

Both minerals melt in the blowpipe flame, the fusing temperature
for tremolite being about 12900 and for actinolite about 11500.

Asbestus is a fibrous variety of tremolite, actinolite or anthophyllite.
It occurs principally in rocks that have been crushed and sheared under
great pressure. The actinolite asbestus is used for the same purpose as
the chrysotile variety (see p. 398), but it is regarded as less valuable.

ANHYDROUS METASILICATES 387

Its principal source in this country is Sails Mountain, Georgia, but prom-
ising deposits have recently been reported near Kamiah, Idaho. At the
Georgian locality the asbestus forms distinct lenses in gneiss. It is
possibly an altered basic intrusive rock.

Smaragdite is a grass-green actinolite, which is often an alteration
product of pyroxenes and olivine. The name is also applied to a bright
green hornblende containing a little chromium.

Nephrite is a finely fibrous actinolite or tremolite and usually some
chlorite, forming dense rock masses that are white or of a light green
color. It was formerly much used, like jade, in the manufacture of
images, charms and implements.

Cummingtonite and griinerite are amphiboles containing notable
quantities of the molecule FeSiQj. In griinerite, the quantity of Mg
present is very small but in cummingtonite it is fairly large. Because
of its similarity to anthophyllite, this mineral is frequently referred
to as amphibole-anthophyllite. It is intermediate in composition
between griinerite and actinolite. Analyses of specimens from several
well known localities are quoted below.

FeO MgO CaO Na20 H20 Total

15.64 21.70 tr. 2.80 99.88

43.40 2.61 1.90 .47 2.22 100.08

I. Cummingtonite, near Baltimore, Md.

II. Griinerite, Collobrieres, France. Contains also, F=.o7, KfO=*.07 and
MnO = .o8.

These two minerals are comparatively rare and have not always
been recognized as worthy of different names. In general appearance
they are much like actinolite, though perhaps more brown or gray in
color, and they occur in nearly the same association. The specific grav-
ity of cummingtonite varies between 3.1 and 3.3 and that of griinerite is
about 3.52. The intermediate refractive index for yellow light is 1.62-
1.65 in cummingtonite and 1.697 m griinerite.

Hornblende is the name given to the monoclinic aluminous amphi-
boles that contain only a small quantity of alkalies. In other words,
most of the hornblendes are isomorphous mixtures of the actinolite mole-
cule and the molecules (Mg- Fe)((Al- Fe)0)2Si04 and (Na- K)Al(Si03)2.
The varieties containing Na20 (known as katofarite) correspond to
aegirine among the pyroxenes.

Si02

A1203

Fe2C>3

I. 57.26

•75

i-73

II. 47.17

1. 00

1. 12

1 .620

1.632

1 .642

1 653

1-725

1-752

388 DESCRIPTIVE MINERALOGY

The varieties of hornblende that are distinguished by distinctive
names are:

Pargasite, the green, bluish green or greenish black variety, and

Edenite, the white, gray or light green variety, both of which con-
tain very little iron in either the ferrous or ferric condition,

Smaragdite, a bright green chromiferous variety of pargasite,

Common Iwrnblende, the greenish black variety,

Basaltic hornblende, which contains a large proportion of ferric iron
and is black in color.

Their refractive indices for yellow light are as follows:

Pargasite, Pargas, Finland 1 . 613

Common Hornblende, Kragero, Norway 1 . 629
Basaltic hornblende, Bohemia 1 . 680

The fusing temperature of pargasite is about 11500 and of horn-
blende about 12000.

Analyses of typical specimens of these varieties follow:

Si02 AI2O3 Fe203 FeO MgO CaO Na20 K20 Ign Total

I. 5169 4.17 2.34 9.83 17.17 12.17 .82 .79 1. 13 100.25

II.42.97 16.42 1.32 20.14 x4-99 i-53 2-85 .87 102.75

III. 49.33 I2-72 172 463 17.44 9.91 2.25 .63 .29 99.13

rv. 39.17 14 .37 12.42 5.86 10.52 11. 18 2.48 2.01 .39 99.91

I. Common Hornblende, Vosges. Also .14 per cent TiCfe.
II. Pargasite, Pargas, Finland. Also 1.66 per cent F.

III. Edenite, Saualpen, Carinthia. Also 1.21 per cent F.

IV. Basaltic, Jan Mayen, Greenland. Also 1.51 per cent MnO.

Among the commonest forms of alteration in the amphiboles
are the following: Tremolite into talc (p. 401) and serpentine, and
hornblende into serpentine, chlorite (p. 428), epidote and biotite, often
with the addition of magnetite and other iron compounds in cases where
iron was present in the original mineral. Most of these changes are
brought about by regional metamorphism. The production of biotite is
also brought about by the action of magmas. The common weathering
products of hornblende are chlorite, epidote, calcite, quartz, magnetite
and siderite. Under the conditions of high temperature and high pres-
sure, hornblende sometimes passes over into augite and magnetite.

Syntheses, — Amphibole crystals have not been found in slags nor
have they been made by dry fusion. Crystals of hornblende, however,

ANHYDROUS METASILICATES 389

have been obtained by heating to 555 ° for three months, a mixture of
its components in a glass tube with water.

Occurrence. — Tremolite occurs in crystalline limestones and dolo-
mites that have been subjected to regional metamorphism and in crys-
talline schists. Actinolite, cummingtonite and griinerite are found in
crystalline schists, in some cases in such large quantity as to constitute
essential parts of the rocks. Actinolite schists are such rocks containing
in addition to the actinolite some quartz, epidote and chlorite. Grii-
nerite schists consist essentially of griinerite, actinolite, magnetite and
quartz.

Common hornblende occurs in igneous and metamorphic rocks,
such as gneisses and schists. In some schists, as the amphibolites,
it is the principal constituent and in others, the hornblende schists,
it is the principal component other than quartz. The mineral is
also a common metamorphic alteration product of pyroxenes which
it frequently pseudomorphs. When the pseudomorphing hornblende
is blue-green and fibrous it is known as uralite. The chemical
changes attending this alteration are illustrated by the analyses of a
pyroxene (I) from the Grua Tunnel in Norway and of the uralite (II)
produced from it.

Si02 Fe203 AI2O3 FeO MnO CaO MgO Na20 Loss Total
I. 50.53 1. 91 .27 7.81 1.99 24.51 10.92 .48 .26 100.37*
II. 42.02 2.30 3.25 9.30 .94 20.90 9.63 .45 1.07 100.04*

* Also .19 per cent K20 in I and .26 per cent in II.

Basaltic hornblende is found only in igneous rocks, and especially
those rich in iron.

Edenite occurs in crystalline limestones that have been metamor-
phosed by contact action.

Pargasite is in gneisses and crystalline limestones.

Localities. — Tremolite crystals occur at Campolonga, Switzerland;
at Rezb&nya, Hungary; at New Canaan, Conn.; and at Diana, Lewis
Co., N. Y. It occurs also in flat plates at Lee, Mass.; near Byram,
N. J.; at Easton, Penn. ; at Edenville, N. Y.; and at Litchfield, Me.,
and other places in the limestones in Quebec, Canada.

Actinolite occurs with chlorite at the Zillerthal, Tyrol; in talc and
chlorite schists near Jekaterinburg, Ural, Russia; at Arendal, Norway;
at Willis Mt., Buckingham Co., Va.; at the Bare Hills, Md.; at Mineral
Hill, in Delaware Co., and at Unionville, Penn., in the soapstone
quarries at Windham and New Fane, Vt.; at Bolton, Brome Co.,
Quebec, and at many other points.

390 DESCRIPTIVE MINERALOGY

Asbestus is abundant at Sterzig, in Tyrol; on the Island of Corsica;
near Greenwood Furnace, N. Y.; in the Bare Hills, near Baltimore, Md. ;
at Pylesville, Harford Co., in the same State; at Barnet's Mills, Fau-
quier Co., Va., and at the localities at which it has been mentioned as
being mined.

The principal occurrences of cummingtonite are Kongsberg, Norway,
Cummington, Mass.; and a layer in gneisses and schists at Mt.
Washington, Md.

Griinerite occurs in a rock composed of this mineral, garnet and hem-
atite near Collobrifcres, Var., France. It has also been described as the
principal constituent of certain schists in the Lake Superior iron region,
but since the amphibole in these rocks contains a notable quantity
of MgO it should better be classed with cummingtonite.

The localities at which crystals of the hornblendes have been
found are very numerous. Excellent crystals occur in the volcanic
bombs in the Lake Laach district, Prussia; in cavities in inclusions
within the lavas of Aranyer Mt., Siebenburgen, Hungary; in the dikes
of porphyry, near Roda, Tyrol; on the walls of cavities in inclusions in
the lavas at Vesuvius, Italy; and at various points in Sweden, etc. . In
North America fine crystals are found at Thomaston, Me.; at Russell
and Pierrepont, N. Y.; at Franconia, N. H.; and in the glacial debris
at Jan Mayen, Greenland. Pargasite occurs at Pargas, Finland, and
Phippsburg, Me.

Alkali Amphiboles

The alkaline amphiboles include riebeckilc, crocidolite, glaucophane
and arfvedsonile. The first two are nonaluminous iron-soda amphiboles
and the last two are aluminous compounds. Glaucophane contains the
molecule NaAl(Si03)2 which is found also in hornblende, and, therefore,
it may be regarded as a connecting link between the common and the
alkaline amphiboles. Glaucophane differs from hornblende, however,
in containing very little CaO. The intermediate link katoforite bridges
the gap between the two.

Glaucophane

NaAl(Si03)2
(Fe-Mg)SiOa t

Glaucophane is, theoretically, a mixture of the two molecules
NaAl(Si03)2 and (Fe* Mg)Si03. It is essentially a mixture of the cum-
mingtonite molecule with one corresponding to the jadeite molecule

ANHYDROUS METASILICATES 391

among the pyroxenes. An analysis of a specimen of katoforite (com-
pare p. 387) from the sanidinite bombs in the lava at Sao Miguel, Azores,
is quoted in line I for comparison with the two glaucophane analyses in
lines II and III.

Si02

AI2O3 Fe203

FeO

MgO

CaO

Na20

K20

Total

I- 45 • 53

410 9-35

23.72

2.46

4.89

6.07

.88

99.96

n. 56.65

12.31 3.01

458

12.29

2. 20

7-93

IOS

100.02

III. 56.71

15.14 9.78

4-31

4-33

4.80

4.83

■25

100.15

I. Katoforite, Sao Miguel, Azores. Also 2.96 per rent TiO*.
II. Glaucophane, He de Groix.
III. Glaucophane, Shikoku, Japan.

Glaucophane is rarely found in crystals with end faces. Even when
these exist they are rough and yield poor measurements.

The mineral occurs in columnar crystals, in needles and in foliated
or granular aggregates in rocks. Their prismatic planes are 00 P 60 (100),
00 P ob (010) and 00 P(no). P(Tn) and oP(ooi) are the only termina-
tions that have been identified. The cleavage angle is about 55 ° 20'.

Glaucophane is blue or bluish black, translucent and strongly pleo-
chroic in yellowish, violet and blue tints. Its streak is grayish blue,
its fracture uneven, its hardness about 6 and its density 3. Its refractive
indices for yellow light are: a= 1.62 12, 0= 1.6381, 7= 1.6300.

Before the blowpipe the mineral turns brown and then melts to an
olive-green glass. It is difficultly attacked by acids.

Glaucophane is distinguished from the other amphiboloids by its
color, and from other blue silicates by its crystallization, hardness and
manner of occurrence.

It is usually unaltered but it has been described in one instance as
being partially changed to chlorite.

Synthesis. — It has not been produced artificially.

Occurrence. — The mineral is found only in metamorphosed limestones,
in mica schists and in the garnet rock known as eclogite. It is charac-
teristically a metamorphic mineral.

Localities. — Glaucophane occurs in long crystals in various schists in
Syra, Cyclades, Greece; in hornblende schists in the He de Groix, Brit-
tany, France; in a glaucophane schist on the Island of Shikoku, Japan;
and abundantly in various SJ Aists in the Coast Ranges of California.

392 DESCRIPTIVE MINERALOGY

Arfvedsonite, Riebeckite and Crocidolite

These amphiboles are comparatively rare. They occur principally
in coarse-grained alkaline igneous rocks, usually as prismatic grains
without terminations, embedded in the rock mass. Arfvedsonite, how-
ever, in some cases, occurs in groups of crystals on some of which ter-
minations can be identified.

Riebeckite, NaFe(S • 03)2, has a composition very near that of acmite,
and crocidolite contains, in addition, the molecule FeSi03. Arfvedsonite
is much more complex than either of these and has no equivalent among
the pyroxenes. Analyses of typical specimens of the two minerals are
quoted below. In line IV is an analysis of crocidolite.

Si02 AI2O3 Fe203 FeO MgO CaO K20 Na20 H20 Total

I. 47.08 1.44 1.70

35-65

... 2.32

2.88 7.14

2.08

100.29

n. 49.65 1.34 17.66

19-55

... 3. 16

.... 7.61

1.67

100.64

in. 50 . 01 .... 28 . 30

9.87

•34 i-32

.72 8.79

• • * •

99.98

rv. 5103 17.88

21 . 19

.09 ....

.... 6.41

364

100.24

I. Black arfvedsonite, Kangerdluarsuk, Greenland.

II. Riebeckite from granite, Quincy, Mass.

III. Riebeckite from Socotra, Indian Ocean.

IV. Dark blue radial aggregates of crocidolite, Cumberland, R. I.

Arfvedsonite is usually in long prisms flattened parallel to
00 P 00 (010), but otherwise very much like hornblende. It is black or
dark green and translucent, and has a dark bluish gray streak. Its hard-
ness is 6 and density 3.4-3.5. It is strongly pleochroic. Thin splinters
parallel to 00 Poo (010), are olive green and those parallel to 00 P 6b
are deep greenish blue. Its refractive indices for yellow light are:
a= 1.687, 18=1.707, 7=1.708.

Before the blowpipe the mineral fuses easily to a black magnetic
globule and colors the flame yellow. It is not acted upon by acids. .

Riebeckite is found only in embedded prisms, showing no termina-
tions. It is black, vitreous and very pleochroic in green and dark blue
tints. Its density is about 3.3, and its hardness 5.5-6. Its refractive
index for yellow light is about 1.687. Before the blowpipe it fuses easily,
imparting an intense yellow color to the flame.

Crocidolite is an asbestus-like, lavender-blue or dark green riebeckite,
that contains a larger amount of iron, due to the presence of the mole-
cule FeSiC>3. It occurs also in earthy masses. Its streak is lavender-blue
or leek-green and its hardness is 4. In all cases it appears to be a
secondary mineral. The green fibrous variety is known as " cat's-eye."

ANHYDROUS METASILICATES 393

Both riebeckite ancU-rfvedsonite weather to aggregates of iron oxides,
quartz and carbonates. The decomposed, brown crocidolite is the well-
known ornamental stone " tiger's-eye."

Occurrence and Localities. — Arfvedsonite is found principally in
igneous rocks rich in soda, especially the coarse, nepheline syenites of
Greenland; Kola, Russia; and in the augite syenites of Norway. It
occurs also in the nepheline syenites of Dungannon township, Ontario,
and of the Trans-Pecos district, Texas.

Riebeckite is also formed in acid rocks rich in soda, such as certain
granites, syenites, etc. It is found on the Island of Socotra in the Indian
Ocean; in fine-grained granitic rocks at Ailsa Crag, Scotland; in Corsica
and a few other places. The crocidolite variety occurs in a clay slate
on the banks of the Orange River in South Africa; at various points in
the Vosges, Salzburg, Tyrol and Andalusia, in Europe; in Templeton,
Ontario; in veins at Beacon Pole Hill, near Cumberland, R. I., in gran-
ites at Quincy and Cape Anne, Mass., near St. Peter's Dome, El Paso
Co., Colorado, and as fibers in rocks at various other points in the United
States.

TRICLINIC AM PHI BOLE

The only known triclinic amphibole is the comparatively rare aenig-
matite, an alkali amphibole with a complicated composition that may
be represented by the formula Na4FeQ(Al*Fe)2(Si*Ti)i2038. The
mineral occurs in very complex crystals, with iioAiTo=66°, in
alkaline rocks at Naujakasik, Greenland; in the Fourch Mts., Ark.;
and at several other places.

It is black, or brownish black, and translucent or transparent and
has a reddish brown streak. It is, moreover, strongly pleochroic in
brownish black and reddish brown tints. It is brittle, has a hardness
of a little more than 5 and a density of 3.7-3.8. Before the blowpipe it
fuses to a brownish black glass. It is partly decomposed by acids. It
is distinguished from other dark hornblendes by the cleavage angle
of 66°.

BASIC METASILICATES

Kyanite ((A10)2Si03)

Kyanite, cyanite, or disthene, is a fairly common product of meta-
morphism in certain schists. The name kyanite suggests the sky blue
color noticed in many specimens. The name disthene refers to the
great difference in hardness exhibited in different directions.

The mineral is regarded as a basic metasilicate of the theoretical

394

DESCRIPTIVE MINERALOGY

composition: Si02=37-02; Al203=r62.98 (compare pages 319, 320).
Nearly all specimens contain a little Fe203 but otherwise they cor-
respond very closely to the calculated composition indicated by the
above formula. A light blue specimen from North Thompson River,
B. C, upon analyses, gave:

S1O2
36.29

AI2O3

62.25

Fe203

♦55

CaO

1.06

MgO

•36

Total
100.51

Fig. 210. — Kyanite Crys-
tal with 00 P * , 100 (a);

00 Poo, 010 (6); oP,
001(c); 00 'P, 1 To (if);

00 P', no (m) and

00 P'2, 210 (/).

Kyanite crystallizes in the triclinic system (triclinic pinacoidal
class), with an axial ratio .8991 : 1 : .7090; a = 90° 55', 0=ioi° 2' and
7=105° 445'. Very few crystals are well developed. Their habit is

columnar or tabular with 00 P 60 (100) predomi-
nating. More frequently the mineral occurs
in long, flat, isolated blades, or in diverging
flat plates (Fig. 210). Some crystals are
very complex. Usually, however, only the
forms ooP<»(ioo), 00 P 60 (010), ooP'(no),
00 'P2~(2io), 00 ,P(iTo) and oP(ooi) are pres-
ent. Twinning is common according to several
laws, most of which, however, yield twins in
which the basal planes (oP) of the twinned in-
dividuals are parallel. The most frequent
twins have 00 P rc (100) as the twinning plane.
Other twinning planes are perpendicular to the axis c, or to the
axis b. The basal plane oP(ooi) also serves as the twinning plane
in some cases. Twinning is often repeated, producing lamellae crossing
columnar crystals approximately parallel to the basal plane, and giving
rise to a definite parting in this direction.

The cleavage of kyanite is very perfect parallel to 00 P 66 (100)
and less perfect parallel to 00 P 06 (010). It frequently possesses also a
parting parallel to oP(ooi), as already stated. The luster on cleavage
faces is pearly. Otherwise it is glassy. The mineral is often light blue
in color, less frequently it is colorless or white, yellow, green, brown or
gray. It is translucent or transparent and the darker blue varieties are
pleochroic in dark and light blue tints. Its hardness varies greatly
on different faces and in different directions on the same face. On the
macropinacoid a it is about 5 parallel to the vertical edges, and 7 in the
direction at right angles to this. The specific gravity of the mineral is
about 3.6, and its refractive indices for yellow light are: a^i.7171,
0=1.7222,7=1.7290.

Before the blowpipe kyanite whitens, but otherwise it reacts like

ANHYDROUS METASILICATES 395

sillimanite. It is insoluble in acids. It is distinguished from the few
other minerals that it resembles by the great differences in hardness on
its cleavage surfaces. At a high temperature (about 1350°) it appar-
ently changes to sillimanite.

Kyanite weathers to muscovite, talc (p. 401) and pyrophylUte
(p. 406), and is itself an alteration product of andalusite and corundum.

Syntkesis. — It is not known that the mineral has been produced in the
laboratory.

Occurrence and Origin. — Kyanite occurs as large plates and small

Fir,, an.— Bladed Kyanite Crystals in a Miraienus Quartz Schist from Pisuso Fomo,

Switzerland. (About natural size.)

crystals in micaceous and other schists (Fig. an), and as an important
constituent of some quartzites. At Horrsjoherg, in Wermland, Sweden,
it forms a distinct layer of schist several meters thick. In a few places
it is found in zones of contact metamorphism, but it is more frequently
the result of dynamic metamorphism (cf. p. 26).

Localities. — Crystals have been found at Greiner in the Tyrol; at
Mte. Campione in Switzerland; and at Graves Mt. in Lincoln Co., Ga.
The mineral also occurs in fine plates at Chesterfield, Mass.; at Litch-
field, Conn.; at Bakersville, N. C; and on North Thompson River,
B. C, Canada.

Uses. — Transparent kyanite is sometimes used as a gem.

396

DESCRIPTIVE MINERALOGY

ZnO

H20

Total

67.49

7-5o

100.00

67.88

813

99.96

65-°5

7.89

99 38

Calamine ((ZnOH)2Si03)

Calamine, or hemimorphite, is an important ore of zinc. It is one of
the few silicates used as a source of metals. While theoretically a
pure zinc compound it usually contains a little Fe2<33 and frequently
small quantities of PbO. In some cases it contains also a little carbon-
ate. A number of formulas have been suggested for it, of which the
one given above is the simplest. According to several prominent miner-
alogists, however, the formula Z^SiO* • H2O is preferable.

Si02 Fe203

Theoretical 25 .01

Wythe Co., Va 23 . 95

Friedensville, Pa 24.32 2.12

The mineral occurs in brilliant crystals that are orthorhombic and
distinctly hemimorphic (rhombic pyramidal class), with an axial ratio

of .7834 : 1 : .4778. The crystals
are usually tabular parallel to
00 P 06 (010). Many are highly
modified but some are fairly sim-
ple, with 00 P(i 10) , 00 P 00 (100)
and 3P<x>(30i) in the pris-
matic zone, 3P06 (031), P66 (101),
P06 (on) and oP(ooi) at the ana-
logue pole and 2P2(i27) at the
Fig. 212.— Calamine Crystals with 00 P, antilogue pole (Fig. 212). The angle
no (m); 00P 00 L 100 (a); 00 P 06 , IIO A lTo= ?6° Q/# Twins are fairly
010(b): 2P2, 121 (t»); Poo,ioi (5); ... -p., N , .

„ w ' „ _ ,t[ nJ common, with oP(ooi) the twinning

Poo, on (e); 3Pqo,3oi (/); 3P00, ' 4 v ; 6

031 (1) and oP, 001 (c). Plane* #0ften manv oystals are

grouped in sheaf-like, fibrous or

warty aggregates and in crusts. The mineral is also granular and

compact. Its cleavage is perfect parallel to 00 P(no).

Calamine is glassy, transparent or translucent, and when pure is
colorless or white. Usually, however, it is gray, yellow, brown, greenish
or bluish. Its streak is white, its hardness 4-4.5 and its density 3.2-3.5.
It is brittle. Its fracture is uneven. The mineral is strongly pyroelectric
with the end of the crystals terminated by dome faces the analogue pole.
In contact twins both ends are analogues. The mineral becomes phos-
phorescent upon rubbing, and is fluorescent in ultra violet light. Its
refractive indices for yellow light are: #=1.6136, 0=1.6170, 7=1.6360.

Before the blowpipe calamine is almost infusible, but on charcoal
it swells, colors the flame greenish and fuses with difficulty on the edges.

ANHYDROUS METASILICATES 397

With soda it gives the zinc sublimate. In the closed glass tube it de-
crepitates and yields water and becomes cloudy. Its powder dissolves
in even weak acids with the production of gelatinous silica.

Calamine is distinguished from smithsonite by its reaction with acids
and from other minerals by its crystallization and reaction for zinc. It
alters to willemite, smithsonite and quartz. Calamine has not been
produced artificially.

Occurrence. — It occurs principally in the upper or oxidized zones of
veins of zinc ore and in layers above the zone of permanent ground water
in certain zinc and lead-bearing limestones. It is associated with lead
ores and various zinc compounds, and it often pseudomorphs calcite,
galena and pyromorphite.

Localities. — Calamine occurs in nearly all places where zinc and
lead ores are found. It is abundant at Altenberg near Aachen in Rhen-
ish Prussia; at Wiesloch, in Baden; near Tamowitz, in Silesia; at
Rezb&nya, Hungary; near Bleiberg, Carinthia; near Santander, Spain;
in Cumberland, England; at Sterling Hill, N. J.; at Friedensville,
near South Bethlehem, Penn.; at the Bertha Mine in Pulaski Co., and
at the Austin Mine, in Wythe Co., Va.; and in the zinc-producing areas
in the Mississippi Valley.

Uses. — It is a common associate of other zinc ores and many lead
ores and is mined with the former as a source of zinc.

ACID METASILICATES

SERPENTINE GROUP

The serpentine group includes a large number of hydrous magnesium
silicates that differ from one another mainly in the proportions of water
present and in the ratio of silica to magnesia. None of them yields
crystals, though their crystallization is thought to be monoclinic. All
occur in dense fibrous or platy aggregates. The most prominent mem-
bers of the group are:

Serpentine H4Mg3Si2C>9, or SiC>2 MgO H2O

H(MgOH)3(Si03)2 =43 50 43-46 13. 04

Meerschaum HiMg2Si30io, or

H3Mg(MgOH)(Si03)3 =60.83 27.01 12.16

Steatite H2Mg3(Si03)4 =63. 52 3172 4. 76

All are soft and nearly infusible, and all are of considerable economic
importance.

398 DESCRIPTIVE MINERALOGY

Serpentine (H4Mg3Si2Oo)

The substance known as serpentine may be two different minerals,
one orthorhombic and the other monoclinic. They, however, cannot
be distinguished, except by microscopic study. Serpentine occurs in
structureless, fibrous, foliated and schistose masses of a white, gray,
brown or green color. It is translucent and has a dull, slightly glistening
or fatty luster, and a white streak. The variety known as " noble ser-
pentine " is nearly transparent and has a clear greenish or yellowish
white, yellowish green, apple-green or dark green color. The mineral,
when pure, has a hardness of 3, but it frequently seems harder because
there are often mixed with it tiny remnants of the much harder minerals
from which it was derived. The specific gravity of pure serpentine is
2.5-2.6. Its refractive indices vary widely. /3=i. 502-1. 570.

Serpentine fuses on thin edges when heated in the blowpipe flame.
It yields water in the closed tube. When heated to about 14000 it crys-
tallizes as olivine. It is decomposed by hydrochloric and sulphuric
acids with the separation of gelatinous silica, which, in fibrous varieties,
retains the shapes of the fibers. It is also soluble in dilute carbonic acid.
Its powder reacts alkaline.

Ckrysotile is a silky, nearly transparent fibrous variety occurring in
veins. It is apparently orthorhombic.

Antigorite is a form occurring in laminated masses or in microscopic
scales, that are possibly monoclinic.

Baltimorite and picrolite are coarse, green, fibrous varieties.

Analyses of a pure green serpentine, and a typical chrysotile, both
from Montville, N. J., are quoted below:

Si02

AI2O3

Fe2C>3

FeO

MgO

CaO

H20

Total

I. 42.05

• • •

•30

.10

42.57

•05

14.66

99-73

II. 42.42

.63

.62

• • •

41.01

■ • •

15-64

100.55

I. Green serpentine, Montville, N. J.
II. Chrysotile, Montville, N. J. Also .23 NiO.

Massive varieties are distinguished from talc by their solubility in
acids and by differences in hardness, and chrysotile is distinguished from
ampkibole asbestus by the presence in it of water.

Synthesis, — Serpentine has been made by the action of a solution of
Na2Si03 upon magnesite for 10 days at ioo°.

Occurrence. — The mineral is a common decomposition product of
several other magnesium silicates, more particularly olivine, pyroxene

ANHYDROUS METAS1LICATES 399

and chondrodite. Many igneous rocks rich in these minerals are com-
pletely changed to serpentine, especially around their peripheries, and
some metamorphosed limestones are also partially or completely ser-
pentinized. It is probably a secondary mineral in all cases.

Localities. — Serpentine occurs in large quantity at Webster, N. C;
Montville, N. J.; Easton, Penn.; at the Tilly Foster Iron Mine,
Brewster, N. Y., at Thetford and Black Lake in the Eastern Townships
of Quebec, and at many other places in North America. It is also known
from many places in Europe.

Uses. — Serpentine when massive is used as a building stone. The
finer varieties are sawed into thin slabs and used for ornamental purposes.
Marble with streaks and spots of serpentine is known as ophicalcite. and
under the name "verd-antique " is employed as an ornamental stone.
Mixtures of serpentine with other soft minerals are ground for a paper
pulp. The fibrous variety — chrysotile — is mined and sold under the
name of asbestos, which, because of its fibrous structure, its flexibility,
its incombustibility, and because it is a nonconductor of heat and
electricity is becoming an exceedingly important economic product. It
is woven into paper and boards that arc used to cover steam pipes, and
to increase electric insulations, and is manufactured into shingles. It
is used also in fireproofing, in the manufacture of automobile tires,
in making paints, and as a substitute for rubber in packing steam
pipes.

Preparation. — The chrysotile mined in Vermont comes from a mass
of serpentine that is cut by many small veins of chrysotile. The rock is
crushed and the fiber is separated by washing, or by some other mechan-
ical method. The pulp rock at Easton is a mass of serpentine, talc and
a few other minerals. It is ground and sized for use in paper manu-
facture.

Production. — Chrysotile is mined in Vermont and Wyoming. The
production Is rapidly increasing but the actual amount mined annually
has not been disclosed. The total aggregate of chrysotile and amphibole
asbestos (see p. 386), produced in the United States during 191 2 was
4.403 tons, valued at $87,959. The imports of unmanufactured asbestos
for the same year were valued at $1,456,012, of which $1,441,475 worth
came from Canada. The total production of this country in the same
year amounted to about $2,979,384, most of which came from the Thet-
ford district in Quebec. This is about 80 per cent of the world's pro-
duction. The value of the serpentine used as an ornamental and build-
ing stone is not known.

400 DESCRIPTIVE MINERALOGY

Garnierite may be regarded as a serpentine or talc in which a portion
of the magnesium has been replaced by nickel, or possibly as a mixture
of a colloidal magnesium silicate and a nickel compound. Its impor-
tance consists in the fact that it is the only commercial source of nickel
aside from the pentlandite in the pyrrhotite of Sudbury, Canada.
Three analyses of garnierite from New Caledonia follow:

Si02

NiO

MgO

A120 • Fe203

H20

Total

35-45

45.15

2.47

•50

15-55

99.12

3778

. 3391

10.66

i-57

15-83

9975

42.61

21.91

18.27

.89

1540

99.08

These show that as MgO diminishes, NiO increases.

Garnierite is a dark green to pale green substance with many of the
physical properties of serpentine. Its luster is dull, or like that of var-
nish. It has a greasy feel, a hardness of 2-3 and a density of 2.3-2.8.
Its streak is light green to white. When touched to the tongue it ad-
heres like clay. It is infusible when heated before the blowpipe, but
decrepitates and becomes magnetic. It is partly soluble in HC1 and
HNO3.

It is readily distinguished from malachite and chrysocolla by its
structure, its greasy feel and the absence of a good copper test.

Occurrence and Localities. — The mineral occurs as earthy masses, as
mamillary coatings and as impregnations and veins in serpentine. In
all cases it appears to have resulted from the weathering of peridotite.
The earthy masses are residual and the veins are deposits from down-
ward percolating water that obtained nickel from the decomposing
rock.

The principal occurrences of garnierite are New Caledonia, where it is
mined as a source of nickel, and at Riddles, Douglas Co., Oregon. A
very closely allied species, genthite, occurs associated with chromite in
serpentine at Texas, Lancaster Co., Penn., at Webster, N. C, at Malaga,
in Spain, and at a few other places.

Production. — Garnierite is mined from 40 mines on the plateau of
Thio, New Caledonia, at the rate of about 130,000 tons annually of a
6 J per cent ore. In 191 2 there were produced 72,315 tons of ore and
5,097 tons of matte containing 2,263 tons 0I" nickel. The aggregate
value of ore and matte was about $1,140,000.

ANHYDROUS METASILICATES 401

Meerschaum (H4Mg2Si3Oi0)

Meerschaum, or sepiolite, occurs as a massive, dense, earthy aggre
gate of a white, yellowish or reddish color, and also as a finely fibrous,
crystalline aggregate (parasepiolile). It is opaque, has a conchoidal
fracture and a shining white streak. Its hardness is 2 and density
about 2. Dry specimens will float on water, because they are not
easily wet. When touched to the tongue a clinging sensation is pro-
duced. Two varieties of the commercial material have been recognized.
Of these, one, a sepiolite, is HsMg2(Si30i2) and the other p sepiolite,
has the composition indicated above.

The analyses of white meerschaum irom Asia Minor and from Utah
gave the following results:

Si02 AI2O3 Fe203 MgO H20 Total

Asia Minor. . 52.45 .80 ... 23.25 23.50 100.00

Utah 52-97 -86 .70 22.50 18.70* 99-74

* Of this 8.80% was driven off at ioo°. Included also are 3.14 MnsOj and .87 CuO.

Before the blowpipe the mineral fuses on its edges to a white enamel.
Often, at first, it turns brown or black vand then, upon higher heating,
it bleaches to white. At low temperature in the closed tube it yields
a little hygroscopic water. At high temperature water is given off freely.
The mineral dissolves in hydrochloric acid, with the production of gelat-
inous silica in the case of the a variety.

Meerschaum resembles chalk and kaolin, from which it is easily dis-
tinguished by treatment with hydrochloric acid.

Occurrence and Localities. — The mineral is found as nodules in young
sedimentary beds in Asia Minor, where it is associated with magnesite.
Both minerals are believed to be alteration products of serpentine. It
occurs also with opal at Thebes, Greece. A red variety occurs in lime-
stone at Quincy, France, and a green and white variety forms a small
vein in a silver ore in Utah. In all of its occurrences it seems to be
secondary.

Uses. — Meerschaum is used for carving into ornaments and pipes.

Steatite (H2Mg3(Si03)4)

Steatite, or talc, usually occurs in flaky, foliated and massive forms,
and in plates that appear to be tabular crystals with hexagonal outlines.
It also forms, with chlorite and a few other substances, the rock soap-
stone. Although its crystallization is unknown, because of the close

402 DESCRIPTIVE MINERALOGY

analogy between its physical properties and those of chlorite and the
micas its symmetry is believed to be monociinic.

The composition of pure white talc and ordinary soapstone are shown
by the two analyses below:

White talc Soapstone

Uraerenthal, Switzerland W. Griqualand, Africa

Si02 60 . 85 63 . 29

AI2O3 1. 71 1.24

Fe«203 .16

FeO 09 4.68

MgO 32.08 27.13

H20 495 4.40

Total 99 . 68 100 . 90

The composition corresponding to the formula H2Mg3(SiC>3)4 is:
Si02=63.5, MgO = 3i.7 and H20=4.8.

The cleavage of talc is well marked and on its cleavage surfaces its
luster is pearly. Its cleavage plates are flexible. The mineral is white,
gray, greenish or bluish, and is transparent or translucent. The massive
forms, known as soapstone, are white, greenish, yellowish, red or brown.
All varieties are soft — the mineral being chosen to represent 1 in the
scale of hardness — and all have a soapy feeling. The density of pure
talc is 2.6-2.8. For yellow light, a= 1.539, /3= 1.589, 7= 1.589.

Before the blowpipe the mineral exfoliates, hardens and glows
brightly, but it is nearly infusible (fusing temperature is about 15300),
melting only on the thinnest edges to a white enamel. It yields water in
the closed tube only at a high temperature. It is unattacked by acids
before and after heating. Its powder reacts alkaline.

It is distinguished from other white, soft minerals by its softness, its
insolubility in acids and its infusibility.

Occurrence. — The mineral is a common alteration product of other
magnesium silicates, often pseudomorphing them. Thus, pseudo-
morphs of the mineral after actinolite, bronzite and sahlite are common.
Pseudomorphs after pectolite, dolomite and quartz are also known. In
these forms it is secondary.

It occurs also in marbles and other crystalline rocks, where it was
produced by regional metamorphism. It is found, further, as small veins
cutting serpentine and metamorphosed limestones, as layers under the
name of talc schists, associated with other schistose rocks and as massive
aggregates of finely matted fibers, probably resulting from the alteration
of basic igneous rocks. The last described variety is the rock soapstone.

ANHYDROUS METASILICATES 403

The vein material is usually white, fibrous and pure. It is gi < und and
placed on the market as talc. The impure variety (soapstone) is sawn
into blocks and boards.

Localities. — Talc and soapstone occur at many places. Good white
platy talc occurs at Lampersdorf, in Silesia; near Pressnitz, in Bohemia;
near Mautern, in Steiermark; at Andermatt, in Switzerland; at Russell,
Gouverneur and other points in New York; at Webster, N. C; and at
Easton, Penn.

Uses. — Ground talc is extensively used as a lubricator, in the manu-
facture of paper, as a filler in curtains, cloth, etc., as a foundry facing, in
the manufacture of molded rubber goods, as a toilet powder, as a polish-
ing material, as a pigment, in the manufacture of gas tips, pencils, cray-
ons, etc. Soapstone is sawn and used as linings of acid vats and laundry
tubs, and in the manufacture of table tops, sinks, etc., in chemical labora-
tories. Because of its nonabsorbent qualities it is also being used
largely in electric switchboards. Its various uses are due to its softness,
infusibility, and its power of resistance to the attacks of acids.

Production. — The principal sources of talc and soapstone in the
United States are in a belt on the east side of the Appalachians ex-
tending from Vermont to Georgia. Largest producers in 1912 were:

Virginia, with a production of 25,313 tons, valued at $576,473,
New York, with a production of 66,867 tons> valued at $656,270,
Vermont, with a production of 42,413 tons, valued at $275,679.

Of the aggregate of 159,270 tons, valued at $1,706,963 produced in 191 2,
15,510 tons were sold* in the rough for $66,798; 2,642 tons, sawed into
slabs, were sold for $50,334, 21,557 tons were manufactured and sold for
$600,105, and 119,561 tons were sold ground for $989,726. Of this
aggregate J33>2^9 tons> valued at $1,097,483 were talc and 25,981 tons,
valued at $609,480 were soapstone. In addition to the home produc-
tion, there were also consumed in the United States 10,989 tons of high-
grade talc, valued at $122,956, which was imported.

KAOLINITE GROUP

The kaolinite group of minerals comprises hydrous aluminium sili-
cates corresponding to the magnesium silicates of the serpentine group.
The principal members of the group are:

Kaolinite, H4Al2Si209, or H2Al(Al(OH)2)3(Si03)4

= 46.50 SK>2, 39.56 AI2O3, 13.94 H2O
Pyropkyllite, H2Al2(Si03)4 =66.65 Si02, 28.35 AI2O3, 5.00 H20

404 DESCRIPTIVE MINERALOGY

Kaolinite corresponds to serpentine in which all the Mg has been re-
placed by Al and pyrophyllite to steatite. In addition to these, there
are other closely related compounds which may be intermediate in com-
position between these two. Among them the most common are alio-
phane, monlmorillonite and haUoysite.

Both minerals are of economic importance. Kaolinite is the base
of all clay products like pottery, tile, bricks, etc.

Kaolinite (H4Al2Si209)

The crystallization of kaolinite is probably monoclinic. The crystals,
which are rare, are thin plates with an hexagonal habit, bounded by the
planes oP(ooi), oo P(no) and oo P «> (oio) and +P(Tn). Their axial
ratio is .5748 : 1 : 1.5997 with P=&$° n\ Their cleavage is perfect
parallel to the base.

Distinct crystals have been found only on the Island of Anglesey,
Wales, and at the National Belle Mine, at Silverton, Colo., where they
comprise a white powder every grain of which is a crystal.

The mineral, when pure, is white or colorless and transparent. It
has a hardness of 1 and a specific gravity of 2.45. It is infusible before
the blowpipe and is only slightly attacked by HC1. It is decomposed
by alkalies and alkaline carbonates with the production of hydrated
silicates. Its index of refraction is about 1.56.

The greater part of the kaolinite known is not in crystals. It usually
occurs in foliated or dense earthy masses to which various names have
been assigned.

Nakrite is a white crystalline mass of kaolinite made up of tiny
flakes often arranged in fan-like or divergent groups. The individual
flakes have a pearly luster. It occurs as vein fillings in certain ore-
bodies.

Steinmarkite is a dense mass of microscopic grains often forming
nodular masses and occurring as veins and nests in rocks. It is harder
than pure kaolin (H= 2-3), and is often yellowish, gray or red in color.

Kaolin is an earthy, friable mass of flaky kaolinite which when moist
becomes plastic, and, therefore, of great value in the manufacture of
pottery. It is more soluble in acids than the crystallized variety. It
fuses at about 17800.

Kaolin is distinguished from chalk by its reaction toward HC1, from
meerschaum and talc by the reaction for Al with Co(NC>3)2, and from
infusional earth by the fact that its powder will not scratch glass.

Clay is a mixture of kaolinite, quartz, fragments of other mineral

ANHYDROUS METASILICATES 405

particles and various decomposition products of kaolinite and other
silicates, among the most important being various colloidal, hydrous,
aluminous silicates and magnesium and calcium carbonates. The
greater the proportion of colloidal material in the clay the more plastic
it is and the more valuable for manufacturing purposes. Different clays
have received different names which indicate in a way their uses. Among
the most important of these are:

China clay, a very pure, white kaolin,
Ball clay, a white, very plastic clay,
Fire clay, a fairly pure clay capable of resisting great heat,
Flint clay, a hard clay which is not plastic even after grinding,
Brick clay, an impure clay suitable for making brick,
Pottery day, stoneware clay, terra-coUa clay, etc., are ?U impure clays
that are adapted to the uses suggested by their names.

Sample analyses of kaolinite and of some of the purer clays follow:

Si02

AI2O3

Fe203

CaO

Na20

H20

Total

I- 46.3S

39-59

.11

•15

• • •

13-93

■15

100.13

II. 46.86

39 24

• a • •

• • • •

• • •

1390

• • ■

100.00

III. 43.46

41.48

• • • •

1.20

•37

13-49

• • •

100.00

IV. 59.92

27.56

io3

tr.

64*

10.82

• • •

99 97

I. Crystals from National Belle Mine, Colo.

II. Kaolin, Seilitz, near Meissen, Saxony.

III. Steinmarkite, Schlaggenwald, Bohemia.

IV. Flint fire clay, Salineville, Ohio.

* NajO+KjO.

Occurrence. — Kaolinite occurs in feldspathic rocks near ore veins.
Here it was formed partly by ascending magmatic solutions and partly
by descending H2SO4, produced by the oxidation of the sulphides in
the upper portions of the veins. Most kaolin, however, is a weathering
product of fefdspar (see p. 408), and of feldspathic rocks. When
acted upon by water, and more particularly by water containing dis-
solved CO2, the feldspars lose alkalies, calcium and some silica, leaving
an aluminium silicate behind. Thus, for the potash feldspar orthoclase:

K20 • AI2O3 • 6Si02( = KAlSi308) - K20 • 4Si02 = AI2O3 • 2Si02, which with
2H2O = HiAl2Si209 (kaolinite) .

Other silicates also yield kaolinite on weathering — in some cases
completely changing so as to yield pseudomorphs of kaolin.

Very complete weathering of this kind takes place in bogs, and

406 DESCRIPTIVE MINERALOGY

some of the best known beds of kaolin are believed to have been formed
at the bottoms of peat bogs.

Localities. — Kaolinite in measurable crystals occurs only at the two
localities that have already been mentioned. The pure, white, dense
kaolin is fairly widely spread. Clay occurs almost universally. The
principal localities of kaolin in North America are near Jacksonville,
Ala.; Mt. Savage, Md.; various points in Tennessee, North Carolina,
Illinois, Missouri, New Jersey and Pennsylvania.

Production. — The total value of clay products manufactured in the
United States during 191 2 was over $172,800,000, of which by far the
largest part is represented by common brick, of which $51,796,000 worth
were made. Pottery followed with an output valued at $36,504,000. It
is not possible to estimate the value of the clay represented in the man-
ufactured product because in most cases the manufacturers mine their
own clay and make no account of the raw material. The quantity of
clay mined in the United States and sold to manufacturers during 191 2
amounted to 2,530,000 tons, valued at $3,946,000. In addition, there
were imported 334,655 tons of clay, valued at $1,952,000.

Pyrophyllite (H2Al2(Si03)4)

Pyrophyllite nearly always occurs in groups of radiating or diverging
fibers that are either orthorhombic or monoclinic in crystallization. It
may be isomorphous with steatite. The bundles of fibers cleave easily
into flexible sheets that have a pearly luster on their cleavage faces.
When pure the mineral is light-colored in shades of yellow, gray or green.
It is transparent or translucent and has a greasy feel. Dense, struc-
tureless masses are known as agalmatolite.

The mineral is very soft, about 1. Its density is 2.8 or 2.9. Before
the blowpipe it melts on the edges to a white enamel and fibrous varieties
exfoliate and swell. Heated in the closed tube pyrophyllite assumes a
silvery luster and gives off water. It is only partially soluble in HC1, but
is completely decomposed by Na2CC>3.

It is best distinguished from ta'c by the reaction for aluminium.

Synthesis. — Upon heating to 3oo°-5oo° a mixture of Si02,Al203 and
potassium silicate a mass is obtained which consists of andalusite,
muscovite and pyrophyllite.

Occurrence and Localities. — Pyrophyllite is found at a number of
points in many different associations, where it is probably the result of
weathering of other silicates. Its principal localities in the United
States are Graves Mt., Ga.; Cotton Stone Mt., Deep River, Car-

ANHYDROUS METASILICATES 407

ft '

bonton and Glendon, N. C; Chesterfield, S. C; and Mahanoy City,
Penn.

Uses. — The massive form of the mineral is used to some extent in
making slate pencils, and for the other purpose for which talc is employed.
Agalmatolite is used by the Chinese as a medium from which they carve
small images.

CHAPTER XVIII
THE SILICATES— C<wtf»M«*

THE ANHYDROUS TRIMETASILICATES

THE FELDSPARS

The feldspars are among the most important ot all minerals. They
are abundant as constituents of many igneous rocks and in mixtures
filling veins. Their principal scientific importance lies in the fact that
they indicate by their composition the nature of the rock magmas from
which they crystallize. Consequently, in some systems of rock classi-
fication the grouping of the rocks is based primarily upon the presence
or absence of feldspar, and the naming of the feldspathic rocks is in
accordance with the nature of their most prominent feldspathic con-
stituent. Moreover, some of the feldspars are of economic importance.

Chemically, the feldspars may be regarded as isomorphous mixtures
of the four compounds, KAlSiaOg, NaAlSiaOg, Na2AlAlSi20g, CaAl AlSi20s
and BaAlAlSi^s, each of which, except the third, has been found nearly
pure in nature as orthoclase and microcliney barbieriU and albite, an-
orthite and celsian. The third, Na2AlAlSi20g, has been made in the
laboratory, but it occurs in nature only in isomorphous mixtures with
the anorthite and albite molecules. The pure compound has been
called carnegieite and its mixtures anemousites. The feldspars have
also been regarded as salts of the acid HsAlSi208 in which the hy-
drogen is replaced by various radicals, thus: (KSi)AlSi20s, orthoclase;
(NaSi)AlSi208, albite; (CaAl)AlSi208, anorthite, and (BaAl)AlSi208,
celsian.

The potash molecule crystallizes from magmas containing potas-
sium, sodium and calcium, but it also frequently forms isomorphous
mixtures with the soda molecule and in some cases with the barium
molecule. Mixtures of the potash and calcium molecules are ex-
tremely rare as minerals, but they have been formed experimentally
in the laboratory. The albite and the calcium molecules are usually
intermixed. Both are known in a nearly pure condition as minerals,
but their mixtures are much more common. Indeed they are so common
that they are separated from the other feldspars and formed into a dis-

408

ANHYDROUS TRIMETASIUCATES 409

tinct subgroup under the name of the plagioclase group, with albite and
anorthite as the two end members. The plagioclases constitute the best
known isomorphous series of compounds in the realm of mineralogy.

The calculated compositions of pure orthoclase (or microcline),
albite, anorthite and celsian with their specific gravities are:

Na20 CaO BaO Sp. Gr

• • • • •••• •••• * . s s

II .8 .... .... 2 .61

.... 20 . 1 .... 2 . 76

.... .... 41 .0 3 • 34

Si02

AI2O3

K20

Orthoclase.

■ 64.7

18.4

16.9

Albite

68.7

19 5

• • • •

Anorthite. . .

43-2

36.7

• • • •

Celsian

32.0

27.2

• • • •

All the feldspars are triclinic, but the pure potassium and sodium com-
pounds, in addition to possessing distinct triclinic phases (microcline and
albite) occur also in crystals which, because of sub-microscopic twinning,
(p. 420) are apparently monoclinic (orthoclase and barbierite). Usually
the forms on orthoclase are designated by symbols that refer to the
monoclinic axes, but since the habits of all feldspars are the same they
can be as readily understood when referred to the triclinic axes. The
crystallographic constants for the members of the group that consist
of unmixed molecules are:

Orthoclase. . 1 ^ 0 0 ,0 / o

Microcline K^s : i : -5554 90° «6° 3' 90°

a b c a 0 y Angle(ooi)A(oio)

90°
890 30'

Celsian 657 : 1 : .554 900 1150 2' 900 900

Albite 6335 : 1 : .5577 94° 3' "6° 29' 88° 9' 86° 24'

Anorthite 6347 : 1 : .5501 930 13' 1150 53' 910 12' 850 50'

lase. . 1
line. . J '

The simple crystals of feldspar exhibit three habits, but on nearly all
the same forms occur. These are oP(ooi), 00 P 60 (010), ooP'(no),
00 ;P(iTo), /P/60 (Toi), 2/P/ 60 (201) and less commonly 2/P' 00(021),
2;P, 66 (021), 00 P/3(i3o), 00 /P3(i3o), ,P(Tn), P,(T7i) and 00 P 60 (100).
In orthoclase and the other apparently monoclinic forms these symbols
may be written oP, 00 P 00 , 00 P, Poo, 2P00, 2P00, 00 P3, P and
00 P66 (Figs. 213 and 214). There have, moreover, been reported on
orthoclase about 90 other planes and on the plagioclases about 45. Of
these, however, a number are probably vicinal, as they have extremely
large indices.

The principal habits are the equidimensional, the columnar (Fig.
213), and the tabular (Fig. 214). The tabular crystals are usually
flattened parallel to 010. The columnar forms are elongated parallel
to the c or the a axes.

410

DESCRIPTIVE MINERALOGY

Twinning is common, according to five laws, and much less common
according to several others. Of the five common laws three apply to all
the feldspars, and the remaining two to the triclinic types alone. The
first three are the Carlsbad, the Manebach and the Baveno. The other
two are the albite and the pericline.

In Carlsbad twins, ioo is the twinning plane and usually oio is the

Fig. 214.

Fig. 213.

Fig. 213. — Orthoclase Crystals with 00 P, no (m); *> P *> . 010 (6); oP, 001 (c) and

2P « , 201 (y).

Fig. 214. — Orthoclase Crystals with m, b, c and y as in Fig. 213. Also P « , Toi (x);

P, In (a); °o P$» 130 (2) and 2P& , 021 (n).

Fig. 215.

«l

ksA/

Fig. 216.

Fig. 215. Carlsbad Interpenetration Twins of Orthoclase. Twinning plane is <» P 00

(100); composition face ooPoj (010).

Fig. 216. — Contact Twin of Orthoclase According to the Carlsbad Law.

composition face. The twinned parts may interpenetrate, as is usually
the case (Fig. 215), or they may lie side by side forming a contact twin
(Fig. 216). If in the contact twins the planes Toi and 001 are equally
prominent, since they are nearly equally inclined to the c axis the twin
may be mistaken for a simple crystal (Fig. 216). In rare cases the
composition face is 100 and the twinned parts are in contact.

ANHYDROUS TRIMETASILICATES 411

The Baveno twins are contact twins, with 021 the twinning and com-
position planes (Fig. 217). As the individuals are elongated parallel to
the a axis the result of the twinning is a square prism with its ends
crossed by a diagonal that separates the same forms on the two twinned
individuals. In some cases the twinning is repeated and a fourling
results.

In Manebach twins, the twinning and composition plane is 001.
These usually occur in columnar crystals elongated parallel to a, or in
tabular crystals flattened parallel to 001 or 010 (Fig. 218).

Carlsbad, Baveno and Manebach twins, as has been stated, are com-
mon to feldspars of both the monoclinic and triclinic phases, but the
pericline and albite laws are found only in the triclinic types. The

Fig. 217. Fig. 218.

Fig. 217. — Baveno Twin of Orthoclase. Twinning and composition plane, 2P 5b (021).
Fig. 2 1 8. — Manebach Twin of Orthoclase. Twinning and composition plane, oP(ooi).

description of these is, therefore, deferred until the plagioclases are dis-
cussed.

Besides occurring in crystals, nearly all the feldspars are known also
in granular and platy masses.

The pure feldspars are colorless and transparent or translucent, and
all have a glassy luster which, on cleavage faces sometimes approaches
pearly. As usually found, the feldspars are white, pink, reddish, yellow-
ish, gray, bluish or green. Some specimens show a bluish white shimmer
or opalescence (moonstone), and others a reddish sparkle (sunstone),
due to enclosures of other minerals or of lamellae of a different refractive
index from that of the main portion of the mass. All have a white
streak. All possess a very perfect cleavage parallel to the base (001)
and a scarcely less perfect one parallel to 010. Their fracture is uneven
to conchoidal, and hardness 6.

Before the blowpipe fragments of the potash, barium, and calcium

412 DESCRIPTIVE MINERALOGY

feldspars are very difficultly fusible on their ed^es to a porous glass.
The soda feldspars are a little more easily fusible. The fusing tempera-
ture of albite is between 12000 and 12500, that of orthoclase approxi-
mately 13000, and that of anorthite 15320. Anorthite is soluble in
hydrochloric acid with the production of gelatinous silica. The other
three feldspars are insoluble.

The feldspars are distinguished from other minerals by their crys-
tallization, their two nearly perfect cleavages approximately perpen-
dicular to one another, and their hardness. They are distinguished
from one another by characters that will be indicated in the descriptions
of the several varieties.

Feldspars rich in orthoclase and soda weather fairly readily to mus-
covite, or kaolin and quartz. The soda feldspars in some cases change
to zeolites (p. 445). With the addition of the calcium molecule calcite
is often found in the weathering products. Under certain conditions,
especially when in rocks containing magnesium and iron minerals, the
calcium feldspars often change to a mixture of zoisite and albite, or a
mixture of these with garnet, chlorite (p. 428), epidote and other com-
pounds. This mixture is often designated by the name saussuriie.

Syntheses. — All crystals of the feldspars, except those of pure albite
and pure orthoclase (including microcline), have been made by slowly
cooling a dry fusion of their components in open crucibles. Albite and
orthoclase have been produced from similar fusions to which tungstic
acid, alkali-tungstates or phosphates, or alkali-fluoride have been added.
They have also been produced with quartz by fusion in the presence
of moisture in closed tubes.

Occurrence and origin. — All except the barium feldspars occur as
important constituents of most igneous and of many metamorphic
rocks. They occur also abundantly ifi a few sandstones (arkoses) and
in a few water-deposited veins, and are found around a few volcanic
craters as products of gaseous exhalations. The barium feldspars are
rare. They have been seen only in dolomite associated with barite and
tourmaline, in manganese ores and manganese epidote; and intergrown
with albite in a pegmatite at Blue Hill, Delaware Co., Pa.

With respect to origin feldspars may be primary separations from a
magma, primary deposits from solutions, pneumatolytic deposits, or
they may be the result of metasomatic process. They are common
products of contact and regional metamorphism.

Uses. — The feldspars, though extremely abundant, have compara-
tively few uses. In the future the potash varieties may become a
source of the potash salts used in the manufacture of fertilizers. At

ANHYDROUS Till MET ASILICATES 413

present the principal use of the feldspars is in the manufacture of por-
celain and other white pottery products and enamel ware. They are
used as fluxes to bind together the grains of emery and carborundum
in the making of grinding and cutting wheels, and are employed also in
the manufacture of opalescent glass, artificial teeth, scouring soaps and
" ready roofing."

Production. — All the feldspar used in commerce comes from pegma-
tites. The total quantity produced for all purposes in the United States
during 191 2 amounted to 86,572 tons, valued at $520,562. Of this,
26,462 tons were sold crude at a value of $89,001 and the balance
ground. The principal varieties mined are orthoclase, microcline and
albite, though oligoclase (a plagioclase rich in soda) is mined in small
quantity.

ALKALI FELDSPARS

Orthoclase and Microcline (KAlSi308)
Barbierite and Albite (NaAlSisOg)

Orthoclase and microcline have the same chemical composition.
Both are potash feldspars, but both may contain sodium. On the
other hand barbierite and albite are both essentially soda feldspars but
both usually contain some potassium. In orthoclase the sodium is
due to the admixture of the barbierite molecule, and in microcline to
the presence of the albite molecule. The soda-rich microcline is gen-
erally known as anorthoclase. The pure barbierite is not known to
exist as a mineral. Analyses of these four varieties follow:

Si02

A1203

CaO

K20

Na20

H20

Total

I. 63.80

21.00

a • • a

13.80

1.40

100.00

II. 65.23

19-35

.76

931

4-52

.27

100.00

III. 67.00

19. 12

.78

115

11.74

• • • *

99-79

IV. 66.18

i9S2

■36

13-03

.91

• • • •

100.00

V. 67.99

19.27

•75

3 05

6.23

.00

99 03

VI. 68.28

19.62

•3i

•39

10.81

.09

99.82

I. Orthoclase, Adularia, Elba.
II. Soda-orthoclase, Drachenfels, Prussia. Also .56 BaO.

III. Barbierite, Krager8, Norway.

IV. Microcline, Ersby, Pargas, Finland.

V. Anorthoclase, from granite, Kekequabic Lake, Minn. Also .82 Fe»Oi and

trace of MgO.
VI. Albite, from litchfieldite. Litchfield. Maine. Also .23 FeO and .09 MgO.

Albite is described among the plagioclases (p. 418).

DESCRIPTIVE MINERALOGY

The most noticeable difference between orthoclase and mkrocline
is that the latter shows dearly its triclinic symmetry by its twinning,

Fig. 119.— Section of Microcline Viewed between Crossed Nicols. The grating
structure indicates twinning. (Aflrr Rosrnbiisch.)

and its optical properties, while in orthoclase the twinning is so
minute as to be unobservable and the optical properties are similar to
those of monoclinic crystals. This difference is best exhibited in thin
sections when viewed ia polarized light under the
microscope. Under these conditions certain sec-
tions of microcline exhibit series of light and dark
bars crossing one another perpendicularly (Fig.
219), while sections of orthoclase do not. The
grating structure is due to repeated twinning
according to the albite and pericline laws at the
same time (p. 419). If this method of twinning
is present in orthoclase the lamellae are so
minute that they cannot be seen even under
high powers of the microscope.

Several names that refer to more or less dis-
tinct varieties of the potash feldspars are in com-
mon use. The most important are:
Adularia, a nearly pure orthoclase, that is nearly transparent, occur-
ring in veins. Its crvstals have the characteristic habit illustrated in
Fig. no.

Fig. ?70. — Adularia
Crystal with «, b.

Figs. 213 and 214.
Also !P 3B . I03 (q).

ANHYDROUS TRIMETASILICATES 415

•

Sanidine, a glassy soda orthoclase, occurring as large crystals often
flattened parallel to oio, embedded in lavas.

Moonstone, a translucent adularia, exhibiting a pearly luster, with
a very slight play of colors.

Sunstone, a translucent variety exhibiting reddish flashes from
inclusions of mica, or other platy minerals.

Perthite, parallel intergrowths of thin lamellae of orthoclase and
albite.

Microcline- perthite, parallel intergrowths of lamellae of microcline
and albite.

Orthoclase and the other pseudomonoclinic feldspars may be dis-
tinguished from the distinctly triclinic forms by the value of the cleavage
angle which in orthoclase is 900, and in the triclinic forms about 86°,
except in microcline. (See p. 409.) The value of the angle 110A1T0
= 6i° 13' in orthoclase. Its refractive indices for yellow light are:
a=i.5ig, &= 1.524, 7 = 1.526. With the admixture of the albite mole-
cule these values increase. The sp. gr. of pure orthoclase is 2.55 and
its fusing point a little higher than that of albite (see p. 412).

Orthoclase may be distinguished from the other pseudomonoclinic
feldspars by its specific gravity and the flame reaction.

Syntheses. — Crystals of orthoclase have been made by fusing
S1O2 and AI2O3 with potassium wolframate, vanadate or phosphate.
Also by heating aluminium silicate with a solution of potassium silicate
and KOH in a tube at ioo°, and by heating muscovite in a solution of
potassium silicate at 6oo°.

Occurrence. — The potash feldspars are essential constituents of the
igneous rocks — granite, syenites, rhyolites and trachytes — and of some
crystalline schists, and are accessory components of a number of other
rocks. They occur in most pegmatite dikes and as gangues in some ore
veins, and in many contact metamorphosed rocks.

Localities. — The potash feldspars are so widely spread that an enu-
meration of their important occurrences is here impossible. The best
known localities of orthoclase are Cunnersdorf, Silesia; Drachenfels
and Lake Laach, Rhenish Prussia (sanidine) ; in the Zillerthal, Tyrol
(adularia); at St. Gothard in the Alps (adularia); at Baveno, Italy,
and at Mt. Antero, Chaffee Co., Col. Microcline crystals are well
developed at Striegau, Silesia; in the pegmatite dikes of southern Nor-
way; and at Pike's Peak, Col. (amazonite). Anorthoclase occurs at
Tyveholmen and other points in Norway and in the lava of Kilimand-
jaro, Africa, and in that on Pantelleria, an island near Sicily. In
North America pegmatites are abundant in southeastern Canada, in

416 DESCRIPTIVE MINERALOGY

New England and in the Piedmont plateau area immediately east of
the Appalachian Mts., and throughout this district all forms of the
opaque potash feldspars are abundant. Soda-potash feldspars have
been described from many places, but whether they are soda orthoclase
or anortholcase has rarely been determined.

All phases of the alkali feldspars occur as components of igneous
and metamorphic rocks.

POTASH-BARIUM FELDSPARS

The feldspars containing potassium and barium comprise an iso-
morphous series with orthoclase and celsian as the two end members as
follows:

Sp. Gr.

Orthoclase (Or)

KAlSiaOg

2-55

Barium orthoclase

OrioCei — OrioCei

2 . 593-2 . 645

Hyalophane

Or4Cei-Or7Ce3i

2.725-2.818

Celsian (Ce)

BaAl2(Si04)2

3384

The chemical composition of some of the barium feldspars are illus-
trated by the analyses quoted below:

Si02 AI2O3 BaO CaO MgO K20 Na20 H20 Total

I. 51.68 21.85 16.38 10.09 100.00

II. 52.67 21.12 1505 .46 .04 7.82 2.14 .58 99.88

III. 53.53 23.33 7.30 3.23 11. 71 ... 99.10

IV. 54.15 29.60 1.26 1. 00 1.52 12.47 ... 100.00

I. Theoretical for Or2Cei.
II. Binnenthal, Tyrol.

III. Jakobsberg, Sweden.

IV. Sjogrufran, Sweden.

The minerals are isomorphous with orthoclase (with the possible
exception of celsian, which may exhibit the triclinic habit and may more
properly be isomorphous with microclinic), and their axial constants are
intermediate between those of orthoclase and celsian. The axial ratio
for hyalophane is .6584 : 1 : .5512. a=9o°, /3=ii5° 35', 7 = 90°. Its
cleavage angles are 900. Its crystals, as a rule, have the adularia habit.
The Indices of refraction of the barium feldspars are:

Barium-orthoclase

•(OrioCei)

I.5201

1.5240

I-5257

Hyalophane

(OnCei)

1-5373

1-5395

1. 5416

Hyalophane

(Or7Ce3)

i.54i9

I-54I9

1 5469

Celsian

1 ■ 5837

1 . 5886

1 • 5940

ANHYDROUS TRIMETASILICATES

417

These feldspars are rare. They have been found only in metamor-
phosed dolomites in the Binnenthal, Valais; at the manganese mines at
Jakobsberg and Sjogrufran, Sweden; and intergrown with albite in a
pegmatite at Blue Hill, Delaware Co., Penn.

SODA-LIME FELDSPARS

Plagioclase is the general name given to the group of isomorphous
feldspars of which albite and anorthite are the end members. The
albite and anorthite molecules are isomorphous in all proportions and
the physical properties of the mixed crystals accord completely with
their composition. Certain mixtures are much more common than
others. These were given individual names before it was recognized
that they were merely members of an isomorphous series and these
names were later applied to mixtures of definite compositions. The
names and the compositions of the mixtures corresponding to them are
given in the following table.

Si02

Albite NaAISi308(Ab) 68. 7

Oligoclase

Andesine

Labradorite

Bytownite

AbftAni
AbsAni

AbsAni
AbiAni

AbiAni
AbiAri3

AbiAn3
AbiAntj

64.9
62.0

AI2O3

19-5
22.1

24.0

55° 283

49-3 32-6

Na20

11. 8
10. o

5-7

CaO

■ ■ • ■

3-0

5-3
10.4

Sp. Gr.
2.605

2.649
2.679

2.8 15.3 2.708

46.6

Anorthite CaAkCSiO-iMAn) . . 43 . 2

34 4
36.7

1.6

17-4
20.1

2.742
2.765

Nearly all plagioclases contain small traces of K2O, MgO and Fe203,
but otherwise their composition is nearly in accord with that demanded
by their symbols, so that if one constituent is known the others may
be calculated. Moreover, the accord between physical properties and
composition is so close that from the former the latter may be de-
termined.

Many oligoclases, however, contain a large admixture of the micro-
cline molecule so that they contain a notable quantity of KoO. These
are known as potash-oligodase and are represented by the feldspar in a
rock at Tyveholmen, Norway, the composition of which is as follows:

Si02 AI2O3 Fe203 CaO MgO K20 Na20 H20 Total
59.50 22.69 2.47 5.05 tr. 2.50 6.38 1.37 100.37

418 DESCRIPTIVE MINERALOGY

Some authors limit the name anorthoclase to feldspars of this kind and
designate the triclinic soda-potash feldspar as soda-microcline.

There is another group of soda-lime feldspars in which the anorthite
molecule and an analogous sodic molecule (Na2Al2(Si04)2) form iso-
morphous mixtures. The pure sodic molecule has not been found among
minerals, but it has been prepared synthetically at temperatures above
12480, under the name carnegieite. Its sp. gr. = 2.513 and its refractive
indices for yellow light are: a= 1.509, 7=1.514. Although not known
to exist independently it is believed to be present in the feldspar of
Linosa, near Tunis, and possibly in other feldspars that have hitherto
been described as plagioclases. If future work establishes the fact that
there is a distinct series of feldspars composed of isomorphous mixtures
of anorthite and carnegieite it is proposed to name the group anemousiie
to distinguish it from the plagioclase group which comprises isomorphous
mixtures of anorthite and albite.

The Linosa feldspar has properties nearly like those of the plagioclase
AbiAni but its analysis yields the results in line I. The composition of
AbiAni is given in line II.

Si02

AI2O3

CaO

Na20

K20

Sp. Gr.

L 53.26

29.78

10.76

5-45

•75

2.684

IL 55 67

28.26

10.34

5 73

.00

2.679

THE PLAGIOCLASES

All the plagioclases have a triclinic habit, which is best expressed by
the value of the angle between their cleavages, which are parallel to
the planes 001 and" 010. The crystal constants of some of the common
mixtures and the values of their cleavage angles are given in the table
below.

Angle

ol p y

001A010

.5577 94° 3' n6°29' 88° 9' 86° 24'
•5524 93° 4' ii6023' 900 5' 86° 32'
.5521 930 23' n6°29' 89°59' 86° 14'

•5547 93° 3i' n6°3' V55' 86° V

= .6347 : 1 : .5501 93° 13' «S° 55' 91° "' ^5° 5°'

Crystals of the soda-rich plagioclases are rich in forms, but those of
anorthite and the lime-rich members are much simpler. Albite crystals
are usually tabular parallel to 00 P 66 (010) and elongated parallel to
c or a. Others are elongated parallel to b (Fig. 221). Oligoclase is

Albite a : b :

£=•6335 : 1

Oligoclase. . .

= .6321 : 1

Andesine. . .

= .6357 : 1

Labradorite.

= .6377 : 1

Bytownite. .

Anorthite. . .

= .6347 : 1

ANHYDROUS TRIMETASILICATES

419

more frequently columnar parallel to c, andesine tabular parallel to
oo P 06 (oio) or oP(ooi), and labradorite and bytownite tabular parallel
to oo P oo (oio). Twins are even more common than among the potash
feldspars. Carlsbad (Fig.
222), Manebach and Ba-
veno twins are not uncom-
mon, but more frequent
than these are the twins
after two laws that are
impossible in the feld-
spars with a monoclinic
habit. The two most
common twinning laws
among the plagioclases are
the albite and the pericline
laws.

In the albite law the twinning plane is oo P 6o (oio) and the com-
position plane the same (Fig. 223). The twinning is usually repeated
many times so that apparently homogeneous crystals may be built up
of numerous lamellae paraUel to 010. Since the angle between 010 and

Fig. 221. — Albite Crystals with 00 'P, 1T0 (Af);
00 P', no (in); 00 P 00 , 010 (6); oP, 001 (c) and
,P, 00 , Toi (x).

Fig. 222.

Fig. 222. — Albite Twinned about 00 Poo, 100. Composition face 00 Poo, 010.

Carlsbad law. Compare Fig. 216.

Fig. 223. — Albite Twinned about 00 Poo, 010. Composition face the same. Albite

law. Compare Fig. 222.

001 in all the plagioclases is greater and less than oo°, it must follow that
the surface of their basal cleavages is not a plane, but that it consists of
parallel strips of surfaces parallel to 010, and inclined to one another at
angles alternately greater and less than 1800.. Therefore basal cleavages

420

DESCRIPTIVE MINERALOGY

of the plagioclases very frequently exhibit parallel striations when exam-
ined in light reflected at the
proper angles (Fig. 224).
It is this twinning which,
repeated in sub microscopic
lamellae, is believed to pro-
duce the monoclinic pseudo-
symmetry of orthoclase.
It will be noted that the
twinning plane has the
position of the plane of
Fig. 124.— Twinning Striations on Cleavage Piece symmetry in monoclinic
of Oligoclase. (About natural size.) crystals, and, consequently,

twins about this plane have
the same symmetry with reference to one another as corresponding
contiguous layers of mono-
clinic crystals.

In the periclinc law the
twinned portions are super-
posed. The individuals are
twinned about b as the twin- Fig. 2!5.— Albite Twins with the Crystal Axis
ningaxis,and are united about 6 the Twinning Axis and the Rhombic Sec-
a plane nearly perpendicular tbn the Composition Face. The form r is

r. - / \t .u 4.P« (403). Perkline law.

to 00 P 00 (010), known as the ' ™ J

" rhombic section " (Fig. 225). The position of this section varies
with the different plagioclases, but is always nearly perpendicular to 010

Fig. 226. Fig. 127-

Fig. 226.— Position of " Rhombic Sections " in Albitc (.1) and Anorthite (B).
Fie. 227.— Diagram of Crystal of Tridinic Feldspar Exhibiting Striations Due to
Polysynthetic Twinning According to the Albitc and the Peridine Laws.

(Fig. 226). As nearly all pericline twins are elongated in the direction
of the b axis, and the twinning is repeated, lamellae are produced,

ANHYDROUS TRIMETASILICATES 421

which, in sections perpendicular to oio, cross the albite lamellae at
angles near 900 (Fig. 227). It is the presence of the two kinds of
twinning in microcline that gives it its peculiar grating structure in
polarized light (see Fig. 219).

The plagioclases are light-colored, but pinkish and greenish shades
are less common in them than in the potash feldspars. Their streak is
colorless. They are usually translucent but in some cases are trans-
parent. Albite often exhibits a pearly luster and often a bluish shimmer.
Oligoclase when containing as little inclusions plates of hematite, glistens
with a red shimmer and affords the finest sunstones. The most bril-

liantly colored plagioclases are some forms of labradorite, which, on
cleavage surfaces, show a great display of yellow, green, red, purple and
blue flashes in reflected light. The cause of the play of colors is not
known, but it is probably due to the presence of numerous very tiny
parallel acicular inclusions.

The refractive indices of the plagioclases vary with their compositions.
For yellow light the values for the specified mixtures are as follows:

Albite

(AbiooAno)

I.52CO

1 • 5333

1.5386

Oligoclase

(Ab78An22)

I - 5389

1 -5431

1 • 5469

Andesine

(Ab6oAn4o)

1-549

i-553

1 -55&

Labradorite

(Ab4sAn52)

1 • 5545

1 • 5589

1 • 5634

Bytownite

(Ab2oAn8o)

1 . 5691

1 . 5760

1-5805

Anorthite

(AbgAngi)

1-5752

1 • 5833

1 • 5884

Before the blowpipe all the plagioclases fuse to a white or colorless
glass, at the same time coloring the flame an intense yellow (albite), or a
yellowish red (anorthite). Albite fuses at a lower temperature than
anorthite. The temperatures at which synthetically prepared plagio-
clases melt completely are as follows:

Anorthite 1ySS°° Ab2Ani I>394°

AbiAns 1,521 AbsAni 1,362

AniAn2 M9° Ab4Ani !»334

AbiAni 1,450 AbsAni 1,265

Albite i,ioo° est.

Albite is unattacked by HC1, but anorthite is decomposed by this reagent
with the separation of gelatinous or pulverulent silica. The intermediate
plagioclases are more or less easily decomposed as they contain more or
less of the anorthite molecule.

The plagioclases are distinguished from the feldspars possessing the

422

DESCRIPTIVE MINERALOGY

monoclinic habit by the twinning striations on their basal cleavages,
and from the potash feldspars of both monoclinic and triclinic habits by
the color imparted to the blowpipe flame. The characteristics of the
plagioclases best distinguishing them from one another are their specific
gravities and their optical properties.

The plagioclases weather to kaolin and mica (paragonite) mixed
with quartz and calcite in the more basic varieties, and to zeolites (see
p. 45). In rock masses the more basic varieties alter to epidote, in
some instances into scapolite (p. 423), and very commonly into the mix-
ture known as saussurite, which is an aggregate containing zoisite or
garnet as its most important component.

Syntheses. — Crystals of plagioclase have been made by processes
analogous to those employed in making orthoclase crystals. For exam-
ple, albite crystals have been produced by fusing Si02 and AI2O3 with
sodium wolframate, and by heating precipitated aluminium silicate with
a solution of sodium silicate in a platinum tube to 5000. Anorthite
crystals have been made by long heating of a mixture of Si02, AI2Q3
and CaCQa in the proper proportions, and by fusing vesuvianite and

garnet.

Occurrence. — Albite occurs in vein masses in certain crystalline schists
but is much less common as a primary rock constituent than the other
plagioclases. It is, however, frequently found as a secondary product
resulting from the changes produced in other plagioclases by metamor-
phic processes, thus it is common in many crystalline schists, Oligo-

clase and andesine occur in granites and the other
more siliceous igneous rocks and labradorite, by-
townite and anorthite in the more basic rocks.
Anorthite has also been found in meteorites.

Localities. — The localities at which crvstals of
the plagioclases are found are too numerous to be
mentioned here. Especially fine crystals of albite
occur at Roc-Tourne in the French Alps, in
Dauphinl, France; at Amelia Court House, Va.;
at Middletown, Conn.; and at Chesterfield in
Massachusetts. Excellent crystals of oligoclase
occur at Arendal and at other places in Norway; and
at McComb and Fine, in St. Lawrence Co., N. Y.
Potash-oligoclase occurs in certain igneous rocks at
Tyveholmen and elsewhere in Norway and in the lava of Kilimandjaro,
Africa. Its habit is prismatic (Fig. 228). Crystals of andesine are
found at Bodenmais, in Bavaria; Arcuentu, in Sardinia; and at Sanford,

Fio. 228. — Potash-
Oligoclase Crystal.
Forms M. m and c
as in Fig. 221. Also
2/P, « , 201 (y).

ANHYDROUS TRIMETASILICATES

423

in Maine. Labradorite crystals occur at Visegrad, Hungary; and at
Mt. Aetna, Italy; and beautiful cleavage pieces come from Labrador,
where it forms one of the constituents of a coarse-grained igneous rock.
Anorthite crystals occur at Volpersdorf, in Silesia; in the Aranya Mt.,
Siebenburgen, Hungary; at Pesmeda, Tyrol; in the inclusions in the
lavas at Vesuvius, Italy; in the lava on the Island of Unjake, Japan;
and at Phippsburg, in Maine.

Uses. — Albite from the pegmatite veins of southeastern Pennsylvania
and northeastern Maryland is mined for use in pottery manufacture.

SCAPOLITE GROUP

(Na4Al,(AlCl)(Si308)»+Ca4AU(A10)(Si04)))

The scapolites comprise a series of isomorphous compounds of which
the two end members are marialite, Na4Al2(AlCl)(Si30s)3 and meionite,
Ca4Al5(A10)(Si04)ft. Between these two are many intermediate com-
pounds known under the collective name mizzonUe. Their composition
is represented in terms of the marialite and meionite molecules, thus,

MamMen.

The theoretical compositions of the two end members of the series
and of several intermediate members, and the actual compositions of
four specimens of natural crystals are given below.

Si02

AI2O3

CaO

Na20

Total

63-95

18.12

• • • • «

14.69

419

100.95

Theoretical, MaaMe. .

5785

22.35

6.53

10.87

310

100.70

Theoretical, Ma2Me. .

55.85

23-73

8.67

9.62

2-75

100.62

Theoretical, MaMe . .

5190

26.47

12.90

715

2.04

100.46

Theoretical, MaMe2. .

48.03

29.16

17.04

476

i-35

100.34

Theoretical, MaMe3..

46.10

30.48

19.10

3-54

1. 01

100.23

Theoretical, Me

4045

3438

2517

■ • « •

■ • • •

100.00

Si02 Al203

CaO

Na20

K20

h2o

Total

I. 61.40 19 .63

4.10

■ • • •

4.00

II. 54.86 22.45

9.09

8.36

1 -13

.86

2.41

100.45

III. 49.40 30.02

15.62

3-"

•79

.64

100.03

IV. 41.80 30.40

19.00

251

.86

3.17*

• • ■ •

98.66

I. Marialite, Pianura, Italy.

II. Riponite, Ripon, Quebec. Contains also .80% SOi, .49 FejOt and a trace
of MgO.

III. Wernerite, Rossie,*N. Y. Contains also .10% SO» and .32 FeO.

IV. Meionite, Mt. Vesuvius. Contains also .46 MgO and .46% undecomposed

material.

♦Volatile.

424

DESCRIPTIVE MINERALOGY

tit

Fig. 229. — Scapolite Crystals with «> P,
no (m); 00 Poo, 100 (a); P, rn (r), and

All the members crystallize in the pyramidal hemihedral division of
the tetragonal system (tetragonal bipyramidal class) in fairly simple
columnar crystals with an axial ratio 1 : .442 for marialite and 1 : .4393
for meionite. The principal forms are oP(ooi), 00 P 00 (ioo), 00 P(no),

ooP2(2io), P(in), Poo(ioi) and |^l(3ii) (Fig. 229). The angle

in A 171=43° 4S'« The habit of the crystals is always columnar, with
00 Poo (ioo) predominating in the prismatic zone, and also »P(no)

prominent. The latter form
predominates only in mizzon-
ites. The scapolites occur also
in crystal grains embedded in
limestones, in columnar and
fibrous aggregates and in struc-
tureless masses.

All the scapolites have a
glassy luster, which approaches
pearly. They are transparent
or translucent, colorless or
white, gray, greenish, bluish or
reddish and have a white
streak. Their cleavage is nearly perfect parallel to 00 P 00 (100) and
imperfect parallel to oop(no). Their fracture is uneven or con-
choidal. They are brittle, have a hardness of 5-6 and a density of
2.54 for marialite and 2.76 for meionite. The refractive indices
naturally vary with the proportions of the two molecules present.
For the two end members of the group the indices for yellow
light are: marialite, w= 1.5463, €=1.5395, meionite, 03=1.5897,
€=1.5564.

Before the blowpipe all members swell and fuse to a white glass. In
hydrochloric acid, mixtures between Ma and Ma2Me are insoluble, those
between Ma2Me and MaMe2 are partially soluble and those between
MaMe2 and Me are nearly completely soluble.

All members of the series are distinguished by their crystallization
and cleavage and all except pure meionite are characterized by the
chlorine reaction. They are distinguished readily from the feldspars
by their fusibility with swelling.

Marialite and meionite are rare. The common scapolites are the
mizzonites of which dipyr and wertterite are the nontransparent vari-
eties. The former includes varieties occurring in elongated prisms con-
taining between 54 per cent and 57 per cent SiC>2, i.e., MagMe to Ma2Me;

ANHYDROUS TRIMETASILICATES 425

and the latter embraces varieties containing between 54 per cent and 46
per cent SiC>2, or Ma2Me to MaMe3.

Occurrence. — The scapolites occur in crystalline schists, crystalline
limestones and also in limestones included in volcanic lavas (meionite),
and on the contacts of igneous masses (wernerite). They are found also
in igneous rocks as the result of alteration of the feldspars, especially
when these rocks are intrusive in limestones, and also as an alteration
product of garnets. In a few places they are associated with magnetite
and apatite in veins of iron ores. In most cases they appear to have
been derived from feldspars by the action of metamorphic processes.
On the other hand, scapolite changes to albite, epidote, biotite, musco-
vite and to a mixture of minerals.

Localities. — Meionite crystals occur in the fragments enclosed in the
lavas of the Lake Laach region, Prussia; and of Monte Somma, the
precursor of Vesuvius, Italy. Mizzonite is associated with meionite
at Monte Somma. Dipyr occurs in clayey limestones in the Pyr-
ennees; wernerite at Arendal and Bamle, Norway; at Malsjo, in
Sweden; at Diana, Lewis Co., and at Gouverneur and Pierrepont,
St. Lawrence Co., N. Y.; at Canaan, Conn.; at Bolton, Mass.; and
marialite at Ripon, Quebec, and at Pianura, near Naples, Italy.

CHAPTER XIX

THE SILICATES— Continued

THE ANHYDROUS POLYSILICATBS

Under the polysilicates are grouped all the minerals that cannot
easily be assigned to the orthosilicates, the metasilicates or the tri-
metasilicates. They are usually very complex in composition and are
commonly regarded as isomorphous mixtures or solid solutions of silicate
molecules of various types.

THE BRITTLE MICAS

The brittle micas are so called because, while they possess a very
marked cleavage which rivals that of the true micas in its perfection,
their cleavage foliae are brittle, and not elastic as are the mica foliae.

The group consists of four minerals of which three are apparently
mixtures of the molecules H2CaMg4(Si04)3 and H2CaMgAleOi2, and
the fourth is approximately EfeCFe- Mg)Al2SiOz. The first three are
known as xanthopkyllite, brandisite and clintonite and the fourth as
chloritoid. Of these the last two are the most important. Chloritoid
is believed to be a basic orthosilicate, but, because of the similarity of its
properties to those of the brittle micas, it is thought best to discuss it
in the same group with them.

All members of the group crystallize in the monoclinic system with
an hexagonal habit.

Clintonite (HeCMg-Ca-FeJioAlioSUOae)

Clintonite, or seybertite, may be regarded as a mixture of the mole-
cules H2CaMg4(Si04)3 and H2CaMgAl60i2 in the proportion 4 : 5,
which requires the percentage composition shown in line I below. The
analysis of a specimen of the mineral from Orange Co., N. Y., is given in
line II:

Si02 AI2O3 Fe203 FeO MgO CaO H20 F Total

I. 1909 40.97 22.28 13.36 4.30 100.00

II. 19-19 39-73 61 1.88 21.09 13-" 485 1.26 101.72

426

ANHYDROUS POLYSILICATES 427

Well developed crystals are so rare that their axial ratio has not been
satisfactorily established. The best crystals appear as long, thick, six-
sided plates with a well developed basal plane and several pyramids and
domes with rounded edges. If the axial ratio is assumed to be the
same as that for biotite the principal forms are oP(ooi), fPob (027),
$P&(o56), fP*>(o52), -iP(n4), -|P(337), and -2P(22i). Many
of the crystals are superposed twins, like
those of muscovite. (Fig. 230.)

The mineral is reddish or brown, and
transparent or translucent. It has a glassy
luster and a white streak. Pressure and Fig. 23o.-Clintonite Twinned

/. -i j 1 Al_ According to the Mica Law.

percussion figures are easily produced on the „ * . .

, ,f , . : A. ri Forms: oP, ooi (c); -?P,

cleavage plates, and in nature parting often 337 ^ and iP fc OI2 (tf)
takes place along these directions, yielding

fragments with rectangular edges. The hardness of clintonite is 4-5
and its density 3.1. Its refractive indices for yellow light are:a= 1.646,
0= 1.657, 7=1.658.

Before the blowpipe clintonite becomes white and opaque but does
not fuse. In the closed tube it gives off water. It is completely decom-
posed by hydrochloric acid.

It is distinguished from most other minerals by its micaceous cleav-
age, and from the true micas by its brittleness and solubility in hydro-
chloric acid.

Clintonite occurs in a coarse, serpentinized limestone at Amity,
Orange Co., N. Y.

Chloritoid (H2(FeMg)Al2Si07)

Chloritoid differs from the other brittle micas in being essentially a
ferrous compound. Its composition approaches the formula given
above, though the analyses of many specimens depart widely from this.

Si02 AI2O3 FeO MgO

I. 23.72 40. 71 28.46

II. 25.50 38.13 23.58 5.19

I. Theoretical for HjFeAkSiOr.
II. Specimen from chlorite schists. St. Marcel, Italy.

The mineral is believed to be monoclinic in crystallization because of
the similarity of its crystals to those of biotite. It often occurs in six-
sided plates, but more frequently in lenticular or spindle-shaped grains
and sheaf-like and ball-like aggregates of plates and grains and in foliated
masses. Twins like those of biotite are also fairly common.

H20

Total

7. II

100.00

6.90

99 30

428 DESCRIPTIVE MINERALOGY

The mineral is dark green or black, and translucent* It is strongly
pleochroic in olive green, blue and yellowish green tints. It has a
glassy or pearly luster on its cleavage faces and a waxy luster on frac-
ture surfaces. Its hardness is 6-7 and density 3.4-3.6. Its refractive
index is 1.741.

Before the blowpipe chloritoid exfoliates on the edges and fuses with
difficulty to a black magnetic mass. In the closed tube it gives off water.
It is unat tacked by hydrochloric acid, but when in fine powder is com-
pletely decomposed by sulphuric acid. Some forms of ottrelite are sol-
uble in strong nitric and hydrochloric acids, with the separation of
gelatinous silica.

Masonite is a dark grayish variety from Natick, R. I.

OUrelite contains a little manganese and has a slightly different
formula from chloritoid. Its composition may be best represented by
H2(Fe* Mn)Al2Si20o. Its sp. gr. = 3.3.

The chloritoids appear to be fairly stable, as their only alteration
products thus far noted are the chlorites and the micas and ottrelite.

Occurrence. — All varieties of chloritoid are found principally in fine-
grained schists where they are believed to be the result of regional and
contact metamorphism.

Localities. — The most noted occurrences of chloritoid are Pregattan,
Tyrol; St. Marcel, Italy; Ottrez, Belgium; Natick, R. L, and Augusta
and Patrick Counties, Va.

CHLORITE GROUP

The chlorite group is so named because its principal members are
green. The group comprises a number of platy hydrous magnesium,
aluminium silicates that appear to be isomorphous mixtures of mole-
cules that are approximately H^Mg* Fe^AkSiOg and Ht(Mg- Fe)3Si2C>9,
the former of which is known as the amesile molecule (designated At),
and the latter as the serpentine molecule (indicated by Sp). The ser-
pentine molecule is represented in the platy form of serpentine known as
antigorite, which may be regarded as one of the end members of the
series. The independent existence of the amesite molecule is doubtful.
The mixture of these two molecules gives rise to the orthocJriorites, which
constitute the principal of the two subgroups of the chlorites. The
other subgroup is known as the group of the leptochlorites. These con-
sist of one or both of the two molecules mentioned above and others that
may be regarded as derived from them. Their composition is too com-
plex to be represented by any simple formula.

MgO

H20

3i-8

12.8

14.9

11. 4

34.8

12.9

37-7

130

ANHYDROUS POLYSILICATES 429

ORTHOCULORl TES

The orthochlorites comprise the minerals:

Si02 AI2O3 FeO

Corundophiltte.SpAU SpzAt7 SpAt4 =26.1 29.3

ProMorite Sp3At7~Sp2At3 SpAt2 =25.5 21.6 26. 6

Clinochlore. . . . Sp2At3-SpAt Sp2At3=30.03 22.0 ....

Penninite SpAt -Sp3At2 Sp3At2 = 347 14.6

Analyses of typical specimens are as follows:

Si02 AI2O3 Fe203 FeO MgO CaO H20 Total
I. Corundophilite 24.77 25-52 •••■ ISI9 21.88 ... 11.98 99.34
II. Prochlorite. . . . 26.02 20.16 1.07 28.08 15.50 .44 9.65 100.92

III. Clinochlore .. . 29.87 14.48 5.52 1.93 33.06 ... 13.60 100.19*

IV. Penninite 3371 12.55 2.74 3.40 34.70 .66 12.27 100.03

I. Chester, Mass.

II. Zillerthal, Tyrol.

III. West Chester, Pa.

IV. Zermatt, Switzerland.

* Contains also NiO=" .17, CrjOi»i.56.

The orthochlorites crystallize in tabular and pyramidal crystals that
are usually repeated twins so that their true nature is difficult to decipher.
The simpler crystals have a monoclinic habit, but the twins are usually
hexagonal or rhombohedral in habit. Their crystallization is believed
to be monoclinic, with the axial ratio .5774 : 1 : 2.2772 and £=89° 40'.
The most common forms appearing on them are oP(ooi), Poo (on),
fP(525), JP(7i2), 4Pfc(Q43), -i4,P 00(4.0.11), 00P 00(101) and
— 6Pj(26i) (Fig. 231). Twins are very common. The two most com-
mon twinning laws are the mica and the pennine laws. In the former
the twinning plane is perpendicular to oP(ooi) and in the zone with
oP(ooi) and — JP(ii2) (Fig. 232, compare Fig. 193). The two parts
are revolved 6o° with respect to one another. In the pennine law
oP(ooi) is the twinning plane and the composition face (Fig. 233).
Twins following the first law have their twinned parts either side by
side (Fig. 234), or superposed (Fig. 232). Those following the pennine
law have their parts superposed. The twinning is often repeated so
that complicated trillings and sixlings are produced.

Clinochlore crystals are tabular with hexagonal outlines but a mono-
clinic habit (Fig. 231), and penninite is in thick tabular crystals with a

430

DESCRIPTIVE MINERALOGY

trigonal outline and a rhombohedral habit, or in slender prismatic ones
resembling steep rhombohedrons (Fig. 235). Its characteristic twins
are according to the pennine law. (Fig. 236). Prochlorite and corun-
dophilite are found in six-sided plates without well developed crystal
forms.

Fig. 231.

Fig. 232.

Fig. 233.

Fig. 231.— Clinochlore Crystal with oP, 001 (c); ooP«>, 010 (b); 4PS0, 401 (/),

and — |P3t 13 2 M-
Fig. 232.— Clinochlore Twinned According to Mica Law, in which the Twinning

Plane is Perpendicular tooP(ooi) and in the Zone with oP(ooi) and — JP(ii2).

Forms: oP, 001 (c); |JP <» , 3T.0.30 (/): -6P3 , 261 (g) and f ZP3 , 0.27.17 (*).

Fig. 233. — Clinochlore with Same Forms as in Fig. 232. Twinned about oP(ooi) as

Twinning and Composition Face. Pennine law.

Fig. 234.

Fig. 235.

Fig. 236.

Fro. 234. — Clinochlore Trilling Twinned According to Mica Law, but with Individuals
Side by Side with oP(ooi) common and Irregular Composition Faces, n— JP,
(225) and y«|P« (205).

FiG. 235.— Penninite Crystal with oP, 001 (c) and a Form Resembling 3R, 3031 (w).
Fig. 236. — Penninite Crystal Twinned about oP(ooi). Pennine Law.

The orthochlorites have a glassy luster with a slightly pearly luster
on the basal plane. They are usually some shade of green, blackish and
bluish green being the most common shades. At a few localities white
or yellow varieties are found. Varieties containing chromium are often

ANHYDROUS POLYSILICATES 431

rose-colored or violet. The streak of all varieties is white or light
green. All are strongly pleochroic in shades of green in green vari-
eties, yellow and brown in brown varieties, and violet and carmine in
rose varieties. Their cleavage is distinct parallel to the base (ooi),
yielding lamellae that are flexible and slightly elastic. Percussion and
pressure figures, with rays in the same relative positions as in the
micas, occur naturally and often a parting takes place along their
planes yielding triangular plates. The hardness of all orthochlorites
is below 3 and their density is 2.5-3. For the different varieties these
properties are:

H Sp. Gr.

Prochlorite 1-2 2.78-2 .96

Clinochlore „ 2-2.5 2.65-2.78

Penninite 2-2 .5 2 . 6 -2 . 85

Corundophilite 2.5 2.9

The refractive indices for yellow light are: in penninite, 0= 1.575, in
clinochlore, a= 1.585, 18=1.585, 7=1.596, in prochlorite, 0= 1.58+ and
in corundophilite, 0=1.583.

Before the blowpipe the orthochlorites exfoliate and fuse with diffi-
culty. Some varieties whiten. The varieties rich in iron fuse more
readily than those in which there is little iron — in some instances to
a black glass. In the closed tube all yield water when strongly heated.
Hydrochloric acid attacks all varieties with difficulty — after fusion with
more ease. Sulphuric acid completely decomposes them.

Synthesis. — Chlorites have been produced artificially by the action
of alkaline solutions on pyroxenes.

Occurrences. — The orthochlorites are alteration products of various
silicates. They occur as essential constituents in crystalline schists
(chlorite schists), and as the alteration products of silicates in igneous
rocks, in which case the latter assume a green color. The orthochlorites
also form pseudomorphs after garnet, biotite, augite, hornblende, etc.,
and sometimes they occur filling little veins cutting through altered
rocks. Corundophilite is frequently associated with the mineral
corundum.

Localities. — The localities at which the orthochlorites occur are so
numerous that even all of the most important cannot be mentioned here.
In the United States corundophilite occurs at Chester, Mass., and
Asheville, N. C; pyrochlorite at Foundryrun, Georgetown, D. C, and
at Batesville, Va.; penninite at Magnet Cove, Arkansas; and clinochlore
at West Chester, Penn.

432 DESCRIPTIVE MINERALOGY

LEPTOCHLORITES

The name leptochlorite is usually given to the chlorites that occur in
fine scales and fibers. They are very complex in composition. Because
they do not occur in distinct crystals their crystallization is not certainly
known.

The leptochlorites are like the orthochlorites in general appearance,
and in origin. They are, however, completely soluble in hydrochloric
acid with the separation of gelatinous silica.

Of this group thuringiie and delessite are the best known. The former
is in very fine dark green and pleochroic scales. It fuses to a black mag-
netic bead. It forms pseudomorphs after garnet at the Spurr Mt. iron
mine, at Spurr, Mich. Delessite is usually green, but is in rare cases
pink. It usually occurs in bundles of fibers that are strongly pleochroic.
The green varieties, viewed across the fibers are dark green. Viewed
along their axes they are yellow. This chlorite is a common alteration
product of pyroxene and amphiboles, and it frequently occurs as the
filling of amygdules in basic volcanic rocks. The mineral when heated
becomes brown or black and finally fuses with difficulty to a black mag-
netic bead.

Analyses of typical specimens of the two minerals are given in the
following table:

Si02 AI2O3 Fe203 FeO CaO MgO H20 Total

Thuringite, Spurr,

Mich 22.35 25.14 34.39 6.41 ii. 25 99.54

Delessite, Dum-
barton, Scot-
land 32.00 17.33 XI9 12.45 1-57 2°-42 15-45 100.41

Vesuvianite

Vesuvianite is a common metamorphic mineral in limestones.
It is extremely complex in composition, apparently consisting of
isomorphous mixtures of the two compounds CaeAkAKOH-FXSiO^s
and Ca2Al(OH)Si207. Its composition may perhaps be better rep-
resented by the general formula R'4Al2Ca7Sie024, in which R'4 may be
Ca2,(A10H)2, (AK>2H)4 or H4. Four analyses, which emphasize the
great variations in composition shown by crystals from different localities
are quoted below:

ANHYDROUS POLYSILICATES

433

Si02
I. 36.08
II. 37.11
III. 36.41

IV. 36.55

Na20

I- 55
II. ...

III. .44

IV. ...

AI2O3 Fe203 FeO

9.35 7.61

1930 3-3*

17.35 1.86

18.89 .74 .74

CaO

29.09
36.24
33-21
35-97

MgO

1.90

389

1.38.

2-33

MnO K20

12.49 .28

1 75 -5°

H20 at ioo*

■58
36

•13

24
.58

H20+

332
.06

3.5i
3-42

Less 0=F Total

100.67
100.49
100.23
100.26

■15
05

100.25
100.08
100 21

I. Garnet colored masses and crystals form Pajsberg, Sweden.
II. Finely crystallized material from Italian Mt., Gunnison Co., Colo.

III. From Franklin Furnace, New Jersey. Contains also ZnO = i.74, CuO«

1.48, and a trace of PbO.

IV. Californite. Fresno Co., Cal. Also .91 per cent CO*.

Vesuvianite occurs both massive and crystallized. Its crystals are
in the tetragonal system (ditetragonal bipyramidal class), with an axial
ratio of about 1 : .5375. This
varies with the composition
and is, therefore, different in
specimens from different lo-
calities. The crystals are
usually thick columnar in
habit, but some crystals are
pyramidal and others acicular.

The columnar crystals usually « „ *r • •* r« * 1 -*\TZ> «

* J Fig. 237. — Vesuvianite Crystals with w P, no

contain 00 P(i 10) and 00 Poo (w); oop*,^ (fl); P> IIX (/>) and oP,

(100) in the prismatic zone, 001 (c).

and oP(ooi), P(in), and

often P 00(101), 3P(33i), *>P2(2io), and 3^3(3") (Fig- 237). In

all about 60 forms have been observed on them. The angle inAm

= 5o° 39'.

The mineral is glassy in luster and yellowish, greenish or brownish,

rarely blue or pink. It is transparent or translucent. A bright green,

or gray and green, translucent, massive variety from points in California

is used as a gem under the name californite. The streak of all varieties

is white. The cleavage of the mineral is indistinct parallel to 00 P(no)

and 00 P 00 (100) and its fracture conchoidal. Its hardness is 6-7 and

density 3.35-345. Its refractive indices for yellow light are: 00=1.705,

6=1.701.

434 DESCRIPTIVE MINERALOGY

Before the blowpipe vesuvianite melts to a swollen brown or green
glass. It is decomposed with difficulty by acids, but after being strongly
heated it dissolves with the separation of gelatinous silica. The min-
eral powder reacts alkaline.

The mineral" is characterized by its form when in crystals and by its
easy fusibility.

The recognized varieties that are used as gems are:

Calif ornite, a white, green or gray and green variety in finely gran-
ular masses, resembling jade.

Cyprine, a blue variety containing copper.

Its principal alteration products are mica, chlorite and steatite;
and other minerals are also known to be formed from it by weathering.

Occurrence. — Vesuvianite is preeminently a contact mineral. It
occurs in limestone metamorphosed by granite and other igneous rocks,
and also in crystalline schists. It is found also as well developed crys-
tals on the walls of veins containing quartz, calcite, garnet and ore
minerals.

Localities. — Good crystals are common at a number of places where
limestones are in contact with igneous rocks, notably at Pfitsch, and in
the Monzoni Mts., in Tyrol; at Zermatt and at other points in Switz-
erland; at Vesuvius, in the Alathal, and the Albanian Mts., in Italy;
and at many places in Norway and Sweden. In North America good
crystals occur at Sandford, Phippsburg and other places in western
Maine; near Amity, N. Y., and at Templeton, Quebec, and a fine-
grained, massive variety occurs in Inyo and Tulare Counties, in Cali-
fornia. Calif ornite is best known from Indian Creek, Siskiyou Co., and
from a point 35 miles east of Selma, in Fresno Co., California. Other
localities are at Big Bar Station, Butte Co., and Exeter, in Tulare Co.,
in the same State.

Production. — The quantity of calif ornite used as a gem stone in
1909 was about 3,000 lb., valued at $18,000. In 191 2, however, only
$275 worth was used.

Tourmaline (RoAlaCB- OH- F)2Si40l9)
R=H, Al, Mg, Fe, Al, Cr, Fe, K, Na

Tourmaline is of great scientific interest because of its complex crys-
tallization, its handsome crystals and the physical properties which it
exhibits so beautifully. Moreover, it furnishes gems of many colors,
which, because of their brilliancy, are greatly admired by many persons.
The mineral appears to be a derivative of the alumino-borosilicic acid

ANHYDROUS POLYSILICATES 435

H9Al3(B-OH)2Si40io in which the hydrogen may be replaced by Al,
by Cr, by Mg and Fe" or by Li or Na, giving rise to four groups of com-
pounds between which are many gradations. Moreover, in most speci-
mens a portion of the hydroxyl is replaced by fluorine. In other words,
the mineral is an isomorphous mixture of several substances that are
derivatives of the alumino-borosilicic acid mentioned. The four groups
of tourmalines that are clearly distinguishable are:

i. Alkali tourmalines, which are colorless, red or green, and trans-
parent.

2. Iron tourmalines, which are usually dark blue or black and trans-
lucent.

3. Magnesium tourmalines, which are yellowish brown, or brownish
and translucent.

4. Chrome tourmalines, which are dark green, black and translucent,
or colorless and transparent.

Typical analyses of these four varieties follow:

i 11 in iv

SiCfe 38.07 34.99 37.39 36.56

B2O3 9-99 9-63 10.73 8.90

AI2O3 42.24 33.96 27.89 32.58

Cr203 4.32

FeO 26 1423 .64

MnO 35 .06 tr.

CaO 56 .15 2.78 .75

MgO 07 1. 01 14.09 9.47

Na20 2.18 2.01 1.72 2.22

K20 44 .34 .16 .13

Li20 1 . 59 tr. tr. tr.

H20 426 3.62 3.83 3.74

F .28 tr. .06

TiC>2 1 . 19 .09

Total 100.29 100.00 100.42 99-70

I. Rose-colored (rubellite), from Rumford, Maine.
II. Black, from Auburn, Maine.

III. Brown, from Gouverneur, N Y. The AljOa includes .10 of Fe&Oi.

IV. Green, from Etchison, Montgomery Co., Md. Contains also .79 Fe^Os, .05

NiO and .04 P,Oft.

The varieties recognized by distinct names are (1) ordinary, black and
brown, (2) rubellite, pink or red, (3) indicolite, blue or bluish black, (4)

436

DESCRIPTIVE MINERALOGY

Brazilian sapphire, blue and transparent, (5) Brazilian emerald, or
Brazilian chrysolite, green and transparent, (6) peridot of Ceylon, honey-
yellow and transparent and (7) achroite, colorless and transparent.

Tourmaline forms handsome crystals that are frequently character-
ized by possessing a triangular cross-section. They crystallize in the
rhombohedral division of the hexagonal system and are hemimorphic
(ditrigonal pyramidal class), with an axial ratio of 1 : .4474. The crys-
tals are usually prismatic or columnar in habit, and are terminated by

Fig. 238.

Fig. 239.

Fig. 240.

OOP _ OOP

Fig. 238. — Tourmaline Crystals with H , 1010 (w); , 0110 (wi); ooPa,

P 2P

1 1 20 (a), and H — «, ion (r); u, 0221 (0) and oP, 001 (c) at analogue pole,

4 4

P _ JP

and H — /, 01 1 i(rO and /, on 2 (e) at antilogue pole.

4 4

Fig. 239. — Tourmaline Crystal with a, m, mi, c, 0, r, r\ and e as in Fig. 238. Also

3P|

H u, 2 13 1 (/). c is at antilogue pole.

Fig. 240. — Cooling Crystal of Tourmaline Powdered with a Mixture of Minium and
Sulphur to Show the Distribution of the Electric Charge. The upper end is the
analogue pole.

rhombohedrons. The most prominent prismatic faces are 00 P(io7o),
00 P2(ii2o) and the most common terminal faces R(ioTi), — ^R(oiT2),
— 2R(o22i), R3(2i3i), R5(325i) and — £R3(i232), though many other
rhombohedrons and scalenohedrons have been observed. Most forms
are hemimorphs so that the opposite ends of the c axis are differently
terminated (Figs. 238 and 239). The prismatic faces are vertically
striated and the interfacial edges are often rounded. The angle 10T1
Alioi = 46° 52'.

The mineral has a vitreous luster whether transparent or opaque. It

• ANHYDROUS POLYSILICATES 437

is brittle and has no distinct cleavage. Its fracture is conchoidal.
Its hardness is 7-7.5 and its density: 3.007-3.134 for alkali varieties;
3*036-3.104 for magnesian varieties; 3. 140-3. 212 for blue iron varieties
and 3.122-3.220 for green and black varieties. The color varies more
than in any other mineral, the same crystals often exhibiting different
colors at opposite terminations. Moreover, many crystals show a zonal
arrangement of colors, with concentric colorless, red and green layers.
The streak of all varieties is uncolored. The mineral becomes elec-
trifled by friction and like other hemimorphic substances is pyroelectric.
The analogue pole is usually more simply terminated than the antilogue
pole, in many instances showing only R(ioii) (Fig. 240). The refrac-
tive indices for yellow light in colorless crystals are : w = 1 .6422, c = 1 .6225.
In iron-bearing varieties the refraction is stronger.

Dark varieties exhibit very strong pleochroism. Viewed in the direc-
tion of the c axis the mineral is always, except in the case of colorless
varieties, darker than when viewed in a direction at right angles to it.
In very dark varieties the ray vibrating perpendicular to c is almost
completely absorbed, while the ray vibrating parallel to c passes
through with a dark brown or dark green tint. Thus, thin slices cut
parallel to the c axis will let through only light that vibrates in the plane
parallel to c. Tourmaline tongs are two such pieces or plates of dark
tourmaline mounted so that they may be revolved in their own planes.
When the c axes in the two plates are parallel light is transmitted. This
light is said to be polarized because it ail vibrates in a single plane.
When the c axes are crossed the light that passes through the first plate
is entirely absorbed by the second, so that no light passes through.

The behavior of tourmaline before the blowpipe varies widely.
Alkaline varieties are practically infusible. Iron varieties fuse with
great difficulty and magnesium varieties very easily to a blebby glass.

When fused with a mixture of acid potassium sulphate and pow-
dered fluorspar all varieties give a distinct reaction for boric acid.

Tourmaline is readily distinguished from all other minerals by its
crystallization, hardness, lack of cleavage and the reaction for boron.
In massive forms it differs from garnet and vesuvianite which it some-
what resembles by its difficult fusibility and brittleness. The mineral
is, on the whole, very stable. It is known, however, to alter into mica,
chlorite and steatite.

Synthesis. — The mineral has not been produced artificially.

Occurrence. — Tourmaline is a characteristic pneumatolitic product.
It occurs in pegmatites, in quartz and ore veins, and in limestones
end schists on the peripheries of granite masses where it is the result of

438 DESCRIPTIVE MINERALOGY

contact action. It occurs also as an original, pyrogenic mineral in acid
igneous rocks. The variety in limestone is usually brown. The lithium
varieties are usually associated with lepidolite.

Uses. — The transparent varieties are used principally as gem stones,
and the darker, translucent varieties in optical instruments.

Localities. — Tourmaline is so common that an enumeration of its
occurrence is impossible in the present place. Red or green transparent
varieties occur at Ekaterinburg, Ural; on the Isle of Elba; at Cam-
polonga, Switzerland; Penig, Saxony, and in Minas Geraes, Brazil.
In the United States fine brown crystals occur in the limestone at Gouver-
neur, N. Y.; and handsome black ones at Pierrepont, N. Y.; New Hope,
Perm. ; and in Alexander Co. , N. C. The gem tourmaline occurs at several
points in western and central Maine; at Haddam, Conn.; and in San
Diego Co., in California. The Maine localities are at Hebron, Paris,
Poland and Auburn. The tourmalines are in pockets in pegmatite.
The green varieties are most common, but all colors occur, and many
crystals are variegated. The centers of the gem industry in California
are Pala and Mesa Grande, San Diego Co., where many pink tourma-
lines and a few green crystals occur associated with the lithium mica,
lepidolite, in pockets in a pegmatite dike. The best of these when cut
bring $20 per carat.

Production. — The total output of gem tourmaline in the United
States during 1909 was 5,110 pounds, valued at $133,192, but in 191 2
the yield had fallen to $28,200.

Cordierite ((Mg-Fe)2Al2(A10)2Si50ic)

Cordierite, dichroite, or iolite, may be an isomorphous mixture of
several molecules. Its composition is apparently as shown by the
formula given above, although the persistent appearance of water in all
recent analyses may indicate the presence of hydroxyl in the molecule.
Since, however, the mineral readily undergoes weathering, most authors
regard the water as due to some hydrous alteration product. If the water
is regarded as essential the formula becomes H2(Mg- Fe)4AlsSiio037.
The calculated composition of the mineral and the actual compositions
of some specimens, as shown by analyses, are:

Si02 AI2O3 Fe203 FeO MnO MgO H20 Total

Theoretical.... 51.36 3496 13. 68 .... 100.00

Haddam, Conn. 49.14 32.84 .63 5.04 .19 10.40 1.84 100.08

CabodeGata.. 48.58 32.44 3.15 9.17 tr. 6.63 .... 99.97

ANHYDROUS POLYSILICATES

439

Cordierite is orthorhombic (bipyramidal class), with the axial ratio
.5871 : 1 : .5584. Its crystals are usually short columnar with an hex-
agonal habit due to the equal prominence of 00 P(no) and 00 P 06 (010).
(Fig. 241). In addition to these planes, there are usually present also
oP(ooi), P 06 (on) and 2P(ii2). The angle noAiTo=6o° 50'. Inter-
penetration twins, with ooP(no) the twinning plane, are known but
they are not common. Contact repeated twins,
twinned parallel to the same plane, are more
common. They usually possess a pseudohex-
agonal habit. The cleavage is good parallel
to 00 P 06 (010) and there is often a parting
parallel to the base (001).

When in fresh condition the mineral has a
glassy luster and a bluish, yellowish or grayish
tinge by reflected light. It is transparent or
translucent and colored varieties are strongly Fig. 241.— Cordierite Crys
trichroic in dark blue, green and grayish tal w,th ooP' IIQ W*
yellow shades, which become more intense
upon heating. Its hardness is 7-7.5 and sp.
gr. = 2.63. Its refractive indices vary with
the composition. In specimens from Ceylon,
a = 1.5918, 18=1.5970, 7=1.5992.

Before the blowpipe cordierite is difficultly fusible. It is very slightly
attacked by acids, but is completely decomposed when fused with alka-
line carbonates.

The mineral is distinguished from quartz most easily by its cleavage
and crystallization.

Cordierite weathers readily into fibrous or scaly aggregates of
micaceous minerals yielding well defined pseudomorphs. The end
product of the alteration is a muscovite, or a mixture of this mineral and
biotite. Several of the alteration products are so characteristic that
they have received distinct names. Among these are chlorophyllite, a
green chloritic mineral; fahlunite, a serpentine-like mass; giganlolite, a
brown, gray or green micaceous aggregate in large 1 2-sided prisms made
up of thick plates; and pinite, a dark green aggregate forming prisms
that are platy parallel to the base.

Synthesis. — Crystals of cordierite have been produced by fusing its
constituents in an open crucible and then cooling the mass very
slowly, but since the result was an anhydrous product its identity with
cordierite is doubtful.

Occurrence, — Cordierite occurs as crystals embedded in gneiss,

00 Poc ,011 (a); 00 Poo ,
010 (6); 00P 3, 130 (d);
oP, 001 (c); P, in (r);
JP,ii2J5); |P3, 134 («)
and 3P3, 131 (0).

440 DESCRIPTIVE MINERALOGY

schists, granite, quartz porphyries, and rhyolitic and andesitic lavas.
It occurs both as a pyrogenetic mineral and as a product of contact
metamorphism.

Uses. — Cordierite is used to some extent as a gem.

Localities. — Good crystals of cordierite are found in gneiss in Boden-
mais, Bavaria, and at Arendal and other points in Norway; in the vol-
canic bombs thrown out by the volcanoes of the Lake Laach district in
Prussia, and the volcano Asama Yama, in Japan, and in the andesite at
Cabo de Gata, Almeria, Spain. It occurs also in granite veins at Had-
dam and near Norwich, in Connecticut; in gneiss, at Guilford, in the
same State; at Bromfield, Mass., and near Richmond and Unity in New
Hampshire.

CHAPTER XX

THE SILICATES--C0«/mMa*

THE HYDRATED SILICATES

Chrysocolla (H2CuSi04-H20, or CuSiOa 2H2O)

Chr ysocolla occurs usually in dense masses without any sign of crys-
tallization; but at several places it has been found in spherulitic forms
that are made up of fibers that are apparently acicular crystals. The
symmetry of these, however, is unknown. The general view is that the
mineral is colloidal.

The theoretical composition of chrysocolla, corresponding to the
formula given above, and the analysis of a specimen from the Old
Dominion Mine, in Arizona, are given below:

Si02 CuO Fe203 AI2O3 Mn203 H20 Total

Theoretical.. 34.23 45. 23 20.541 00.00

Globe, Ariz.. 31.58 30.28 .84 6.27 2.22 28.71 9990

Many analyses show the presence of MgO, CaO and FeO, and some the
presence of ZnO.

The various analyses that have been recorded vary so widely, espe-
cially in the determinations of water, that the true composition of the
mineral is still in doubt. It is possibly a solid solution of colloids.

An analysis of a specimen from Huiquintipa, Chile, which is thought
to have been except ionably pure gave:

Si02

AI2O3

CuO

FeO

CaO

MgO

H2O

Total

46.14

■58

28.8s

1.38

1.64

•«3

20.15

99- 57

This corresponds to the formula H3(CuOH)(Si03)2'H20. The spec-
imen was a turquoise blue enamel, with a hardness of 3.5 and a sp. gr.

= 2.532.

Chrysocolla has an opal-like or earthy structure. It is green or

turquoise blue and translucent. Its streak is greenish white. Impure
varieties may be brown or black and have a dark brown or dark green

441

142 DESCRIPTIVE MINERALOGY

streak. It has a conchoidal fracture and is brittle. Its hardness varies
between 2 and 4 and its density between 2 and 2.2.

The mineral is infusible before the blowpipe, but it colors the flame
green. It yields water in the closed tube and is decomposed by HC1
with the production of pulverulent silica.

It is distinguished from other green and blue silicates by its reaction
toward HC1 and the green flame it imparts to the blowpipe flame.

Occurrence. — Chrysocolla is produced by the oxidation of copper
compounds and combination of these oxidation products with silicic
acid in the upper portions of ore veins. It sometimes replaces other
minerals, as atacamite, cerussite and labradorite and forms pseudo-
morphs after them.

Uses. — Chrysocolla is mined with other ores of copper and is treated
with them for the metal it contains. Exact statistics of the quantity pro-
duced are not obtainable.

Localities. — The mineral occurs in many copper mines, especially in
Bohemia, Hungary, Italy and Russia. It occurs as blue crusts on the
basalts near Somer ville, N. J. ; as a bluish green matrix cementing black
masses at the Old Dominion Copper Mine, Globe, Ariz.; and intimately
intergrown with opal at the Boleo Mine, California. It is also abundant
in Chile, where it occurs in all varieties.

Glauconite [Hydrous Silicate of Iron and Potassium]

Glauconite, or greensand, is an important constituent of some sedi-
ments. It is probably a mixture of several substances, of which the
compound FeK(Si03)2 • ffH20 may be most essential. It occurs as little
round grains and pellets, mixed with the shells of foraminifera, forming
beds of sand, and also as a component of limestone, marl, clay and sand-
stone. Glauconitic sands, because of their richness in potash were
formerly used as fertilizers in the regions in which they are found.

Analyses of glauconite grains from Ashgrove, near Elgin, in Scot-
land (I), and of glauconite sand from Antwerp, Belgium (II), are as
follows:

S1O2 AI2O3 Fe203 FeO MgO CaO Na20 K20 H20 Total
I. 4909 15.21 10.56 3.06 2.65 .55 1. 21 6.05 11.64 100.02
II. 50.42 4.79 19.90 5.96 2.28 3.21 .21 7.87 5.28 99.92

Glauconite is blackish, or yellowish green, in color, with a light green
streak. It resembles earthy chlorite, but is probably amorphous. Its
hardness is 2 and its density 2.2-2.8. • It is opaque.

HYDRATED SILICATES 443

The mineral fuses with difficulty to a black magnetic slag and is
decomposed in part by strong hydrochloric acid, but after fusion is com-
pletely dissolved with the separation of gelatinous silica. It yields
water in the closed tube.

Occurretice and Localities. — Glauconite occurs in oceanic deposits
and in sedimentary rocks of nearly all geological ages. Its principal
occurrences in this country are in the belt of cretaceous beds on the
Atlantic coastal plain. It is best known from the coastal portions of
New Jersey and from Spotsylvania and Stafford Counties, in Virginia.
It apparently occurs also as a decomposition product of augite in certain
basaltic rocks. In all cases it appears to have been produced by sec-
ondary processes, w'z., by the absorption of potassium compounds and
soluble silica by colloidal ferric hydroxide. In the ocean these com-
pounds result from the action of decaying animal matter upon ferrugi-
nous clays and fragments of potassic silicates in rocks; when of later
origin than the rocks themselves, by the action of solutions of potassic
salts upon iron hydroxids.

Greenalite differs from glauconite in containing no potassium. It
may be a hydrated ferrous silicate (FeSi03 • *H20) or a ferrous-ferric
silicate (Fe2Fe3(Si04)3-3H20). It occurs as round grains in the cherts
of the Lake Superior region, and in its physical properties it closely
resembles the glauconite granules in rocks. It is believed to be the
source of the hematite ores of the district.

Apophyllite (H7KCa4(Si03V4§H20)

Apophyllite differs from the zeolites (p. 445) in containing no aluminia
and in having some of its water replaced by fluorine; but in its general
appearance and its manner of occurrence it is like them. The calculated
composition corresponding to the formula usually assigned to the mineral
is given in I. Analysis II is of a specimen from Bergen Hill, N. J., and
III of a specimen from Golden, Colo. Some specimens contain also
small quantities of ammonia.

Si02 AI2O3 Fe203 CaO Na20 K20 H20 Fl Total

I. 53.7 25.0 ... 5.2 16. 1 .... 100.00

II. 52.24 25-°3 ••• 4°5 16.61 2.21 100.14

III. 51.89 1.54 .13 24.51 .59 3.81 16.52 1.70 100.69

The mineral is tetragonal (ditetragonal bipyramidal class), with
a : b : c= 1 : 1.2464. Its crystals usually contain the forms 00 P 00 (100),

444

DESCRIPTIVE MINERALOGY

P(iii) and oP(ooi), and often ooP3(3io) or ooP2(2io). In addition,
about 55 other forms have been identified, but most of them are rare.
Many of these are vicinal planes with large parameters. The crystals
are of four types, (i) pyramidal with P(ni) predominating; (2) pris-
matic with 00 Poo (100) and P(m), the former predominating; (Fig.
242A), (3) cubical, with 00 P (100) and oP(ooi) equally prominent (Fig.
242B), and (4) tabular parallel to oP(ooi) (Fig. 242C). Twinning par-
allel to P(m) is rare. The angle in AiTi = 76°. The mineral also
occurs in granular and lamellar masses.

Apophyllite is glassy on fracture surfaces and most crystal faces, but
on oP(ooi) it is distinctly pearly. It is white, grayish, flesh-colored or
red, and transparent. Its streak is white. It possesses a very perfect
cleavage parallel to oP(ooi) and a less perfect one parallel to 00 P(no).

ff=^r\

Fig. 24 2.-* Apophyllite Crystals with *> P*> . 100 (0); P,iii (p),6P> 001 (c) and
00 P3, 3io (?)■ A. Prismatic. B. Cubical. C. Tabular.

It is brittle. Its hardness is 4.5-5 and its density 2.2-2.4. It is strongly
pyroelectric. For yellow light, (0=1.5356, €=1.5368.

Before the blowpipe apophyllite exfoliates and fuses easily to a blebby
white enamel, and imparts a violet color to the flame near the assay.
In the closed tube it loses water and becomes opaque. It also loses
water upon being pulverized. Most specimens give the reaction for
fluorine. Half the water is lost at a comparatively low temperature
(24o°-26o°), but the last remnant of the remainder is driven off only at
a red heat. At 400 ° fluorine begins to escape. The mineral dissolves in
HC1 with the separation of slimy silica. At i8o°-i9o°, under a pressure
of 10-12 atmospheres, it dissolves in water, and from this solution it
crystallizes upon cooling.

Apophyllite is recognized by its crystallization, its pearly luster on
the basal plane, and its fluorine reaction.

Syntheses. — Apophyllite crystals have been obtained from solutions
of its constituents in water containing CO2, heated in a closed tube to
150-1600. They have also been formed by the action of a solution of

HYDRATED SILICATES

445

potassium silicate on gypsum. The mineral has also been described
from the ruins of old Roman masonry around hot springs.

Occurrence. — The mineral occurs in the cavities of volcanic rocks,
in veins in granite and gneiss and in ore veins and ore deposits in lime-
stone. It is also found in the rocks surrounding hot springs. Under
some conditions it alters to calcite, and to pectolite (p. 369).

Localities. — Good crystals of apophyllite occur at St. Andreasberg
and Radauthal, Harz; at St riegau, Silesia; near Cipitbach, in the Seisser
Alps, Tyrol; in the magnetite mines at Uto, Sweden; at Disko, Green-
land; at many points in eastern Nova Scotia; at Bergen Hill, N. J.; at
Table Mt., Golden, Colo., and at Santa Barbara, in Brazil.

THE ZEOLITES

The group known as the zeolites comprises minerals that are hydrous
silicates of aluminium with calcium, sodium, potassium, barium or
strontium. The calcium compounds are commonest, followed by the
sodium compounds. Compounds with the other elements are com-
paratively rare.

While it is probable that some of them are primary products resulting
from the cooling of a magma, in the great majority of cases the zeolites
are secondary products derived by the alteration and hydration of
alkali-aluminium silicates, such as the feldspars, leucite, nepheline, etc.
They are nearly always found in veins, or on the walls of crevices in
rocks (especially volcanic rocks), where they have been deposited by
circulating water. They are commonly associated with calcite, pecto-
lite, datolite or prehnite. All are well crystallized and some of them are
in complicated crystals.

Many of the zeolites have been recrystallized from solutions in
superheated water. The solutions having been produced by the action
of various reagents upon aluminous silicates.

Before the blowpipe ail the zeolites fuse with intumescence, or bub-
bling, and all give water in the closed tube. They are comparatively
soft (3.5-5.5), and have a low specific gravity (2-2.4). The most com-
mon zeolites are:

Ptilolite

Heidandite

Pkillipsite

Harmotome

Stilbite

Laumontite

(Ca- K2- Na2)Al2Siio024- 5H2O
H4CaAl2(Si03)6-3H20
(Ca-K2)Al2(Si03)4-4iH20
(H2(Ba- K2)Al2(Si03)3- 5H20
(Ca- Na2)Al2Si60i6- 6H2O
CaAl2(SiQ3)4-4H20

Monoclinic
Monoclinic
Monoclinic
Monoclinic
Monoclinic

446 DESCRIPTIVE MINERALOGY

Scolecite Ca(A10H)2(Si03V 2H2O Monoclinic

Natrolite Na2Al(A10)(Si03)3- 2H2O Orthorhombic

Thomsonite (Ca- Na2)Al2(Si04)2* 25H2O Orthorhombic

Chabazite (Ca • Na2) AI2 (SiOa)4 • 6H2O Hexagonal

A nalcite NaAl(SiOs)2 • H2O Isometric

Ptilolite ((CaK2'Na2)Al2Siio024-5H20) occurs in short, hairlike,
white or colorless crystals, aggregated into delicate tufts or spongy
masses. Their system of crystallization is unknown. Their luster is
vitreous. The needles apparently have a cleavage perpendicular to
their long axes. The mineral is scarcely acted upon by boiling hydro-
chloric acid.

The composition of ptilolite from Colorado is quoted as follows:

Si02

AI2O3

CaO

Na20

K20

H20

Total

7Q-35

11 .90

3-87

•77

2.83

10.18

99.90

Its refractive indices are about 1.480.

The mineral is found in the cavities of a volcanic rock in Green and
Table Mts., Jefferson Co., Colo.

Heulandite (H4CaAl2(Si03V3H20)

Heulandite occurs in monoclinic crystals (monoclinic prismatic class),
with the axial ratio .4035 : 1 : .4293 and #=91° 25', in foliated and
granular masses and in globular aggregates

The theoretical composition of heulandite (the formula of which may
also be written CaAloSioOie* 5H2O), and the analysis of a specimen from
Anthracite Creek, Gunnison Co., Colo., are given below:

Si02 AI2O3

CaO

Na20

K20

H20

Total

I. 59.22 16.79

9.20

■ ■ •

1479

100.00

II.57.38 17.18

8.07

.82

.40

16.27

100.12

I. Theoretical.

II. Gunnison Co., Colo.

Its crystals are usually tabular parallel to 00 P 00 (010). Their most
prominent forms are: 00 Poo (010), — 2P 00 (201), 2P 00 (201), oP(ooi),
ooP(no), 2Poo(o2i) and P(Tn) (Figs. 243 and 244). The angle
no A iTo=43° 56'. Twins are known, with oP(ooi) the twinning plane.
The cleavage is perfect parallel to 00 P 00 (010) and the fracture is
uneven or conchoidal.

The mineral has a glassy luster, which becomes pearly on 00 P 00 (010).

HYDRATED SILICATES

447

It is colorless, white, yellow, brown, pink or red. Its streak is white.
It is brittle, has a hardness of 3-4 and a density of 2.2. For yellow

light, 0= 1.4998, 0= i.5°°3» 7- i-S°70--

Before the blowpipe heulandite whitens, exfoliates, crinkles and melts
to a white glass. It yields water in the closed glass tube and becomes
dull and opaque. It is decomposed by hydrochloric acid with pre-
cipitation of pulverulent or gelatinous silica. Its powder reacts
alkaline.

Heulandite is distinguished by its crystallization and its reactions
before the blowpipe.

Synthesis. — Crystals have been made by heating anorthite powder
to 200 ° with gelatinous silica in water containing carbon dioxide.

Fig. 243.

Fig. 244.

Fig. 243. — Heulandi*e Crystal with 00 Pob , 010 (6); 00 P, no (w); 2P06 , 201 (5);

— 2 P06 , 201 (/) and oP, 001 (r).

Fig. 244. — Heulandite, var. Beaumontite. Forms same as in Fig. 243.

Occurrence. — The mineral occurs in the cavities of porous basalts,
and occasionally in gneisses and granites, associated with other zeolites.
It is found also in some ore veins.

Localities. — Good crvstals occur in the druses and veins in volcanic
rocks at Fassa, Tyrol; at Montecchio Maggiore, Italy; at Lake Mien,
Sweden; and along the north shore of Lake Superior. It also occurs in
druses in gneisses at the Campsie Hills, Scotland, and at Jones Falls
quarries Xbeaumontite) , Baltimore, Md. ,

Phillipsite ((Ca- K2)Al2(Si03)4 - 4*H20)

Phillipsite is a calcium, potassium alumino-silicate with the theoretical
composition indicated in line I. The composition of a specimen from
Richmond, Australia, is shown in line II. Many specimens contain
barium and sodium.

448 DESCRIPTIVE MINERALOGY

SiOa AI2O3 CaO NanO K20 H2O Total

I. 48.8 20.7 7;6 .... 6.4 16.5 100.00

II. 45.60 22.70 4.5a 4.51 6.05 16.62 100.00

The mineral crystallizes in the monoclinic system with the axial ratio
.7005 '• 1 : 1.3563 and 0=124° 23'. Its crystals are never simple but
are always twinned parallel to oP(ooi), forming groups with an ortho-
rhombic or tetragonal habit (Fig. 245). These are often twinned again
with P So (01 1) the twinning plane, producing interpenetration fourlings
(Fig. 246A). Three fourlings twinned again, with 00 P(i 10) the twinning
plane, result in a group of 12 individuals (Fig. 2466). The individual
crystals are usually bounded by oP(ooi), =0 P So (010) and ooP(no),

Fto. 145. P"3- *4&

Fro. 145. — Phillipsite Interpenetration Twin about oP(oot). Forms are oP, 001

(*); °°P«,oio(*)and » P. no(m).
Fig. 346. — Phillipsite. — A. Fourling of two twins like Fig. 145 twinned again about
P« (011). The c faces are on the outside. B. Three fourlings twinned about
wP(no).

though ooPoo(ioo), 00 P3(i2o) and several other forms also occur on
them. Theangle noAiTo=6o°42'. The faces =oP(i 10) and°oP&(oio)
are usually striated parallel to the edge between the two. Besides occur-
ring in distinct crystals the mineral is also found in radially fibrous glob-
ular aggregates.

Phillipsite has a glassy luster; is colorless or white, yellowish, gray-
ish, reddish or bluish; is transparent or translucent and has a white
streak. Its cleavage is distinct parallel to oP(ooi) and «P5i(oto).
It is brittle, has a hardness of 4 and a density of 2.2. Its refractive
index, £=1.51.

Before the blowpipe it fuses to a white glass. In the closed glass tube
it gives off water and becomes cloudy and milky. It is decomposed in
HCI with the separation of gelatinous silica, and in dilute H2SO4 without
precipitation.

HYDRATED SILICATES 449

It is distinguished by its crystallization and by the fact that it dis-
solves in H2SO4 without precipitation of BaS04 (see Harmotome,
below).

Synthesis. — Crystals of phiilipsite have been produced by heating
potassium aluminate and silicate in a closed glass tube at 200°.

Localities, — The mineral occurs in the vacuoles of basic igneous rocks
at the Giant's Causeway, Ireland; at Capo di Bove, near Rome, Italy;
at Aci Castello, in Sicily, and at various points in the state of Victoria,
Australia.

Harmotome (H2(BaK2)Al2(SiO3)55H20)

Harmotome is a barium compound almost identical in crystallization
with phiilipsite.

Its theoretical (I) composition (also written (Ba-KnjAljSisOus^O)
and the analysis of a specimen (II) from Thunder Bay, Canada, are
shown below.

CaO

SiOs

Al2Oi

I. 46.64

15. ,8

II. 46.36

17.16

BaO

H20

Total

23.67

13 01

100.00

21.18

14. 54

101.49

The crystallization and twinning of harmotome are the same as in
phiilipsite. Its axial ratio is .7032 : 1 : 1.2310, with /9=iz4° 50'. The
crystals more commonly contain the form
«P«i(ioo), and a few more orthodomes.
Fourlings are common, but in these the planes
c*Pw(oio) form ihc outside of the group,
whereas in phiilipsite the outside planes are
oP(ooi). The planes coP(no) and *> P So
(010) arc striated as in phiilipsite (Fig.
247)-

In general appearance and physical prop-
erties harmotome resembles phiilipsite. Tt Fio. 147.— Harmotome Four-
has, however, but one distinct cleavage, which !inf> Twinned like Phillips-
is parallel to °oPSo(oio\ Its hardness is ""■=. FiR. a46 A, Except
4-S and densitv 2.;. Its refractive indices Lhat ('"m">only the b
_ . , Faces arc on ihc Outside,

are: a= 1.503, 7- 1.508. It acts very much Nolo (jjfferences in direc.
like phiilipsite before the blowpipe and in the (jons 0[ stations on this
closed tube. It, however, dissolves readily in figure and 246 A.
HCI with the separation of pulverulent silica,

and in dilute H2SO.1 with precipitation of BaS04- Its powder reacts
weaklv alkaline.

450 DESCRIPTIVE MINERALOGY

The mineral is distinguished from all others but pkUUpsi'.e by its

crystallization, and from this mineral by its reaction with H2SO.i.

It occurs in the vacuoles of volcanic rocks, in gneisses, granitic rocks
and a few ore veins.

Localities. — It is found at St. Andreasberg in Harz; in veins in granite
at Strontian, in Scotland; in druses in the syenite near Christ i;uii;i,
Norway; on calcitein mines at Rabbit Mt., and in the Beaver Mine,
near Thunder Bay, Ontario; and in the gneiss under New York City.

Stilbite (Ca-Na2)AI2Si«0,6-6H20)

Stilbite, or desmine, is found in twinned crystals with an ortho-
rhombic habit resembling the simple twins of phillipsite, and in sheaf-

F1G. 248.— Sheaf-like Aggregates of Stilbite.

like aggregates (Fig. 248), in radiating bundles and in thin platy
prisms.

Its composition calculated from the formula given above is as in I.
The result of the analysis of a soda-free specimen from French Creek
Mines, Pa., is given in II and of a sodium -hearing specimen from Golden,
Colo., in III.

S1O2 Al203 CaO MgO NaaO K20 H20 Total

I. 57.4 16.3 7.7 .... 1.4 --■■ 172 100.00

II. 58.00 13.40 7.80 1.40 tr. 1.03 18.30 99.93

III. 5467 16.78 7.98 .... 1.47 ■■■ ■ 19 "6 100.06

The crystals arc monoclinic (prismatic class), with an axial ratio of
.7625 : 1 : 1. 1940, with 13=129" 10'. They are always intcrpcnct.ration
twins, with oP(ooi) the twinning plane as in phillipsite. The individ-

HYDRATED SILICATES 451

uals are simple combinations of oo Poo (oio), oP(ooi) and ooP(no),
and they are usually tabular parallel to oo P ob (oio). Their cleavage is
perfect parallel to oo P ob (oio) and imperfect parallel to oP(ooi).

Stilbite is colorless or white, grayish, greenish, yellowish, red or
brown. It has a white streak and a glassy luster that is nearly pearly on
oo P ob (oio). It is transparent or translucent, is brittle, has a hardness
of 3-4 and a density of 2.2. Its refractive indices are: a =1.494, 0=
1.498, 7=1.500.

Before the blowpipe it exfoliates, swells and crinkles to a white blebby
glass. In the closed tube it yields water and becomes cloudy and opaque.
It is decomposed by HC1 with the production of pulverulent silica. Its
powder reacts alkaline.

Occurrence. — Stilbite occurs in the vacuoles of amygdaloidal basalts,
in veins cutting granites and other coarse-grained rocks, and on the walls
of cracks in gneisses and schists. It occurs also as deposits around hot
springs.

Localities. — Its principal localities are the basalt rocks of the Isle
of Skye, Arran in Scotland; Mourne Mts. and the Giant's Causeway, in
Ireland; and the Deccan, in India. It occurs in veins at Radauthal in
the Harz; at Striegau, in Silesia; and at Falun, in Sweden. It is abun-
dant in the old volcanic rocks of Nova Scotia; of Lake Superior, and
of Table Mt., near Golden, Colo., and near Bergen Hill, N. J., and is
present in cavities in gneisses at several points in Connecticut and
Pennsylvania.

Laumontite (CaAl2(Si03)4-4H20)

Laumontite occurs in monoclinic crystals and in radiating fibrous
aggregates. Its formula demands the composition shown in I. The
analysis of a specimen from Table Mt., Colo., is quoted in II.

Si02 AI2Q3 FC2O3 CaO Na20 K20

I. 51 .07 21 .72 ... 11 .90
II. 51.43 21.52 .94 11.88 .19 .35

Its crystals are usually very simple monoclinic (prismatic class),
combinations with an axial ratio 1.1451 : 1 : .5906 with #=99° 18'.
The most common forms observed are ooP(no) and 2P60 (201), and
often these are the only two present (Fig. 249). Frequently crystals of
this type are twinned parallel to 00 P 60 (100). Their cleavage is perfect
parallel to 00 Poo (010) and ooP(no). The value in A 110=93° 44'.

Laumontite is white, grayish, yellowish or reddish, and has a glassy

H20

Total

15-31

100.00

13.81

100.12

452

DESCRIPTIVE MINERALOGY

luster except on cleavage surfaces. On these it is pearly. It is trans-
parent or translucent and its streak is white. It is brittle, has a hard-
ness of 3-3.5 and a density of 2.3-2.4. Its
refractive indices are: a= 1,513, 0=1,524, 7=

1,5*5-

Before the blowpipe it swells and melts to a

,. white glass. It gelatinizes with HC1. . It readily

Cf^ yields some water at low temperature in a closed

-^ tube, but a red heat is required to drive off the last

traces. When melted and cooled the glass crys-
tallizes to anorthite and a pyroxene mineral.
Laumontite is best recognized by its crystals.
Occurrence. — It occurs in the cavities of basic
volcanic rocks. It is also found in veins in clay slates, and schists
and as a gangue mineral in certain ore veins.

Localities. — Its best known localities are the Isle of Skye and Dum-
bartonshire, in Scotland; in the Zillerthal, Tyrol; at Table Mt., Colo.;
at Bergen Hill, N. J. ; at many points on the north shore of Lake Superior,
and on Keweenaw Point, on the south shore, and in the trap rocks
near Annapolis, Nova Scotia.

Fig. 249. — Laumontite
Crystal with 00 P,
1 10 (m) and 2P w ,
201 (e).

Scolecite (Ca(A10H)2(Si03)3-2H20)

Scolecite is white and it occurs in silky, fibrous and dense radiating
masses and also in crystals that are often aggregated into divergent
groups (Fig. 250).

Its formula (written also CaAl2Si30io.3H20), demands the composi-
tion indicated in I. The analysis of a specimen from Table Mt., Colo.,
is quoted in II.

Si02

AI2O3

Fe203

CaO

Na20

K20

H20

Total

L 45 -92

26.05

• • ■

1427

• • • ■

• • •

13 75

100.00

II. 46.03

25.28

.27

12.77

1.04

•13

14.48

100.00

The mineral is monoclinic (domatic class), with alb: ^=.9764 : 1 :
•3434 and 0=90° 42'. Its crystals are columnar or acicular in the direc-
tion of c and are usually bounded by 00 P 00 (010), 00 P(no), — P(in)
and P(Tn) (Fig. 251). Other planes are sometimes present in the pris-
matic zone, and — P «> (101), — 3P(.33i) and — 3P3(i3i) at the termina-
tions. Twins are more common than simple crystals, the twinning plane
being 00 P 66 (100) and the composition plane the same. The angle
noAiTo=88° 37'.

HYDRATED SILICATES

Scolecite is glassy in luster, transparent or translucent, and colorless
or white. Its cleavage is perfect parallel to oo P{no) and its fracture

(£ft

FlC. 350. — Divergent Groups of Scolecite Crystals from near Bombay, India.

conchoidal or uneven. Its hardness is 5-5.5 and density 2.2-2.4. ^ts
crystals are strongly pyroelectric. On a cooling crystal the front pris-
matic faces (no) are positively charged and the
corresponding back faces (1T0) negatively charged.
Their hemihedrism is brought out clearly by etch
figures. The refractive indices for yellow light are:
01=1.5122, (3=1.5187,7=1.5194.

Before the blowpipe scolecite crinkles and fuses
to a white blebby enamel. In the closed tube it
yields water and becomes white and opaque. It
gelatinizes with acids.

Scolecite is distinguished by its crystalliza-
tion.

Synthesis. — Scolecite has been obtained by treat-
ing natrolite (p. 454) with a solution of CaCb.
Crystals occur on Roman tiles that have been ex-
posed for centuries to the waters of the hot
springs at Plombieres, France.

Occurrence. — It occurs in the cavities of basic volcanic rocks and in
veins in crystalline schists.

Fig. 951. — Scolecite

Crystal with »P,
uo(«); <»PS>oro
(6); P, in («),

e d about

454 DESCRIPTIVE MINERALOGY

Localities. — Its principal occurrences are veins in siliceous rocks in
Canton Uri, Switzerland; and in the cavities of basalts in the Bern
Fjord, Iceland; at Staffa and the Isle of Mull, Scotland; at Table Moun-
tain, near Golden, Colo.; and in the Deccan, India.

Natrolite (NauAKAlOXSiOsJa-aHaO)

Natrolite occurs in acicular crystals, and in radial fibrous, gran-
ular and dense masses.

Its theoretical composition (I) and the analysis of a specimen (II)
from Magnet Cove, Ark., corres[)ond very closely.

Si02 AI2O3 FeO CaO MgO Na20 H20 Total

I.47.36 26.86 ... 1632 946 100.00

II. 47.56 26.82 .20 .13 .09 15.40 9.63 99.83

Natrolite is orlhorhombk (bipyramidat class), with a: b : £=.9785

: 1 : .3536 and «P(no), «>P*(ioi), oopa(izo), oop*(oio),

P(in) the most commonly occurring forms- (Fig. 252). Additional

forms that are fairly common are PfJ (ii.io.ii), $P(33i) and 3p3(i3i).

--r-..^ The prismatic angle is nearly oo° (88° 45').

causing the crystals to appear tetragonal.

Some crystals are apparently monoclinic

(prismatic class) with £ = 90° 5', in which

case the substance is dimorphous. The habit

of the crystals is columnar, or acicular, in the

Fie. 152.— Natrolite Crystals direction of the c axis with striatums on the

with oop, no (m); P, hi prismatic planes parallel to this direction. In

(0}; *>PoS,oio (i) and the case of a few crystals from Norway, how-

«' II10-:i (*)■ ever, the donga t ion is in the direction of b.

Twins are known, with 3P « (301) the twinning plane.

Natrolite is glassy and transparent or translucent. It is colorless or
while, yellowish, reddish or green. Its streak is white. Its cleavage is
perfect parallel to °o P(uo). Its fracture is uneven or conchoidal, its
hardness 5-5.5 and density 2.2-2.5. Its refractive indices for yellow
light are: 01=1.4754, 0=1.4790.7=1.4887.

Before the blowpipe the mineral fuses quietly to a colorless glass at
the same time coloring the flame yellow. In the closed tube it loses
water and becomes cloudy and opaque. Its powder reacts alkaline.

Natrolite is easily distinguished from other zeolites by its crystalliza-
tion and action before the blowpipe.

Syntheses. — Crystals of natrolite have been obtained by dissolving

HYDRATED SILICATES 455

the powdered mineral in a closed tube with carbonated water at 1600
and cooling. Crystals supposed to be those of natrolite have been pro-
duced by treating nepheline in a closed tube at 2000 with a solution of
alkaline carbonates in carbonated water.

Occurrence. — The mineral occurs in the cavities of volcanic rocks, and
as an alteration product of nepheline, sodalite and plagioclase in coarse-
grained rocks.

Localities. — Crystallized natrolite is abundant in the volcanic rocks
of Hegau and the Kaiserstuhl in Baden, in the basalts of Silesia and
Bohemia, in the volcanic rocks of Tyrol and Italy; in those of the
Auvergne, France; in veins in the syenites of La ngesund fjord, in Nor-
way; in the basalts of Cape Blomidon and other points in Nova Scotia;
at Eagle River, in Michigan; and Bergen Hill, N. J.; and in the nephe-
line syenites of Magnet Cove, Ark., and elsewhere,

Thomsonite ((Ca • Na2) AI2(Si04)2 • 2§H20)

Thomsonite, or comptonitc, is evidently an isomorphous mixture of
soda and lime molecules — the ratio of Ca to Na2 varying between
3 : 1 and 1:1. The calculated composition represented by the formula
(Ca • Na2)Al2(Si0.i)2 ■ 2 2H20 is given in III. In I is given the calculated
formula of the compound in which Ca : Na2 is as 3 : 1 and in II, that in
which this ratio is 2 : 1. The analysis of tabular crystals from the
basalt of Table Mt., near Golden, Colo., is given in IV.

Si02

I- 37 .0
II. 36.9

III. 36.8

IV. 40.68

Thomsonite crystallizes in the orthorhombic system with a: b : c=
.9932 : 1 : 1.0066. The crystals, which are rare, usually have a pris-
matic habit. They are bounded by 00 P do (100), 00 P(i 10), 00 P 60 (010)
oP(ooi), 4P 60 (401), 8P 6b (801), and often JP 06 (012), and are striated
parallel to c (Fig. 253). The angle no A 110=89° 37'. The crystals
are commonly grouped in radial aggregates or spherical concretions.
Rarely, the mineral is in fine-grained structureless masses.

Thomsonite has a glassy luster that in some cases is slightly pearly,
especially on cleavage planes. It is transparent or translucent, colorless,
white, gray, green or red and has a colorless streak. Some radial aggre-
gates are red and white in concentric zones. The cleavage of thorn-

A1203

CaO

Na20

H20

Total

31-4

12.9

4.8

13-9

100.00

31-4

"•5

6.4

138

100.00

31-3

8.6

9-5

138

100.00

30.12

11.92

444

12.86

100.02

456

DESCRIPTIVE MINERALOGY

Fig. 253. — Thomsonite
Crystal with « p. no
(m); «Pw, 100 (a);
ocP«,oio(6); 8P5c,
801 (*);4P<», 401(d)
and oP, 001(c).

sonite is perfect parallel to 00 P 06 (010) and less perfect parallel to
00P66 (100). Its fracture is uneven. It is brittle, has a hardness of

5-5.5 and a density of 2.3-2.4, and is pyro-
electric. Its refractive indices are: 0=1.498,
*T~ 0= 1.503, 7= 1.525.

"H Before the blowpipe it swells and fuses to a

white glass. In the closed tube it gives up
water and becomes opaque. It gelatinizes with
HC1. Its powder reacts alkaline.

Lintonite is a green, prehnite-like variety
occurring as little structureless pebbles on the
north shore of Lake Superior. It is used to
some extent as a gem stone. Its hardness is 5-6,
and its sp. gr. 2.34.

Chlorastrolite is a fibrous variety, also oc-
curring as pebbles on the shores of Lake
Superior, especially on Isle Royale. It is often
pink and white in concentric zones. It also is employed as an orna-
mental stone. Some of the chlorastrolite is probably fibrous prehnite.

Occurrence. — The mineral occurs in the vacuoles in igneous rocks, as a
constituent of pegmatite dikes, and as an alteration product of nepheline
in nepheline rocks, and of the plagioclases in crystalline schists. It is
found also as little pebbles on the north shore of Lake Superior, where it
was washed from amygdaloidal basalts.

Localities. — It is found in the basalt of Kaaden and other places in
Bohemia; in the porphyries of Kilpatrick, Kilmalcom and Port Glasgow,
in Scotland; in the inclusions in the lavas of Mte. Somma, near Naples,
Italy; in veins on Laven, Ar6 and at other places in Norway; in the
basalts at Port George and Cape Split in Nova Scotia; on the shore of
Lake Superior near Grand Marais, Minnesota, where it originally filled
amygdaloidal cavities in diabases and basalts; in cavities in the neph-
eline syenites at Magnet Cove, Ark.; and in the basalt at Table Mt.
near Golden, Colo.

Production. — Chlorastrolite to the value of $350 was sold during
1912.

Chabazite ((Ca-Na2)Al2(Si03)4-6H20)

Chabazite has a variable composition. It is probably an isomor-
phous mixture of the Ca, Na and K molecules corresponding to the
general formula (R"R'2)Al2(Si03)4-6H20. Analyses of the three
chemical types of the mineral are given below.

HYDRATED SILICATES 457

Si02 AI2O3 Fe2Q3 CaO MgO Na20 K20 H20 Total

I.45.84 20.99 ... 5.89 ... 5.78 1.83 21.97 100.30

II.47.52 1948 ... 9.63 ... .52 .36 22.11 100.05

III. 49.24 18.07 .84 5.16 .86 .... 3.00 21.31 99.95

I. Phacolite from Richmond, Victoria.

II. From the basalt of Table Mt., Golden, Colo. Also .43 SrO.
III. Haydenite from Jones Falls quarry, Baltimore, Md. Also 1.47 BaO.

Chabazite occurs in crystals and in compact aggregates. It crys-
tallizes in the rhombohedral division of the hexagonal system (ditrigonal
scalenohedral class), with a: c=i : 1.0860. Crystals are usually of a
cubical habit because of the predominance of the rhombohedron which

Fig. 254. Fig. 255. Fig. 256.

Fig. 254 — Chabazite Crystal with R, 10T1 (r); — |R, 01 12 (e) and — aR, 0221 (s).

Fig. 255. — Chabazite Interpenetration Twin, with c the Twinning Axis and oR(oooi)

the Twinning Plane.

Fig. 256. — Phacolite with Same Forms as in Fig. 254 and also oR, 0001 (c); JP2,
1 123 (0 and — JR, 0223 (p). Interpenetration twin about oR(oooi).

has nearly equal a and c axes. Besides R(ioTi), the most common
forms are oR(oooi), — £R(oil2 and — 2R(o22i) (Fig. 254), though other
minus rhombohedrons, scalenohedrons and a prism (00P2, 1120) and
pyramid (IP2, 11 23) of the second order are also known. The angle
10T1 aTioi = 85° 14'. The crystals are often striated parallel to the
edge between R and— JR. Twinning is not uncommon. Both con-
tact and interpenetration twins are known, the former with R(ioTi)
the twinning plane, and the latter with oR(oooi) the twinning plane
(Fig. 255). In the variety of chabazite known as phacolite, the crystal
habit is lenticular because of the nearly equal prominence of |P2(ii23)
and — 2R(o22i), and twinning parallel to oR (0001) (Fig. 256).

Chabazite is glassy in luster, is transparent or translucent, colorless
or white, gray, yellowish or pink. Its streak is colorless. Its cleavage

458 DESCRIPTIVE MINERALOGY

is distinct parallel to R(ioTi) and its fracture uneven. Its hardness
is 4-5 and density 2.08-2.16. Its indices of refraction are about
1.48.

Before the blowpipe fragments of the mineral usually, swell and fuse
to a porous translucent glass. In the closed tube they yield water and
become cracked, but remain clear. The variety from Victoria (phacolite),
however, becomes cloudy and red and breaks into pieces. The mineral
is decomposed by HCi and the separation of slimy silica, but after fusion
is insoluble. Its powder reacts weakly alkaline.

Chabazite is distinguished by its crystallization and its reaction in
the closed tube.

Syntheses. — Chabazite crystals have been obtained by dissolving the
powder of the mineral in carbonated water in a closed tube at 1500 and
cooling, and by heating to 2000 a mixture of freshly precipitated Si02,
AI2O3 and Ca(OH)2 in water containing CO2.

When chabazite is fused alone it crystallizes as anorthite.

Occurrence. — The mineral occurs in the vacuoles of basalts and other
volcanic rocks and on the walls of crevices in gneisses and schists. It
is found also in ore veins and as a deposit from thermal springs.

Localities. — It is abundant in nearly all regions in which basic vol-
canic rocks occur, especially in Rhenish Prussia; Hesse; Silesia; Bo-
hemia; Tyrol; Italy; Canton Uri, Switzerland; Kilmalcolm and Skye,
Scotland; Iceland; near Richmond, Victoria (phacolite), and elsewhere.
In North America it occurs in the basalts in southwestern Nova Scotia;
on the walls of clefts in a gneiss at Jones Falls and Baltimore, Md.
(haydenite) ; and in the basalt of Table Mt. and Golden, Colo.

Analcite (NaAl(Si03)2H20)

Analcite corresponds to the monohydrate of a sodium leucite. Its
formula demands the composition shown in I. In II is given the analy-
sis of a specimen from Table Mt., Colo. Many analcites contain small
quantities of CaO. In III is the analysis of calciferous crystals from the
Highwoods Mts., Mont.

Si02 AI2O3 Fe203 CaO MgO Na20 K20 H20 Total

I. 54.54 23.20 14 .09 .... 8.17 100.00

II. 55.81 22.43 13 .47 .... 8.37 100.08

III. 54.90 23.30 tr. 1.90 .70 10.40 1.60 7.50 100.30

Analcite forms isometric crystals that are usually icositetrahedrons,
202(211) (Fig. 257). More rarely they are modified cubes (Fig. 258),

HYDRATED SILICATES 459

containing ooOoo(ioo), ooO(no), 2000(210), 202(211), O(in) and
occasionally 10(332) and icositetrahedra with large parameters. Some
crystals show double refraction which is regarded as due to strain.

The mineral has a glassy luster. It is transparent or translucent,
colorless or white, gray, yellowish, greenish or reddish. Its streak is
white. It possesses a very imperfect cleavage parallel to 00 O 00 (100)
and an uneven fracture. Its hardness is 5-5.5 and density 2.2-2.3.
For yellow light, n= 1.487.

Before the blowpipe analcite fuses to a colorless glass, imparting a
yellow color to the flame. In the closed tube it yields water, but retains
its form and luster. It gelatinizes with HC1. Its powder reacts alka-
line.

Analcite resembles leucite and light-colored transparent garnets.
It is distinguished from garnets by its less hardness and from leucite

Fig. 257. Fig. 258.

Fig. 257. — Analcite Crystal with 2O2, 211 («).
Fig. 258. — Analcite Crystal with ooO<*> , 100 (a) and 2O2, 211 (w).

by the presence of water and by its easy fusibility. It differs from
chabazite by fusing without intumescence to a colorless glass.

Syntheses. — Crystals of analcite have been made by heating sodium
silicate, or a hydrate, with an aluminous glass to i8o°-i9o° in a closed
tube, and by heating in a similar manner a mixture of sodium silicate
and aluminate with limewater. Crystals have also been obtained by
heating to 500 ° a mixture of finely powdered laumontite with an aqueous
solution of sodium silicate.

Occurrence. — Analcite occurs as a primary constituent of certain
alkaline volcanic rocks in the Little Belt and the Highwood Mts.,
Mont., and elsewhere. It occurs also filling cavities in volcanic lavas
and as a secondary mineral, replacing nepheline, leucite and sodalite in
both volcanic and plutonic rocks.

Localities. — It is found in the vacuoles of basalts on the Cyclopean
Islands, near Catonia, Sicily; in the Kaiser stuhl, Baden; in the Seisser

460 DESCRIPTIVE MINERALOGY

Alps, Tyrol; at Dumbarton, Old Kilpatrick and elsewhere in Scotland;
at Bergen Hill, N. J.; Table Mt. near Golden, Colo.; on Keweenaw Pt.,
Lake Superior; in southwestern Nova Scotia, and elsewhere. It occurs
in veins in southern Norway; in druses near Richmond, Victoria, and
as an original component of igneous rocks in the High wood Mts., and
the Little Belts Mts., in Montana; near Cripple Creek, Colo.; near
Sydney, N. S. Wales; at Winchester, Mass., and elsewhere.

CHAPTER XXI

THE TITANATES AND TITANO-SILICATES

. The titanates are salts of titanium acids that are in all respects anal-
ogous to silicic acids. Thus, the normal titanate is a salt of the acid
H4Ti(>4 and the metatitanate a salt of metatitanic acid (H4Ti04— H2O
= H2TiOa). The mineral, perovskite, for instance, is a calcium metati-
tanate (CaTiQa) and UmeniU a ferrous metatitanate. Dititanates are
salts of H2Ti205(2H4Ti04~3H20=H2Ti206). There are no dititanates
known among minerals, but there is one mineral which is fairly common
that may be regarded as a dititanate in which one of the Ti atoms has
been replaced by Si, giving rise to a titano-silicate. This mineral is
sphcne, which is the calcium salt CaSiTiOs.

Perovskite (CaTi03)

Perovskite occurs almost exclusively in small crystals with a cubic
habit. Although apparently complexly modified cubes, they are in fact
complicated intergrowths of orthorhombic lamellae, with a I b : c=
1:1: .7071 (approximately).

The formula CaTi03 is equivalent to 41 .1 per cent CaO and 58.9
per cent Ti02, but the mineral usually contains also some Fe.

The cleavage of perovskite is cubic. Its fracture is uneven to con-
choidal. It is brittle, has a hardness of 5.5 and density of 4.02. Its
color varies from pale yellow through orange-yellow to reddish brown
and grayish black. Its streak is colorless and luster adamantine. The
mineral is transparent to opaque. Its refractive indices for yellow light
are about 2.38.

Perovskite is infusible in the blowpipe flame. The salt of phos-
phorus bead in the oxidizing flame is green while hot, colorless when cold.
In the reducing flame it is green-gray when hot, and violet blue when
cold. The mineral is completely soluble in hot H2SO4.

It alters to ilmenite and magnetite, and possibly anatase.

Syntheses. — Crystals have been formed by heating a mixture of
Ti02, CaC03 and an alkaline carbonate until all the alkali volatilized,
and by fusion of Ti02, CaC03 and CaCl2.

461

462 DESCRIPTIVE MINERALOGY

Occurrence and Localities. — Microscopic crystals of perovskite occur
in some igneous rocks, where they are probably separated from the
magma producing the rock. It also occurs in chlorite schist and lime-
stone as small crystals embedded in the rocks, and also implanted on the
walls of cracks at the Achmaton Mine in the District Slatonst, in the
Urals; near the Findelen glacier near Zermatt, Switzerland; in Val
Malenco, Italy; at Magnet Cove, Arkansas, in coarse-grained, nepheline
syenite; and associated with magnetite in great quantity at Catalao,
Goyaz, Brazil.

Ilmenite (FeTi03)

Hmenite or menaccanite, is one of a series of isomorphous compounds
consisting of the titanates of Mg, Mn and Fe, all of which crystallize in
the rhombohedral tetartohedral division of the hexagonal system (trig-
onal rhombohedral class). The crystallographic constants of ilmenite
are, however, so nearly like those of the mineral hematite, which is
ditrigonal skalenohedral, that the two compounds often crystallize
together, and consequently many specimens of ilmenite when analyzed
show notable quantities of Fe203. These are regarded as solid solu-
tions of Fe203 in an isomorphous mixture of FeTi(>3 and MgTiC>3. The
axial ratios of the two minerals are:

Emenite a : c=i : 1.385.
Hematite a : c=i : 1.365.

The composition corresponding to the above formula is Ti = 3i.6
per cent, Fe" = 36.8 per cent and 0 = 31.6 per cent, but the mineral
nearly always contains some Mg and ferric iron (Fe2C>3). An analysis of
ilmenite separated from a peridotite in Kentucky gave:

Ti02

FeO

MgO

Fe203

AI2O3

Si02

Other

Total

49 -32

27.81

8.68

9i3

2.84

.76

1-56

100.10

Ilmenite is rarely found in crystals. It is usually in large homo-
geneous masses, in granular aggregates, in thin plates and in sand grains.
The crystals have a tabular or rhombohedral habit and resemble very
closely those of hematite. The predominant forms are R(ioTi), oR(oooi)

P2., _

K4223), — 2R(o22i) and — -JR(oii2) (Fig. 259). The angle ion A
2

Tioi = 94° 29'. Simple crystals, bounded by oR(oooi), R(ioTi) and

— R(oiTi) are also common.

The mineral is black and opaque, and its streak is black to brownish

TITANATES AND TITANO-SILICATES 463

red. Its cleavage is parallel to oR(oooi), and its fracture conchoidal.
It has a submetallic luster, a hardness of 5 to 6, and a specific gravity
of 4.5-5. It is slightly magnetic, and is a good conductor of electricity.

Before the blowpipe ilmenite is nearly infusible. It gives the reac-
tions for iron with beads. When the micro-
cosmic salt beady which is brownish red in
the reducing flame, is treated with tin on
charcoal it changes to a violet-red color.
The pulverized mineral is slowly dissolved in
hot HC1 to a yellow solution. If this is filtered
and boiled with the addition of tin it changes pic. 259.— Ilmenite Crystal
to blue, indicating titanium. with R, 10T1 (r); oP,

Ilmenite can be distinguished from hemor OOOI , * V^ — ,.
tile by its streak, from magnetite by its _ ' 2J

lack of strong magnetism and from most '

other heavy black minerals by its reaction for titanium.

Upon weathering ilmenite alters to sphene and limonite.

Synthesis. — Crystals have been obtained by melting together THD2
and FeCb.

Occurrence. — The mineral occurs as a constituent of many igneous
rocks, and of the crystalline schists produced from them by meta-
morphism, especially of gabbros and diorites and their derived schists,
where it has crystallized from the magma forming the original rocks.
It occurs also in veins cutting these rocks and also as great masses near
their contacts with other rocks. In a few places it forms the main com-
ponent of sand.

Localities. — The mineral is found at many places where gabbros
and diorites abound. Its principal occurrences in Europe are in the
Ilmen Mountains, Ural; at Menaccan, Cornwall, England, and at
Kragero, Arendal and Snarum in Norway. In North America it is
found as crystals in pegmatites at several points in Orange County,
New York, at Litchfield, Connecticut; at Bay St. Paul, Quebec; and
in large masses in the Adirondacks, New York, and in northeastern
Minnesota.

Uses. — Because of its abundance, many attempts have been made to
utilize ilmenite as an ore of iron, but on account of the large quantity of
titanium in it, no satisfactory means of smelting it on a commercial
scale have been successful, and consequently the mineral has little value
at present. With improvements in the processes of electric smelting,
however, it may before long become an economically important source
of iron.

464 DESCRIPTIVE MINERALOGY

Titanite (CaSiTi05)

Titanite, or sphene, usually occurs as crystals, but in some places
in granular and compact masses. Although the formula for the mineral
is simple, as given above, requiring as it does 28.6 per cent CaO, 40.8
per cent TiC>2, and 30.6 per cent SiC>2, many specimens show also the
presence of Fe203, AI2O3, and in many cases considerable quantities of

Y2O3.

Analyses of three specimens from different localities yielded:

Si02 Ti02 CaO Fe203 AI2O3 Y203 MnO Total

Zillerthal . . . 32.29 41.58 26.61 1.07 ioi-55

Arendal.... 30.00 29.01 18.92 6.35 6.09 9.62 * 100.98

St. Marcel. . 30 ..40 42.00 24.30 tr 3.80 100.50

* Besides .94% MgO. .60% K20 and .54% loss.

The crystals are monoclinic (prismatic class), with alb: ^=.7547
: 1 : .8543 and 0=119° 43'- Their habit varies widely. Some are

Fir.. 260. Fig. 261. Fig. 262.

Fig. 260. — Titanite Crystal with ooP55, 100 (a); — |P56, 102 (*); oP, 001 (c)

and JP, T12 (/).

Fig. 261. — Titanite Crystal with a, x and c as in Fig. 260. Also — P, 11 1 (n) and

00 P, no (;«)•
Fig. 262. — Titanite Crystal with w, n and c as in Fig. 261. Also +P, In (f).

double-wedge-like, others are envelope-shaped, others prismatic, and
others tabular. On the wedge-shaped crystals £P(Ti 2) and — \? 00 (102)
predominate (Fig. 260). On the envelope-shaped ones 00 P 06 (100),
— P(iii) and oP(ooi) are most prominent (Fig. 261), and on the tabular
ones oP(ooi) is the largest face (Fig. 262). The prismatic crystals are
often more complicated. In all about 75 forms have been identified.
Both contact and penetration twins are common, with 00 P 56 (100)

TITANATES AND TITANO-SILICATES 465

the twinning plane. The cleavage is distinct parallel to oo P(no), and
there is often, in addition, a very perfect parting parallel to — 2P(22i),
which is due to polysynthetic twinning. The planes oo P » (ioo) and
.JP(Ti2) are often striated parallel to their intersection with °°P(iio).
The angle iioAiTo=66° 29'.

The mineral is brown, gray, yellow, green, black, rose or white. Its
streak is white or pink, its luster is vitreous or resinous and it is trans-
parent, translucent or opaque. Its hardness is 5-5.5 and gravity 3.5.
It is pleochroic in yellow, pinkish and nearly colorless tints. Its refrac-
tive indices vary widely with the composition. In a specimen from St.
Got hard, the indices for yellow light are: a= 1.874, 0= 1.8940, 7 = 2.0093.
The principal recognized varieties are:

Titanite, opaque or translucent with black or brown colors.

Spheney translucent, light-colored, brown or yellow.

Titanomorphite, white, granular alteration product of rutile or
ilmenite.

Greenovile, rose-red, translucent variety containing manganese.

When heated before the blowpipe the mineral fuses to a dark glass,
its fusing point being i2io°-i23o°. With beads some varieties exhibit
the reaction for manganese and all show the colors characteristic of
titanium. All varieties are sufficiently soluble in HC1 to give the violet-
colored solution when treated with tin, and all are completely decom-
posed by H2SO4.

Sphene is distinguished from staurolite and farnet by its crystalliza-
tion and softness; from sp'alerite by its greater hardness; from other
similarly colored minerals by the reaction for titanium.

Upon decomposition it yields calcite, magnetite, rutile and other
oxides of titanium and ilmenite.

Synthesis. — Crystals of titanite have been made by fusing Si02 and
Ti02 with an excess of CaCb.

Occurrence. — Sphene is a widely spread constituent of igneous rocks
where it has probably formed directly by crystallization from a molten
magma, and is in many schists and limestones that have been meta-
morphosed. In the latter cases it is of metasomatic origin. It occurs
also as implanted crystals on the walls of cracks and cavities in
acid granular rocks, under which conditions it is pneumatolytic.
Further, it is a common decomposition product of ilmenite and
rutile.

Localities. — The mineral occurs so widely spread that even its prin-
cipal localities are too numerous to mention here. Particularly fine
crystals are found at Ala and St. Marcel, in Piedmont; at various points

466 DESCRIPTIVE MINERALOGY

in the Zillerthal, Tyrol; at Zoptau, in Moravia; near Tavistock and
Tremadoc, in Wales; at Sandford, Maine; at various points in Lewis,
St. Lawrence and Orange Counties, New York, principally in lime-
stones; at Franklin Furnace, New Jersey, also in limestone; in Iredell,
Buncombe and Alexander Counties, North Carolina, and near Egan-
ville, Renfrew County, Ontario.

PART III
DETERMINATIVE MINERALOGY

CHAPTER XXII

GENERAL PRINCIPLES OF BLOWPIPE ANALYSIS

Determinative Mineralogy. — Minerals are identified by means of
their chemical and physical properties. A mineral specimen may be
analyzed by the ordinary methods of chemistry. This procedure will
reveal its empirical composition but it will not distinguish between
dimorphs. For this other means must be relied upon, and of these the
most convenient are those based upon physical properties.

Since chemical analysis in the ordinary way is a long and tedious
process, requiring bulky reagents and laboratory apparatus, it is not
applicable in the field or when rapid determinations are desired. Conse-
quently, chemical analyses are employed only when other methods of
determining a mineral are inadequate or when the accurate composition
of the specimen is desired.

The usual methods of determining minerals employed by mineral-
ogists are based on their physical properties and upon blowpipe tests;
the latter being utilized to differentiate substances with nearly similar
physical properties.

Blowpipe Analysis. — By means of the high temperatures that may
be secured with the aid of the blowpipe, many chemical reactions may
be made to take place which are impossible at ordinary temperatures.
The reagents used are few and generally in the solid form, and conse-
quently may be made to occupy little space. Many of the reactions are
delicate and characteristic of the different elements and most of them
may be made rapidly and with small quantities of material. The
results are qualitative only, but when combined with the study of the
physical properties of the substance tested, they are usually sufficiently
definite to enable one to recognize its nature. In a few instances liquid

467

468 DETERMINATIVE MINERALOGY

reagents must be employed to give decisive results, but they are few and
easily obtained.

The Blowpipe. — The blowpipe (Fig. 26.1), in its simplest form, is a
tube with a small outlet through which a current of air may be directed
through a flame upon a small particle of substance. A practical instru-

Fio. 363.— Simple Blowpipes.

ment consists of a moulhpiece, a tube, an air-chamber to catch moisture,
a side tube and a tip pierced by a small hole. The tip is placed in the
flame of a Bunsen burner, an alcohol lamp or some other source of flame,
and a current of air is blown through it by placing the mouthpiece to the
lips, breathing full, and allowing the contraction of the cheeks to force

the air from the mouth. Other

forms of blowpipe are advocated
for special purposes. Frequently
the side tube is curved in such a
way that the air passing through
it is heated before it issues from
the tip and a hotter flame is pro-
duced than is possible with the
simpler instrument.

Since it is often desirable to
F,c. ,6,,-BelI™, In, U» with Blo„- ^^ "" ha"d' ''" "> ™'»iP»l»<«

pip.. It intended lo be miked by the ™y. lhe blowpipe is some-
hand Ihe apparatus is lighter arid of a
little different shape.

times fastened to a stand and a
blower is attached to it. This
not only releases the hand that
is employed in holding the simpler blowpipe but it also relieves the
cheeks from the somewhat tiresome process of blowing. The blower
employed is usually a rubber bag {Fig. 264), protected by a net and
provided with a suitable valve to prevent a return current when the
pressure that forces the air from the reservoir is removed. The

BLOWPIPE ANALYSIS 469

pressure required to force the air from the reservoir is applied by the
foot

Source of Heat. — The best source of flame for general use with the
blowpipe is the Bunsen burner supplied by ordinary gas, and furnished
with a tip which is flattened at the upper end and cut off obliquely.
The blowpipe is supported on the upper end of this tip and pointed
downward parallel with it. Thus, the flame is blown down upon the
assay.

Since, however, illuminating gas often contains noticeable traces of
sulphur, for the detection of this substance it is often advisable to sub-
stitute an alcohol lamp for the gas burner. With the alcohol should be
mixed a little turpentine in the proportion of one part of the latter to
twelve of th? former to increase the reducing power of the flame.

Supports. — The principal supports used to hold the material under
investigation — the assay — are charcoal, platinum, and glass. Sheets of
aluminium, plaster slabs and unglazed porcelain are also sometimes em-
ployed, but for most purposes the first three are entirely adequate.

Charcoal. — Charcoal is used in reduction tests and in the study of
sublimates. It should have a flat surface and should be well burned.

Platinum. — Platinum is used principally in the form of wire and foil.
The wire should be of about the thickness of coarse horsehair (.4 mm.),
and should be fused into a 3-inch long glass tube to serve as a handle.
It is employed mainly in the production of colored glasses or beads.
The foil should be thin. When about to be used, it should be bent into
a shallow cup in which mixtures may be fused.

Glass. — Glass is used in the form of tubes. These should be of a
hard glass about 90 mm. long and 6 mm. inside diameter. When closed
at one end, they serve to hold substances which are to be heated to a
high temperature in the study of their volatile constituents. Tubes
open at both ends are employed to study the effect of roasting the assay
in a current of air.

Other Apparatus. — Other pieces of apparatus desirable for satis-
factory blowpipe work are: A magnet, a magnifier, a pair of forceps, a
small hammer, an anvil, a pair of cutting pincers, a piece of blue glass or
a screen composed of strips of celluloid colored different shades of blue,
or a hollow glass prism filled with indigo solution.

Reagents. — Since blowpipe tests are made on minute quantities of
material, it is necessary that all reagents used be as pure as possible.
Those most frequently employed are: Borax, Na2B407- 10H2O; microcos-
mic saltt or salt of phosphorus, NH4NaHP04*4H20; fused sodium car-
bonate, Na2C03; acid potassium sulphate, HKSO4; niter. KNO3; cobalt

470 DETERMINATIVE MINERALOGY

nitrate, Co(NOa)2 ■ 6H2O, in solution; copper oxide, CuO; magnesium
ribbon, Mg; granulated zinc, Zn; sulphuric acid, H2SO4; hydrochloric
acid, HC1, and blue litmus and turmeric papers. Other reagents are
employed in special tests, but those mentioned above are used generally.
The Blowpipe Flame. — The blowpipe flame is used not only for
producing a high temperature, but also to produce oxidizing and reduc-
ing effects. The oxidizing flame aids in adding oxygen to the substance
heated and the reducing flame abstracts it.

A luminous flame, such as is produced by a candle or a Bunsen burner,
with the airholes at the foot of the tube closed, consists of (c) an inner,
non-luminous cone (Fig. 265) containing unignited
gas, (6) a luminous envelope surrounding this, in
which there is partial combustion of the gas passing
out from the nonluminous cone, and an outer purplish
mantle.

Because protected from the air by the outer
mantle, the gas in the luminous inner cone is not
entirely consumed. The available oxygen combines
with the easily combustible hydrogen, while the carbon
of the gas is separated in extremely fine particles.
These are at a high temperature and are, therefore,
incandescent. In this condition, carbon is an active

_ reducing agent, combining with oxygen readily, ab-

FlC. 165. — Candle ._...' r .,. , , ■

Flame, Showing stracllng lt for tlus purpose from any oxygen-beanng
Three Mantles, compound with which it is brought m contact. Con-
sequently this portion of the flame exerts a reducing
action upon anything within its sphere. In the outer mantle, there
is an abundance of oxygen. This combines with the carbon par-
ticles as they pass out from the luminous envelope, forming, at first,
carbon monoxide, CO. This unites with more oxygen forming carbon
dioxide, CO2, and giving a blue flame. Since the temperature in this
portion of the flame is very high and there is an abundance of oxygen
present, substances subjected to its action are oxidized.

The use of the blowpipe accentuates the effects of the different por-
tions of the flame and serves to direct it upon the particle to be tested.
To produce the reducing flame (R.F.), the blowpipe jet is placed at the
edge of the burner flame near its base, and a gentle current of air is
blown (Fig. 266). This deflects the flame without mixing too much
oxygen with it — and it remains luminous. Its most energetic part is
near the end of the luminous cone (a).

The oxidizing flame (O.F.) is produced by passing the tip of the blow-

BLOWPIPE ANALYSIS 471

pipe into the flame a short distance (Fig. 367) and blowing strongly, but
steadily. A sharp-pointed, nonluminous flame results, with cm toner
blue cone. The most effective oxidizing area is just beyond the Up of
the inner blue cone.

Before attempting to use the blowpipe for producing oxidizing and
reducing effects, the two flames should be practiced with until they can
be manipulated with certainty. The reducing flame is the most difficult
to use successfully. It must be maintained unchanged for some time
and the assay must be completely enveloped in it to secure satisfactory
results. Otherwise, oxidation may ensue. In order to test one's ability

Fie. 266.— Reducing Flame.

Fm. 267.— Oxidizing Flame.

to reduce with the blowpipe flame, a little borax should be melted in a
small loop made at the end of a platinum wire. It will form a colorless
glass. Into this should be introduced a tiny grain of some manganese
compound. If the borax with the added manganese is heated in the
oxidizing flame, an amethyst -colored glass will result. This, if heated
in the reducing flame, will again become colorless, but the color will
return if the assay is touched by the oxidizing flame. When the color
can be made to disappear and reappear at will, the proper amount of
skill for the manipulation of the flames will have been attained.

Use of the Closed Tube.— The closed glass tube is used to discover
whether a substance contains water or not, to detect its volatile con-

472 DETERMINATIVE MINERALOGY

stituents, and to discover the nature of its decomposition products.
It is also employed in the observation of certain other characteristic
changes in a substance produced by heating it to a high temperature.

The material to be tested is powdered and slid into the tube with the
help of a little, narrow paper trough, which is long enough to reach nearly
to its bottom. The tube is then tapped to settle the material and the
end containing the assay is heated, at first gently, later more vigorously,
even to redness, either in the burner flame or in the flame produced by
the blowpipe.

Water is indicated by the condensation of little drops on the upper,
cooler portion of the tube. If the water, when tested with litmus paper,
reacts acid, a volatile acid (H2SO4, HC1, HNO3 or HF) is indicated. If
it reacts alkaline, ammonia has been evolved.

Gases. — The character of the gases evolved is best recognized by
their color and odor.

(a) Hydrogen sulphide (H*S) is recognized by its odor. It indicates a
sulphide containing water.

(b) Nitrogen peroxide (N204) is recognized by its reddish brown fumes and
its characteristic odor. It indicates a nitrate or a nitrite. In the case of
HNO3, the reaction is 2HN03=0+H80+ N204.

Sublimates or coatings may be deposited in the cooler portion of
the tube.

(a) If while, they may indicate ammonia salts, antimony trioxide, arsenic
trioxide or tellurium dioxide.

(b) If gray or black, they indicate arsenic, mercury or tellurium.

(c) If black, while hot, and reddish brown, when cold, antimony sulphide;
and if reddish brown, while hot, and reddish yellow, when cold, arsenic sulphide.

Changes of Color are very characteristic for certain substances, the
following being of greatest importance:

(a) From white to yellow and to white again on cooling: zinc oxide.

(b) From white to brownish red and back to yellow: lead oxide.

(d) From red to black and red again when cold : mercuric and ferric oxides.
The mercury oxide is volatile.

Use of the Open Tube. — The open tube is used when it is desired to
treat the assay with a current of hot oxygen. It is charged in the same
manner as the closed tube, the assay being placed about 12 mm. from

BLOWPIPE ANALYSIS 473

the end. The tube is then held in the forceps over the flame, care being
taken to incline it slightly for the purpose of producing an upward cur-
rent of hot air. By this means, the following substances are easily
detected:

Suipkur is detected by the choking odor of SO,.

Arsenic yields a while volatile sublimate, which disappears upon heating.

Antimony gives white fumes which may partly condense on the cooler
portion of the tube as a while sublimate and partly escape from its end. The
sublimate is only slightly volatile.

Mercury yields globules of mercury.

Tellurium yields a white sublimate, which, when heated, fuses to colorless

Selenium gives a sublimate which is white or steel-gray near the assay
(SeOi) and red at a greater distance (SeO, and Se). The odor of the volatile
metal is exceedingly disagreeable. If the tube is allowed to discharge through
the flame, it will produce a blue color.

The Use of the Charcoal. — A shallow depression is made near one
end of a piece of charcoal, the powdered assay placed in this, and the

Fie. 268. — Proper position of charcoal.

blowpipe flame played upon it, while the charcoal is held in a tilted
position by the left hand (Fig. 268). If the assay decrepitates when
heated, it should be moistened with a drop of water. The principal
phenomena to be noted are: Volatilization, fusibility, decrepitation,
deflagration, odor, reduction and the production of sublimates.

Volatilization. — The substance vaporizes and disappears.

Fusibility.— The substance melts entirely, or partially, in the different
parts of the flame, some substances fusing easily and others only with great
difficulty.

Decrepitation. — The substance flies to pieces when heat is applied, indicat-
ing decomposition or the presence of water, or included gases.

474 DETERMINATIVE MINERALOGY

Deflagration. — The substance suddenly burns with little explosions charac-
teristic of nitrates.

Reduction and Sublimation. — When heated on charcoal with the R.F.,
some substances may easily be reduced to the metallic state, others are reduced
with difficulty. Thus, 2PbO+C==Pbi+COj. Reduction takes place most
readily if the assay is powdered and mixed with about four times its volume of
dry sodium carbonate (Na»CO»). Thus:

2PbS+2Na,CO,+C= 2Na4S+Pb,+3CO,.

In cases of great difficulty, a little potassium cyanide L (KCN) or borax
(NasB407 • 10H2O) added to the mixture will frequently hasten the result.
In any case, the heat must be applied until nearly all the assay sinks into the
charcoal.

When sufficiently heated, some substances yield a globule of metal, others
are completely volatilized, others yield fumes, produced by the oxidation of
portions of the assay, while yet others aie partly reduced to a globule of metal
and partly volatilized. Thus, during the reduction of PbS, some of the lead
may be oxidized according to the reaction:

PbS+Na,CO,=Na2S+PbO+COa,

and a portion of the oxide may settle on the coal. When fumes are pro-
duced, they are deposited upon the coolei portions of the charcoal in the form
of sublimates which possess characteristic properties.

Gold, silver, and copper compounds yield globules of metal without
sublimates. The metals are separated for examination by cutting
out the charcoal beneath the assay, and crushing the mass with
water in a small mortar. Upon pouring off the water, the metal
remains as spangles, grains or powder. The silver is recognized by
its color and by the fact that its solution in nitric acid yields a
white precipitate upon the addition of a drop or two of hydro-
chloric acid. Copper and gold have nearly the same color, but
copper dissolves in nitric acid while gold is insoluble. Addition
of an excess of ammonia to the solution of copper gives a char-
acteristic, deep blue color.

Iron, nickel, and cobalt give gray infusible powders which are mag-
netic, but yield no sublimates.

Molybdenum, tungsten, and some of the rarer metals give gray powders
that are nonmagnetic and no sublimates.

Antimony yields copious white fumes, forming a volatile white sub-
limate (Sbj03), which becomes black when touched with the R.F.

1 Potassium cyanide must always be used with care, as it is a deadly poison, even
in minute quantities.

BLOWPIPE ANALYSIS 475

When touched by the tip of the O.F., it will volatilize and color
the flame yellowish green. The metallic bead, when dropped
upon a sheet of glazed paper, breaks into a number of smaller
ones.

Arsenic volatilizes completely and consequently yields no globule of
metal. It gives abundant white fumes which form a white subli-
mate and have a garlic odor. The flame at the same time is
colored blue.

Bismuth yields a reddish white, brittle globule and an orange-yellow
sublimate which becomes lemon-yellow when cold.

Cadmium gives brown fumes in the O.F. and yields a reddish brown
sublimate, while the flame is colored dark green.

Lead yields a gray malleable bead, and incrusts the charcoal with
a lemon-yellow sublimate near the assay. The flame at the same
time is colored blue. The yellow incrustation is composed of lead
oxide.

Molybdenum gives a crystalline incrustation which is yellow when
hot and white when cold. When touched by the O.F. it becomes
dark blue, and when heated for a longer time dark copper-red.
The blue incrustation may be molybdenum molybdate (M0M0O4)
and the red one, molybdenum dioxide (MoOj).

Selenium yields brown fumes, but the sublimate which is near the
assay is gray. When heated with the reducing flame, it disappears
and the characteristic bad odor is evolved. The flame becomes
blue.

Tellurium coats the charcoal with a white sublimate bordered by
dark yellow. The coating disappears in the R.F., which acquires
a green color.

Tin gives a white globule which is malleable and a yellowish white
coating, turning white upon cooling. When moistened with a
drop of Co(N03)i solution and heated in the O.F., its color
changes to blue-green.

Zinc burns in the O.F. with a bluish white color and evolves thick
white fumes which condense as a yellowish sublimate. This be-
comes white on cooling, and, when moistened with a drop of
cobalt nitrate and again heated, it turns grass-green (compare
tin).

Other metals also give characteristic reactions on charcoal, but the
above are the most important.

476

DETERMINATIVE MINERALOGY

Use of the Beads. — The beads are used for the detection of metals
that produce characteristic, colored compounds when fused with borax
or microcosmic salt or some other reagent. A piece of platinum wire
fused into a glass rod serves as a support. The end of the wire is bent
into a little loop. This is moistened and plunged into powdered borax,
microcosmic salt or other reagent and then heated carefully until the
adhering material is fused to a clear glass. New material is added by
dipping the loop again and again into the powdered salt and heating
until the globules of glass are large enough to fill it completely. A tiny
portion of the material to be tested is taken up by heating the bead and
pressing it while still soft upon a bit of the powdered assay, which has
been placed in a clean watch-glass. The bead containing the substance
is then heated with the O.F. and afterward with the R.F., and the phe-
nomena resulting are carefully observed. If the reduction is difficult, a
little stannous oxide or chloride will hasten it. If the bead becomes
opaque because saturated with the assay, a portion is jerked off while it
is hot and it is built up again by the addition of more of the reagent.

In some cases, compounds other than the oxides do not yield the
characteristic beads of the metallic oxides. Therefore, it is safer in all
cases when testing by the bead reaction, to first roast the substance by
gently heating on charcoal with the O.F. to drive off its volatile constit-
uents.

The colors of the most characteristic beads of metallic oxides are
tabulated below.

COLORS OF BORAX BEADS

Oxidizing Flame.

Rkducing Flame.

Hot.

Cold.

Hot.

■

Cold.

Yellow or red

Grass-green

Chromium

Green

Emerald-green

Blue

Cobalt

Blue

Green

Blue

Copper

Colorless

Reddish brown,
opaque

Colorless

Didymium

Rose

Yellow or red

Colorless or
yellow

Iron

Bottle-green

Pale bottle-green

Violet

Reddish violet

Manganese

Colorless

Yellow or red

Colorless to
opalescent
Reddish brown

Molybdenum

Brown

Opaque brown

Violet

Nickel

Gray

Colorless

Columbium

Colorless or gray

Colorless or yel-

Colorless

Titanium

Yellow or brown

low

Colorless or yel-

Colorless

Tungsten

Yellow

Yellow brown

low

Yellow or red

Colorless or yel-
low

Uranium

Pale green

Pale green to
nearly colorless

Yellow

Green-yellow, or

Vanadium

Brownish green

Emerald-green

nearly colorless

BLOWPIPE ANALYSIS

477

COLORS OF MICROCOSMIC SALT BEADS

OxiDtzim

: Flame.

Reducing Flame.

Hot.

Cold.

Hot.

Cold.

Reddish green

Emerald-green

Chromium

Reddish green

Emerald-green

Blue

Cobalt

Blue

Green

Blue

Copper

Dirty green

Green, or opaque

red
Blue

Colorless

Dtdymiuxn

Colorless

Yellow or red

Colorless, yellow
or brown

Iron

Yellow or red

Nearly colorless

Violet

Manganese

Colorless

Green

Paint yellowish

Molybdenum

Dirty green

Green

Reddish to brown

(jreen
Yellowish to red-
dish

Nickel

Reddish

Yellowish to red-
dish vellow

Colorless

Columbium

Blue or brown

Skeleton

Silica

Skeleton

Colorless

Titanium

Yellow

Violet

Colorless

Tungsten

Dirty green-blue

Blue

Yellow

Yellow-green
to colorless

Uranium

Dirty green

Bright green

Dark yellow

Light yellow to
colorless

Vanadium

Brownish green

Emerald-green

Cobalt is the only metal which produces the same colored bead under
all conditions. This is a beautiful blue. Other oxides give blue beads
under some one or more conditions, but under other conditions their
beads have other colors.

The cold bead of chromium oxide is always green and the oxidized
bead of manganese is always violet.

Flame Coloration. — Many substances impart a distinct color to the
nonluminous flame of the burner or the blowpipe. Frequently, these
colors are best seen after the substance in powdered form has been
moistened with hydrochloric acid, as the chlorides are usually more
volatile than other compounds. In the case of silicates, it is often ad-
visable to mix the powdered assay with an equal volume of powdered
gypsum. In testing for flame coloration a very small particle of the
substance, or its moistened powder, or of the mixture of the substance
and gypsum is held in the flame by the aid of the platinum loop which
has been cleaned by dipping into HC1, and heated repeatedly until it
no longer colors the flame.

When several different flame-coloring elements are present in the
assay, the stronger color may mask the fainter one, and, therefore, some
means must be made use of to shut off the brighter color, while allowing
the fainter one to persist. This is usually accomplished by viewing
the flame through some medium (a screen) that is transparent to the
faint rays and opaque to the brighter ones. In other cases, two flames
which are really different in color appear of nearly the same tint to the
unaided eye. In this case, the screen is again used to cut off certain

478 DETERMINATIVE MINERALOGY

rays that are common to the two colors, when the remaining rays may
be different enough to be distinguishable. The screens most frequently
used for this purpose are pieces of colored glass, which are held close to
the eye. Red glass absorbs all but red rays. Blue glass stops certain
red and green rays and all the yellow ones. Great difficulty is some-
times experienced in securing glass exhibiting pure colors, so that in
most cases it is more convenient to use transparent celluloid films that
have been manufactured expressly for the examination of colored flames.
These films are given. the tints that are most useful for the purpose
desired. Care must be taken in using them, however, since celluloid
is highly inflammable.

For more accurate work the spectroscope is often employed. The
use of this instrument depends upon the fact that each substance, when
in the form of gas, emits light composed of one or more rays of definite
wave lengths, and the spectroscope separates these so that each may
be identified. The most convenient instrument for blowpipe work is
the Browning direct vision pocket spectroscope, but since the con-
stituents of all common minerals can be recognized without the aid of
the spectroscope there is no need for further reference to it.

The most characteristic colors imparted to the blowpipe flame are:

Red by lithium, strontium, and calcium. Sodium salts obscure the
lithium flame and barium salts the strontium and calcium flames.

Yellow by sodium.

Green by most copper compounds, thallium, barium, antimony, phosphoric
acid, boric acid, molybdic acid, and nitric acid. The flame of phosphoric
acid is bluish green, the flames of boric acid and barium are yellow green, and
those of molybdic acid and antimony are very faint. The copper and thallium
flames are vivid greens. The nitric acid flame coloration is bronze green and
exists as a flash only.

Blue by copper chloride, copper bromide, selenium, arsenic and lead.
The arsenic flame is faint. The selenium and the copper chloride flames are
brilliant azure-blue.

Violet by potassium, caesium and rubidium. Sodium and lithium salts
obscure the reaction.

Detection of Certain Elements in the Presence of Others. — In

many cases, as has been stated, the color imparted to the flame by one
substance entirely obscures that given it by another when the two are
present in the same compound. Thus, the faint violet color of the
potassium flame is obscured by the strong yellow of sodium and the
brilliant red of lithium. When this is the case, the light is viewed
through the proper screens and the different rays in this manner are

BLOWPIPE ANALYSIS

479

differentiated. Since the flame tests afford the readiest means of detect-
ing the alkalies and alkaline earths, considerable attention has been
devoted to means of differentiating their flame colors. Among the
methods proposed for this purpose is that based upon the use of blue and
green glass screens.

Detection of the Alkalies and the Alkaline Earths. — The potas-
sium flame is reddish violet through blue glass, while the sodium flame is
invisible or is blue; hence, the potassium flame is detected in the pres-
ence of sodium by viewing the mixed flame through a blue screen.
Lithium is also detected in the presence of sodium with the aid of blue
glass, since the lithium flame is violet-red when viewed through a blue
screen. Since the flame colors of Li and K are so nearly alike when
viewed through a blue screen, they cannot easily be distinguished.
When viewed through a green screen, however, the Li flame is nearly
invisible, while that of K is bluish green. Through the green screen the
Na flame appears orange.

If search is to be made for the alkaline earths, the assay is repeatedly
moistened with sulphuric acid and placed in the hottest portion of the
flame. After the alkalies are driven off, the flame will become yellowish
green, if barium is present; through green glass it will appear bluish
green. The assay is then repeatedly moistened with pure hydrochloric
acid and again brought, while still moist, into the hottest portion of the
flame. A red coloration, appearing after the yellowish green barium
flame has disappeared, indicates calcium or strontium or both. Through
green glass the calcium flame appears green and the strontium flame
faint yellow for an instant. Through blue glass calcium gives a faint
greenish gray and strontium a purple or rose color.

The phenomena exhibited by the alkalies and alkaline earths may be
summarized as follows:

Flame Color

Through Blue Glass

Through Green Glass

Potassium

Violet

Reddish violet

Bluish green

Sodium

Yellow

Blue to invisible

Orange-yellow

Lithium

Carmine

Violet-red

Invisible

Barium

Yellow-green

Bluish green

Calcium

Yellow-red

Green-gray

Green

Strontium

Scarlet

Purple

Faint yellow

The detection of the alkalies in silicates is accomplished by fusing
the powdered assay on platinum wire with a little pure gypsum. If the
alkaline earths are sought for, the assay is fused with sodium carbonate
on platinum wire, or better, on a piece of platinum foil. The fused mass

480 DETERMINATIVE MINERALOGY

is then extracted with water and the residue treated with hydrochloric
acid. Silica will be precipitated, leaving in the solution a mixture
of sodium chloride and the chlorides of the alkaline earths. The solu-
tion is then tested in the flame with the aid of a clean platinum wire.

The Copper Test. — An almost certain test for copper and for chlorine
is afforded by the difference in the color imparted to the flame by copper
chloride and most other copper salts. Several substances besides copper
give green flames, but in the case of copper alone the color of the flame
is changed to sky blue by touching the assay with HC1, or a chloride.

Special Tests. — A few tests with special reagents are so charac-
teristic for certain elements that they are specific:

Tests with Na2C03. — (i) When a powdered substance containing S
is fused with four times its volume of dry Na2C03 and heated intensely
for some time on charcoal, the residue, when placed on a silver coin and
moistened with water or hydrochloric acid, will yield a black or brown
stain. This reaction is due to the production of Na2S(BaS04+Na2C03
+C2 = Na2S+BaC03+2(X)2), which is soluble. The solution containing
the sulphide reacts with the silver, producing insoluble Ag2S, which is
brown or black. Thus: Na2S+Ag2+H20+0=Ag2S+2NaOH. Sul-
phides and sulphates are distinguished by roasting the compound on
charcoal without Na2CC>3. Sulphides yield the sulphur-dioxide odor.

(2) Manganese and chromium compounds, fused with Na2CC>3
(especially when a little niter is added), yield colored masses — the
manganese compound a bright green mass (Na2MnC>4) and the chro-
mium compounds a bright yellow mass (Na2CrC>4). In the case of
the manganate, the reaction may be

Mn02+Na2C03+0= Na2Mn04+C02.

(3) Sodium carbonate may also be employed for decomposing silicates
and detecting silicic acids. If a silicate is fused with 4 or 5 times its
volume of Na2CC>3 on charcoal, it will break up, the silica combining
with soda to form sodium silicate, thus:

(ZnOH)2Si03+ 2Na2C03 = 2ZnO+Na4Si04+ 2CO2+H2O.

Upon treatment with acid, HiSiC^ is produced (NaiSiC>4+4HCl=4NaCl
+H4SiC>4). This appears as a gelatinous precipitate in the solution;
but upon evaporating to dryness, moistening with strong acid, and again
evaporating to dryness, the H4SiOi is broken down into 2H2O and SiC>2,
the latter of which is insoluble, and can be filtered off, leaving the bases
in the filtrate.

Tests with the Cobalt Solution.— Certain metallic oxides, when

BLOWPIPE ANALYSIS 481

moistened with a few drops of a solution of crystallized cobalt nitrate
dissolved in ten parts of water, and heated, yield distinctive colors that
may often serve as aids in their detection. The assay is powdered,
moistened with a drop of the cobalt solution, and placed on charcoal
and heated intensely. Compounds containing alumina yield a mass of a
blue color, without luster. A few other substances may also give blue
masses, but the materials are fused and, consequently, show a glassy
luster. Magnesium compounds give a pink color.

In testing for other substances, it is necessary first to obtain their
oxides. This is done by roasting on charcoal until a distinct subli-
mate is produced. This sublimate is moistened with a drop of the
solution and heated gently by the O.F. Under these conditions, the
white zinc sublimate (ZnO) changes to a bright yellowish green and tin
oxide (SnCfe) to a bluish green.

Tests with Acid Potassium Sulphate. — Hydrogen potassium sul-
phate (HKSO4) when fused with a powdered substance in a closed tube,
may cause the evolution of gases. For example:

2HKS04+CaF2 = K2S04+CaS04+2HF,

which in many cases may easily be recognized.

Nitrites and nitrates yield reddish brown fumes (N204) with the character-
istic odor of nitrogen peroxide.

Chlorates yield a yellowish green explosive gas (C102).

Iodides yield a violet gas, which colors blue a paper soaked in starch paste,
when a little Mn02 is added to the HKS04.

Bromides yield a reddish brown gas (Br), turning starch paste yellow,
when Mn02 is mixed with the HKS04.

Otic rides yield hydrochloric acid (HC1), recognized by its odor and the
voluminous white fumes it forms with ammonia.

Sulphides yield hydrogen sulphide (H2S) with its characteristic odor. This
gas blackens paper moistened with lead acetate.

Fluorides yield hydrofluoric acid (HF) gas, which has a pungent odor and
etches glass. The etching is due to the reaction between the SiO» of the glass
and the HF. Thus, Si02+4HF = SiF4+2H20. The SiF4 is volatile and is
driven up the tube, leaving tiny pits from which the Si02 was taken. This
reaction is best seen by heating the assay with four times its volume of the
reagent and then cleaning and drying the tube.

The reaction is more delicate if the finely powdered assay is mixed with
microcosmic salt and heated in an open tube. When the salt is heated, it
breaks up, yielding NaP03 (thus: HNa(NH4)P04.4H20=NaP03-fNH3-f5H20)
which reacts with the fluoride as follows:

CaF2+NaP02+H20= CaNaP04+ 2HF.

482 DETERMINATIVE MINERALOGY

By Reduction with Metallic Zinc and Hydrochloric Add certain

metallic salts yield colored solutions which are characteristic. The
substance to be tested (if not soluble in HC1) is powdered and mixed
thoroughly with sodium carbonate and niter, and the mass is slightly
moistened and placed in a little spiral at the end of a fine platinum wire.
After fusion, it is dissolved in a little water, a few drops of hydrochloric
acid are added and a strip of zinc or tin, or a few grains of the metal, are
then placed in the solution. The hydrogen, evolved by the contact of
the metal and the acid, reduces the oxides and the solution becomes
colored. The most important elements detectable by this method are:

Molybdenum, which gives a blue, then green, and finally a blackish brown
solution.

Tungsten, a blue, then brown or copper-red solution.

Vanadium, a blue, green or violet solution.

Columbium, a blue solution which loses its color on addition of water.

Chromium, a green solution.

Titanium, a violet solution.

In the case of titanium the reactions are:

Ti02+ 2Na,CO, = Na4Ti04+ 2CO,;
Na4Ti04+8HCl=TiCl4+4NaCl+4Hrf);
TiCl4+H=TiCl,+HCl.

The TiCla produces the violet solution.

Magnesium ribbon is generally employed as an aid in the detection
of phosphorus. The powdered assay is placed in the bottom of a closed
glass tube with a piece of magnesium ribbon about 5 mm. long, so that
the powder is in close contact with the metal. This is then heated in-
tensely until partial fusion ensues. The completion of the reaction is
known by the formation of a brown or black glass, which is the phos-
phide of magnesium. Upon crushing the tube and moistening its con-
tents with water the characteristic odor of phosphine is perceived (the
odor of wet phosphorus matches).

Hydrochloric acid furnishes the readiest test for carbonates. If the
powdered substance is heated gently with dilute acid in a test tube, a
brisk effervescence will result if it contains the carbonic acid radical.
Sometimes the effervescence can be detected by holding the mouth of
the test tube to the ear, even when the escape of gas cannot be seen.
The gas (CO2) is colorless, and when allowed to bubble through lime
water will cause turbidity.

CHAPTER XXIII

CHARACTERISTIC REACTIONS OF THE MORE IMPORTANT ELEMENTS

AND ACID RADICALS

Aluminium (p. 481). — Fusible minerals cannot be satisfactorily
tested for Al by the method using Co(N03)2, since cobalt imparts a
blue color to all glasses.

Since zinc silicates yield the same color reaction with Co(N(>3)2 as
do infusible aluminium compounds, the presence of aluminium in silicates
cannot be assured unless the absence of zinc is proven.

Antimony (pp. 472, 473, 474, 478). — In the presence of lead or bis-
muth, the assay is heated on charcoal with fused boric acid, which dis-
solves the lead and bismuth oxides, while the antimony oxide coats the
charcoal.

When antimony and lead are present in the same compound, the anti-
mony oxide forms a white incrustation surrounding a dark orange-yellow
incrustation of lead antimonate.

Arsenic (pp. 472, 473, 475, 478). — Arsenic in arsenates and arsen-
ites may usually be detected by heating the powdered assay with six
times its volume of a mixture of equal parts of Na2CC>3 and KCN (or
powdered charcoal) in a dry closed glass tube, when an arsenic mirror
will form on the cold part of the tube. This may be further tested by
breaking off the end of the tube and heating the mirror in the burner
flame. The escaping fumes will have the characteristic garlic odor. If
allowed to pass through the flame, they will tinge it violet.

If there is doubt as to whether a white sublimate on charcoal con-
tains arsenic, or if it is desired to test for arsenic in the presence of anti-
mony, a little of the coating which is farthest away from the assay may
be scraped from the surface of the charcoal and placed in a narrow glass
tube and heated. If arsenic oxide is present in the coating, the arsenic
mirror will form on the walls of the cooler part of the tube.

Barium (pp. 478, 479). — Before applying the flame test for barium,
silicates should first be fused with four parts of dry Na2C03 and charcoal
in a loop of platinum wire, crushed, placed in a test tube, treated with a

483

484 DETERMINATIVE MINERALOGY

few cc. of dilute HNO3 and evaporated to dryness. After cooling, warm
with a very little HC1, then add about 10 cc. of water and filter off the
insoluble silica. To the filtrate add a few drops of H2SO4, collect the
precipitate on a small filter, and test with the flame (see also under
Calcium).

Bismuth (pp. 472, 475). — A very characteristic test is the following:
The powdered substance is mixed with twice its volume of a mixture
composed of equal parts of KI and flowers of sulphur, and heated in the
R.F. on charcoal. If Bi is present, a brick-red iodide of bismuth will
form a coating at some little distance from the assay. This test serves
to distinguish between Pb and Bi, both of which yield yellow oxide
coatings when tested on charcoal.

Boron (p. 478). — To obtain the green flame in the case of most com-
pounds containing boron, it is usually sufficient to moisten the fine pow-
der with a drop of strong sulphuric acid and introduce a small quantity
into the flame on a platinum wire. The flame will be colored green,
but only for a moment. More resistant compounds, like the silicates,
must be fused with a flux composed of one part of powdered fluorspar
and four parts of KHSO4 before the green coloration can be obtained.
The HF generated decomposes the silicate and sets free the boron.

In the presence of copper compounds or phosphates, which also give
green flames, the finely powdered assay is moistened on platinum foil
with sulphuric acid. The excess of acid is then removed by heating, and
the powder mixed into a paste with glycerine and a little sodium car-
bonate. When heated in the flame, the sodium will mask the green color
due to the copper and phosphorus, but not that produced by boron.

If boron compounds are fused with Na2CC>3 and then treated with
dilute HC1, a drop of the resulting solution will cause turmeric paper to
turn reddish brown after being dried at ioo°. If moistened with am-
monia, the color changes to black.

Bromine (pp. 478, 481). — Solutions of bromides in water or HNO3
(after fusion with Na2CC>3 if insoluble otherwise) will yield with a drop
or two of silver nitrate solution a yellowish precipitate of AgBr, which is
soluble in ammonia. If this precipitate is mixed with Bi2S3 and heated
in a closed tube, a yellowish sublimate of BiBr3 will result. (Compare
Chlorine and Iodine.)

Cadmium (pp. 475, 478).— When present with Pb or Zn, it is often
difficult to recognize the cadmium coating on charcoal. In this case, the

CHARACTERISTIC REACTIONS, ETC. 485

coating may be scraped from the coal and heated very gently in the
closed tube. A yellow sublimate of cadmium oxide will form just
above the assay. On further heating, this will be masked by the zinc
and lead oxides.

Calcium (pp. 478, 479). — Calcium in silicates and other insoluble
compounds may be detected by the same method as that used for the
detection of barium. The precipitate of CaS04, however, is dissolved
when heated with a large volume of water.

Carbonates. — See p. 482.

Chlorine (pp. 480, 481). — Chloride solutions, when treated with
AgN03, yield a white precipitate of AgCl, soluble in ammonia. When
exposed to the light,- it darkens. If mixed with Bi2S3 and heated in a
closed tube, a white sublimate of BiCfo is formed. (Compare Bromine
and Iodine.)

Chromium (pp. 476, 477, 480, 482). — In the presence of large
quantities of Fe, Cu, etc., the powdered assay (if not a silicate) is mixed
with double its volume of equal parts of Na2C03 and KNO3 and fused
on a platinum spiral in the O.F., when an alkaline chromate will be
formed. This, dissolved in water and boiled with an excess of acetic
acid yields a solution which gives a yellow precipitate of PbCr04 with a
few drops of lead acetate.

Silicates containing small quantities of chromium and large quanti-
ties of copper and iron should first be fused on charcoal with a mixture
of one part of sodium carbonate and a half part of borax. The clear
glass thus produced is dissolved in hydrochloric acid and the solution
evaporated to dryness. This is then treated with water, filtered, and
the filtrate boiled with a few drops of nitric acid to oxidize the iron. By
the addition of ammonia, the chromic and other oxides are precipitated.
The precipitate is collected on a filter, washed, and treated as above, or
tested with the borax bead.

Cobalt (pp. 474, 476, 477). — For the detection of cobalt in the pres-
ence of iron or nickel, see under those metals.

Columbium (pp. 476, 477, 482). — When a compound containing
columbium is fused with five parts of borax on platinum foil, dissolved
in concentrated HC1 and diluted with a little water, the solution be-
comes blue when boiled with granulated tin. The color does not
change to brown on continued boiling. It disappears, however, when
diluted with water. If titanium is present in the same solution the

486 DETERMINATIVE MINERALOGY ~

color will be first violet, then blue. Tungsten, which gives a blue solu-
tion under the same conditions, can be distinguished from columbium by
the bead test. If the solution is boiled with zinc, instead of tin, its
color changes rapidly from blue to brown.

Or the finely powdered substance may be fused in a test tube or
crucible with ten parts KHSO4, and then digested with cold water for a
long time. If columbium is present, an insoluble white residue will be
left. This, if collected on a filter, washed, and then treated in a test
tube with hot concentrated HC1, will yield the blue solution when boiled
with granulated tin.

Copper (pp. 474, 476, 477, 478, 480). — A very delicate test for
soluble copper compounds is to dissolve them in HC1 or HNO3, dilute
with water and add ammonia in excess. A deep purple-blue solution
of CuCl2-6NH3 or Cu(N03)2 • 6NH3 will result.

Fluorine (pp. 472, 481). — If the mineral to be tested is a silicate, its
powder is mixed with four parts of fused microcosmic salt and this mix-
ture is heated in a closed tube. If fluorine is present, the glass above the
assay will be etched by the HF produced. At the same time, a ring of
Si02 is deposited in the cool portion of the tube in consequence of the
reaction.

3SiF4+2H20= 2H2SiF6+Si02.

Upon heating, the ring moves up the tube to a cooler portion.

Gold (p. 474). — The metal is best detected by treatment with
aqua regia of the metallic bead, produced by fusion with Na2CC>3 on
charcoal. This yields a light yellow solution, which, when taken up on a
filter paper and moistened with stannous chloride, gives the " purple of
Cassius."

Or, if the mineral is to be tested for free gold, it is powdered and
treated with aqua regia and the solution diluted and filtered. The fil-
trate is evaporated nearly to dryness, diluted with water and a few drops
of a solution of ferrous sulphate are added. If gold is present in small
quantity only, the solution will be colored bluish or purple. If the gold
is present in larger quantity, the metal will be precipitated as a brown
powder.

Free gold may also be detected by powdering the substance until all
will pass through a fine sieve. Brush the material adhering to the sieve
and add to the powder. Then place in a basin containing a little mer-
cury (J cc), and immerse the basin and its contents in water. Shake
the basin gently with a rocking motion and gradually allow the rock

CHARACTERISTIC REACTIONS, ETC. 487

powder to escape. The gold will fall to the bottom and amalgamate
with the mercury. After the mass has been reduced to a small volume,
transfer to a mortar and grind in a gentle stream of water, until nothing
but the amalgam is left. Then place in an iron spoon and heat in the
open air until all the mercury is driven off; or the amalgam may be
placed in a shallow cavity on charcoal and heated with a small blowpipe
flame until all the mercury volatilizes. The residual gold may be col-
lected into a globule by placing a little borax or sodium carbonate in
the cavity and heating until quiet fusion takes place.

When driving off the mercury from the amalgam extreme care must be
taken not to breathe its fumes, since they are poisonous. The operation
should not be performed in a closed room.

Iodine (p. 481). — Substances containing iodine, when fused in a
glass tube with KHSO4 and Mn02, yield a vapor which is recognized
as that of iodine by its violet color.

In the presence of other halogens, iodine may be detected by mixing
the powdered substance with IM2S3 (prepared by fusing together small
quantities of bismuth and sulphur) and heating in a closed tube or on
charcoal before the blowpipe. If iodine is present, a red sublimate of
bismuth iodide is produced. (Compare Chlorine and Bromine.)

Iron (pp. 472, 474, 476, 477). — To distinguish ferrous and ferric
conditions, the assay is added to a borax bead containing copper. If
the iron is in the ferric condition, the bead will be bluish green; if in
the ferrous condition, it will contain red streaks of cuprous oxide.

In the presence of easily fusible metals like lead, tin, zinc, etc., the
substance is heated on charcoal with borax in the R.F. The easily
reducible metals do not become oxidized and, consequently, are not
absorbed by the glass. The glass is separated from the metallic bead,
and is heated on a fresh piece of charcoal in the R.F., when it acquires
the characteristic bottle-green color produced by iron, and becomes
vitriol-green on addition of tin.

In the presence of cobalt, the blue color of the cobalt bead masks the
green of the iron bead. In this case, iron is detected by heating the blue
glass on platinum wire in the O.F. sufficiently long to convert all the
iron into peroxide. With very little iron present, the bead is green when
hot, and blue when cold; with more iron the bead is dark green when
hot, and pure green when cold, this latter color resulting from a mixture
of the yellow iron and the blue cobalt colors.

Manganese colors the borax bead in the O.F. red. Upon reduction
with tin on charcoal, the bead becomes bottle-green. If cobalt also is

488 DETERMINATIVE MINERALOGY

present, the bead produced in the O.F. is dark violet. In the R.F. it
becomes green when hot and blue when cold.

Lead (pp. 472, 475, 478,). — The coating of lead oxide resembles very
closely that of bismuth. The two may be distinguished by the pro-
cedure described under bismuth. The iodide of lead is lemon-yellow.

Lithium (pp. 478, 479). — In the case of silicates, before testing for
flame coloration, it is advisable to mix the powder of the assay with one
part of fluorspar and one and a half parts of KHSO4 and form into a paste
with a drop of water. If boron is present, the flame is at first green,
then red. The presence of phosphoric acid is shown by the production
of a green flame together with the red one. This is especially noticeable
after moistening the assay with sulphuric acid.

Magnesium (p. 481). — The Co(NC>3)2 test for magnesium is applica-
ble only to white or colorless minerals and is by no means conclusive.
The most satisfactory test is that employed generally in ordinary quali-
tative analysis, viz., precipitation with the aid of sodium phosphate
(Na3P04). The powdered mineral, if insoluble in acids, is fused with
Na2C03, powdered, dissolved in a few cc. of dilute HNO3 and evapo-
rated to dryness. It is then dissolved in 2 or 3 cc. HC1 and warmed for
a few minutes. There is next added about 10 cc. of water and the solu-
tion is boiled and filtered to remove silica. The filtrate is heated to
boiling and NH4OH is added in slight excess to precipitate iron and
aluminium. This is now filtered and the filtrate is boiled again, and to
it is added some ammonium oxalate ((NH4)2C204) to separate calcium.
After ten or fifteen minutes, the calcium oxalate is removed by several
filtrations until the filtrate is clear. To the nitrate a solution of sodium
phosphate and strong ammonia are added. If magnesium is present
after standing for some time, a fine white crystalline precipitate of
NH4MgP04-6H20 will form.

Manganese (pp. 477, 480). — Manganese compounds soluble in
HNO3 are readily detected by oxidation with persulphates. The pro-
cedure is to dissolve in a few cc. of moderately dilute HNO3 (sp. gr.
1.2), add about one-half its volume of dilute solution of AgNCfe and a
few drops of ammonium persulphate (200 gr. (NH4)2S20s to one liter of
water) and gently heat. The manganese will be oxidized to perman-
ganic acid, which is purple. The reaction is

2Mn(N03)2+ 5(NH4)2S208+8H20
= 5(NH4)2S04+5H2S04+4HN03+2HMn04.

CHARACTERISTIC REACTIONS, ETC. 489

Compounds that are insoluble in HNO3 must first be fused with Na2C03
on charcoal.

Mercury (pp. 472, 473). — In the presence of sulphur, chlorine, iodine
and a few acids, the assay is best heated with dry Na2CQ3 in a closed
glass tube. The acid combines with the Na and the Hg sublimes.

Molybdenum (pp. 474, 475, 477, 478, 482). — The white coating of
M0O3 on charcoal, if touched with the R.F., is partly reduced, be-
coming blue. If heated by the O.F., some of it volatilizes, but some
is reduced by the charcoal, forming a copper-red coating.

Small quantities of molybdenum are detected by treating the pow-
dered assay with a little strong sulphuric acid on a platinum foil. After
heating until most of the acid is evaporated, and then cooling, the result-
ing mass becomes blue, particularly after being repeatedly breathed
upon, or after being moistened with alcohol and dried by heating.

Nickel (pp.474, 476, 477). — In the presence of Co, the color of the Ni
borax bead is often masked. In such cases, a small portion of the mineral
is fused in the R.F. to a globule. A fragment of borax " twice the size
of the globule is placed beside it on charcoal and the two are heated by
the O.F. The two globules will roll around under the flame in contact,
but will remain quite distinct; any cobalt will be oxidized by the O.F.
and be absorbed by the borax, which will become blue. If the mineral
is placed upon a clean part of the coal and the treatment is continued
with fresh portions of borax until all the cobalt has been oxidized and
the borax no longer becomes blue, the nickel present will impart its
characteristic violet and reddish brown color to the borax." (Phillips.)

Nickel is best detected by treating its solution with dimethyl gly-
oxime ((CH3)2C2(NOH)2). The assay is dissolved in acid, after fusion
with Na2COa, if necessary, and the solution is neutralized with (NH^OH.
Add one-half volume of dimethyl glyoxime solution, made by dissolving
one part of the compound in 100 pts. of a 40 per cent, alcohol, and again
add a little (NH4)OH to neutralize. A bright red crystalline precipitate
will form if nickel is present, according to the reaction:

NiCl2+ 2(CH3)2C2(NOH)2
= (CH3)2C2(NOH)2 • (CH3)2C2(NO)2Ni+ 2HCL

Nitric Acid (pp. 472, 478, 481). — Nitric acid is best detected by dis-
solving the assay in dilute (1:1) H2S04, cooling and adding to the solu-
tion in a test tube a few drops of a strong solution of FeSCU in water,

490 DETERMINATIVE MINERALOGY

holding the tube slanting and allowing the FeSOi to trickle quietly down
its side and form a layer upon the acid solution. If nitrates are present,
a brown ring will form at the contact of the two solutions.

Oxygen, in some of the higher oxides, may be detected by the liber-
ation of chlorine when they are treated with HC1. This is particularly
the case with the higher oxides of manganese, thus:

Mn02+4HC1 = MnCl2+ 2H2O+ 2CL

The chlorine is recognized by its color, its odor and its bleaching
action.

Phosphoric Acid (pp. 478, 482). — In the test with magnesium ribbon,
it is best to fuse the phosphates of Al and the heavy metals with two
parts of Na2C03 on charcoal, to remove and grind the fused mass, and
then to ignite the powder with magnesium ribbon in a closed glass tube
(Brush and Penfield).

If a small crystal of ammonium molybdate (NH4)2Mo04 be placed
on a phosphate and a little dilute HNO3 be dropped upon it, the crystal
will turn yellow in consequence of the production of ammonium phos-
phomolybdate ii(Mo03)(NH4)3P04-6H20. This test is available
only for compounds that are soluble in HNO3.

If the mineral is insoluble in HNO3, it must first be fused with sodium
carbonate on platinum wire. The bead is then dissolved in nitric acid
and the solution when cold is added drop by drop to a little of an ammo-
nium molybdate solution and allowed to stand without warming. If
the assay contained the phosphoric acid radical, a yellow phospho-
molybdate will be formed.

Potassium. — See pp. 478 and 479.

Selenium (pp.473,475, 478). — Selenates and selenites must be reduced
with sodium carbonate on charcoal before the peculiar odor is evolved.

Silicon (pp. 477, 480). — Small splinters of silicates yield an infusible
skeleton of silica when heated in a bead of microcosmic salt. This floats
around in the liquid bead as a particle with the shape of the original
splinter, or as a transparent flake. In some cases the original splinter
remains undecomposed.

Many silicates decompose in strong HNO4 or HC1 with the produc-
tion of a gelatinous mass of silicic acid. If the solution containing the
gelatinous silica is evaporated to dryness, the silica becomes insoluble

CHARACTERISTIC REACTIONS, ETC. 491

and remains as a residue when the mass is warmed with a little strong
acid and digested with water.

In case of insoluble silicates it is necessary to fuse with Na2C03
before proceeding with the test. The fusion results in the production
of a sodium silicate which is soluble in acids. The gelatinous precip-
itate will appear only after the acid solution of the fused mass is evap-
orated.

Silver. — See p. 474.

Sodium. — See pp. 478 and 479.

Strontium (pp. 478, 479). — In the case of insoluble compounds
treat as in the test for Ba. If both Ba and Sr are present in the final pre-
cipitate, the flame will first be crimson. Upon repeated moistening
with HC1 and heating, the Sr will gradually disappear and the green
color of the Ba flame will be seen.

Sulphur (pp. 472, 473, 480, 481). — If a substance containing sulphur
is heated with Na2C03 on charcoal in the R.F. and the fused mass is
transferred to a watch glass and moistened with water, the addition of
a little dilute solution of ammonium molybdate, to which HC1 has
been added, will produce a blue color.

Sulphides are distinguished from most sulphates (except those con-
taining water or the OH group) by heating in the O.F. The sulphides
yield an odor of SO2. The sulphates yield no odor. Another means of
distinguishing between these two classes of compounds is as follows:
The finely powdered substance is fused with caustic potash (KOH) in a
platinum spoon, or on a piece of platinum foil. The spoon or foil with
its contents is thrown into water containing a strip of silver. If the
silver remains quite white, the S is present as sulphate; if the silver
becomes black, S is present as sulphide. Substances exercising a reduc-
ing action must, of course, not be present.

Tantalum cannot be recognized in the presence of columbium by any
simple tests.

Tellurium (pp. 473, 475).— A powdered tellurium compound, heated
with Na2C03 and charcoal powder in a closed glass tube and treated
when cold with hot water, yields a purple red solution of sodium tel-
luride. This color will disappear if air is blown through the solution.

Tellurides may be detected by gently warming the finely powdered
substances with a few cc. of concentrated sulphuric acid. The solution

492 DETERMINATIVE MINERALOGY

will become carmine. After cooling, the addition of water will precip-
itate the tellurium as a blackish gray powder, and the carmine color
will disappear.

Thallium. — See p. 478.

Tin (pp. 475, 481). — The reduction of tin compounds is accomplished
fairly easily by mixing borax with Na2CC>3 and treating with the R.F.
on charcoal. The metallic tin thus obtained, when heated on charcoal
by the O.F., yields a white incrustation which becomes bluish green
when moistened with cobalt nitrate and heated (see Zinc). Or, if
warmed in a test tube with moderately dilute HNO3, a white powdery
metastannic acid (H2Sn03) will result.

If to a borax bead colored blue by a copper, a small quantity of tin
compound be added and the R.F. be applied, the bead will turn
brown.

Titanium (pp. 476, 477, 482). — If iron is present, the bead of micro-
cosmic salt in the O.F. has the iron color, and in the R.F. a blood-red
color. When this is fused with tin in the R.F. on charcoal, the color
becomes violet.

A very characteristic reaction is obtained as follows: Fuse on char-
coal or platinum foil one part of the assay with 6 parts of Na2CC>3 and a
little borax. Then dissolve in a small quantity of concentrated HC1
(2-2.5 cc-^ and ac*d granulated tin. The hydrogen generated by the
tin and HC1 will reduce the TiCU in the original acid solution to TiCb
and the solution will assume a violet color, especially after standing
several hours.

For an extremely delicate test, fuse the |K>wdered assay with Na2COs
and borax, as in the color test with tin. If the fused mass is dissolved
by heating in a test tube with 2 cc. of a mixture of equal parts of H2SQ1
and water, and, after cooling, is diluted with about 10 cc. of cold water,
the addition of a few drops of H2O2 to the diluted solution will produce a
golden yellow or orange color if titanium is present.

Tungsten (pp. 474, 476, 477,482). — When present in small quanti-
ties, tungsten may be detected by fusing the assay with five or six times
its weight of Na2C03, extracting the resulting mass with water, filtering
and adding to the filtrate strong hydrochloric acid. White tungstic
hydroxide will be precipitated and this precipitate will become pale
yellow (WO3) on boiling. Upon acidification and boiling with a few
particles of tin, a blue mixture of oxides results. The blue color will not

CHARACTERISTIC REACTIONS, ETC. 493

disappear on the addition of water. (Compare tests for columbium.)
On long-continued boiling, the color will change to brown (WO2).

If the tungstate be decomposed by boiling with HC1, it is not neces-
sary to fuse. Simply boil with strong acid until a light yellow precipi-
tate (WO3) is obtained. Then dilute with an equal quantity of water,
add tin and boil, and the clue color will result. This will change to
brown on long-continued boiling (WO2).

Uranium (pp. 476, 477,). — If the uranium is so mixed with other
metals that its characteristic bead is obscured, dissolve the assay in HCi
(first fusing with Na2C03 or borax, if necessary), then nearly neutralize
with ammonia and add a strong solution of Na2C03 until precipita-
tion ceases, then about half as much more and let stand for some time.
The excess of Na2C03 will dissolve the compound first precipitated.
Filter, acidify the filtrate with HCI and boil until all the CO2 is expelled.
Then add ammonia in excess. If uranium is present, it will be precipi-
tated as a gelatinous light yellow ammonium uranate (NH-O2U2O7. To
confirm, filter and test the precipitate in the bead of microcosmic salt.

Vanadium (pp. 476, 477, 482). — Vanadium compounds, first roasted
on charcoal and then fused with four parts Na2C03 and two parts potas-
sium nitrate on a platinum spiral, when extracted with hot water,
filtered, acidified with acetic acid, and treated with a few drops of lead
acetate, yield a pale yellow precipitate of Pbs(V04)2. This may be
tested for vanadium in a microcosmic salt bead.

If the solution obtained by extracting the fused mass be filtered and
acidified with HCI and well shaken with hydrogen peroxide, it will
become reddish brown or garnet color. If to the acidified solution
metallic zinc be added, a green blue color will result. This, howrever,
will gradually become violet if the solution is left standing in contact
with zinc.

If the substance is soluble in concentrated HCI or H2SO4, the solu-
tion thus produced will be red-brown. On the addition of water the
color wiD change to green-blue or will disappear. Upon the addition
of H2O2 the reddish brown color will reappear if the dilution be not
too great. If treated with metallic zinc the green blue color will again
appear, but will gradually change to violet on continued action of the
zinc. If the blue or violet solution is poured off the zinc and a few
drops of hydrogen peroxide be added, the characteristic brown color
will again result. For a more accurate determination of the presence
of vanadium, add NH4OH in excess to the acid solution and pass

494 DETERMINATIVE MINERALOGY

through it H2S. The solution will become garnet if vanadium is
present.

Zinc (pp. 472, 475, 481). — Infusible white or light-colored zinc com-
pounds, when finely powdered and made into a paste with a drop of
Co(NOs)2 solution, and then heated on charcoal by an O.F., assume a
green color. But silicates of zinc when treated in this way with a hot
flame often form a fusible cobalt silicate which is blue.

In the presence of antimony and tin, it is almost impossible to detect
zinc by blowpipe tests, as all three metals exhibit nearly the same
blowpipe reactions. However, the zinc sublimate when moistened with
Co(N03)2 solution and heated in the O.F. becomes grass-green,
whereas the tin sublimate, under the same treatment, becomes blue-
green.

Zirconium, in the absence of titanium, molybdates and boric acid,
may be detected, after fusion of the assay with a little Na2C03, by dis-
solving the assay in a few drops of strong HC1 and diluting with water
to four times the volume, and then moistening with this dilute solution a
piece of turmeric paper. When the paper is dried gently its color will
change to reddish or orange if zirconium is present.

APPENDICES
L GUIDE TO THE DESCRIPTIONS OF MINERALS

Because of the great number of minerals known and the difficulty
of recognizing them at sight, some means must be employed to aid in
their systematic study in order that they may be identified without an
inordinate expenditure of time. The most convenient method of
arriving at the name of a mineral is by means of a guide, or a set of
tables similar in scope to the " keys " used in Botany for determining
the names of plants. Many tables have been proposed by mineralogists
for this purpose and many different kinds are still in use. Some
of these are based on the chemical properties of minerals, and others
on their physical properties. Both kinds possess advantages. Those
based on chemical properties are more effective in leading to the name
of the mineral being studied, but those based on physical properties
are more apt to lead to a better knowledge of its most evident charac-
teristics.

The most serious objection to the use of determinative tables lies
in the danger that the student will feel, when the name of the mineral
is obtained, that the object of his search is at an end, whereas their
true aim should be to lead him to such a thorough study of the mineral
that there will remain no doubt in his mind as to its real nature.

In the present volume the tables are intended to serve simply as
guides to the descriptions of the minerals given in the body of the text.
It is here that the distinctions between the different species must be
found. In many instances the differentiation between several minerals
is dependent upon chemical tests; hence it is desirable to familiarize
oneself with the characteristic tests of the various metals and the acid
radicals.

The tables in the following pages are divided into two great divisions.
The first division includes those minerals that have a metallic luster,
and a few which might be confused with these. Minerals possessing a
metallic luster are opaque on their thinnest edges. Most of them give a
black or dark-colored streak. The second division includes the remain-
ing minerals, i.e., those with a nonmetallic luster. These are trans-
parent in splinters and on their thin edges, and most of them give a

495

496 APPENDICES

colorless or light-colored streak. The subdivisions are based on color
of streak, color in reflected light and hardness. With reference to hard-
ness it is convenient to remember that minerals with a hardness of less
than 2.5 will leave a mark on paper; those with a hardness of less than
3.5 can be scratched by a cent; those with a hardness of less than 6 can
be scratched by a good knife blade; and those with a hardness of less
than 7 can be scratched by quartz.

In testing for hardness it is important to know not only that the
scratching substance will actually scratch the substance being tested,
but also that the latter will not scratch the former. Further, it is like-
wise important that the scratching substance be clean and fresh. If a
cent or a knife blade is being used for scratching, it should be bright;
if a mineral is being used, it should not be coated with a tarnish or a layer
of weathered substance.

It is also to be remembered that the color of a mineral is its color on a
fresh fracture and not on a weathered surface.

Again, it must be stated that the tables in this book are not expected
to determine for their users the names of minerals; they are to serve
merely as guides to the pages on which the minerals are described.
Recourse must be had to the descriptions of the individual minerals
before the nature of the substance being studied can be established.

APPENDICES

497

KEY TO THE DETERMINATION OF MINERALS
A— MINERALS WITH METALLIC LUSTER*

STREAK BLACK OR DARK GRAY

Color

Name

Hardness

Ref.
Page

122
72

"4
8l

Color

Name

Hardness

Ref.1
Page

Lead

1. 5-2

2.0

2-2.5

2-3

2-5

2.5-3

2-5-3

White

or
Light
Gray

Arsenic

Domeykite . . .
Lollingite . . .

Cobaltite

Smaltite

Arsenopyrite . .
Chloanthite . . .

Sperrylite

3-4

3-5
5-5-5
55
55
55-6
5-5
6H3.5
6-7

50
78

"3
106

107

III

108

109
108

White

or
Light
Gray

Tetradymite . .
Bismuthinite . .
Jamesonite . . .

Stibnite

Calaverite

Galena

Clausthalite. . .
Stromeyerite. .

Brassy
Bronze

Calaverite ....

Millerite

Domeykite. . . .
Chalcopyrite . .

^3
3-3-5
3-3-5
3-5
3-5-4

114

130
95
78

131

175
189

149

122

125

125
124

79
81

84
120

86
100

Brassy
Bronze

Pentlandite. . .
Pyrrhotite ....

Niccolite

Pyrite

35-4

35-45
5-5
5-6-5
6H3.5

109

Molybdenite . .
Wad

1-1.5
1-2

1-2.5

1-3
2-2.5

2-2.5

2-5

2-5-3
2-5-3
2-5-3

Dark
Gray

or
Black

Enargite

Tetrahedrite . .
Arsenic

Staurolite. ....
Iron

3-4

3-5-5
4
4.5-5

5-5-5

5-6

5-6
5-5-6-5
55-6.5

6-6.5

6-6.5
6-^.5
7-9

123
126
50
297
337
655
258
188
462
108

199

174
204

293
293
155

Melaconite. . . .

Jamesonite. . . .
Polybasite. . . .

Pearceite

Stephanite ....

Argentite

Galena

Chalcocite. . . .
Boumonite. . . .
Stromeyerite. .
Metacinna-

Dark
Gray

or
Black

Wolframite

Psilomelane . . .

Ilmenite

Magnetite ....
Franklinite. . . .

Columbite. . . .

Tantalite

Corundum ....

Blue

*- —

1.5-2

1 The references are to pages in this book.

498

APPENDICES

A.— MINERALS WITH METALLIC LUSTER— (Con.)

STREAK BLACK OR DARK GRAY — (Cotl.)

Color

Name

Hardness: ££

Color

Name

Hardness

Ref.
Page

Brown

Wad 1 1-3 ! 189

• 1

Brown

Uraninite

3-5-5

297

STREAK BROWN

Dark
Gray

or
Black

Brown

Yellow

Wad

Dufrenosite. .
Hematite ....
Tetrahedrite .

Uraninite

Siderite

Sphalerite

Manganite . . .

Wurtzite

Cuprite

Triplite

Thorite

Goethite

Limonite

Plattnerite. . .
Hausmannite.
Huebnerite. . .

Wad

Limonite

Hematite ....
Uraninite ....

Siderite

Sphalerite. . . .

Wurtzite

Thorite

Triplite

Limonite ....

Goethite

Huebnerite. . .
Wolframite. . .

Limonite. . . .
Pentlandite .

Siderite

Sphalerite. . .

i-5.5

3.5-4

3-5-4

3.5-4
Thorite I 4 . %

i-3
2-3
2-3
3-4
3-5
5-4
5-4
5-4
5-4
5-4
4-5
5-5
5-5
5-5
5-5
5-5
5-5

i-3
i-3

3-55

5-4

4-5

5-55

5-5-5

5-«

189

275

153
126

297

219

87
191

147

273

319

193

183

175
204

258

189

183

153
297

219

87
00

3i9
273
183
193
258
258

183
00

219

87
310

Dark
Gray

or
Black

Brown

Yellow

Wolframite.
Hornblende
Psilomelane
Ilmenite . . .
Samarskite.
Chromite. .
Brookite. . .
Fergusonite
Allanite. . . .
Franklinite .
Hematite. .
Columbite .
Tantalite. .

Rutile

Cassiterite .
Corundum .
Spinel

Ilmenite . . .
Limonite . .
Brookite. . .
Allanite . . .
Franklinite.
Hematite . .
Columbite .
Tantalite. .
Braunite. . .

Rutile

Cassiterite .
Spinel

Goethite. . .
Huebnerite.
Cassiterite .
Spinel

5-6

5-6
5-6
5-6

5-5
5-6

5-«

5"*
5-6.5

6-6.
6-^.5

6-6.5
6-7

6-7
7-9
5-8

5-6

5-5
55-6

5-5-6
55-6
6

6-6
6-6
6-6

6-7

7.5-8

5
5

4-5-55
4.5-5.5

6-7
75-8

258
388
188
462

295
200

176

293

330
109

153

293

171
168

155
196

462

183
176

330
199

153

293

293
204

171

168

196

193
258
168
196

APPENDICES

499

A.— MINERALS WITH METALLIC LUSTER— (Con.)

STREAK BROWN — (Con.)

Color

Name

Hardness

Ref. 1
Page

Color

Name

Hardness

Ref.
Page

Red

. Cinnabar

2-2.5
35-4

147

Red

Breithauptite. .
Rutile

6-7

95
171

STREAK RED

Dark
Gray

or
Black

Brown

Wad

Hematite ....

Copper

Pyrargyrite. .
Tetrahedrite .
Manganite . . .

Wad....
Hematite

Red

Hematite. .
Cinnabar. .
Proustite. .
Pyrargyrite

1-3

189

2-3

153

Dark

25-3

Gray

2-5-3

117

3-4

126

Black

3-5-4

191

i-3
2-3

189
153

Brown

2-3

153

2-2.5
25

98
119

Red

2-5-3

117

Cuprite. . . .
Wolframite.
Samarskite.
Franklinite.
Hematite . .
Columbite. .

Wolframite.

Copper

Gold

Hematite ....
Breithauptite.

5-4

5-55
5-6

5-6-5
6-6.5

6-6.5

5-5-5

25-3

3-6

STREAK YELLOW

147
258

295
I99

153
293

258

53
58

153
95

Dark
Gray

or
Black

Triplite

Limonite

Huebneritc. . . .

35-4

3 • 5-4
4-5-5

4-5-5-5
5-55
5-5-5

219

»73
193
183
258

Dark
Gray

or
Black

Hornblende. . .
Samarskite. . . .

Brookite

Rutile

Cassiterite ....

5-6

5-5-6

6-7
6-7

388

295
176

171

168

Brown

Limonite

Sphalerite

Zincite

Triplite

1-5-5

3-5-4
4-4-5
4-5-5

45-5-5

183

I50

273
193

183 j
114

58
91
87

Brown

Huebneritc . . .

Brookite

Rutile

Cassiterite ....

4-5-5-5
5-55
5-5-6

6-7
6-7

258

183
176
171
168

Yellow

Limonite

Calaverite. . . .

Gold

Greenockite . . .

1-5-5

2-5-3

3-3-5
3 5-4

| Yellow

Goethite

Huebneritc . . .

Limonite

Cassiterite ....

45-55
4.5-5.5

5-5-5

6-7

193
258
183
168

500

APPENDICES

A.— MINERALS WITH METALLIC LUSTER— (Cow.)

STREAK YELLOW — (Ctfrt.)

Color

Name

Hardness

Ref.
Page

Color

Name

Hardness

Ref.
Page

Red

Sphalerite

Zincite

Goethite.

35-4

4-45
4- 5-5 -5

87
I50
193

Red

Rutile

55.-6

6-7

176
171

STREAK

GREEN

Green

Uraninite

Alabandite. . . .
Hornblende. . .

3-5-5

35
5-6

297

388

Green

Gadolinite ....
Spinel

5H3

6-7

75-8

374

335
196

Black,
Brown
or Red

Alabandite

35
3-55

00
297

Black,
Brown
or Red

Huebnerite. . . .
Gadolinite ....

45-5-5
6-7

*58
335

STREAK GRAY

SQver
White

Sylvanite

Bismuth

Silver

Calaverite. . . .

1.5-2
2-2.5
2-2.5

2-5-3
25

114

55
114

349

79
86

87
464
258

258
330
176
176

Silver
White

Dyscrasite ....

Platinum

Palladium ....
Iridosmine ....

3-4
3-5
4-5
4-5
6-7

5i
78

63
66

Dark

Gray

or
Black

Molybdenite . .

Tetradymite . .

Silver

Biotite

Petzite

Stromeyerite . .

Sphalerite

Titanite

Huebnerite. . . .

i-i-5
1-2

1.5-2

25-3

3-5-4
5-55
5-5-5

Dark
Gray

or
Black

Hornblende. . .

Hypersthene . .

Allanite

Anatase

Perovskite ....

Rutile

Gadolinite. . . .
Spinel

5-6
5-6

5-6
5-5-6
55-6
55-6
5 5-6
6-7
6-7

6-7

388

374
365
330
176
176
461
171

335
196

Brown

Huebnerite. . . .

Anatase

Brookite

5-55
55-6
5-5-6
55-6

Brown

Perovslcke ....

Rutile

Gadolinite ....
Cassiterite ....

5 5"^
6-7

6-7

461

171

335
168

APPENDICES

50L

A.— MINERALS WITH METALLIC LUSTER— (Con.)

STREAK WHITE

Color

Name

Hardness

Ref.
Page

CoJor

Name

Hardness

Ref.
Page

Silver
White

Sylvanite

Altaite

1-2

114

55
84

Silver
White

Antimony. . . .

3-3-5

3-4

6-7

63
51

Dark
Gray

or
Black

Biotite

Titanite

Hornblende. . .

Hypersthene . .

'•5-3
2 • 5-3

5-5-5

5-«

5H5

5-6

349

55
464

388
374
365

Dark
Gray

or
Black

Anatase

Perovskite ....
Cassiterite ....

Garnet

Tourmaline. . .
Spinel

55-6

5 5-6

6-7

6.5-7

7-75
75-8

176

461

168

312

434
196

Brown

Anatase

Perovskite ....

5 5-<>
5-5-6

176
461

Brown

Cassiterite ....

6-7

168

B.— MINERALS WITH NONMETALLIC LUSTER

STREAK DARK GRAY OR BLACK

Color

Name

Hardness

Ref.

Page

Color

Name

Hardness

Ref.
Page

Dark

Gray or

Black

Graphite

Melaconite. . . .
Wad

1-2

1-2. s

1-3

44
I49

189

Dark

Gray or

Black

Wolframite

Psilomelane. . .
Corundum ....

5-5-5

5-6

7-9

258
188

155

Brown

Wad

1-3

189

STREAK BROWN

Dark

Gray

Black

Wad

Uraninite. .
Siderite. . . .
Sphalerite. .
Cuprite. . . .
Thorite. . . .
Goethite. . .
Ferberite. .
Wolframite.

i-3

3-55

5-4

5-5

189
297
219

87
147
3i9
193
258
258

Dark
Gray

or
Black

Hornblende
Psilomelane
Chromite. .
Uraninite . .

Allanite

Brookite. . .

Rutile

Cassiterite .
Spinel

5-6
5-6
5-6

55
55-6
5 5-6
6-7

6-7

75-8

388
188
200
297

330
176

171

168

196

502

APPENDICES

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK BKOWN — (Con.)

Color

Name

Hardness

Ref.
Page

Color

Name

Hardnes*

Ref.
Page

Wad

i-3
i-3
i-3
i-3

2-2. e
2-5

2-5

3
3"5 - 5

189

153
183 1
186
98

288
441

153
183
186

277 !
297 1

Brown

Siderite

Thorite

Goethite

Huebnerite. . .
Wolframite . .
Hornblende. .

AUanite

Brookite

Rutile

Cassiterite. . .
Spinel

3-54
3-5-4
4-5

4-5-5

45-5
5-5-5
5-5-5
5-6

5-5-6

5 5-6

6-7
6-7

75-8

219

87
265

319
193
258
258
388

33°
176

171
168

196

Brown

Hematite

Limonite

Bauxite

Cinnabar

Pharmaco-

siderite

Chrysocolla. . .

Hematite

Limonite

Bauxite

Olivenite

Uraninite

Red

Hematite. . . .

Cinnabar

Hematite

Cuprite

Sphalerite

Xenotime

i-3
2-2.5

3-6

35-4

4-5

153 1
98

153

147

87
265

Red

Huebnerite. . .
Wolframite. . .
Hematite ....

Rutile

Cassiterite

4-5-5

5-5-5
6

6-^.5
6-7

258
258

153
171

168

Yellow

Bauxite

Limonite

i-3
i-3

186

183

Yellow

Goethite

4-5-5-5

193

STREAK RED

Dark

Gray or

Black

Hematite

i-3

153

Dark
Gray or

Black

Cuprite

Hematite

3-5-4
5-5-6- 5

147
153

Brown

Cinnabar

2-2.5

98 |

Brown

Hematite

3-6

153

Red

Bauxite

Hematite

Erythrite

Cinnabar

Proustite . : . . .

i-3
i-3
15-2
2-2.5
2-2.5

186

153
282

119

Red

Pyrargyrite. . .

Crocoite

Zincite

Xenotime

Wolframite. . . .

2-5-3
2-5-3

4-4-5
4-5
5-5-5

117

253

150
265

258

Yellow

Hematite ......

3-o

153

APPENDICES

5C3

B— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK YELLOW

Color

Name

Hardness

Ref.
Page

Color

Name

Hardness

Ref.
Page

Dark
Gray

or
Black

Siderite

Huebnerite. . . .
Goethite

3 • 5"4
45-5
4-5-5-5

219

258
193

| Dark
Gray

or
Black

Brookite

Rutile

Cassiterite ....

55-6

6-7
6-7

176

171
168

Wad

i-3
i-3
i-3
3-5-4
3-5-4
4-5

189 1

183
186
219

265

Brown

Huebnerite. . . .

Goethite

Brookite

Rutile

Cassiterite ....

45-55

4-5-5-5
5-5-6

6-7
6-7

258

193
176

171
168

Brown

Limonite

Bauxite

Siderite

Xenotime

Red

Wulfenite

Vanadinite. . . .
Sphalerite

i-3
3
3
3 • 5-4

186

257
271

1
1

Red

Zincite

Huebnerite. . . .

Rutile

Cassiterite ....

4-45
45-5-5
6-7
6-7

I50
258

171
168

Yellow

Bauxite

Limonite

Orpiment

Sulphur

Autunite

Carnotite

Pharma-
cosiderite. . .

i-3

i-3
1-5-2
1.5-2

2-2.5

2-3

2-5

186

183

47
289

290

288

1
Yellow

Wulfenite

Vanadinite. . . .
Greenockite . . .
Pyromorphite .

Sphalerite

Zincite

Goethite

Crocidol'tr ....

3
3
3-35
3-5-4
35-4

4-45
4-5-5
S-6

257
271

91
270

87
I50

193
,*02

STREAK ORANGE

Brown

Thorite

45-5

3i9

Red

Realgar

15-2

69 I

Red

Crocoite

Zincite

2-5
4-4 5

253
150

Yellow

Greenockite ... 3-5 . 5

91 !

Yellow

Thorite

45-5

3i9

STREAK GREEN

Dark

Uraninite

3-3-5

297

Gray

Black

Dark
Gray

or
Black

Augite.
Spinel. .

504

APPENDICES

B— MINERALS WITH NONMETALLIC LUSTER— (Cm.)

STREAK GREEN — iC(m.)

Color

Name

Hardness

Ref.
Page

Color

Name

Hardness

Ref.
Page

Green

Glauconite. . . .

Chlorite

Annabergite. . .
Torbemite ....
Chrysocolla . . .
Gamierite
Pharmaco-

Atacamite. . . .

1-2
1-2.5
1-2.5
2-2.5

2-3
2-3

2.5

3
3-3 5

442
428
283
289
441

400

288

277
144

Green

Brochantite . . .

Malachite

Pyromorphite .

Dufrenite

Libethenite . . .

Hornblende . . .
Augite

3-5

35-4

3-5-4

5-o

5-6
6

6-7

245
231

270

275
278

347
388

374

279
427

STREAK

BLUE

Blue

Vivianite

Chrysocolla. . .

Azurite

Crocidolite. . . .

1.5-2

2-3
3.5-4

281
441

233
392

Blue

Lasurite

Glaucophane. .
Dumortierite . .

5-55
6-6.5

343
390

338

Green

Vivianite

Crocidolite ....

1.5-2

281
392

Green

Dumortierite. .

338

STREAK WHITE

Dark
Gray

or
Black

Gypsum

Halite

Apatite

Biotite

Calcite

Anhydrite. . . .
Cerussite. . . .
Serpentine . . .
Wavellite

Ankerite

Dolomite
Sphalerite. . . .
Magnesite.. . .
Fluorite

■5-2
2-2.5

2-5

2-5
3

3'3

3-3

3-4
•5-4
•5-4
•5-4
•5-4
•5-5
4

247

134
266

349
214

238
227

398
287
230
229

87
218

139

Dark
Gray

or
Black

Huebnerite. .
Titanite. . . .
Glaucophane
Yttrotantalite
Hornblende .

Augite

Schefferite. .
Hypersthene
Wagnerite. .

Allanite

Anatase. . .
Brookite. . . .
Perovskite . .
Labradorite .

5
5

5-55

5-5-5

5-55

5-6

55
5-6
5-6
5-6

5-6
6-6. *

258
464
300

295
388

374
373
365
273
330
176
176
461
418

APPENDICES

505

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (Con.)

Color

Dark
Gray

or
Black

Brown

Name

Epidote

Piedmontite
Chloritoid. .
Gadolinite .

Rutile

Cassiterite .

Ccrargyritc
Carnallite. .
Pyrophyllite
Tripolite. . .
Kaolinite. .
Gypsum . . .

Halite

Muscovite .
Zinnwalditc
Phlogopitc .
Apatite. . . .
Greenockite
Leadhillitc .

Biotite

Chrysotile.

Stolzitc

Senarmontit

Barite

Vanadinite.
Wulfenite. .
Calcite ....
Anglesite . .
Serpentine .
Heulandite.
Stiibite ....
Laumontite
Apatite. . . .
Dolomite. .
Sphalerite. .
Wavellite . .
Aragonite. .

Hardness

)
>

6-7
6-7
6-7
6-7
6-7
6-7

i-i. =■

1-2

1-2-5

1-2.5

5-2

2-2.5

2-3
2-3
2-3
2-3
5-3
5-3
5-3
5-3
5-3
5-3-/

3
3-3-5
3"4
3-4
3"4
3-4
3-5
5"4
5-4
5-4
5-4

Ref.
Page

Color

327

329

Dark

427

Gray

335

I7i

Black

168

138

142

406

180

404

247

134

355

352 !

350

266

252

349

398
256

•

Brown

152

239

271

257

214

242

398

446

450

45i

266

229

287

223

Name

Garnet

Quartz

Tourmaline. . .

Staurolite

Spinel

Diamond

Skorodite

Strontianite . . .

Siderite

Pyromorphite .

Mimetite

Rhodochrosite
Magnesite. . . .

Fluorite

Clintonite

Chabazite

Harmotomc. . .

Xenotime

Wollastonite . .

Apatite

Calamine

Huebneritc. . . .
Lit hiophy lite. .
Smithsonite. . .
Thomsonite . . .

Datolite

Titanite

Monazite

Yttrotantalitc .

Nephelite

Anthophyilite .

Enstatite

Bronzite

Hypersthenc . .

Diopside

Hornblende. . .

Hardness

^5-7.5
7
7-7.5
7-7-5

7-5-8
IO

3.5-4

35-4

3-5-4

3-5-5

4-5

5-5

•5-5

5-5

5-6

5-6
5-6
5-6
5-6
5-6

-4

4
4
4
4

Ref. 1
Page

159

434

337
196

285
225

219

270

271

220

218

139
426

456

449
265

368
266
396
258
262
221

455
334
464
263

295
314
^3
365
365
365
372
388

506

APPENDICES

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (Cotl.)

Cclor

Name

Hardness

Ref.
Page

Color

Name

Hardness

Ref.
Page

Babingtonite . .

Acmite

Fowlerite

Willemite

Troostite

Opal

5-6
5-6

5-6

5-6
5-5-6
5 5-6
55-6
55-6
55-6
6
6

6-6.5

6-7

374

380

375
380

306

179

330
176

176

461

305

274

333
326

321

345

327
100

Brown

Rtttile

Gadolinite ....
Cassiterite
Andalusitc ....
Vesuvianitc . . .

Olivine

Garnet

Quartz

Boracite

Danburite. . . .
Tourmaline. . .
Staurolite

Spinel

Chrysoberyl. . .
Corundum ....
Diamond

6-7
6-7

6-7
6-7-5

6-5

6-5-7

5-5-7-5
7
7
7-75
7-75
7-7-5
7-8

75
75-8

8-5

9
10

171

335
168

320

432

303
312

Brown

Allanite

Anatase

Perovskite ....

Amblygonite. .
Chondrodite. . .

Sillimanite ....

Axinite

Epidote

159

210

325

434
337
307

3*7
196
202

155
37

Cerargyrilc . . .
Glauconite. . . .
Pyrophyllite. . .
Chrysotile. . . .

Kaolinite

Vivian ite

Talc

1-2
1-2

1-2.5
1-2.5
1-2-5
1-2.5
1-2-5
1-2-5
i-3

2
2-2.5
2-2.5

2-3
2-3
2-3
2-4

2-5

138
442
406

398
404
281
401
428
283
429
251

134
181

400

352
386
441
432

Green

Stolzite

Phlogopitc ....

Biotite

Barite

Gibbsite

Wulfenite

Anhydrite

Anglesite

Stilbite

Serpentine ....

Wavellite

Aragonite

Scorodite

Strontianite . . .

Pyromorphite

Rhodochrosite

Fluorite

Variscite

V5"3
2-5-3
2-5-3
2-5-3
2-5-35
3

3-35

3~3-5

3-4

3-4
35-4
3.5-4
3-5-4
3-5-4
3-5-4
3-5-4-5
4
4

256

350

349

23»
182

257
23&

Green

Chlorite

Annabergite. . .
Orthochlorite .
Melanterite. . .

Halite

Brucite

Garnicrite

Zinnwaldite. . .

Actinolite

Chrysocolla. . .
Leptochlorite. .

242

450

39*
287

223,

285
225

270

22a

139
284.

APPENDICES

507

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (Con.)

Color

Green

Pink

Scheelite

Apatite

Calamine ....
Triphylite. . . .
Smithsonite. .

Datolite

Cummington-

ite

Griinerite
Anthophyllite

Gedrite

Thomson ite . .

Titanite

Wagnerite. . .
Hornblende. .

Augite

Acmite

Hypersthene .
Cancrinite. .
Nephelite . . .
Scapolite. . . .
Actinolite. . .
Enstatite. . .
Bronzite ....
Diopside. . . .
Troostite. . .

Opal

Turquoise. . .

4-5
5-5
5-5
•5-5
5
5-5-5

5-5
5-5
5-5
5-5
5"5
5-5
5-5
5-o
5-6
5-6

Laumontitc. .

Gypsum

Zinnwaldite. .
Lepidolite. . . .
Glauberite . . .
Senarmontite.

Kainite

Calcite

Laumontite. .

254
266

396
262
221

334

387

383

455

464

273
388

374
375

5-6

365

5-6

315

I 5"6

314

' 5-6

423

5-6

386

; *-*

365

1 5^

365

S-6

372

5-6

306

179

1 6

279
45i

1
i-5-2

1.5-2

247

1-2-3

352

2-4

354

2-5

236

2 • 5-3

152

-' • 5-3

251

214

3-4

45i

Color

Green

Pink

Name

Amblygonite .
Labradorite . .
Microcline. . .

Zoisite

Prehnite

Spodumene. .
Forsterite. . . .
Sillimanite . . .

Axinite

Epidote

Piedmont ite. .

Jadeite

Diasporc

Chloritoid. . . .
Gadolinitc . . .
Andalusite . . .
Vesuvianite. .

Olivine

Fayalite

Uvarovite. . . .

Quartz

Boracite ....
Tourmaline . .

Spinel

Beryl

Topaz

Chrysoberyl.
Corundum . .

Hardness

Margarite. . . .
Dolomite. . . .

Alunite

Rhodochrosite

Fluorite

Xenotime. . . .
Apophyilite. .
Lithiophylite .
Datolite

6-6.
6H3.
6-6.
6-6.

6-7
6-7
6-7
6-7
6-7
6-7
6-7
6-7
6-7
6-7
6-7
6-5
6-5
6-5
•5-7

7-7
5-8
5-8

3-4

35-4

3-5-4

4-5
5-5
5-5
5-5

Ref.
Page

274
418

413
326

343
378

303
321

345

327

329

377
190

427

335
320

432

303

159
210

434
196

359
322

202
155

352
229

244
220

139
265

443
262

334

508

APPENDICES

B.— MINERALS WITH NONMETALLIC LUSTER— (Cow.)

STREAK WHITE — (Cott.)

Color

Name

Hardness

Ref.
Page

Color

Name

Hardness

Ref.
Page

Pink

Wagnerite. . . .

Sodalite

Cancrinite. . . .

Tremolite

Fowlerite

Rhodonite. . . .
Bustamite. . . .
Willemite

Orthoclase ....

55
5-6

5-6

5"*
5-6
5-6
5H5

5-6
5-6
6
6-0.5

273
340

315

423
386

38o

306

305
413

Pink

Andalusite ....

Garnet

Tourmaline. . .
Spodumene . . .

Topaz ".

Corundum ....

6HS.5
I-6-7

6-7-5
6-5-7
7-7-5
7-75
7-8

326

327
320

312

434
378

307
322
196

155

Carnallite

Kaolinite

Talc

1-2

1-2.5

i-3
1.5-2
2
2-2.5
2-2.5

2-5
25-3
2-5-3
2. 5-3-5
25-4
3
3
3
3
3-3-5
3-3-5
3-35
3-4
3-4
3-4
3-4
3-5-4
3-5-4

142
404
4OI

451
247
237
137
134
236

350
256

182

251

143
214

257
271

238
24I

239
450
446

451
398
229
223

Red

Alunite

Rhodochrosite

Clintonite

Chabazite

Harmotome . . .

Xenotime

Apophyllite . . .
WoUastonite . .

Apatite

Huebnerite

Analcite

Natrolite

Thomsonite . . .

Datolite

Titanite

Monazite

Cancrinite. . . .

Nephelite

Enstatite

Diopside

Rhodonite ....
Willemite

35-4
3-5-4
^. 5-4.

230

244

87
220

426

456

449

447
265

254

443
368

266

258

458

454

455

334

464
263

3IS
314
365
372
380
306

Red

Laumontite. . .

Gypsum

Thenardite. . . .

Sylvite

Halite

Glauberite ....
Phlogopite ....

Stolzite

Gibbsite

Kainite

Cryolite

Calcite

Vanadinite. . . .

Barite

Stilbite

Heulandite. . . .
Laumontite. . .
Serpentine ....

Dolomite

Aragonite

3-5-4
4-5
4-5'
4-5
4-5
4-5
4-5
45-5
4-5-5
45-5
45-5
5-5
5-5
5-5
5-5
5-5
5-5-
5-6
5-6
5-6
5-6
5-6
5-6

3
5
5
•5
5
5
5

APPENDICES

509

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (Con.)

Color

Red

Yellow

Name

Hardness

Troostite. . . .

Opal

Perovskite . . .
Amblygonite .
Orthoclase . . .
Chondrocyte. .

Zoisite

Axinite

Epidote

Diaspore

Vesuvianitc . .
Garnet 6

5-6
5-6

5-6
6
6-6
6-6
6-6
6-7
6-7
6-7
6-5
5-7

Cerargyrite . .
Carnallite. . . .
Pyrophyllite. .

Tripolite

Kaolinite ....

Talc

Chrysotile . . .
Orthoehlorite .

Gypsum

Sulphur

Hanksite ....

Sylvite

Halite

Muscovite. . .
Phlogopite . . .
Gaylussite. . .
Zinnwaldite . .
Glauberite. . .
Leadhillite . . .

Kainite

Trona <2.

Gibbsite ....

Barite

Calcite

Kieserite. . . .
Wulfenite. . .

i-i-5

1-2
1-2

1-2 5
1-2-5

1-2-5
i-3
i-3
5-2

5-2-5

2-2.5

I
2-2-5;

2-3
2S
2-3

2-5
25
2-5

5-3
5-3.5

5-3-5
3
3
3

Ref.
Page

306

179
461

274

413

333
326

345

327
190

432
312

138
142

406

180
404
401

398

429

247

47
252

137
134
355
350

235
352
236
252

251

235
182

239
214
246

257

Color

Red

Yellow

Name

Hardness

Quartz

Boracite

Danburite. .
Tourmaline .
Cordierite. . .
Phenacite. . .

Zircon

Beryl

Spinel

Topaz

Chrysoberyl.
Corundum . .

7-7
7-7 ■
7-7
7-8

5-8

8.5
9

Vanadinite. . .

Celestite

Anglesite ....
Cerussite. . . .
Heulandite. . .

Stilbite

Laumontite. .
Serpentine . . .
Margarite. . . .

Wavellite

Dolomite. . . .
Aragonite. . . .
Strontianite. .
Sphalerite. . . .
Pyromorphite
Mimetite. . . .
Rhodochrosite
Magnesite. . .

Fluorite

Chabazite. . . .
Harmotome . .
Phillipsite. . . .
Xenotime. . . .

Scheelite

Wollastonite .

3
3-35
3-3-5
3-3-5
3-4
3-4
3-4
3-4
3-45
35-4
5-4
•5-4
■5-4
3-5-4
-5-4
5-4
5-4-
-5-5

4
4-5
4-5
4-5
4-5
4-5
5-5

4-5-

Ref.
Page

159
2IO

325

434

438

307

317

359
196

3*2
202

155

271

241
242
227
446
450
451
398
352
287
229
223
225

87
270

271

220

218

139

456

449

447
265

254
368

510

APPENDICES

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (Con.)

Color

Name

Hardness

Ref.
Page

Color

Name

Hardness

Ref.
Page

Apatite

Huebnerite. . . .
Lithiophylite . .
Smithsonite . . .

Natrolilc

Thomsonite . . .

Datolite

Titanite

Monazite

Wagnerite. . . .

Sodalite

Cancrinite. . . .
Nephelite

Rhodonite. . . .

4-5-5

4-5-5
5
5-5-5
5-5 ■ 5
5-5-5
5-5-5
5-5-5

5-5-5
5-6
5-6
5-6

5-6
5-6

266
396
258
262
221

454

455

334

464
263

273
340

315
314
423

380

404
281

137
134
181
441

246

239
214
182

238
241
242
223
287

285

139

393
266

396
262

Yellow

Willemite

Opal

5-6

5-4
6-6.5

6HS.5
6-7

6-7
6-7

6-75
6-5-7
6-5-7
7

7-75

75
8

8
9

306

179

413

333

327
171

168

320

303
312

159

434

317
322

196
155

Yellow

Orthoclase. . . .
Chondrodite. . .

Rutile

Cassiterite ....
Andalusite ....
Olivine

Quartz

Tourmaline. . .

Topaz

Spinel

Corundum ....

Blue

Kaolinite

Vivianite

Sylvite

Halite

Brucite

Chrysocolla. . .
Chalcanthite. .

Barite

Calcite

Gibbsite

Anglesite

Wavellite

Skorodite

Fluorite

Calamine

1-2.5
1-2.5

2-2.5

2-4

2-5
2-5-3 5

3
3-3-5
3-35
3-35
3-35

1-5-4

3-5-4

3-5-4
4
4-5

L5-5

45-5

Blue

Smithsonite . . .

Lazulite

Hatiynite

Sodalite

Cancrinite ...

Nephelite

Scapolite

Willemite

Opal

5-5-5

5-5-5
5-6

5-6

5 5-6
6

6-6.5
6-7
6-7
6-7
6-7

7
7-75

221

343
275
34i
340

315
314

423
306

372
170

Turquoise

Amblygonite. .
Glaucophane . .

Axinite

Diaspore

Kyanite

Vesuvianite. . .

Quartz

Boracite

279

274
390

345
190

393
432

159
210

438

APPENDICES

511

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (CoH.)

Color

Name

Hardness

Ref.
Page

434
359

134

214

139
266

423
386

350
271 |

Color

Name

Hardness

Ref.
Page

Blue

Tourmaline. . .
Beryl

7-7-5
7-5-8

Blue

Spinel

Topaz

Corundum ....

75-8

8
9

196
322

155

Purple

Halite

Cakite

Fluorite

Apatite

Tremolite

2-2.5

4-5-5
5-o

5-o

Purple

Quartz

Spodumene. . .

Topaz

Spinel

Corundum ....

7-7-5
8

8
9

378
322
196

155

Bronze

PMogopite ....

2-5-3

Orange

Vanadinite

Orange

Spinel

196

STREAK COLORLESS OR WHITE

White

or
Light
Gray

Soda

Cerargyrite . .
Arsenolite. . . .
Carnallite. . . .
Chrysotile. . .

Tripolite

Calcite

Talc

Pyrophyllite. .
Orthochlorite

Bauxite

Mirabilite. . . .

Niter

Soda-niter. . .

Gypsum

Vivianite. . . .
Melanterite. .
Meerschaum .

Hanksite

Thenardite. . .

Kaolinite

Borax

Epsomite ....
Sylvite

I-I 5

234

i-i -5

138

1-2

152

1-2

142

1-2.5

398

1-25

l8o

1-25

214

1-25

40I

1-25

406

i-3

429

i-3

186

i-5-2

246

1-5-2

206

1-5-2

205

i-5-2

247

*-5-2

28l

1.5-2

251

4OI !

252

237

2-2.5 404

2-2.5

207

2-2.5

250

2-2 . 5

137

White

or
Light
Gray

Halite

Brucite

Pharmacolite .
Senarmontite. .

Kainite

Muscovite

Paragonite

Zinnwaldite . . .

Grtinerite

Gaylussite. . . .

Lepidolite

Apatite

Glauberite
Claudetite

Stolzite

Trona

Cryolite

Gibbsite

Barite

Valentinite. . . .

Kieserite

Calcite

Wulfenite

Anhydrite

2-2.5

2-5

2-2.5

2-3

2-3
2-4

2-5
2-5
2-5
5-3
5-3
5-3
5-3
2-5-3
2.5-3

3
3-35

134
181

292
152
251
355
358
352
387
235

354
266

236

152
256

235

143
182

239
152
246
214

257
238

512

APPENDICES

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK COLORLESS OR WHITE — (Con.)

Color

White

or
Light
Gray

Name

Celestite

Anglesite. . . .
Cerussite. . . .
Heulandite. . .

Stilbitc

Laumontite. .
Margarite. . . .
Andulusite. . .

Alunite

Wavellite ....
Dolomite ....
Aragonite. . . .
Strontianite . .

Siderite

Ankerite

Witherite ....
Pyromorphite
Mimetite ....
Rhodochrosite
Magnesite. . .

Fluorite

Colemanite. . .
Chabazite. . . .
Apophyllite. .
Harmotome . .
Phillipsite. . . .

Pectolite

Kyanite

Scheelite

Wollastonite .

Apatite

Calamine ....
Smithsonite . .

Analcite

Thomson ite . .
Natrolite. . . .

Datolite

Scolecite

Sodalite

Cancrinite . . .

Hardness

3-3-5

3-4

3-6
•5-4
•5-4
•5-4
-5-4
•5-4
•5-4
■5-4
■5-4
■5-4
•5-4
•5-4
•5-4
4

4-5

•5-5

5-5

Ref.
Page

5-5
5-5
5-5
5-6
5-6

241
242
227
446
450

45i
352
320
244
287
229
223
225
219
230
226
270
271
220
218

134
208

456

443

449

447

369

393

254
368
266

396
221

458
455
454
334
452
340
315

Color

White

or
Light
Gray

Name

Nephelite

Scapolite

Tremolite

Anthophyllite

Enstatite

Diopside

Willemite

Gedrite

Opal

Leucite

Beryllonite. . . .
Amblygonite. .
Orthoclase. . . .
Microcline
Plagioclase. . . .

Prehnlte

Spodumene . . .
Sillimanite

Jadeite

Axinite

Zoisite

Diaspore

Kyanite

Andalusite
Californite

Garnet

Quartz

Dumortierite . .

Boracite

Cordierite

Danburite. . . .
Tourmaline. . .

Phenacite

Zircon

Beryl

Topaz

Chrysoberyl. . .
Corundum ....
Diamond

Hardness

5-6

5-4
5-6

5-6

5-6
5 5-6
5 5-6

5 5-$
5-5-6
6

6-6.5
6-6.5
6-6.5
6-7
6-7
6-7
6-7
6-7
6-7
6-7
6-7
6-7-5
6-5
6-5-7-5

7-7-5
7-7-5
7-75
7-8

75
7-5-8
8

8-5

9
10

Ref.
Page

314
423
386

443
365
372
306

3^3
179
362
263

274

413

413
418

343
378
321
377

345
326

190

393
320

434
312

159
338
210

438
325
434
307
317

359
322
202

155
37

APPENDICES

513

n. UST OF THE MORE IMPORTANT MINERALS AR-
RANGED ACCORDING TO THEIR PRINCIPAL
CONSTITUENTS

ALUMINIUM

AJbite

Epidote

Orthoclase

Alum

Feldspars

Piedmontite

Alunite

Garnet

Prehnite

Amblygonite

Gibbsite

Pyrophyllite

Analcite

Glaucophane

Sillimanite

Andalusite

Harmotome

Sodab'te

Anorthite

Heulandite

Spinel

Augite

Hornblende

Spodumene

Axinite

Jadeite

Staurob'te

Bauxite

Kaolin

Stilbite

Beryl

Kyanite

Thomsonite

Brittle micas

Laumontite

Topaz

Cancrinite

Lazulite

Tourmaline

Celsian

Lazurite

Turquoise

Chabazite

Lepidolite

Uvarovite

Chrysoberyl

Leucite

Variscite

Cordierite

Margarite

Vesuvianite

Corundum

Micas

Wavelite

Cryolite

Microcline

Zeolite

Cyanite

Natrolite

Zoisite

Diaspore

Nephelite

Many other silicates

Dumortierite

ANTIMONY

Antimony

Jamesonite

Stibnite

Bournonite

Pyrargyrite

Sulphantimonites

Breithauptite

Senarmontite

Tetrahedrite

Dyscrasite

Stephanite

ARSENIC

Valentinite

Arsenates

Enargite

Proustite

Arsenic

Erythrite

Realgar

Arsenob'te

Gcrsdorffite

Scorodite

Arsenopyrite

Lollingite

Smaltite

Chloanthite

Mimetite

Sperrylite

Claudetite

Niccolite

Sulpharsenites

Cobaltite

Olivenite

Tennantite

Domeykite

Orpiment

514

APPENDICES

BARIUM

Barite
Celsian

Harmotome
Hyalophane

BERYLLIUM

Psilomelane
Witherite

Bertrandite

Beryl

Beryllonite

Chrysoberyl
Gadolinite

BISMUTH

Herderite
Phenacite

Bismite
Bismuth

Bismuthinite
Bismutite

BORON

Sulpho-bismuthinites
Tetradymite

Axinite
Boracite
Borax
Colemanite

Danburite

Datolite

Dumortierite

BROMINE

Sassolite

Tourmaline

Ulexite

Bromyrite

Embolite

CADMIUM

Iodobromite

Greenockite
Pollucite

Actinolite

Andradite

Anhydrite

Ankerite

Anorthite

Apatite

Apophyllite

Aragonite

Asbestus

Augite

Autunite

Babingtonite

Bustamite

Calcite

Cancrinite

Carnotite

CiESIUM

CALCIUM

Chabazite

Colemanite

Danburite

Datolite

Diopside

Dolomite

Epidote

Fluorite

Gaylussite

Glauberite

Grossularite

Gypsum

Harmotome

Heulandite

Hornblende

Laumontite

Margarite

Perovskite

Phillipsite

Piedmontite

Prehnite

Scheelite

Scolecite

Stilbite

Thomsonite

Titanite

Tremolite

Uvarovite

Vesuvianite

Wollastonite

Zoisite

Many other silicates

APPENDICES

CARBON

Cancrinite '

Diamond

Hanksite

Carbonates

Graphite

CERIUM

Allanite

Monazite

Thorite

Fergusonite

Samarskite

Xenotime

Gadolinite

CHLORINE

Apatite

Cryolite

Pyromorphite

Atacamite

Halite

Scapolite

Boracite

Hanksite

Sodalite

Carnallite

Kainite

Sylvite

Cerargyrite

Mimetite

CHROMIUM

Vanadinite

Chromite

Crocoite

COBALT

Uvarovite

Cobaltite

Glaucodite

Smaltite

Erythrite i

Linnaeite

COLUMBIUM

•

Columbite

Samarskite

Tantalite

Columbates .

Polycrase

Ytrrotantalite

Fergusonite

COPPER

Atacamite

Chrysocolla

Malachite

Azurite

Copper

Melaconite

Berzelianite

Covellite

Olivenite

Bornite

Cuprite

Stromeyerite

Bournonite

Cyprine

Tennantite

Brochantite

Dioptase

Tetrahedrite

Chalcanthite

Domeykite

Tenorite

Chalcocite

Enargite

Torbernite

Chalcopyrite

Libethenite

Turquoise

DIDYMIUM

Allanite

Gadolinite

Monazite

Cerite

515

-MINERALS WITH NONMETALLIC LUSTER— (Cow.)

STREAK WHITE — (Cotl.)

Color

„„■_

Rei.

Color

Name

HirdntM

?»„=

Pink

Wagnerite ....

Sodalite

Cancrinite ....

Tremolite

Fowlerite

Rbodonite. . .
Bustamite. . . .
WUlemite

Orthoclase ....

5-5
5^
5~6
5-6
5-6
5-6
5-6
5-6
S-6
6
6-6.5

273
340
315
433
386
38o
38o

380

306
305
413

Pink

Andalusite ....

Garnet

Tourmaline. . .
Spodumene . . .
Phenacite

Corundum ....

6-6.5

1-6-7
6-7.5

6.5-7
7-7-5
7-7-5
7-8

326
327
320
312
434
378
307
322
196
'55

Camallile

Kaolinite .....

1-2.5
i-a-S

i-3

1. 5-1

2
2-3.5

2-2. s

15
2-5-3
2-5-3
2-5-3 5
2.5-4

142
404
401
451
347
237
137
134

336

350
256

182
351
143

214

2 57
271

Red

Ankerite

Alunite

Rhodochrosiie
Clintonite. ....

Chabazite

Harmotomc.. .
Phillipsile
Xenotime

Apophyllite . . .
Wollastonile . .

Apatite

Huebnerite —

Analcite

Natrolite

Thomsonite . . .

3 5-4

3-5-4

3 5-4
4-5
4-5-
4-5
4-5
4-5
4-5

4-5-5

45-5

4-5-5

4-5-5-3
5-5-5
5-5-5
5-5-5

330
244

Red

Laumontite. . .

Gypsum

Thenardite. . .

Sylvite

Halite

Glauberite ....
Phlogopite. . . .

Stolzite

Gibbsite

Kainite

Cryolite

Calcite

Wulfenite
Vanadinite. . . .

220
426
456
449
447
263
254
443
368
266
258
458
454
455

APPENDICES

509

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (Con.)

Color

Red

Yellow

Name

Hardness

Ref.
Page

< -
5

Troostite. . . .

Opal

Perovskite . . .
Amblygonite .
Orthoclase . . .
Chondroditc. .

Zoisite

Axinite

Epidotc

Diaspore

Vesuvianite. .
Garnet 6

5-6

5"6

5-6

6-6.5
6-6.5
6-6.5
6-7
6-7
6-7

6-5

5-7-5

Cerargyrite .
Carnallite. . .
Pyrophyllite.

Tripolite

Kaolinite. . . ,

Talc

Chrysotile. . .
Orthochlorite

Gypsum

Sulphur

Hanksite . . . .

Sylvite

Halite

Muscovite. . .
Phlogopite . . .
Gaylussite. . .
Zinnwaldite . .
Glauberite . . .
Leadhillite . . .
Kainite

i..s-

Trona 2 . $-

Gibbsite 2

Barite 2

Calcite ■

Kieserite

Wulfenite. . . .

1- 1. 5
1-2

1-2

1-2-5
1-2-5

1-2.5
i-3
i-3
5-2

5-2-5

2-2

2-2.5

2-3

2~3

2-3

2~3

2-5

2 5

2-5

5-3

5-3-5

306

179
461

274

413

333
326

345

327
100

432
312

138
142
406
180
404
401
398
429
247
47
252
137
134
355
350

235
352
236
252

251

235
182

239
214

246

257

Color

Name

Red

Yellow

Quartz

Boracite

Danburite. .
Tourmaline .
Cordierite. . .
Phenacite.. .

Zircon

Beryl

Spinel

Topaz

Chrysoberyl.
Corundum . .

Hardness

Ref.
Page

159

2IO

7-7-5

325

7-7-5

434

7-7-5

438

7-8

307

317

,7-5-8

359

7-5-8

196

322

8-5

202

155

Vanadinite. . .

Celestite

Anglesite. . . .
Cerussite. . . .
Heulandite. . .

Stilbite

Laumontitc. .
Serpentine . . .
Margarite. . . .
Wavellite ....
Dolomite ....
Aragonite. . . .
Strontianite. .
Sphalerite. . . .
Pyromorphite
Mimetite. . . .
Rhodochrosite
Magnesite. . .

Fluorite

Chabazite. . . .
Harmotome. .
Phillipsite. . . .
Xenotime. . . .

Scheelite

Wollastonite . .

3
3-35
3-3-5
3-3-5
3-4
3-4
3-4
3-4
3-4-5
3-5-4
5-4
•5-4
•5-4
3-5-4
■5-4
■5-4
-5-4-
•5-5

4
4-5
4-5
4-5
4-5
45
5-5

271

241
242
227
446
450
451
398
352
287
229
223
225

87
270

271

220

218

139
456

449

447
265

254
368

510

APPENDICES

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (Con.)

Color

Name

Hardness

Ref.
Page

Color

Name

Hardness

Ref.
Page

Calamine

Huebnerite. . . .
Lithiophylite. .
Smithsonite. . .

Natrolitc

Thomsonite . . .

Datolite

Titanite ......

Monazite

Wagnerite. . . .

Sodalite

Cancrinite. . . .

Nephelite

Scapolite

Rhodonite. . . .

4-5-5

45-5

45-5
5
5-55
5-5 • 5
5-5-5
5-5.5
5-5.5
5-5-5
5-6
5-6
5-6
5-6
5-6

266
396
258
262
221

454

455

334

464
263

273
340

315
314
423
380

404
281

137
134
181
441

246

239
214

182

238
241

242

223

287

285

139

393
266

396
262

Yellow

Willemite
Opal

5-6

5-6
6-6.5

6^6.5

6-7

6-75
65-7
6-5-7
7

7-7-5

75
8

8
9

306

179
413

333
327
171
168
320

303
312

159

434

317
322

196
155

Yeljow

Orthodase ....
Chondrodite. . .

Rutile

Cassiterite ....
Andalusite ....

Olivine

Garnet

Quartz

Tourmaline . . .

Topaz

Spinel

Corundum ....

Blue

Kaolinite

Vivianite

Syl viie

Halite

Brucite

Chrysocolla . . .
Chalcanthite . .

Barite

Calcite

Gibbsite

Anhydrite

Anglesite

Aragonite

Wavellite

Skorodite

Fluorite

Apatite

Calamine

1-2.5
1-2.5
2-2.5
2-2.5
2-2.5

2-4
2-5

2-5-3-5
3
3-3-5
3-3-5
3-3-5
3-3-5

35-4

3-5-4

3-5-4
4
4-5

45-5

4-5-5

Blue

Smithsonite . . .

Hatiynite

Sodalite

Cancrinite ...

Nephelite

Scapolite

Willemite

Opal

5-5-5

5-5-5
5-6

5-6
5-6
5-6
5-6

5-6

5 5-6
6
6
6-6.5

6-7
6-7

6-7

7
7
7-7-5

221

343
275
34i
340

315
314

423
306

372
170

Turquoise

Amblygonite. .
Glaucophane . .

Axinite

Diaspore

Vesuvianite. . .

Quartz

Boracite

* / y
279
274
390

345
190

393
432

159
210

438

APPENDICES

511

B.— MINERALS WITH NONMETALLIC LUSTER— (Con.)

STREAK WHITE — (Con.)

Color

Name

Hardness

Ref.
Page

Color

Name

Hardness

Ref.
Page

Blue

Tourmaline. . .
Beryl

7-75
75-8

434
359

Blue

Spinel

Topaz

Corundum ....

7-5-8
8

196
322

155

Purple

Halite

Calcite

Fluorite

Scapolite

Tremolite

2-2.5

4-5-5
5-6

5-6

134
214

139
266

423
386

350

Purple

Quartz

Spodumene. . .

Topaz

Spinel

Corundum

7-7-5
8

8
9

W9
378
322

196

155

Bronze

Phlogopite ....

25-3

Orange

Vanadinite

271 J

Orange

Spinel

196

STREAK COLORLESS OR WHITE

White

or
Light
Gray

Soda

Cerargyrite . . .

Arsenolite

Carnallite

Chrysotile. . . .

Tripolite

Calcite

Talc

Pyrophyllite. . .
Orthochlorite .

Bauxite

Mirabilite

Niter

Soda-niter. . . .

Gypsum

Vivianite

Melanterite. . .
Meerschaum . .

Hanksite

Thenardite. . . .

Kaolinite

Borax

Epsomite

Sylvite

1-1.5

234

1-1-5

138

1-2

152

1-2

142

1-25

398

1-25

l8o

1-25

214

1-25

4OI

1-25

406

i-3

429

White

i-3

186

1-5-2

246

Light

1-5-2

206

Gray

15-2

205

1-5-2

247

1.5-2

28l

1.5-2

251

40I

252

237

2-2.5

4O4

2-2.5

207

2-2.5

250

2-2 . 5

137

Halite

Brucite

Pharmacolite .
Senarmontite. .

Kainite

Muscovite. . . .

Paragonite

Zinnwaldite . . .

Griinerite

Gaylussite

Lepidolite

Apatite

Glauberite
Claudetite

Stolzite

Trona

Cryolite

Gibbsite

Barite

Valentinite. . . .

Kieserite

Calcite

Wulfenite

Anhydrite

2-2.
2.2-5
2-2.
2-2.

2-3

2-3
2-4

2-5

2-5
25-3
25-3
25-3
25-3
2.5-3
2.5-3

3-3-

134
181

292
152
251
355
358
352
387
235
354
266
236

152
256

235

143
182

239
152
246
214

257
238

520

APPENDICES

THALLIUM

Crookesite

THORIUM

Lorandite

Aeschynite
Monazite

Pyrochlore
Thorite

TIN

Uraninite
Yttrialite

Canfieldite

Cassiterite

TITANIUM

Stannite

Anatase

Astrophyllite

Brookite

Hmenite

Perovskite

Pseudobrookite

TUNGSTEN

Rutile

Schorlomite

Titanite

Ferberite
Huebnerite

Polycrase
Scheelite

URANIUM

Stolzite
Wolframite

Autunite
Carnotite

Gummite
Torbernite

VANADIUM

Uraninite
Uranophanc

Carnotite
Desdoizite

Patronite
Roscoelite

Vanadinite

YTTRIUM

Allanite

Fergusonite

Gadolinite

Samarskite
Xenotime

ZINC

Yttrialite
Yttrotantalite

Calamine
Fowlerite
Franklinite
Gahnite

Goslarite
Hydrozincite
Smithsonite
. Sphalerite

ZIRCONIUM

Troostite
Willemite
Wurtzite
Zincice

Baddeleyite

Zircon

APPENDICES

YIELDING WATER IN CLOSED TUBE

Allanite

Dufrenite

Opal

Alunite

Dumortierite

Piedmontite

Analcite

Epidote

Phaimacolite

Annabergite

Epsomite

Pharmacosiderite

Apophyllite

Garnierite

Phlogopite

Atacamite

Gaylussite

Prehnite

Autunite

Gibbsite

Psilomelane

Axinite

Glauconite

Pyrophyllite

Azurite

Goethite

Skorodite

Bauxite

Gypsum

Serpentine

Biotite

Kainite

Staurolite

Borax

Kaolinite

Steatite

Brochantite

Kieserite

Struvite

Brittle micas

Lazulite

Torbernite

Brucite

Leadhillite

Tourmaline

Calamine

Lepidolite

Topaz

Cancrinite

Libethenite

Trona

Carnalb'te

Limonite

Turquoise

Chlorites

Malachite

Variscite

Chondrodite

Manganite

Vesuvianite

Chrysocolla

Margarite

Vivianite

Chrysotile

Meerschaum

Wad

Colemanite

Micas

WaveUite

Cordierite

Mirabilite

Zeolites

Datolite

Muscovite

Zinnwaldite

Diaspore

Olivenite

Zoisite

Dioptase

521

HI. LIST OF MINERALS ARRANGED ACCORDING TO

THEIR CRYSTALLIZATION

amorphous (firobably colloidal)

Bauxite
Chrysocolla
Garnierite
Glauconite

Limonite
Opal

Psilomelane
Pyrolusite (?)

Skorodite
Turquoise
Wad

ISOMETRIC

Arsenolite (?)
Boracite above
a-Cristobalite

2650

Lasurite

Leucite above 5000

Senarmontite (?)
Uraninite

522

APPENDICES

HEXOCTAHEDRAL CLASS (Holohedral)

Altaite

Franklinite

Magnetite

Amalgam

Gahnite

Mercury

Argentite

Galena

Palladium

Bornite •

Garnet

Petzite

Cerargyrite

Gold

Picotite

Chromite

Halite

Platinum

Clausthalite

Hessite

Schorlomite

Copper

Iron

Silver

Fluorite

Lead

Spinel

DYAKISDODECAHEDRAL CLASS

(Hemihedral)

Alum

Cobaltite

Smaltite

Chloanthite

Pyrite

Sperrylite

HEXTETRAHEDRAL CLASS (Hemihedral)

Alabandite

Noselite

Sphalerite

Boracite

Pentlandite

Tetrahedrite

Diamond

Perovskite (?)

Tennantite

Hallynite

Pharmacosiderite

Tiemannite

Metacinnabarite Sodalite

PENTAGONAL ICOSITETRAHEDRAL CLASS (Hemihedral)
Cuprite Sylvite

Analcite

Breithauptite
Carnotite (?)
Covellite

PSEUDO-ISOMETRIC

Leucite

HEXAGONAL

Hanksite

Molybdenite

Niccolite

Perovskite

Pyrrhotite (?)
0 Tridymite

Beryl

DIHEXAGONAL BIPYRAMIDAL CLASS (Holohedral)

Cancrinite

DIHEXAGONAL PYRAMIDAL CLASS (Holo-hemimorphic)
Greenockite Wurtzite Zincite

HEXAGONAL BIPYRAMIDAL CLASS (Hemihedral)
Apatite Mimetite Pyromorphite Vanadinite

APPENDICES 523

HEXAGONAL PYRAMIDAL CLASS (Hemihedral-hemimorphic)
Nephelite

HEXAGONAL TRAPEZOHEDRAL CLASS (Hemihedral)

0 Quartz

DITRIGONAL SCALENOHEDRAL CLASS (Hemihedral)

Alunite

Corundum

Selenium

Antimony

Graphite

Siderite

Arsenic

Hematite

Smithsonite

Bismuth

Iridosmine (?)

Soda-niter

Brucite

Magnesite

Tellurium

Calcite

Millerite

Tetradymite

Chabazite

Rhodochrosite

DITRIGONAL PYRAMIDAL CLASS (Hemihedral-hemimorphic)
Tee Tourmaline Proustite Pyrargyrite

TRIGONAL TRAPEZOHEDRAL CLASS (Tetartohedral)
Quartz Cinnabar

TRIGONAL RHOMBOHEDRAL CLASS (Tetartohedral)

Ankerite

Phenacite

Willemite

Dioptase

Troostite

Dolomite

Umenite

TETRAGONAL

•a Cristobalite (?)

DITETRAGONAL BIPYRAMIDAL

CLASS (Holohei

Anatase

Phosgenite

Rutile

Apophyllite

Plattnerite

Vesuvianite

Bra unite ,

Polianite

Xenotime

Cassiterite

Thorite

Zircon

Hausmannite

Torbernite

TETRAGONAL SCALENOHEDRAL. CLASS (Hemihedral)
•Chalcopyrite

524

APPENDICES

TETRAGONAL BIPYRAMIDAL CLASS (Hemihedkai

Marialite

Scapolite

Wernerite

Meionite

Scheelite

Wulfenite

Mizzonite

ORTHORHOMBIC

Acanthite

Dumortierite

Samarskite

Anthophyllite (?)

Enstatite (?)

Serpentine (?)

Boracite below 26 5 °

Gedrite (?)

Steatite (?)

Bronzite (?)

Hypersthene (?)

Tan tali te

Brookite

Jamesonite

a Tridymite

Chrysotile (?)

Kaolinite (?) .

Thomsonite

Columbitc

Meerschaum (?)

Variscite

Domeykite

Perovskite (?)

Yitrotantalite

Dufrenite

Pyrophyllite (?)

•

ORTHORHOMBIC BIPYRAMIDAL CLASS (Holohedr,

Andalusite

Cordierite

Sillimanite

Anhydrite

Danburite

Skorodite

Anglesite

Diaspore

Staurolite

Aragonite

Dyskrasite

Stephanite

Arsenopyrite

Enargite

Stibnite

Atacamite

Fayalite

Stromeyerite

A11 1 unite

Forsterite

Strontianite

Barite

Glaucodot

Sulphur

Beryllonite

Goethite

Tephroite

Bismuthi nite

Libethenite

Thenardite

Bournonite

Lithiophilitc

Topaz

Brochantite

Lollingite

a Tridymite

Brookite

Manganite

Triphylite

Caraallite

Marcasite

Valentinite

Celestite

Natrohte

Wavellite

Cerussite

Niter

Witherite

Chalcocite

Olivenite

Zoisite

Chrysoberyl

Olivine

ORTHORHOMBIC BISPHENOIDAL CLASS (Hemihedral)

Epsomite

ORTHORHOMBIC PYRAMIDAL CLASS (Hemimorphic)

Bertrandite Prehnite Struvite

Calamine Stephanite

APPENDICES

525

MONOCLIrUC

Anthophyllite (?)

Antigorite

Bronzite (?)

Chlorites

Chloritoid

Clinochlore

Clintonite

Durangite
Enstatite (?)
Gedrite (?)
Gibbsite
Herderite
Hyper st hene (?)
Kaolinite (?)

Meerschaum (?)
Natron
Penninite
Prochlorite
Pyrophyllite (?)
Serpentine (?)
Steatite (?)

MONOCLINIC PRISMATIC CLASS (Holohedkal)

Acmite

Actinolite

Adularia

Algirine

Allanite

Annabergite

Anomite

Amphibole

Arfvedsonite

Augite

Azurite

Barbierite (?)

Barytocalcite

Biotite

Borax

Brushite

Calaverite

Celsian (?)

Chondrodite

Claudetite

Clinochlore

Clinohumite

Colemanite

Crocidolitc

Crocoite

Cryolite

Cummingonite

Datolite

Diopside

Dufrenoysite

Epidote

Erythrite

Fassaite

Ferberite

Gadolinite

Gaylussite

Glauberite

Glaucophane

Griinerite

Gypsum

Harmotome

Hedenbergite

Heulandite

Hornblende

Huebnerite

Hyalophcnc (?)

Jadeite

Kainite

Kieserite

Laumontite

Lazulite

Leadhillite

Lepidolite

Lepidomelane

Malachite

Margarite

Melanterite

Meroxene

Mirabilite

Monazite

Muscovite

Orpiment

Orthoclase (?)

Paragonitc

Pearceitc

Pectolite

Pharmacolite

Phillipsite

Phlogopite

Piedmontite

Polybasite

Realgar

Riebeckite

Sahlite

Schefferite

Spodumene

Stilbite

Titanite

Tremolite

Triplite

Trona

Vivianite

Wagnerite

Wolframite

Wollastonite

Zinnwaldite

Scolecite

MONOCLINIC DOMATIC CLASS (Hemihedral)

526 APPENDICES

TRICLINIC

Aenigmatite Fremontite Montebrasite

Amblygonite Melaconite Turquoise

TRICLINIC PINACOIDAL CLASS (Holohedral)

Aenigmatite Babingtonite Labradorite

Albite Bustamite Microcline

Andesine Bytownite Oligoclase

Anemousite Celsian (?) Orthoclase (?)

Anorthite Chalcanthite Rhodonite

Anorthoclase Fowlerite

Axinite Kyanite

IV. REFERENCE BOOKS

General Texts
Handbuch der Mineralogie, by Dr. Carl Hintze. Vdt & Comp., Leipzig, 1897. —

(2 volumes).
System of Mineralogy (6th edition), by E. S. Dana. John Wiley & Sons, New York,

1892. 1st Appendix, 1899. 2d Appendix, 1009. 3d Appendix, 1916.
Useful Minerals of the United States, by S. Sanford and R. W. Stone. U. S.

Geological Survey. Bulletin No. 624. Washington, D. C, 191 7.

Determinative Tables
Determinative Mineralogy with Tables, for the Determination of Minerals by

Means of Their Chemical and Physical Characters, by J. V. Lewis. John Wiley

& Sons, New York, 1913.
Manual of Determinative Mineralogy (16th edition), by Geo. J. Brush and S. L.

Penfield. John Wiley & Sons, New York, 1906.
Tables for the Determination of Minerals, by £. H. Kraus and W. F. Hunt.

McGraw-Hill Book Co., New York, 191 1.

Crystallography

Crystallography, by T. L. Walker. McGraw-Hill Book Co., New York, 1913.
Elementary Crystallography, by W. S. Bayley. McGraw-Hill Book Co., New

York, 1 910.
Essentials of Crystallography, by E. H. Kraus, George Wahr, Ann Harbor, Mich.,

1006.
Grundriss der Kristallographie, by Dr. G. Linck. Verlag von Gustav Fischer,

Jena, 1913.

Physical Properties

Optical Properties of Crystals, by P. Groth. Translated by B. H. Jackson. John
Wiley & Sons, New York, 1910.

Physikalische Krystallographie (4th edition), by P. Groth. Wilhelm Engelmann,
Leipzig, 1905.

Rock Minerals (2d edition), by Jos. P. Iddings. John Wiley & Sons, New York,
1911.

Petrographic Methods, by E. Wcinschenk. Translated by R. W. Clark. McGraw-
Hill Book Co., New York, 191 2.

Chemical Properties

Handbuch der Mineralchemie, 4 volumes, edited by C. Doelter. Theodor Stein*

kopff, Dresden and Leipzig, 191 2.
Chemische Krystallographie, by P. Groth. Wilhelm Engelmann, Leipzig, 1906,

1008, 1910.
The Data of Geochemistry, by F. W. Clarke. Bulletin No. 616. U. S. Geological

Survey, Washington, 19 16.

527

528 REFERENCES

Origin and Associations
Economic Geology (4th edition), by Heinrich Ries. New York, 1016.
The Examination of Prospects, by C. G. Gunther. McGraw-Hill Book Co., New

York, 191 2.
Gems and Minerals, by 0. C. Farrington. A. W. Mumford, Chicago, 1903.
The Nature of Ore Deposits (2d edition), by Dr. R. Beck. Translated by W. H.

Weed. McGraw-Hill Book Co., New York, 191 1.
The Non-Metallic Minerals, by G. P. Merrill. John Wiley & Sons. New York, 1910.
Mineral Deposits, by W. Lindgren. McGraw-Hill Book Co., New York, 1913.

Alterations.
A treatise on Metamorphism, by C. R. Van Hise. U. S. Geological Survey, Mono-
graph, VoL 47, 1904. Washington, D. C.
A Treatise on Rocks, Rock-weathering, and Soils, by G. P. Merrill. The
Macmillan Co., New York, 1906.

GENERAL INDEX

Acid arsenates, 292.
Acid phosphates, 279, 292
Acid silicates, metasilicates, 397

orthosilicates, 343
Acids, silicic, 300
Albite twinning, 419
Alkali amphiboles, 390
Alkali feldspars, 413
Alkali micas, 353
Alkali pyroxenes, 375
Alteration of minerals, 30
Alteration pseudomorphs, 31
Alum group, 246, 251
Aluminates, 195
Aluminium, tests for, 483
Aluminosilicic acids, 301
Analyses, calculation of, 4

records, of, 6
Analysis, blowpipe, 12, 467
microchemical, 13
wet, 4
Andalusite group, 319
Anhydrous arsenates, 261

basic, 274
Anhydrous carbonates, 212

basic, 231
Anhydrous metasilicates, 359
orthosilicates, 302
polysilicates, 426
trimetasilicates, 408
Anhydrous phosphates, 261

basic, 274
Anhydrous sulphates, 236
Antimonides, 68, 77
metallic, 77, 100
Antimony, tests for, 483
Apatite group, 266
Aragonite group, 223
Arrow-head twin, 248
Arsenates, 261
anhydrous, 261

Arsenates, anhydrous, basic, 274

normal, 261
hydrated, 281

basic, 274, 286

normal, 281
Arsenic group, 49
Arsenic, tests for, 483
Arsenides, 68, 77

metallic, 77, 100
Arsenolite-claudetite groups 151
Atmospheric water, deposits from, 20
Atomic weights, 6

Barite group, 238

Barium, tests for, 483

Basic arsenates, 274

Basic anhydrous arsenates, 274

Basic anhydrous carbonates, 231

Basic anhydrous phosphates, 274

Basic carbonates, 231

Basic hydrated arsenates, 286

Basic hydrated phosphates, 286

Basic metasilicates, 393

Basic orthosilicates, 319

Basic phosphates, 274

Basic silicates, metasilicates, 393

orthosilicates, 319
Basic sulphates, 243
Basic sulpho-salts, 124
Basic vanadates, 288
Baveno twinning, 411
Beads, 476

borax, 476

microcosmic salt, 477
Bellows, 468
Bismuth, tests for, 484
Blende group, 87
Blowpipe tests for aluminium, 483

antimony, 483

arsenic, 483

barium, 483

529

530

GENERAL INDEX

Blowpipe tests for bismuth, 484

boron, 484

bromine, 484

cadmium, 484

calcium, 485

carbonates, 485

chlorine, 485

chromium, 485

cobalt, 485

columbium, 485

copper, 486

fluorine, 486

gold, 486

iodine, 487

iron, 487

lead, 488

lithium, 488

magnesium, 488

manganese, 488

mercury, 489

molybdenum, 489

nickel, 489

nitric acid, 489

oxygen, 490

phosphoric acid, 490

potassium, 490

selenium, 490

silicon, 490

silver, 491

sodium, 491

strontium, 491

sulphur, 491

tantalum, 491

tellurium, 491

thallium, 492

tin, 492

titanium, 492

tungsten, 492

uranium, 493

vanadium, 493

zinc, 494

zirconium, 494
Blowpipes, 468
Blowpipe analysis, 12, 467
Blowpipe apparatus, 469
Blowpipe flame, 470

oxidizing, 470

reducing, 470
Blowpipe reagents, 469

Bonanza, 21
Borates, 205, 206
Borax beads, 476
Boron, tests for, 484
Brittle micas, 426
Bromides, 134
Bromine, tests for, 484

Cadmium, tests for, 484
Calcite group, 213
Calcite-aragonite group, 2x2
Calcium micas, 352
Calcium, tests for, 485
Calculation of analyses, 4
Calculation of formulas, 6, 10
Caliche, 205
Carbonates, 212

anhydrous, 212
normal, 212
basic, 231

hydrous, 234
Carbonates, tests for, 485
Carbon group, 37
Carlsbad twinning, 410, 419
Cerargyrite group, 137
Chalcocite group, 84
Charcoal, use of, 473
Chemical pseudomorphs, 32
Chemical substances as minerals, x
Chlorides, 134, 142
Chlorine, tests for, 485
Chlorite group, 428
Chondrodite group, 332
Chromates, 253
Chromites, 195
Chromium, tests for, 485
Cinnabar group, 97
Classification of minerals, 15
Clay ironstone, 154
Closed tube, use of, 471
Cobalt, tests for, 485
Cockscomb twin, no
Colored beads, 476, 477
Colored flames, 477
Columbates, 293
Columbium, test for, 485
Combined water, n
Composition of minerals, 4
I Composition of water of Atlantic Ocean, 23

GENERAL INDEX

531

Composition o! water of Borax Lake, 23

Dead Sea, 23

Great Salt Lake, 23

Goodenough Lake, 23

Lake Beisk, 23
Contact minerals, 25
Copper test, 480
Copper, tests for, 486
Corundum group, 152

Datolite group, 334
Decomposition, of rocks, 29

of minerals, 30
Deposits from atmospheric water, 20

hot springs, 22

lakes, 22

magmatic water, 2$

ocean, 22

springs, 21
Detection of alkalies, 479
Detection of alkaline earths, 479
Detection of elements by flame colors,

478
Determinative mineralogy, 467

Diantimonides, 100

Diarsenides, 100

Diaspore group, 189

Differentiates, 25

Dike, 28

Dioxides, 158

Diselenides, 100

Disulphides, 68, 100

Ditellurides, 100

Dolomitic limestone, 229

Double carbonates with sulphates, 251

Double chlorides, 142

Double chlorides with sulphates, 251

Double sulphates, 251

with carbonates, 251

with chlorides, 251
Double fluorides, 142
Druse, 21, 28
Dyskrasite group, 77

Eclogite, 391

Elbow twin, 172, 173, 317

Elements, 36

Epidote group, 326

Epsonite group, 246, 249

Feldspar group, 408
Ferrites, 195
Flames:

blowpipe, 470

candle, 470

colored, 477

oxidizing, 470

reducing, 470
Fluorides, 134, 139, 142"
Fluorine, tests for, 486
Formation of minerals, 17
Formulas, calculation of, 6, 10

Galena group, 78

Garnet group, 308

Genthite, 400

Geodes, 29

Glanz group, 100

Gold group, 53

Gold, tests for, 486

Gossan, 104, 185

Guide to descriptions of minerals, 495

Honestone, 165

Hot springs, deposits from, 22

Hydrated arsenates, 281

acid, 292

basic, 286

normal, 281
Hydrated carbonates, 234
Hydrated phosphates, 281

acid, 292

basic, 286

normal, 281
Hydrated silicates, 441
Hydrated sulphates, 246
Hydroxides, 179

Impregnations, 29
Iodides, 134
Iodine, tests for, 487
Iron, tests for, 487

Key to mineral descriptions, 497
with metallic luster, 497
with nonmetallic luster, 501

Lake George diamonds, 164
Lakes, composition of water of, 23
deposits from, 20

532

GENERAL INDEX

Lead, tests for, 488
Limestone, 216

dolomitk, 229
Lists of minerals according to compo-
sition, 513

according to crystallization, 521
List of reference books, 527
Lithium, tests for, 488
Lithium-iron micas, 352
Lithographic stone, 216

Magmatic water, 23

Magnesium - calcium - iron amphiboles,

384
Magnesium-calcium-iron pyroxenes, 370

Magnesium-iron micas, 349

Magnesium tests for, 488

Manebach twinning, 411

Manganese, tests for, 488

Manganites, 195

Marble, 216

Marcasite group, 109

Mechanical pseudomorphs, 32

Melanterite group, 246, 249

Mercury, tests for, 489

Metallic antimonides, 77, 100

Metallic arsenides, 77, 100

Metalloids, 37

Metals, 52

Metamorphism, 24

contact, 25

dynamic, 26
Metasilicates, 359

anhydrous, 359
normal, 359
basic, 393
acid, 397
Metasomatism, 24, 25
Mica group, 348
Mica twinning, 344, 427, 430
Microchemical analysis, 13
Microcosmic salt beads, 477
Millerite group, 04
Mineral names, 36
Molybdates, 253, 254
Molybdenum, tests for, 489
Monoantimonides, 77
Monoarsenides, 77
Monoclinic anphiboles, 382, 384

Monoclinic pyroxenes, 367
Monoselenides, 77
Monosulphides, 68, 69, 77
Monotellurides, 77
Monoxides, 146

Nelsonite, 269
Nepheline group, 313
Nickel, tests for, 489
Nitrates, 205
Nitric acid, tests for, 489
Non-metals, 37

Occurrence, of minerals, 28
Ocean, composition of water of, 23

deposits from, 22
Oilstone, 165
Olivenite group, 277
Olivine group, 302
Oolitic ore, 154
Open tube, use of, 472
Organic secretions, 26
Origin of minerals, 17
Orthorhombic amphiboles, 382, 383
Orthorhombic pyroxenes, 365
Orthosilicates, 302
anhydrous, 302

normal, 302

basic, 319

acid, 343
Ortho sulpho-salts, 117
Oxides, 146
Oxidized zone, 33
Oxychlorides, 144
Oxidizing flame, 470
Oxygen, tests for, 490

Pangenesis, 26
Paramorphs, 31
Partial pseudomorphs, 31
Pennine twinning, 429, 430
Pericline twinning, 420
Phosphates, 261
anhydrous, 261

acid, 279

basic, 274
hydrated, 281

acid, 292

basic, 286

GENERAL INDEX

533

Phosphoric acid, tests for, 490
Placer, 29

Platinum-iron group, 63
Pneumatolysis, 17, 25
Pneumatolytic products, 25
Polysilicates, anhydrous, 426
Potash-barium feldspars, 416
Potassium, tests for, 490
Precipitation, 18, 20

from atmospheric water, 20

from magmas, 25

from ocean, 22

from solutions, 18

from springs, 21
Primary minerals, 17
Pseudomorphs, 30

alteration, 31

chemical, 32

mechanical, 32

partial, 31
Pseudowollastonite, 369
Pyrargyrite group, 117
Pyrite group, 101

Quartz! te, 165

Record of analyses, 6
Reducing flame, 470
Reduction tests, 482
Rhombic section, 420
Rutile group, 168

Sandstone, 165
Scapolite group, 423
Scheelite group, 254
Screens, 477, 478
Secondary enrichment, ^$f 34
Selenides, 68, 69
of the metalloids, 69
of the metals, 77, 100
Serpentine group, 397
Sesquioxides, 151
Silica, 158
Silicates, 300
anhydrous,
metasilicates, 359
orthosilicates, 302
trimetasilicates, 408
polysilicates, 426

Silicates, hydrated, 441
Silica group, 158
Silicates, hydrated, 441
Silicic acids, 300
Silicon, tests for, 400
Silver, tests for, 491
Soapstone, 401
Soda-lime feldspars, 417
Sodalite group, 339
Sodium, tests for, 491
Solidification of magmas, 25
Solubility of minerals,

in water, 18, 19

in carbonated water, 20
Spearhead twin, no
Sphalerite group, 87
Spinel group, 195
Spinel twinning, 196
Springs, deposits from, 21
Stalactite, 21, 216
Stalagmite, 216
Stibnite group, 72
Strontium, tests for, 491
Sulphantimonates, 116, 122
Sulphantimonites, 116, 117
Sulpharsenates, 116, 122
Sulpharsenites, 116, 117
Sulphates, 236

anhydrous, 236
basic, 243 '
normal, 236

hydrated, 246
Sulphdiantimonites, 122
Sulphdiarsenites, 122
Sulphides, 68

of metalloids, 69

of metals, 77, 100
Sulpho-ferrites, 116, 129
Sulpho-salts, 116

basic, 124

ortho, 117
Sulphur group, 47
Sulphur, tests for, 491
Swallow-tail twin, 247
Sylvanite group, 113
Synthesis, 15

Tantalates, 293
Tantalum, tests for, 491

534

GENERAL INDEX

Table of atomic weights, 7
Tellurides, 68, 69

of metalloids, 69

of metals, 77, 100
Tellurium, tests for, 491
Tests with cobalt solution, 480

with HC1, 482

with HKSO4, 481

with magnesium ribbon, 482

with metallic zinc, 482

with Na,CO , 480
Tetradymite group, 75
Tetrahedrite group, 126
Thallium, tests for, 492
Tin, tests for, 492
Titanates, 461
Titanium, tests for, 492
Titano-silicates, 461
Triclinic amphiboles, 383, 393
Triclinic pyroxenes, 365, 380
Trimetasilicates, 408
Tungstates, 253, 254
Tungsten, tests for, 492

Ultramarine, 343
Uranates, 293
Uranite group, 288
Uranium, tests for, 493

Vanadates, 261
normal, 261

Vanadates, basic, 288
Vanadium, tests for, 493
Vadose water, 21
Veins, 21, 24, 27, 28
Verd-antique, 399
Visor- twin, 169
Vitriol group, 249
Vivianite group, 281

Wagnerite group, 273

Water, atmospheric, deposits from, 20

Water, carbonated, solubility of minerals

in, 20
Water, combined, ix

Water, lakes and ocean, composition of, 23
Water, magmatic, 23
Water of crystallization, 11
Water, solubility of minerals in, 18, 19, 20
Water, vadose, 21
Weathering, 32
Whetstone, 165
Willemite group, 306
Wolframite group, 258
Wollastonite subgroup, 368
Wurtzite group, 90

Zeolite group, 445
\. Zinc, tests for, 494
Zircon group, 316
Zirconium, tests for, 404
Zone of secondary enrichment, 33

INDEX OF MINERALS

The italicised figures are the numbers of the pages on which the principal descrip-
tions appear.

Achroite, 436

Acmite, 365, 375, 506, 507

Actinolite, 382, 386, 506, 507

Adularia, 414

Aegirihe, 365, 375

Aegirine-augite, 375

Aenigmatite, 383, jpj

Agalmatolite, 406

Agate, 164

Aguilarite, 78

Alabandite, 87, go, 500

Alabaster, 248

Albite, 301, 408, 409, 4i3i 417, 4i8, 419

Algodonite, 78

Allanite, 326, 330, 408, 500, 501, 502,

504, 506
Allopalladium, 66

Allophane, 404

Almandite, 309 312

Alstonite, 231

Altaite, 79, 84, 501

Alum, 246, 251

Alunitc, 243, ^44, 5°7, 5°8> 5™

Amalgam, 53, 63, 501

Amazonite, 415

Amber mica, 350

Amblygonite, 274, 503, 506, 507, 509,

Amesite, 428
Amethyst, 164
Oriental, 156
Amphiboloids, 363
Amphiboles, 363
Analcite, 446, 458> 5°8, 5"
Anatase, 167, 176, 500, 501, 504, 506
Andalusite, 319, 320 , 506, 507, 508, 512
Andesine, 417 418
Andradite, 309, 312
Anemousite, 408, 418
Anglesite, 238, 242, 505, 508, 509, 510, 512

Anhydrite, 238, 5°4, 5°6» 5°8» S*o, 5"

Ankerite, 230, 504 ,508, 512

Annabergite, 281, 283, 504, 506

Anomite, 34Q

Anorthite, 301, 408, 409, 417, 418

Anorthoclase, 413, 418

Anthracite, 45

Anthophyllite, 382, 383, 505, 507

Antigorite, 398, 428

Antimony, 49, 51, 500, 501

Apatite, 261, 266, 504, 505, 507, 508,

510,511,512
Apophyllite, 19, 443, 507, 508, 512
Aquamarine, 361
Aragonite, 21, 26, 31, 212, 22 3, 505, 506,

508, 509, 510, 512
Arfvedsonite, 383, 390, 392
Argentite, 31, 78, 79, 497
Ante, 94

Arsenic, 49, $0, 497
Arsenolite, 151, 132, 511
Arsenopyrite, 1 01, 111, 497
Asbestos, 386, 398
Atacamite, 144, 504
Augite, 365, 370, 374, 500, 501, 503,

504, 506, 507
Autunite, 288, 280, 503
Aventurine, 164

Axinite, 345, 506, 507, 509, 510, 512,
Azurite, 231, 233, 504

Babingtonite, 365, 380, 506

Baddeleyite, 167

Baltimorite, 398

Barbierite, 408, 413

Baricalcite, 223, 231

Barite, 238,230, 505, 506, 508, 509, 510,511

Barium orthoclase, 416

Barytocalcite, 231

Bauxite, 186, 502, 503, 511

535

536

INDEX OF MINERALS

Beaumontite, 447

Beryl, jjp, 507, 509, 511, 512

Beryllonite, 263, 512

Biotite, 349, 500, 501, 504, 505, 506

Bismuth, 49, 50, 500

Bismuthinite, 72, 74, 497

Blende, 87

Bloodstone, 164

Blue beryl, 361

Bobierite, 281

Bog iron, 185

Boracite, 207, 2/0, 506, 507, 509, 510, 512

Borax, 207, 209, 221, 511

Bornite, 129, 130, 497

Bort, 39

Bortz, 39

Bournonite, 117, 120, 497

Brandisite, 426

Braunite, 204, 497, 498

Brazilian chrysolite, 436

Brazilian emerald, 436

Brazilian pebble, 164

Brazilian sapphire, 436

Breithauptite, 04, 05, 409

Brittle micas, 426

Brochantite, 243 245, 504

Broggerite, 298

Bromargyrite, 137

Bromlite, 231

Bronzite, 365, 505, 507

Brookite, 167, 176, 498, 409, 500, 501,

502, 503, 504, 506
Brown clay ironstone, 185
Brown hematite, 183
Brucite, 2, 12, 181 , 506, 510, 511
Brushite, 292
Brucklandite, 329
Bustamite, 365, 380, 508
Bytownite, 417, 418

Cabrerite, 281

Cacholong, 180

Cairngorm stone, 164

Calamine, 396, 505, 506, $10,512

Calaverite, 114, 497, 499, 500

Calcite, 4, 19, 21, 26, 30, 31, 32, 212, 213,

21 4> 504, 50S, S07, S08, 509, 5ic, S"
Californite, 433, 434» 5"
Cancrinite, j/j, 507, 508, 510, 512

Carbonado, 39

Carnallite, 142, 505, 508, 509, 511

Carnegieite, 314, 408, 418

Carnelian, 164

Carnotite, 288, 290

Cassiterite, 167, 168, 498, 499, 500, 501,

502, 505* S06, 510
Cat's-eye, 393

Celestite, 238, 241, 508, 509, 510, 512
Celsian, 408, 409, 416
Cerargyrite, 134, 137, *J*i 5°5» 506, 5«o,

Cerussite, 223, 227, 321, 504, 509, 512

Ceylonite, 196, 197

Chabazite, 446, 456, 505, 508, 509, 512

Chalcanthite, 246, 510

Chalcedony, 159, 164

Chalcocite, 84, 497

Chalcotrichite, 148

Chalcopyrite, 116, 129, 131, 497

Chalk, 216

Chathamite, 108

Chert, 165, 180

Chiastolite, 321

Chile saltpeter, 205

Chloanthite, 101, 108, 497

Chlorapatite, 266

Chlorastrolite, 345, 456

Chlorite, 37, 428, 405, 506

Chloritoid, 426, 427, 504, 505. 507

Chloromelanite, m

Chlorophane, 140

Chlorophyll ite, 439

Chlorspinel, 196

Chondrodite, 332, 333, 506, 509, 510

Chrome diopside, 372

Chrome spinel, 197

Chromite, 100, 195, 196, 200, 498, 501

Chrysoberyl, 202, 506, 507, 509, 512

Chrysocolla, 44 1, 502, 504, 506, 510

Chrysolite, 302

Chrysolite, Brazilian, 436

Chrysoprase, 164

Chrysotile, 398, 505, 506, 509, 511

Cinnabar, 22, 97, 98, 499, 502

Citrine, 164

Claudetite, 151, 152, 511

Clausthalite, 79, 84, 497

Clay, 405 -

INDEX OF MINERALS

537

Clcvcite, 298
Clinochlore, 429, 430
Clinohumite, 332
Clinozoisite, 326
Clintonite, 426, 505, 508
•Cobaltite, 101, 106 , 497
Colemanite, 207, 208, 512
Columbite, 293, 497, 49$, 499
Coloradoite, 97
. Comptonite, 4$$
Cookeite, 355
Copper, 31, 32, 52, S3* 499
Copper pyrites, 131
Cordicrite, 438, 509, 510, 512
Corundophyllite, 429
Corundum, 152, 155, 497, 498, 501, 506,

507,508.5091510.511,512
Covellite, 96 } 497
Cristobalite, 158
Crocidolite, 383, 391, 392, 504
Crocoite, 253, 502, 503
Cryolite, 3, 143, 508, 511
Cryophyllite, 353
Cumatolite, 379
Cummingtonite, 382, 387, 507
Cuprite. 2, 32, 147, 498, 499, 501, 502
Cuprotungstite, 254
Cymatolite, 379
Cyprine, 434

Damourite, 357

Danburite, 319, 320, 325, 506, 509, 512

Datolite, 334, 505, 507, 508, 510, 512

Delessite, 432

Delvauxite, 276

Demantoid, 312

Diallage, 374

Diamond, 37 ; 505, 506, 512

Diaspore, 189, igo, 506, 507, 509, 512

Dichroite, 438

Diopside, 365, 370, 372, 505, 507, 508,

510,512
Dioptase, 347 y 504
Dipyr, 424
Disthene, 319, 393
Dog-tooth spar, 214, 215
Dolomite, 229, 504, 5°5> 508, 509, 512
Domeykite, 78, 497
Dry-bone ore, 221

Dufrenite, 274, 275, 498, 504
Dufrenoysite, 122
Dumortierite, 338 ', 504, 512
Dyskrasite, 77,78, 500
Dysluite, 196

Edenite, 388

Electrum, 59

Eleolite, 314

Emerald, 361

Emerald, Brazilian, 436

Emerald, Oriental, 156

Emery, 155, 156

Enargite, 116, 122, 123, 497

Enstatite, 365, 505, 507, 508, 512

Epidote, 526, 327, 505, 506, 507, 508,

509, 510
Epsomite, 246, 249, 250, 51 z
Erythrite, 281, 282 , 502
Essonite, 309, 311
Eucryptite, 313
Eukarite, 79

Fahlunite, 439

Fairy stones, 338

False topaz, 164

Famatinite, 123

Fassaite, 374

Fayalite, 2, 302, 303, 507

Feldspars, 408

Ferberite, 258, 501

Fergusonite, 293, 498

Fibrolite, 32 r, 322

Fleches d'amour, 174

Flint, 165, 180

Flos ferri, 225

Fluorapatite, 266

Fluorite, 139, 504, 505, 506, 507, 509,

510,511,512
Fool's gold, 1C4
Forsterite, 302, joj, 507
Fowlerite, 365, 380, 506, 508
Franklinite, 190, 195, 196, ipp, 497, 498,

499
Fremontite, 274

Fuchsite, 357

Gadolmite, 334, 335, 500, 505, 506, 507
Gahnite, 196

538

INDEX OF MINERALS

Galena, 32, 79, 81, 497

Garnet, 308, 312, 501, 505, 506, 508, 509,

Garnierite, 400 y 504, 506

Gaylussite, 234, 23s, 5°9> 5"

Gedrite, 382, 383, 507, 512

Genthite, 400

Gersdorffite, 101

Gibbsite, 182, 506, 508, 509, 510, 511

Gigantolite, 439

Girasol, 180

Glanz, 100

Glauberite, 236, 507, 508, 509, 511

Glauber salt, 246

Glaucodot, 101

-Glauconite, 442, 504, 506

Glaucophane, 383, 390, 504, 510

Goethite, 2, 4, 37, 193, 498, 499> 5«>>

501, 502, 503
Gold, 19, 52, 53, 58, 409
Gold amalgam, 53
Golden beryl, 361

Graphite, 37, 44% 479> 5<». 5°i
Graphitite, 45
Greenalite, 443

Greenockite, 90, 91, 499, 503, 305
Greenovite, 465
Greensand, 442
Grossularite, 309, 311
Griinerite, 382, 387, 507, 511
Guano, 268
Gypsite, 248

Gypsum, 18, 19, 21, 22, 28, 32, 246;
247% 504, 5°5» 507i 508, 509, 511

Halite, 17, 32, 134% 5<M, 5°5> 5°6> 508,

509. 5io, 5"
Halloysite, 404

Hancockite, 326

Hanksite, 251, 252, 509, 511

Harmotome, 445> 449% 5°5> S°&> 5°9» 512
Hauerite, 101
Hausmannite, 204, 498
HaUynite, 339, 340, 341, 510
Haydenite, 457
Hedenbergite, 365, 372
Heliotrope, 164

Hematite, 17, 37, 151, 152, 153, 498,
499, 502

Hematite, brown, 183

fibrous, 154

specular, 154
Hemimorphite, 396
Hercynite, 196
Herderite, 278
Hessite, 78, 79, 500
Hessonite, 309, 311

Heulandite, 445, 446, 505, 508, 509, 512
Hiddenite, 379
Hornblende, 382, 385, 387, 498, 499,

500, 501, 502, 504, 5051 507
Horn silver, 138
Hornstone, 165
Horse-flesh ore, 130
Horsfordite, 78
Hubnerite, 258, 498, 499, 500, 502, 503,

504, 505i S<&% 5x0
Humite, 332
Hussakite, 266
Hyacinth, 311,317
Hyalite, 180
Hyalophane, 416
Hyalosiderite, 303
Hydroherderite, 278
Hydromagnesite, 234
Hydrozincite, 231
Hypersthene, 363, 500, 501, 504, 505,

507
Hyrnesite, 281

Ice, 146

Iceland spar, 216

Iddingsite, 304

Ilmenite, 25, 461, 462 , 497, 498

Infusorial earth, 180

Indicolite, 435

Iodyrite, 137

Iolite, 438

Iridium, 52, 63, 66, 501

Iridosmine, 67, 500

Iron, 52, 63, 6$, 497

Iron-platinum, 05

Jacobsite, 196

Jade, 377

Jadeite, 365, 377, 507, 512

Jalpaite, 78

Jamesonite, 122, 497

INDEX OF MINERALS

539

Jasper, 165
Jeffersonite, 373

Karaite, 251, 507, 508, 509, 511
Kalraite, 251
Kaliophilite, 313

Kaolinite, 403, 4<>4f 5°5» S«6» 5<*> 5°9»

510,511
Kaolin, 404

Katoforite, 388, 300, 391
Kieserite, 246, 511
Korynite, iox
Kottingite, 281
Kraurite, 275
Kreittonite, 196
Krennerite, 114
Kunzite, 379
Kyanite, 319, 393* 510, 512

Labradorite, 417, 41S, 504, 507

Lake George diamonds, 164

Lapis lazuli, 343

Lasurite, 339, 340, 343t 5Q4, S"

Laumontite, 445, 451, 505, 507, 508,

509, 5«
Lazulite, 274, 275, 510
Lead, 52, 53, 62, 497
Leadhillite, 251, 252, 505, 509
Lcpidolite, 353, 354, 507, 511
Lepidomelane, 349, 350
Leptochlorites, 428, 432 1 506
Leucite, 362 , 512
Libethenite, 274, 277, 278, 504
Limestone, 216
Limonite, 21, 32, 33, 183, 498, 499, 502,

503
Lintonite, 456

Lithiophilite, 262 y 505, 507, 510
Lithographic stone, 216
Lollingite, 101, 113, 497
Lucinite, 284

Magnesioferrite, 106

Magnesite, 213, 218, 504, 505, 509, 512

Magnetic pyrites, 92, 497

Magnetite, 2, 25, 37, 190, 195, 106,

198, 497
Magnoferrite,
Malachite, 12, 30, 31, 213, 231, 232, 504

Malacolite, 372

Manganapatite, 268

Manganite, 191 1 498, 499

Manganopectolite, 370

Manganotantalite, 293

Marble, 216

Marcasite, 101, iogt 497

Margarite, 332, 507, 509, 512

Marialite, 423

Martite, 154

Masooite, 428

Meerschaum, 397, 401, 511

Meionite, 423

Melaconite, 149, 497, 501

Melanite, 309, 312

Melanterite, 246, 249, 25/, 506, 511

Mercury, 52, 53 62

Meroxene, 349, 350

Metacinnabarite, 97, 100, 497

Mexican onyx, 216

Mica, 348

first order, 348

second order, 348

amber, 350
Microcline, 408, 409, 41 j, 507, 512
Microcline perthite, 415
Milky quartz, 164
Millerite, 94, pj, 497
Mimetite, 266, 27 /, 505, 512
Mirabiltte, 246 , 511
Mispickel, 111
Mizzonite, 423
Molybdenite, 75, 479, 500
Monazite, 263, 505, 508, 510
Montebrasite, 274
Monticellite, 30, 302
Montmorillonite, 404
Moonstone, 415
Muscovite, 354, 355, 505, 509, 511

Nail-head spar, 214, 215
Nakrite, 404

Natrotite, 446, 454, 508, 510, 512
Natron, 234, 233
Naumannite, 78
Neotype, 223
Nepheline, 313, 314

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