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Full text of "Dana's manual of mineralogy for the student of elementary mineralogy, the mining engineer, the geologist, the prospector, the collector, etc"

:" 5 * K E L E Y 
SARY 
JNIVERSITY OF 
CALIFORNIA 

EARTH 

SCIENCES 
LiC.v 





DANA'S MANUAL 
OF MINEBALOGY 



FOR THE STUDENT OF ELEMENTARY MINER- 
ALOGY, THE MINING ENGINEER, THE 
GEOLOGIST, THE PROSPECTOR, 
THE COLLECTOR, ETC. 



BY 

WILLIAM E. FORD 

Assistant Professor of Mineralogy in the Sheffield Scientific 
School of Yale University 



THIRTEENTH EDITION 

ENTIRELY REVISED AND REWRITTEN 
TOTAL ISSUE, THIRTY-FIVE THOUSAND 



NEW YORK 
JOHN WILEY & SONS, INC. 

LONDON: CHAPMAN & HALL, LIMITED 



EARTH 

SCIENCES 

LIBRARY 



GOPTBIGHT, 1912, 
BY 

S. DANA. AKD: WILLIAM E. FORD 



, 19t2, ( K GBEfAT BRITAIN 



Stanbopc ipreas 

H. GILSON COMPANY 
BOSTON. U.S.A. 



EARTH 

PREFACE. SCIENCES 

LIBRARY 

THE " Manual of Mineralogy " was first published by James 
D wight Dana in 1848. A second edition was printed in 1850 
and a "New Edition," which had been revised and enlarged, 
was published in 1857. The book was rearranged and rewritten 
for the third edition which appeared in 1878. This edition 
included an extensive chapter on rocks, and the title of the book 
was changed to "Manual of Mineralogy and Petrography." The 
fourth and last revision was published in 1887. Since that time 
the book has been frequently reprinted, so that the last edition 
was the twelfth. But it is now twenty-five years since the last 
revision of the text. Believing that the Manual has amply 
proved its usefulness, and with the desire of keeping the series 
of the Dana Mineralogies complete, Professor Edward S. Dana 
asked the author to prepare a new and revised edition. 

It was found that it was desirable to rewrite the book, and 
consequently, as far as the text and figures are concerned, this 
present edition is almost wholly new. The scope and character 
of the book, however, have been kept as nearly as possible the 
same. The book has been primarily designed to fill the ordinary 
needs of the elementary student of Mineralogy, the mining 
engineer, the geologist and the practical man who may be 
interested in the subject. It has been made brief and direct 
and the treatment has been as untechnical as possible. 

The chapter on Petrography has been omitted and only a 
brief and general description of the various important rock types 
given. This change was made in view of the fact that since 
1887 the subject of Petrography has had so large a development 
as to render impossible its adequate treatment in a single 
chapter. Moreover, several elementary books on the subject, 

iii 



469983 



IV PREFACE 

notably "Rocks and Rock Minerals" by L. V. Pirsson, are now 
available. Because of this, the title has been changed again to 
its original form and the book is to be known in the future as 
" Dana's Manual of Mineralogy." 

The order adopted in the description of species has been 
changed to that of the chemical classification as used in the 
System of Mineralogy. It was felt that this was, on the whole, 
the most logical and useful arrangement. Following the de- 
scription of the individual species, however, various tables are 
given, among them one in which the minerals are grouped 
according to their chief element. After each such list a general 
description of the association and occurrence of the minerals 
which it contains is given. Statistics of mineral production, 
etc., are given in Appendix II. It is intended by frequent 
revision of this portion of the book to keep the figures reasonably 
up to date. 

The author has made free use of many sources in the prepara- 
tion of the book. He is especially indebted to the sixth edition 
of "Dana's System of Mineralogy" and the "Text Book of 
Mineralogy" by E. S. Dana, to the " Brush-Penfield Deter- 
minative Mineralogy and Blowpipe Analysis " and to " Rocks 
and Rock Minerals" by L. V. Pirsson. He acknowledges 
gratefully the constant advice and criticism of Professor Edward 
S. Dana. 

SHEFFIELD SCIENTIFIC SCHOOL OF YALE UNIVERSITY, 
NEW HAVEN, CONN., June, 1912. 



INTRODUCTION. 



MINERALS are the materials of which the earth's crust consists 
and are therefore among the most common objects of daily obser- 
vation. A mineral may be defined as a naturally occurring sub- 
stance having a definite and uniform chemical composition with 
corresponding characteristic physical properties. This elimi- 
nates all artificial products of the laboratory which may conform 
to the last part of the definition. It also eliminates all natural 
products of organic agencies, since they will not show the uni- 
form chemical and physical characters demanded of a mineral. 

In the form of rocks, minerals make up the solid matter of the 
earth's crust. But in the great majority of cases a rock is not 
made up of a single mineral, but is a more or less heterogeneous 
aggregate of several different species. A few rocks, like lime- 
stone and quart zite, consist of but one mineral in a more or less 
pure state. In addition to occurring as essential and integral 
parts of rocks, minerals are found distributed through them in 
a scattered way, or in veins and cavities. Water is a mineral, 
but generally in an impure state from the presence of other 
minerals in solution. The atmosphere and all gaseous materials 
set free in volcanic and other regions are mineral in nature. 

Characters of Minerals. 

1. Minerals, as previously stated, have a definite chemi- 
cal composition. This composition, as determined by chemical 
analysis, serves to define and distinguish the species, and indi- 
cates their profoundest relations. Owing to difference in com- 
position, minerals exhibit great differences when subjected to the 
action of various chemical reagents, and these peculiarities are 
a means of determining the kind of mineral under examination 



VI INTRODUCTION 

in any case. The department of the science treating of the com- 
position of minerals and their chemical reactions is termed Chem- 
ical Mineralogy. 

2. Each mineral, with few exceptions, has its definite form, 
by which, when in good specimens, it may be known. These 
forms are cubes, prisms, pyramids, etc. They are included 
under plane surfaces arranged in symmetrical order, according 
to mathematical law. These forms are called crystals. Besides 
these outward forms there is also a distinctive internal structure 
for each species. The facts of this branch of the science come 
under the head of Crystallographic Mineralogy. 

3. Minerals differ in hardness, from talc at one end of the 
scale to the diamond at the other. Minerals differ in specific 
gravity, and this character, like hardness, is a most important 
means of distinguishing species. Minerals differ in color, trans- 
parency, luster and other optical properties. The facts and 
principles relating to the above characters and others of a similar 
nature are included in the department of Physical Mineralogy. 

4. The detailed descriptions of individual mineral species, 
including their chemical, crystallographic and general physical 
characters, together with their occurrence, associations, uses, etc., 
are included under the division known as Descriptive Mineralogy. 

5. Lastly, the discussion of the methods that are used for 
identifying minerals forms the division known as Determinative 
Mineralogy. 

These different branches of the subject are taken up in this 
book in the following order: I. Crystallographic Mineralogy; 
II. Physical Mineralogy; III. Chemical Mineralogy; IV. 
Descriptive Mineralogy; V. Determinative Mineralogy. 



TABLE OF CONTENTS. 

PAGE 

INTRODUCTION v 

I. CRYSTALLOGRAPHY. 

INTRODUCTION 1 

SYMMETRY 7 

CRYSTAL NOTATION , 9 

DEFINITION OF VARIOUS TERMS 12 

ISOMETRIC SYSTEM 16 

TETRAGONAL SYSTEM 31 

HEXAGONAL SYSTEM 37 

ORTHORHOMBIC SYSTEM 47 

MONOCLINIC SYSTEM 50 

TRICLINIC SYSTEM 54 

H. GENERAL PHYSICAL PROPERTIES OF MINERALS. 

STRUCTURE OF MINERALS 57 

CLEAVAGE, PARTING AND FRACTURE 59 

HARDNESS OF MINERALS . 60 

TENACITY OF MINERALS 62 

SPECIFIC GRAVITY OF MINERALS 62 

PROPERTIES DEPENDING UPON LIGHT 

Luster 65 

Color of Minerals 67 

Refraction of Light in Minerals 68 

Double Refraction in Minerals 71 

PYROELECTRICITY 72 

III. CHEMICAL MINERALOGY. 

CHEMICAL GROUPS 74 

DERIVATION OF A CHEMICAL FORMULA 75 

CALCULATION OF PERCENTAGE COMPOSITION 76 

ISOMORPHISM 77 

ISOMORPHOUS GROUPS 79 

DIMORPHISM, TRIMORPHISM, ETC 80 

INSTRUMENTS, REAGENTS AND METHODS OF TESTING 80 

TESTS FOR THE ELEMENTS 93 

vii 



Vlll CONTENTS 

FACM 

IV. DESCRIPTIVE MINERALOGY. 

DESCRIPTION OF SPECIES 115 

LISTS OF MINERALS ARRANGED ACCORDING TO ELEMENTS. . 309 
OCCURRENCE AND ASSOCIATION OF MINERALS 

Rocks and Rock-making Minerals 328 

Pegmatite Dikes and Veins 345 

Contact Metamorphic Minerals 347 

Veins and Vein Minerals ' 349 

LISTS OF MINERALS ARRANGED ACCORDING TO SYSTEMS OF 

CRYSTALLIZATION 354 

V. DETERMINATIVE MINERALOGY. 

INTRODUCTION 364 

DETERMINATIVE TABLES 369 

INDEX TO DETERMINATIVE TABLES 434 

APPENDIX I. LIST OF MINERALS FOR A COLLECTION 436 

APPENDIX II. MINERAL STATISTICS 437 

INDEX 451 



MANUAL OF MINERALOGY. 



I. CRYSTALLOGRAPHY. 
I. INTRODUCTION. 

THE great majority of our minerals, when the conditions of 
formation are favorable, occur in definite and characteristic 
geometrical forms which are known as crystals. To gain a com- 
prehensive knowledge of the laws which govern the shape and 
character of crystals is a very important part of the study of 
mineralogy. This division of the subject is called crystallog- 
raphy. It forms almost a separate science in itself, and to ade- 
quately and exhaustively discuss it would require a volume 
much larger than the present one. In the following section, 
however, the attempt will be made to present the elements of 
crystallography in a brief and simple manner and at least to 
introduce the reader to the more essential facts and principles 
of the subject. 

A crystal has been defined as follows: A crystal is a body which 
by the operation of molecular affinity has assumed a definite internal 
structure with the form of a regular solid inclosed by a certain num- 
ber of plane surfaces arranged according to the laws of symmetry* 
This is a very compact definition and several pages will be devoted 
to its discussion. 

A better idea of the fundamental laws of crystallography will 
be obtained by first considering the three prominent modes of 
crystallization. Crystals are formed by crystallization either 
(1) from a solution, (2) from fusion, or (3) from a vapor. The 
first case, that of crystallization from solution, is the most familiar 
to our ordinary experience. Take for example a water solution 

* Century Dictionary. 

1 



OF -MINERALOGY 

containing sodium chloride (common salt). Suppose that by 
evaporation the water is slowly driven off. The solution will, 
under these conditions, gradually contain more and more salt 
per unit volume, and ultimately the point will be reached where 
the amount of water present can no longer hold all of the salt 
in solution, and this must begin to precipitate out. In other 
words, part of the sodium chloride, which has up to this point 
been held in a state of solution by the water, now assumes a solid 
form. If the conditions are so arranged that the evaporation of 
the water goes on very slowly, the separation of the salt in solid 
form will progress equally slowly and definite crystals will result. 
The particles of sodium chloride as they separate from the solu- 
tion will by the laws of molecular attraction group themselves 
together and gradually build up a definitely shaped solid which 
we call a crystal. Crystals can also be formed from solution by 
lowering the temperature or pressure of the solution. Hot 
water will dissolve much more salt, for instance, than cold, and 
if a hot solution is allowed to cool, a point will be reached where 
the solution becomes supersaturated for its temperature and 
salt will crystallize out. Again, the higher the pressure to which 
water is subjected the more salt it can hold in solution. So 
with the lowering of the pressure of a saturated solution super- 
saturation will result and crystals form. Therefore, in general, 
crystals may form from a solution by the evaporation of the 
solvent, by the lowering of the temperature or by a decrease in 
pressure. 

A crystal is formed from a fused mass in much the same way 
as from a solution. The most familiar example of crystalliza- 
tion from fusion is the formation of ice crystals when water 
freezes. While we do not ordinarily consider it in this way, 
water is fused ice. When the temperature is sufficiently lowered 
the water can no longer remain liquid, and it becomes solid by 
crystallization into ice. The particles of water which were free 
to move in any direction in the liquid now become fixed in their 
position, and by the laws of molecular attraction arrange them- 
selves in a definite order and build up a solid crystalline mass. 
The formation of igneous rocks from molten lavas, while more 



INTRODUCTION 3 

complicated, is similar to the freezing of water. In the fluid 
lava we have many elements in a dissociated state. As the 
lava cools these elements gradually group themselves into differ- 
ent mineral molecules, which gather together and slowly crystal- 
lize to form the mineral particles of the resulting solid rock. 

The third mode of crystal formation, that in which the crys- 
tals are produced from a vapor, is less common than the other 
two described above. The principles that underlie the crystal- 
lization are much the same. The dissociated chemical atoms 
through the cooling of the gas are brought closer together until 
they at last form a solid with a definite crystal structure. An ex- 
ample of this mode of crystal formation is seen in the formation 
of sulphur crystals about the mouths of fumeroles in volcanic 
' regions, where they have been crystallized from sulphur-bearing 
vapors. 

The most fundamental and important fact concerning crystals 
is that they possess a definite internal structure. A crystal is to 
be conceived as made up of an almost infinite number of exces- 
sively minute mineral particles which have a regular arrange- 
ment and relation to each other and form, as it were, a crystal 
network. Little is definitely known as to the character or size of 
these mineral particles. They may be the same as the chemical 
molecule, but more probably consist in definite groups of that 
molecule. There are many proofs that a crystal does possess a 
Infinite internal arrangement of its mineral particles, but the 
following three are the most important. 

Cleavage. Many minerals when fractured break with definite 
and smooth flat surfaces which are known as cleavage planes. 
Common salt, halite, for instance, cleaves in three different planes 
which are at right angles to each other. It is said, therefore, to 
have a cubic cleavage. When it crystallizes it usually shows 
cubic forms also. The planes of cleavage are found to be always 
parallel to the natural cubic crystal faces. If the internal struc- 
ture of halite was heterogeneous, the fact that it always shows this 
cubical cleavage would be inexplicable. It can only be explained 
by assuming some definite internal arrangement which permits 
and controls such a cleavage. 



4 MANUAL OF MINERALOGY 

Optical Properties. All transparent crystals have definite 
effects upon the light which passes through them. Many of 
them further produce changes in the character of the light which 
cannot be accounted for except through the constraining influ- 
ence of the internal structure of the mineral. Take the case of 
calcite as an example. In general, if you look at an object through 
a clear block of calcite you will observe a double image. The 
mineral, in other words, has the power of doubly refracting light. 
Further, it can be proved that each of the two rays into which 
calcite breaks up light has a definite plane of vibration, i.e., each 
ray is polarized. A piece of glass similar in shape to the calcite 
block would not have produced these effects, because the internal 
structure of glass is heterogeneous, while that of calcite is definite 
and regular. 

Regular and Constant Outward Form. If a series of objects 
all having the same shape and size are grouped together accord- 
ing to some regular arrangement, the resulting mass will have a 
definite form which will bear a strict relationship to the char- 
acter of the individual objects and the law which was followed 
in assembling them. As a simple illustration, consider an ordi- 
nary pile of bricks. If each individual brick is exactly like 
every other in size and all of them are piled together according 
to a regular plan, the shape of the resulting mass will depend 
directly upon the shape of the individual bricks and the law 
which governed their arrangement. Figs. A and B, Plate I, arfc 
reproductions from photographs of models which are built up 
solidly of small steel balls. All of the constituent particles of 
each model are exactly alike in shape and size, and they have 
been piled together according to a regular arrangement. The 
result has been, as is shown in the figures, to produce regularly 
and definitely shaped solids. If therefore a regular arrange- 
ment of uniform particles produces a solid with a definite shape, 
the converse proposition must be true. If we have a mineral 
which occurs in certain characteristic and uniformly shaped 
crystals (halite, for example, in cubes), it must follow that this 
could only be accomplished through the mineral possessing a 
regular internal structure. 



PLATE I. 




A. Cube. 




B. Octahedron. 
Models made of Steel Balls. 



INTRODUCTION 



The Outward Crystal Form May Be Varied with the 
Same Internal Crystalline Structure. There may be several 
different limiting forms possible upon crystals of the same min- 
eral. Galena, PbS, for example, usually crystallizes in the form of 
a cube, but it also at times shows octahedral crystals. The in- 
ternal structure of galena is constant, but both the cube and 
octahedron are forms that conform to that structure. The 
models shown on Plate I illustrate this point. Both are built 
up of similar particles and their arrangement is the same in each 
case. In one, however, (Fig. A), the planes of a cube, and in 
the other (Fig. B) the planes of an octahedron, limit the figure. 

With the same internal structure there are, however, only a 
certain number of possible planes which can serve to limit a 
crystal. And it is to be noted, B ( 
moreover, that of these possible 
planes there are only a com- < 
paratively few which commonly 
occur. The positions of the 
faces of a crystal are deter- 
mined by those directions in 
which on account of the in- , 
ternal structure a large number 
of the individual mineral parti- 
cles lie. And those planes 
which include the greater num- 
ber of particles are the ones 
most commonly found as faces upon the crystals. Consider 
Fig. 1, which might represent one layer of particles in a certain 
crystal network. The particles are equally spaced from each 
other and have a rectilinear arrangement. It will be observed 
that there are several possible lines through this network that 
include a greater or less number of the particles. These lines 
would represent the cutting direction through this network of 
certain possible crystal planes; and it would be found that of 
these possible planes those which include the larger number 
of particles, like those cutting along the lines A-B and A-C, 
would be the more common in occurrence. 




Fig. 1. 



6 



MANUAL OF MINERALOGY 



Law of the Constancy of Interfacial Angles. Since the 
internal structure of any mineral is always constant, and since 
the possible crystal faces of that mineral have a definite relation- 
ship to that structure, it follows that the faces must have also a 
definite relationship to each other. This fact may be stated as 
follows: The angles between two similar faces on the same substance 
are always the same. Fig. 1 will also illustrate this point. The 
face which cuts the network along the line A-C must make an 
angle of 45 degrees with the face which cuts along the line 
A-B, etc. This law is the most fundamental and important in 
the science of crystallography. It frequently enables one to 
identify a mineral by the measurement of the interfacial angles 
on its crystals. A mineral may be found in crystals of widely 
varying shapes and sizes, but the angle between two similar faces 
will always be the same. 

An important part of the study of crystallography consists 
in the measuring and classifying of the interfacial angles on the 
crystals of all minerals. These measurements are accomplished 
by means of instruments known as goniometers. For accurate 
work, particularly in the case of small crystals, a type of in- 
strument known as a reflection goniometer is used. This is an 
instrument upon which the 
crystal to be measured is 
mounted so as to reflect 
beams of light from its faces 
through a telescope to the 
eye. The size of the angle 
through which a crystal has 
to be turned in order to 
throw successive beams of 
light from two adjacent faces 
into the telescope deter- 
mines the angle existing 

. c Fig. 2. Contact Goniometer. 

between the faces. A sim- 
pler instrument used for approximate work and with larger 
crystals is known as a contact goniometer. Its character and use 
are illustrated by Fig. 2. 




SYMMETRY 1 

The regular internal structure of crystals requires that the 
ultimate individual mineral particles must be at least physically 
alike. A physical likeness between these particles necessitates 
that they should also be the same chemically, or at least closely 
similar. Consequently we can state that in general a crystal 
must be made up of a regular assemblage of particles which are 
chemically the same, and therefore that a crystallized mineral 
must have a definite and uniform chemical composition. This 
statement is a general one and will suffice for the present; certain 
modifications will be found stated on page 77 under isomor- 
phism. A crystal is a guarantee of the chemical homogeneity 
of a mineral. From this it follows that only definite chemical 
compounds are capable of crystallization. 

To sum up the conclusions of the preceding paragraphs: A 
crystal is a solid with definite chemical composition which possesses 
a definite internal arrangement of its mineral particles. These 
internal characteristics are expressed outwardly in a definite external 
form. And since the internal structure of the same substance is 
always constant, the angles between the similar bounding planes of 
the crystals of that substance are also constant. 

II. SYMMETRY. 

Crystals are grouped together into different classes according 
to the symmetry which they show. The symmetry of crystals 
is of three kinds, namely: 1. Symmetry in respect to a plane; 
2. Symmetry in respect to a line; 3. Symmetry in respect to a 
point. 

Symmetry Plane. A symmetry plane is an imaginary plane 
which divides a crystal into halves, each of which is the mirror 
image of the other. Fig. 3 will illustrate the character of such 
a plane. The shaded portion of the figure shows the position 
of the one plane of symmetry that a crystal of this sort possesses. 
For each face, edge or point on one side of the plane there is a 
corresponding face, edge or point in a similar position on the other 
side of the plane. 

Symmetry Axis. A symmetry axis is an imaginary line 
through a crystal about which the crystal may be revolved as 



8 



MANUAL OF MINERALOGY 



upon an axis and repeat itself in appearance two or more times 
during the revolution. In Fig. 4 the line C-C f is an axis of 
symmetry, for when the crystal represented is revolved upon it, 
it will have, after a revolution of 180, the same appearance as 
at first; or in other words, similar planes, edges, etc., will appear 
in the places of the corresponding planes and edges of the 
original position. Point A' will occupy the original position of 
A, B' that of B, etc. Since the crystal is repeated twice in 
appearance during a complete revolution, this axis is said to 
be one of binary or twofold symmetry. In addition to axes 
of binary symmetry, we have axes of trigonal (threefold), tet- 
ragonal (fourfold) and hexagonal (sixfold) symmetry. 




Fig. 3. 
Symmetry Plane. 



Fig. 4. 
Symmetry Axis. 



Fig. 5. 

Symmetry Center. 



Center of Symmetry. A crystal has a center of symmetry 
if an imaginary line is passed from some point on its surface 
through its center, and a similar point is found on the line at an 
equal distance beyond the center. The crystal represented in 
Fig. 5 has a center of symmetry, for the point A is repeated at 
A' on a line passing from A through the center, C, of the crystal, 
the distances AC and A'C being equal. 

All possible crystal forms can be grouped into thirty-two 
classes depending upon the different degrees of symmetry which 
they show. These thirty-two classes may be further grouped 
into six systems, the classes of each system having certain close 



CRYSTAL NOTATION 9 

relations to each other. These systems are known as the Iso- 
metric, Tetragonal, Hexagonal, Orthorhombic, Monoclinic and 
Triclinic Systems. All crystals will be found to belong to one or 
the other of these systems. As stated above, there are thirty-two 
possible subdivisions of these six systems, but the majority of 
them are only of theoretical interest, since practically all known 
species can be placed in one or the other of some ten or twelve 
classes. 

III. CRYSTAL -NOTATION. 

A system of notation has been developed by which we can 
describe the different crystal classes and the crystal forms found 
in each. One of the important conceptions to this end is that of 
crystallographic axes, 

Crystallographic Axes. Crystallographic axes are imaginary 
lines or directions within a crystal to which the crystal faces are 
referred and in terms of which they are described. In the differ- 
ent systems the axes vary in number (three or four), in their 
relative lengths and in the angles of inclination to each other. 
As a general case we will consider the crystallographic axes of 
the Orthorhombic System. They are three in number, at right 
angles to each other, and each has a characteristic relative length. 
Fig. 6 represents such axes for the Orthorhombic mineral sulphur. 
When placed in the proper position for description, or "orien- 
tated" as it is termed, one axis called a is horizontal and per- 
pendicular to the observer, another axis, called 6, is horizontal 
and parallel to the observer, while the third axis, 'called c, is 
vertical. The ends of each axis are designated by either a plus 
or a minus sign, the front end of a, the right-hand end of b and 
the upper end of c being positive, while in each case the opposite 
end is negative. When, as in the Orthorhombic System, the 
three axes have different relative lengths, these values have to 
be determined experimentally by making the necessary measure- 
ments on crystals of each mineral. Fig. 7 would represent a 
crystal of sulphur in which each face of the crystal form, known 
as a pyramid, intercepts each axis at what is considered as its 
unit length. From the values obtained by measuring the angles 



10 



MANUAL OF MINERALOGY 



between the different faces of this crystal an expression of the 
relative lengths of the three axes can be obtained by calculation. 
The length of the b axis is taken as unity and the lengths of the 
a and c axes are expressed in terms of it. The axial ratio for 
sulphur is a : b : c = 0.813 : 1.00 : 1.903. It must be borne in 
mind that these lengths are only relative in their value. They 
do not represent any actual distances. A sulphur crystal may 
be of microscopic size or several inches in diameter, but in either 
case the above ratio would hold true. 



-C 

Fig. 6. 

Orthorhombic 
Crystal Axes. 




Fig. 7. 

Orthorhombic 
Pyramid. 





i _i ""*! 




lCt!,l&,ooC. 






, 




-? 






- 


- 1 -- . 


Fig. 8. 


Orthorhombic 


Prism. 



Parameters. Crystal faces are described according to their 
relations to the crystallographic axes. A series of numbers which 
indicate the relative distances by which a face intersects the 
different axes are called' its parameters. A face which cuts all 
three axes at distances from the point of their intersection which 
are relatively the same as the unit lengths of the axes is said to 
have the following parameters: la, 16, Ic (see Fig. 7). A face 
which cuts the two horizontal axes at distances which are rela- 
tively to each other as the unit lengths of those axes but is paral- 
lel to the vertical axis would have for parameters la, 16, ooc (see 
Fig. 8). If a face cuts the two horizontal axes at distances 
proportional to their unit lengths and cuts the vertical axis at 



CRYSTAL NOTATION 



11 



a distance twice its relative unit length, it will have for param- 
eters la, 16, 2c. It is to be emphasized that these parameters 
are strictly relative in their values and do not indicate any 
actual cutting lengths. To further illustrate this, consider 
Fig. 9, which represents a possible sulphur crystal. The forms 
present upon it are two pyramids 
of different slope but each inter- 
secting all three of the crystal axes 
when properly extended. The lower 
pyramid intersects the two hori- 
zontal axes at distances which are 
proportional to their unit lengths _ 
and if it was extended as shown by 
the dotted lines would also cut the 
vertical axis at a distance propor- 
tional to its unit length. The pa- 
rameters of the face of this form 
which cuts the positive ends of the 
three axes would be la, 16, Ic. 
The upper pyramid would cut the 
two horizontal axes, as shown by the dotted lines, also at dis- 
tances which, although greater than in the case of the lower 
pyramid, are still proportional to their unit lengths. It cuts the 
vertical axis, however, at a distance which, when considered in 
respect to its intersections with the horizontal axes, is propor- 
tional to one-half of the unit length of c. The parameters of a 
face of this form would therefore be la, 16, %c. From this ex- 
ample it will be seen that the parameters la, 16, do not in the two 
cases represent the same actual cutting distances but express only 
relative values. The parameters of a face do not in any way 
determine its size, for a face may be moved parallel to itself for 
any distance without changing the relative values of its intersec- 
tions with the crystallographic axes. 

Law of Definite Mathematical Ratio. It is to be noted that 
in general the ratio of the intercepts of a crystal face upon the 
crystallographic axes can be expressed by whole numbers or 
definite fractions. These numbers, or fractions, are commonly 




Fig. 9. 



12 MANUAL OF MINERALOGY 

simple, such as 1, 2, 3, |, %, f , etc., and in the great majority of 
cases are 1 or oo. This law, that the axial intercepts of all 
crystal faces form a definite mathematical ratio, is an extremely 
important one. It is a necessary corollary to the theoretical 
considerations given on page 5 and following. 

Indices. Various methods of notation have been devised to 
express the intercepts of any crystal face upon the crystal axes, 
and several different ones are in common use. The most uni- 
versally employed is the system of indices of Miller. While not 
as simple for a beginner, perhaps, as some one of the systems in 
which the parameters of the crystal faces are used, it adapts itself 
so much more readily to crystallographic calculations and con- 
sequently has so wide a use that it seems wise to introduce it here. 

The indices of a face consist of a series of whole numbers which 
have been derived from its parameters by their inversion and, if 
necessary, the subsequent clearing of fractions. The indices of 
a face are always given, so that the three numbers refer to the 
a, b and c axes respectively, and therefore ordinarily the letters 
which indicate the different axes are omitted. The pyramid 
illustrated in Fig. 7, which has la, Ib, Ic for parameters, would 
have 111 for indices. The face, Fig. 8, which has la, 16, ooc 
for parameters, would have 110 for indices. The face, Fig. 9, 
which has la, 16, |c for parameters, would have 112 for indices. 
A face which has la, 16, 2c for parameters would have 221 for 
indices. 

Common use is made of what is known as the symbol of a 
form. A symbol of any form consists of the indices of the face 
having the simplest relations to the axes. This is used when 
it is desired to refer to some particular crystal form, and the sym- 
bol then stands for the whole form and not simply for the single 
face whose indices it is. 

IV. DEFINITIONS OF VARIOUS TERMS. 

Crystal Form. By the expression " crystal form" is meant 
the assemblage of all similar faces which are possible with a 
certain degree of symmetry. In Fig. 7 is represented a crystal 
form known as a pyramid. In the particular symmetry class 



DEFINITIONS OF VARIOUS TERMS 



13 




to which it belongs the three crystal axes are axes of binary 
symmetry and the axial planes are planes of symmetry. Under 
these conditions, if we assume the presence of the face A we must 
have the other seven faces also in order to satisfy the demands 
of the symmetry. In this case the assemblage of the eight 
pyramidal faces constitutes the crystal form. A crystal form 
does not necessarily make a solid 
figure. Consider Fig. 10, which is 
of a crystal of the Monoclinic Sys- 
tem. In this system the b axis is 
an axis of binary symmetry and the 
plane of the a and c axes is a sym- 
metry plane. Under these condi- 
tions, if we assume the presence of 
the plane 6, the symmetry demands 
only the parallel face b'. So these 
two faces, being all the possible 
similar planes with this particular 
symmetry, constitute a crystal form, 
forms present on the crystal represented in Fig. 10. 

Crystal Habit. By the crystal habit of any mineral is meant 
the common and characteristic form or combination of forms in 
which that mineral crystallizes. Galena, for example, has a cubic, 
magnetite an octahedral and garnet a dodecahedral habit. By 
this is meant that, although these minerals are found in crys- 
tals which show other forms, such occurrences are comparatively 
rare, and their "habit" is to crystallize as indicated. 

Crystal Combinations. In the great majority of cases, a 
crystal will show a combination of two or more crystal forms 
rather than one single form. In fact, many crystal forms, since 
they do not make a solid figure by themselves, must occur in 
combination with other forms. The combination in which it 
occurs may quite change the appearance of a forrn, and its recog- 
nition will depend upon the position and relation of its faces 
rather than upon their shape. Fig. 11 is of a simple form known 
as a cube, and Fig. 12 is of a simple form known as an octahedron. 
Fig. 13 shows a combination of the two, in which the corners of 



Fig. 10. 

There are three crystal 



14 



MANUAL OF MINERALOGY 



the cube are truncated by the faces of the octahedron, while 
Fig. 14 shows the same two forms in a combination in which 
the points of the octahedron are truncated by the faces of the 
cube. When a corner or an edge of one form is replaced by a 
face of another form, the first is said to be truncated by the 
second. If an edge is replaced by two similar faces it is said to 
be beveled. 



^ a - 


X 


a 


a 


s'' 


^^ 


Fig. 11. 
Cube. 






Fig. 13. Fig. 14. 

Cube Truncated Octahedron Trun- 
by Octahedron. cated by Cube. 

Crystal Distortion. It seldom happens that the conditions 
for crystal growth are such as to permit the development of 
crystals of ideal symmetry. The crystal may have grown more 
rapidly in one direction than in another; other surrounding min- 
erals may have interfered, and in various ways its symmetrical 
growth been prevented. Such a crystal is said to show distortion. 




Fig. 15. Cube. Fig. 16. Distorted Cube. Fig. 17. Octahedron. 

Ordinarily the amount of distortion is not so great as to prevent 
one from readily imagining what the ideally developed crystal 
would be like and so determining its symmetry and character. 
It is to be noted that the real symmetry of a crystal does not 
depend upon the symmetrical shape and size of its faces, but 
rather upon the symmetrical arrangement of its interfacial 



DEFINITIONS OF VARIOUS TERMS 15 

angles. In the Figs. 15 and 16, 17 and 18, 19 and 20, are given 
various crystal forms, first ideally developed and then distorted. 





Fig. 18. Fig. 19. Fig. 20. 

Distorted Octahedron. Dodecahedron. Distorted Dodecahedron. 

Crystal Pseudomorphs. At times we find a mineral occur- 
ring in crystals which prove to be not the characteristic forms 
for that mineral, but are rather the typical forms of some other 
species. Such crystals are said to be pseudomorphs, or false 
forms. They originate in various ways. The mineral may have 
changed in its composition without, however, changing its crystal 
form. We find, for example, that cuprite, Cu 2 0, frequently 
alters to malachite, CuC0 3 .Cu(OH) 2 , but without a change 
in the crystal shape. The resulting crystals would have the 
composition of malachite but the crystal form of cuprite. An- 
other mode of origin is to have one mineral deposited on the 
crystals of another and so form, as it were, a cast of the second. 
Smithsonite, ZnC0 3 , is at times found in pseudomorphic crystals 
whose forms are those of calcite. In this case the smithsonite 
has been deposited in a thin layer over the crystal of calcite, 
which may have subsequently been removed. The resulting 
crystal is a pseudomorph of smithsonite after calcite. Pseudo- 
morphs cannot be regarded as true crystals, since their internal 
structure does not correspond to the outward crystal form. 

Twin Crystals. When two or more crystals intergrow accord- 
ing to some definite law, the resulting group is said to be a twin 
crystal. The different members, ordinarily two, of a twin 
crystal have usually a plane, known as a twinning plane, or an 
axis, known as a twinning axis, which is common to both. In 
Fig. 21, which represents a twin crystal of fluorite, we have two 
cubes intergrown in such a way that the diagonal axis A-A' is 



16 



MANUAL OF MINERALOGY 



common to the two individuals. The individual, the faces of 
which are shaded in the figure, lies as if it had been turned about 
this axis from the position occupied by the other individual 
through an angle of 60 degrees. The line A- A' is known as the 
twinning axis. Tn Fig. 22 is represented a twinned octahedron. 
The two individuals here are grown together with an octahedral 





Fig. 21. Twinned Cubes. 



Fig. 22. Twinned Octahedron. 



face in common. It will be noted that the composition plane, 
which is shaded, is parallel to one face of each individual. This 
plane is known as the twinning plane. The twin of Fig. 21 is 
known as a penetration twin, since the two individuals inter- 
penetrate each other; while the twin of Fig. 22 is a contact twin, 
since the two individuals lie simply in contact with each other 
upon a certain plane. 

V. ISOMETRIC SYSTEM. 

Crystallographic Axes. The crystallographic axes of the Iso- 
metric System are three in number, of equal lengths, and make 
right angles with each other. When 
properly orientated one axis is vertical 
and the other two are horizontal, one 
a2 being parallel and the other perpendicu- 
lar to the observer, as is shown in Fig. 
23. Since the three axes are identical 
in character, they are interchangeable, 
and any one of them may serve as the 
vertical axis, etc. In giving the indices 
of a face of an isometric form, the order of the axes, etc., is the 
same as described in a previous paragraph, page 9. 



-0,2 



-Cti 



-ct 8 
Fig. 23. Isometric Axes. 



ISOMETRIC SYSTEM 



17 



Normal CJass. 

Symmetry and Forms. The symmetry shown by the crys- 
tals of the Normal Class of the Isometric System is as follows. 
The three crystallographic axes are axes of tetragonal symmetry 
(see Fig. 24). There are also four diagonal axes of trigonal sym- 
metry. These axes emerge in the middle of each of the octants 
formed by the intersection of the crystallographic axes (see 
Fig. 25). Further, there are six diagonal axes of binary sym- 
metry, each of which bisects one of the angles between two of 
the crystallographic axes, as illustrated in Fig. 26. 





Fig. 25. Fig. 26. 

Axes of Symmetry, Isometric System, Normal Class. 





-Ct3 



Fig. 27. Fig. 28. 

Planes of Symmetry, Isometric System, Normal Class. 

This class shows nine planes of symmetry, three of them being 
known as the axial planes, since each includes two crystallo- 
graphic axes (see Fig. 27), and six being called diagonal planes, 
since each bisects the angle between two of the axial planes 
(see Fig. 28). 



18 



MANUAL OF MINERALOGY 



To summarize the symmetry of this class: 

3 crystallographic axes of tetragonal symmetry; 

4 diagonal axes of trigonal symmetry; 
6 diagonal axes of binary symmetry; 
3 axial planes of symmetry; 

6 diagonal planes of symmetry. 

This symmetry, which is of the highest degree possible in 
solids with plane surfaces, defines the Normal Class of the Iso- 
metric System. Every crystal form and every combination of 
forms that belongs to this class must show its complete sym- 
metry. It is important to remember that in this class the three 
crystallographic axes are axes of tetragonal symmetry, since this 
fact distinguishes the class from all others and by means of it the 
crystallographic axes can be easily located and a crystal properly 
orientated. 

The forms of the Isometric System, Normal Class, are as 
follows: 

1. Cube or Hexahedron. The cube is a form composed of six 
square faces which make 90 angles with each other, Each face 
intersects one of the crystallographic axes and is parallel to the 
other two. Its symbol is (100). Fig. 29 represents a simple cube. 



a ,001 



100 > 

_ 



a 

i ! 
j [__. 



010 
a 




Fig. 29. Cube. Fig. 30. Octahedron. 

2. Octahedron. The octahedron is a form composed of eight 
equilateral triangular faces, each of which intersects all three of 
the crystallographic axes equally. Its symbol is (111). Fig. 30 
represents a simple octahedron and Figs. 31 and 32 show com- 
binations of a cube and an octahedron. When in combination 



ISOMETRIC SYSTEM 



19 



the octahedron is to be recognized by its eight similar faces, each 
of which is equally inclined to the three crystallographic axes. 
It is to be noted that the faces of an octahedron truncate sym- 
metrically the corners of a cube. 



\/ 



Fig. 31. 
Cube and Octahedron. 




Fig. 32. 
Octahedron and Cube. 



Fig. 33. 
Dodecahedron. 



3. Dodecahedron. The dodecahedron is a form composed of 
twelve rhombic-shaped faces. Each face intersects two of the 
crystallographic axes equally and is parallel to the third. Its 
symbol is (110). Fig. 33 shows a simple dodecahedron, Fig. 34 
shows a combination of dodecahedron and cube, Figs. 35 and 36 
combinations of dodecahedron and octahedron, and Fig. 37 a 
combination of cube, octahedron and dodecahedron. It is to be 
noted that the faces of a dodecahedron truncate the edges of 
both the cube and the octahedron. 



i 




Fig. 34. 
Cube and Dodecahedron. 



Fig. 35. 
Octahedron and Dodecahedron. 



4. Tetrahexahedron. The tetrahexahedron is a form com- 
posed of twenty-four isosceles triangular faces, each of which in- 
tersects one axis at unity, the second at some multiple, and is 



20 



MANUAL OF MINERALOGY 



parallel to the third. There are a number of tetrahexahedrons 
which differ from each other in respect to the inclination of 
their faces. Perhaps the one most common in occurrence has 
the parameter relations la, 2b, <x>c, the symbol of which would 
be (210). The symbols of other forms are (310), (410), (320), 
etc. It is helpful to note that the tetrahexahedron, as its name 
indicates, is like a cube, the faces of which have been replaced by 
four others. Fig. 38 shows a simple tetrahexahedron and Fig. 39 
a cube with its edges beveled by the faces of a tetrahexahedron. 






*<r\ ._. 


(-\ 


' Vf d / n > 


ly 


| [ 

a d 



j 



Fig. 36. Fig. 37. 

Dodecahedron and Octahedron. Cube, Octahedron and Dodecahedron. 





Fig. 38. 
Tetrahexahedron. 



Fig. 39. 
Cube and Tetrahexahedron. 



5. Trapezohedron or Tetragonal Trisoctahedron. The trapezo- 
hedron is a form composed of twenty-four trapezium-shaped 
faces, each of which intersects one of the crystallographic axes 
at unity and the other two at equal multiples. There are vari- 
ous trapezohedrons with their faces having different angles of 
inclination. A common trapezohedron has for its parameters 



ISOMETRIC SYSTEM 



21 



la, 26, 2c, the symbol for which would be (211). The symbols 
for other trapezohedrons are (311), (411), (322), etc. It will be 
noted that a trapezohedron is an octahedral-like form and may 
be conceived of as an octahedron, each of the planes of which has 
been replaced by three faces. Consequently it is sometimes 
called a tetragonal trisoctahedron. The qualifying word, tet- 
ragonal, is used to indicate that each of its faces has four edges 
and to distinguish it from the other trisoctahedral form, the 





Fig. 40. 
Trapezohedron. 



Fig. 41. 
Dodecahedron and Trapezohedron. 





Fig. 42. 
Dodecahedron and Trapezohedron. 



Fig. 43. 
Cube and Trapezohedron. 



description of which follows. Trapezohedron is the name, how- 
ever, most commonly used. The following are aids to the recog- 
nition of the form when it occurs in combinations: the three 
similar faces to be found in each octant; the relations of each 
face to the axes; and the fact that the middle edges between the 
three faces in any one octant go toward points which are equi- 
distant from the ends of the two adjacent crystallographic axes. 
Fig. 40 shows a simple trapezohedron, and Figs. 41 and 42 show 



22 



MANUAL OF MINERALOGY 



each a trapezohedron in combination with a dodecahedron. It 
is to be noted that the faces of the common trapezohedron (211) 
(Fig. 41) truncate the edges of the dodecahedron. Fig. 43 shows 
a combination of cube and trapezohedron. 

6. Trisoctahedron or Trigonal Trisoctahedron. The trisocta- 
hedron is a form composed of twenty-four isosceles triangular 
faces, each of which intersects two of the crystallographic axes 
at unity and the third axis at some multiple. There are various 
trisoctahedrons the faces of which have different inclinations. 
A common trisoctahedron has for its parameters la, 16, 2c, its 
symbol being (221). Other trisoctahedrons have the symbols 
(331), (441), (332), etc. It is to be noted that the trisoctahedron, 
like the trapezohedron, is a form that may be conceived of as an 
octahedron, each face of which has been replaced by three others. 
Frequently it is spoken of as the trigonal trisoctahedron, the 
modifying word indicating that its faces have each three edges 
and so differ from those of the trapezohedron. But when the 
word "trisoctahedron" is used alone it refers to this form. The 
following points would aid in its identification when it is found 
occurring in combinations: the three similar faces in each octant; 
their relations to the axes; and the fact that the middle edges 
between them go toward the ends of the crystallographic axes. 





Fig. 44. 
Trisoctahedron. 



Fig. 45. 
Octahedron and Trisoctahedron. 



Fig. 44 shows the simple trisoctahedron and Fig. 45 a combina- 
tion of a trisoctahedron and an octahedron. It will be noted 
that the faces of the trisoctahedron bevel the edges of the octa- 
hedron. 



ISOMETRIC SYSTEM 



23 



7. Hexoctahedron. The hexoctahedron is a form composed of 
forty-eight triangular faces, each of which cuts differently on all 
three crystallographic axes. There are several hexoctahedrons, 
which have varying ratios of intersection with the axes. A 
common hexoctahedron has for its parameter relations la, 16, 
3c, its symbol being (321). Other hexoctahedrons have the 
symbols (421), (531), (432), etc. It is to be noted that the hex- 




Fig. 46. 
Hexoctahedron. 



Fig. 47. 
Cube and Hexoctahedron, 





Fig. 48. 
Dodecahedron and Hexoctahedron. 



Fig. 49. 

Dodecahedron, Trapezohedron and 
Hexoctahedron. 



octahedron is a form that may be considered as an octahedron, 
each face of which has been replaced by six others. It is to be 
recognized when in combination by the facts that there are six 
similar faces in each octant and that each face intercepts the 
three axes differently. Fig. 46 shows a simple hexoctahedron, 
Fig. 47 a combination of cube and hexoctahedron, Fig. 48 a 
combination of dodecahedron and hexoctahedron, and Fig. 49 a 
combination of dodecahedron, trapezohedron and hexoctahedron. 



24 



MANUAL OF MINERALOGY 



Occurrence of the Above Forms. The cube, octahedron and 
dodecahedron are the most common of the isometric forms. 
The trapezohedron is also frequently observed on a few min- 
erals. The other forms, the tetrahexahedron, trisoctahedron and 
hexoctahedron, are rare and are ordinarily to be observed only 
as small truncations in combinations. 

The following is a list of the commoner minerals upon the 
crystals of which each form is prominent: 

Cube: Galena, halite, sylvite, fluorite, cuprite. 

Octahedron: Spinel, magnetite, franklinite, chromite. 

Dodecahedron: Magnetite, garnet. 

Trapezohedron: Leucite, garnet, analcite. 

Pyritohedral Class. 

The Pyritohedral Class is one of the subordinate divisions of 
the Isometric System. It differs from the Normal Class, since 
its crystals commonly show forms that do not possess as high 
a symmetry as those of that class. The name of the class is 
derived from that of its chief member, pyrite. 

Symmetry and Forms. The symmetry of the Pyritohedral 
Class is as follows: The three crystal axes are axes of binary 





Fig. 50. Fig. 51. 

Symmetry of Pyritohedral Class, Isometric System. 

symmetry; the four diagonal axes, each of which emerges in the 
middle of an octant, are axes of trigonal symmetry; the three 
axial planes are planes of symmetry (see Figs. 50 and 51). 

The characteristic forms of the Pyritohedral Class are as 
follows: 



ISOMETRIC SYSTEM 



25 



1. Pyriiohedron or Pentagonal Dodecahedron. This form con- 
sists of twelve pentagonal-shaped faces, each of which intersects 
one crystallographic axis at unity, the second axis at some mul- 
tiple, and is parallel to the third. There are a number of pyrito- 
hedrons which differ from each other in respect to the inclination 
of their faces. Perhaps the most common in occurrence has 
the parameter relations la, 26, ooc, the symbol of which would 
be (210) (see Fig. 52). It is to be noted that the parameter rela- 
tions of the pyritohedron are the same as those of the tetra- 
hexahedron (see page 19). A pyritohedron may be considered 
as derived from a corresponding tetrahexahedron by the omission 
of alternate faces and the extension of those remaining. Fig. 53 





Fig. 52. 
Pyritohedron. 



Fig. 53. 

Showing Relation between Pyrito- 
hedron and Tetrahexahedron. 



shows the relations of the two forms, the shaded faces of the 
tetrahexahedron being those which when extended would form 
the faces of the pyritohedron. 

2. Diploid. The diploid is a rare form found only in this 
class. It is composed of twenty-four faces which correspond 
to one-half the faces of a hexoctahedron. Fig. 54 represents a 
diploid. 

In addition to the two forms described above, minerals of 
this class show also the cube, octahedron, dodecahedron, trapezo- 
hedron and trisoctahedron. Sometimes these forms may appear 
alone and so perfectly developed that they cannot be told from 
the forms of the Normal Class. This is often true of octahedrons 
of pyrite. Usually, however, they will show by the presence of 
striation lines or etching figures that they do not possess the 



26 



MANUAL OF MINERALOGY 



high symmetry of the Normal Class but conform rather to the 
symmetry of the Pyritohedral Class. This is shown in Fig. 55, 
which represents a cube of pyrite with characteristic striations, 
which are so disposed that the crystal shows the lower symmetry. 





Fig. 54. Diploid. 



Fig. 55. Striated Cube. 




Fig. 56. Cube and Pyritohedron. Fig. 57. Octahedron and Pyritohedron. 





Fig. 58. 
Octahedron and Pyritohedron. 



Fig. 59. 
Pyritohedron and Octahedron. 



Fig. 56 represents a combination of cube and pyritohedron, in 
which it will be noted that the faces of the pyritohedron truncate 
unsymmetrically the edges of the cube. Figs. 57, 58 and 59 
represent combinations of pyritohedron and octahedron with 



ISOMETRIC SYSTEM 



27 



various developments. Fig. 60 shows a cube truncated with 
pyritohedron and octahedron. Fig. 61 represents a combination 
of cube and the diploid / (421). These figures should be studied 
in order to impress upon one's mind the characteristic symmetry 
of the class. 





Fig. 60. 
Pyritohedron, Cube and Octahedron. 



Fig. 61. 
Diploid and Cube. 



The chief mineral of the Pyritohedral Class is pyrite; other much 
. rarer members are smaltite, chloanthite, cobaltite, gersdorfBte and 
sperrylite. 

Tetrahedral Class. 

Another subordinate division of the Isometric System is known 
as the Tetrahedral Class, deriving its name from its chief form, 
the tetrahedron. 





Fig. 62. Fig. 63. 

Symmetry of Tetrahedral Class, Isometric System. 

Symmetry and Forms. The symmetry of this class is as 
follows: The three crystal! ographic axes are axes of binary sym- 
metry; the four diagonal axes are axes of trigonal symmetry; 
there are six diagonal planes of symmetry (see Figs. 62 and 63). 



28 



MANUAL OF MINERALOGY 



The characteristic forms of the Tetrahedral Class are as fol- 
lows: 

1. Tetrahedron. The tetrahedron is a form composed of 
four equilateral triangular faces, each of which intersects all of 

the crystallographic axes at equal 
lengths. It can be considered as 
derived from the octahedron of the 
Normal Class by the omission of the 
alternate faces and the extension of 
the others, as shown in Fig. 64. 
This form, shown also in Fig. 65, is 
known as the positive tetrahedron 
and has for its symbol (111). If 
the other four faces of the octa- 
hedron had been extended, the 
tetrahedron resulting would have 
had a different orientation, as shown in Fig. 66. This is known 
as the negative tetrahedron and has for its symbol (111). The 




Fig. 64. 

Showing Relation between Octa- 
hedron and Tetrahedron. 




Fig. 65. 
Positive Tetrahedron. 



Fig. 66. 
Negative Tetrahedron. 



Fig. 67. 

Positive and Negative 

Tetrahedrons. 



positive and negative tetrahedrons when occurring alone are 
geometrically identical, and the only reason for recognizing the 
possibility of the existence of two different orientations lies in 
the fact that at times they may occur truncating each other, 
as shown in Fig. 67. If a positive and negative tetrahedron 
occurred together with equal development, the resulting crystal 
could not be distinguished from an octahedron, unless, as is 
usually the case, the faces of the two forms showed different lus- 
ters, etchings or striations that would serve to differentiate them. 



ISOMETRIC SYSTEM 



29 



Other possible but rare tetrahedral forms are the following: 
The tristetrahedron (Fig. 68), the faces of which correspond to 
one-half the faces of a trapezohedron ; the deltoid dodecahedron 
(Fig. 69), the faces of which correspond to one-half those of 
the trisoctahedron ; the hexakistetrahedron (Fig. 70), the faces 
of which correspond to one-half the faces of the hexoctahedron. 




Fig. 68. 
Tristetrahedron. 



Fig. 69. 
Deltoid Dodecahedron. 



Fig.- 70. 

Hexakistetrahedron. 




Fig. 71. 
Cube and Tetrahedron. 



Fig. 72. 
Tetrahedron and Cube. 





Fig. 73. 
Tetrahedron and Dodecahedron. 



Fig. 74. 
Dodecahedron, Cube and Tetrahedron. 



The cube and dodecahedron are also found on minerals of the 
Tetrahedral Class. Figs. 71 and 72 show combinations of cube 




30 MANUAL OF MINERALOGY 

and tetrahedron. It will be noted that the tetrahedron faces 
truncate the alternate corners of the cube, or that the cube faces 
truncate the edges of a tetrahedron. Fig. 73 shows the com- 
bination of tetrahedron and dode- 
cahedron. Fig. 74 represents a 
combination of cube, dodecahedron 
and tetrahedron. Fig. 75 shows a 
combination of tetrahedron and 
tristetrahedron. 

Tetrahedrite and the related ten- 
nantite are the only common min- 
erals that ordinarily show distinct 

Fig. 75. Tetrahedron and J 

Tristetrahedron. tctrahedral forms. Sphalerite oc- 

casionally exhibits them, but commonly its crystals are quite 
complex and distorted. 

Characteristics of Isometric Crystals. 

The striking characteristics of isometric crystals which would 
aid in their recognition may be summarized as follows: 

The crystals are equidimensional in three directions at right 
angles to each other. These three directions in crystals of the 
Normal Class are axes of tetragonal symmetry. The crystals 
commonly show faces that are squares or equilateral triangles 
or these figures with truncated corners. They are characterized 
by the large number of similar faces, the smallest number on 
any form of the Normal Class being six. Every form by itself 
would make a solid. 

Important Isometric Angles. Below are given various inter- 
facial angles which may assist in the recognition of the commoner 
isometric forms: 

Cube (100) A cube (010) = 90 O'_0". 

Octahedron (111) A octahedron (111) = 70 31' 44". 

Dodecahedron (110) A dodecahedron (101) = 60 0' 0". 

Cube (100) A octahedron (111) = 54 44' 8". 

Cube (100) A dodecahedron (110) = 45 0' 0". 

Octahedron (111) A dodecahedron (110) = 35 15' 52". 



TETRAGONAL SYSTEM 



31 



VI. TETRAGONAL SYSTEM. 

Crystallographic Axes. The crystallographic axes of the 
Tetragonal System are three in number and make right angles 
with each other. The two horizontal axes are equal in length 
and interchangeable, but the vertical axis is of some different 
length which varies with each tetragonal mineral. Fig. 76 
represents the crystallographic axes 
for the tetragonal mineral zircon. 
The length of the horizontal axes ~ a 

is taken as unity, and the relative 
length of the vertical axis is expressed 
in terms of the horizontal. This 
length has to be determined for each 
tetragonal mineral by measuring the 



-c 
Fig. 76. Tetragonal Axes. 



interfacial angles on a crystal and making the proper calcu- 
lations. For zircon the length of the vertical axis is expressed 
as c = 0.640. The proper orientation of the crystallographic 
axes and the method of their notation is like that of the Iso- 
metric System and is shown in Fig. 76. 

Normal Class. 

Symmetry and Forms. The symmetry of the Normal Class 
of the Tetragonal System is as follows: The vertical crystal- 
lographic axis is an axis of tetragonal symmetry. There are 





Fig. 77. Fig. 78. 

Symmetry of Normal Class, Tetragonal System. 

four horizontal axes of binary symmetry, two of which are coin- 
cident with the crystallographic axes, while the other two bisect 
the angles between these. Fig. 77 shows the axes of symmetry. 



32 



MANUAL OF MINERALOGY 



There are four vertical and one horizontal planes of symmetry. 
Each vertical plane of symmetry passes through one of the 
horizontal axes of symmetry. The position of the planes of 
symmetry is shown in Fig. 78. 

The forms of the Normal Class, Tetragonal System, are as 
follows : 

1. Prism of First Order. The prism of the first order consists 
of four rectangular vertical faces, each of which intersects the 
two horizontal crystallographic axes equally. Its symbol is (110). 
The form is represented in Fig. 79. 

001 ^ 001 



^" 


H^P^ 
j i 




i 


^ 




<4-, 


1 


^~ 




m 


! m 




a J 


a 






i 






..__ 


4i~ 












j ^ 






110 


1! 




loo i 


010 




210 


^10 


120 


-210 




| 




1 








1 








1 i 


















"^^LT" 






.^_t"-~ 


^^ 




_--~- 


-4--L. 


--- 




Fig. 79. Fig. 80. 


Fig. 81. 


irst Order Prism. Second Order Prism. Ditetragonal Prism. 



2. Prism of Second Order. The prism of the second order 
consists of four rectangular vertical faces, each of which inter- 
sects one horizontal crystallographic axis and is parallel to the 
other two axes. Its symbol is (100). The form is represented 
in Fig. 80. 

3. Ditetragonal Prism. The ditetragonal prism is a form con- 
sisting of eight rectangular vertical faces, each of which inter- 
sects the two horizontal crystallographic axes unequally. There 
are various ditetragonal prisms, depending upon their differing 
relations to the horizontal axes. The symbol of a common 
form is (210), which is represented in Fig. 81. 

4. Pyramid of First Order. The pyramid of the first order is a 
form consisting of eight isosceles triangular faces, each of which 
intersects all three crystallographic axes, the intercepts upon 
the two horizontal axes being equal. There are various pyramids 



TETRAGONAL SYSTEM 



33 



of the first order, depending upon the inclination of their faces. 
The unit pyramid which intersects all the axes at their unit 
lengths is the most common, its symbol being (111). Symbols 
for other pyramids of the first order are (221), (331), (112), 
(113), etc. Fig. 82 represents the unit pyramid on zircon. 

5. Pyramid of Second Order. The pyramid of the second 
order is a form composed of eight isosceles triangular faces, each 
of which intersects one horizontal axis and the vertical axis and 
is parallel to the second horizontal axis. There are various pyra- 
mids of the second order, with different intersections upon the 
vertical axis. The most common form is the unit pyramid, 




Fig. 82. 
First Order Pyramid. 



Fig. 83. 
Second Order Pyramid. 



Fig. 84. 
Ditetragonal Pyramid. 



which has (101) for its symbol. Other pyramids of the second 
order would have the symbols (201), (301), (102), (103), etc. 
Fig. 83 represents a unit pyramid of the second order upon 
zircon. 

6. Ditetragonal Pyramid. The ditetragonal pyramid is a form 
composed of sixteen isosceles triangular faces, each of which in- 
tersects all three of the crystallographic axes, cutting the two 
horizontal axes at different lengths. There are various ditet- 
ragonal pyramids, depending upon the different axial intersec- 
tions possible. One of the most common is the pyramid having 
(311) for its symbol. This is shown as it would appear upon 
zircon in Fig. 84. 



34 



MANUAL OF MINERALOGY 



7. Basal Pinacoid. The basal pinacoid, basal plane, or base, 
as it is variously called, is a form composed of two horizontal 
faces. Its symbol is (001). It is shown in combination with a 
prism in Figs. 79, 80 and 81. 





Fig. 85. Zircon. 



Fig. 86. Zircon. Fig. 87. Zircon. Fig. 88'. Zircon. 





Fig. 89. Vesuvianite. Fig. 90. Vesuvianite. 




Fig. 91. Rutile. 





Fig. 92. Cassiterite. Fig. 93. Apophyllite. Fig. 94. Apophyllite. 

Tetragonal Combinations. The different pyramids are the 
only tetragonal forms that can occur alone, and even they are 
ordinarily found in combination with other forms. Character- 
istic combinations are represented in Figs. 85-94. 



TETRAGONAL SYSTEM 



35 



Sphenoidal Class. 

The Sphenoidal Class corresponds in the Tetragonal System 
to the Tetrahedral Class in the Isometric System. It is charac- 
terized by the following symmetry: The three crystallographic 
axes are axes of binary symmetry (see Fig. 95), and there are two 
vertical diagonal planes of symmetry (see Fig. 96). 

2, 





Fig. 95. Fig. 96. 

Symmetry of Sphenoidal Class, Tetragonal System. 

Sphenoid. The characteristic form of the class is known as 
a sphenoid (from a Greek word meaning axlike): It consists of 
four isosceles triangular faces which intersect all three of the 
crystallographic axes, the intercepts on the two horizontal axes 
being equal. The faces correspond in their position to the alter- 






Fig. 97. 
Sphenoid. 



Fig. 98. 
Sphenoid. 



Fig. 99. 
Positive and Negative Sphenoids. 



nating faces of the tetragonal pyramid of the first order. There 
may be different sphenoids, depending upon their varying inter- 
sections with the vertical axes. Two different sphenoids are 
shown in Figs. 97 and 98. There may also be a positive and a 
negative sphenoid, the combination of the two being represented 
in Fig. 99. 



MANUAL OF MINERALOGY 



The sphenoid differs from the tetrahedron in the fact that its 
vertical crystallographic axis is not of the same length as the 
horizontal axes. The only common sphenoidal mineral is chal- 
copyrite. The length of the vertical axis in chalcopyrite is very 
close to that of the horizontal axes, c = 0.985. In the case of 
the unit sphenoid, therefore, it would require accurate measure- 
ments in order to differentiate it from an isometric tetrahedron. 
Chalcopyrite crystals ordinarily show only the unit sphenoid 
(Fig. 98), but at times show a steeper sphenoid (Fig. 97). 



Tri-Pyramidal Class. 

Another division of lower symmetry of the Tetragonal System 
is known as the Tri-pyramidal Class. It is characterized by a 
form known as the pyramid of the third order. 
This form consists of eight faces which correspond 
in their position to one-half of the faces of a di- 
tetragonal pyramid. The minerals found in this 
class are few and rare. Moreover, their crystals 
seldom show the faces of the pyramid of the third 
order, and when these do occur they are usually 
quite small. Therefore it seems hardly necessary 
in this place to consider this class in greater detail. 
Fig. 100 is of a crystal of scapolite, upon which the 
faces of the third-order pyramid z are shown. 




Fig. 100. 
Scapolite. 



Characteristics of Tetragonal Crystals. 

Since the only common tetragonal mineral that does not be- 
long to the Normal Class is chalcopyrite, which, moreover, is to 
be easily recognized by its general physical characteristics, we 
may confine ourselves here to the consideration only of the 
crystals of the Normal Class. 

The striking characteristics of tetragonal crystals may be 
summarized as follows: One axis of tetragonal symmetry; the 
length of the crystal parallel to this axis is usually greater or less 
than its other dimensions; the cross section of a crystal when 
viewed in the direction of the axis of tetragonal symmetry con- 
sists usually of a square or a truncated square. 



HEXAGONAL SYSTEM 



37 



VII. HEXAGONAL SYSTEM. 

Crystallographic Axes. The crystallographic axes of the 
hexagonal system are four in number. Three of these lie in the 
horizontal plane, while the fourth is vertical. The three hori- 
zontal axes are of equal length and interchangeable. They 
make angles of 60 and 120 with each other. The vertical axis 
varies in its relative length for each hexagonal mineral, and this 
is expressed in terms of the length of the horizontal axes, which 
is taken as unity. Thus in the case of beryl, the vertical axis, 
designated as c, has a length which in relation to the length of 
the horizontal axes can be expressed as c = 0.499. 



-a 2 




+a 2 



-a s 



Fig. 101. 



-a 3 



-c 

Fig. 102. 



Hexagonal Axes. 



When properly orientated, one of the horizontal crystallo- 
graphic axes is parallel to the observer, and the other two make 
30 angles on either side of a line perpendicular to him. Fig. 
101 shows the proper position of the horizontal axes when 
viewed in the direction of the vertical axis. As the three hori- 
zontal axes are interchangeable with each other, they are usually 
designated a h a* and a 3 . Note that ai is to the left of the observer 
with its positive end at the front, that o 2 is parallel to the ob- 
server and its positive end is at the right, while a 3 is to the right 
of the observer and its positive end is at the back. Fig. 102 
shows the four axes in clinographic projection. In giving the 
indices of any face upon a hexagonal crystal four numbers must 



38 



MANUAL OF MINERALOGY 



be given, since there are four axes. The numbers referring 
to the intercepts of the face with the three horizontal axes are 
given first in their proper order, while the number referring to 
the intercept on the vertical axis is given last. 

Normal Class. 

Symmetry and Forms. The symmetry of the Normal Class 
of the Hexagonal System is as follows: The vertical crystallo- 
graphic axis is an axis of hexagonal symmetry. There are six 
horizontal axes of binary symmetry, three of them being coin- 
cident with the crystallographic axes and the other three lying 
midway between them (see Fig. 103). There is a horizontal 





Fig. 103. Fig. 104. 

Symmetry of Normal Class, Hexagonal System. 

plane of symmetry and six vertical planes of symmetry (see 
Fig. 104). The forms of the Normal Class are as follows: 

1. Prism of First Order. This is a form consisting of six 
rectangular vertical faces each of which intersects two of the 
horizontal crystallographic axes equally and is parallel to the 
third. Fig. 105 shows the prism of the first order. The symbol 
for the form is (1010). 

2. Prism of Second Order. This is a form consisting of six 
rectangular vertical faces, each of which intersects two of the 
horizontal axes equally and the intermediate horizontal axis at 
one-half this distance. Fig. 106 shows the prism of the second 
order. The symbol for the form is (1120). 



HEXAGONAL SYSTEM 



89 



3. Dihexagonal Prism. The dihexagonal prism has twelve rec- 
tangular vertical faces, each of which intersects all three of the 



^~ 


oc 


101 C 


~NS, 

_-t 


1100 


10 


to 


ofio 


m 


u 


r 


1 




i 




I 
1 




I 






\ 






_ -* 



2110 



1120 




Fig. 105. 
Prism of First Order. 



Fig. 106. 
Prism of Second Order. 



Fig. 107. 
Dihexagonal Prism. 



horizontal crystallographic axes at different lengths. There are 
various dihexagonal prisms, depending upon their differing rela- 
tions to the horizontal axes. The symbol of a common dihexago- 
nal prism is (2130) (see Fig. 107). 




Fig. 108. Fig. 109. Fig. 110. 

Pyramid of First Order. Pyramid of Second Order. Dihexagonal Pyramid. 

4. Pyramid of First Order. This form consists of twelve 
isosceles triangular faces, each of which intersects two of the 
horizontal crystallographic axes equally, is parallel to the third 
horizontal axis and intersects the vertical axis (see Fig. 108). 
There are various pyramids of the first order possible, depending 
upon the inclination of their faces. The unit form would have 
the symbol (lOTl). 



40 



MANUAL OF MINERALOGY 



5. Pyramid of the Second Order. This is a form composed of 
twelve isosceles triangular faces, each of which intersects two of 
the horizontal axes equally, the third and intermediate horizon- 
tal axis at one-half this distance, and also intersects the vertical 
axis (see Fig. 109). There are various pyramids of the second 
order possible, depending upon the inclination of their faces. A 
common form would have for its symbol (1122). 

6. Dihexagonal Pyramid. The dihexagonal pyramid is a form 
of twenty-four isosceles triangular faces, each of which intersects 
all three of the horizontal axes differently and intersects also the 
vertical axis. This form is shown in Fig. 110. There are differ- 
ent dihexagonal pyramids which vary in their intercepts, one of 
the most common having for its symbol (2131). 

7. Basal Pinacoid. The basal pinacoid is a form composed 
of two horizontal faces. It is shown in combination with the 
different prisms in Figs. 105, 106 and 107. Its symbol is (0001). 

?r^= 

Y n\n 



11 





Fig. 111. 



Fig. 112. Fig. 113. 

Beryl Crystals. 



Fig. 114. 



Figs. 111-114 show various combinations of the forms of this 
class. 

Tri-Pyramidal Class. 

A division of the Hexagonal System showing lower symmetry 
than that of the Normal Class is known as the Tri-pyramidal 
Class. It has a vertical axis of hexagonal symmetry and a 
horizontal plane of symmetry. It is characterized by the form 
known as the pyramid of the third order. This form consists 
of twelve faces, which correspond in their position to one-half 
of the faces of a dihexagonal pyramid. The minerals of the 



HEXAGONAL SYSTEM 



41 



Apatite Group are the only ones of importance in this class, and 
upon their crystals the pyramid of the third order is rarely to be 
seen. When it is observed it shows usually only small faces. 
Fig. 115 represents a complex crystal of apatite with the faces 
of a third-order pyramid (AI) upon it. 





Fig. 115. Apatite. 



Fig. 116. Zincite. 



Hemimorphic Class. 

The crystals of certain rare minerals show the forms of the 
Normal Class but with hemimorphic development. A hemi- 
morphic crystal is one that shows different forms or combinations 
of forms at the opposite ends of a symmetry axis. Fig. 116 
represents a crystal of zincite with a prism terminated by a 
pyramid above and a basal pinacoid below. 

Rhombohedral Class. Normal Division. 

The forms of this class are to be referred to the hexagonal 
crystallographic axes, but show a lower symmetry than those of 
the Normal Class. 
8J 




Fig. 117. Fig. 118. 

Symmetry of Rhombohedral Class, Hexagonal System. 

Symmetry and Forms. The vertical crystallographic axis 
is one of trigonal symmetry, and the three horizontal crystallo- 



42 



MANUAL OF MINERALOGY 



graphic axes are axes of binary symmetry (see Fig. 117). There 
are three vertical planes of symmetry bisecting the angles be- 
tween the horizontal axes (see Fig. 
118). 

1. Rhomhohedron. The rhombohe- 
dron is a form consisting of six rhom- 
bic-shaped faces, which correspond in 
their position to the alternate faces of 
a hexagonal pyramid of the first order. 
The relation of these two forms to each 
other is shown in Fig. 119. There may 

Fig. 119. Showing Relation be- . 

tween First Order Pyramid be two different orientations of the 
rhombohedron. A positive rhombo- 

hedron is shown in Fig. 120 and a negative rhombohedron in 
Fig. 121. It is to be noted that when properly orientated the 






Fig. 120. Positive Rhombohedron. Fig. 121. Negative Rhombohedron. 

positive rhombohedron has one of its faces, and the negative 
rhombohedron one of its edges, toward the observer. There 
are various rhombohedrons, which differ from each other in 
the inclination of their faces. The symbol of the unit positive 
rhombohedron is (lOll) and of the unit negative rhombohedron 
(0111). Characteristic combinations of positive and negative 
rhombohedrons with each other and with other hexagonal forms 
are shown in Figs. 122-130. 

2. Scalenohedron. This form consists of twelve scalene tri- 
angular faces. These faces correspond hi their position to the 
alternate pairs of faces of a dihexagonal pyramid. The relation 
of the two forms to each other is shown in Fig. 131. The striking 
characteristics of the scalenohedron are the zigzag middle edges 



HEXAGONAL SYSTEM 



43 






Fig. 122. Caloite. Fig. 123. Caloite. Fig. 124. Calcite. 





Fig. 126. Calcite. Fig. 127. Calcite. 




Fig. 128. Chabazite. Fig. 129. Corundum. Fig. 130. Corundum, 





Fig. 131. Showing Relation between Dihex- Fig. 132. Scalenohedron. 
agonal Pyramid and Scalenohedron. 



44 



MANUAL OF MINERALOGY 





Fig. 133. Calcite. 



Fig. 134. Calcite. 





Fig. 135. Calcite. Fig. 136. Calcite. Fig. 137. Tourmaline. 




Fig. 138. Tourmaline. Fig. 139. Tourmaline. Fig. 140 Tourmaline 



HEXAGONAL SYSTEM 45 

which differentiate it from an ordinary pyramid and the alter- 
nating, relatively obtuse and acute angles over the edges that 
meet at the vertices of the form. There are many different 
possible scalenohedrons, depending upon the varying slope of 
their faces. A common scalenohedron having the symbol (2131) 
is represented in Fig. 132. Characteristic combinations of sca- 
lenohedrons with other forms are shown in Figs. 133-136. 

Rhombohedral Class. Hemimorphic Division. 

Tourmaline crystals show the forms of the Rhombohedral 
Class but with hemimorphic development. They are also com- 
monly characterized by the presence of three faces of a triangular 
prism. Figs. 137-140 represent characteristic hemimorphic tour- 
maline crystals. 

Rhombohedral Class. Tri-Rhombohedral Division. 

This is a subdivision of the Rhombohedral Class, which con- 
tains only a few and rare minerals. It is characterized by the 
forms known as the rhombohedrons of the second and third 
orders. The faces of a second-order rhombohedron correspond 
in position to one-half the faces of the second-order hexagonal 
pyramid, and those of the third order to one-quarter of the faces 
of the dihexagonal pyramid. 

Rhombohedral Class. Trapezohedral Division. 

The only important mineral of this class that is commonly 
found in crystals is quartz, and its crystals as a rule do not show 
forms other than those of the Rhombohedral Class, Normal 
Division. At times, however, small faces may occur of a form 
known as a trapezohedron, which shows a lower symmetry. This 
form has six faces, which correspond in their position to one-quar- 
ter of the faces of a dihexagonal pyramid. The quartz crystals 
are said to be right- or left-handed, depending upon whether these 
faces are to be observed truncating the edges between prism and 
rhombohedron faces at the right or at the left. Figs. 141 and 
142 represent these two types. 



MANUAL OF MINERALOGY 





Fig. 141. 
Right-handed Quartz. 



Fig. 142. 
Left-handed Quartz. 



Characteristics of Hexagonal Crystals. 

Hexagonal crystals are most readily recognized by the follow- 
ing facts: The vertical crystallographic axis is one of either 
hexagonal or trigonal symmetry. The crystals are commonly 
prismatic in habit. When viewed in the direction of the vertical 
axis, they usually show a hexagonal cross section. 

VIII. ORTHORHOMBIC SYSTEM. 

Crystallographic Axes. The crystallographic axes of the 
orthorhombic system are three in number. They make 90 
angles with each other and are of unequal lengths. The rela- 
te 



o 

Fig. 143. 
Orthorhombic Axes. 





1 


~12'^~~~-~~-~^ 




| 


i* 


* 


H $ 
i. 


^--^^ 






Fig. 144. 
Axes of Symmetry. 
Drthorhombic System 




Fig. 145. 

Planes of Symmetry. 
Orthorhombic System, 



ORTHORHOMBIC SYSTEM 



47 



tive lengths of the axes, or the axial ratio, has to be deter- 
mined for each orthorhombic mineral. Any one of the three 
axes may be chosen as the vertical or c axis. The longer of the 
other two is taken as the b axis and is called the macro-axis. 
The shorter of the horizontal axes is taken as the a axis and is 
called the br achy-axis. The length of the b axis is taken as unity 
and the relative lengths of the a and c axes are given in terms 
of it. Fig. 143 represents the crystallographic axes for the 
orthorhombic mineral sulphur, whose axial ratio would be as 
follows: a : b : c = 0.813 : 1 : 1.903. 

Normal Class. 

Symmetry and Forms. The symmetry of the Normal Class, 
Orthorhombic System, is as follows : The three crystallographic 
axes are axes of binary symmetry and the three axial planes are 
planes of symmetry (see Figs. 144 and 145). 

1. Pyramid. An orthorhombic pyramid has eight triangular 
faces, each of which intersects all three of the crystallographic 
axes. There are various different pyramids with varying inter- 
cepts on the axes. A unit pyramid (see Fig. 146) would have 
for its symbol (111). 




no 



no 



Fig. 146. Pyramid. 



Fig. 147. Priam and Base. 



2. Prism. An orthorhombic prism has four vertical rectan- 
gular faces, each of which intersects the two horizontal axes. 
There are various prisms, depending upon their differing rela- 
tions to the horizontal axes. A unit prism (see Fig. 147) would 
have for its symbol (110). 



48 



MANUAL OF MINERALOGY 



3. Macrodome. A macrodome is a form consisting of four 
rectangular faces, each of which intersects the a and c axes and 
is parallel to the b or macro-axis. It is named from the axis to 
which it is parallel. There are various macrodomes with differ- 
ent axial intercepts. A unit form (see Fig. 148) would have 
for its symbol (101). 




Fig. 148. 
Macrodome and Brachypinacoid. 




Oil 



Oil 



Fig. 149. 
Brachydome and Macropinacoid. 



)0] 



4. Brachydome. The brachydome consists of four rectangular 
faces, each of which intersects the b and c axes and is parallel 
to the a or brachy-axis. There are various brachydomes with 
different axial intercepts. A unit form (see Fig. 149) would 
have for its symbol (Oil). 

5. Macropinacoid. The macropinacoid has two parallel faces, 
each of which intersects the a axis and is parallel to the b and c 

axes. It derives its name from the 
fact that it is parallel to the b or 
macro-axis. It is represented in Fig. 
150 and its symbol is (100). 

6. Brachypinacoid. This is a form 
consisting of two parallel faces, each 
of which intersects the b axis and is 
parallel to the a (brachy) and the c 
axes. It is represented in Fig. 150 
and its symbol is (010). 
7. Basal Pinacoid. The basal pinacoid is a form consisting 

of two horizontal faces. It is represented in Fig. 150 and its 

symbol is (001). 



010 



Fig. 150. 

Macropinacoid, Brachypinacoid, 
and Basal Pinacoid. 



ORTHORHOMBIC SYSTEM 



49 





m 



Fig. 151. Sulphur. Fig. 152. Sulphur. Fig. 153. Staurolite. 




Fig. 157. Brookite. 



Fig. 158. Anglesite. 



Fig. 159. Barite. 




Fig. 160. Barite. 




Fig. 161. Celeatite. 




50 MANUAL OF MINERALOGY 

Combinations. Practically all orthorhombic crystals consist 
of combinations of two or more forms. Characteristic com- 
binations of the various forms are given in Figs. 
151-161. 

Hemimorphic Class. 

The only orthorhombic mineral of importance 
belonging to this class is calamine. When its 
crystals are doubly terminated they show dif- 
erent forms at either end of the vertical axis. 
Fig. 162. pig. 162 represents a characteristic crystal. 

Calamine. 

Characteristics of Orthorhombic Crystals. 

The most distinguishing characteristics of orthorhombic crys- 
tals are as follows: The three chief directions at right angles 
to each other are of different lengths. These three directions 
are axes of binary symmetry. The crystals are commonly pris- 
matic in their development and show usually cross sections that 
are either rectangles or truncated rectangles. 



IX. MONOCLINIC SYSTEM. 

Crystallographic Axes. The crystallographic axes of the 
Monoclinic System are three in number. They are of unequal 
lengths. The axes a and b, and 6 and c, make 90 angles with 
each other, but a and c make some oblique angle with each 
other. The relative lengths of the axes and the angle between 
the a and c axes vary for each monoclinic mineral and have to be 
determined in each case from appropriate measurements. The 
a axis is known as the dino-axis, while the b axis is known as 
the ortho-axis. The length of the b axis is taken as unity and the 
lengths of the a and c axes are expressed in terms of it. When 
properly orientated the c axis is vertical, the b axis is horizontal 
and parallel to the observer, and the a axis is inclined down- 
ward toward him. The smaller of the two supplementary 
angles that a and c make with each other is designated as /?. 



MONOCLINIC SYSTEM 



51 



Fig. 163 represents the crystallographic axes of the monoclinic 
mineral orthoclase, the axial constants of which are expressed 
as follows: a : b : c = 0.658; 1 : 0.555; ft = 63 57'. 







Fig. 163. Monoclinic Axes. 

Normal Class. 

Symmetry and Forms. The symmetry of the Normal Class 
of the Monoclinic System is as follows: The crystallographic 
axis b is an axis of binary symmetry and the plane of the a and 





Fig. 164. Fig. 165. 

Symmetry of Monoclinic System. 



The 



c axes is a plane of symmetry (see Figs. 164 and 165). 
forms are as follows: 

1. Pyramid. A monoclinic pyramid is a form consisting of 
four triangular faces, each of which intersects all three of the 
crystallographic axes. There are different pyramids, depending 
upon varying axial intercepts. There are, further, two inde- 
pendent types of monoclinic pyramids, depending upon whether 
the two faces on the upper half of the crystal intersect the 



52 



MANUAL OF MINERALOGY 



positive or the negative end of the a axis. A unit pyramid of 
the first of these types is shown in Fig. 166 and has for its symbol 
(111). A unit pyramid of the second of these types is repre- 
sented in Fig. 167 and has for its symbol (111). Fig. 168 shows 
these two types in combination with each other. It should be 
emphasized that a monoclinic pyramid consists of only four 
faces, two of which are to be found intersecting the upper end 
of the c axis and the other two intersecting its lower end. The 
two types described above are entirely independent of each other. 




Fig. 166. 



Fig. 167. 
Monoclinic Pyramids. 



Fig. 168. 



2. Prism. The monoclinic prism has four vertical rectangular 
faces, each of which intersects the a and b axes. There are 
various prisms with different axial intercepts. A unit prism is 
represented in Fig. 169 and has for its symbol (110). 

3. Orthodome. An orthodome consists of two parallel faces, 
each of which intersects the a and c axes and is parallel to the b 
or ortho-axis. Its name is derived from that of the axis to which 
it is parallel. There are different orthodomes with different 
axial intercepts. There are also two distinct and independent 
types of orthodomes, depending upon whether the face upon the 
upper end of the crystal intersects the positive or negative end 
of the a axis. These two types of orthodomes are represented 
in combination in Fig. 170, but it should be emphasized that they 
are entirely independent of each other. The symbol of the unit 
orthodome in front is (101) and that of the one behind is (T01). 

4. Clinodome. The clinodome is a form having four faces, 
each of which intersects the b and c axes and is parallel to the a 
or clino-axis. There are various clinodomes with differing axial 



MONOCLINIC SYSTEM 



53 



intercepts. A unit form is represented in Fig. 171 and would 
have for its symbol (Oil). 

5. Orthopinacoid. The orthopinacoid has two parallel faces, 
each of which intersects the a axis and is parallel to the b and c 
axes. It derives its name from the fact that it is parallel to the 
b or ortho-axis. It is represented in Fig. 171 and its symbol is 
(100). 

6. Clinopinacoid. The clinopinacoid consists of two parallel 
faces, each of which intersects the b axis and is parallel to the a 
(clino) and the c axes. It is represented in Fig. 170 and its 
symbol is (010). 





Fig. 169. 
Prism and Base. 



Fig. 170. 
Orthodomes and Clinopinacoid. 



Fig. 171. 
Clinodome and 
Orthopinacoid. 



7. Basal Pinacoid. The basal pinacoid is a form consisting 
of two parallel faces, each of which intersects the vertical axis 
and is parallel to the a and b axes. It is represented in Fig. 169 
and its symbol is (001). 

Monoclinic Combinations. Characteristic combinations of the 
forms described above are given in Figs. 172-179. 

Characteristics of Monoclinic Crystals. 

Monoclinic crystals are to be distinguished chiefly by their 
low symmetry. The fact that they possess but one plane of 
symmetry and one axis of binary symmetry at right angles to 
it would serve to differentiate them from the crystals of all 
other systems and classes. Usually the inclination of the crystal 
faces which are parallel to the clino-axis is marked. 



54 



MANUAL OF MINERALOGY 




Fig. 172. Fig. 173. 

Pyroxene. 




Fig. 176. 
Gypsum. 



Fig. 177. 







Fig. 174. Fig. 175. 

Amphibole. 




Fig. 178. 
Orthoclase. 



Fig. 179. 



X. TRICLINIC SYSTEM. 



Crystallographic Axes. The crystallographic axes of the 
Triclinic System are three in number. They are of unequal 
lengths and make oblique angles with each other. The axial 
directions for each triclinic mineral are chosen arbitrarily, but in 
such a way as to yield the simplest relations. Any one of them 
may be taken as c, the vertical axis. The longer of the other 
two is designated as the b or macro-axis, while the shorter is 
called a or the brachy-axis. The relative lengths of the three 
axes and the angles which they make with each other have to 
be calculated for each mineral from appropriate measurements. 
The angles which the different axes make with each other are 



TRIG LIN 1C SYSTEM 



55 



designated respectively as , ft and 7 (see Fig. 180). For ex- 
ample, the crystal constants of the triclinic mineral axinite are 
as follows: a : b : c = 0.482 : 1 : 0.480; a = 82 54'; ft = 91 52'; 
T = 131 32'. 

Normal Class. 

Symmetry and Forms. The symmetry of the Normal Class 
of the Triclinic System consists only in a center of symmetry 
(see Fig. 5, page 8). It has no axes or planes of symmetry. 
All forms of the Triclinic System consist of two similar and paral- 
lel faces. In this respect all triclinic forms might be spoken of 
as pinacoids. They are, however, usually designated as pyramids 
when their faces intersect all three axes, as prisms or domes 
when they intersect two axes and as pinacoids when they inter- 
sect but one axis. 




Fig. 180. 
Triclinic Axes. 



Fig. 181. 
Pyramids. 



Fig. 182. 
Prisms and Basal Pinacoid. 



1. Pyramid. A triclinic pyramid consists of two parallel 
faces, each of which intersects all three crystallographic axes. 
There are four possible types, depending upon the octants in 
which the faces lie. Fig. 181 shows a combination of four unit 
pyramids. 

2. Prisms. A triclinic prism consists of two parallel faces, 
each of which intersects the a and b axes and is parallel to the 
c axis. There are two possible types, a combination of which 
is shown in Fig. 182. 

3. Domes. A triclinic dome consists of two similar parallel 
faces, each of which intersects the c axis and either the a or 6 
axes and is parallel to the other. They are spoken of as either 
macro- or brachydomes, depending upon the axis to which they 
are parallel. There are two types of each. Fig. 183 represents 



56 



MANUAL OF MINERALOGY 



a combination of the two types of macrodome and Fig. 184 
combination of the two brachydomes. 




Fig. 183. 
Macrodomes and 
Brachypinacoid. 



Fig. 184. 

Brachydomes and 
Macropinacoid. 



Fig. 185. 

Macropinacoid, Brachypin- 
acoid, and Basal Pinacoid. 





Fig. 186. 
Axinite. 



Fig. 187. 
Rhodonite. 



Fig. 188. 
Chalcanthite. 



4. Pinacoids. A triclinic pinacoid is a form consisting of two 
parallel faces, each of which intersects one crystallographic axis 
and is parallel to the other two. They are designated as the 
macropinacoid with the symbol (100), as the brachypinacoid 
with the symbol (010), and as the basal pinacoid with the symbol 
(001). A combination of the three forms is shown in Fig. 185. 

Triclinic Combinations. Figs. 186-188 represent characteristic 
triclinic crystals. 

Characteristics of Triclinic Crystals. 

There are only a few triclinic minerals and they seldom show 
distinct and well-developed crystals. When such crystals do 
occur they are to be recognized by the fact that they have no 
plane or axis of symmetry and by the fact that each form consists 
of only two similar and parallel faces. 



II. GENERAL PHYSICAL PROPERTIES 
OF MINERALS. 

I. STRUCTURE OF MINERALS. 

IF by the phrase "structure of minerals" is meant their internal 
or molecular structure, all minerals may be included in one of 
two classes: (1) Crystalline; (2) Amorphous. With only a few 
exceptions, minerals are crystalline in their structure. This does 
not signify, however, that these minerals necessarily occur in 
distinct crystals, but only that their internal structure is such 
that they may under favorable circumstances definitely crystal- 
lize. The few mineral species that are classified as amorphous 
possess no regular internal structure and therefore cannot crys- 
tallize. 

Commonly, however, the expression "structure of minerals" 
refers to their outward shape and form. Various descriptive 
terms are used in this connection that will need short definitions. 

1. When a mineral consists of distinct crystals the follow- 
ing terms may be used: 

a. Crystallized. In definite crystals (see A, pi. II). 

b. Acicular. In slender needlelike crystals. 

c. Capillary. In hairlike crystals. 

d. Filiform. In threadlike crystals. 

e. Dendritic. Arborescent, in slender divergent branches, 
somewhat plantlike, made up of more or less distinct crystals. 

f. Reticulated. Latticelike groups of slender crystals. 

g. Divergent or Radiated. Radiating crystal groups (see C, 
pi. II). 

h. Drusy. A surface is drusy when covered with a layer of 
very small crystals. 

57 



58 MANUAL OF MINERALOGY 

2. When a mineral consists of columnar individuals the 
following terms may be used: 

a. Columnar. In stout columnlike individuals. 

b. Fibrous. In slender columnar individuals. The fibers 
may be parallel or radiated (see D, pi. II.) 

c. Stellated. When the radiating individuals form starlike or 
circular groups. 

d. Globular. When the radiating individuals form spherical 
or hemispherical groups. 

e. Botryoidal. When the globular forms are in groups. The 
word is derived from the Greek for a "bunch of grapes" (see 
B, pi. III). 

f. Reniform or Mammillary. When a mineral is in broad 
rounded masses resembling in shape either a kidney or mamma3 
(see A, pi. III). 

3. When a mineral consists of scales or lamellae. 

a. Foliated. When a mineral separates easily into plates or 
leaves. 

b. Micaceous. Similar to foliated but the mineral can be split 
into exceedingly thin sheets, as in the micas. 

c. Lamellar or tabular. When a mineral consists of flat plate- 
like individuals superimposed upon and adhering to each other. 

d. Plumose. Consisting of fine scales with divergent or 
featherlike structure. 

4. When a mineral consists of grains. 

Coarse to fine granular. When a mineral consists of an 
aggregate of large or small grains. 

5. Miscellaneous. 

a. Compact Earthy. A uniform aggregate of exceedingly 
minute particles. 

b. Stalactitic. When a mineral has the shape of cylinders or 
cones which have been formed by deposition from mineral- 
bearing waters dripping from the roof of some cavity (see B, 
pi. II). 

c. Concentric. Consisting of more or less circular layers super- 
imposed upon one another about a common center (see C, 
pi. III). 



PLATE II. 




A. 




D. 




A. Crystallized Quartz. 

B. Stalactitic Limonite. 



C. Radiated Natrolite. 

D. Fibrous Serpentine. 



PLATE III. 





A. Mammillary or Reniform Hematite. B. Botryoidal Chalcedony, 
C. Concentric Malachite. 



CLEAVAGE, PARTING AND FRACTURE 59 

d. Banded. When a mineral occurs in narrow parallel bands 
of different color or texture. 

e. Geodes. When a cavity has been lined by the deposition 
of mineral material but not wholly filled, the more or less spherical 
mineral shell is called a geode. The mineral is often banded 
owing to successive depositions of the material, and the inner 
surface is frequently covered with projecting crystals. 

f . Massive. When a mineral is composed of compact material 
with an irregular form and does not show any peculiar structure 
like those described above, it is said to be massive. 

II. CLEAVAGE, PARTING AND FRACTURE. 

1. Cleavage. If a mineral, when the proper force is applied, 
breaks so that it shows definite plane surfaces, it is said to possess 
a cleavage. These cleavage surfaces resemble natural crystal 
faces. They are always parallel to some possible crystal face, 
and usually to one having simple relations to the crystallographic 
axes. They may be perfect, as in the cases of the micas, calcite, 
gypsum, etc., or they may be more or less obscure. Cleavage is 
due to the fact that in the mineral 

structure there is a certain plane or 
planes along which the molecular co- 
hesion is weaker than in other direc- 
tions. All minerals do not show 
cleavage, and only a comparatively 
few show it in an eminent degree. 
The quality of the cleavage and its 
crystallographic direction are often 
important aids in the identification of Fi e- 189 - Cubic Cleavage - 
a mineral. The cleavage of a mineral 

is described according to the crystal face to which it is parallel, 
as cubic cleavage (galena, halite) (see Fig. 189), octahedral 
cleavage (fluorite), dodecahedral cleavage (sphalerite), rhombo- 
hedral cleavage (calcite), prismatic cleavage (amphibole), basal 
cleavage (topaz), pinacoidal cleavage (stibnite), etc. 

2. Parting. Certain minerals when subjected to a strain or 
pressure develop planes of molecular weakness along which they 




60 MANUAL OF MINERALOGY 

may subsequently be broken. When plane surfaces are produced 
on a mineral in this way it is said to have a parting. This 
phenomenon resembles cleavage, but is to be distinguished from 
it by the facts that not every specimen of a certain mineral will 
exhibit it, but only those specimens which have been subjected 
to the proper pressure, and that even in these specimens there 
are only certain planes in the given direction along which the 
mineral will break. In the case of cleavage, every specimen of the 
mineral will in general show it, and it can be produced in a given 
direction in all parts of a crystal. Familiar examples of part- 
ing are the cases of the octahedral parting of magnetite, the basal 
parting of pyroxene and the rhombohedral parting of corundum. 
3. Fracture. By the fracture of a mineral is meant the way 
in which it breaks when it does not show plane surfaces as in 

cleavage or parting. The fol- 
lowing terms are commonly 
used to designate different sorts 
of fracture : 

a. Conchoidal. When the 
fracture has smooth, curved 
surfaces like the interior surface 
of a shell it is said to be con- 
choidal (see Fig. 190). This 
pis most commonly observed 

Fig. 190. Conchoidal Fracture Vol- in Such Substances as glaSS, 
canic Glass. quartz, etc. 

b. Fibrous or Splintery. When the mineral breaks showing 
splinters or fibers. 

c. Hackly. When the mineral breaks with a jagged, irregular 
surface with sharp edges. 

d. Uneven or Irregular. When the mineral breaks into rough 
and irregular surfaces. 

in. HARDNESS OF MINERALS. 

Minerals vary quite widely in their hardness, and a determi- 
nation of their degree of hardness is often an important aid to 
their identification. A series of minerals has been chosen as a 




HARDNESS OF MINERALS 61 

scale by comparison with which the relative hardness of any 
mineral may be told. The scale consists of crystallized varieties 
of the following minerals, each species being harder than those 
preceding it in the scale. 

Scale of Hardjiess. 

1. Talc. 4. Fluorite. 8. Topaz. 

2. Gypsum. 5. Apatite. 9. Corundum. 

3. Calcite. 6. Orthoclase. 10. Diamond. 

7. Quartz. 

In order to determine the relative hardness of any mineral in 
terms of this scale, it is necessary to find which ones of these 
minerals it can and which it cannot scratch. In making the 
determination the following precautions should be observed: 
Sometimes when a mineral is softer than another, portions of 
the first will leave a mark on the second which may be mis- 
taken for a scratch. It can be rubbed off, however, while a 
true scratch will be permanent. Some minerals are frequently 
altered on the surface to material which is much softer than the 
original mineral. A fresh surface of the specimen to be tested 
should therefore be used. Sometimes the physical structure of 
a mineral may prevent a correct determination of its hardness. 
For instance, if a mineral is pulverulent, granular or splintery 
in its structure, it may be broken down and apparently scratched 
by a mineral much softer than itself. It is always advisable 
when making the hardness test to confirm it by reversing the 
order of procedure. 

The following materials may serve in addition to the above 
scale: The finger nail is a little over 2 in hardness, since it can 
scratch gypsum and not calcite. A cent is about 3 in hardness, 
since it can just scratch calcite. The steel of an ordinary pocket- 
knife is just over 5, and ordinary window glass has a hardness of 
5.5. 

Crystals frequently show different degrees of hardness, depend- 
ing upon the direction in which they are scratched. Ordinarily 
the difference is so small that it can be detected only by the use 
of delicate instruments. 



62 MANUAL OF MINERALOGY 



IV. TENACITY OF MINERALS. 

The following terms are used to describe various kinds of 
tenacity in minerals : 

1. Brittle. When a mineral breaks or powders easily. 

2. Malleable. When a mineral can be hammered out into 
thin sheets. 

3. Sectile. When a mineral can be cut into thin shavings 
with a knife. 

4. Flexible. When a mineral bends but does not resume its 
original shape when the pressure is released. 

5. Elastic. When, after being bent, the mineral will resume 
its original position upon the release of the pressure. 



V. SPECIFIC GRAVITY OF MINERALS. 

The specific gravity of a mineral is a number which expresses 
the ratio existing between its weight and the weight of an equiva- 
lent volume of water. If a mineral has a specific gravity of 2, 
it means that a given specimen of that mineral weighs twice 
as much as the same volume of water. The specific gravity of 
a mineral which does not vary in its composition is a constant 
factor, the determination of which is frequently an important 
aid to its identification. 

After a little experience one can frequently judge quite accu- 
rately the specific gravity of a mineral by weighing it in the hand. 
Minerals containing the heavy metals like lead, copper, iron, etc., 
can be at once differentiated from those containing lighter ele- 
ments by this means. And by practice one can become expert 
enough to be able to distinguish from each other minerals that 
have comparatively small differences in specific gravity; for 
instance, topaz (sp. gr. = 3.52) from orthoclase (sp. gr. = 2.57), 
and fluorite (sp. gr. = 3.18) from quartz (sp. gr. = 2.6). 

'In order to accurately determine the specific gravity of a 
mineral, the following conditions must be observed : The mineral 
must be pure. It must also be solid, with no cracks or cavities 



SPECIFIC GRAVITY OF MINERALS 



63 



within which bubbles or films of air could be imprisoned. The 
fragment used should be reasonably large, about one cubic inch 
being a convenient size. If these conditions cannot be met, 
it is of little use to attempt a specific gravity determination by 
any rapid and simple method. 

The necessary steps in making an ordinary specific gravity 
determination are briefly as follows : The mineral is first weighed 
in air. Let this weight be represented by x. It is then immersed . 
in water and weighed again. Under these conditions it weighs 
less, since any object immersed in water is buoyed up by a force 
equivalent to the weight of the water displaced. Let the weight 
in water be represented by y. Then x y equals the loss of 
weight caused by immersion in water, or the weight of an equal 

volume of water. The expression - will therefore yield a 

x-y 

number which is the specific gravity of the mineral. 

The specific gravity of a mineral may be determined in various 
ways, those most commonly used 
being described below. 

1. By Means of a Chemical 
Balance. The most accurate 
method of determining the specific 
gravity of a mineral is by the use 
of a chemical balance. To one 
beam of the balance is suspended 
a wire basket which is so arranged 
that it can be immersed in a beaker 
of water (see Fig. 191). The bas- 
ket is hung in the water and then 
counterbalanced by weights on the 
opposite pan of the balance. The 
mineral specimen to be tested, hav- 
ing been first weighed on the bal- 
ance in the ordinary fashion, is now 
placed in the basket under the water Flg> 191< 

and weighed again. These two weights are the necessary data 
for calculating the specific gravity as explained above. 




64 



MANUAL OF MINERALOGY 



2. By Means of a Jolly Balance. Fig. 192 represents the bal- 
ance of Jolly, by which the specific gravity is measured through 

the stretching of a spiral wire spring. From 
the spring is suspended two small metal pans 
(c and d), one above the other. The ap- 
paratus is so arranged that the lower pan 
(d) is always immersed in 'a beaker of water 
which, resting upon the adjustable platform 
B, can be placed at any required height. On 
the side of the upright A, which faces the 
spiral wire, there is a mirror with a gradu- 
ated scale engraved upon it. The position 
of the balance is determined by means of a 
small bead (m) which is strung on the wire 
above the upper pan and which serves as an 
indicator. The eye is brought into such a 
position that the bead exactly covers its 
image in the mirror, and its position is then 
determined by means of the scale. 

Three readings must be taken : first, simply 
the position of the balance with the lower 
Fig. 192. pan in the water, x\ second, its position 

when the mineral is placed in the upper pan, y; and third, its 
position when the mineral is in the lower pan and covered with 
water, z. The platform B with the beaker of water must be 
properly adjusted for each of these readings so as to always have 
the lower pan immersed in the water. The expression x y 
will give a number representing the weight of the mineral in air, 
while x z will yield a number corresponding to its weight in 
water. From these values the specific gravity of the mineral 
can be calculated as described above. 

3. By Means of a Beam Balance. This is a very convenient 
and quite accurate method of determining specific gravity. The 
balance illustrated in Fig. 193 was devised by S. L. Penfield, 
who describes its operation as follows: 

"The beam of wood is supported on a fine wire, or needle, at 
6 and must swing freely. The long arm be is divided into a 




PROPERTIES DEPENDING UPON LIGHT 65 

decimal scale, commencing at the fulcrum 6; the short arm car- 
ries a double arrangement of pans so suspended that one of them 
is in the air and the other in water. A piece of lead on the short 
arm serves to almost balance the long arm, and, the pans being 
empty, the beam is brought to a horizontal position, marked 
upon the upright, near c, by means of a rider d. A number of 
counterpoises are needed, which do not have to be of any specific 




Fig. 193. 

denomination, as it is their position on the beam and not their 
actual weight which is recorded. The beam being adjusted by 
means of the rider d, a fragment of the mineral is placed in the 
upper pan and a counterpoise is chosen, which, when placed 
near the end of the long arm, will bring it into a horizontal 
position. The weight of the mineral in air is given by the posi- 
tion of the counterpoise on the scale. The mineral is next 
transferred to the lower pan, and the same counterpoise is 
brought nearer the fulcrum b until the beam becomes again 
horizontal, when its position gives the weight of the mineral in 
water." From these two values the specific gravity of the min- 
eral can be calculated. 

VI. PROPERTIES DEPENDING UPON LIGHT. 
A. Luster. 

The luster of a mineral is its appearance due to the effect of 
light upon it. In general we divide minerals into three classes 
depending upon their luster, namely, metallic luster, submetallic 



66 MANUAL OF MINERALOGY 

luster and nonmetallic luster. A mineral having the appearance 
of a metal like lead or copper is said to have a metallic luster. 
The term is further defined by saying that a mineral with a 
metallic luster is strictly opaque to light when examined on its 
thinnest edges. The metallic luster of a mineral can be proved 
by observing the color of its powder. If the powder is black 
or very dark in color, it means that each little particle of the 
mineral is still opaque to light, and therefore the mineral has a 
metallic luster. This test is made usually by the aid of what 
is called a streak plate. This consists of a piece of unglazed 
white porcelain upon which the mineral is rubbed so that a 
streak of its powder is formed upon the plate. The color of this 
" streak" of the mineral, as it is called, will determine its luster 
and also frequently will materially help in its identification. 
Examples of minerals with metallic luster would be, galena, 
PbS, with a bluish gray streak; pyrite, FeS 2 , with a black streak; 
chalcopyrite, CuFeS 2 , with a greenish black streak; and hema- 
tite, Fe 2 3 , with a dark reddish brown streak. 

Nonmetallic Luster. Minerals with a nonmetallic luster are 
transparent to light on their thin edges. In general they are 
light colored, but not necessarily so. When a streak is obtained 
from a nonmetallic mineral, it is either colorless or very light, in 
color. Various descriptive terms are used to further describe 
the appearance of nonmetallic minerals, the more common being 
as follows: 

Vitreous. Having the luster of glass. Example, quartz. 

Resinous. Having the appearance of resin. Example, sphal- 
erite. 

Pearly. Having the appearance of pearl. This is usually 
observed in minerals on surfaces that are parallel to cleavage 
planes. Example, basal plane on apophyllite. 

Greasy. Looking as if covered with a thin layer of oil. Ex- 
amples, some specimens of sphalerite and massive quartz. 

Silky. Like silk. It is. the result of a fine fibrous structure. 
Examples, fibrous malachite, serpentine, etc. 

Adamantine. Having a hard, brilliant luster like that of a 
diamond. It is due to the mineral's high index of refraction 



PROPERTIES DEPENDING UPON LIGHT 67 

(see p. 71). The transparent lead minerals, like cerussite and 
anglesite, show it. 

Submetallic Luster. There is no sharp divisional line between 
minerals with metallic and those with nonmetallic luster, and the 
group of minerals lying between is said to have a submetallic 
luster. They show a colored streak, but one which is not black 
or very dark in color. Examples of minerals with submetallic 
luster are limonite and some of the darker varieties of sphalerite. 

B. Color of Minerals. 

The color of minerals is one of their most important physical 
properties. In the case of many minerals, especially those 
showing a metallic luster, color is a definite and constant prop- 
erty and will serve as an important means of identification. 
For example, the brass-yellow col6r of chalcopyrite, the blue- 
gray of galena, the black of magnetite, the green of malachite, 
etc., is in each case a striking property of the mineral. It is to 
be noted, however, that surface alterations may change the color 
even in minerals whose color is otherwise constant. This is 
shown in the yellow tarnish frequently observed on pyrite and 
marcasite, the purple tarnish on bornite, etc. In noting the 
color of a mineral, therefore, a fresh surface should be examined. 
Many minerals, however, do not show a constant color in their 
different specimens. This variation in color in the same species 
may be due to different causes. A change in color is often pro- 
duced by a change in composition. The progressive isomor- 
phous replacement of zinc by iron in sphalerite (see page 77) 
will change its color from white through yellow and brown to 
black. The minerals of the Amphibole Group show a similar 
variation in color. The amphibole tremolite, which is a silicate 
with only calcium and magnesium as bases, is very light in color, 
at times almost white; while actinolite and hornblende, which 
are amphiboles that contain increasing amounts of iron, range in 
color from green to black. Again, a mineral may show a wide 
range of color without any apparent change in composition. 
Fluorite is a striking example of this, since it is found in crystals 
that are colorless, white, pink, yellow, blue, green, etc. Such 



68 MANUAL OF MINERALOGY 

extreme cases are, however, rare. Minerals are also frequently 
colored by various impurities. The red variety of quartz, known 
as jasper, is colored by small amounts of hematite. From the 
above it is seen that, while the color of a mineral is one of its im- 
portant physical properties, it is not always constant, and must 
therefore often be used with some caution in the identification 
of a species. 

Play of Colors. Iridescence, Opalescence, etc. A mineral is 
said to show a play of colors when on turning it several prismatic 
colors are seen in rapid succession. This is to be seen especially 
in the diamond and precious opal. A mineral is said to show 
a change of color when on turning it the colors change slowly, 
being different for varying positions. This is observed in labra- 
dorite. A mineral is iridescent when it shows a series of pris- 
matic colors in the interior of the crystal or on the surface. It 
is usually caused by the presence of small fractures or cleavage 
planes which serve to break up the light into the prismatic colors. 
Opalescence is a milky or pearly reflection from the interior of 
a specimen. It is observed at times in opal and cat's-eye. A 
mineral is said to show a tarnish when the color of the surface 
differs from that of the interior. 

Asterism. Some crystals, especially those of the Hexagonal 
System, when viewed in the direction of the vertical axis, present 
starlike rays of light. This arises from peculiarities of texture 
along the axial directions, or from some inclusions. A remark- 
able example is the star sapphire. 

Phosphorescence. Several minerals when rubbed or heated 
give out light. This property is known as phosphorescence. 
Fluorite often shows phosphorescence when fragments are gently 
heated. The color of the emitted light may be green, purple, 
rose, yellow, etc. 

C. Refraction of Light in Minerals. 

When light comes into contact with a transparent mineral, 
part of it is reflected from the surface of the mineral and part 
enters the mineral. The light which enters the mineral is in 
general refracted. When light passes from a rarer into a denser 



PROPERTIES DEPENDING UPON LIGHT 



69 



medium, as in the case of passing from air into a mineral, its 
velocity is retarded. This change in velocity is accompanied 
by a corresponding change in the direction in which the light 
travels, and it is this change in direction of propagation that is 
known as refraction of light. The amount of refraction of a 
given light ray is directly proportional to the ratio existing be- 
tween the velocity of light in air and in the mineral. The ratio 
between these two velocities is known as the index of refraction 
of the mineral and is designated by n. That is, if the index of 
refraction, or n, of a mineral is 2, light will travel in it with one- 
half the velocity it has in air. 

In Fig. 194 let M-M represent the surface of a crystal of flu- 
orite. Let N-0 be normal to that surface. Let A-0 be one of 
a number of parallel light rays striking the surface M-M in such 
a way as to make the angle i (angle of incidence) with the normal 




Fig. 194. 



Refraction of Light. 



Fig. 195. 



N-0. Let 0-P be at right angles to the rays and representing the 
wave front of the light in air. As the crystal is the denser me- 
dium the light will travel in it more slowly. Therefore, as each 
ray in turn strikes the surface M-M, it will be retarded and the 
direction of its path be changed proportionately. In going from 
a rarer into a denser medium, the direction of the ray will be bent 
toward the normal N-O. To find the direction of the rays and 
line of wave front in the crystal, proceed as follows: Since the 



70 MANUAL OF MINERALOGY 

index of refraction of fluorite is 1.43, ray A will travel in the 

crystal, in the time it takes ray C to travel from P to R, - of 

1.43 

that distance, or to some point on the circular arc the length of 

whose radius OA' is the distance P-R. Similarly, ray B 
I A3 

will travel in the mineral during the period of time in which 

ray C travels from S to R a distance equal to - - of the distance 

1.43 

S-R, or the radius TB f . The same reasoning will hold true for 
all other rays. The wave front in the crystal can then be de- 
termined by drawing a tangent the line A'B'R to these 
various circular arcs; and lines perpendicular to this wave front 
will represent the direction in which the light travels in the min- 
eral, and the angle NO A' or r will be the angle of refraction. 
Fig. 195 shows the same construction as that of Fig. 194, only 
in this case the mineral in question is assumed to be diamond. 
Since the index of refraction of diamond (n = 2.42) is much 
greater than that of fluorite, light will travel in it with a still 
slower velocity. Consequently in diamond the amount of re- 
fraction will be greater. This is shown in the two figures, in 
both of which the angle of incidence is the same. 

The refractive power toward light which a mineral possesses 
has often a distinct effect upon the appearance of the mineral. 
For example, a mass of cryolite may almost always be told at 
sight, though, as is generally the case, there is no crystal shape 
to aid in the identification. The mass has a peculiar appearance, 
something like that of wet snow, and quite different from that 
of ordinary white substances ; and this is due to the fact that the 
index of refraction of cryolite is unusually low for a mineral. 
An instructive experiment may be tried by finely pulverizing 
some pure white cryolite and throwing the powder into water, 
when it will apparently disappear, as if it had instantly gone into 
solution. The powder, however, is insoluble, and may be seen 
indistinctly as it settles to the bottom of the vessel. The reason 
for this disappearance of the cryolite is that its index of refraction 
(about 1.34) is near that of water (1.335), hence the light travels 
almost as readily through the mineral as through water, and 
consequently it undergoes little reflection or refraction. 



PROPERTIES DEPENDING UPON LIGHT 



71 



Substances having an unusually high index of refraction have 
an appearance which it is hard to define, and which is generally 
spoken of as adamantine luster. This kind of luster may be com- 
prehended best by examining specimens of diamond (n 2.419) 
or of cerussite (n = about 3.2). They have a flash and quality, 
some diamonds almost a steel-like appearance, which is not 
possessed by minerals of low index of refraction; compare, for 
example, cerussite and fluorite (n 1.434). It is their high 
index of refraction that gives to many gem minerals their great 
brilliancy and charm. 

In the majority of cases the index of refraction of a mineral 
is not far from 1.5, and gives to minerals a luster which is desig- 
nated as vitreous. Quartz (n = 1.55), feldspar (n = 1.52) and 
calcite (n = 1.57) are good examples. 

D. Double Refraction in Minerals. 

All minerals except those belonging to the Isometric System 
show in general a double refraction of light. That is, when a 
ray of light enters such 
a mineral it is broken up 
into two rays, each of 
which travels with a dif- 
ferent velocity through 
the mineral. Since each 
ray has its own charac- 
teristic velocity, it fol- 
lows that the angle of re- 
fraction will be different 
in each case and the 
paths of the two rays will ^^^^^^^^^^^^^^^^^ 

be divergent. In Other p^. 196 . Double Refraction in Calcite. 

words, the light has un- 
dergone double refraction. In the majority of cases the amount 
of this double refraction is small, and the fact that it exists 
can only be demonstrated by special and delicate instruments. 
Calcite, however, shows such a strong double refraction that 
it can be easily observed. Take a cleavage block of clear 
calcite (Iceland spar), for instance, and place it over an 




72 MANUAL OF MINERALOGY 

image marked on paper. The image will appear double (see 
Fig. 196). 

The amount of double refraction, or in other words the amount 
of divergence of the two rays, shown by any mineral depends, 
first, upon the refracting power of the mineral, or its strength of 
birefringence, as it is called; second, upon the thickness of the 
block of the mineral ; and lastly, upon the crystallographic direc- 
tion in which the light is traveling in the mineral. In the case 
of tetragonal and hexagonal minerals, there is one direction (that 
of the vertical crystallographic axis) in which no double refrac- 
tion takes place. As soon as a ray of light in the mineral diverges 
from this direction it is doubly refracted, and the amount of 
double refraction increases as the path of the light becomes more 
oblique, and attains its maximum when it is at right angles to 
the vertical axis. Such minerals belong to the optical class known 
as uniaxial. In the case of orthorhombic, monoclinic and triclinic 
minerals, there are two directions similar to the one described 
above, in which no double refraction takes place, and the minerals 
of these systems are therefore spoken of as optically biaxial. 

In addition to doubly refracting light, all minerals except those 
of the Isometric System polarize it as well. Ordinary light is 
conceived as made up of vibrations taking place in all planes. 
Light is polarized when it vibrates in a single plane. In the case 
of both uniaxial and biaxial crystals, each of the two rays into 
which a beam of light is refracted is polarized and in planes 
which are perpendicular to each other. For a fuller considera- 
tion of the optical properties of minerals, the reader must be 
referred to books of a more detailed character. 

VII. PYROELECTRICITY. 

Crystals of certain minerals, on cooling after being heated to 
about 100 C., will develop upon different portions a positive 
and a negative electric charge. This can be proved by the power 
that such minerals show under these conditions to attract and 
hold to themselves small pieces of paper, etc. Minerals which 
are hemimorphic in their crystallographic character, like cala- 
mine, tourmaline, etc., exhibit this property. 



III. CHEMICAL MINERALOGY. 

A MINERAL may be defined as a naturally occurring substance 
having a definite chemical composition. The chemical compo- 
sition of a mineral is the most fundamentally important fact 
about it, for upon this all its other properties must in great 
measure be dependent. The physical characteristics of a mineral 
may sometimes serve as means of its positive identification, and 
in the great majority of cases they will be of material assistance; 
but the final proof of its identity will more often lie in the deter- 
mination of its chemical character by means of chemical tests. 
Consequently the study of the chemistry of minerals is the most 
important single division of the subject. This section will, 
therefore, be devoted to a brief and elementary discussion of 
chemical mineralogy. First some general aspects of the subject 
will be presented, followed by a short description of the methods 
of testing for the different elements most commonly observed. 
The scope and size of this book necessitate the assumption that 
the reader is familiar with at least the essentials of chemical fact 
and nomenclature. 

Scientists up to the present time have established the occur- 
rence of more than eighty different elements. The greater part 
of these, however, are extremely rare and are only of scientific 
interest. Some forty-four elements are found in sufficient 
amount, or because of their properties are of sufficient impor- 
tance, to warrant a discussion of them here. A considerable 
proportion of this list also must "be considered as rare in occur- 
rence. The following table gives the names and symbols of the 
eighteen most common elements arranged in the approximate 
order of their importance as constituents of the earth's crust: 

73 



T4 MANUAL OF MINERALOGY 

Oxygen 0. Sodium Na. Phosphorus P. 



Silicon Si. 
Aluminium Al. 
Iron Fe. 
Calcium Ca. 
Magnesium Mg. 


Potassium K. 
Hydrogen H. 
Titanium Ti. 
Carbon C. 
Chlorine Cl. 


Sulphur S. 
Barium Ba. 
Manganese Mn. 
Strontium Sr. 
Fluorine F. 



It is to be noted that the above list fails to include such im- 
portant elements as copper, lead, zinc, silver, gold, tin, mercury, 
nickel, antimony, arsenic, etc., all of which form much less than 
one-hundredth of one per cent of the rocks of the earth's crust. 

These elements occur alone or in various chemical combina- 
tions in the form of minerals. Below is given a brief discussion 
of the various classes of chemical compounds in which the ma- 
jority of minerals occur. 

Chemical Groups. 

Elements. There are a few minerals that consist of single 
elements alone. For example, gold, Au. 

Sulphides. A very important group of minerals, consisting 
of combinations of the various metals with the element sulphur, 
are known as sulphides. They include the majority of the 
metallic ore minerals. For example, pyrite, FeS2. 

Sulpho-salts. This group of minerals includes a series which 
mostly contain lead, copper or silver in combination with sulphur 
and either antimony or arsenic. For example, tetrahedrite, 
Cu 8 Sb 2 S 7 . 

Haloids. This group includes minerals that are salts of the 
halogen acids, chiefly hydrochloric or hydrofluoric acids. Ex- 
amples are halite, NaCl, and fluorite, CaF 2 . 

Oxides. The minerals of this group contain a metal in com- 
bination with oxygen. For example, hematite, Fe 2 3 . 

Hydroxides. An hydroxide is a mineral that contains the 
hydroxyl group, OH, as an important radical. For example, 
limonite, Fe 4 3 (OH) 6 . 

Carbonates. The carbonates are salts of carbonic acid, 
H 2 C0 3 . For example, calcite, CaC0 3 . 






DERIVATION OF A CHEMICAL FORMULA 75 

Silicates. The silicates form the largest chemical group among 
minerals. They contain various elements as bases, the most 
common of which are sodium, potassium, calcium, magnesium, 
aluminium and ferrous and ferric iron. They are frequently 
very complex in their chemical structure. They are salts of a 
number of different silicic acids, the most important of which 
are as follows: 

Orthosilicate acid = H 4 Si04, which is represented by alman- 
dite, Fe 3 Al 2 (Si04) 3 . 

Metasilicic acid = H 4 Si 2 6 or H 2 Si0 3 , represented by leucite, 
KAl(Si0 3 ) 2 . 

Polysilicic acid = H 4 Si 3 8 , represented by orthoclase, KAlSi 3 8 . 

Niobates and Tantalates. These are combinations of vari- 
ous metals with the rare niobic'and tantalic acids. For example, 
columbite, FeNb 2 6 , and tantalite, FeTa 2 6 . 

Phosphates. The phosphates are salts of some phosphoric 
acid. The most common member of the group is the mineral 
apatite, Ca 4 (CaF) (P0 4 ) 3 . 

Sulphates. The sulphates are salts of sulphuric acid, H 2 S0 4 . 
For example, gypsum, CaS0 4 .2H 2 0. 

Tungstates. These are salts of the rare tungstic acid H 2 W0 4 . 
For example, scheelite, CaW0 4 . 

Derivation of a Chemical Formula from the Analysis of 
a Mineral. 

The chemical formulas which are assigned to minerals have in 
every case been calculated from chemical analyses. An analysis 
gives the percentage composition of a mineral, or, in other words, 
the parts by weight in one hundred of the different elements or 
radicals present. Consider the following analysis of chalcopy- 
rite: 

Percentages. Atomic weights. Ratio. 

S = 34.82 ^ 32.06 = 1.086 = 2.00 

Gu = 34.30 -r- 63.6 = 0.539 = 0.99 or 1.00 

Fe = 30.59 -r- 55.9 = 0.547 = 1.00 

99.71 

The percentage numbers given indicate the proportions by 

weight of the different elements in the mineral. But as these 



76 MANUAL OF MINERALOGY 

elements have different atomic weights, the numbers do not 
represent the ratio of the different atoms to each other in the 
chemical molecule. In order to derive the relative proportions 
of the atoms of the different elements to each other, the percent- 
ages as given are divided in each case by the atomic weight of 
the element. This gives a series of numbers which does repre- 
sent the ratio of the atoms to each other in the molecule. In the 
analysis of chalcopyrite this ratio becomes S : Cu : Fe = 2 : 1 ; 1. 
Consequently CuFeS 2 will constitute the chemical formula for 
the mineral. 

If the mineral is an oxygen compound the results of the analy- 
sis are given as percentages of the oxides present, and by a cal- 
culation similar to that outlined above the ratio of these oxide 
radicals to each other in the molecule is determined; the only 
difference in the process being that in this case the percentage 
numbers are divided by the sum of the atomic weights of the 
elements present in the different radicals. As an example con- 
sider the following analysis of gypsum: 

Percentages. Molecular weights. Ratio. 

SO 3 = 46.61 -r- 83.06 = 0.583 = 1.00 

CaO = 32.44 + 56.1 = 0.578 = 0.99 or 1.00 

H 2 O = 20.74 + 18.0 = 1.152 = 1.98 or 2.00 
99.79 

From this it is seen that the ratio of the radicals to each other 
in the molecule is S0 3 : CaO : H 2 = 1 : 1 : 2, and consequently 
the composition of gypsum can be represented by the formula 
CaO.S0 3 .2H 2 or CaS0 4 .2H 2 0. 

Calculation of the Percentage Composition of a Mineral 
from Its Chemical Formula. 

It frequently happens that it is desirable to determine what 
the theoretical composition of a mineral is, having given its 
formula. The process of calculation is the reverse of that 
described in the preceding division. Take, for example, the 
mineral chalcopyrite, CuFeS 2 ; what are the proportions by 
weight of the different elements in one hundred parts of the 
mineral? The process consists in first adding up the atomic 



ISOMORPHISM 



77 



weights of the different elements present and so obtaining the 
molecular weight of the compound, as follows: 

Atomic weights. 
Cu = 63.6 

Fe = 55.9 

S = 32.06 X 2 = 64.12 
Molecular weight CuFeS 2 = 183.62 

It is obvious from the above that in 183.62 parts by weight of 
chalcopyrite there are 63.6 parts of copper, etc. In order to find 
the parts of copper in 100 parts of the mineral, or in other words, 
its percentage, the following proportion is made: 

183.62 : 63.6 = 100 : x. 

When this equation is solved, x becomes 34.64, or the percent- 
age of copper in chalcopyrite. The percentages of the iron and 
sulphur are to be obtained in a similar manner. 

Isomorphism. 

It is to be noted frequently that the results of a mineral analy- 
sis do not agree with the theoretical composition of the mineral 
as calculated from its formula. Further, it often happens that 
the analyses of different specimens of the same mineral will 
show marked variations in the proportions of the different ele- 
ments present. If the material analyzed was pure and the analy- 
sis accurately made, these variations are commonly to be ex- 
plained by the principle of isomorphism. To make clear what 
is meant by this term, it will be best to consider some illustrative 
examples. Sphalerite, for instance, is a mineral which shows in 
its different specimens a wide range in color, from white through 



I. 


At. Ra- 

wt. tio. 


II. 


At. Ra- 
wt. ti9- 


III. 


At. .Ra- 
wt. tio. 


S =32.22 
Zn =67.46 
Fe= 
Cd = . . . 


32.06=1.00 
65.4 =1.03 


33.36 
63.36 
3.60 


32.06=1.04 =1.00 
65.4 =0.96) , ft9 
55.9 =0.06) L - v 


33.25 
50.02 
15.44 
0.30 


32.06=1.037 =1.0 
65.4 =0.764] 
55.9 =0.2761 . mft 
112.4 =0.0021 - 1 - 018 


Pb= . 








1.01 


206.9 =0 004J 














Total.... 99. 68 




100 32 




100.02 

















78 MANUAL OF MINERALOGY 

brown to black, with a corresponding variation in composition. 
In column I is given an analysis of white sphalerite from Frank- 
lin Furnace, N. J., in column II is given an analysis of a brown 
sphalerite from Roxbury, Conn., and in column III that of a 
black sphalerite from Felsobanya. 

It will be noted that in the three analyses there is a progressive 
increase in the percentages of iron present and a corresponding 
decrease in the amount of zinc. It would appear as if the iron 
had replaced a portion of the zinc in the mineral and was play- 
ing the same part as the zinc in the molecule. Further, if the 
atomic ratios are derived from each analysis by the method de- 
scribed in the preceding division, it will be found that in analy- 
ses II and III the series of numbers do not show any rational 
relations to each other. But, if the numbers derived in each 
case from the percentages of the different metals present are 
combined, their sum will equal the number derived from the per- 
centage of the sulphur. In other words, the number of atoms of 
zinc plus those of iron, lead and cadmium equals the number of 
atoms of sulphur. The formula of sphalerite could therefore be 
written R"S, where R" equals chiefly zinc, with smaller amounts 
of iron and other metals. Another way of expressing the same 
thing would be (Zn,Fe)S. In this case the iron is said to be 
isomorphous with the zinc, since it has the power to replace the 
zinc in the mineral in varying proportions without changing its 
molecular structure or crystal form. 

The garnets form a series of minerals with the same crystal- 
lization and general physical properties, but show quite a wide 
variation in chemical composition. Consider the following analy- 
sis of an almandine garnet : 

Percentages. Molecular weights. Ratio. 

SiO 2 = 35.92 4- 60.4 =0.594 =3.00 

A1 2 O 3 = 19.18 4- 102.2 = 0.187 I n 917 - 1 no 

Fe 2 3 = 4.92 -M59.8 = 0.030 U ' 

FeO = 29.47 -f- 71.9 =0.409 

MnO= 4.80; ^ 71.0 =0.067 

MgO = 3.70 + 40.36 = 0.091 

CaO = 2.38 ^ 56.1 = 0.042 
100.37 



0.609 = 3.02 



ISOMORPHISM 79 

It is a silicate containing chiefly ferrous and aluminium oxides 
but with smaller amounts of manganese, magnesium, calcium and 
ferric oxides. If the ratio of the series of oxides to each other 
in the molecule is obtained, it is seen that it is not a rational one. 
But if the ratio numbers of the similar oxides are combined, 
that is, the number from the A1 2 3 with that from the Fe 2 3 , and 
that from the FeO with those from the MnO, MgO and CaO, 
it will be found that the relationship of the different groups of 
radicals can be expressed as Si0 2 : A1 2 3 -j- Fe 2 3 : FeO + MnO 
+ MgO -f CaO = 3:1:3. From this it is seen that some of 
the possible A1 2 3 has been replaced by isomorphous Fe 2 3 , 
and that a part of the FeO has been replaced by the isomor- 
phous oxides of MnO, MgO and CaO. The formula for this 
garnet might be written, therefore, as 3R // 0.1R 2 /// 3 .3Si0 2 or 
R 3 // R 2 /// (Si0 4 ) 3 , in which R" = Fe, Mn, Mg and Ca, and R'" = A1 
and Fe. 

Isomorphous Groups. A series of compounds which have 
analogous chemical compositions and closely similar crystal 
forms are said to make an isomorphous group. The artificial 
compounds known as the alums form a striking example. They 
are double salts of sulphuric acid, similar to the following, 
KA1(S0 4 ) 2 .12H 2 0, which is known as potash alum. They may 
vary, in their composition by the substitution of Na, Li, NH 4 , 
etc., for the potassium and of Fe"' and Cr for the aluminium. 
All these compounds have, therefore, different but analogous 
compositions, and it is found also that they all crystallize in the 
Isometric System with an octahedral habit. Further, if a crys- 
tal of one alum is suspended in a saturated solution of another 
member of the series, the crystal will continue to grow. From 
this it is proved that the molecules of the different alums are 
physically so closely alike that they can be substituted for each 
other in any proportion. Therefore this series of compounds is 
said to be an Isomorphous Group. 

Many such groups are to be found in minerals, and attention 
is called to them in various places in Section IV. Reference 
might be made to one of the most prominent of these in the case 
of the Calcite Group (see page 203). This is a series of minerals 



80 MANUAL OF MINERALOGY 

all of which are carbonates of similar bivalent metals, and there- 
fore they can be said to have analogous chemical compositions. 
Further, they all crystallize in the same crystal system and class, 
and have closely agreeing angles between similar crystal faces. 
Consequently they conform to the second requirement for an 
Isomorphous Group, namely, that the minerals of it should show 
similar crystal forms. 

Dimorphism, Trimorphism, Etc. 

A number of cases are well known among minerals in which 
two or three different species have the same chemical com- 
position but distinctly different physical properties. When one 
compound appears in two different forms, it is said to be dimor- 
phous ; when in three different forms, trimorphous. Carbon in 
the forms of graphite and diamond, calcium carbonate as calcite 
and aragonite, iron sulphide as pyrite and marcasite, are familiar 
examples of dimorphism. The two minerals in each case differ 
from each other in such physical properties as crystallization, 
hardness, specific gravity, color, reactions with acids, etc. Ti- 
tanium oxide, Ti0 2 , is trimorphous, since it occurs in the three 
distinct minerals, rutile, octahedrite and brookite. 

Instruments, Reagents and Methods of Testing. 

The Blowpipe and Its Use. Many of the chemical tests 
made on minerals are performed by aid of an instrument known 
as a blowpipe. The blowpipe consists essentially of a tapering 
tube ending in a small and symmetrical opening through which 
air can be forced in a thin stream at high pressure. This current 
of air, when directed into a luminous flame, converts it into a 
small and very hot flame, by means of which many important 
tests can be made. 

Fig. 197 represents a common type of blowpipe. The air is 
forced from the lungs into the mouthpiece, c, which fits into the 
upper end of the tube and issues from the small opening at the 
other end. The tip of the blowpipe, b, is placed just within a 



INSTRUMENTS, REAGENTS, ETC. 



81 



flat flame which is rich in carbon, such as is obtained from a 
candle or ordinary illuminating gas. A convenient method of 
producing a blowpipe flame is to use illuminating gas in a Bunsen 
burner, in which an inner tube, e (Fig. 198), has been placed so as 
to shut off the supply of air at the base of the burner and thus 
convert the flame into a luminous one. The upper end of this 
tube is flattened and cut at an angle, as is shown in Fig. 198. The 





Fig. 197. 



Fig. 198. 



gas flame is ordinarily adjusted so that it measures about 1 
inch in height and \ inch hi breadth. The blowpipe is intro- 
duced into this flame as shown in Fig. 199. The resulting blow- 
pipe flame should be nonluminous, narrow, sharp-pointed and 
clean-cut. If illuminating gas is not available, a candle with a 
flat wick or even an ordinary candle can be used. The latter 
require, however, more skill in manipulation. 

The Art of Blowpiping. It usually requires some practice 
before one can produce a steady and continuous blowpipe flame. 



82 MANUAL OF MINERALOGY 

Many tests can be made by means of a flame produced by ex- 
hausting the supply of air in the lungs simply once. But fre- 
quently an operation takes a longer time than this would, give, 
and the interruption necessary in order to fill the lungs afresh 
would materially interfere with the success of the experiment. 
Consequently it often becomes important to be able to maintain 
a steady stream of air from the blowpipe for a considerable time. 
This is accomplished by distending the cheeks so as to form a 
reservoir of air in the mouth. When the supply of air in the 
lungs is exhausted, the passage from the mouth into the throat 




Fig. 199. 

is closed by lifting the root of the tongue and while a new supply 
is being obtained by breathing in through the nose a steady 
stream of air is also being forced out of the reservoir in the mouth. 
In this way a constant flame may be obtained. It requires, 
however, considerable practice to do this skillfully. 

The Character of the Blowpipe Flame. Fig. 199 represents 
a typical blowpipe flame. The inner cone, c, which is light blue 
in color and the most distinct part of the flame, is composed of 
unburned gas mixed with air from the blowpipe. There is no 
combustion taking place in this part of the flame. Around 
this cone is a narrow pale-violet cone, b, which is almost 
invisible and in which the combustion does take place. Any 
gas that is used for the production of the flame will consist of 
some combination of carbon and hydrogen. These elements 
when the gas is burned are converted into their respective oxides. 
The hydrogen burns directly to water vapor, H 2 0. The carbon 



INSTRUMENTS, REAGENTS, ETC. 83 

burns first to its lower oxide, CO, known as carbon monoxide. 
Later this oxide will be changed by the addition of another atom 
of oxygen to the higher oxide, C0 2 , carbon dioxide. The final 
products of the combustion will, therefore, be the gases H 2 and 
C0 2 . In cone b, where combustion is taking place, there will 
necessarily be considerable amounts of the lower oxide of carbon, 
CO. Surrounding cone b there will be an invisible cone, a, con- 
sisting of the final products of combustion, C0 2 and H 2 0. 

Fusion by Means of Blowpipe Flame. A good blowpipe 
flame may reach a temperature as high as 2000 C. When skill- 
fully handled small pieces of fine platinum wire may be melted 
in it. The determination of the degree of fusibility of a mineral 




Fig. 200. 

is an important aid to its identification. In order to make the 
test, a small and if possible a sharply pointed fragment of the 
mineral should be inserted into the blowpipe flame just beyond 
the tip of the inner cone, where the combustion is most rapid 
and the temperature the highest. The fragment should be held 
as illustrated in Fig. 200, so that it projects beyond the end of the 
forceps by which it is held in such a manner that the entire heat 
of the flame can be concentrated upon it. If it melts and rounds 
over, losing its sharp outline, it is said to be fusible in the blow- 
pipe flame. Minerals can therefore be divided into two classes, 
as to whether they are fusible or infusible in this flame. The 
minerals which are fusible can be further classified according to 



84 MANUAL OF MINERALOGY 

the degree of ease with which they fuse. To assist in this classi- 
fication, a series of six minerals which show different degrees of 
fusibility has been chosen as a scale to which all fusible minerals 
may be approximately referred. For instance, when a mineral 
is said to have a fusibility of 3, it means that it will fuse with 
the same degree of ease as the mineral which is listed as 3 in the 
scale. In making such comparative tests, it is necessary to use 
fragments of the same size and to have the conditions of the 
experiments uniform. The minerals of the scale of fusibility 
are as follows : . 

1. Stibnite. Very easily fusible. A small splinter will readily 
melt in a candle flame. 

2. Chalcopyrite. Easily fusible. A small fragment will fuse 
in the Bunsen burner flame. 

3. Almandine Garnet. Infusible in the Bunsen burner flame 
but fuses easily in the blowpipe flame. 

4. Adinolite. A sharp-pointed splinter fuses without much 
difficulty in the blowpipe flame. 

5. Orthoclase. The edges of a fragment are rounded at the 
highest heat of the blowpipe flame. 

6. Enstatite. Practically infusible in blowpipe flame, only 
the fine ends of sharp-pointed fragments being rounded. 

Reducing and Oxidizing Flames. Reduction consists essen- 
tially in taking oxygen away from a chemical compound, and 
oxidation consists in adding oxygen to it. These two opposite 
chemical reactions can be accomplished by means of a blowpipe 
flame. Cone 6, Fig. 199, as explained above, contains CO, or car- 
bon monoxide. This is what is known as a reducing agent, since, 
because of its strong tendency to take up oxygen in order to be- 
come C0 2 , or carbon dioxide, it will, if possible, take oxygen away 
from another substance in contact with it. For instance, if a 
small fragment of the ferric oxide of iron, hematite, Fe 2 3 , is 
held in this part of the blowpipe flame, it will be reduced by the 
removal of one atom of oxygen to the ferrous oxide, FeO, accord- 
ing to the following equation : 

Fe 2 3 -f CO = 2FeO + C0 2 . 



INSTRUMENTS, REAGENTS, ETC. 85 

This change can be proved by noting that the ferric oxide is red 
in color and nonmagnetic, while the ferrous oxide is black and 
strongly magnetic. This cone 6 is therefore known as the re- 
ducing part of the blowpipe flame, and when it is wished to per- 
form a reduction test the mineral fragment is placed at r, as 
shown in Fig. 199. 

On the other hand, if oxidation is to be accomplished, the 
mineral must be placed entirely outside of the flame, where the 
oxygen of the air can have free access to it, but where it can still 
get in large degree the heat of the flame. Under these condi- 
tions, if the reaction is possible, oxygen will be added to the 
mineral and the substance will be oxidized. The oxidizing part of 
the blowpipe flame is at o (Fig. 199). Pyrite, FeS 2 , for instance, 
if placed in the oxidizing flame, would be converted into ferric 
oxide, Fe 2 3 , and sulphur dioxide, S0 2 , according to the following 
equation : 

2FeS 2 + 110 = Fe 2 3 + 4S0 2 . 

The ferric oxide would form a dark-red residue, while the sulphur 
dioxide would come off as a pungent-smelling gas. 

Use of Charcoal in Blowpiping. Small charcoal blocks, that 
should best be about 4 inches long, 1 inch wide and | inch thick, 




Fig. 201. An Oxide Coating on Charcoal. 

are employed in a number of blowpipe tests. They are used as 
a support upon which various reactions are accomplished. For 
instance, metals like lead, silver, copper, etc., may be reduced 
from their minerals by means of the blowpipe flame, the experi- 
ment being performed upon charcoal. Characteristic oxide coat- 
ings also may be obtained upon the surface of a charcoal block (see 
Fig. 201). The charcoal should be of a fine and uniform grain. 
It should not be so soft as to readily soil the fingers, nor should 
it be so hard as not to be easily cut and scraped by a knife. 
The following table gives a list of the elements which yield 



86 



MANUAL OF MINERALOGY 



characteristic oxide coatings when their minerals are heated in 
the oxidizing flame on charcoal: 



Oxide. 


Color and character of 
coating. 


Remarks. 


Arsenious Oxide. 
Aa 2 3 . 


White and volatile, depositing at 
some distance from the mineral. 


Usually accompanied by 
garlic odor. 


Antimony Oxides. 
Sb 2 O 3 , Sb 2 O 4 . 


White and volatile, depositing close 
to the mineral. 


Heavier than arsenic 
oxide. 


Zinc Oxide. 
ZnO. 


Yellow when hot, white when cold. 
Nonvolatile in the oxidizing flame. 
Deposits very close to mineral. 


If coating is moistened 
with cobalt nitrate 
and heated intensely, 
it turns green. 


Tin Oxide. 
Sn0 2 . 


Faint yellow when hot, white when 
cold. Nonvolatile in the oxidizing 
flame. 




Molybdenum Oxide. 
Mo0 3 . 


Pale yellow when hot, white when 
cold. Sometimes crystalline. Vol- 
atile in the oxidizing flame. 


If the coating is touched 
for a moment by a 
reducing flame, it be- 
comes dark blue. 


Lead Oxide. 
PbO 


Yellow near the mineral and white 
farther away. 


Coating at times is com- 
posed of white sul- 
phite and sulphate 
of lead in addition to 
the oxide. 


Bismuth Oxide. 
Bi 2 3 . 


Yellow near the mineral and white 
farther away. 


To be told from the 
lead-oxide coating by 
iodine tests (see p. 97). 



Open Tube Test. Glass tubing of hard glass is used in mak- 
ing what are known as open tube tests. The tubing should 
be cut into approximately 8-inch lengths and have an internal 
diameter of | inch. An open tube is used ordinarily for making 
oxidation tests. A small amount of the mineral to be tested is 
commonly powdered and placed in the tube at a point about 
one-third of its length from one end. A narrow strip of paper 
folded into a shallow trough will serve as a boat to introduce the 
powder into the tube. The tube is then inclined at as sharp an 
angle as possible, with the mineral lying nearer the lower end. 
The tube is then held over a Bunsen burner flame in such a way 
that the flame plays on the upper part of the tube. This serves 
to convert the inclined tube into a chimney, up which a current 
of air flows. After a moment the tube is shifted so that the flame 



INSTRUMENTS, REAGENTS, ETC. 87 

heats it at a point just above the mineral, or in some cases the 
flame may be directly beneath the mineral. The mineral is 
being heated under these conditions in a steady current of air, 
and it will be oxidized if such a reaction is possible. Various 
oxides may come off as gases and either escape at the end of the 
tube or be condensed as sublimates upon its walls. The follow- 
ing table gives a list of those elements which yield characteristic 
reactions when heated in open tubes: 

Element. Description of Test. 

Sulphur. Sulphur dioxide, S0 2 , comes out of upper end of tube 
as a gas with a pungent and irritating odor. If a 
moistened strip of blue litmus paper is placed at the 
upper end of the tube, it becomes red, due to the acid 
reaction caused by the sulphurous acid. 

Arsenic. Arsenious oxide, As 2 3 , condenses at a considerable 
distance above the heated portion as a volatile coat- 
ing of small colorless octahedral crystals. 

Antimony. Antimonious oxide, Sb 2 3 , deposits as a volatile 
white ring closer to the heated portion of the tube 
than the arsenious oxide. Antimony sulphides yield 
also a dense nonvolatile white sublimate of antimo- 
nate of antimony, Sb 2 4 , which collects along the 
bottom of the tube. 

Molybdenum. Molybdenum trioxide, Mo0 3 , collects near the 
heated portion as a network of pale yellow to white 
crystals. 

Mercury. Collects in minute gray globules which can be rubbed 
together. 

Note. Other reactions may be obtained from some of the 
above elements if the mineral is heated too rapidly or without 
the establishment of a strong current of air flowing through the 
tube. 

Closed Tube Test. Frequently a small glass tube which has 
been closed at one end is useful in testing minerals. The tube 



88 MANUAL OF MINERALOGY 

is made out of soft glass and should have a length of about 
3 1 inches and an internal diameter from to T \ of an inch. 
Two closed tubes can easily be made by fusing the center of a 
piece of tubing 7 inches in length and pulling it apart. The 
closed tube test is used to determine what takes place when a 
mineral is subjected to heat practically out of contact with the 
air. Ordinarily there is no chemical reaction involved. In 
general, in the closed tube the mineral will break down into 
simpler parts if that is possible, but otherwise nothing will take 
place except possibly a fusion of the mineral. The following 
table gives a list and brief description of the important closed 
tube tests : 

Substance. Description of Test. 

Water, H 2 0. All minerals containing water of crystallization or 
the hydroxyl radical will give on moderate heating a 
deposit of drops of water on the cold upper walls of 
the tube. 

Sulphur, S. All sulphides which contain an excess of sulphur 
will give a sublimate of sulphur, which is red when 
hot and yellow when cold. 

Arsenic, As. Native arsenic and some arsenides will give a 
deposit of metallic arsenic. This consists of two 
rings, one being composed of a black and amorphous 
material, the other lying nearer the bottom of the 
tube, of a silver-gray and crystalline material. 

Oxysulphide of antimony, Sb 2 S 2 0. Sulphide of antimony and 
some sulphantimonites give this sublimate in the 
form of a slight coating which deposits close to the 
bottom of the tube. It is black when hot and red 
when cold. It is accompanied by a faint deposit of 
sulphur further up the tube. 

Sulphide of mercury, HgS. A black amorphous sublimate which 
forms when cinnabar is heated. 



INSTRUMENTS, REAGENTS, ETC. 



89 



Mercury, Hg. Gray metallic globules of metallic mercury are 
obtained when native mercury or amalgams are 
heated or when the sulphide is mixed with dry sodium 
carbonate and heated. 

Flame Test. Certain elements may be volatilized when 
minerals containing them are heated intensely before the blow- 
pipe and so impart characteristic colors to the flame. The 
flame color to be obtained from a mineral will often serve as an 
important means of its identification. A flame test may be 
made by heating a small fragment of the mineral held in the for- 
ceps, but a more decisive test is usually obtained when the fine 
powder of the mineral is introduced into the Bunsen burner 
flame on a piece of fine platinum wire. The following table gives 
a list of the important elements which yield flame colors. It is 
to be noted that a mineral may contain one of these elements, 
but because of the nonvolatile character of the chemical com- 
bination will fail to give a flame color. 



Element. Color of Flame. 
Strontium. Crimson. 



Lithium. 



Calcium. 



Sodium. 



Crimson. 



Orange. 



Intense yellow. 



Remarks. 

Strontium minerals which give 
the flame color also give alka- 
line residues after being heated. 
Lithium minerals which give 
the flame color do not give 
alkaline residues after being 
heated. 

In the majority of cases a dis- 
tinct calcium flame will be ob- 
tained only after the mineral 
has been moistened with HC1. 
A very delicate reaction. The 
flame should be very strong 
and persistent to indicate the 
presence of sodium in the min- 
eral as an essential constit- 
uent. 



90 



MANUAL OF MINERALOGY 



Element. Color of Flame. 

Barium. Yellow green. 

Molybdenum. Yellow green. 
Boron. Yellow green. 

f Emerald-green. 

Copper. \ 

Azure-blue. 



Zinc. 



Lead. 



Bluish green. 



Pale azure-blue. 



Remarks. 

Minerals which give the barium 
flame also give alkaline resi- 
dues after ignition. 

Obtained from the oxide or sul- 
phide of molybdenum. 

Minerals giving a boron flame 
rarely give alkaline residues 
after ignition. 

Obtained from the oxide of 

copper. 

Obtained from the chloride of 

copper. 

Appears usually as bright 
streaks and threads in the 
flame. 

Tinged with green in the outer 
parts. 



Color Reactions with the Fluxes. Some elements, when 
dissolved in certain fluxes, give a characteristic color to the 
fused mass. The fluxes that are most commonly used are borax, 
Na 2 B 4 07.10H 2 0, sodium carbonate, Na 2 C0 3 , and salt of phos- 
phorus, HNaNH 4 P0 4 .4H 2 0. The operation is best performed by 
first fusing the flux on a small loop of platinum 
wire into the form of a lens-shaped bead. The 
loop on the wire should best have the shape and 
size shown in Fig. 202. After the flux has been 
fused into a bead on the wire, a small amount of 
the powdered mineral is introduced into it and is 
Fig. 202. Loop dissolved by further heating. The color of the 

of Platinum . i . . . , , . , . 

wire for Bead resulting bead may depend upon whether it was 
. heated in the oxidizing or reducing flame and 



whether the bead is hot or cold, 
list of the important bead tests : 



The following table gives a 



INSTRUMENTS, REAGENTS, ETC. 



91 



Table of Color Reactions with the Fluxes. 



Oxides of 


Borax Bead. 


Phosphorus Salt Bead. 






Oxidizing flame. 


Reducing 
flame. 


Oxidizing flame 


Reducing 
flame. 


Chromium. 


Hot. 


Yellow. 


Green. 


Dirty green. 


Dirty green. 


Cold. 


Yellowish green. 


Green. 


Fine green. 


Fine green. 


Vanadium. 


Hot. 


Yellow. 


Dirty green. 


Yellow. 


Dirty green. 


Cold. 


Yellowish green 
almost color- 
less. 


Fine green. 


Yellow. 


Fine green. 


Uranium. 


Hot. 


Deep yellow to 
orange-red. 


Pale green. 


Yellow. 


Pale dirty 
green. 


Cold. 


Yellow. 


Pale green to 
nearly colorless. 


Pale greenish 
yellow. 


Fine green. 


Iron. 


Hot. 


Deep yellow to 
orange-red. 


Bottle-green. 


Deep yellow to 
brownish red. 


Red-yellow 
to yellow- 
green. 


Cold. 


Yellow. 


Pale bottle- 
green. 


Yellow to al- 
most colorless. 


Almost color- 
less. 


Copper. 


Hot. 


Green. 


Colorless to 
green. 


Green. 


Brownish 
green. 


Cold. 


Blue. 


Opaque red 
with much 
oxide. 


Blue. 


Opaque red. 


Cobalt. 


Hot. 


Blue. 


Blue. 


Blue. 


Blue. 


Cold. 


Blue. 


Blue. 


Blue. 


Blue. 


Nickel. 


Hot. 


Violet. 


Opaque gray. 


Reddish to 
brownish red. 


Reddish to 
brownish 
red. 


Cold. 


Reddish brown. 


Opaque gray. 


Yellow to red- 
dish yellow. 


Yellow to red- 
dish yellow. 


Manganese. 


Hot. 


Violet. 


Colorless. 


Grayish violet. 


Colorless. 


Cold. 


Reddish violet. 


Colorless. 


Violet. 


Colorless. 



Sodium carbonate with oxide of manganese gives when heated 
in the oxidizing flame an opaque bead, green when hot, bluish 



92 MANUAL OF MINERALOGY 

green when cold. When heated in the reducing flame the bead 
is colorless. 

Dry Reagents. 

The following paragraphs give a brief description of the more 
important dry reagents used in testing minerals : 

Sodium Carbonate, Na 2 C0 3 , is a white salt that is used chiefly 
as a flux to decompose minerals by fusion on charcoal and more 
rarely as a flux in a bead test. 

Borax, Na2B 4 07.10H 2 0, is a white salt that is used chiefly in 
making bead tests and more rarely as a flux on charcoal. 

Microcosmic Salt or Salt of Phosphorus, HNaNH 4 P0 4 .4H 2 0, 
is a white salt used in making bead tests. 

Acid Potassium Sulphate, HKS0 4 , is a white salt that is used 
in making a test for fluorine (see page 100). 

Acid Potassium Sulphate and Fluorite Mixture is a mixture 
of three parts of the former and one part of the latter. It is used 
in making a test for boron (see page 97). 

Potassium Iodide and Sulphur Mixture. A mixture of equal 
parts of these two materials is used in making a test for bismuth 
(see page 97). 

Tin and Zinc are used in granulated form to make certain re- 
duction tests in hydrochloric acid solutions. 

Test Papers. Blue litmus paper is a test paper which changes 
in color from blue to red when exposed to the action of an acid. 
It is most commonly used in the open tube test for sulphur (see 
page 109). Yellow turmeric paper is a test paper that turns 
brown when exposed to the action of an alkali. It is most 
commonly used in making a test for the presence of an alkali 
or alkaline earth in a mineral (see under sodium, page 109; 
calcium, page 98, etc.). Red litmus paper can be substituted 
for the yellow turmeric. It turns blue when exposed to the 
action of an alkali. 

Wet Reagents. 

The following paragraphs give a brief description of the more 
important wet reagents used in testing minerals : 



TESTS FOR THE ELEMENTS 93 

Hydrochloric Acid, Muriatic Acid, HC1, is an acid which is 
commonly used for the solution of minerals, etc. It is a non- 
oxidizing acid. The ordinary laboratory acid is diluted with 
three parts of water. 

Nitric Acid, HN0 3 , is a strong solvent and oxidizing agent. 
It is commonly used in its concentrated form. 

Sulphuric Acid, H 2 S0 4 , is less commonly used than the others 
as a solvent. It may be used in its concentrated form, but 
usually is diluted with four parts of water. When water is added 
to the acid a large amount of heat is generated. Water should 
never be added to the hot acid. The acid boils at 337 C. 

Ammonium Hydroxide, NH 4 OH, is a strong alkali used 
chiefly to neutralize acid solutions and as a precipitant for alu- 
minium and ferric hydroxides (see pages 95 and 101). For labo- 
ratory use it is commonly diluted with three parts of water. 

Ammonium Carbonate, (NH 4 ) 2 C0 3 , and Ammonium Oxa- 
late, (NH 4 )2C 2 04, are chiefly used in the form of aqueous solutions 
to precipitate the alkaline earths, calcium, strontium and barium, 
from their solutions (see page 98). 

Hydrogen Sodium Phosphate, HNaaPCX, is used in the form 
of an aqueous solution to test for the presence of magnesium 
(see page 103); Barium Hydroxide, Ba(OH) 2 , in testing for car- 
bon dioxide (see page 98) ; Barium Chloride, BaCl 2 , for sulphu- 
ric acid (see page 110); Ammonium Molybdate, (NH 4 ) 2 Mo0 4 , 
for phosphoric acid (see page 106); Silver Nitrate, AgN0 3 , for 
chlorine (see page 99). 

Potassium Ferrocyanide, K 4 Fe(CN) 6 .3H 2 0, and Potassium 
Ferricyanide, K 6 Fe 2 (CN)i 2 , are used in dilute solutions to test for 
ferric and ferrous iron respectively (see page 102). Ammonium 
Sulphocyanate, NH 4 CNS, is also used to test for ferric iron. 
Cobalt Nitrate, Co(N0 3 ) 2 , is used in the form of a dilute solution 
in blowpipe tests for aluminium and zinc (see pages 95 and 112). 

Tests for the Elements. 

On the following pages will be given brief descriptions of the 
more important blowpipe and chemical tests for the elements 
as they occur in minerals. In order to facilitate reference to 



94 



MANUAL OF MINERALOGY 



this section, the different elements will be treated in alphabetical 
order. Under each element the tests will be given in the approxi- 
mate order of their importance. For a fuller discussion of this 
part of the subject reference must necessarily be made to the 
textbooks that treat of it alone. Below is a list of the elements 
whose tests are discussed, with their chemical symbols, valence 
and atomic weights. 



Element. 


Sym- 
bol. 


Valence. 


Atomic 
Weight. 




Al 


Trivalent... 


27 




Sb 


Trivalent and pentavalent 


120 




\s 




75 




Ba 


Bivalent 


137 




Be 




g 


Bismuth 


Bi 


Trivalent 


208 


Boron ' 


B 


Trivalent 


H 


Calcium *. . . 


Ca 


Bivalent 


40 




c 


Tetravalent 


12 


Chlorine 


Cl 


Univalent 


35 5 




Cr 




52 5 


Cobalt 


Co 


Bivalent 


59 


Columbium, see Niobium. 
Copper 


Cu 


Univalent and bivalent 


63 4 


Fluorine . . 


F 


Univalent 


19 


Glucinum, see Beryllium. 
Gold 


Au 




197 3 


Hydrogen 


H 


Univalent 


1 




Fe 


Bivalent and trivalent 


56 


Lead 


Pb 




207 


Lithium 


Li 


Univalent 


7 




Me 


Bivalent 


24 


Manganese 


Mn 


Bivalent, trivalent and tetravalent 


55 




Hg 




200 


Molybdenum 


Mo 


Tetravalent and sexivalent 


96 


Nickel 


Ni 




59 


Niobium 


Nb 


Pentavalent 


94 


Oxygen ... 


o 


Bivalent 


16 


Phosphorus 


P 


Pentavalent 


31 


Platinum 
Potassium 


Pt 
K 


Bivalent and tetravalent 
Univalent 


195 
39 1 


Silicon 


Si 


Tetravalent 


28 


Silver 


Ae 




108 


Sodium 


N! 


Univalent 


23 


Strontium 


Sr 




87 5 


Sulphur 


s 


Bivalent and sexivalent 


32 


Tantalum 


Ta 




182 6 


Tellurium. . . 


Te 


Bivalent. 


125 


Tin 


Sn 




119 


Titanium 
Tungsten 


Ti 
W 


Trivalent and tetravalent 
Sexivalent. 


48 
185 


Uranium 


u 


Tetravalent and sexivalent . . 


240 


Vanadium 


v 




51 4 


Zinc 


Zn 


Bivalent 


65 4 



ANTIMONY 95 



Aluminium. 

1. Precipitation by Ammonium Hydroxide. Aluminium is 
precipitated in the form of aluminium hydroxide, A1(OH) 3 , when 
an excess of ammonium hydroxide is added to an acid solution. 
The precipitate is flocculent in form and colorless or white. It is 
precipitated under the same conditions as ferric hydroxide (see 
page 101), and since the latter has a dark color a small amount 
of aluminium hydroxide might be overlooked in a mixture of 
the two. To make a further test under these conditions, filter 
off the precipitate and treat it with a hot solution of sodium 
hydroxide, which will dissolve any aluminium hydroxide present 
but will not affect the ferric hydroxide. Filter, and to the filtrate 
add hydrochloric acid in slight excess, and then make alkaline 
with ammonium hydroxide again. This will precipitate any 
aluminium that may be present as pure aluminium hydroxide. 

2. Blowpipe Test with Cobalt Nitrate. Light colored and 
infusible aluminium minerals when moistened with a drop of 
cobalt nitrate and heated intensely before the blowpipe assume 
a dark blue color. 



Antimony. 

1. Oxide Coating on Charcoal. When an antimony mineral 
is heated in the oxidizing flame on charcoal, a heavy white coat- 
ing of antimony oxide settles on the charcoal at a short distance 
from the mineral. The coating is readily volatile when heated. 

2. Open Tube Test. When metallic antimony or a compound 
of antimony with sulphur is heated in the open tube, a white 
powdery sublimate of antimony oxide, Sb 2 3 , forms in a ring 
on the inner wall of the tube, a short distance above the mineral. 
It is a volatile coating. If the mineral contains sulphur, as is 
usually the case, a second coating will form as a white powder 
along the bottom of the tube. It is another oxide of antimony, 
Sb 2 C>4. It is nonvolatile and is usually more conspicuous than 
the first. 



96 MANUAL OF MINERALOGY 

Arsenic. 

The test to be used for arsenic depends upon whether the 
mineral contains oxygen. In the majority of cases an arsenic 
compound does not contain oxygen, and then tests 1, 2 and 3 
will serve. If, on the other hand, the mineral is an oxygen com- 
pound, test 4 must be used. 

1. Oxide Coating on Charcoal. When an arsenic mineral 
is heated in the oxidizing flame on charcoal, a white coating of 
arsenious oxide, As 2 3 , is deposited on the charcoal at some dis- 
tance from the mineral. The coating is very volatile. Its for- 
mation is usually accompanied by a characteristic odor of garlic. 

2. Open Tube Test. When an arsenic mineral is carefully 
heated in the open tube a colorless or white crystalline sublimate 
of arsenious oxide, As 2 3 , forms in a ring on the inner wall of 
the tube at a considerable distance above the mineral. It is 
very volatile. When examined with a lens the coating will 
usually show well-defined octahedral crystals. If the mineral 
is heated too rapidly, metallic arsenic may sublime instead of the 
oxide (see the next test). 

3. Closed Tube Test. Many arsenic minerals when heated 
in a closed tube yield a sublimate of metallic arsenic, known as 
the arsenic mirror. This sublimate shows an amorphous black 
band above and a silver-gray crystalline band below. If the 
bottom of the tube be broken off and the metallic arsenic volatil- 
ized by heat, the characteristic garlic odor will be obtained. 

4. Closed Tube Test for an Arsenate. When arsenic occurs 
in a mineral in the form of an arsenate, i.e., an oxidized com- 
pound, none of the above tests will serve. In this case place the 
mineral in a closed tube with a splinter of charcoal and then 
heat. The charcoal will act as a reducing agent and set metallic 
arsenic free, which will condense on the wall of the tube as an 
arsenical mirror similar 'to that described under test 3. 

Barium. 

1. Flame Test. Barium minerals when heated intensely give 
a yellowish green flame color. 



BORON 97 

2. Precipitation as Barium Sulphate. Barium is precipi- 
tated as barium sulphate, BaS0 4 , from an acid solution by the 
addition of dilute sulphuric acid. The precipitate is white and 
finely divided and being very insoluble will form in a quite dilute 
solution (distinction from calcium and strontium). 

3. Alkaline Reaction. Barium is an alkaline earth metal. 
When a mineral contains barium in combination with a volatile 
acid, it will give, after ignition, a residue which will react alkaline 
on a piece of moistened turmeric paper. 

Beryllium or Glucinum. 

Beryllium is a rare element which has no simple blowpipe or 
chemical test. 

Bismuth. 

1. Charcoal Tests. When heated with sodium carbonate on 
charcoal in the reducing flame, a bismuth mineral will yield a 
metallic globule and an oxide coating. The metal is easily 
fusible, lead-gray when hot, but becomes covered with an oxide 
coating on cooling. It is only imperfectly~malleable, for when 
hammered out it flattens at first but later breaks into small 
grains. The oxide coating, Bi 2 3 , is white with a yellow ring 
next the mineral. These bismuth reactions are quite similar to 
those for lead (see page 102), consequently the following modi- 
fication is useful. If the bismuth mineral is fused on charcoal 
with a mixture of potassium iodide, KI, and sulphur (see page 
92), a characteristic and distinctive coating is obtained. This 
sublimate is yellow next to the mineral and brilliant red on 
the outside. Under similar conditions with lead a solid yellow 
coating would be obtained. 

Boron. 

1. Flame Test. Some boron minerals give a yellow-green 
flame when heated alone. Most boron minerals, however, will 
only yield the flame color when their powder is mixed with acid 
potassium sulphate and fluorite mixture (see page 92) and then 



98 MANUAL OF MINERALOGY 

introduced on a platinum wire into a Bunsen burner flame. As 
the mixture fuses, a momentary but distinct green flame is 
obtained. 

Calcium. 

1. Flame Test. When calcium occurs in a mineral in such 
a state that it can be volatilized by heat, it will yield a charac- 
teristic orange flame color. Frequently the mineral has to be 
moistened by hydrochloric acid before heating. The flame 
should not be confused with the crimson and more persistent 
flame of strontium or lithium. 

2. Alkaline Reaction. Calcium is an alkali-earth metal. 
When a mineral contains calcium in a combination with a vola- 
tile acid, it will give, after ignition, a residue which will react 
alkaline on a piece of moistened turmeric paper. 

3. Precipitation as Calcium Oxalate or Carbonate. Cal- 
cium is readily and completely precipitated from alkaline solu- 
tions as calcium oxalate, CaC 2 4 , or calcium carbonate, CaC0 3 , 
by the addition of ammonium oxalate, (NH 4 ) 2 C 2 04, or ammonium 
carbonate, (NH 4 ) 2 C0 3 . Both precipitates are white and finely 
divided. 

4. Precipitation as Calcium Sulphate. Calcium is precipi- 
tated from a concentrated hydrochloric acid solution as calcium 
sulphate on the addition of a little dilute sulphuric acid. The 
precipitate is quite readily soluble in water and therefore will 
not form in a dilute solution (distinction from barium and 
strontium). 

Carbon. 

Carbon exists in minerals chiefly in the form of carbonic acid 
in the carbonates. 

1. Test for Carbon Dioxide with an Acid. All carbonates 
when treated with a strong acid (best hydrochloric) dissolve 
with a vigorous effervescence of carbon dioxide gas. In some 
cases (for example, dolomite, CaMg(C0 3 ) 2 ) the acid needs to be 
heated to start the reaction, and in others (for example, cerussite, 
PbC0 3 ) a dilute acid is necessary. Carbon dioxide gas is colorless 
and odorless. It will not support combustion, as is shown when 



COPPER 99 

a lighted match is placed in a test tube that contains it. The 
gas is heavier than air and can be poured from the test tube in 
which it has been generated into another in which some barium 
hydroxide solution has been placed. When the contents of the 
latter tube are shaken together, the carbon dioxide reacts with 
the barium hydroxide to form a white precipitate of barium 
carbonate, BaC0 3 . 

Chlorine. 

1. Precipitation as Silver Chloride. Chlorine is precipi- 
tated from a dilute nitric acid solution as silver chloride, AgCl, 
by the addition of a small amount of silver nitrate, AgN0 3 . 
The test is very delicate, traces of chlorine being shown by a 
milky appearance of the solution. When in any quantity the 
precipitate is curdy in form. It is white on precipitation but 
darkens on exposure to light. It is soluble in ammonium 
hydroxide. 

Chromium. 

1. Bead Tests. Chromium is usually tested for by the color 
it gives to the fluxes (see page 91). The salt of phosphorus bead 
when fused in the oxidizing flame yields a fine green color. This 
is the most characteristic chromium bead. 

Cobalt. 

1. Bead Tests. A cobalt mineral when fused in either a 
borax or salt of phosphorus bead yields a distinctive dark blue 
color. The test is very delicate. 

Columbium, see Niobium. 

Copper. 

1. Flame Tests. An oxidized compound of copper when 
introduced into the flame gives it a vivid green flame color due 
to the copper oxide volatilized. When the mineral is moistened 
with hydrochloric acid and then heated, the flame color is an 
intense blue. If the mineral is a sulphide, it must be roasted in 
the oxidizing flame before moistening with hydrochloric acid. 



100 MANUAL OF MINERALOGY 

2. Blue Solution with Ammonium Hydroxide. If an acid 
solution containing copper is made alkaline with ammonium 
hydroxide, it will assume a deep blue color. 

3. Reduction to Metal on Charcoal. When a small 
amount of a copper mineral is mixed with a flux (best equal 
parts of sodium carbonate and borax), placed on charcoal and 
heated intensely in the reducing flame, metallic globules of cop- 
per will be formed. They are difficultly fusible, bright when 
hot, but become coated with an oxide coating on cooling. They 
are malleable and show the characteristic copper color. Sul- 
phides of copper must first be roasted in the oxidizing flame in 
order to remove the sulphur before mixing with the flux. 

Fluorine. 

1. Etching Tests. The ordinary test for fluorine consists 
in converting it into hydrofluoric acid and observing the latter's 
etching effect upon glass. A watch glass or other piece of glass 
may be covered with paraffin and then the coating removed 
in spots. Upon this is placed the powdered mineral with a 
few drops of concentrated sulphuric acid. The action of the 
acid upon the fluoride will serve to liberate hydrofluoric acid, 
which will in turn etch the glass where it has been exposed. 
The action should be allowed to continue for some time, when 
on cleaning the glass the etched spots will be visible. 

A modification of the above test can be made in a closed tube. 
Take a closed tube of about j inch diameter and made preferably 
of hard glass. Into this introduce a powdered mixture of the 
mineral, glass and acid potassium sulphate, and then heat in 
the Bunsen burner flame. When heated, acid potassium sul- 
phate is converted into the normal -potassium sulphate with 
the liberation of sulphuric acid. The acid attacks the fluoride 
and sets free hydrofluoric acid. This in turn acts upon the glass 
present and etches it. The etching, however, is not readily 
apparent on account of the conditions of the experiment. As a 
secondary reaction, however, there will be formed in the upper 
part of the tube a white sublimate of silicon dioxide. This 
sublimate is volatile because of the presence with it of small 



IRON ' 101 

amounts of hydrofluosilicic acid. If the bottom of the tube is 
broken off and its interior gently washed with water, this acid 
will be dissolved and removed. If the tube is now dried again, 
the white coating will prove to be no longer volatile. This 
silicon dioxide coating is a proof of the action of hydrofluoric 
acid in the bottom of the tube and therefore of the presence 
of fluorine in the mineral. 

Glucinum, see Beryllium. 

Gold. 

There is no simple blowpipe or chemical test for gold. Or- 
dinarily its physical characteristics are sufficient to identify it. 
For a discussion of the occurrence and tests for gold see page 126. 

Hydrogen. 

1. Closed Tube Test for Water. Hydrogen exists in min- 
erals either as water of crystallization (for example, gypsum, 
CaS0 4 .2H 2 0) or as the hydroxyl radical (for example, brucite, 
Mg(OH) 2 ). In either case its presence may be detected by 
heating a fragment of the mineral in a closed tube and observing 
the water which condenses upon the upper cold wall of the tube. 
Water of crystallization is driven off more readily than water of 
hydroxyl, but the test is easily obtained in either case. 

Iron. 

1. Magnetic Test. Any mineral that contains a sufficient 
amount of iron to permit it to be classified as an iron mineral 
will readily become magnetic when heated in the reducing part 
of the blowpipe flame. A comparatively small fragment should 
be used and the test made with a magnet after it has cooled. 

2. Precipitation with Ammonium Hydroxide. Ferric iron 
is readily and completely precipitated as ferric hydroxide, 
Fe(OH) 3 , from an acid solution by adding an excess of ammo- 
nium hydroxide. It is a flocculent precipitate with a reddish 



102 'MANUAL OF MINERALOGY 

brown color. If there is any doubt as to the state of oxidation 
of the iron in the original solution, a few drops of nitric acid 
should be added and the solution heated in order to make cer- 
tain that the iron is ferric. 

3. Cyanide Tests for Ferrous and Ferric Iron. Occa- 
sionally it may be important to determine whether the iron in 
a mineral is ferrous or ferric in its valence. This can be done 
only when the mineral is soluble in a nonoxidizing acid like 
hydrochloric and when it is not a sulphide. If these conditions 
can be fulfilled, then divide the solution into two parts. To one 
add a few drops of a dilute solution of potassium /m'cyanide, 
and if the solution contains any ferrous iron a heavy dark blue 
precipitate will form. If, on the other hand, it contained only 
ferric iron, there would be no precipitate but only a darkening 
of the color of the solution. To the second portion of the 
solution add a few drops of a dilute solution of potassium fero- 
cyanide, and if there is any ferric iron present a heavy dark blue 
precipitate similar to the one in the previous case will form. 
But if the solution contained only ferrous iron, a light blue 
precipitate would be formed. The characteristic dark blue pre- 
cipitate must contain both valences of iron and will only form 
when a cyanide is added containing the opposite kind of iron to 
that already in the solution. 

Ammonium or potassium sulphocyanate is also used in making 
the ferric test. A few drops of one of these reagents added to 
a ferric iron solution will give it a deep red color. All of these 
tests are extremely delicate and will give good results if only a 
trace of iron is present. They should never be used to deter- 
mine the presence of iron in a mineral but only to differentiate 
ferrous from ferric iron. 

Lead. 

1. Charcoal Test. Any lead mineral when powdered and 
mixed with sodium carbonate will yield a metallic globule when 
the mixture is heated on charcoal in the reducing flame. The 
globule is bright lead color when hot, but becomes covered with 
a dull oxide coating on cooling. It is very malleable and can 



MAGNESIUM 103 

be hammered out into a thin sheet. A coating on the charcoal 
of lead oxide, PbO, will also form, which varies in color from 
yellow next to the fused mass to white at a distance. It will be 
best obtained by removing the lead globule to a fresh piece of 
charcoal and heating it in the oxidizing flame. 

2. Acid Tests. Lead minerals as a rule are only slowly 
attacked by acids. Dilute nitric acid is the best solvent to use. 
If to a nitric acid solution a few drops of hydrochloric or sul- 
phuric acid are added, white precipitates will form, which are 
respectively lead chloride, PbCl 2 , and lead sulphate, PbS0 4 . 
The latter is quite insoluble. 

Lithium. 

1. Flame Test. Lithium is a rare element which is to be 
distinguished by the persistent and strong crimson color which 
it gives to the flame. 

Magnesium. 

1. Precipitation as Ammonium Magnesium Phosphate. 
The only common test for magnesium is to precipitate it in the 
form of ammonium magnesium phosphate, NH 4 MgP0 4 , by the 
addition of hydrogen sodium phosphate, HNa 2 P0 4 , to a strongly 
ammoniacal solution. The precipitate usually forms somewhat 
slowly, is white in color and frequently is granular in texture. 
In order to make a decisive test certain precautions are neces- 
sary. As the precipitation is made in an ammoniacal solution, 
any precipitates formed by an excess of ammonium hydroxide 
must be first filtered off. It may be necessary before adding 
the ammonium hydroxide to add a few drops of nitric acid so 
as to make certain that any iron in the solution is in the ferric 
state. Also, before making the final test, any elements, such 
as calcium, strontium and barium, that are precipitated in am- 
moniacal solution by means of ammonium oxalate, must be 
removed. In any case their presence must be tested for before 
adding the hydrogen sodium phosphate, because, if present, they 
would be precipitated by that reagent along with the magnesium. 



104 MANUAL OF MINERALOGY 

Manganese. 

1. Bead Tests, a. Manganese gives to the sodium carbo- 
nate bead when heated in the oxidizing flame a characteristic 
bluish green color. The bead is opaque when cold. 

b. With the borax bead, when heated in the oxidizing flame 
manganese gives a purple or amethystine color. The bead is 
transparent when cold. 

Both tests are very delicate. 

Mercury. 

1. Closed Tube Tests. The powdered mineral is thoroughly 
mixed with dry sodium carbonate and placed in a closed tube 
and then heated. The sodium carbonate will decompose the 
mineral and liberate metallic mercury, which will volatilize and 
condense in the upper part of the tube. 

2. Precipitation on Copper. Boil the powdered mineral 
with hydrochloric acid, into which some powdered pyrolusite, 
Mn0 2 , has been placed. The chlorine evolved by the action 
of the acid on the manganese dioxide will serve to dissolve the 
mercury mineral. If into this solution a clean strip of copper 
is placed (a cent which has been cleaned with a little nitric acid 
will serve), it will become covered by a thin coating of metallic 
mercury. 

The chief and only common mineral of mercury is cinnabar, 
HgS, and for its distinctive physical and chemical tests see 
page 145. 

Molybdenum. 

The tests for the rare element molybdenum depend upon 
whether it is in combination with sulphur or in an oxygen com- 
pound. See under molybdenite, page 137, and under wulfenite, 
page 308, for descriptions of the various tests. 

Nickel. 

1. Borax Bead Test. When dissolved in a borax bead in the 
oxidizing flame, nickel will give it a brownish color. If the bead 
is heated in the reducing flame for some time, it will become 



OXYGEN 105 

opaque because of the separation in it of metallic nickel. The 
brown color due to nickel is often masked by the deep blue color 
due to the presence of cobalt, which is frequently associated 
with nickel in its occurrence. In this case there is no simple 
test for nickel. 

2. In Ammoniacal Solution. A comparatively strong acid 
solution of nickel will on the addition of an excess of ammonium 
hydroxide become light blue in color. The test should not be 
confused with the similar but stronger test for copper. 

Niobium. 

Niobium, or columbium, as it is sometimes called, is a rare 
acid element that is associated with tantalum in the niobates 
and tantalates. 

1. Reduction Test with Tin. The best test for niobium 
is to fuse some of the powdered mineral with several parts of 
sodium carbonate. The resulting mass is dissolved in a few 
cubic centimeters of dilute hydrochloric acid and then a few 
grains of metallic tin are added. The solution is boiled and the 
hydrogen set free by the action of the acid on the tin serves as 
a reducing agent. The result is to form a compound of niobium 
which is dark blue in color. This color does not readily change 
to brown on continued boiling, and disappears on addition of 
water. This distinguishes the niobium test from a similar one 
for tungsten (see page 111). 

Oxygen. 

While oxygen is one of the most common elements in minerals, 
its presence is ordinarily determined indirectly by testing for 
the different oxygen acids. In the case of a few oxides in which 
there is an excess of oxygen, a direct test may be made. 

1. Closed Tube Test. The powdered oxide is placed in a 
closed tube with a small splinter of charcoal resting just above 
it. The tube is heated and if free oxygen is evolved the charcoal 
will at first glow and then burn with a bright light. It is to be 
noted that only a few oxides which contain an excess of oxygen 
will give this test. 



106 MANUAL OF MINERALOGY 

Phosphorus. 

1. Precipitation with Ammonium Molybdate. Phosphorus 
exists in minerals in the form of phosphoric acid in the phos- 
phates. It is best tested for by forming a dilute nitric acid 
solution of the mineral and adding a few cubic centimeters of 
this to an excess of ammonium molybdate solution. A canary- 
yellow precipitate of ammonium phosphomolybdate will be 
formed. The precipitate forms slowly at first and comes down 
best in a warm solution. 

2. Flame Test. Many phosphates when heated before the 
blowpipe give a pale bluish green flame color. This may fre- 
quently be obtained better when the mineral has previously 
been moistened with a drop of concentrated sulphuric acid. 

Platinum. 

There are no simple blowpipe or chemical tests for platinum. 
The physical characteristics of the metal are usually sufficient 
for its identification (see page 132). 

Potassium. 

1. Flame Test. Volatile potassium salts give a character- 
istic pale violet flame color. The potassium flame will, how- 
ever, commonly be obscured by the stronger yellow flame of 
sodium. This difficulty can be overcome by filtering the flame 
through a piece of blue glass. The sodium flame, being a mono- 
chromatic light, cannot pass through the blue glass, while the 
violet flame of potassium will be visible. 

When the potassium does not exist in the mineral in a volatile 
state, as in the case with potassium silicates, the powdered min- 
eral must be first thoroughly mixed with gypsum (CaS0 4 .2H 2 0) 
and the mixture introduced into the Bunsen burner flame on 
a platinum wire. There will be a reaction between the two, 
and the potassium will be liberated in the form of a sulphate, 
which, being a volatile salt, will give the flame color. It will 
be momentary in duration and must be viewed through the 
blue glass. 



SILICON 107 

Silicon. 

Silicon exists as the acid element in the large group of minerals 
known as the silicates. Some of these are readily soluble in 
acids, but the greater part are quite insoluble. The tests em- 
ployed differ somewhat in the two cases. .-\- 

1. Test for a Soluble Silicate. If the silicate is soluble, it 
should be powdered and dissolved in boiling hydrochloric acid. 
When this solution is evaporated a jellylike material will sepa- 
rate out just before dryness is reached. This silica jelly, as 
it is called, is a form of silicic acid and proves the presence of 
silicon in the mineral. On continued evaporation it will be 
dehydrated and converted into a sandy and insoluble substance 
having the composition of silicon dioxide, Si0 2 . 

2. Test for an Insoluble Silicate. In the case of an in- 
soluble silicate, the mineral must be decomposed by fusion 
with sodium carbonate before treating it with an acid. Make 
a mixture of one part of the powdered mineral to three parts of 
sodium carbonate and fuse thoroughly before the blowpipe on a 
loop of platinum wire. It is best to make two or three such 
beads. The fusion serves to decompose the silicate and to 
render the resulting mass wholly soluble in acids. The beads 
are powdered and dissolved in boiling dilute nitric acid. The 
evaporation is conducted as explained in experiment 1 and a 
similar silica jelly is obtained. 

Frequently it is desirable to make tests for the bases which 
are present in the silicate. In this case, after the formation of 
the jelly, continue the evaporation to complete dryness. This 
converts the silicon into the insoluble oxide but leaves the bases 
in the form of various soluble salts. Treat the residue in the 
test tube with a little water and hydrochloric acid, warm and 
filter from the insoluble silica. Add an excess of ammonium 
hydroxide to the filtrate to precipitate any aluminium or ferric 
iron as their respective hydroxides. Filter if necessary, and to 
the filtrate add a little ammonium oxalate to precipitate any 
calcium as calcium oxalate. Filter again, and to the filtrate add 
more ammonium hydroxide if necessary and then a little hydro- 



108 MANUAL OF MINERALOGY 

gen sodium phosphate, which will precipitate any magnesium 
present as ammonium magnesium phosphate. 

3. Decomposition of Silicates by Acids. Certain silicates, 
when their powder is treated with boiling hydrochloric acid, 
are decomposed, the bases going into solution and the silicon 
separating as the dioxide, Si0 2 . In this case there would be 
no jelly formed when the solution is evaporated. The mineral 
powder in such cases disappears, but the solution never becomes 
perfectly clear owing to the silica, which remains in suspension 
in the solution. It gives the solution a translucent appearance. 
The surest proof that the mineral has been decomposed is to 
filter the solution and test for various bases in the filtrate in a 
similar manner to that described under test 2. 

4. Test with the Salt of Phosphorus Bead. When the 
powder of a silicate is heated in a salt of phosphorus bead, the 
bases are dissolved, leaving the silica present as an insoluble 
translucent skeleton. 

Silver. 

1. Reduction to the Metal on Charcoal. Silver can fre- 
quently be reduced to a metallic globule from its compounds 
by heating the powdered mineral on charcoal with sodium car- 
bonate. The resulting globule is bright both when hot and 
cold. It is malleable. No accompanying coating is formed 
on the charcoal. This test for silver is frequently complicated 
by the presence of lead, arsenic or antimony in the mineral. 
Usually the mineral should be carefully roasted on charcoal in 
the oxidizing flame before attempting the reduction in order to 
remove the last two; otherwise a brittle globule will result. 
In many cases the only satisfactory test for silver is the fire 
assay. 

2. Precipitation as Silver Chloride. When a silver mineral 
is dissolved in nitric acid and to the solution a few drops of 
hydrochloric acid is added, a white curdy precipitate of silver 
chloride, AgCl, is formed. The test is quite delicate, and if 
there is only a trace of silver in the solution its presence will be 
indicated by a milky-blue coloration. The precipitate is white 



SULPHUR 109 

at first but darkens on exposure to light. It is soluble in am- 
monium hydroxide. Frequently when a silver mineral is treated 
with nitric acid a precipitate will result at once. This may be 
metantimonic acid, lead sulphate, etc., and should be filtered 
off before making the silver test. 

Sodium. 

1. Flame Test. Sodium compounds when heated give a 
strong and persistent yellow flame. The test is very delicate 
and must be used with care, for only a trace of sodium may 
yield a distinct flame. If the mineral contains sodium in any 
notable amount, it should give an intense and continuous flame 
color. 

Strontium. 

1. Flame Color. Strontium compounds give a very strong 
and persistent crimson flame. The only other flame which is 
similar is that obtained from lithium. Strontium can be posi- 
tively determined from lithium by the following tests. 

2. Alkaline Reaction. When a mineral contains strontium 
in combination with a volatile acid, it will give, after ignition, a 
residue which will react alkaline on a piece of moistened turmeric 
paper. 

3. Precipitation as Strontium Sulphate. Strontium is pre- 
cipitated from a mediumly dilute solution as strontium sulphate, 
SrS0 4 , on the addition of -a little dilute sulphuric acid. The 
precipitate is somewhat soluble and will not form in very dilute 
solutions (distinction from calcium and barium, which see). 

Sulphur. 

Sulphur exists in minerals either without oxygen, as in the 
sulphides, or with oxygen, as in the sulphates. These two types 
of sulphur compounds require different tests. 

Tests for Sulphur in Sulphides. 

1. Open Tube Test. Sulphides when heated in the open 
tube give off sulphur dioxide gas, which escapes with the current 



HO MANUAL OF MINERALOGY 

of air from the upper end of the tube. Its presence can be de- 
tected by its pungent and irritating odor. A piece of moistened 
blue litmus paper inserted into the upper end of the tube will 
turn red on account of the sulphurous acid formed. 

2. Charcoal Test. The odor of sulphur dioxide may be 
obtained when a sulphide is roasted on charcoal. 

3. Fusion with Sodium Carbonate. When a sulphide is 
fused on charcoal with sodium carbonate, the residue, unless the 
heating has been too prolonged, will contain sodium sulphide. 
If the slag is removed and placed with a drop of water on a 
clean silver surface (a coin will serve), there will result a dark 
brown stain due to the formation of silver sulphide. 

Tests for Sulphur in Sulphates. 

The test for sulphuric acid depends upon whether the sulphate 
is soluble or insoluble in acids. 

1. Test for a Soluble Sulphate. If the sulphate is soluble, 
treat it with hydrochloric acid, and to the resulting solution add 
a little barium chloride. A heavy white precipitate of barium 
sulphate will result. 

2. Test for an Insoluble Sulphate. Powder the mineral, 
mix with sodium carbonate and charcoal dust and fuse on char- 
coal in the reducing flame. The charcoal serves to reduce the 
sulphate to a sulphide, so that the resulting slag contains sodium 
sulphide. When the fused mass is placed with a drop of water 
on a clean silver surface, a dark brown stain of silver sulphide 
will form. It is to be noted that a sulphide would yield the 
same test (see above) , so that it is necessary to make certain that 
the mineral being tested does not belong to that chemical group. 

Tantalum. 

There is no simple test for tantalum. It is usually associated, 
however, with niobium (see page 105). 

Tellurium. 

1. Test with Sulphuric Acid. When a telluride is heated 
in concentrated sulphuric acid, it gives a deep crimson color to 



TUNGSTEN 111 

the solution. The color will disappear if the acid is heated too 
hot, or if after cooling it is diluted with water. 

2. Charcoal Test. When heated on charcoal a white sub- 
limate of TeO 2 is formed which somewhat resembles antimony 
oxide. It is volatile and when touched with the reducing flame 
gives a pale greenish color to it. 

Tin. 

1. Reduction to Metallic Globule. Take a small amount 
of the finely powdered mineral and mix it with five or six volumes 
of sodium carbonate and considerable charcoal dust and fuse 
intensely on charcoal in the reducing flame. Small bright 
globules of metallic tin will result. They become covered with 
an oxide coating on cooling. A white and difficultly volatile 
tin oxide coating will form on the charcoal. If the tin globule 
is treated with a little concentrated nitric acid, it will be con- 
verted into a white powder, which is metastannic acid. 

Titanium. 

1. Reduction Test in Hydrochloric Acid. A compara- 
tively concentrated hydrochloric acid solution containing tita- 
nium will become pale violet in color when it is boiled with a 
few grains of metallic tin. The hydrogen liberated by the ac- 
tion of the acid on the tin is a reducing agent and forms TiCl 3 
in the solution which gives this color. The color is not a strong 
one, and the solution may have to be evaporated nearly to dry- 
ness in order to show it distinctly. Most titanium minerals 
are insoluble in hydrochloric acid and must first be thoroughly 
fused with sodium carbonate in order to bring the titanium into 
soluble form. The fusion is best done by introducing the finely 
powdered mineral into a sodium carbonate bead made on a 
platinum wire. Several such beads should be used. 

Tungsten. 

1. Reduction Test in Hydrochloric Acid. Treat a tungsten 
mineral with hydrochloric acid. If it is decomposed by the acid' 
a yellow precipitate of tungstic oxide, W0 3 , will result. Add 



112 MANUAL OF MINERALOGY 

to the acid a few grains of metallic tin and boil. The hydrogen 
set free by the action of the hydrochloric acid on the tin serves 
as a reducing agent and converts the yellow W0 3 to a blue pre- 
cipitate which is a mixture of the two oxides W0 3 and W0 2 . On 
continued reduction the oxide becomes all W0 2 and is brown in 
color. The test is similar to the one for niobium, but is to be 
distinguished from that, since the blue color in the tungsten test 
does not disappear on dilution of the solution; and further, it 
turns to brown on continued reduction. If the tungsten mineral 
is not attacked by hydrochloric acid, its powder must first be 
thoroughly fused with sodium carbonate. The resulting mass 
is powdered and digested with water, which will dissolve the 
sodium tungstate formed during the fusion. After filtering the 
reduction test is made as described above. 

Uranium. 

1. Bead Tests. The tests for uranium consist in the colors it 
imparts to the fluxes (see page 91). The yellowish green color 
given to the salt of phosphorus bead when heated in the oxidiz- 
ing flame is the most characteristic. 

Vanadium. 

1. Bead Tests. The tests for vanadium consist in the colors 
it imparts to the fluxes (see page 91). The amber color given to 
the salt of phosphorus bead when heated in the oxidizing flame 
is the most characteristic. 

Zinc. 

1. Oxide Coating on Charcoal. Metallic zinc is easily ob- 
tained from the zinc minerals by fusing them with sodium car- 
bonate on charcoal in the reducing flame. But, since the metal 
is volatilized at a temperature considerably below that of the 
blowpipe flame, no metallic globule can be formed. The metallic 
zinc is therefore all volatilized, and, meeting the oxygen of the 
surrounding air, is converted into the oxide, ZnO, which drops 
upon the charcoal as a nonvolatile coating, which is yellow when 



ZINC 113 

hot but white when cold. The coating deposits very close to 
the fusion. It may frequently be obtained in more distinct form 
by making the fusion on a loop of platinum wire, which is held 
about one-quarter of an inch from the surface of a charcoal block 
and the blowpipe flame so directed that the oxide coating is de- 
posited upon the charcoal behind the bead. If the coating is 
moistened with a drop of cobalt nitrate and then heated intensely 
by the blowpipe flame, it will become dark green in color. 

2. Flame Color. Some zinc minerals, when a fragment is 
held in the forceps and heated in the reducing flame, will show 
a characteristic flame color. This is due to the burning in the 
flame of the metallic zinc which has been volatilized. It takes 
the form of momentary streaks or threads in the flame and has 
a pale greenish blue color. 



IV. DESCRIPTIVE MINERALOGY. 
INTRODUCTION. 

DESCRIPTIVE Mineralogy should include first of all a descrip- 
tion of the crystallographic, general physical .and chemical charac- 
ters of each mineral species, and should further give an account 
of its mode of occurrence and characteristic associations. The 
localities at which a mineral occurs in notable amount or quality 
should also be mentioned. In the case of minerals possessing an 
economic value, a brief statement of their uses is of interest. The 
order in which these various items are given under each mineral 
in this Section is as follows: 

1. Chemical Composition. 

2. Crystallization. 

3. Structure. 

4. General Physical Properties. 

5. Tests. 

6. Occurrence. 

7. Use. 

Descriptive Mineralogy should also point out the chemical 
and physical relationships existing between the different mineral 
species. It will be noted that many minerals fall into definite 
groups the members of which have chemical and crystallographic 
features in common. The most scientific classification of min- 
erals recognizes these facts and places the minerals having analo- 
gous chemical compositions together, and further groups them 
according to crystallographic and physical similarities. Short 
paragraphs will be found in various parts of this Section which 
explain more fully these relationships. The prominent chemical 

114 



ELEMENTS 115 

groups of this classification and the order in which they are 
treated are given below: 

1. Native Elements. 

2. Sulphides, etc. 

3. Sulpharsenites, etc. 

4. Chlorides, etc. 

5. Oxides. 

6. Carbonates. 

7. Silicates, Titanates. 

8. Niobates, Tantalates. 

9. Phosphates, etc. 

10. Borates. 

11. Uranates. 

12. Sulphates, etc. 

13. Tungstates, Molybdates. 

At the end of the matter descriptive of individual species will 
be found small sections devoted to (a) Minerals of economic 
importance arranged according to the chief elements they con- 
tain; (b) Occurrence and association of minerals; (c) Table of 
minerals arranged according to the systems of crystallization. 

ELEMENTS. 

Comparatively few of the elements are found in the native 
state, and moreover, these are in general rare in occurrence. The 
elements occurring as minerals may be divided into three classes : 
(1) Nonmetals, (2) Semimetals and (3) Metals. The important 
minerals among the nonmetals are diamond, graphite and sul- 
phur. The semimetals tellurium, arsenic, antimony and bis- 
muth belong together in a crystal group, all of them showing 
rhombohedral crystals with closely agreeing fundamental angles. 
The Gold Group is the most important one among the metals, 
including the isometric minerals, gold, silver and copper. An- 
other group contains the rare metals platinum and iron. 



116 



MANUAL OF MINERALOGY 



I. NONMETALS. 
Diamond. 

Composition. Pure carbon. 

Crystallization. Isometric ; tetrahedral. Crystals are usually 
octahedral in habit, but the faces are commonly curved or pitted 





Fig. 203. Fig. 204. 

(Fig. 203). Curved faces of the hexoctahedron are frequently 
observed (Fig. 204). Cubic and dodecahedral planes rare. 





Fig. 205. Fig. 206. 

Twins, with the octahedron as twinning plane (Fig. 205) ; often 
flattened. 

Structure. Usually in crystals, but commonly distorted into 
elongated and irregular forms. At times in spherical forms with 
radiating structure. Rarely massive. 

Physical Properties. Perfect cleavage parallel to the octa- 
hedral faces. H. = 10 (hardest substance known). G. = 3.5. 
Luster adamantine or greasy. Usually colorless or pale yellow. 



DIAMOND 117 

Also pale shades of red, orange, green, blue and brown. Rarely 
in deep shades of blue, red or green; at times black. Usually 
transparent but may be translucent or opaque. Very high index 
of refraction (diamond = 2.42, quartz = 1.55). Strong disper- 
sion of light. Electrified by friction and becomes phosphorescent 
when rubbed with a cloth. Some stones after exposure to sun- 
light give off a phosphorescent glow in the dark. 

Varieties. Ordinary. In rounded crystals, some of which are 
perfectly transparent and colorless (first water). Others are 
faintly colored in various shades and frequently contain inclu- 
sions and are flawed. Sort. In rounded spherical forms with 
radiating structure or made up of confused crystalline aggre- 
gates; usually gray, brown or black in color and translucent to 
opaque. Fragments of crystals that are unavailable for cutting 
are also frequently called bort. Carbonado or black diamond. 
Massive with crystalline structure or granular to compact with- 
out cleavage. Black or grayish black; opaque. 

Tests. To be distinguished by its great hardness, its ada- 
mantine luster and its octahedral cleavage. Burns at a high 
temperature to C0 2 gas, leaving no ash. Will burn readily in 
oxygen gas, giving off a brilliant light. 

Occurrence. The diamond is a rare mineral. It has been found 
in many different localities, but only a few have furnished the mineral 
in notable amount. Most commonly the diamond is found in the 
sands and gravels of stream beds, where it has been preserved by its 
great hardness and fairly high specific gravity. In South Africa 
and recently in Arkansas it has been found embedded in masses of 
an igneous rock, known as peridotite. Three countries have up to 
the present furnished practically the entire world's output of dia- 
monds, namely, India, Brazil, and South Africa. 

The important diamond fields of India are located in the eastern 
and southern portions of the. peninsula. Many of the famous old 
diamond fields in this region are now abandoned, but work is still 
carried on by the natives in the mines in a district lying to the south 
of Allahabad and Benares. Many of the world's famous diamonds 
were found in India, but at present the yield is small. 

Diamonds were discovered in Brazil in the first half of the eight- 
eenth century, and have been mined there ever since. At present, 
however, the production is comparatively small. They are found in 
the stream gravels in several different districts, the two most im- 



118 MANUAL OF MINERALOGY 

portant being located in the provinces of Minas Geraes and Bahia. 
The city of Diamantina, Minas Geraes, is situated in the center of the 
most productive field, the diamonds being found chiefly in the gravels 
of the Rio Jequitinhonha and Rio Doce. Extensive upland deposits 
of diamond-bearing gravels and clays are also worked. 

About 96 per cent of the world's output of diamonds comes at 
present from South Africa. The first diamonds were discovered in 
the gravels of the Vaal River in 1867. The diamond-bearing gravels 
covered a considerable area but were not very thick. Later the 
diamonds were discovered embedded in the rock of several volcanic 
necks located near the present town of Kimberly in Griqualand- 
West, south of the Vaal River, near the boundary of the Orange 
Free State. The diamonds in this district were first discovered in the 
soil resulting from the disintegration of the underlying diamond- 
bearing rock. This soil was colored yellow by iron oxides, and was 
known as the "yellow ground." The underlying, undecomposed 
peridotite rock from which the diamonds are obtained at present 
is called the "blue ground." The principal mines are the Kimberly, 
Du Toitspan, De Beers and Bultfontein, near Kimberly, the Jagers- 
fontein in the Orange Free State, and the Premier in the Transvaal. 
The mines were originally worked as open pits, but, as they have 
increased in depth, underground methods have been adopted. The 
blue rock containing the diamonds is brought to the surface, crushed 
into coarse fragments and spread out on platforms to gradually dis- 
integrate under atmospheric influences. The resulting gravel is 
washed over and concentrated, the diamonds being finally separated 
on shaking tables that have been coated with grease, to which the 
diamond crystals stick, while the rest of the material is washed 
away. Diamonds have also recently been discovered in alluvial 
deposits near Liideritzbuchte, German Southwest Africa. 

Diamonds have been found sparingly in various parts of the 
United States. Small stones have occasionally been discovered in 
the stream sands along the eastern slope of the Appalachian Moun- 
tains from Virginia south to Georgia. Diamonds have also been 
reported from the gold sands of northern California and southern 
Oregon. Sporadic occurrences of diamonds have been noted in the 
glacial drift in Wisconsin, Michigan and Ohio. In 1906 the first 
diamond was found at a new locality situated near Murfreesboro, 
Pike County, Arkansas. The stones are found here not only in the 
detrital soil but also embedded in the underlying peridotite rock in 
a manner quite similar to that of the South African occurrence. 

General. The diamond is the most important of the gem stones. 
Its value depends upon its hardness, its brilliancy, which is due to 
its high index of refraction, and to its "fire," which is due to its strong 
dispersion of light into the prismatic colors. In general the most 



DIAMOND 119 

valuable stones are those which are flawless and colorless or possess 
a "blue-white" color. A faint straw-yellow color, which diamond 
often shows, detracts much from its value. Deep shades of yellow, 
red, green or blue are greatly prized, and fine stones of these colors 
bring very high values. 

The diamond is cut by first cleaving off any undesirable or flawed 
portions of the crystal and then grinding facets upon it by use of 
diamond powder. The crystal is fixed at the end of a stick by means 
of soft solder, leaving the part projecting which is to be cut. A cir- 
cular plate of soft iron is then charged with diamond dust, and this 
by its revolution grinds and polishes the stone. Most diamonds are 
cut into the form known as the brilliant (see Fig. 206). This is a 
stone cut with a large eight-sided facet on top and a series of small 
inclined faces around it. The lower half consists of steeply inclined 
faces giving the stone on this side a pyramidal shape. The depth 
of a brilliant is nearly equal to its breadth, and it, therefore, can only 
be cut from a thick stone. Thinner stones, in proportion to the 
breadth, are cut into what is known as the rose diamond. This is 
a stone which has its upper surface covered with small triangular 
facets. Its lower surface may be one plane face, or the cutting of 
the upper half may be duplicated. With exceptional-shaped stones 
other cuttings are used. 

The value of a cut diamond depends upon its color and purity, 
upon the skill with which it has been cut and upon its size. A one- 
carat stone weighs 205 milligrams, and if cut in the form of a brilliant 
would be 6.25 millimeters in diameter and 4 millimeters in. depth, 
and if of good color would be valued from $150 to $175. A two- 
carat stone of the same quality would have a value three or four 
times as great. 

Famous Stones. The older famous diamonds include the follow- 
ing: the Kohinoor, weighing 106 carats, is one of the crown jewels of 
Great Britain; the Regent or Pitt, weighing 136 carats, belonging to 
France; the Orloff, which is mounted in the Russian imperial scepter, 
weighs 193 carats; Austria owns the Florentine yellow diamond, 
which weighs 139 carats; the Star of the South, weighing 125 carats, 
is said to be in India. 

Large stones found more recently in South Africa include the 
following: The Victoria or Imperial, which weighed 457 carats when 
found, and 230 when cut. It was, however, later recut, its present 
weight being 180 carats. The Stewart weighed before and after 
cutting 288 and 120 carats respectively. The Tiffany diamond, 
which is of a brilliant yellow color, weighs 125 carats. The Colenso 
diamond, presented to the British Museum in 1887 by John Ruskin, 
weighs 129| carats. The Excelsior diamond, found at Jagersfontein 
in 1903, is now known as the Jubilee, and weighs 239 carats. The 



120 MANUAL OF MINERALOGY 

Cullinan or Premier diamond was found at the Premier Mine, Trans- 
vaal, and was the largest stone ever found, weighing 3024 carats or 
1.7 pounds troy, and measured 4 by 2\ by 2 inches. This stone was 
presented to King Edward VII by the Transvaal Government and 
has been cut into 9 large stones, the larger ones weighing 516, 309, 
92 and 62 carats respectively, and into 96 smaller brilliants. 

Name. The name diamond comes from the Greek word 
adamas, meaning " in vincible." 

Use. In addition to its wide use as a gem, the diamond is 
extensively used as an abrasive. Crystal fragments are used to 
cut glass. The fine powder is employed in grinding and polish- 
ing diamonds and other stones. The noncrystalline, opaque 
varieties, especially that known as carbonado, are used in the 
bits of diamond drills. These drills are frequently employed 
in mining operations to explore the rocks and to determine the 
position and size of ore bodies. Recently the diamond has been 
used in wiredrawing and in the making of tungsten filaments 
for electric lights. 

Graphite. 

Composition. Carbon, like the diamond. Sometimes im- 
pure with iron oxide, clay, etc. 

Crystallization. Hexagonal-rhombohedral. In tabular crys- 
tals with hexagonal outline. Prominent basal plane. Distinct 
planes of other forms very rare. Rhombohedral symmetry 
sometimes shown by triangular markings on base. 

Structure. In foliated masses; scaly; granular to compact; 
earthy. Sometimes in globular forms with radiated structure. 

Physical Properties. Perfect basal cleavage. H. = 1-2 (read- 
ily marks paper and soils the fingers). G. = 2.2. Luster metal- 
lic, sometimes dull earthy. Black color with brownish tinge. 
Black streak. Greasy feel. Folia flexible but not elastic. 

Tests. Infusible. Very refractory in its chemical nature. 
Recognized by its color, foliated structure and softness. Dis- 
tinguished from molybdenite by the brownish tinge to K black 
color (molybdenite has a blue tone) and the lack of cnemical 
tests. 



GRAPHITE 121 

Occurrence. Graphite most commonly occurs in metamorphic 
rocks, such as crystalline limestones, schists and gneisses. It may 
occur as large crystalline plates inclosed in the rock or disseminated 
in small flakes in sufficient amount to form a considerable proportion 
of the rock. In these cases, it has probably been derived from carbon 
material of organic origin which has been converted into graphite 
during the metamorphism of the rock. Instances are known in 
which coal beds, under influence of strong metamorphic action, such 
as the intrusion into them of an igneous rock, have in a greater or 
less degree been converted into graphite. Examples of such an 
occurrence are to be found in the graphitic coals of Rhode Island, 
and in the coal fields of Sonora, Mexico. Graphite also occurs in 
fissure veins associated with calcite, quartz, orthoclase, pyroxene, 
etc. An example of such veins is to be found in the deposits at 
Ticonderoga, New York. Here the veins traverse a gneiss and 
besides the graphite contain quartz, biotite, orthoclase, tourmaline, 
apatite, pyrite, titanite, etc. The graphite may have been formed 
in these veins from hydrocarbons introduced into them during the 
metamorphism of the region and derived from the surrounding 
carbon-bearing rocks. Graphite occurs occasionally as an original 
constituent in igneous rocks. It has been observed in the basalts 
of Ovifak, Greenland, in an elasolite syenite from India, in a granite 
pegmatite from Maine, in meteorites, etc. 

The most productive deposits of graphite at present are on the 
island of Ceylon, where it occurs in coarsely foliated masses in veins 
in gneiss. It occurs in large amounts in various localities in Austria, 
Italy, India, Mexico, etc. The chief deposits in the United States 
are in the Adirondack region of New York, in Essex, Warren, Wash- 
ington and Saratoga counties. 

Artificial. Artificial graphite is manufactured on a large scale in 
the electrical furnaces at Niagara Falls. Anthracite coal with a 
small amount of evenly distributed ash is subjected to the intense 
heat of the electrical current and converted into graphite. The 
output of artificial graphite is considerably in excess of that of the 
natural mineral. 

Name. Derived from the Greek word "to write." 
Use. Used in the manufacture of refractory crucibles for 
the steel, brass and bronze industries. Most of the graphite 
used in this way is imported from Ceylon. Used widely, when 
mixed with oil, as a lubricant. Mixed with fine clay, it forms 
the "lead" of pencils. Much of the graphite used in the United 
States for this purpose comes from Sonora, Mexico. Used in 
the manufacture of a protective paint for structural iron and 



122 



MANUAL OF MINERALOGY 



steel works. Used in the coating of foundry facings, for elec- 
trodes, stove polishes, in electrotyping, etc. 

Sulphur. 

Composition. Sulphur; often impure with clay, bitumen, etc. 

Crystallization. Orthorhombic. Pyramidal in habit (Fig. 
207). Often with two pyramids, brachydome and base in com- 
bination (Figs. 208 and 209). 




Fig. 207. 



Fig. 209. 



Structure. Often in irregular masses imperfectly crystallized. 
Massive, reniform, stalactitic, as incrustations, earthy. 

Physical Properties. H. = 1.5-2.5. G. = 2.05-2.09. Res- 
inous luster. Color sulphur-yellow, varying with impurities to 
yellow shades of green, gray and red. Transparent to opaque. 
Imperfect conductor of heat. When a fragment is held in the 
hand close to the ear it will be heard to crack. This is due to 
the expansion of the surface layers because of the heat from the 
hand, while the interior, on account of the slow heat conductivity, 
is unaffected. Crystals of sulphur should, therefore, be handled 
with care. 

Tests. Fusible at 1 and burns with a blue flame giving strong 
odor of sulphur dioxide. Sublimes in C. T. giving a red to dark 
yellow liquid when hot, yellow solid when cold. Told by its 
yellow color and the ease with which it burns. 

Occurrence. Found either associated with beds of gypsum, as 
an alteration product of a sulphate, or in connection with active or 
extinct volcanoes, as a result of fumerole action. Sometimes in 
connection with sulphides in metallic veins and derived from their 



ARSENIC 123 

oxidation. Found in large deposits and in fine crystals near Gir- 
genti, Sicily, associated with celestite, gypsum, calcite, aragonite, 
etc.; also in connection with the volcanoes of Mexico, Hawaii, 
Japan, Iceland, etc. In the United States is mined in Calsasieu 
Parish, Louisiana, and in Wyoming and Utah. 

Use. Used in the manufacture of sulphuric acid, in the manu- 
facture of matches, gunpowder, fireworks, insecticides, for vul- 
canizing rubber and in medicine. 



II. SEMIMETALS. 
Tellurium. 

Native tellurium with sometimes a small amount of selenium, 
gold, iron, etc. Hexagonal-rhombohedral. Crystals rare; usually 
minute hexagonal prisms with rhombohedral terminations. Com- 
monly massive, columnar to fine granular. Perfect prismatic cleav- 
age. H. = 2-2.5. G. = 6.1-6.3. Metallic luster. Tin-white color. 
Gray streak. Wholly volatile B. B. Fusible at 1. On charcoal 
tinges reducing flame green and gives a white oxide coating. Heated 
with concentrated sulphuric acid gives deep red color to solution. 
A rare species, found usually associated with the rare teilurides 
of gold and silver. Occurs with sylvanite near Zalathna, Transyl- 
vania, at the Good Hope Mine, Vulcan, Colorado, and in other dis- 
tricts in that state. Tellurium has little commercial value. 

Arsenic. 

Composition. Arsenic, often with some antimony and traces 
of iron, silver, gold, bismuth, etc. 

Crystallization. Hexagonal-rhombohedral. Crystals rare. 

Structure. Usually granular massive, sometimes reniform 
and stalactitic. 

Physical Properties. Perfect basal cleavage. H.=3.5. G.=5.7. 
Metallic luster. Color tin-white on fresh fracture, tarnishes 
on exposure to dark gray. Gray streak. 

Tests. Volatile without fusion. B. B. on charcoal gives 
white volatile coating of arsenious oxide and odor of garlic. In 
0. T. gives volatile crystalline deposit of arsenious oxide. In 
C. T. gives arsenic mirror. 



124 MANUAL OF MINERALOGY 

Occurrence. A comparatively rare species found in veins in crys- 
talline rocks associated with antimony minerals, the ruby silvers, 
realgar, orpiment, sphalerite, etc. Found in the silver mines of 
Saxony, in Bohemia, Norway, Zmeov in Siberia, Chile, Mexico. 
Sparingly in the United States. 

Name. The name arsenic is derived from a Greek word 
meaning masculine, a term first applied to the sulphide of arsenic 
on account of its potent properties. 

Use. Very minor ore of arsenic. 

Antimony. 

Composition. Antimony, with (at times) small amounts of 
arsenic, iron or silver. 

Crystallization. Hexagonal-rhombohedral. Distinct crystals 
rare. 

Structure. Usually in granular masses showing distinct cleav- 
age; radiated; botryoidal. 

Physical Properties. Perfect basal cleavage. H. = 3-3.5. 
G. = 6.6-6.7. Metallic luster. Tin-white color. Gray streak. 

Tests. Easily and completely volatile. Fusibility 1. When 
heated on charcoal gives a dense white coating of antimony 
trioxide. Heated in 0. T. gives a white, slowly volatile subli- 
mate of antimony trioxide. 

Occurrence. A rare species, found usually in connection with 
silver veins and associated with arsenic and antimony compounds. 
Occurs at Sala, Sweden; Andreasberg, Harz Mountains; at Pfibram, 
Bohemia; Allemont, France; Chile; South Ham, Canada; York 
County, New Brunswick, etc. 

Use. Minor ore of antimony. 

Bismuth. 

Composition. Bismuth, with sometimes small amounts of 
arsenic, sulphur, tellurium. 

Crystallization. Hexagonal-rhombohedral. Distinct crys- 
tals rare. 

Structure. Usually laminated and granular; sometimes re- 
ticulated or arborescent. 



GOLD 125 

Physical Properties. Basal and rhombohedral cleavage. H. = 
2-2.5. G. = 9.8. Sectile. Brittle. Metallic luster. Color 
silver-white with decided reddish tone. Streak silver-white, 
shining. 

Tests. Fusible at 1. B. B. on charcoal gives metallic globule 
and yellow to white coating of bismuth oxide. The globule is 
somewhat malleable but cannot be hammered into as thin a 
sheet as in the case of lead. Mixed with potassium iodide and 
sulphur and heated on charcoal gives a brilliant yellow tp red 
Boating. Recognized chiefly by its laminated structure, its 
reddish silver color and its sectility. 

Occurrence. A comparatively rare mineral, occurring usually in 
connection with ores of silver, cobalt, lead and zinc. Found in the 
silver veins of Saxony; in Norway and Sweden; Cornwall, England; 
with the silver and cobalt minerals at Cobalt, Ontario, Canada; only 
sparingly in the United States. 

Use. Ore of bismuth. The greater part of the bismuth of 
commerce is produced from the sulphide, bismuthinite, or from 
other ores that contain a small per cent of the metal. It is 
chiefly employed in the manufacture of low-fusing alloys which 
are used as safety plugs in boilers and in automatic fire sprinklers, 
etc. Its salts are used in medicine. 

III. METALS. 

GOLD GROUP. ISOMETRIC. 
Gold. 

Composition. Gold, commonly alloyed with small amounts 
of silver and at times with traces of copper and iron. Ordinarily, 
native gold contains varying amounts of alloyed silver up to 
16 per cent. California gold contains between 10 and 15 per 
cent of silver. The greater part of native gold is about 90 per 
cent "fine" or contains 10 per cent of other metals. Gold con- 
taining unusually high percentages of silver (25 to 40 per cent) 
is known as electrum. 

Crystallization. Isometric. Crystals are commonly octahe- 
dral in habit, showing also at times the faces of the dodeca- 



126 



MANUAL OF MINERALOGY 



hedron, cube, etc. (see Figs. 210, 211 and 212) . Often in arbores- 
cent crystal groups with crystals elongated in the direction of an 




Fig. 210. 
Octahedron. 



Fig. 211. 
Dodecahedron. 



Fig. 212. 
Cube and Octahedron. 



octahedral axis. Crystals irregularly distorted and passing into 
filiform, reticulated and dendritic shapes. 

Structure. Usually in irregular plates, scales or masses. 
Seldom definitely crystallized. 

Physical Properties. H. = 2.5-3. G. = 15.6-19.3 (becomes 
greater as the percentages of the other metals present decrease). 
Very malleable and ductile. Color various shades of yellow, 
depending upon purity, becoming paler with increase in the per- 
centage of silver present. 

Tests. Easily fusible at 2.5-3. Insoluble in ordinary acids 
but soluble in a mixture of hydrochloric and nitric acids. To 
be distinguished from certain yellow sulphides (particularly pyrite 
and chalcopyrite) and from yellow flakes of altered micas by its 
malleability, its insolubility and its great weight. 

Occurrence. Although gold is a rare element, it is to be found 
widely distributed in nature, occurring in small amounts. Its pres- 
ence as a primary constituent of igneous rocks, more particularly of 
the acidic type, has been abundantly proved. It is to be found most 
commonly in quartz veins. It occurs in detrital sands and gravels 
in what are known as placer deposits. It is present in small amounts 
in sea water. It is important to note that gold occurs almost wholly 
as the native metal, the only class of compounds which it forms in 
nature being the tellurides. 

The chief source of gold is the gold-quartz veins. It occurs in 
these veins usually as very small specks scattered uniformly through- 
out the quartz gangue. The contents of these veins are in general 



GOLD 127 

considered to have been deposited from ascending mineral-bearing 
solutions. That gold is capable of solution and subsequent precipi- 
tation by means of underground waters has been repeatedly demon- 
strated. In the majority of veins the gold is so finely divided and 
uniformly distributed that its presence in the ore cannot be detected 
with the eye. It is interesting to note that with the value of gold 
at $20.67 a troy ounce, ore which contains one per cent of gold by 
weight would be worth $6028 to the ton, while an ore containing 
only 0.01 per cent of gold would still be a rich ore, having a value of 
$60 per ton. Ores are mined at a profit sometimes which contain 
only 0.001 per cent of gold and yield but $6 to the ton. So it might 
be quite impossible x> detect the presence of gold in a valuable ore 
by any ordinary tests. A definite estimation of the amount of gold 
present by means of a careful assay is the only way usually to deter- 
mine the value of an ore. But occasionally, under favorable con- 
ditions, the gold may collect in larger amounts, in nests and pockets 
in the veins, occurring usually as irregular plates and masses between 
the crystals of quartz. In the quartz veins the gold is frequently 
associated with sulphides, particularly with pyrite. It is thought 
that the gold does not exist in any chemical combination with the 
pyrite, but has ,the same mechanical relation to it that it has to the 
quartz. The upper portions of the gold-quartz veins as a rule have 
been enriched in their values. The gold present in this upper zone 
was in part deposited contemporaneously with the formation of the 
vein, but frequently the greater part has been transported, either 
in solution or by mechanical settling, from that upper portion of the 
vein which has been gradually eroded away! And so the gold in 
this part of the vein represents the concentration in a small space 
of the original gold content of a much greater length of vein. By 
the oxidation of the gold-bearing sulphides originally deposited in 
this portion of the vein the gold embedded in them has been set free, 
rendering the gold easy of extraction. Ores that contain the gold 
free from intimate association with sulphides are known as "free- 
milling" because their gold content can be recovered by amalgama- 
tion with the mercury of the plates over which the finely crushed ore 
runs from the stamp mill. Where sulphides are present in any 
quantity all of the gold cannot be recovered by amalgamation and a 
chemical process, either the cyanide or chlorination process, must 
be used, either alone, or in addition to the amalgamation. 

In addition to occurring with quartz and pyrite, gold has been 
found associated with chalcopyrite, sphalerite, galena, stibnite, 
cinnabar, arsenopyrite, limonite, calcite, etc. 

Gold, on account of its great weight, is mechanically sorted in 
running water from the lighter material of the sands and gravels in 
which it may occur. In this way a concentration frequently takes 



128 MANUAL OF MINERALOGY 

place in stream beds and gold placer deposits are formed. In general 
these deposits will be found where the current of the water has been 
suddenly checked and the heaviest particles of its load dropped in 
the bottom of the stream. Sand bars, etc., formed in this way may 
contain rich placer deposits. Irregularities in the bottom of a 
stream frequently act as natural riffles and catch behind them the 
heavier gold traveling along the bottom of the stream. In general, 
also, such deposits will be richer as the stream is ascended and the 
original veins from which the gold has been derived are approached. 
The larger masses of gold which have been rolled together by the 
action of the stream are called nuggets. These sometimes attain 
considerable size. The very fine gold which is known as float gold 
may be carried by the streams for long distances. 

In California, at the close of the glacial epoch, large amounts of 
gold-bearing gravels were deposited in the stream beds. Subse- 
quent changes in the elevation of the country and extensive lava 
flows have caused a rearrangement of the drainage, and in places 
these old gravel beds are to be found to-day upon the liillsides and 
are known as the hill gravels. In places they have been covered 
over with lava flows and so preserved from erosion. At Cape Nome, 
Alaska, the beach sands contained gold, where by the action of the 
waves the gold has been concentrated to form placer deposits. 

The important gold-producing states and territories of the 
United States, in their approximate order of importance, are Colo- 
rado, Alaska, California, Nevada, South Dakota, Utah, Montana, 
Arizona and Idaho. There are several other states that also produce 
the metal, but in comparatively small amounts. The most im- 
portant gold-producing districts of California are those of the series 
of gold-quartz veins known as the Mother Lode which lie along the 
western slope of the Sierras in Nevada, Amador, Calaveras, Eldorado, 
Tuolumne and Mariposa counties. Between one-third and one-half 
of California's gold production comes from placer deposits, mostly 
worked by dredging operations in Butte and Yuba counties. The 
gold of Alaska has been derived chiefly from placer deposits, but 
recently the vein deposits have been of .increasing importance. The 
chief producing districts are the Yukon Basin, the Fairbanks Dis- 
trict and the Seward Peninsula, including Nome. Although Colo- 
rado is one of the first states in the production of gold, about one- 
half of its output comes from the Cripple Creek District in Teller 
County, where the gold occurs only sparingly native, but chiefly in 
the form of the tellurides, sylvanite and calaverite. The other 
chief producing counties are San Miguel and Ouray in the San Juan 
District, and Lake County, containing the Leadville District, and 
Gilpin, Clear Creek and Boulder counties in the Clear Creek District. 
The chief gold districts of Nevada are Goldfield and Tonopah and 



SILVER 129 

other smaller camps in Nye and Esmeralda counties. The gold 
from South Dakota comes from the Black Hills, the Homestake Mine 
at Lead being the largest producer. The gold-producing districts 
of Utah are the Tintic and Bingham districts in Juab and Salt Lake 
counties respectively, and the Mercur District in Tooele County. 

Important foreign gold-producing countries are as follows: South 
Africa, Australia, Russia, Mexico and Canada. The region known 
as the Rand, near Johannesburg in the Transvaal, South Africa, is 
the most productive gold district in the world. The gold occurs 
here scattered throughout inclined beds or " reefs" of a quartzose 
conglomerate, which has been mined in enormous amounts and to 
great depths. Australia has the following chief gold districts: 
Kalgoorlie in western Australia (largely tellurides), Ballarat and 
Bendigo in Victoria, Mount Morgan in Queensland and various fields 
in New South Wales. In Russia gold is mined in western Siberia 
and the Urals, in the Irkutsk Province, in Transbaikalia and Amur. 
The production of Mexico comes chiefly from the districts of Guana- 
juato, El Oro and Dolores. 



Silver. 

Composition. Silver, frequently containing small amounts of 
alloyed copper and gold, more rarely traces of platinum, anti- 
mony, bismuth, mercury. 

Crystallization. Isometric. Crystals commonly distorted and 
in branching, arborescent or reticulated groups. 

Structure. Commonly in irregular masses, plates, scales, etc.; 
at times as coarse or fine wire. 

Physical Properties. H. = 2.5-3. G. = 10.1-11.1, pure 10.5. 
Malleable and ductile. Color silver-white, often tarnished to 
brown or gray-black. 

Tests. Easily fusible at 2 to bright globule. No oxide coat- 
ing on charcoal. Easily soluble in nitric acid, giving on addition 
of hydrochloric acid a curdy white precipitate of silver chloride, 
which turns dark on exposure to light. Deposited from its solu- 
tion by action of a clean copper plate. 

Occurrence. Occurs usually as small irregular flakes and masses 
disseminated through various vein minerals, often invisible. Found 
associated with native copper, galena, argentite, chalcocite, the ruby 
silvers, tetrahedrite, calcite, barite, etc. While native silver is not 



130 



MANUAL OF MINERALOGY 



an uncommon mineral, the larger part of the world's output of the 
metal is obtained from its various compounds with sulphur, anti- 
mony, arsenic, etc. Most of the native silver occurring in nature is 
probably secondary in its origin, having been derived by reduction 
from some of its compounds. 

Native silver has been found in the United States with native 
copper in the copper mines of Lake Superior; in crystal groups at 
the Elkhorn Mine, Montana; in large masses in the silver mines at 
Aspen, Colorado. Is found, at present, in large quantities as platy 
masses, associated with various cobalt and nickel minerals, at Cobalt, 
Ontario, Canada. An important silver ore in the mines of Chihua- 
hua, Guanajuato, Durango, Sinaloa and Sonora, Mexico. Occurs 
commonly in the mines of Peru. Was found in large masses, one 
of which weighed 500 pounds, in the mines at Kongsberg, Norway. 
One of the ores of the silver mines of Saxony and Bohemia. 

Use. Silver is used for ornamental purposes, for coinage, 
plating, etc. It is usually alloyed with copper. The standard 
silver coin in the United States contains one part of copper to 
nine parts of silver. 

Copper. 

Composition. Copper, often containing small amounts of 
silver, bismuth, mercury, etc. 

Crystallization. Isometric. Tetrahexahedron faces common 
on crystals, (see Fig. 213). Also cube and dodecahedron. Crys- 
tals usually distorted and in branching 
and arborescent groups, (see PL IV). 
Structure. Usually in irregular masses, 
plates, scales, etc. In twisted and wire- 
like forms. 

Physical Properties. H. = 2.5-3. 
G. = 8.8-8.9. Highly ductile and mal- 
leable. Color copper-red, usually dark 
Cube and Tetra- and with a dull luster on account of 

tarnish. 

Tests. Fuses at 3 to a globule, which becomes covered with 
an oxide coating on cooling. Dissolves readily in nitric acid, and 
the solution is colored a deep blue on addition of ammonium 
hydroxide in excess. 



Fig. 213. 

hexahedron 



PLATE IV. 




Arborescent Copper, Lake Superior. 



PLATINUM 131 

Occurrence. A mineral found widely distributed in copper veins, 
but usually in small amount. Associated with various copper min- 
erals, most commonly with the oxidized ores, cuprite, malachite and 
azurite. Ordinarily is strictly a secondary mineral and is to be 
found only in the upper parts of copper veins. 

The most notable deposit of native copper known in the world 
is on Keweenaw Peninsula in northern Michigan, on the southern 
shore of Lake Superior. The region is occupied by a series of igneous 
flows of trap rock interbedded with sandstone conglomerates. The 
whole series dips toward the north. The copper is found in veins 
intersecting this rock series; in the amygdaloidal belts at the top 
of the various trap flows; and as a cementing material in the sand- 
stone conglomerate. This last type has furnished the most impor- 
tant ore deposits, some of which have been worked for considerably 
over a mile in vertical depth. -Not only does the copper act as a ce- 
ment to bind the conglomerate together, but it has often penetrated 
the quartz boulders of the rock to a depth of a foot or more. It is 
associated with such minerals as epidote, datolite, calcite and various 
zeolites. The mines were worked superficially by the Indians, and 
have been actively developed since the middle of the eighteenth 
century. Most of the copper of the district occurs in very small 
irregular specks, but notable large masses have been found, one 
weighing 420 tons being discovered in 1857. 

Sporadic occurrences of copper similar to that of the Lake Superior 
District have been found in the sandstone areas of the eastern 
United States, notably in New Jersey, and in the glacial drift over- 
lying a similar area in Connecticut. Native copper occurs in small 
amounts, associated with the oxidized ores of Arizona, New Mexico 
and northern Mexico. 

Use. The most important uses to which the metal is put are 
as an electrical conductor; in the manufacture of brass (an alloy 
of copper and zinc), of bronze (an alloy of copper and tin with 
frequently zinc); for sheet copper; and as copper sulphate, 
which is used in calico printing, in galvanic cells, etc. 

Mercury, Amalgam (Ag,Hg) and Lead are rare metals. 

PLATINUM-IRON GROUP. 
Platinum. 

Composition. Platinum, usually alloyed with several per cent 
of iron and with smaller amounts of iridium, osmium, etc. The 
amount of metallic platinum present seldom exceeds 80 per cent. 



132 MANUAL OF MINERALOGY 

Crystallization. Isometric. Crystals very rare. Commonly 
distorted. 

Structure. Usually in small grains or scales. Sometimes in 
irregular masses and nuggets of larger size. 

Physical Properties. H. = >4.5 (unusually high for a'metal) . 
G. = 14-19 native; 21-22 when chemically pure. Malleable 
and ductile. Color steel-gray, with bright luster. 

Tests. B. B. infusible. Unattacked by ordinary reagents; 
soluble in a mixture of hydrochloric and nitric acids. Deter- 
mined by its high specific gravity, infusibility and insolubility. 



Occurrence. Platinum is a rare metal which occurs almost ex- 
clusively native (only one rare compound, sperrylite, PtAs 2 , being 
known). It is found in quantity in only a few localities, and then 
only in the stream sands, as placer deposits, where it has been pre- 
served on account of its great weight and hardness. Occurs in the 
alluvial deposits associated with the rarer metals of the Platinum 
Group, gold, iron-nickel alloys, chromite, etc. Its original source 
is probably usually in peridotite rocks or the serpentine rocks re- 
sulting from their metamorphism. It occurs so sparingly dissemi- 
nated through such rocks, however, that it is only after their disin- 
tegration and the subsequent concentration of the platinum in the 
resulting sands that workable deposits of the metal are formed. 
Placer deposits of platinum are therefore to be looked for in the 
vicinity of masses of such peridotite rocks. 

Practically the entire world's supply of platinum at present comes 
from the Ural Mountains in Russia. The central and northern end 
of this range has large masses of altered peridotite rocks, and in the 
sands of the streams descending from it, chiefly on the eastern slope 
in Siberia, platinum is found in considerable quantity. The chief 
districts are Nizhni Tagilsk, Bissersk and Goroblagodat, and far- 
ther to the north, Bogoslowsk. 

Platinum was first discovered in the United States of Colombia, 
South America, where it received its name platina from plata (silver) . 
It is to be found there in two districts near the Pacific coast. The 
chief district covers the greater part of the intendencia of Choco, 
while the second, that of Barbacoas, is in the department of Cauca. 
The platinum occurs here with gold in placer deposits, and, while 
the fields are not largely productive at present, they may become so. 

The only platinum found in the United States comes from the 
gold placer deposits of Oregon and California, but the yearly yield 
amounts to only a few thousand dollars in value. 



SULPHIDES 133 

Use. The uses of the metal depend chiefly upon its insolu- 
bility, infusibility and superior hardness. It is used for various 
scientific instruments such as crucibles, dishes, etc., in the chemi- 
cal laboratory; to line the distilling apparatus in the manufac- 
ture of sulphuric acid; in the electrical industry for contacts, 
etc.; in jewelry, chiefly as the setting for diamonds; as anodes 
in the electrolytic chemical industry; for electric heating appa- 
ratus; for the measurement of high temperatures by the use of 
thermoelectricity; for sparking plugs in explosive motors; in 
incandescent electric lights; in the manufacture of false teeth 
and in fillings for teeth; and in various chemical reactions which 
are facilitated by the use of finely divided platinum. 

Iron. 

Native iron, with always some nickel and usually small amounts 
of cobalt and frequently traces of copper, manganese, sulphur, car- 
bon, phosphorus, etc. Isometric. Practically always massive. 
H. = 4-5. G. = 7.3-7.8. Malleable. Metallic luster. Color steel- 
gray to black. Strongly magnetic. Occurs very sparingly as terres- 
trial iron, and in the form of meteorites. Found, included in basalt, 
on the west coast of Greenland, varying in size from small dissemi- 
nated grains to large masses. Has been noted in a few other locali- 
ties with a similar association. Nickel-iron alloys have been found 
in the gold sands of New Zealand (awaruite), from Josephine County, 
Oregon (josephinite) , and from the Fraser River, British Columbia 
(souesite). Most meteorites contain native iron. The metal some- 
times forms practically the entire body of the meteorite, while at 
other times it forms a cellular mass, inclosing grains of chrysolite, etc. 
In the stony meteorites, iron is found disseminated through them 
in the shape of small grains. Meteorites are to be recognized usually 
by their fused and pitted exterior. At first they are coated with a 
film of iron oxide, which disappears, however, on continued exposure 
to the weather. 

Indium, Iridosmine, an alloy of iridium and osmium, and 
Palladium are rare metals in the Platinum-Iron Group. 

SULPHIDES. 

The sulphides form an important gi*oup of minerals which in- 
cludes the majority of the ore minerals. With them are classed 
the similar but rarer selenides, tellurides, arsenides and anti- 



134 



MANUAL OF MINERALOGY 




monides. The sulphides may be divided into two groups de- 
pending upon the character of the metal present: (1) Sulphides 
of the Semimetals, (2) Sulphides of the Metals. 

SULPHIDES OF THE SEMIMETALS. 

Realgar. 

Composition. Arsenic monosulphide, AsS = Sulphur 19.9, 
arsenic 70. 1. 

Crystallization. Monoclinic. Short prismatic crystals, ver- 
tically striated. (See Fig. 214.) 

Structure. In crystals, coarse to fine granu- 
lar, often earthy and as an incrustation. 

Physical Properties. Cleavage parallel to 
clinopinacoid. H. = 1.5-2. G. = 3.55. Resin- 
ous luster. Color and streak red to orange. 
Transparent to opaque. 

Tests. Fusible at 1. Easily volatile. Heated 
on charcoal yields a volatile white sublimate of 
arsenious oxide with characteristic garlic odor. 
Roasted in 0. T. gives volatile, crystalline subli- 
mate of arsenious oxide and odor of sulphur dioxide. Charac- 
terized chiefly by deep red color and resinous luster. 

Occurrence. A rare mineral, occurring usually with orpiment, 
As 2 S 3 . Found associated with silver and lead ores in Hungary, 
Bohemia, Saxony, etc. Found in good crystals at Nagyag, Tran- 
sylvania; Binnenthal, Switzerland; Allchar, Macedonia. Occurs 
in Iron County, Utah. Found deposited from the geyser waters in 
Yellowstone Park. 

Name. The name is derived from the Arabic, Rahj al ghar, 
powder of the mine. 

Use. Was used in fireworks to give a brillant white light when 
mixed with saltpeter and ignited. Artificial arsenic sulphide is 
at present used for this purpose. 

Orpiment. 

Composition. Arsenic trisulphide, As 2 S a = Sulphur 39, arse- 
nic 61. 



Fig. 214. 



STIBNITE 135 

Crystallization. Monoclinic. Crystals small and rarely dis- 
tinct. 

Structure. Usually foliated. 

Physical Properties. Very perfect cleavage parallel to clino- 
pinacoid. Folia flexible but not elastic. Sectile. H. = 1.5-2. 
G. = 3.4-3.5. Resinous luster, pearly on cleavage face. Color 
lemon-yellow. Translucent. 

Tests. Same as for realgar (which see). Characterized by 
its yellow color, perfect cleavage and foliated structure. 

Occurrence. A rare mineral, associated usually with realgar. 
Found in various places in Hungary; in Kurdistan; in Peru, etc. 
Occurs at Mercur, Utah. Deposited from geyser waters in the 
Yellowstone Park. 

Name. Derived from the Latin, auripigmentum, "golden paint." 
Use. For a pigment, in dyeing and in a preparation for the 

removal of hair from skins. Artificial arsenic sulphide is largely 

used in place of the mineral. 

Stibnite. 

Composition. Antimony trisulphide, Sb 2 S 3 = Sulphur 28.6, 
antimony 71.4. Sometimes carries gold or silver. 

Crystallization. Orthorhombic. Slender prismatic habit, 
prism zone vertically striated. Crystals often steeply termi- 
nated. (See Fig. 216.) Often in radiating groups. Crystals 
sometimes curved or bent (Fig. 215). 

Structure. In radiating crystal groups or in bladed forms with 
prominent cleavage. Massive, coarse to fine columnar. 

Physical Properties. Perfect cleavage parallel to brachy- 
pinacoid. H. =2. G. = 4.55. Metallic luster, splendent on 
cleavage surfaces. Color and streak lead-gray. 

Tests. Very easily fusible at 1. B. B. on charcoal gives dense 
white coating of antimony trioxide and odor of sulphur dioxide. 
When roasted in 0. T. gives nonvolatile white sublimate on 
bottom of tube and a white volatile sublimate as ring around 
tube. Heated in C. T. gives a faint ring of sulphur and below 
a red (when cold) deposit of oxysulphide of antimony. Char- 



136 



MANUAL OF MINERALOGY 



acterized by its bladed structure, perfect cleavage in one direc- 
tion, its lead-gray color and soft black streak. 





Fig. 215. 



Fig. 216. 



Occurrence. Deposited by alkaline waters in connection usually 
with quartz. Found in quartz veins or beds in granite and gneiss. 
Associated with other antimony minerals, as the products of its 
decomposition, and with galena, cinnabar, sphalerite, barite and 
sometimes gold. Found in various mining districts in Saxony, and 
Bohemia, Mexico, New South Wales, China, etc. Occurs in mag- 
nificent crystals in Province of lyo, island of Shikoku, Japan. 
Found in quantity only sparingly in the United States, the chief 
deposits being in California, Nevada and Idaho. 

Use. Used in various alloys, as type metal, pewter and anti- 
friction metal. The sulphide is employed in the manufacture 
of fireworks, matches, percussion caps, etc. Used in vulcanizing 
rubber. Used in medicine as tartar emetic and other compounds. 
Antimony trioxide is used as a pigment and for making glass. 



Composition, 
muth 81.2. 

Crystallization. 



Bismuthinite. 

Bismuth trisulphide, Bi 2 S 3 = Sulphur 18.8, bis- 

Orthorhombic. In acicular crystals. 



MOLYBDENITE 137 

Structure. Usually massive, foliated or bladed. 

Physical Properties. Perfect cleavage parallel to brachy- 
pinacoid. H. = 2. G. = 6.4-6.5. Metallic luster. Color and 
streak lead-gray. 

Tests. Easily fusible (1). Roasted in 0. T. or B. B. on char- 
coal gives odor of sulphur dioxide. Mixed with potassium iodide 
and sulphur and heated on charcoal gives characteristic yellow 
to red coating. Resembles stibnite; recognized by the test for 
bismuth. 

Occurrence. A rare mineral, found in Cumberland, England; in 
Saxony, Sweden, Bolivia, Beaver County in Utah, etc. 

Use. An ore of bismuth. See under native bismuth. 

Molybdenite. 

Composition. Molybdenum disulphide, MoS 2 = Sulphur 40, 
molybdenum 60. 

Crystallization. Hexagonal. Crystals in hexagonal-shaped 
plates or short, slightly tapering prisms. 

Structure. Commonly foliated massive or in scales. 

Physical Properties. Perfect basal cleavage. Laminae flex- 
ible but not elastic. Sectile. H = 1. G. = 4.75. Greasy feel. 
Metallic luster. Color lead-gray. Grayish black streak. 

Tests. Infusible. Heated B. B. gives yellowish green flame. 
Roasted in 0. T. gives odor of sulphur dioxide and deposit of 
thin plates of molybdenum oxide, crossing the tube above the 
mineral. Heated on charcoal in 0. F. gives a white coating of 
molybdenum oxide; when this coating is touched with R. F. 
turns to deep blue color. Resembles graphite but is distin- 
guished from it by having a blue tone to color, while graphite 
has a brown tinge, and by its reactions for sulphur and molyb- 
denum. 

Occurrence. Occurs in granite, gneiss and granular limestone, 
either as nests or disseminated through the rock. Found in the 
United States in many localities, but usually not in commercial quan- 
tity. Found at Blue Hill and Cooper, Maine; Westmoreland, New 
Hampshire; Pitkin, Colorado; in Okanogan County, Washington. 

Use. An ore of molybdenum. See under wulfenite. 



138 MANUAL OF MINERALOGY 



SULPHIDES, ETC., OF THE METALS. 

The sulphides of the metals are divided into the following 
groups: A. Basic Division; B. Monosulphide Division; C. In- 
termediate Division; D. Disulphide Division. 



A. BASIC DIVISION. 

This division includes several rare compounds of silver or cop- 
per with antimony or arsenic such as dyscrasite, Ag 3 Sb to Ag 6 Sb; 
domeykite, Cu 3 As; algodonite, Cu 6 As; whitneyite, 



B. MONOSULPHIDE DIVISION. 

1. GALENA GROUP. ISOMETRIC. 

Argentite. Silver Glance. 

Composition. Silver sulphide, Ag 2 S = Sulphur 12.9, silver 
87.1. 

Crystallization. Isometric. Cube, dodecahedron and octa- 
hedron the most common forms. Crystals often distorted and 
arranged in branching or reticulated groups. 

Structure. Commonly massive, platy, earthy or as a coating. 
More rarely in crystals. 

Physical Properties. H. = 2-2.5. G. = 7.3. Easily sectile, 
can be cut with a knife like lead. Metallic luster. Color and 
streak blackish lead-gray. Streak shining. Bright on fresh 
surface but on exposure becomes dull black, due to the forma- 
tion of an earthy sulphide. 

Tests. Easily fusible at 1.5 with intumescence. When fused 
alone on charcoal in 0. F. gives off odor of sulphur dioxide and 
yields a globule of pure silver. Distinguished by these tests 
and by its color, sectility and high specific gravity. 

Occurrence. A fairly common ore of silver. Usually found in 
silver veins as small masses, often earthy or as a coating. Associated 
with native silver, the ruby silvers, stephanite and other silver min- 
erals; also galena. In the United States it was an important ore 
in the mines of the Comstock Lode, Nevada; at present found in 
Nevada at Tonopah and elsewhere. Found also in some of the silver 



GALENA 



139 



districts of Arizona. An important ore in the silver mines of Guan- 
ajuato and elsewhere in Mexico; in Peru, Chile and Bolivia. Im- 
portant European localities for its occurrence are Freiberg in Saxony, 
Annaberg in Austria, Joachimsthal in Bohemia, Schemnitz and 
Kremnitz in Hungary, Kongsberg in Norway. 

Use. An important ore of silver. 

Galena. Galenite. 

Composition. Lead sulphide, PbS = Sulphur 13.4, lead 86.6. 
Almost always carries traces of silver sulphide, frequently enough 
to make it a valuable silver ore. At times also contains small 
amounts of selenium, zinc, cadmium, antimony, bismuth and 
copper. 

Crystallization. Isometric. Most common form is the cube, 
octahedron sometimes as truncations to cube, more rarely as the 





Fig. 217. 
Cube. 



Fig. 218. 
Cube and Octahedron. 




Fig. 219. 
Octahedron and Cube. 



simple form (Figs. 217, 218 and 219; see also A, pl.V.). Dode- 
cahedron and trisoctahedron rare. 

Structure. Commonly crystallized or massive cleavable; 
coarse or fine granular. 

Physical Properties. Perfect cubic cleavage, H. = 2.5-2.75.' 
G. = 7.4-7.6. Bright metallic luster. Color and streak lead- 
gray. 

Tests. Easily fusible at 2. Reduced on charcoal to lead 
globule with formation of yellow to white coating of lead oxide. 
When heated rapidly in the 0. F. the coating is heavier and con- 
sists chiefly of a white volatile combination of oxides of lead and 
sulphur, which resembles the antimony oxide coating. Odor of 
sulphur dioxide when roasted on charcoal or in 0. T. When 



140 MANUAL OF MINERALOGY 

treated with strong nitric acid is oxidized to white lead sulphate. 
Determined chiefly by its high specific gravity, softness,] black 
streak and cubic cleavage. 

Alteration. By oxidation it is converted into the sulphate, 
anglesite, the carbonate, cerussite, or other compounds. 

Occurrence. A very common metallic sulphide, associated with 
sphalerite, pyrite, marcasite, chalcopyrite, cerussite, anglesite, dolo- 
mite, calcite, quartz, barite, fluorite, etc. Frequently found with 
silver minerals, often containing that metal itself and so becoming 
an important silver ore. A large part of the supply of lead comes 
as a secondary production from ores mined chiefly for their silver. 
Occurs most commonly in connection with limestones, either as 
veins or irregular deposits, or as replacement deposits. 

The following are the important lead producing localities in the 
United States: Southeastern Missouri, in which the ore occurs in 
the form of beds with the mineral disseminated through the lime- 
stone; southwestern Missouri, where it is associated with zinc ores, 
and is found in irregular veins and pockets in limestone and chert; 
Idaho, where the lead is derived chiefly from lead-silver deposits, 
the greater part of which come from near Wallace in Shoshone 
County; Utah, in connection with the silver deposits of the Tintic 
and Park City districts; Colorado, chiefly from the lead-silver ores 
of the Leadville District. 

The most famous foreign localities are, Freiberg, Saxony; the 
Harz Mountains; Pfibram, Bohemia; Cornwall, Derbyshire and 
Cumberland, England. 

Name. The name galena is derived from the Latin galena, a 
name originally given to lead ore. 

Use. Practically the only source of lead and an important 
ore of silver. Metallic lead is used chiefly as follows: for con- 
version into white lead (a basic lead carbonate), which is the 
principal ingredient of the best white paints, or into the oxides 
used in making glass and in giving a glaze to earthernware; as 
pipe and sheets; for shot; it is one of the ingredients of solder 
(an alloy of lead and tin), of type metal (an alloy of lead and 
antimony) and of low-fusion alloys consisting of lead, bismuth 
and tin. 

The following rare tellurides belong in this "group; hessite, 
Ag 2 Te; petzite (Ag,Au) 2 Te; dtaite, PbTe. 



PLATE V. 




A. Galena with Dolomite, Joplin, Missouri. 




B. Fluorite, Cumberland, England. 



CHALCOCITE 



141 



2. CHALCOCITE GROUP. ORTHORHOMBIC. 

Chalcocite. Copper Glance. 

Composition. Cuprous sulphide, Cu 2 S = Sulphur 20.2, cop- 
per 79.8. 

Crystallization. Orthorhombic. Usually in small tabular 
crystals with hexagonal outline. Striated parallel to the brachy- 





Fig. 220. 



Fig. 221. 



axis (Fig. 220). Often twinned in pseudohexagonal forms (Fig. 
221). 

Structure. Massive. Crystals very rare. 

Physical Properties. Conchoidal fracture. H. = 2.5-3. G. 
= 5.5-5.8. Metallic luster. Color shining lead-gray, tarnish- 
ing on exposure to dull black. Streak grayish black. 

Tests. Easily fusible at 2-2.5. In 0. T. or B. B. on charcoal 
gives odor of sulphur dioxide. Roasted mineral, moistened with 
hydrochloric acid, gives azure-blue flame. Soluble in nitric acid; 
and the solution with an excess of ammonia turns dark blue. 
Recognized by its massive structure, its high specific gravity, 
its color, softness and black streak. 

Occurrence. Found in crystals in Cornwall, England, and Bris- 
tol, Connecticut. Occurs as a mineral of secondary origin in the en- 
riched zone of copper veins associated with bornite, chalcopyrite, 
enargite, malachite, pyrite, etc. Found as an ore at Monte Catini, 
Tuscany; Mexico, Peru, Bolivia, Chile, etc. Occurs in immense 



142 



MANUAL OF MINERALOGY 



deposits at Butte, Montana. Found in Alaska at Kennecott, 
Copper River District. 

Use. An important copper ore. 

Stromeyerite. 

A sulphide of silver and copper (Ag,Cu) 2 S or Ag 2 S.Cu 2 S. Ortho- 
rhombic. Commonly massive. H. = 2.5-3. G.= 6.15-6.3. Me- 
tallic luster. Color and streak grayish black. Fusible at 1.5. In 
O. T. gives odor of sulphur dioxide. Roasted mineral with hydro- 
chloric acid gives azure-blue flame. Nitric acid solution with hydro- 
chloric acid gives precipitate of silver chloride. A rare silver mineral 
found with other silver ores. 

3. SPHALERITE GROUP. ISOMETRIC, TETRAHEDRAL. 
Sphalerite. Zinc Blende, Black Jack. 

Composition. Zinc sulphide, ZnS = Sulphur 33, zinc 67. Al- 
most always contains at least a small percentage of iron replac- 
ing the zinc, but the amount of iron may rise as high as 15 to 
18 per cent. Also frequently contains small amounts of manga- 
nese, cadmium, mercury, etc. 

Crystallization. Isometric; tetrahedral. Tetrahedron (Fig. 
222), dodecahedron and cube common forms, but the crystals 





Fig. 222. 



Fig. 223. 



frequently highly complex and usually distorted or in rounded 
forms. Often twinned. 

Structure. Usually massive cleavable, coarse to fine granular. 
Compact, botryoidal. Also in rounded crystal masses. 



SPHALERITE 143 

Physical Properties. Perfect dodecahedral cleavage. H. = 
3.5-4. G. = 4-4.1. Nonmetallic and resinous to submetallic 
luster; also adamantine. Color white when pure,' and green 
when nearly so. Commonly yellow, brown to black, darkening 
with increase in the amount of iron present. Transparent to 
translucent. Streak white to yellow and brown. 

Tests. Infusible with pure zinc sulphide to difficultly fusible 
with increase in amount of iron. Gives odor of sulphur dioxide 
when heated on charcoal or in 0. T. Decomposed in powder by 
warm hydrochloric acid with evolution of hydrogen sulphide gas, 
which may be detected by its disagreeable odor. When heated 
on charcoal gives a coating of zinc oxide (yellow when hot, white 
when cold) which is nonvolatile in oxidizing flame. Recognized 
usually by its striking resinous luster and perfect cleavage. The 
dark varieties (black jack) can be told by noting that a knife 
scratch leaves a reddish brown streak. 

Occurrence. Sphalerite, the most important ore of zinc, is an 
extremely common mineral, especially as a constituent of metallic 
veins. Found widely distributed, but chiefly in veins and irregular 
bodies in limestone rocks. Associated with galena, pyrite, marcasite, 
chalcopyrite, smithsonite, calcite, dolomite, siderite, etc. May carry 
silver or gold. Large deposits are found in the United States in 
Missouri, Kansas, Arkansas, Wisconsin, Iowa, Illinois, Colorado. 
The chief locality for its production is the Joplin District in south- 
western Missouri. Found in large quantities in connection with the 
lead-silver deposits of Leadville, Colorado. Noteworthy European 
localities are at Alston Moor and other places in the lead-mining dis- 
tricts of northern England; Binnenthal, Switzerland, in fine crystals; 
at Schemnitz and other localities in the gold and silver-mining dis- 
tricts of Hungary. 

Name. The name blende is from the German, blind or decep- 
tive, because while often resembling galena it yielded no lead. 
Sphalerite, for the same reason, is derived from a Greek word 
meaning treacherous. 

Use. The most important ore of zinc. The chief uses for 
metallic zinc, or spelter, are in galvanizing iron, making brass, 
an alloy of copper and zinc, in electric batteries, and as sheet 
zinc. Zinc oxide, or zinc white, is used extensively for making 



144 MANUAL OF MINERALOGY 

paint. Zinc chloride is used as a preservative for wood. Zinc 
sulphate is used in dyeing and in medicine. Sphalerite also 
serves as the most important source of cadmium. 

Alabandite. 

Manganese sulphide, MnS. Isometric; tetrahedral. Usually gran- 
ular massive. Cubic cleavage. H. = 3.5-4. G. = 3.95. Subme- 
tallic luster. Color iron-black, tarnished to brown on exposure. 
Streak olive-green. Fusible at 3. Gives odor of sulphur dioxide 
when roasted in O.T. Soluble in hydrochloric acid with evolution 
of hydrogen sulphide gas. With sodium carbonate in O. F. gives 
opaque greenish blue bead (manganese). A rare mineral, occurring 
usually with gold or silver ores. 

Pentlandite. 

A sulphide of iron and nickel (Ni,Fe)S. Isometric. Massive 
granular. Octahedral cleavage. H. = 3.5-4. G. = 4.55-5. Metal- 
lic luster. Yellowish bronze color. Black streak. Fusible at 1.5-2. 
Gives odor of sulphur dioxide in O. T. Magnetic on heating in 
R. F. Roasted mineral in O. F. colors borax bead reddish brown 
(nickel). Closely resembles pyrrhotite in appearance but to be 
distinguished by the octahedral cleavage. A rare mineral, found 
with chalcopyrite near Lillehammer, Norway, and with pyrrhotite 
and chalcopyrite in the nickel deposits at Sudbury, Canada. 

Other minerals which are rare in occurrence that belong in 
this group are, metacinnabarite, HgS; tiemannite, HgSe; onofrite, 
Hg(S,Se); coloradoite, HgTe. 



4. CINNABAR-MILLERITE GROUP. HEXAGONAL. 
Cinnabar. 

Composition. Mercuric sulphide, HgS = Sulphur 13.8, mer- 
cury 86.2. Usually impure from admixture of clay, iron oxide, 
etc. 

Crystallization. Hexagonal-rhombohedral; trapezohedral. 
Crystals usually rhombodedral, often in penetration twins. 
Trapezohedral faces rare. 

Structure. Usually fine granular massive; also earthy and 
as incrustations. Crystals rare. 



COVELLITE 145 

Physical Properties. H. = 2-2.5. G. = 8.10. Adamantine 
luster when pure, to dull and earthy when impure. Color ver- 
milion-red when pure, to brownish red when impure. Scarlet 
streak. Transparent to opaque. 

Tests. Wholly volatile when free from gangue. Gives black 
sublimate of mercury sulphide when heated alone in C. T. 
When carefully heated in C. T. with dry sodium carbonate gives 
globules of metallic mercury. Carefully roasted in 0. T. gives 
odor of sulphur dioxide and sublimate of metallic mercury. 
Recognized usually by color, streak and high specific gravity. 

Occurrence. The most important ore of mercury, but found in 
quantity at comparatively few localities. Occurs filling fissures, 
cavities, etc., usually in sedimentary rocks; frequently as impregna- 
tions in sandstone or limestone. Associated with pyrite, marcasite, 
sulphur, calcite, barite, gypsum, opal, quartz, etc. Always found 
in the neighborhood of igneous rock masses from which it is thought 
that the mercury was derived. Deposited probably through the 
agency of ascending hot waters. Deposits of mercuric sulphide are 
being' formed to-day by the hot springs at Steamboat Springs, Ne- 
vada, and at Ohaiawai, New Zealand. The important localities for 
the occurrence of cinnabar are at Almaden, Spain; Idria in Carniola; 
Huancavelica in southern Peru; Kwei Chaw, China; New Idria in 
San Benito County, Napa County, and New Almaden in Santa Clara 
County, California; Terlingua, Brewster County, Texas. Hepatic 
cinnabar is an inflammable variety with liver-brown color and some- 
times a brownish streak, usually granular or compact. 

Name. The name cinnabar is supposed to have come from 
India, where it is applied to a red resin. 
Use. The only important source of mercury. 

Covellite. 

Cupric sulphide, CuS. Hexagonal. Rarely in tabular hexagonal 
crystals with prominent basal plane. Usually massive. Perfect 
basal cleavage. H. = 1.5-2. G. = 4.59. Metallic luster. Color 
indigo-blue. Fusible at 2.5. Gives odor of sulphur dioxide in 
O. T. and much sulphur in C. T. The roasted mineral, moistened 
with hydrochloric acid and ignited, gives a blue flame (copper). 
When moistened with water shows a strong purple color. A rare 
mineral, found only in the enriched sulphide zone of copper deposits, 
associated with chalcocite, bornite, etc. 



146 MANUAL OF MINERALOGY 

Greenockite. 

Composition. Cadmium sulphide, CdS = Sulphur 22.3, cad- 
mium 77.7. 

Crystallization. Hexagonal; hemimorphic. Crystals hemi- 
morphic, showing prism faces and terminated usually below with 
base and above with pyramids. 

Structure. Usually pulverulent, as thin powdery incrusta- 
tions. Crystals small and rare. 

Physical Properties. H. = 3-3.5. G. = 4.9-5. Luster ada- 
mantine to resinous, earthy. Color yellow. 

Tests. Infusible. Yields odor of sulphur dioxide when 
heated B. B. or in 0. T. Decomposed by hydrochloric acid 
with the evolution of hydrogen sulphide gas, which may be de- 
tected by its disagreeable odor. Gives a reddish brown coating 
of cadmium oxide when heated with sodium carbonate on char- 
coal. Characterized by its yellow color and pulverulent form. 

Occurrence. Most common mineral containing cadmium but 
found only in a few localities and in small amount. Associated 
usually with zinc ores, often as a coating on sphalerite and smith- 
sonite. Found in crystals at Bishopton, Renfrewshire, Scotland; 
with the zinc ores of southwestern Missouri and in Arkansas, also 
in various localities in Bohemia and Greece. 

Use. A source of cadmium. Cadmium-bearing zinc ores fur- 
nish the greater part of the metal produced. Cadmium is used 
in alloys for dental and other purposes. The sulphide serves as 
a yellow pigment. 

Millerite. Capillary Pyrites. 

Composition. Nickel sulphide, NiS = Sulphur 35.3, nickel 
64.7. 

Crystallization. Hexagonal-rhombohedral. 

Structure. Usually in hairlike tufts and radiating groups of 
slender to capillary crystals. Sometimes in velvety incrusta- 
tions. 

Physical Properties. Cleavage rhombohedral. H. = 3-3.5. 
G. = 5.65. Metallic luster. Pale brass-yellow; with a green- 



PYRRHOTITE 147 

ish tinge when in fine hairlike masses. Streak black, somewhat 
greenish. 

Tests. 'Fusible at 1.5-2 to magnetic globules. Gives odor 
of sulphur dioxide when heated on charcoal or in 0. T. The 
roasted mineral colors the borax bead reddish brown in 0. F. 

Occurrence. Occurs in various localities in Saxony and Bohemia; 
in Cornwall; with hematite and siderite at Antwerp, N. Y.; with 
pyrrhotite at the Gap Mine, Lancaster County, Pennsylvania; in 
calcite at St. Louis, Missouri, Keokuk, Iowa, etc. 

Use. A subordinate ore of nickel. 

Niccolite. Copper Nickel. 

Composition. Nickel arsenide, NiAs = Arsenic 56.1, nickel 
43.9. Usually with a little iron, cobalt and sulphur. Arsenic 
frequently replaced in part by antimony. 

Crystallization. Hexagonal; hemimorphic (?). 

Structure. Usually massive. Crystals rare. 

Physical Properties. H. = 5-5.5. G. = 7.5. Metallic lus- 
ter. Color pale copper-red, (hence called copper-nickel) with 
gray to blackish tarnish. Brownish black streak. 

Tests. Fusible (2). When heated B. B. on charcoal a white 
volatile deposit of arsenious oxide forms and a garlic-like odor 
is given off. Gives to borax bead a reddish brown color (nickel). 
Characterized chiefly by its color. 

Occurrence. Associated usually with cobalt, silver and copper 
minerals. Not very common. Found in the silver mines of Saxony, 
in Sweden, at Cobalt, Canada, etc. 

Use. A minor ore of nickel. 

Pyrrhotite. Magnetic Pyrites. 

Composition. A sulphide of iron, varying in composition from 
Fe 6 S 6 up to FeieSn. FenSi 2 is the usually accepted formula. 
Often carries a small amount of nickel. 

Crystallization. Hexagonal. Crystals usually tabular, or 
sometimes pyramidal. 



148 MANUAL OF MINERALOGY 

Structure. Practically always massive with granular or lamel- 
lar structure. 

Physical Properties. H. = 4. G. = 4.65. Metallic luster. 
Brownish bronze color. Black streak. Usually slightly mag- 
netic, but sometimes scarcely at all so. 

Tests. Easily fusible. Strongly magnetic after heating. 
B. B. or in 0. T. gives odor of sulphur dioxide. Little or no 
sulphur in C. T. Decomposed by hydrochloric acid, giving off 
hydrogen sulphide gas. Recognized usually by its massive 
structure and bronze color. 

Occurrence. A common minor constituent of igneous rocks. 
Occurs in large masses in intimate association with basic igneous 
rocks and is thought by many to have been formed through mag- 
matic differentiation. This view is doubted by many and is still 
open to question. Associated with the ferromagnesian minerals of 
the rocks in which it occurs, and also with chalcopyrite, and nickel 
minerals, as pentlandite, millerite, etc. Found in large quantities 
in Norway and Sweden, at Sudbury, Ontario, Canada; at Stafford 
and Ely, Vermont; at Ducktown, Tennessee. Was found at the 
Gap Mine, Lancaster County, Pennsylvania. 

Name. Derived from a Greek word meaning reddish. 
Use. Serves as an important ore of nickel, particularly at 
Sudbury, Ontario. 

In this group belongs also the rare mineral, wurtzite, ZnS, which 
differs from sphalerite, since it is Hexagonal in crystallization. 

C. INTERMEDIATE DIVISION. 
Bornite. Purple Copper Ore, etc. 

Composition. Cu 5 FeS 4 = Sulphur 25.5, copper 63.3, iron 
11.2. Analyses of different specimens show quite a wide varia- 
tion in the percentages of the elements present, copper ranging 
from 55 to 71 per cent. Analyses of the purest material, how- 
ever, agree with the above formula. 

Crystallization. Isometric. Crystals rare. Usually in rough 
cubes, sometimes in penetration twins. Dodecahedron and octa- 
hedron at times. 

Structure. Commonly massive. 



LINNMITE 149 

Physical Properties. H. = 3. G. = 4.9-5.4. Metallic lus- 
ter. Color brownish bronze on fresh fracture but quickly tar- 
nishing on exposure to variegated purple and blue and finally to 
almost black. Streak grayish black. 

Tests. Easily fusible at 2.5. Gives odor of sulphur dioxide 
on charcoal or in 0. T. Yields only a very little sulphur in C. T. 
Becomes magnetic in R. F. If, after roasting, it is moistened 
with hydrochloric acid and heated, it gives an azure-blue flame 
(copper). Easily soluble in nitric acid with separation of sul- 
phur; solution neutralized with ammonia gives red-brown pre- 
cipitate of ferric hydroxide and blue color to filtrate. Charac- 
terized chiefly by its purple tarnish. 

Occurrence. An important and widely occurring ore of copper, 
but usually with other copper minerals and in subordinate amount. 
It has been found as a primary constituent in igneous rocks and in 
pegmatite veins. Bornite and chalcopyrite are the two common 
original copper minerals, from which other copper minerals have 
been derived through secondary action. It is also frequently, itself, 
a secondary mineral, formed in the upper, enriched zone of copper 
veins through the action of descending copper-bearing solutions, 
upon chalcopyrite. The minerals with which it is commonly asso- 
ciated are chalcopyrite, chalcocite, enargite, malachite, azurite, 
pyrite, etc. It frequently occurs in intimate mixture with chal- 
copyrite and chalcocite. Found in the United States at Butte, 
Montana; in the copper mines of Virginia and North Carolina. It 
was found in unusual crystals, associated with crystallized chalcocite 
at Bristol, Connecticut. Occurs at Acton,. Canada. Found in 
Cornwall; Monte Catini, Tuscany, and in various other European 
countries. An important ore in Chile, Peru, Bolivia and Mexico. 

Name. Bornite was named after the mineralogist von Born 
(1742-1791). Sometimes called horseflesh ore in reference to 
the color on the fresh fracture, or variegated copper ore or peacock 
ore because of its purple tarnish. Called for the latter reason 
erubescite by English mineralogists. 

Use. An important ore of copper. 

Linnagite. 

A sulphide of cobalt, Co 3 S 4 or CoS.Co 2 S 3 , with the cobalt replaced 
in varying amount by nickel. Isometric. In small octahedral 



150 MANUAL OF MINERALOGY 

crystals or granular massive. H. = 5.5. G. = 4.9. Metallic lus- 
ter. Color pale steel-gray. Grayish black streak. Fusible at 2. 
Gives odor of sulphur dioxide in O. T. Fuses in R. F. to a magnetic 
globule. Roasted mineral colors the borax bead blue (cobalt). A 
rare mineral, found with chalcopyrite near Riddarhyttan, Sweden; 
with barite and siderite at Miisen, Prussia; with lead ores at Mine La 
Motte, Missouri. 



Chalcopyrite. Copper Pyrites. Yellow Copper Ore. 

Composition. A sulphide of copper and iron, CuFeS 2 = Sul- 
phur 35, copper 34.5, iron 30.5. 

Crystallization. Tetragonal; sphenoidal. Crystals usually in 
unit sphenoids (Fig. 224), which because the vertical axis is close 
to unity (c = 0.985) are very near to the isometric tetrahedron 





Fig. 224. Fig. 225. 

in angles. Steeper sphenoids (Fig. 225), and other more complex 
forms occasionally observed. 

Structure. Usually massive, compact; at times in crystals. 

Physical Properties. H. = 3.5. G. = 4.2-4.3. Metallic lus- 
ter. Color brass-yellow; often tarnished to bronze or iridescent. 
Streak greenish black. 

Tests. Easily fusible to a magnetic globule. Gives odor of 
sulphur dioxide when heated B. B. or in O. T. Gives sulphur in 
C. T. After roasting, and moistening with hydrochloric acid, 
gives an azure-blue flame. Readily decomposed by nitric acid, 
giving separated sulphur; solution made ammoniacal gives red- 
brown precipitate of ferric hydroxide and blue filtrate (copper). 
Recognized by its brass-yellow color, greenish black streak and 
its softness. Distinguished from pyrite by its being softer than 



PYRITE 151 

steel and from gold by its being brittle. Known sometimes as 
"fool's gold/' a term which is also applied at times to pyrite. 

Occurrence. The most common ore of copper. Occurs widely 
distributed in metallic veins associated with pyrite, pyrrhotite, 
bornite, chalcocite, tetrahedrite, malachite, azurite, sphalerite, 
galena, quartz, calcite, dolomite, siderite, etc. May carry gold or 
silver and become an ore of those metals. Often in subordinate 
amount with large bodies of pyrite, making them serve as low-grade 
copper ores. Chief ore of copper mines at Cornwall, England; 
Falun, Sweden; Rio Tinto, Spain; Sudbury, Canada; in South 
Africa, Chile, etc. Found widely in the United States but usually 
in connection with other copper minerals in equal or greater amount; 
found at Butte, Montana; Bingham, Utah; various districts in 
California, Colorado, Arizona, etc. 

Name. Derived from Greek word meaning brass and from 
pyrites. 

Use. Most important ore of copper. 

Stannite. 

A sulphide of copper, tin and iron, Cu 2 S.FeS.SnS 2 . Zinc at 
times also present. Tetragonal, sphenoidal, but pseudo-isometric 
through twinning. Practically always massive. H. = 4. G. = 4.4. 
Metallic luster. Color steel-gray. Streak black. Fusible at 1.5. 
Slightly magnetic after heating in R. F. After roasting, and moist- 
ening with hydrochloric acid, gives when ignited a blue flame (cop- 
per). Fused alone on charcoal gives a nonvolatile white coating 
of tin oxide. A rare mineral, found in various places in Cornwall 
and with the tin ores of Bolivia. 



D. BISULPHIDE DIVISION. 
1. PYRITE GROUP. ISOMETRIC; PYRITOHEDRAL. 

Pyrite. Iron Pyrites. 

Composition. Iron disulphide, FeS 2 = Sulphur 53.4, iron 46.6. 
Sometimes contains small amounts of nickel, cobalt and copper. 
Frequently carries minute quantities of gold (auriferous pyrite) . 

Crystallization. Isometric; pyritohedral. Most common 
crystal forms are the cube, the faces of which are usually striated, 
the striae on adjacent faces being perpendicular to each other 



152 



MANUAL OF MINERALOGY 



(Fig. 226) ; the octahedron, and the pentagonal dodecahedron, 
known commonly as the pyritohedron (Fig. 227). Figs. 228 to 





Fig. 226. Striated Cubes. 



Fig. 227. Pfyritohedron 




Fig. 228. 

Cube 
and Pyritohedron. 



Fig. 229. 
Octahedron 
and Pyritohedron. 




Fig. 230. 

Octahedron 

and Pyritohedron. 



230 show characteristic combinations of these forms. Fig. 231 
shows a penetration twin that is at 
times observed. 

Structure. Often in crystals. Also 
massive, granular, reniform, globular 
and stalactitic. 

Physical Properties. Brittle. 
H. = 6-6.5 (unusually hard for a sul- 
phide). G. = 4.95-5.10. Luster me- 
tallic, splendent. Color pale brass- 
yellow, becoming darker at times on 
Streak greenish or brownish black. 




Fig. 231. Twinned 
Pyritohedrons. 

account of tarnish. 



PYRITE 153 

Tests. Easily fusible (2.5-3) to a magnetic globule. Yields 
much sulphur in C. T. Gives off sulphur dioxide in 0. T. or 
B. B. on charcoal. Insoluble in hydrochloric acid. Fine pow- 
der completely soluble in nitric acid, but may yield separated 
sulphur when too rapidly decomposed. Distinguished from 
chalcopyrite by its paler color and the fact that it cannot be 
scratched by steel; from gold by its being brittle. 

Occurrence. Pyrite is the most common of the sulphides. It is 
a common vein mineral, occurring in rocks of all ages and associated 
with many different minerals. Found frequently with chalcopyrite, 
sphalerite, galena, etc. Is widely distributed as an accessory rock 
mineral in both igneous and sedimentary rocks. Important de- 
posits of pyrite in the United States are in Prince William, Louisa 
and Pulaski counties, Virginia, where it occurs in large lenticular 
masses which conform in position to the foliation of the inclosing 
schists; in St. Lawrence County, New York; at the Davis Mine, 
near Charlemont, Massachusetts; in various places in California. 
Largo deposits occur at Rio Tinto and other mines in Spain, also in 
Portugal. 

Alteration. Pyrite is easily altered to oxides of iron, usually 
limonite. It is, however, in general much more stable than 
marcasite. Pseudomorphic crystals of limonite after pyrite are 
common. Pyrite veins are usually capped by a cellular deposit 
of limonite, termed gossan. Rocks that contain pyrite are un- 
suitable for structural purposes because the ready oxidation of 
the pyrite in them would serve both to disintegrate the rock 
and to stain it with iron oxide. 

Name. The name pyrite is from a Greek word meaning fire, 
in allusion to the fact that when struck with steel it gives off 
brilliant sparks. 

Use. Pyrite is often mined for the gold or copper associated 
with it. Because of the large amount of sulphur present in the 
mineral it is never used as an iron ore. It is chiefly used to fur- 
nish sulphuric acid and copperas (ferrous sulphate). Sulphuric 
acid is perhaps the most important of all chemicals, being used 
for many different purposes, some of the more important being 
in the purification of kerosene and in the preparation of mineral 
fertilizers. The gas S0 2 derived either through burning sulphur 



154 MANUAL OF MINERALOGY 

or by roasting pyrite is used extensively in the preparation of 
wood pulp for manufacture into paper. Copperas is used in 
dyeing, in the manufacture of inks, as a preservative of wood, 
and for a disinfectant. 

Smaltite-Chloanthite. 

Smaltite is cobalt arsenide, CoAs2; chloanthite, nickel arsenide, 
NiAs 2 . The two molecules are isomorphous and all gradations 
between the two species occur. Isometric; pyritohedral. Usually 
massive, granular. Octahedral cleavage. H. = 5.5-6. G. = 6.3- 
6.8. Metallic luster. Color tin-white. Streak black. Fusible at 
2-2.5. Roasted on charcoal give a volatile coating of arsenious 
oxide with characteristic garlic odor. In borax bead in O. F. give 
blue color (cobalt). Rare species, occurring with other cobalt and 
nickel minerals, often associated with silver and copper ores. 

Cobaltite-Gersdorffite. 

Cobaltite is a sulpharsenide of cobalt, CoAsS; gersdorffite a 
sulpharsenide of nickel, NiAsS. The two molecules are isomor- 
phous with each other, and may occur together in varying amounts. 
Usually, however, any specimen will be found to be near one or the 
other ends of the series. Iron is frequently present, replacing the 
cobalt or the nickel, and sometimes in considerable amount. Iso- 
metric; pyritohedral. Cobaltite commonly in cubes, pyritohedrons 
and octahedrons, also massive. Gersdorffite usually massive. Cubic 
cleavage. H. = 5.5-6. G. = 5.8-6.2. Metallic luster. Color, tin- 
white, in cobaltite inclining to reddish tone. Streak black. Fusible 
2-3. On charcoal give a volatile white sublimate of arsenious oxide 
with characteristic garlic odor. In O. T. give volatile crystalline 
sublimate of arsenious oxide with odor of sulphur dioxide. In O. F. 
in borax bead give deep blue color (cobalt) ; if gersdorffite contains 
no cobalt, gives brown bead (nickel). Rare minerals, cobaltite 
being the commoner. Found associated with other cobalt and 
nickel minerals and with silver and copper ores. Notable occur- 
rences of cobaltite are at Tunaberg, Sweden, and Cobalt, Ontario, 
Canada. 

Sperrylite. 

A platinum arsenide, PtAs 2 . Isometric; pyritohedral. Usually 
in small grains, or in almost microscopic crystal fragments. H. = 
6-7. G. = 10.6. Metallic luster. Tin-white color. Black streak. 
Fusible at 2. Roasted on charcoal gives volatile white coating of 



MARCASITE 155 

arsenious oxide with characteristic garlic odor. Roasted in O. T., 
at first very gently, a platinum sponge is left, which is insoluble in 
any single acid. A very rare mineral and the only known compound 
of platinum occurring in nature. Found with chalcopyrite in a 
gold-quartz vein near Sudbury, Canada, and with covellite at the 
Rambler Mine, Encampment, Wyoming. 

2. MARCASITE GROUP. ORTHORHOMBIC. 
Marcasite. White Iron Pyrites. 

Composition. Iron disulphide, like pyrite, FeS 2 = Sulphur 
53.4, iron 46.6. 

Crystallization. Orthorhombic. Crystals commonly tabular 
parallel to basal plane, showing also short prisms and low brachy- 
domes (Fig. 232). The brachydomes usually striated parallel 





Fig. 232. Fig. 233. 

to the brachy-axis. Often twinned, giving coxcomb and spear- 
shaped groups (Fig. 233). Closely related in crystal forms and 
habit to arsenopyrite. 

Structure. Usually in radiating forms. Often stalactitic, 
having an inner core with radiating structure and covered on the 
outside with irregular crystal groups. Also globular, reniform, 
etc. More rarely in crystals. 

Physical Properties. H. = 6-6.5. G. = 4.85-4.9. Metallic 
luster. Color pale yellow to almost white, yellow to brown tar- 
nish. Streak grayish black. 

Tests. Fusible (2.5-3) to a magnetic globule. B. B. on char- 
coal or in 0. T. gives odor of sulphur dioxide. Much sulphur in 



156 'MANUAL OF MINERALOGY 

C. T. When fine powder is treated by cold nitric acid, and the 
solution allowed to stand until vigorous action ceases and then 
boiled, the mineral is decomposed with separation of sulphur. 
Pyrite treated in the same manner would have been completely 
dissolved. Recognized usually by its pale yellow color, its crys- 
tals or its fibrous structure. 

Occurrence. Marcasite is found in metalliferous veins, frequently 
with lead and zinc ores. Also at times in sedimentary rocks. It 
is more unstable than pyrite, being easily decomposed, and is not 
nearly as common in its occurrence. Found abundantly in clay 
near Carlsbad and elsewhere in Bohemia; in various places in 
Saxony; in the chalk marl of Folkestone and Dover, England; with 
zinc and lead deposits of Joplin, Missouri, and of Mineral Point, 
Wisconsin. 

Name. Derived from an Arabic word, at one time applied 
generally to pyrite. 
Use. To a slight extent as a source of sulphuric acid, etc. 

Arsenopyrite. Mispickel. 

Composition. Sulpharsenide of iron, FeAsS = Arsenic 46, 
sulphur 19.7, iron 34.3. Sometimes cobalt replaces a part of the 
iron (danaite). 

Crystallization. Orthorhombic. Usually in tabular diamond- 
shaped crystals, formed by a short prism terminated by low 
brachydomes. The brachydomes are usually striated parallel 





Fig. 234. Fig. 235. 

to the brachy-axis (Fig. 234). Twinned at times, giving stellate 
groups; the different individuals of the twin groups being dis- 



SYLVANITE 157 

tinguished from each other by the direction of the striations 
upon them (Fig. 235). Agrees closely in angles and crystal habit 
with marcasite. 

Structure. In crystals. Massive, granular to compact. 

Physical Properties. H. = 5.5-6. G. = 6-6.2. Metallic lus- 
ter. Silver-white color. Black streak. 

Tests. Fusible at 2 to a magnetic globule. B. B. on charcoal 
gives a volatile coating of arsenious oxide and a characteristic 
garlic odor. In 0. T. gives odor of sulphur dioxide and a volatile 
ring of arsenious oxide. In C. T. gives arsenic mirror. Recog- 
nized usually by its silver-white color, its crystals and a test for 
arsenic. 

Occurrence. Arsenopyrite is the most common mineral contain- 
ing arsenic. Found in veins in crystalline rocks, associated with 
ores of tin, silver, lead and with pyrite, chalcopyrite, sphalerite, etc. 
Sometimes it is auriferous and serves as a gold ore. Occurs in quan- 
tity at Freiberg and Munzig, Saxony; in the Harz Mountains; with 
tin ores in Cornwall, England; in various places in Bolivia; New 
South Wales; Deloro, Canada, where it is mined as a gold ore; Rox- 
bury, Connecticut, etc. 

Use. An ore of arsenic. Arsenious oxide is used in the manu- 
facture of glass, as a poison and a preservative. Paris green, an 
arsenate and acetate of copper, is used as a poison and a pigment. 
Sulphides of arsenic are used for paints and fireworks. 

3. SYLVANITE GROUP. 

Sylvanite. 

Composition. Telluride of gold and silver (Au,Ag)Te 2 . The 
ratio of the amounts of gold and silver varies somewhat; when 
Au : Ag = 1 : 1 = Tellurium 62.1, gold 24.5, silver 13.4. 

Crystallization. Monoclinic. Distinct crystals rare. 

Structure. Usually bladed or granular. Often in skeleton 
forms deposited on rock surfaces and resembling writing in 
appearance. 

Physical Properties. Perfect cleavage parallel to clinopina- 
coid. H. =1.5-2. G. =8-8.2. Brilliant metallic luster. Color 
silver-white. Streak gray. 



158 MANUAL OF MINERALOGY 

Tests. Easily fusible (1). If a little of the powdered mineral 
is heated in concentrated sulphuric acid the solution assumes a 
deep red color (tellurium). When decomposed in nitric acid 
leaves a rusty-colored, spongy mass of gold, and the solution 
with hydrochloric acid gives white precipitate of silver chloride. 
With sodium carbonate on charcoal gives a globule of gold and 
silver. Determined, by above tests, by its silver color and good 
cleavage. 

Occurrence. A rare mineral, found with gold ores at Offenbdnya 
and Nagydg in Transylvania; Kalgoorlie, West Australia; Cripple 
Creek, Colorado. 

Name. Derived from Transylvania, where it was first found. 
Use. An ore of gold. 

Calaverite. 

Composition. Gold telluride, AuTe 2 = Tellurium 55.97, gold 
44.03. Silver usually present isomorphous with the gold, to a 
small extent. 

Crystallization. Monoclinic. Crystals usually developed 
parallel to the ortho-axis and the faces of the orthodome zone 
deeply striated. Terminated at the ends of the ortho-axis with 
a large number of faces. Crystallization complicated. Twin- 
ning frequent. 

Structure. Usually granular. Distinct crystals rare. 

Physical Properties. H. = 2.5. G. = 9.35. Metallic luster. 
Silver-white color, sometimes with yellowish tarnish. Streak 
gray. 

Tests. Easily fusible (1). If a little of the powdered mineral 
is heated in concentrated sulphuric acid the solution assumes a 
deep red color (tellurium). When decomposed by nitric acid 
leaves a rusty-colored, spongy mass of gold, and on addition of 
hydrochloric acid gives only a slight precipitate of silver chloride. 
Distinguished from sylvanite by small amount of silver present 
and by its lack of a cleavage. 

Occurrence. Found with sylvanite and other tellurides in the 
Cripple Creek District, Colorado, and at Kalgoorlie, West Australia. 



JAMESONITE 159 

Name. Found originally at the Stanislaus Mine, Calaveras 
County, California, whence name. 
Use. An ore of gold. 

Other rare tellurides belonging to this group are, krennerite, 
AuTe 2 , and nagyagite, a sulpho-telluride of lead and gold. 



SULPHARSENITES, ETC. 

The minerals in this division are considered to be salts of the 
sulpho-acids of trivalent arsenic, antimony and bismuth. Vari- 
ous types of these acids are found, such as H 3 AsS 3 , H 2 AsS 2 , 
13^8285, etc. A subdivision includes the sulpharsenates, etc., 
being chiefly salts of the acid H 3 AsS 4 . The metals observed are 
most commonly copper, silver and lead; also at times iron, zinc 
and mercury. 

Jamesonite. Feather Ore. 

Composition. Sulphantimonite of lead, Pb 3 Sb 2 S 6 or 
3PbS.Sb 2 S 3 = Sulphur 19.7, antimony 29.5, lead 50.8. 

Crystallization. Orthorhombic. 

Structure. Usually in acicular crystals or in capillary forms. 
Also fibrous to compact massive. 

Physical Properties. Basal cleavage. Brittle. H. = 2-3. 
G. = 5.5-6. Metallic luster. Color and streak steel-gray to 
grayish black. 

Tests. Fusible at 1. On charcoal gives a combination coat- 
ing of lead and antimony oxides. Roasted in 0. T. gives sub- 
limates of antimony oxides. Heated on charcoal with a mixture 
of potassium iodide and sulphur gives a chrome-yellow coating 
of lead iodide. Recognized by above tests and characteristic 
fibrous structure. Difficult to distinguish from similar species 
(see below). 

Occurrence. Found in Cornwall, England, and from various 
localities in Hungary, Saxony, etc.; from Bolivia. Noted in the 
United States from Sevier County, Arkansas, and the Montezuma 
Mine, Nevada. 



160 MANUAL OF MINERALOGY 

Similar Species. There are a number of minerals similar 
to jamesonite in composition and general physical charac- 
teristics whose relations to each other in many cases are not 
thoroughly understood. These include such minerals as zinken- 
ite, PbS.Sb 2 S 3 ; plagionite, 5PbS.4Sb 2 S 3 ; warrenite, 3PbS.2Sb 2 S 3 ; 
boulangerite, 3PbS.Sb 2 S 3 ; meneghinite, 4PbS.Sb 2 S 3 ; geocronite, 
5PbS.Sb 2 S 3 . 

Bournonite. 

Composition. Sulphantimonite of lead and copper 
(Pb,Cu 2 ) 3 Sb 2 S 6 or 3(Pb,Cu 2 )S.Sb 2 S 3 . The relative amounts of 
the lead and copper present vary, but in general correspond 
closely to the ratio, Pb : Cu 2 =2:1. 

Crystallization. Orthorhombic. Crystals usually short pris- 
matic to tabular. Sometimes quite complex with many prism, 
pyramid and dome faces. Frequently 
twinned, giving tabular crystals with 
recurring reentrant angles in the prism 
zone (Fig. 236), whence the common 
name of cogwheel ore. 

Structure. Massive; granular to 
compact; in crystals. 

Physical Properties. H. = 2.5-3. 
Fig. 236. G. = 5.7-5.9. Metallic luster. Color 

and streak steel-gray to black. 

Tests. Fusible at 1. B. B. on charcoal gives a combination 
coating of antimony and lead oxides. Roasted in 0. T. gives 
sublimates of antimony oxides. Heated on charcoal with a 
mixture of potassium iodide and sulphur gives a chrome-yellow 
coating of lead iodide. Decomposed with nitric acid, solution 
turns blue with excess of ammonia (copper). Recognized either 
by characteristic crystals or above tests. 

Occurrence. A rare mineral. Found at Neudorf and other locali- 
ties in the Harz Mountains; Kapnik in Hungary; Liskeard in Corn- 
wall, etc. Has been found, also, in various places in the United 
States, but not in notable amount or quality. 




PROUSTITE 161 

Pyrargyrite. Dark Ruby Silver. 

Composition. Sulphantimonite of silver, Ag 3 SbS 3 or 
SAgaS.SbaSs = Sulphur 17.8, antimony 22.3, silver 59.8. 
Sometimes contains a small amount of arsenic. Compare 
proustite. 

Crystallization. Hexagonal-rhombohedral ; hemimorphic. 
Crystals prismatic with rhombohedral and scalenohedral termi- 
nations. Usually distorted and often with complex develop- 
ment. Frequently twinned. 

Structure. In crystals or massive; compact; in disseminated 
grains. 

Physical Properties. Rhombohedral cleavage. H. = 2.5. G. 
= 5.85. Luster adamantine. Color usually dark red to black, 
in thin splinters deep ruby-red. Indian-red streak. 

Tests. Fusible at 1. On charcoal gives dense white coating 
of antimony trioxide. After prolonged heating, coating becomes 
tinged with a reddish color near assay due to a small amount of 
volatilized silver. Odor of sulphur dioxide and coatings of anti- 
mony oxides when heated in 0. T. Decomposed by nitric acid 
and solution with hydrochloric acid gives white precipitate 
of silver chloride. Characterized chiefly by its dark red color 
and streak. 

Occurrence. A rare silver mineral associated with proustite, 
argentite, galena, calcite, etc. Found in the silver mines at Andreas- 
berg, Harz Mountains; at Freiberg, Saxony; Pfibram, Bohemia; 
in Hungary; Transylvania; Norway; in Guanajuato, Mexico; at 
Chanarcillo, Chile. Found in various silver veins in the San Juan 
Mountains and elsewhere in Colorado; in the silver districts of 
Nevada, New Mexico, etc. 

Name. Derived from two Greek words meaning fire-silver. 
Use. An ore of silver. 

Proustite. Light Ruby Silver. 

Composition. Sulpharsenite of silver, Ag 3 AsS 3 or 3Ag 2 S.As 2 S 3 
= Sulphur 19.4, arsenic 15.2, silver 65.4. May contain a small 
amount of antimony. Compare pyrargyrite. 



162 MANUAL OF MINERALOGY 

Crystallization. Hexagonal-rhombohedral; hemimorphic. 
Crystals commonly with prominent steep rhombohedrons and 
scalenohedrons. Often distorted and frequently complex in 
development. 

Structure. Commonly massive, compact, in disseminated 
grains. 

Physical Properties. Rhombohedral cleavage. H. = 2-2.5. 
G. = 5.55. Adamantine luster. Color ruby-red. Transparent 
to translucent. Red streak. High index of refraction. 

Tests. Fusible at 1. Heated on charcoal gives volatile sub- 
limate of arsenious oxide with characteristic garlic odor. In O.T. 
gives odor of sulphur dioxide and volatile crystalline sublimate 
of arsenious oxide. In C. T. gives abundant sublimate of arsenic 
sulphide, reddish black when hot, reddish yellow when cold. 
With sodium carbonate on charcoal gives a globule of silver. 
Characterized chiefly by its ruby-red color and streak and its 
brilliant luster. 

Occurrence. A rare mineral, occurring in silver veins associated 
with various other sulpharsenites and sulphantimonites. Found in 
the silver mines of Saxony; Bohemia; at Chaftarcillo, Chile, in fine 
crystals; common in the silver mines of Peru and Mexico. Found 
in Colorado in the silver mines of the San Juan Mountains and else- 
where; in various silver districts in Nevada, etc. 

Use. An ore of silver. 



Tetrahedrite-Tennantite. Gray Copper. Fahlore. 

Composition. Tetrahedrite, Cu 8 Sb 2 S 7 or 4Cu 2 S.Sb 2 S 3 = Sul- 
phur 23.1, antimony 24.8, copper 52.1. Tennantite, Cu 8 As 2 S 7 or 
4Cu 2 S.As 2 S 3 = Sulphur 25.5, arsenic 17.0, copper 57.5. Anti- 
mony and arsenic are usually both present and the two species 
graduate into each other, so that no sharp line can be drawn 
between them. The copper is often replaced in varying amounts 
by iron, zinc, silver, mercury, lead, etc. 

Crystallization. Isometric; tetrahedral. Habit tetrahedral. 
Tetrahedron (Fig. 237), tristetrahedron, dodecahedron and cube 
the common forms. 




STEPHANITE 163 

Structure. Frequently in crystals. Also massive, coarse or 
fine granular. 

Physical Properties. H. = 3-4. G. = 4.7-5. Metallic lus- 
ter, often splendent. Color grayish black to black. Streak 
black. 

Tests. Easily fusible at 1.5. On charcoal or in O. T. gives 
tests for antimony or arsenic, or both. After roasting, and 
moistening with hydrochloric acid, gives 
azure-blue flame. Decomposed by nitric 
acid with separation of sulphur and anti- 
mony trioxide; solution made alkaline 
with ammonia turns blue. The two 
species are only to be told apart by test- 
ing for the presence of antimony and 
arsenic, and as both are often present in Fig 237 

the same specimen a quantatitive analysis 

may be necessary in order to positively determine to which end 
of the series it belongs. Recognized by its tetrahedral crystals, 
or when massive by its fine-grained structure and by its gray 
color. 

Occurrence. Found in metallic veins usually associated with 
chalcopyrite, pyrite, sphalerite, galena and various other silver, lead 
and copper ores. May carry sufficient silver to become an important 
ore of that metal (the highly argentiferous variety is known as 
freibergite) . Is found in the United States in various silver and 
copper mines in Colorado, Nevada, Arizona, etc. Found in Corn- 
wall, England; the Harz Mountains, Germany; Freiberg, Saxony; 
Pfibram in Bohemia; various places in Hungary; in the silver mines 
of Mexico, Chile, Peru and Bolivia. 

Use. An ore of silver and copper. 

Stephanite. 

Composition. Sulphantimonite of silver, Ag 6 SbS 4 or 
5Ag 2 S.Sb 2 S 3 = Sulphur 16.3, antimony 15.2, silver 68.5. 

Crystallization. Orthorhombic. Crystals usually short pris- 
matic and tabular parallel to the base. Edges of crystals trun- 
cated by various pyramids. Prism zone usually shows the four 
prism faces and the two of the brachypinacoid, all making 



164 MANUAL OF MINERALOGY 

nearly 60 angles with each other and so giving the crystals a 
hexagonal aspect. Also twinned in pseudohexagonal crystals. 
Crystals usually small. 

Structure. Massive, in disseminated grains; crystallized. 

Physical Properties. H. = 2-2.5. G. = 6.2-6.3. Metallic 
luster. Color and streak iron-black. 

Tests. Fusible at 1. B. B. on charcoal gives dense white 
sublimate of antimony trioxide and odor of sulphur dioxide. 
Decomposed by nitric acid, and if after filtering a little hydro- 
chloric acid is added to filtrate, it gives a white precipitate of 
silver chloride. Recognized by its stout hexagonal crystals 
and the above tests. 

Occurrence. A rare silver mineral. Found associated with other 
sulphantimonites of silver, etc. Occurs at Freiberg and other locali- 
ties in Saxony; in Bohemia and Hungary; at Guanajuato and Arizpe, 
Sonora, etc., Mexico; in Peru and Chile. In the United States was 
an abundant ore at the Comstock Lode and other silver deposits in 
Nevada. 

Use. An ore of silver. 

Polybasite. 

Composition. Sulphantimonite of silver, Ag 9 SbS 6 or 
9Ag 2 S.Sb 2 S 3 = Sulphur 15, antimony 9.4, silver 75.6. Copper re- 
places a part of the silver and arsenic replaces the antimony. 

Crystallization. Monoclinic. Crystals are pseudorhombohe- 
dral in symmetry, occurring in short hexagonal prisms, often thin 
tabular. Basal planes show triangular markings. 

Structure. In crystals. Granular. 

Physical Properties. H. = 2-3. G. = 6-6.2. Metallic lus- 
ter. Color steel-gray to iron-black. Streak black. 

Tests. Fusible at 1. B. B. on charcoal gives dense white 
coating of antimony trioxide with odor of sulphur dioxide. After 
decomposition by nitric acid, the filtrate with hydrochloric acid 
gives white precipitate of silver chloride. To be distinguished 
from other similar species chiefly by its crystals. 

Occurrence. A comparatively rare silver mineral, associated with 
other sulphantimonides of silver and with silver ores in general. 



CHLORIDES 165 

Found in the silver mines of Mexico, Chile, Saxony and Bohemia. 
Found in the United States at the Comstock Lode, Nevada; near 
Ouray, Colorado, etc. 

Name. Name is in allusion to the many bases contained in the 
mineral. 
Use. An ore of silver. 

Enargite. 

Composition. Sulpharsenate of copper, Cu 3 AsS 4 or 
3Cu 2 S.As 2 S 5 = Sulphur 32.6, arsenic 19.1, copper 48.3. Anti- 
mony may replace in part the arsenic, and the species graduate 
toward famatinite (3Cu 2 S.Sb 2 S 5 ). 

Crystallization. Orthorhombic. Prismatic crystals with 
prism zone vertically striated. 

Structure. Columnar, bladed, massive. 

Physical Properties. Perfect prismatic cleavage. H. = 3. 
G. = 4.43-4.45. Metallic luster. Color and streak grayish 
black to iron-black. 

Tests. Easily fusible (1). B. B. on charcoal gives volatile 
white sublimate of arsenious oxide and characteristic garlic odor. 
In 0. T. gives white crystalline sublimate of arsenious oxide and 
odor of sulphur dioxide. Roasted on charcoal, then moistened 
with hydrochloric acid and again ignited, gives azure-blue flame. 
Characterized by its color, its cleavage and the above tests. 

Occurrence. A comparatively rare mineral, found associated with 
other copper minerals, as chalcocite, bornite, tennantite, etc. Found 
abundantly at Morococha, Peru; also in the United States of Col- 
ombia; Argentine Republic; island of Luzon, Philippines. Found 
in considerable quantity with the copper ores at Butte, Montana. 
Occurs in the silver mines of the San Juan Mountains, Colorado. 

Use. An ore of copper. Arsenic oxide also obtained from it 
at Butte, Mont. 

CHLORIDES, ETC. 

The chlorides with the related bromides, iodides and fluorides 
are grouped into the following divisions: (1) Anhydrous Chlor- 
ides, etc.; (2) Oxychlorides, etc.; (3) Hydrous Chlorides, etc. 



166 MANUAL OF MINERALOGY 

1. ANHYDROUS CHLORIDES, ETC. 
HALITE GROUP. 

The Halite Group includes the isometric minerals halite, NaCl; 
sylvite, KC1; cerargyrite, AgCl; embolite, Ag(Cl,Br); bromyrite, 
AgBr. 

Halite. Common Salt. 

Composition. Sodium chloride, NaCl = Chlorine 60.6, so- 
dium 39.4. Commonly contains impurities, such as calcium 
sulphate and calcium and magnesium chlorides. 

Crystallization. Isometric. Habit cubic 
(Fig. 238). Other forms very rare. 

Structure. In crystals or granular crystal- 
line, in masses showing cubical cleavage, 
known as rock salt. Also massive, granular 
to compact. 

Physical Properties. Perfect cubic cleav- 
age. H. = 2.5. G. = 2.1-2.6. Transparent 
to translucent. Colorless or white, or when impure may have 
shades of yellow, red, blue, purple. Readily soluble in water. 
Salty taste. Diathermous. 

Tests. Easily fusible at 1.5, giving strong yellow flame of 
sodium. After intense ignition B. B. residue gives alkaline re- 
action to moistened test paper. Readily soluble in water; 
solution made acid with nitric acid gives with silver nitrate a 
heavy white precipitate of silver chloride. Salty taste. Dis- 
tinguished from sylvite (KC1) by its yellow flame color and by 
the latter having a somewhat more bitter taste. 

Occurrence. A common and widely disseminated mineral, oc- 
curring often in extensive beds and irregular masses, intersfcratified 
in rocks of all ages, in such a manner as to form a true rock mass. 
Associated with gypsum, sylvite, anhydrite, calcite, clay, sand, etc. 
Occurs also dissolved in the waters of salt springs, salt seas and the 
ocean. 

The deposits of salt have been formed by the gradual evaporation 
and ultimate drying up of inclosed bodies of salt water. The salt 



HALITE 167 

beds formed in this way have subsequently been covered by other 
sedimentary deposits and gradually buried beneath the rock strata 
formed from them. The salt beds range from a few feet up to one 
hundred in thickness and have been found at depths of two thousand 
feet and more from the surface. The history of the formation of 
these salt beds is as follows: River waters contain a small but 
appreciable amount of various soluble salts. When these waters 
are collected in a sea which has no outlet, or in other words, a sea 
where the evaporation equals or exceeds the amount of water flowing 
in, there is a gradual concentration in the sea of the salts brought 
into it by the rivers. The sea water, therefore, in time becomes 
heavily charged with soluble salts, particularly sodium chloride. 
When the points of concentration of the various salts held in solu- 
tion are reached, they will be deposited progressively upon the sea 
bottom, commencing with the most insoluble. This process may 
continue for a long period of time and ultimately a thick layer of 
salt and other soluble minerals be formed on the bottom. The 
process may be interrupted by seasons of flood in which the sea 
water becomes freshened beyond the concentration point. Silt 
materials may be brought in at such times and deposited upon the 
bottom and so form beds of clay alternating with -those of salt. 
Such deposits of salt have been formed whenever favorable condi- 
tions occurred, and are now to be found buried in rock strata of all 
ages. At the present time similar deposits are being formed in the 
Great Salt Lake and the Dead Sea. 

In the United States salt is produced, on a commercial scale, in 
some fifteen states, either from rock-salt deposits, or by evaporation 
of salt lake or sea waters. Beds of rock salt are found in New York 
State from the Oatka Valley in Wyoming County east to Morrisville, 
Madison County, and south of this line wherever wells have been 
driven deep enough to reach the beds. The important producing 
localities are near Syracuse, Ithaca, Watkins and Ludlowville, and 
at various places in Wyoming, Genesee and Livingston counties. 
Extensive deposits of salt occur in Michigan, chiefly in Saginaw, 
Bay, Midland, Isabella, Detroit, Wayne, Manistee, and Mason 
counties. Notable deposits are also found in Ohio, Kansas, Louisi- 
ana. Salt is obtained by the evaporation of saline waters in Cali- 
fornia, Utah and Texas. 

Important foreign localities for the production of salt are to be 
found in Austrian Poland, Hungary, Bavaria, Prussia, Spain and 
Great Britain. 

Use. The chief uses of salt are for culinary and preserva- 
tive purposes. It is used also in the manufacture of soda ash 
(sodium carbonate) , which is used in glass making, soap making, 




168 MANUAL OF MINERALOGY 

bleaching, etc., and in the preparation of sodium salts in general. 
Salt is used also in the extraction of gold by the chlorination 
process. 

Sylvite. 

Composition. Potassium chloride, KC1 = Chlorine 47.6, po- 
tassium 52.4. Sometimes contains sodium chloride. 

Crystallization. Isometric. Cube and oc- 
tahedron frequently in combination (Fig. 239). 
Structure. Usually in granular crystalline 
masses showing cubic cleavage; compact. 

Physical Properties. Perfect cubical cleav- 
Fig 239 age. H. = 2. G. = 1.9. Transparent when 

pure. Colorless or white; also shades of blue, 
yellow or red from impurities. Readily soluble in water. Salty 
taste but more bitter than in the case of halite. 

Tests. Easily fusible at 1.5, giving violet flame of potassium, 
which may be obscured by yellow flame due to sodium present. 
The yellow sodium flame may be filtered out by use of a blue 
glass, and the violet of the potassium rendered visible. After 
intense ignition, residue gives alkaline reaction on moistened 
test paper. Readily soluble in water; solution made acid with 
nitric acid gives with silver nitrate a heavy precipitate of silver 
chloride. Distinguished from halite by the violet flame color of 
potassium and its slightly bitter taste. 

Occurrence. Has the same origin, mode of occurrence and asso- 
ciations as halite (which see) but is much more rare. Found in 
some quantity and at times well crystallized in connection with the 
salt deposits at Stassfurt, Prussia. 

Name. Potassium chloride is the sal digestivus Sylvii of early 
chemistry, whence the name for the species. 

Use. One source of potassium compounds which are exten- 
sively used as fertilizers. Other potassium minerals that are 
found in Germany in sufficient amount to make them valuable 
as sources of potassium salts are, carnallite, KCl.MgCl 2 .6H 2 
(see page 173); kainite, MgS0 4 .KC1.3H 2 0; polyhalite, 
K 2 S0 4 .MgS0 4 .2CaS0 4 .2H 2 0. 



EMBOLITE 169 

Cerargyrite. Horn Silver. 

Composition. Silver chloride, AgCl = Silver 75.3, chlorine 
24.7. Some varieties contain mercury. 

Crystallization. Isometric. Habit cubic. 

Structure. Usually massive, resembling wax; often in plates 
and crusts. 

Physical Properties. H. = 2-3. G. = 5.8-6. Sectile, can be 
cut with a knife like horn. Transparent to translucent. Color 
pearl-gray to colorless. Rapidly darkens to violet-brown on 
exposure to light. 

Tests. Very easily fusible at 1. B. B. on charcoal gives a 
globule of silver. Insoluble in nitric acid, but slowly soluble 
in ammonium hydroxide. When heated with galena in C. T. 
gives a white sublimate of lead chloride. Distinguished chiefly 
by its horny or waxlike appearance and its sectility. 

Occurrence. Cerargyrite is an important secondary ore of silver. 
It is only to be found in the upper, enriched zone of silver veins where 
descending waters containing small amounts of chlorine have acted 
upon the oxidized products of the primary silver ores of the vein. 
Found associated with other silver ores, galena, etc.; with native sil- 
ver, cerussite and secondary minerals in general. Was an important 
mineral in the mines at Leadville and elsewhere in Colorado, at the 
Comstock Lode in Nevada, in crystals at the Poorman's Lode in 
Idaho. Notable amounts have been found in Peru, Chile and 
Mexico, and in the silver mines of Saxony. 

Name. Cerargyrite is derived from two Greek words mean- 
ing horn and silver, in allusion to its hornlike appearance and 
characteristics. 

Use. Silver ore. 



Embolite. 

Composition, Ag(Cl,Br). Crystallization, structure and physical 
properties, like those of Cerargyrite (which see). Tests, same as for 
cerargyrite, except that, when heated in C. T. with galena, it gives 
a lead bromide sublimate, which is yellow when hot and white when 
cold. Occurrence, same as for cerargyrite, with which it is usually 
found, but much rarer. 



170 



MANUAL OF MINERALOGY 



Other similar silver -compounds which are still rarer in their 
occurrence are, bromyrite, AgBr; iodobromite, Ag(Cl,Br,I); My- 
rite, Agl. 



Fluorite. Fluor Spar. 

Composition. Calcium fluoride, CaF 2 = Fluorine 48.9, cal- 
cium 51.1. 

Crystallization. Isometric. Habit cubic (Fig. 240) often in 
twinned cubes (Figs. "241 and 242). Other forms are rare, but 
examples of all the forms of the Normal 
Class have been observed; the tetrahexa- 
hedron (Fig. 243) and hexoctahedron (Fig. 
244) are characteristic. 

Structure. Usually crystallized. Also 
massive; coarse or fine granular, columnar. 
Physical Properties. Perfect octahedral 
cleavage. H. = 4. G. = 3.18. Transpar- 
Vitreous luster. Color widely various; 



Fig. 240. 

ent to sub translucent. 

most commonly light green, yellow, bluish green or purple, also 





Fig. 241. 



Fig. 242. 



colorless, white, rose, blue, brown. A single crystal may show 
varying bands of color; the massive variety is also often banded 
in color. The bluish green varieties often show fluorescence 
(green by transmitted light, blue by reflected light). Some 
varieties phosphoresce when heated, giving off variously colored 



FLUORITE 



171 



lights which are independent of the actual color of the specimen. 
The variety affording a green light is known as chlorophane. 

Tests. Fusible at 3, and residue gives alkaline reaction to 
moistened test paper. Gives a reddish flame (calcium). When 
mixed with potassium bisulphate and heated in C. T., hydro- 



Fig. 243. 



Fig. 244. 



fluoric acid is evolved which etches the glass, and a white deposit 
of silica forms upon the walls of the tube. Determined usually 
by its cubic crystals and octahedral cleavage, also vitreous luster 
and usually fine coloring, and by the fact that it can be scratched 
with a knife. 

Occurrence. A common and widely distributed mineral. Usually 
found either in veins in which it is the chief mineral or as a gangue 
mineral with metallic ores, especially those of lead and tin. Com- 
mon in dolomites and limestone and has been observed also as a 
minor accessory mineral in various igneous rocks. Associated with 
many different minerals, as calcite, dolomite, gypsum, celestite, 
barite, quartz, galena, sphalerite, cassiterite, topaz, tourmaline, 
apatite. 

The more important deposits in the United States are in southern 
Illinois near Rosiclare, and in the adjacent part of Kentucky. The 
fluorite occurs here in limestone, in fissure veins which at times 
become 40 feet in width. Fluorite is found in quantity in England, 
chiefly from Cumberland, Derbyshire and Durham; the first two 
localities being famous for their magnificent crystallized specimens. 
Found commonly in the mines of Saxony. 

Use. Fluorite is used mainly as a flux in the making of steel, 
in the manufacture of opalescent glass, in enameling cooking 
utensils, for the preparation of hydrofluoric acid, and occasionally 
as an ornamental material in the form of vases, dishes, etc. 



172 MANUAL OF MINERALOGY 

Cryolite. 

Composition. A fluoride of sodium and aluminium, Na s AlF 6 
= Fluorine 54.4, aluminium 12.8, sodium 32.8. 

Crystallization. Monoclinic. Prominent forms are prism 
and base. Crystals rare, usually cubic in aspect, and in parallel 
groupings growing out of massive material. 

Structure. Usually massive. 

Physical Properties. H.= 2.5. G.= 2.95-3. Vitreous to 
greasy luster. Colorless to snow-white. Transparent to trans- 
lucent. A low index of refraction, giving the mineral an appear- 
ance of watery snow or of paraffin. Powdered mineral almost 
disappears when immersed in water. 

Tests. Easily fusible (1.5), with strong yellow sodium flame. 
After intense ignition, residue gives alkaline reaction on moist- 
ened test paper. Fused in C. T. with potassium bisulphate, 
evolves hydrofluoric acid and gives a volatile white ring of 
silica. Characterized by its massive structure, white color and 
peculiar luster. 

Occurrence. Occurs in a large vein lying in granite at Arksuk- 
fiord on the west coast of Greenland. The following minerals are 
found in small amounts associated with the cryolite: quartz, siderite, 
galena, sphalerite, pyrite, chalcopyrite, wolframite, fluorite, cassit- 
erite, molybdenite, arsenopyrite, columbite. Found also in very 
small amounts at Miask, Ilmen Mountains, Siberia, and at foot of 
Pike's Peak, Colorado. 

Name. Name is derived from two Greek words meaning frost 
and stone, in allusion to its icy appearance. 

Use. It is used for the manufacture of sodium salts, of certain 
kinds of glass and porcelain, and as a flux in the electrolytic 
process for the production of aluminium. 

2. OXYCHLORIDES, ETC. 

Atacamite. 

Composition. Copper chloride with copper hydroxide, 
CuCl 2 .3Cu(OH) 2 = Chlorine 16.6, copper 14.9, cupric oxide 55.81. 
water 12.7. 



CARNALLITE 173 

Crystallization. Orthorhombic. Commonly slender pris- 
matic in habit, with vertical striations. Also tabular parallel 
to brachypinacoid. 

Structure. In confused crystalline aggregates; fibrous; gran- 
ular. As sand. 

Physical Properties. Cleavage perfect parallel to brachy- 
pinacoid. H.= 3-3.5. G. = 3.75-3.77. Adamantine to vitre- 
ous luster. Color various shades of green. Transparent to 
translucent. 

Tests. Fusible (3-4), giving an azure-blue flame of copper 
chloride. B. B. on charcoal with sodium carbonate gives globule 
of copper. Nitric acid solution with silver nitrate gives white 
precipitate of silver chloride ; with ammonia in excess gives blue 
solution. Gives acid water in C. T. Characterized by its 
green color and granular crystalline structure. Distinguished 
from malachite by its lack of effervescence in acids. 

Occurrence. A comparatively rare copper mineral. Found 
originally as sand in the province of Atacama in Chile. Occurs with 
other copper ores in various localities in Chile and Bolivia. Found 
in some of the copper districts of Australia; occurs sparingly in the 
copper districts of Arizona. 

Use. A minor ore of copper. 



3. HYDROUS CHLORIDES, ETC 
Carnallite. 

A hydrous chloride of potassium and magnesium, KCl.MgCl 2 . 
6HaO. Orthorhombic. Massive, granular. Crystals rare. Lus- 
ter nonmetallic, shining, greasy. Color milk-white, often reddish, 
due to included hematite. Transparent to translucent. H. = 1. 
G.= 1.6. Bitter taste. Deliquescent. Fusible at 1-1.5 with vio- 
let flame. After ignition gives an alkaline reaction on moistened 
test paper. Easily and completely soluble in water; on addition of 
nitric acid and silver nitrate gives a white precipitate of silver 
chloride. Acid solution neutralized with ammonia and sodium 
phosphate added gives a white precipitate of ammonium magnesium 
phosphate. Found associated with halite, sylvite, etc., in the salt 
deposits at Stassfurt, Prussia. Used as a source of potassium 
compounds. 



174 



MANUAL OF MINERALOGY 



OXIDES. 

The oxides are subdivided into three sections: (1) Oxides of 
Silicon; (2) Oxides of the Semimetals; (3) Oxides of the Metals. 

1. OXIDES OF SILICON. 

Quartz. 

Composition. Silicon dioxide, Si0 2 = Oxygen 53.3, silicon 
46.7. Often with various impurities. 

Crystallization. Hexagonal-rhombohedral; trapezohedral. 
Crystals commonly prismatic, with prism faces horizontally 
striated. Terminated usually by a combination of a positive 
and negative rhombohedron, which often are so equally devel- 
oped as to give the effect of a hexagonal pyramid (Fig. 245). 






Fig. 245. 



Fig. 246. 



Fig. 247. 



Sometimes one rhombohedron predominates or occurs alone 
(Fig. 246) . At times the prism faces are wanting, and the com- 
bination of the two rhombohedrons gives what appears to be a 
doubly terminated hexagonal pyramid (known as a quartzoid) 
(Fig. 247). Crystals at times very much distorted, when the 
recognition of the prism faces by their horizontal striations will 
assist in the orientation of the crystal. The trapezohedral faces 
are to be occasionally observed as small truncations between a 
prism face and that of an adjoining rhombohedron either to the 
right or left, forming what are known as right- or left-handed 
crystals (Figs. 248 and 249). Crystals are often elongated in 
tapering and sharply pointed forms, due to an oscillatory com- 
bination between the faces of the different rhombohedrons and 



QUARTZ 



175 



those of the prism (A, PI. VI). Sometimes twisted and bent. 
Crystals frequently twinned. The twins at times are so inti- 





Fig. 248. Right-handed Crystal. 



Fig. 249. Left-handed Crystal. 



mately intergrown that they can only be determined by the 
irregular position of the trapezohedral faces, by etching the 
crystal or by the pyroelectric phenomena that they show. 

Structure. Commonly in crystals. From large crystals 
usually attached at one end, to finely crystalline coatings, form- 
ing "drusy" surfaces. Also common in massive forms of great 
variety. From coarse- to fine-grained crystalline to flintlike or 
cryptocrystalline varieties. Sometimes in concretionary forms, 
mammillary, etc. As sand. 

Physical Properties. H.= 7. G. = 2.65-2.66. Vitreous lus- 
ter, sometimes greasy, splendent to nearly dull. Color widely 
various. Usually colorless or white, but frequently colored by 
various impurities, yellow, red, pink, amethyst, green, blue, 
brown, black. Transparent to opaque. Conchoidal fracture. 

Tests. Infusible. Insoluble. Yields a clear glass when the 
finely powdered mineral is fused with an equal volume of sodium 
carbonate. Usually told by its glassy luster, conchoidal fracture, 
hardness (7) and crystal form. 

Varieties. A great many different forms of quartz exist to 
which varietal names have been given. The more important 
varieties with a brief description of each follow. 

A. CRYSTALLINE VARIETIES. 



1. Rock Crystal. 
crystals. 



Colorless quartz, commonly in distinct 



176 MANUAL OF MINERALOGY 

2. Amethyst. Quartz colored purple or violet, often crys- 
tallized. 

3. Rose Quartz. Usually massive, color a rose-red or pink. 
Often fades somewhat on exposure to light. 

4. Smoky Quartz; Cairngorm Stone. Crystallized quartz of a 
smoky yellow to brown and almost black color. Named cairn- 
gorm from the locality of Cairngorm in Scotland. 

5. Milky Quartz. Milky white in color and nearly opaque. 
Sometimes with greasy luster. 

6. Cat's-eye. A stone, which when cut in a round shape (en 
cabochon) exhibits an opalescent or chatoyant effect, as it is 
termed, is called a cat's-eye. Quartz among other minerals gives 
at times this effect, which is due either to fibrous inclusions or 
to a fibrous structure of the quartz itself. The latter is seen in 
the tiger's-eye, a yellow fibrous quartz from South Africa, which 
is pseudomorphic after another fibrous mineral, crocidolite. 

7. With Inclusions. Many other minerals occur at times as 
inclusions in quartz. Rutilated quartz has fine needles of rutile 
penetrating it. Tourmaline and other minerals are found in 
quartz in the same way. Aventurine is quartz including brilliant 
scales of hematite or mica. Liquids and gases at times occur 
as inclusions; both liquid and gaseous carbon dioxide exist in 
some quartz. 

B. CRYPTOCRYSTALL1NE VARIETIES. 

1. Chalcedony. An amorphous quartz material, translucent 
with a waxy luster. White, yellowish brown to dark-brown in 
color. Often mammillary, stalactitic, etc., in structure. De- 
posited from aqueous solutions and found lining or filling cavities 
in rocks (see Fig. B, pi. III). 

2. Cornelian. A red chalcedony. 

3. Chrysoprase. An apple-green chalcedony. 

4. Agate. A variegated chalcedony. The different colors 
usually in delicate, fine parallel bands which are commonly 
curved, sometimes concentric (Fig. B, pi. VI). The color is 
sometimes strengthened or even changed by artificial means. 
Some agates have the different colors arranged not in bands but 



PLATE VI. 




A. Smoky Quartz, Pike's Peak, Colorado. 




B. Agate, Oberstein, Germany. 



QUARTZ 177 

irregularly distributed. Moss agate is a variety in which the 
variation in color is due to visible impurities, often manganese 
oxide. 

5. Onyx. A banded chalcedony like agate, except the bands 
are arranged in straight parallel lines. 

6. Flint. Something like chalcedony but of dull, often dark 
color. It breaks with a prominent conchoidal fracture and gives 
a sharp edge. Used for various implements by early man. 

7. Jasper. Opaque quartz, usually colored red from hematite 
inclusions. 

Occurrence. Quartz is the most common of minerals. Occurs 
as an important constituent of the acid igneous rocks, such as 
granite, rhyolite, pegmatite, etc. It is a common mineral of sedi- 
mentary rocks, forming the chief mineral in sandstone. Occurs 
largely also in metamorphic rocks, as gneisses and schists, while it 
forms practically the only mineral of quartzites. Deposited often 
from solution and forms the most common vein and gangue mineral. 
In rocks it is associated chiefly with feldspar and muscovite; in 
veins with practically the entire range of vein minerals. Often 
carries gold and becomes an important ore of that metal. Occurs 
in large amount as sand in stream beds and upon the seashore and 
as a constituent of soils. 

Rock crystal is found widely distributed, some of the more notable 
localities being: the Alps; Minas Geraes and Goyoz, Brazil; on the 
island of Madagascar; in Japan. The best quartz crystals from the 
United States are found at Hot Springs, Arkansas, and Little Falls, 
New York. Important occurrences of amethyst are located in the 
Ural Mountains and in Brazil. Found at Thunder Bay on the north 
shore of Lake Superior and in the United States in Oxford 
County, Maine; Delaware and Chester counties, Pennsylvania; 
Black Hills, South Dakota, etc. Smoky quartz is found in large and 
fine crystals in Canton Uri, Switzerland; at Pike's Peak, Colorado; 
Alexander County, North Carolina; at Auburn, Maine, etc. The 
chief source of agates at present is a district in southern Brazil and 
northern Uruguay. They are mostly cut at Oberstein, Germany, 
itself a famous agate locality. Found in Laramie County, Wyoming, 
and numerous other places in the United States. Massive quartz, 
occurring in quartz veins or with feldspar in pegmatite veins, is 
mined for its various commercial uses in Connecticut, New York, 
Maryland, Wisconsin, etc. 

Use. Widely used in its various colored forms as ornamental 
material, as amethyst, rose quartz, cairngorm, cat's-eye, tiger's- 



178 MANUAL OF MINERALOGY 

eye, aventurine, carnelian, agate, onyx, etc. Used for abrading 
purposes either as quartz sand or as sandpaper. Used in the 
manufacture of porcelain, of glass, as a wood filler, in paints, 
scouring soaps, etc. As sand is used in mortars and cements. 
As quartzite, sandstone, and in its various other rock forms as 
a building stone, for paving purposes, etc. Large amounts of 
quartz sand are used as an acid flux in certain smelting opera- 
tions. 

Opal. 

Composition. Silicon dioxide, like quartz, with a varying 
amount of water, Si0 2 nH 2 0. 

Crystallization. Amorphous. 

Structure. Massive; often botryoidal, stalactitic, etc. 

Physical Properties. H. = 5.5-6.5. G. = 1.9-2.3. Vitre- 
ous luster; often somewhat resinous. Colorless, white, pale 
shades of yellow, red, brown, green, gray and blue. With 
darker colors, which are due to various impurities. . Often has 
a milky or "opalescent" effect and sometimes shows a fine play 
of colors. Transparent to opaque. 

Tests. Infusible. Insoluble. Reacts like quartz. Gives a 
little water upon intense ignition in C. T. 

Varieties. Precious Opal. White, milky blue, yellow. Some- 
times dark, as in so-called black opal. Translucent, with an 
internal play of colors. This phenomenon is said to be due to 
thin curved laminae which refract the light differently from the 
mass of the material, and so serve to break it up into the various 
prismatic colors. Fire opal is a variety with intense orange to 
red reflections. 

Common Opal. Milk-white, yellow, green, red, etc., without 
internal reflections. 

Hyalite. Clear and colorless opal with a globular or botry- 
oidal structure. 

Geyserite. Opal deposited by hot springs and geysers. Found 
about the geysers in the Yellowstone Park. 

Wood Opal. Fossil wood with opal as the petrifying material. 

Tripolite, or Infusorial earth. Fine-grained deposits, resem- 



CUPRITE 179 

bling chalk in appearance. Formed by the accumulation of the 
siliceous shells of small sea organisms. 

Occurrence. Opal is found lining and filling cavities in igneous 
and sedimentary rocks, where it has evidently been deposited through 
the agency of hot waters. In its ordinary variety it is of widespread 
occurrence. Precious opals are found at Czernowitza, Hungary; 
in Queretaro and other states in Mexico; in Honduras; and from 
various localities in Australia, the chief district being White Cliffs, 
New South Wales. Recently black opal has been found in Idaho. 

Use. As a gem. The stones are usually cut in round shapes, 
en cabochon, and gems of one-carat size are valued up to $20. 
Stones of large size and exceptional quality are very highly 
prized. 

2. OXIDES OF THE SEMIMETALS. 
The minerals of this division are all rare in occurrence. Some 
of the more important species are, arsenolite, As 2 3 ; senarmon- 
tite, Sb 2 3 ; valentinite, Sb 2 3 ; tellurite, Te0 2 ; tungstite, W0 3 ; cer~ 
vantite, Sb 2 4 . 

3. OXIDES OF THE METALS. 

The oxides of the metals are grouped into two main divisions: 
A. Anhydrous Oxides; B. Hydrous Oxides. Further, the Anhy- 
drous Oxides are further subdivided into: (1) Protoxides; (2) 
Sesquioxides; (3) Intermediate Oxides; (4) Dioxides. 

A. ANHYDROUS OXIDES. 
1. PROTOXIDES. 

Cuprite. Ruby Copper. Red Copper Ore. 

Composition. Cuprous oxide, Cu 2 = Oxygen 11.2, copper 
88.8. 

Crystallization. Isometric. Common 
forms are cube, octahedron and dodecahedron, 
frequently in combination (Fig. 250). Some- 
times in much elongated cubic crystals, ca- 
pillary in size; known as "plush copper" or 
chalcotrichite. Fig. 250. 




180 MANUAL OF MINERALOGY 

Structure. Usually massive, more rarely in crystals or capil- 
lary forms. 

Physical Properties. H. = 3.5-4. G. = 6. Luster adaman- 
tine in clear crystallized varieties to submetallic and earthy in 
massive varieties. Color red of various shades. Ruby-red in 
transparent crystals. Streak brownish red, Indian-red. High 
index of refraction, giving brilliant luster to transparent variety. 

Tests. Easily fusible at 3, giving emerald-green flame, or, 
if moistened with hydrochloric acid and then heated, flame is 
azure-blue. Gives globule of copper on charcoal in R. F. 
When dissolved in small amount of concentrated hydrochloric 
acid and solution diluted with cold water gives a white precipi- 
tate of cuprous chloride (test for cuprous copper). Usually to 
be determined by its color and streak. 

Occurrence. An important ore of copper of secondary origin. 
Found in the upper, oxidized portions of copper veins, associated 
with the other secondary copper minerals, native copper, malachite, 
azurite, chrysocolla, etc. Found in the United States in connection 
with the copper deposits at Bisbee, Morenci, etc., Arizona. Found in 
small amount with the native copper from Lake Superior. An im- 
portant ore in Chile, Peru and Bolivia. Fine crystals come from 
Bisbee, Arizona; Cornwall, England; Chessy, France; the Urals. 

Name. Derived from the Latin, cuprum, copper. 
Use. Ore of copper. 

Zincite. 

Composition. Zinc oxide, ZnO = Oxygen 19.7, zinc 80.3. 
Manganese protoxide often present. 

Crystallization. Hexagonal; hemimorphic. Terminated 
above by faces of a steep pyramid and below with a basal 
plane. Sometimes shows short prism. 

Structure. Usually massive with platy or granular structure. 

Physical Properties. Perfect basal cleavage. H. = 4-4.5. 
G. = 5.5. Luster subadamantine. Color deep red to orange- 
yellow. Streak orange-yellow. Translucent to almost opaque. 

Tests. Infusible. Soluble in hydrochloric acid. When the 
finely powdered mineral is mixed with sodium carbonate and 
charcoal dust and intensely heated B. B., gives a nonvolatile 



CORUNDUM 



181 



coating of zinc oxide, yellow when hot, white when cold. Usually 
with borax bead in 0. F. gives a reddish violet color (manganese). 
Told chiefly by its color and streak. 

Occurrence. Found in the zinc deposits at Franklin Furnace, 
New Jersey, associated with franklinite and willemite, often in an 
intimate mixture. Sometimes embedded in pink calcite. 

Use. An ore of zinc, particularly used for the production of 
zinc white (zinc oxide). 

In this division also belong water, ice, H 2 0, which is hexagonal 
in crystallization, and tenorite or melaconite, CuO. 

2. SESQUIOXIDES. 
HEMATITE GROUP. 

The Hematite Group includes the closely related rhombohe- 
dral minerals, corundum, A1 2 3 , hematite, Fe 2 3 , and ilmenite 
(Fe,Ti) 2 3 . 

Corundum. 

Composition. Aluminium oxide, A1 2 3 = Oxygen 47.1, alu- 
minium 52.9. 

Crystallization. Hexagonal-rhombohedral. Crystals usually 
prismatic in habit or tapering hexagonal pyramids (Figs. 251 and 






Fig. 251. Fig. 252. Fig. 253. 

252). Often rounded into barrel shapes (Fig. 253). Frequently 
with deep horizontal striations. At times shows rhombohedral 
and pyramidal faces. 



182 MANUAL OF MINERALOGY 

Structure. Rudely crystallized or massive with parting planes 
nearly cubic in angle; coarse or fine granular. 

Physical Properties. Parting basal and rhombohedral, the 
latter giving nearly cubic blocks. H. = 9 (next to the diamond 
in hardness). G. = 3.95-4.1 (unusually high for a nonmetallic 
mineral). Adamantine to vitreous luster. Color various. Usu- 
ally some shade of brown, pink or blue. May be white, gray, 
green, ruby-red or sapphire-blue. Transparent to opaque. 

Tests. Infusible. Insoluble. Finely pulverized material 
moistened with cobalt nitrate and intensely ignited assumes a 
blue color (aluminium). Characterized chiefly by its great 
hardness, adamantine luster and high specific gravity. 

Varieties. Ordinary Corundum. In translucent to opaque 
masses, showing often the nearly cubical parting; also granular 
to compact. 

Gem Corundum. When transparent and finely colored, corun- 
dum furnishes various gem stones. The ruby is deep red corun- 
dum; sapphire is blue corundum. Stones of other colors are 
sometimes spoken of as yellow, violet, etc., sapphires or are 
designated by prefixing the word oriental to the name of some 
other mineral similar in color; thus, oriental topaz is a brownish 
yellow corundum; oriental amethyst, a reddish violet corundum, 
etc. 

Emery. Is a fine-grained corundum mixed with other min- 
erals, chiefly magnetite. 

Occurrence. Common in the metamorphic rocks, such as crys- 
talline limestone, mica-schist, gneiss, etc. Found also as an original 
constituent of certain igneous rocks, usually those deficient in silica. 
Found sometimes in large masses, evidently the product of magmatic 
differentiation. Found frequently in crystals and rolled pebbles in 
detrital soil and stream sands, where it has been preserved through 
its hardness. Associated minerals are commonly chlorite micas, 
chrysolite, serpentine, magnetite, spinel, cyanite, diaspore, etc. 

Rubies are found chiefly in Burmah, Siam and Ceylon. The 
most important locality in Burmah is near Mogok, 90 miles north 
of Mandalay. The stones are found here chiefly in the soil resulting 
from the decay of a metamorphosed limestone. They have also 
been found in situ in the limestone. The rubies of Siam are found 
near Bangkok, on the Gulf of Siam, where they occur in a clay, 



CORUNDUM 183 

derived from the decomposition of a basalt. The rubies of Ceylon 
are found with other gem stones in the stream gravels. A few 
rubies have been found in the gravels and in connection with the 
larger corundum deposits of North Carolina. 

Sapphires are found associated with the rubies of Siam and Cey- 
lon. They occur also at Banskar in Cashmere, India. In the 
United States small sapphires of fine color are found in various -lo- 
calities in Montana. They were first found in the river sands east 
of Helena when washing them for gold. They have since been 
found embedded in the rock of lamprophyre dikes. The rock is 
quarried and after exposure to the air for a time it gradually de- 
composes, setting the sapphires free. Sapphires are also found 
over an extensive area in central Queensland, Australia. 

Massive corundum is found in the United States in various locali- 
ties along the eastern edge of the Appalachian Mountains from North 
Carolina south. It has been extensively mined in southwestern 
North Carolina. It occurs here in large masses lying at the edges 
of intruded masses of a chrysolite rock (dunite) and is thought to 
have been a separation from the original magma. Found as an 
original constituent of a nepheline syenite in the Province of Ontario, 
Canada. At times the corundum is so abundant as to form more 
than 10 per cent of the rock mass. 

The impure corundum, known as emery, is found in large quanti- 
ties on Cape Emeri on the island of Naxos and in various localities 
in Asia Minor. In the United States emery has been extensively 
mined at Chester, Massachusetts. 

Artificial. Artificial corundum is now being made in the elec- 
trical furnaces at Niagara. Small synthetic rubies and sapphires, 
colored with minute amounts of chromium, have been success- 
fully made. Also small grains of the natural stone have been 
fused together into larger masses, from which stones of two or 
three carats in size can be cut. These are known as recon- 
structed rubies arid sapphires. 

Use. As a gem stone. The ruby at times yields the most 
valuable of gems; a stone of the deep red known as "pigeon's 
blood" may bring $1500 to $2000 a carat. The blue sapphire is 
less valuable, ranging at times, however, as high as $125 a carat. 
Corundum stones of various other color are valued up to $30 
a carat. 

Used also as an abrasive, either ground from the pure massive 
material, or in its impure form as emery. Artificial corundum 



184 



MANUAL OF MINERALOGY 



and carborundum, which in composition is a carbide of silicon, 
are now manufactured on a large scale in electric furnaces and 
are being used in considerable amount as abrasives instead of 
the naturally occurring corundum. 

Hematite. 

Composition. Iron sesquioxide, Fe 2 3 = Oxygen 30, iron 70. 
Sometimes with titanium and magnesium, passing into ilmenite. 

Crystallization. Hexagonal-rhombohedral. Crystals usually 
thick to thin tabular. Basal planes prominent, often showing 





Fig. 254. 



Fig. 255. 



triangular markings (Figs. 254 and 255). Edges of plates some- 
times beveled with rhombohedral and pyramidal forms (Fig. 





Fig. 256. 



Fig. 257. 



256). Thin plates at times grouped in rosette forms (iron roses) 
(Fig. 257). More rarely crystals are distinctly rhombohedral, 
often with nearly cubic angles. 

Structure. Usually earthy or in botryoidal to reniform shapes 
with radiating structure. At times micaceous; crystallized. 

Physical Properties. Rhombohedral parting with nearly cubic 
angles. H. = 5.5-6.5. G. = 4.8-5.3. Metallic luster. Color 
reddish brown to black. Streak light to dark Indian-red. 

Tests. Infusible. Becomes strongly magnetic on heating in 
R. F. Slowly soluble in hydrochloric acid; solution with potas- 
sium ferrocyanide gives dark blue precipitate (test for ferric 
iron). Told chiefly by its characteristic Indian-red streak. 



HEMATITE 185 

Varieties. Specular Hematite. Black hematite with brilliant 
splendent luster (whence name, specular, mirrorlike), in crystals 
or in foliated masses with micaceous structure. 

Columnar to Reniform Hematite, Kidney Ore. Brownish black 
color, in columnar to reniform shapes with radiating structure, 
having fibrous appearance (A, pi. III). 

Oolitic and Fossil Ore. Impure hematite in small globular or 
lenticular concretions. At times with fossils. 

Earthy Hematite. In pulverulent, earthy form of various 
shades of reddish brown. Often somewhat hydrated and pass- 
ing into limonite. 

Occurrence. Hematite is a widely distributed mineral in rocks 
of all ages and forms the most abundant ore of iron. Occurs as an 
accessory mineral in feldspathic igneous rocks, such as granite. 
Found from microscopic scales to enormous masses in connection 
with metamorphic rocks. It is found in red sandstones as the 
cementing material that binds the quartz grains together. 

The crystallized variety is found at many places, more particu- 
larly from the island of Elba; St. Gothard, Switzerland, in "iron 
roses " ; in the lavas of Vesuvius; at Cleator Moor, Cumberland, etc. 
In the United States the columnar and earthy varieties are found 
in enormous beds that furnish a large proportion of the iron ore of 
the world. The chief iron-ore districts of the United States are 
grouped around the southern and northwestern shores of Lake 
Superior in Michigan, Wisconsin and Minnesota. The chief dis- 
tricts, which are spoken of as iron-ore ranges, are, from east to west, 
the Marquette Range in northern Michigan; the Menominee Range 
in Michigan to the southwest of the Marquette; the Penokee- 
Gogebic Range in northern Wisconsin; the Mesabi Range, north 
of Duluth in Minnesota; and the Vermillion Range farther north 
in Minnesota, near the Canadian boundary. The iron ore of these 
different ranges varies from the hard black micaceous specular 
variety to the soft red earthy type. All of the ore bodies lie in rock 
troughs which furnish impervious underlying basements to the 
deposits. In all of the districts, except the Mesabi, these under- 
lying rocks are in the nature of altered igneous dikes, known aa 
soapstone dikes. The ore bodies lie in more or less broken quartz 
material, frequently colored red by inclusions of hematite and called 
jasper. The origin of these deposits is attributed to the slow con- 
centration of the iron content of a siliceous carbonate rock by down- 
ward moving waters. These waters were at last collected in the 
impervious rock troughs and there deposited their iron content by 



186 MANUAL OF MINERALOGY 

a replacement of the quartz of the overlying rock. The ores are 
mined in part by underground methods, and in part, where the ore is 
soft and lies sufficiently near the surface, by the use of steam shovels. 
Hematite is also found in the United States in various places in 
connection with the outcrop of rocks of the Clinton formation, from 
central New York south along the line of the Appalachian Moun- 
tains to central Alabama. The most important deposits of the 
series lie in eastern Tennessee and northern Alabama, near Birming- 
ham. Hematite has been found at Iron Mountain and Pilot Knob 
in southeastern Missouri. Deposits of considerable importance are 
located in Wyoming, in Laramie and Carbon counties. 

Name. Derived from a Greek word meaning blood, in allusion 
to the color of the powdered mineral. 

Ilmenite. Menaccanite. Titanic Iron Ore. 

Composition. Ferrous titanate, FeTi0 3 = Oxygen 31.6, tita- 
nium 31.6, iron 36.8. By the introduction of ferric oxide, the 
ratio between the titanium and iron often varies widely. Some- 
times contains magnesium replacing the ferrous iron. 

Crystallization. Hexagonal-rhombohedral ; tri-rhombohe- 
dral. Crystals usually thick tabular with prominent basal planes 
and small rhombohedral truncations. Faces of the third order 
rhombohedron rare. Crystal angles, etc., close to those for 
hematite. 

Structure. Usually massive, compact; also in grains or as 
sand. Often in thin plates. 

Physical (Properties. H. = 5.5-6. G.=4.7. Metallic to 
submetallic luster. Color iron-black. Streak black to brownish 
red. Sometimes magnetic without heating. 

Tests. Infusible. May be magnetic without heating. Fine 
powder fused in R. F. with sodium carbonate yields a magnetic 
mass. After fusion with sodium carbonate the fusion can be 
dissolved in hydrochloric acid, and when the solution is boiled 
with tin it assumes a violet color (titanium). 

Occurrence. Occurs as beds and lenticular bodies enveloped in 
gneiss and other crystalline metamorphic rocks. Often associated 
with magnetite. Also as an accessory mineral in eruptive rocks. 
Found in large quantities at Kragero and other localities in Norway; 



SPINEL 187 

at Miask in the Ilmen Mountains; at Bay St. Paul in Quebec, 
Canada. Found at Washington, Connecticut; in Orange County, 
New York, etc. 

Use. Has practically no commercial use. A little of it pres- 
ent in a body of magnetite iron ore makes the ore so difficult to 
smelt as to render it of little value. 

3. INTERMEDIATE OXIDES. 
SPINEL GROUP. 

A group of oxides which in composition are combinations of a 
bivalent oxide with a trivalent oxide, the general formula being, 
R"O.R 2 '"0 3 . R"0 may be MgO, ZnO, FeO, MnO, while R 2 /// 3 
may be A1 2 3 , Fe 2 3 , Mn 2 3 , Cr 2 3 . The chief members of the 
group are as follows: 

Spinel, Mg O.A1 2 3 or MgAl 2 4 . 

Gahnite, ZnO.Al 2 3 or ZnAl 2 4 . 

Magnetite, FeO.Fe 2 3 or FeFe 2 4 . 

Franklinite, (Fe,Mn,Zn)0.(Fe,Mn) 2 3 
or (Fe,Mn,Zn)(Fe,Mn) 2 O 4 . 

Chromite, (Fe,Mg)O.Cr 2 3 or (Fe,Mg)Cr 2 4 . 

The crystalline habit of all the members of the group is octa- 
hedral. The dodecahedron is sometimes present, but other forms 
are rare. 

Spinel. 

Composition. MgAl 2 4 or MgO. A1 2 3 = Alumina 71.8, mag- 
nesia 28.2. The magnesium may be, 
in part, replaced by ferrous iron or 
manganese and the aluminium by 
ferric iron and chromium. 

Crystallization. Isometric. Habit 
strongly octahedral (Fig. 258). Some- 
times in twinned octahedrons (spinel 
twins) (Fig. 259). Dodecahedron at 
times as small truncations (Fig. 260). 
Other forms rare. Fig - 258 ' 




188 MANUAL OF MINERALOGY 

Structure. Usually crystallized. 

Physical Properties. H.= 8. G. = 3.5-4.1. Nonmetallic. 
Vitreous luster. Color various, red, lavender, blue, green, 
brown, black, sometimes almost white. Streak white. Usually 
translucent to opaque, at times clear and transparent. 





Fig. 259. Fig. 260. 

Tests. Infusible. The finely powdered mineral dissolves 
completely B. B. in the salt of phosphorus bead (proving the 
absence of silica). Recognized chiefly by its hardness (8), its 
octahedral crystals and vitreous luster. 

Varieties. 1. Ruby Spinel. Nearly pure magnesian spinel. 
Clear red; transparent to translucent. When rose-red known 
as balas ruby, yellow or orange-red, rubicelle; violet-red, alman- 
dine ruby. 

2. Pkonaste. Iron-magnesia spinel. Color dark green, brown 
to black. Opaque or nearly so. 

3. Chlorospinel. Magnesia-iron spinel. Color grass-green ow- 
ing to the presence of copper. 

4. Picotite, or Chrome Spinel. Contains chromium and has 
iron replacing magnesium. Color yellowish or greenish brown. 
Translucent to opaque. 

Occurrence. A common metamorphic mineral occurring em- 
bedded in granular limestone, associated with calcite, serpentine, 
etc. Occurs also as an accessory mineral in many basic igneous 
rocks, as peridotites, etc. Found frequently as rolled pebbles in 
stream sands, where it has been preserved on account of its hard- 
ness. The ruby spinels are found in this way, often associated with 



MAGNETITE 189 

the corundum ruby, in the sands of Ceylon, Siam, Upper Burmah, 
Australia and Brazil. Ordinary spinel is found in various localities 
in New York, New Jersey and Massachusetts. 

Use. When transparent and finely colored is used as a gem. 
Usually red in color and known as the spinel ruby, balas ruby, 
etc. Some stones are blue in color. The largest cut stone 
known weighs in the neighborhood of 80 carats. The stones 
usually are comparatively inexpensive, although a stone of excep- 
tionally fine color may bring as high as $100 per carat. 

Gahnite. 

A zinc spinel, ZnAl 2 O 4 or ZnO.Al 2 O 3 , with ferrous iron and man- 
ganese isomorphous with the zinc and ferric iron with the aluminium. 
Isometric. Commonly octahedral, also rarely showing dodecahe- 
drons and cubes. H. =7.5-8. G. =4.55. Vitreous luster. Dark 
green color. Infusible. The fine powder fused with sodium car- 
bonate on charcoal gives a white nonvolatile coating of zinc oxide. 
A rare mineral. Found in the United States in notable crystals at 
Franklin, New Jersey, and Rowe, Massachusetts. 

Magnetite. 

Composition. Fe 3 4 or FeO.Fe 2 3 = Iron sesquioxide 69.0, 
iron protoxide 31.0 or oxygen 27.6, iron 72.4. The ferrous iron 
is sometimes replaced by magnesium, 
rarely nickel; also* at times titaniferous. 

Crystallization. Isometric. -Octa- 
hedral habit (Fig. 261), sometimes 
twinned octahedrons. Dodecahedron 
at times (Fig. 262) either alone or with 
octahedron (Fig. 263) . Other forms rare. 

Structure. Usually granular mas- 
sive, coarse or fine; sometimes as sand; . 
also frequently crystallized. 

Physical Properties. Often under pressure develops octahe- 
dral parting. H. = 6. G. = 5.18. Metallic luster. Color iron- 
black. Streak black. Strongly magnetic; sometimes a natural 
magnet, known as lodestone. 




190 MANUAL OF MINERALOGY 

Tests. Infusible. Slowly soluble in HC1 and solution re- 
acts for both ferrous and ferric iron. Distinguished chiefly by its 
strong magnetism, its black color and streak, and its hardness (6). 





Fig. 262. Fig. 263. 

Occurrence. A common ore of iron. It is found as an accessory 
mineral in rocks of all classes and sometimes becomes their chief 
constituent. Most commonly associated with crystalline meta- 
morphic rocks, also frequently in rocks that are rich in ferromagne- 
sium minerals, such as diabase, gabbro, peridotite. In many cases 
forms large ore bodies that are thought to be the result of magmatic 
differentiation; such bodies are often highly titaniferous. Occurs 
at times in immense beds and lenses, inclosed in old metamorphic 
rocks. Found in the black sands of the seashore. Occurs as thin 
plates and dendritic growths between plates of mica. Often inti- 
mately associated with corundum, forming the material known as 
emery. 

In the United States, found in large beds with the Archaean rocks 
of the Adirondacks in Warren, Essex and Clinton counties of north- 
ern New York; in various places in New Jersey; at Cornwall, 
Pennsylvania. Important foreign localities are in Norway and 
Sweden, where it is the chief iron ore. Natural magnets or lode- 
stones are found in Siberia; in the Harz Mountains, Germany; 
at Magnet Cove, Arkansas. 

Name. Probably derived from the locality Magnesia, border- 
ing on Macedonia. A fable, told by Pliny, ascribes its name to 
a shepherd named Magnes, who first discovered the mineral on 
Mount Ida by noting that the nails of his shoes and the iron 
ferrule of his staff adhered to the ground. 

Use. An important iron ore. 



CHROMITE 191 

Franklinite. 

Composition. (Fe,Zn,Mn)0.(Fe,Mn) 2 3 . Shows wide vari- 
ation in the proportions of the different elements present, but con- 
forms to the general formula, RO.R 2 3 . 

Crystallization. Isometric. Habit strongly octahedral. Do- 
decahedron sometimes as truncations. Other forms rare. Crys- 
tals often rounded. 

Structure. Massive, coarse or fine granular, in rounded grains 
or crystallized. 

Physical Properties. H.= 6. G.= 5.15. Metallic luster. 
Color iron-black. Streak dark brown. Not magnetic. 

Tests. Infusible. Becomes strongly magnetic on heating in 
R. F. Gives a bluish green color to sodium carbonate bead in 
0. F. (manganese) . When very fine powder is mixed with sodium 
carbonate and heated intensely on charcoal gives a coating of 
zinc oxide. Distinguished by above tests and its black color 
and brown streak. 

Occurrence. Found practically only in the zinc deposits at Frank- 
lin Furnace, New Jersey, which are in the form of large beds, in- 
closed in granular limestone. Associated chiefly with zincite and 
willemite, with which it is often intimately intergrown. 

Use. As an ore of zinc and manganese. The zinc is converted 
into zinc white and the residue is smelted to form an alloy of 
iron and manganese, spiegeleisen, which is used in the manu- 
facture of steel. 

Chromite. 

Composition. FeCr 2 4 or FeO.Cr 2 3 = Chromium sesqui- 
oxide 68.0, iron protoxide 32.0. The iron may be replaced by 
magnesium and the chromium by aluminium and ferric iron. 

Crystallization. Isometric. Habit octahedral. Crystals small 
and rare. 

Structure. Commonly massive, granular to compact. 

Physical Properties. H. = 5.5. G. = 4.6. Metallic to sub- 
metallic luster. Color iron-black to brownish black. Streak 
dark brown. 



192 MANUAL OF MINERALOGY 

Tests. Infusible. When finely powdered and fused on char- 
coal with sodium carbonate gives a magnetic residue. Imparts 
a green color to the borax and salt of phosphorus beads (chro- 
mium). 

Occurrence. A common constituent of peridotite rocks and the 
serpentines derived from them. One of the first minerals to separate 
from a cooling rock magma, and its large ore deposits are thought to 
have been derived by such magmatic differentiation. Associated 
with chrysolite, serpentine, corundum, etc. 

Found only sparingly in the United States. Pennsylvania, Mary- 
land, North Carolina and Wyoming have produced it in the past. 
California is the only producing state at present (1910). The 
important countries for its production are New Caledonia, Greece 
and Canada. 

Uses. Chromium is used with various other metals to give 
hardness to steel. Chromite bricks are used to a considerable 
extent as linings for metallurgical furnaces, on account of their 
neutral and refractory character. The bricks are usually made 
of crude chromite and coal tar but sometimes of chromite with 
kaolin, bauxite, milk of lime or with other materials. Chromium 
is a constituent of certain green, yellow, orange and red pigments 
and of similarly colored dyes. 



Chrysoberyl. 

Composition. Beryllium aluminate, BeAl 2 4 = Alumina 80.2, 
beryllium oxide 19.8. 

Crystallization. Orthorhombic. Crystals usually tabular par- 
allel to macropinacoid, which face is vertically striated. Com- 
monly twinned, often in pseudohexagonal forms. 

Structure. Usually in crystals. 

Physical Properties. Prismatic cleavage. H. = 8.5 (un- 
usually high). G.= 3.65-3.8. Vitreous luster. Color various 
shades of green, brown, yellow, sometimes red by transmitted 
light. 

Tests. Infusible. Insoluble. The finely powdered mineral 
is wholly soluble in the salt of phosphorus bead (absence of silica). 
Mineral, moistened with cobalt nitrate and ignited, turns blue 



CASSITERITE 193 

(aluminium). Characterized by its extreme hardness, its yel- 
lowish to emerald-green color and its twin crystals. 

Varieties. 1. Ordinary. Color pale green, yellow; some- 
times transparent. 

2. Alexandrite. Emerald-green variety, but red by trans- 
mitted light and generally also by artificial light. 

3. Cat's-eye, or Cymophane. A variety which when polished 
shows an opalescent luster, and across whose surface plays a 
long narrow beam of light, changing its position with every 
movement of the stone. This effect is known as chatoyancy, 
and is best obtained when the stone is cut in an oval or round 
form (en cabochori). This property of the mineral is thought 
to be due to numerous minute tubelike cavities, arranged in a 
parallel position. Chrysoberyl is the true cat's-eye, and is not 
to be confused with various other minerals possessing similar 
properties (e.g., quartz). 

Occurrence. A rare mineral. Found in the alluvial gem deposits 
of Brazil and Ceylon; the alexandrite variety comes from the Ural 
Mountains. In the United States it has been found at Norway and 
Stoneham, Maine; Haddam, Connecticut; and in North Carolina. 

Name. Chrysoberyl means golden beryl. Cymophane is de- 
rived from two Greek words meaning wave and to appear, in 
allusion to the chatoyant effect of some of the stones. Alexan- 
drite was named in honor of Alexander II of Russia. 

Use. Serves as a gem stone. The ordinary yellowish green 
stones are valued up to $5 a carat. Alexandrite brings as high 
as $60 for a one-carat stone. A one-carat cat's-eye may have a 
value up to $50. 

Two rare manganese minerals belong in the section of Inter- 
mediate Oxides: hausmannite, MnO.Mn 2 3 , and braunite, 3Mn 2 3 . 
MnSi0 3 . 

4. DIOXIDES. 
Cassiterite. Tin Stone. 

Composition. Tin dioxide, Sn0 2 = Oxygen 21.4, tin 78.6. 
Crystallization. Tetragonal. Common forms are prisms and 
pyramids of first and second orders (Fig. 264). Frequently in 



194 



MANUAL OF MINERALOGY 



elbow-shaped twins; twinning plane being a pyramid of the 
second order (Fig. 265). 



a 


m 




Fig. 264. 



Fig. 265. 



Structure. Usually massive granular; often in reniform 
shapes with radiating fibrous-like structure (wood tin) ; crystal- 
lized. 

Physical Properties. H. = 6-7. G.= 6.8-7.1 (unusually 
high for a mineral with nonmetallic luster). Nonmetallic, ada- 
mantine luster to submetallic and dull. Color usually brown or 
black; rarely yellow or white. Streak white. 

Tests. Infusible. Gives globule of tin with coating of white 
tin oxide when finely powdered mineral is fused on charcoal with 
a mixture of sodium carbonate and charcoal powder. Insoluble. 
Recognized by its high specific gravity, its color and light streak. 

Occurrence. Cassiterite is widely distributed in small amounts 
but is only produced on a commercial scale in a few localities. Cas- 
siterite has been noted as an original constituent of igneous rocks, 
but it is more commonly to be found in veins associated with quartz. 
As a rule tin-bearing veins are found in or near pegmatites or granitic 
rocks. Tin veins usually have minerals which contain fluorine and 
boron, such as tourmaline, topaz, fluorite, apatite, etc., and the min- 
erals of the wall rocks are commonly much altered. It is thought, 
therefore, that the tin veins have been formed through the agency 
of vapors which carried tin with boron and fluorine. Cassiterite is 
at times a minor constituent of pegmatite veins. Also it is found 
in the form of rolled pebbles in placer deposits. 

Cassiterite is not found in large quantities in the United States, 
the only productive locality at present being on the Seward Penin- 
sula, Alaska. Found also in the pegmatites of North and South 



RUTILE 



195 



Carolina; in the Black Hills, South Dakota; near El Paso, Texas. 
The world's supply of tin ore comes from Tasmania, from New 
South Wales, Queensland and other states of Australia, from Bolivia 
and from the Malay States. Cornwall, England, has produced large 
amounts of tin ore in the past. 

Use. Only ore of tin. Chief use of tin is in coating or "tin- 
ning" metals, particularly iron, to form what is known as sheet 
tin. Tin is also used in various alloys: solder, containing tin 
and lead; bell-metal and bronze, containing copper and tin. 

Rutile. 

Composition. Titanium dioxide, Ti0 2 = Oxygen 40, titanium 
60. A little iron is usually present and may amount to 10 per 
cent. 

Crystallization. Tetragonal. Usually prismatic with pyra- 
mid terminations (Fig. 266). Vertically striated. .Frequently 




Fig. 266. 



Fig. 267. 



Fig. 268. 



in elbow twins, often repeated (Figs. 267 and 268). Twinning 
plane is pyramid of second order. Crystals sometimes slender 
acicular. 

Structure. Usually crystallized. Sometimes compact mas- 
sive. 

Physical Properties. H.= 6-6.5. G.= 4.18-4.25. Luster 
adamantine to submetallic. Color red, reddish brown to black. 
Usually nearly opaque, may be transparent. 



196 MANUAL OF MINERALOGY 

Tests. Infusible. Insoluble. Fused with sodium carbonate, 
then fused mass dissolved in hydrochloric acid and boiled with 
tin, the solution assumes a violet color. 

Occurrence. Rutile is found in granite, gneiss, mica schist, meta- 
morphic limestone and dolomite, sometimes as an accessory mineral 
in the rock, sometimes in quartz veins traversing it. Often occurs 
as slender crystals penetrating quartz. Remarkable crystals come 
from Graves Mountain, Lincoln County, Georgia. Also found in 
Alexander County, North Carolina, in Randolph County, Alabama, 
and at Magnet Cove, Arkansas. Has been mined near Roseland, 
Nelson County, Virginia. Notable European localities are Kragero, 
Norway; Yrieux, near Limoges, France; in the Ural Mountains. 

Use. Source of titanium. Titanium is used to a small extent 
in steel and cast iron; for electrodes in arc lights; to give a yel- 
low color to porcelain and false teeth. 

Octahedrite. Anatase. 

Titanium dioxide, TiC>2, same as rutile and brookite. Tetragonal. 
Usually in pyramidal crystals, also tabular parallel to base. H. = 
5.5-6. G. = 3.8-3.95. Adamantine luster. Color yellow, brown, 
blue, black, transparent to opaque. Tests same as for rutile (which 
see). A comparatively rare mineral, found usually as an accessory 
mineral in metamorphic rocks. 

Brookite. 

Titanium dioxide, TiO 2 , like rutile and octahedrite. Orthorhom- 
bic. Habit varied. Tabular parallel to macropinacoid, square 
prismatic and at times by an equal development of 4 prism and 8 
pyramid faces resembles a hexagonal pyramid. Occurs only in crys- 
tals. H. = 6. G. = 4-4.07. Luster adamantine to submetallic. 

Color hair-brown to black. Translucent to opaque. Tests, same 
as for rutile. A rare mineral, occurring with one of the other forms 
of titanium dioxide, rutile or octahedrite. Occurs in good crystals 
at St. Gothard, Switzerland; in the Tyrol; Trenadoc, Wales; Ellen- 
ville, New York; Magnet Cove, Arkansas. 

Pyrolusite. 

Composition. Manganese dioxide, Mn0 2 . Commonly con- 
tains a little water. 

Crystallization. Crystals probably always pseudomorphous 
after manganite. 



PYROLUSITE 197 

Structure. Radiating columnar to fibrous (Fig. A, pi. VII); 
also granular massive; often in reniform coats. 

Physical Properties. H. = 2-2.5 (often soiling the fingers). 
G. = 4.75. Metallic luster. Iron-black color and streak. Splin- 
tery fracture. 

Tests. Infusible. A small amount of powdered mineral 
gives in 0. F. a reddish violet bead with borax or a bluish green 
opaque bead with sodium carbonate. Gives oxygen in C. T., 
which will cause a splinter of charcoal to ignite when placed in 
tube above the mineral and heated. Only a small amount of 
water in C. T. In hydrochloric acid, chlorine gas evolved. 

Occurrence. A secondary mineral. Manganese is dissolved out 
of the crystalline rocks, in which it is almost always present in small 
amounts, and redeposited under various conditions, chiefly as pyro- 
lusite. Dendritic coatings of pyrolusite are frequently observed 
on rock surfaces, coating pebbles, etc. Nodular deposits of pyro- 
lusite are found on the sea bottom. Nests and beds of manganese 
ores are found inclosed in residual clays, derived from the decay 
of manganiferous limestones. As the rock has weathered and its 
soluble constituents -been taken away, the manganese content has 
been concentrated in nodules and masses composed chiefly of 
pyrolusite. Also found in veins with quartz and various metallic 
minerals. 

Mined in Thuringia, Moravia, Transylvania, Bohemia, West- 
phalia, Australia, Japan, India, New Brunswick, Nova Scotia. In 
the United States, manganese ores are found in Virginia, Georgia, 
Arkansas and California. 

Name. Pyrolusite is derived from two Greek words meaning 
fire and to wash, because it is used to free glass through its oxidiz- 
ing effect of the colors due to iron. 

Uses. Most important manganese ore. Manganese is used 
in the manufacture of the alloys with iron, spiegekisen and ferro- 
manganese, employed in making steel; also in various alloys 
with copper, zinc, aluminium, tin, lead, etc. Pyrolusite is used 
as an oxidizer in the manufacture of chlorine, bromine and oxy- 
gen; as a disinfectant in potassium permanganate; as a drier 
in paints, a decolorizer of glass, and in electric cells and bat- 
teries. Manganese is also used as a coloring material in bricks, 
pottery, glass, etc. 



198 MANUAL OF MINERALOGY 

Polianite, Mn0 2 , is a rare mineral, occurring in minute tet- 
ragonal crystals. 

B. HYDROUS OXIDES. 

Turgite. Hydrohematite. 

Composition is Fe4O 5 (OH) 2 or 2Fe 2 O 3 .lH 2 O. Compare limonite 
and goethite. Reniform and stalactitic, with radiating fibrous 
structure. Sometimes earthy. H. = 5.5-6. G. = 4.14. Subme- 
tallic luster. Color black to reddish black. Streak Indian-red. 
Difficultly fusible at 5-5.5. Strongly magnetic after heating in R. F. 
In C. T. gives 5 percent of water and generally decrepitates. Dis- 
tinguished from limonite by red streak and from hematite by giving 
water in C. T. Found usually associated with limonite. Occurred 
in considerable amount at Salisbury, Conn., where it often formed 
an outer layer an inch or more in thickness on the masses of limonite. 

Diaspore. 

Composition. AIO(OH) or A1 2 3 .H 2 = Alumina 85, water 15. 

Crystallization. Orthorh.ombic. Usually in thin crystals, 
tabular parallel to the brachypinacoid. 

Structure. Bladed; foliated massive. 

Physical Properties. Perfect- cleavage parallel to brachy- 
pinacoid. H. = 6.5-7. G.= 3.35-3.45. Vitreous luster except 
on cleavage face, where it is pearly. Color white, gray, yellowish, 
greenish. 

Tests. Infusible. Insoluble. Fine powder wholly soluble 
in salt of phosphorus bead (absence of silica). Ignited with 
cobalt nitrate turns blue (aluminium). Gives water in C. T. 
Characterized by its good cleavage, scaly structure and its 
hardness (6.5-7). 

Occurrence. Usually a decomposition product of corundum and 
found associated with that mineral in dolomite, chlorite-schist, etc. 
Found in the Urals; at Schemnitz, Hungary; Campolongo in Swit- 
zerland. In the United States in Chester County, Pennsylvania; 
at Chester, Massachusetts; near Franklin, North Carolina, etc. 

Name. Derived from a Greek word meaning to scatter, in 
allusion to its decrepitation when heated.' 



PLATE VII. 




A. Pyrolusite, Negaunee, Michigan. 




B. Manganite, Ilefeld, Harz Mts. 



MANGANITE 199 



Goethite. 

Composition. FeO(OH) or Fe 2 3 .H 2 = Oxygen 26, iron 
62.9, water 10.1. 

Crystallization. Orthorhombic. Prismatic, vertically stri- 
ated. Often flattened parallel to brachypinacoid. In acicular 
crystals at times. 

Structure. Massive, reniform, stalactitic, with radiating 
fibrous structure. Foliated. Rarely in distinct crystals. 

Physical Properties. Perfect cleavage parallel to brachy- 
pinacoid. H.= 5-5.5. G. = 4.37. Adamantine to dull luster. 
Silky luster in certain fine scaly or fibrous varieties. Color 
yellowish brown to dark brown. Streak yellowish brown (same 
as for limonite). 

Tests. Difficultly fusible (5-5.5). Becomes magnetic in R. F. 
Water in C. T. Told chiefly by the color of its streak and dis- 
tinguished from limonite by its tendency to crystallize and the 
smaller amount of water which it contains. 

Occurrence. Occurs with the other oxides of iron, hematite and 
limonite. Found at Eisenfeld in Nassau; near Bristol, England; 
at Lostwithiel, Cornwall. In the United States in connection with 
the Lake Superior hematite deposits, particularly at Negaunee, 
Michigan. 

Use. A minor ore of iron. 



Manganite. 

Composition. MnO(OH) or Mn 2 3 .H 2 = Oxygen 27.3, 
manganese 62.4, water 10.3. 

Crystallization. Orthorhombic. Crystals usually long pris- 
matic with obtuse terminations, deeply striated vertically (Fig. B, 
pi. VII). Often twinned. 

Structure. Usually in radiating masses ; crystals often grouped 
in bundles. Also columnar. 

Physical Properties. Perfect cleavage parallel to brachy- 
pinacoid. H. = 4. G. = 4.3. Metallic luster. Steel-gray to 
iron-black color. Dark brown streak. 



200 MANUAL OF MINERALOGY 

Tests. Infusible. A small amount of the powdered mineral 
gives in 0. F. a reddish -violet bead with borax or a bluish green 
opaque bead with sodium carbonate. Much water when heated 
in C. T. Told chiefly by its black color, prismatic crystals, hard- 
ness (4) and brown streak. The last two will serve to distinguish 
it from pyrolusite. 

Occurrence. Found in connection with pyrolusite and other man- 
ganese minerals and with iron oxides. Occurs at Ilefeld, Harz 
Mountains, in fine crystals; also at Ilmenau, Thuringia; Cornwall, 
England; Negaunee, Michigan, etc. 

Use. A minor ore of manganese. 

Limonite. Brown Hematite. Bog-iron Ore. 

Composition. Fe 4 3 (OH) 6 or 2Fe 2 3 .3H 2 = Oxygen 25.7, 
iron 59.8, water 14.5. Often impure. Compare turgite and 
goethite. 

Crystallization. Noncrystalline. 

Structure. In mammillary to stalactitic forms with radiat- 
ing fibrous structure (Fig. B, pi. II); also concretionary; some- 
times earthy. 

Physical Properties. H. = 5-5.5. G. = 3.6-4. Submetallic 
luster. Color dark brown to nearly black. Streak yellowish 
brown. 

Tests. Difficultly fusible (5-5.5). Strongly magnetic after 
heating in R. F. Much water in C. T. (15 per cent). Charac- 
terized chiefly by its structure and yellow-brown streak. 

Occurrence. Limonite is a common ore of iron and is always 
secondary in its origin, formed through the alteration or solution 
of previously existing iron minerals. Pyrite is often found altered 
to limonite, the crystal form being at times preserved, giving limonite 
pseudomorphs. Sulphide veins are often capped near the surface, 
where oxidation has taken place, by a mass of cellular limonite, 
which is known as gossan, or an iron hat. Iron minerals existing in 
the rocks are among the first to undergo decomposition, and their 
iron content is often dissolved by percolating waters through the 
agency of the small amounts of carbonic acid which they contain. 
The iron is transported as a carbonate by the waters to the surface 
and then often carried by the streams finally into marshes and 
stagnant pools. There, under the effect of the evaporation of the 



BAUXITE 201 

water and its consequent loss of the carbonic acid, which served to 
keep the iron carbonate in solution, and through the agency of the 
reducing action of carbonaceous matter present, the iron carbonate 
is changed to an oxide, which separates from the water and collects 
first as an iridescent scum on the surface of the water, and then later 
sinks to the bottom. In this way, under favorable conditions, beds 
of impure limonite can be formed in the bottom of marshes and bogs. 
Such deposits are very common and are known as bog-iron ores, 
but, because of the foreign materials deposited along with the 
limonite, are seldom of sufficient purity to be worked. 

Limonite deposits are also to be found in connection with iron- 
bearing limestones. The iron content of the limestone is gradually 
dissolved out by circulating waters and transported by them to 
some favorable spot, and there the iron is slowly redeposited as 
limonite, gradually replacing the calcium carbonate of the rock. 
Or, by the gradual weathering and solution of the limestone, its iron 
content may be left in the form of residual masses of limonite, lying 
in clay above the limestone formation. 

Such deposits are often of considerable size, and because of their 
greater purity are much more often mined than the bog-iron ores. 
Deposits of this type are to be found chiefly along the Appalachian 
Mountains, from western Massachusetts as far south as Alabama. 
These ores have been of considerable importance in western Massa- 
chusetts, northwestern Connecticut, southeastern New York, and 
in New Jersey. To-day they are chiefly mined in Alabama, Virginia, 
Tennessee and Georgia. Limonite deposits of various kinds are 
found throughout the western country, but as yet they have not been 
extensively developed. 

Limonite is the coloring material of yellow clays and soils, and 
mixed with fine clay makes what is known as yellow ocher. Limo- 
nite is commonly associated in its occurrence with hematite, turgite, 
pyrolusite, calcite, siderite, etc. 

Name. Derived from the Greek word meaning meadow, in 
allusion to its occurrence in bogs. 

Use. As an iron ore. As a pigment, in yellow ocher. 

Bauxite. 

Composition. A1 2 0(OH) 4 or A1 2 3 .2H 2 = Alumina 73.9, 
water 26.1. Often impure. 

Crystallization. Noncrystalline. 

Structure. In round concretionary grains; also massive, 
earthy, claylike. 



202 MANUAL OF MINERALOGY 

Physical Properties. G. = 2-2.55. Dull to earthy luster. 
Color white, gray, yellow, red. 

Tests. Infusible. Insoluble. Assumes a blue color when 
moistened with cobalt nitrate and then ignited (aluminium). 
Gives water in C. T. 

Occurrence. Probably usually a secondary mineral derived from 
the decomposition of rocks containing aluminium silicates. Some- 
times as a residual deposit, preserving evidences of the original rock 
structure; sometimes oolitic and concretionary in character and 
evidently deposited from water. May, perhaps, at times, be de- 
posited by waters from hot springs. Occurs at Baux, near Aries, 
France, in disseminated grains in limestone; at Allauch, near Mar- 
seilles, France, in oolitic form with calcite as cement. In the 
United States the chief deposits are found in Georgia, Alabama and 
Arkansas. 

Use. As an ore of aluminium, in the manufacture of alumin- 
ium salts; artificial abrasives and bauxite brick. 

Brucite. 

Composition. Magnesium hydroxide, Mg(OH) 2 = Magnesia 
69.0, water 31.0. Iron and manganese sometimes present. 

Crystallization. Hexagonal-rhombohedral. Crystals usu- 
ally tabular with prominent basal planes, showing at times small 
rhombohedral truncations. 

Structure. Commonly foliated, massive. 

Physical Properties. Perfect basal cleavage. Folia flexible 
but not elastic. Sectile. H. = 2.5. G. = 2.39. Luster on base 
pearly, elsewhere vitreous to waxy. Color white, gray, light 
green. Transparent to translucent. 

Tests. Infusible. B. B. glows. Gives water in C. T. Easily 
soluble in hydrochloric acid, and after solution has been made 
ammoniacal an addition of sodium phosphate gives a white 
granular precipitate of ammonium magnesium phosphate (test 
for magnesium). Recognized by its foliated structure, light 
color and pearly luster on cleavage face. Distinguished from 
talc by its greater hardness and lack of greasy feel. 

Occurrence. Found associated with serpentine, dolomite, mag- 
nesite, chromite, etc., as a decomposition product of magnesium 



CARBONATES 203 

silicates. Notable localities for its occurrence are at Unst, one of 
the Shetland Islands; Aosta, Italy; at Tilly Foster Iron Mine, 
Brewster, New York; at Wood's Mine, Texas, Pennsylvania. 

Gibbsite. Hydrargillite. 

Aluminium hydroxide, A1(OH) 3 . Monoclinic. Rarely in hex- 
agonal-shaped tabular crystals. Stalactitic or botryoidal. Basal 
cleavage. H. = 2-3.5. G. = 2.3-2.4. Luster pearly, vitreous or 
dull. Color white. Infusible. Insoluble in hydrochloric acid. 
Moistened with cobalt nitrate and ignited assumes a blue color. 
Water in C. T. A rare species, most commonly found with corun- 
dum. 

Psilomelane. 

Of uncertain composition, chiefly manganese oxides, MnO 2 with 
MnO and H^O, also small amounts of barium oxide, cobalt oxide, 
etc. Noncrystalline. Massive, botryoidal, stalactitic. H. = 5-6. 
G. = 3.7-4.7. Submetallic luster. Black color. Brownish black 
streak. Infusible. A small amount of mineral fused in O. F. with 
sodium carbonate gives an opaque bluish green bead. Gives much 
water in C. T. Distinguished from the other manganese oxides 
by its greater hardness. An ore of manganese, occurring usually 
with pyrolusite. 

CARBONATES. 

The carbonates are grouped into two divisions: (1) Anhydrous 
Carbonates; (2) Add, Basic and Hydrous Carbonates. 

1. ANHYDROUS CARBONATES. 
CALCITE GROUP. 

The Calcite Group consists of a series of carbonates of the 
bivalent metals, calcium, magnesium, ferrous iron, manganese 
and zinc. They all crystallize in the rhombohedral class of the 
Hexagonal System with closely agreeing crystal constants. They 
all show a perfect rhombohedral cleavage, with the angle between 
the cleavage faces varying from 105 to 108. The Calcite 
Group forms one of the most marked and important groups of 
isomorphous minerals, its chief members being as follows: 

Calcite, CaC0 8 . 

Dolomite, (Ca,Mg)CO,. 



204 



MANUAL OF MINERALOGY 



Magnesite, MgC0 3 . 
Siderite, FeC0 3 . 
Rhodochrosite, MnCO s . 
Smithsonite, ZnC0 3 . 

Calcite. 

Composition. Calcium carbonate, CaC0 3 = Carbon dioxide 
44.0, lime 56.0. Small amounts of magnesium, ferrous iron, 
manganese and zinc may replace the calcium. 

Crystallization. Hexagonal-rhombohedral. Crystals are very 
varied in habit, often highly complex. Over 300 different forms 
have been described. Three important habits: (1) Prismatic, in 
which the prism faces are prominent, in long or short prisms with 






Fig. 269. 



Fig. 270. 



Fig. 271. 



basal plane or rhombohedral terminations (Figs. 273 and 274); 
(2) Rhombohedral, in which rhombohedral forms predominate, 





m 



Fig. 272. 



Fig. 273. 




both low and steep rhombohedrons, the unit (cleavage) form is 
not common (Figs. 269, 270, 271 and 272); (3) Scalenohedral, in 
which the scalenohedrons predominate, often with prism faces 



CALCITE 



205 



and rhombohedral truncations (Figs. 275, 276, 277, 278 and 
A, pi. VIII). All possible combinations and variations of these 






Fig. 275. 



Fig. 276. 



Fig. 277. 



types. Twinning according to several different laws frequent. 
Fig. 279 represents one type of twinning in which the basal 
plane is the twinning plane. 





Fig. 278. 



Fig. 279. 



Structure. Crystallized or crystalline granular, coarse to fine. 
Also fine-grained to compact, earthy. In stalactitic forms, etc. 

Physical Properties. Perfect cleavage parallel to unit rhom- 
bohedron (angle of rhombohedron = 105 and 75). H.= 3. 
G. = 2.72. Luster vitreous to earthy. Color usually white or 
colorless. May be variously tinted, gray, red, green, blue, 
yellow, etc. Also, when impure, brown to black. Usually 
transparent to translucent. Opaque when impure. Strong 
double refraction, hence the name doubly-refracting spar. 

Tests. Infusible. After intense ignition, residue gives alka- 
line reaction to moistened test paper. Fragment moistened with 



206 MANUAL OF MINERALOGY 

hydrochloric acid and heated gives orange-red flame. Frag- 
ments effervesce freely in cold dilute hydrochloric acid. Concen- 
trated solution gives precipitate of calcium sulphate when a few 
drops of sulphuric acid are added; no precipitate will form if 
solution is dilute. Distinguished by its softness (3), its perfect 
cleavage, light color, vitreous luster, etc. Distinguished from 
dolomite by the fact that fragments of calcite effervesce freely 
in cold hydrochloric acid, while those of dolomite do not. 

Varieties. 1. Ordinary. Calcite in cleavable or crystalline 
masses. When transparent and colorless known as Iceland spar, 
because of its occurrence in quantity in Iceland. 

2. Limestone, Marble, Chalk. Calcite exists in enormous 
quantities in the form of limestone rocks, which form a large 
part of the sedimentary strata of the earth. When these rock 
masses have been subjected to great heat and pressure they 
develop a crystalline structure, usually showing cleavage faces 
of greater or less size. Crystalline limestones are known as 
marble. On account of various impurities and through the 
presence in them of other minerals, they assume a wide range of 
colors, and form a long series of ornamental stones to which 
various names are given. Chalk is a very fine-grained, pulveru- 
lent deposit of calcium carbonate, occurring at times in large 
beds. It has been formed through the slow accumulation on 
the sea bottom of fragments of shells and of the skeletons of 
minute sea animals. 

3. Cave Deposits, etc. Calcareous waters often deposit calcite 
in the form of stalactites, concretions, incrustations, etc. It is 
usually semitranslucent, of light-yellow colors. Many caves in 
limestone regions are lined with such deposits. Hot calcareous 
spring waters may form a deposit of calcite, known as travertine, 
around their mouths. Such a deposit is being formed at the 
Mammoth Hot Springs, Yellowstone Park. 

4. Siliceous Calcites. Calcite crystals may inclose consider- 
able amounts of quartz sand (up to 60 per cent) and form what 
are known as sandstone crystals. Such occurrences are found 
at Fontainebleau, France (Fontainebleau limestone), and in the 
Bad Lands, South Dakota. 



CALCITE 207 

Occurrence. Calcite is one of the most common and widely 
diffused of minerals. It occurs as enormous and widespread sedi- 
mentary rock masses, in which it is the predominant, at times prac- 
tically the only mineral present. Such rocks are the limestones, 
marbles (metamorphosed limestones), chalks, calcareous marls, cal- 
careous sandstones, etc. The limestone rocks have, in great part, 
been formed by the deposition on a sea bottom of great thicknesses 
of calcareous material in the form of shells, skeletons of sea ani- 
mals, etc. A smaller proportion of these rocks have been formed 
directly by precipitation of calcium carbonate. It occurs as a 
secondary mineral in igneous rocks as a product of decomposition 
of lime silicates. It is found lining the amygdaloidal cavities in 
lavas. It occurs in many sedimentary and metamorphic rocks in 
greater or less proportion. It is the cementing material in the light- 
colored sandstones. Calcite is also one of the most common of 
vein minerals, occurring as a gangue material, with all sorts of 
metallic ores. 

It would be quite impossible to specify all of the important dis- 
tricts for the occurrence of calcite in its various forms. Some of 
the more notable localities in which finely crystallized calcite is 
found are as follows: Andreasberg in the Harz Mountains; various 
places in Saxony; in Cumberland, Derbyshire, Devonshire, Corn- 
wall, Lancashire, England; Iceland; Guanajuato, Mexico; Joplin, 
Missouri; Lake Superior copper district; Rossie, New York, etc. 

Use. The most important use for calcite is for the manu- 
facture of lime for mortars and cements. Limestone when 
heated to about 1000 F. loses its carbonic acid, and is converted 
.into quicklime, CaO. This, when mixed with water (staked 
lime), swells, gives off much heat, and finally by absorption of 
carbon dioxide from the air hardens, or, as commonly termed, 
"sets." Quicklime when mixed with sand forms the common 
mortar used in building. Certain limestones contain various 
clayey materials as impurities. Cements made from these lime- 
stones have the valuable property of hardening under water, 
and are known as hydraulic cements. Many hydraulic cements 
are made up artificially by combining their ingredients in experi- 
mentally determined proportions. The chemistry of the process 
of their hardening is not fully understood, but various silicates 
of calcium and aluminium are probably formed. Portland 
cement, used so largely in concrete construction, is a mixture 
of about 6 parts of lime, 2 parts of silica, and 1 part of alumina. 



208 



MANUAL OF MINERALOGY 



Chalk is used as a fertilizer, for whiting and whitewash, for 
crayons, etc. It is found in many places in Europe, the chalk 
cliffs of Dover being famous. 

Limestone is largely used as a building material, and is ob- 
tained in the United States chiefly from Pennsylvania, Indiana, 
Ohio, Illinois, New York, Missouri, Wisconsin. Limestone is 
largely used as a flux for smelting various metallic ores. A 
fine-grained limestone is used in lithographing. 

Marbles are used very extensively as ornamental and building 
material. The most important marble quarries in the United 
States are found in Vermont, New York, Georgia, Tennessee, etc. 

Iceland spar is valuable for optical instruments, being used in 
the form of the Nicol prism to produce polarized light. Obtained 
at present only from Iceland. 

Dolomite. 

Composition. Carbonate of calcium and magnesium, 
CaMg(C0 3 ) 2 = Carbon dioxide 47.8, lime 30.4, magnesia 21.7. 
Varieties occur in which the proportion of CaC0 3 to MgC0 3 
is not as 1 : 1. Small amounts of ferrous carbonate frequently 
replace some of the magnesium carbonate. Manganese is also 
present at times. 





Fig. 280. 



Fig. 281. 



Crystallization. Hexagonal-rhombohedral. Crystals are 
usually the unit rhombohedron (cleavage rhombohedron) (Fig. 
280). Faces often curved, and sometimes so acutely as to form 
"saddle-shaped" crystals (Fig. 281). Other forms rare. 

Structure. In coarse, granular, cleavable masses to fine- 
grained and compact and in crystals. 



PLATE VIII. 





B. Aragonite, Cleator Moor, England. 



MAGNESITE 209 

Physical Properties. Perfect rhombohedral cleavage (cleav- 
age angle = 106 15'). H. = 3:5-4. G. = 2.85. Vitreous lus- 
ter; pearly in some varieties (pearl spar). Color usually some 
shade of pink, flesh color; may be colorless, white, gray, green, 
brown and black. Transparent to translucent. 

Tests. Infusible. After intense ignition a fragment will give 
an alkaline reaction to moistened test paper. Readily soluble, 
with effervescence in hot hydrochloric acid; fragment only slowly 
attacked by cold dilute acid (difference from calcite). Solution 
oxidized by nitric acid and then made ammoniacal (may pre- 
cipitate ferric hydroxide) will with ammonium oxalate give a 
white precipitate of calcium oxalate; nitrate with sodium phos- 
phate gives granular white precipitate of ammonium magnesium 
phosphate. Crystallized variety told by its curved rhombohe- 
dral crystals and usually by its flesh-pink color. 

Occurrence. Dolomite occurs chiefly in widely extended rock 
masses as dolomite limestone and marble. Occurrence same as for 
calcite rocks. The two varieties can only be told apart by tests, 
the simplest being to see if a drop of cold hydrochloric acid placed 
on the rock will produce effervescence (if so, rock is calcite; if not, 
dolomite). Often intimately mixed with calcite. Occurs also as a 
vein mineral, chiefly in the lead and zinc veins that traverse lime- 
stone. Found in large rock strata in the dolomite region of southern 
Tyrol; Binnenthal, Switzerland; northern England; Joplin, Mis- 
souri, etc. 

Use. As a building and ornamental stone. For the manu- 
facture of certain cements. For the manufacture of magnesia 
used in the preparation of refractory linings of the converters in 
the basic steel process. 

Ankerite, CaC0 3 .(Mg,Fe,Mn)C0 3 , is a subspecies interme- 
diate between calcite, dolomite and siderite. 

Magnesite. 

Composition. Magnesium carbonate, MgC0 3 = Carbon di- 
oxide 52.4, magnesia 47.6. Iron carbonate also often present. 

Crystallization. Hexagonal-rhombohedral. In rhombohe- 
dral crystals. 



210 MANUAL OF MINERALOGY 

Structure. Compact earthy forms common, also less fre- 
quently in cleavable granular masses, coarse to fine. Also com- 
pact. Crystals rare. 

Physical Properties. Perfect rhombohedral cleavage, some- 
times distinct. H. = 3.5-4.5. G. = 3-3.1. Vitreous luster. 
Color white, gray, yellow, brown. Transparent to opaque. 

Tests. Infusible. After intense ignition gives a faint alkaline 
reaction on moistened test paper. Scarcely acted upon by cold 
but dissolves with effervescence in hot hydrochloric acid. Solu- 
tion, after the precipitation of any iron and calcium, gives in 
the presence of an excess of ammonia, with sodium phosphate, a 
white granular precipitate of ammonium magnesium phosphate. 

Occurrence. Found associated with serpentine rocks as a product 
of their alteration, with dolomite, brucite, etc. Magnesite is mined 
to a small extent in Tulare County, California. Most of the mag- 
nesite used in the United States is imported, coming chiefly from 
Stryia in Austria-Hungary and from Greece. 

Use. Magnesite is chiefly used in the preparation of mag- 
nesite bricks for refractory linings in metallurgical furnaces. 
Also used in the preparation of magnesium salts (Epsom salts, 
magnesia, etc.). 

Siderite. Spathic Iron. Chalybite. 

Composition. Ferrous carbonate, FeC0 3 = Carbon dioxide 
37.9, iron protoxide 62.1, iron = 48.2. Manganese, magnesium 
and calcium may be present in small amounts. 

Crystallization. Hexagonal-rhombohedral. Crystals usually 
unit rhombohedrons (same as cleavage form), frequently with 
curved faces. 

Structure. Usually cleavable granular. At times botryoidal, 
compact and earthy. More rarely in crystals. 

Physical Properties. Perfect rhombohedral cleavage (cleav- 
age angle = 107). H. = 3.5-4. G. = 4.5-5. Vitreous luster. 
Color usually light to dark brown. Transparent to opaque. 

Tests. Difficultly fusible (4.5-5). Becomes strongly mag- 
netic on heating. Heated in C. T. decomposes and gives a 
black magnetic residue. Soluble in hydrochloric acid with 



RHODOCHROSITE 211 

effervescence; solution gives with potassium ferricyanide a dark 
blue precipitate (test for ferrous iron). Recognized usually by 
its color and cleavage. 

Varieties. 1. Crystallized. In crystals or granular cleavable 
masses. 

2. Concretionary. In globular concretions. 

3. Clay Ironstone. Impure by admixture with clay materials. 
Sometimes in concentric layers. Forms stratified bodies with 
coal formations, etc. 

4. Black-band Ore. An impure stratified deposit of siderite, 
containing considerable carbonaceous matter. Associated with 
coal beds. 

Occurrence. Found in the form of clay ironstone and black-band 
ore in extensive stratified formations associated with coal measures. 
These ores are the chief source of iron in Great Britain and are found 
in Staffordshire, Yorkshire and Wales. Clay ironstone is also abun- 
dant in the coal measures of western Pennsylvania and eastern Ohio, 
but it is not used to any great extent as an ore. Siderite, in its 
crystallized form, is a common vein mineral associated with various 
metallic ores, as silver minerals, pyrite, chalcopyrite, tetrahedrite, 
galena, etc. 

Name. The original name for the mineral was spherosiderite, 
given to the concretionary variety and subsequently shortened 
to siderite to apply to the entire species. Spathic ore is a com- 
mon name. Chalybite, used by some mineralogists, was derived 
from the Chalybes, who lived on the Black Sea, and were in 
ancient times workers in iron. 

Use. An ore of iron. Important in Great Britain, but of 
very subordinate value in the United States. 

Rhodochrosite. 

Composition. Manganese protocarbonate, MnC0 3 = Carbon 
dioxide 38.3, manganese protoxide 61.7. Iron is usually pres- 
ent, replacing a part of the manganese and sometimes calcium, 
magnesium, zinc, etc. 

Crystallization. Hexagonal -rhombohedral. Crystals unit 
rhombohedrons (same as cleavage rhombohedron), frequently 
with curved faces. 



212 MANUAL OF MINERALOGY 

Structure. Usually cleavable massive; granular to compact. 
Rarely in crystals. 

Physical Properties. Perfect rhombohedral cleavage (cleav- 
age angle = 107). H. = 3.5-4.5. G. = 3.45-3.6. Vitreous 
luster. Color usually some shade of rose-red; may be light pink 
to dark brown. Transparent to translucent. 

Tests. Infusible. Soluble in hot hydrochloric acid with 
effervescence. Gives reddish violet color to borax bead when 
heated in 0. F. Told usually by its pink color, rhombohedral 
cleavage and hardness (4). Distinguished by its hardness from 
rhodonite (MnSi0 3 ) (H. = 5.5-6.5). 

Occurrence. A comparatively rare mineral, occurring in veins 
with ores of silver, lead and copper, and with other manganese 
minerals. Found in the silver mines of Hungary and Saxony. In 
the United States at Branch ville, Connecticut; Franklin, New 
Jersey; in good crystals at Alicante, Colorado, etc. 

Name. Derived from two Greek words meaning rose and 
color, in allusion to its rose-pink color. 
Use. A minor ore of manganese. 



Smithsonite. 

Composition. Zinc carbonate, ZnC0 3 = Carbon dioxide 35.2, 
zinc protoxide 64.8. Iron and manganese often replace a part 
of the zinc; also at times calcium and magnesium. 

Crystallization. Hexagonal-rhombohedral. Rarely in small 
rhombohedral or scalenohedral crystals. 

Structure. Usually reniform, botryoidal or stalactitic and in 
crystalline incrustations or in honeycombed masses known as 
dry-bone ore. Also granular to earthy. Distinct crystals rare. 

Physical Properties. Perfect rhombohedral cleavage, which, 
on account of the usual structure, is seldom observed. H. = 5 
(unusually high for a carbonate). G. = 4.30-4.35. Vitreous 
luster. Color usually dirty brown. May be white, green, blue, 
pink, etc. Translucent to opaque. 

Tests. Infusible. Soluble in hydrochloric acid with effer- 
vescence. A fragment heated B. B. in R. F. gives bluish green 



ARAGONITE GROUP 213 

streaks in the flame, due to the burning of the volatilized zinc. 
Heated in R. F. on charcoal gives a nonvolatile coating of zinc 
oxide, yellow when hot, white when cold; if coating is moistened 
with cobalt nitrate and again heated it turns green. Distin- 
guished by its effervescence in acids, its tests for zinc, its hard- 
ness (5) and its high specific gravity. 

Occurrence. It is a zinc ore of secondary origin. Found in con- 
nection with zinc deposits near the surface, and where the oxidized 
ores have been acted upon by carbonated waters. Common in 
connection with zinc deposits lying in limestone rocks. Associated 
with sphalerite, galena, calamine, cerussite, calcite, limonite, etc. 
Often found in pseudomorphs after calcite. "Dry-bone ore" is a 
honeycombed mass, with the appearance of dried bone, whose 
structure has resulted from the manner of deposition of the mineral. 
Some calamine, the silicate of zinc, is included under the term. 
Occurs, as an ore, in the zinc deposits of Missouri, Arkansas, Wis- 
consin, Virginia, etc. Found at times in translucent green or 
greenish blue material which is available for ornamental uses. Such 
smithsonite is found at Laurium, Greece, and at Kelly, New Mexico. 

Name. Named in honor of James Smithson (1754-1829), 
who founded the Smithsonian Institution at Washington. Eng- 
lish mineralogists call the mineral calamine, using either electric 
calamine or hemimorphite as the name for the silicate. 

Use. An ore of zinc. 



ARAGONITE GROUP. 

The Aragonite Group consists of a series of carbonates of the 
bivalent metals, calcium, strontium, barium and lead, which 
crystallize in the Orthorhombic System with closely related crys- 
tal constants and similar habits of crystallization. All of them 
appear at times in twin crystals which are pseudohexagonal in 
character. The members of the group are: 

Aragonite, CaC0 3 . 
Strontianite, SrC0 8 . 
Witherite, BaC0 8 . 
Cerussite, PbCO,. 



214 



MANUAL OF MINERALOGY 



Aragonite. 

Composition. Calcium carbonate, like calcite, CaC0 3 = Car- 
bon dioxide 44, lime 56. May contain a little strontium or lead, 
rarely zinc. 

Crystallization. Orthorhombic. Three prominent habits of 
crystallization: (1) Acicular pyramidal; consisting of a prism 
terminated by a combination of a very steep pyramid and 
brachydome (see Fig. 282; and B, pi. VIII). Usually in radi- 
ating groups of large to very small crystals. (2) Tabular; con- 
sisting of prominent brachypinacoid faces modified by a prism 




rA 





Fig. 282. 



Fig. 283. 



Fig. 284. 



Fig. 285. 



and a low brachydome (Fig. 283) . Often twinned with a prism 
face as a twinning plane (Fig. 284). (3) In pseudohexagonal 
twins (Fig. 285). This type shows a hexagonal-like prism ter- 
minated by a basal plane, and is formed by an intergrowth of 
three individuals with basal planes in common and their prism 
faces falling partly in the same plane, and partly with only 
slightly different positions. The crystals are distinguished from 
true hexagonal forms by noting that the basal plane is striated 
in three different directions, and also by the fact that, because 
the prism angle of the simple crystals is not exactly 60, the 
composite prism faces for the twin will often show slight re- 
entrant angles. 

Structure. In crystals. Also reniform, columnar, stalactitic, 
etc. 



WITHERITE 215 

Physical Properties. Vitreous luster. Colorless, white, pale 
yellow and variously tinted. Transparent to translucent. H.= 
3.5-4. G.= 2.95 (harder and heavier than calcite). 

Tests. Infusible. Decrepitates. After intense ignition the 
powder gives an alkaline reaction on moistened test paper. 
Fragments fall to powder (change to calcite) when heated at low 
redness in C. T. Chemical tests same as for calcite (page 205). 
Distinguished from calcite by its lack of cleavage, and the fact 
that fragments fall to powder when heated in C. T. 

Occurrence. Less stable than calcite and much less common in 
its occurrence. Usually found as a vein mineral. Experiments have 
shown that carbonated waters containing calcium more often deposit 
aragonite when they are hot and calcite when they are cold. Some sea 
shells are composed entirely or in part of aragonite. The pearly layer 
of many shells is aragonite. It has been noted that the aragonite 
shells are not readily preserved as fossils, being easily dissolved or 
disintegrated, or at times apparently slowly changing to calcite. 
Aragonite is most commonly found associated with beds of gypsum and 
deposits of iron ore (where it sometimes occurs in forms resembling 
coral, and is called flos Jerri, flower of iron). At times found lining 
amygdaloidal cavities in basalt. Found frequently with pyrite, 
chalcopyrite, galena, malachite, etc. Notable localities for the 
various crystalline types are as follows: Pseudohexagonal twin 
crystals are found at Aragon, Spain; Bastennes, in the south of 
France; and at Girgenti, Sicily. The tabular type of crystals is 
found near Bilin, Bohemia. The acicular type is found at Alston 
Moor and Cleator, Cumberland, England. Flos ferri is found in 
the Stryian iron mines. Stalactitic forms occur in Buckingham- 
shire and Devonshire, England, and Lanarkshire, Scotland. A 
fibrous banded form of a delicate blue color comes from Chile. 

Witherite. 

Composition. Barium carbonate, BaC0 3 = 
Carbon dioxide 22.3, barium oxide 77.7. 

Crystallization. Orthorhombic. Crystals 
always twinned, forming pseudohexagonal pyra- 
mids by the intergrowth of three individuals 
terminated by brachy domes (Fig. 286). Crys- 
tals sometimes doubly terminated ; often deeply 
striated horizontally and by a series of re- Fig. 286. 




216 MANUAL OF MINERALOGY 

entrant angles have the appearance of one pyramid capping 
another. 

Structure. In twin crystals, also botryoidal to globular; 
columnar or granular. 

Physical Properties. H. = 3.5. G. = 4.3. Vitreous luster. 
Colorless, white, gray. Translucent. 

Tests. Easily fusible at 2.5-3, giving a yellowish green flame 
(barium). After intense ignition gives an alkaline reaction on 
moistened test paper. Soluble in hydrochloric acid with effer- 
vescence. All solutions, even the very dilute, give precipitate of 
barium sulphate with sulphuric acid (difference from calcium 
and strontium). Heavy. 

Occurrence. A comparatively rare mineral. Found in fine crys- 
tals at Hexham in Northumberland and Alston Moor in Cumber- 
land. Occurs at Tarnowitz in Silesia; Leogang in Salzburg; near 
Lexington, Kentucky; Thunder Bay, Lake Superior. 

Use. A minor source of barium compounds. 



Strontianite. 

Composition. Strontium carbonate, SrC0 3 = Carbon dioxide 
29.9, strontia 70.1. A little calcium sometimes present. 

Crystallization. Orthorhombic. Crystals usually acicular, 
like type (1) under aragonite. Twinning also frequent, giving 
at times pseudohexagonal forms. 

Structure. Radiating crystallized, also columnar; fibrous 
and granular. 

Physical Properties. H.= 3.5-4. G.= 3.7. Vitreous luster. 
White, gray, yellow, green. Transparent to translucent. 

Tests. Infusible. On intense ignition throws out fine 
branches and gives a crimson flame (strontium) and residue 
gives alkaline reaction on moistened test paper. Effervescence 
in hydrochloric acid, and the mediumly dilute solution will give 
precipitate of strontium sulphate on addition of a few drops of 
sulphuric acid; no precipitate will form in the very dilute solu- 
tion (difference from calcium and barium). Usually necessary 
to make the above tests to determine the mineral. 



PLATE IX. 




Cerussite, Broken Hill, New South Wales. 



CERUSSITE 



217 



Occurrence. A comparatively rare mineral. Originally found 
at Strontian in Argyllshire. Occurs also with lead ores at Pateley 
Bridge Yorkshire; at Hamm and Miinster, Westphalia; at Schoharie, 
New York, etc. 

Use. Has no great commercial use. A minor source of stron- 
tium compounds, used in fireworks and in the separation of 
sugar from molasses. 

Cerussite. 

Composition. Lead carbonate, PbC0 3 = Carbon dioxide 
16.5, lead, oxide 83.5. 

Crystallization. Habit varied and crystals show many forms. 
Crystals often tabular parallel to brachy- 
pinacoid (Fig. 287). Frequently twinned, 
forming lattice-like groups with the plates 
crossing each other at 60 angles (pi. IX). 
Sometimes pyramidal in habit; also twinned 
in pseudohexagonal pyramids, frequently 
with deep reentrant angles in the prism 
zone. 

Structure. In crystals or in granular 
crystalline aggregates; fibrous; granular 
massive; compact; earthy. 

Physical Properties. H.= 3-3.5. G.= 6.55 (high for a 
mineral with nonmetallic luster). Adamantine luster. Color- 
less, white or gray. Transparent to almost opaque. 

Tests. Easily fusible (1.5). With sodium carbonate B. B. 
on charcoal gives globule of lead and yellow to white coating of 
lead oxide. Soluble in warm dilute nitric acid with effervescence. 
In C. T. usually decrepitates and is changed to lead oxide, which 
is dark yellow when hot. Recognized by its high specific gravity, 
white color and adamantine luster. 

Occurrence. An important and widely distributed lead ore of 
secondary origin, formed by the oxidation of galena in the presence 
of carbonated waters. Found in the upper and oxidized zone of 
lead veins, associated with galena, anglesite, sphalerite, smithsonite, 
silver ores, etc. Notable localities for its occurrence are Ems in 
Nassau; Mies, Bohemia; Nerchinsk, Siberia; Broken Hill, New 




Fig. 287. 



218 MANUAL OF MINERALOGY 

South Wales; Phoenix ville, Pennsylvania; Leadville, Colorado, 
various districts in Arizona, etc. 

Use. An important ore of lead. 



Phosgenite, a chlorocarbonate of lead (PbCl) 2 C0 3 , tetragonal 
in crystallization, is a rare member of the Anhydrous Carbonate 
Division. 

2. ACID, BASIC AND HYDROUS CARBONATES. 
Malachite. Green Copper Carbonate. 

Composition. Basic carbonate of copper, (Cu.OH) 2 C0 3 or 
CuC0 3 .Cu(OH) 2 = Carbon dioxide 19.9, cupric oxide 71.9, water 
8.2. Copper = 57.4. 

Crystallization. Monoclinic. Crystals usually slender pris- 
matic but seldom distinct. 

Structure. Usually radiating fibrous with botryoidal or stal- 
actitic structure (see Fig. C, pi. III). Often granular or earthy. 

Physical Properties. Perfect basal cleavage. H. = 3.5-4. 
G. = 3.9-4.03. Adamantine to vitreous luster in crystals; often 
silky in fibrous varieties; dull in earthy type. Color bright green. 
Translucent to opaque. 

Tests. Fusible (3), giving a green flame. With fluxes in R. F. 
on charcoal gives copper globule. Soluble in hydrochloric acid 
with effervescence. Solution turns deep blue with excess of 
ammonia. Much water in C. T. .Recognized by its bright 
green color and radiating fibrous structure. 

Occurrence. An important and widely distributed copper ore of 
secondary origin. Found in the oxidized portions of copper veins 
associated with azurite, cuprite, native copper, iron oxides and the 
various sulphides of copper and iron. Usually occurs in copper 
veins that lie in limestones. Notable localities for its occurrence 
are at Nizhni Tagilsk in the Ural Mountains; at Bembe on west 
coast of Africa; in the copper mines in Chile; in New South Wales. 
In the United States, an important copper ore in the southwestern 
copper districts; at Bisbee, Morenci, and other localities in Arizona; 
in New Mexico; at Cannanea, in northern Mexico. 



GAY-LUSSITE 219 

Name. Derived from the Greek word for mallows, in allusion 
to its green color. 

Use. An important ore of copper. Has been used to some 
extent as an ornamental material for vases, veneer for table tops, 
etc. 

Azurite. Chessylite. Blue Copper Carbonate. 

Composition. A basic carbonate of copper, Cu(Cu.OH) 2 (C0 3 ) 2 
or 2CuC0 3 .Cu(OH) 2 = Carbon dioxide 25.6, cupric oxide 69.2, 
water 5.2. Copper = 55.3. 

Crystallization. Monoclinic. Habit varied. Crystals fre- 
quently complex and distorted in development, sometimes in 
radiating spherical groups. 

Structure. Crystallized. In radiating botryoidal structure. 
Earthy. 

Physical Properties. H. = 3.5-4. G. = 3.77. Vitreous lus- 
ter. Intense azure-blue color. Transparent to opaque. 

Tests. Same as for malachite (which see). Characterized 
chiefly by its azure-blue color. 

Occurrence. Origin and associations same as for malachite. 
Found in fine crystals at Chessy, France; in Siberia; at Copper 
Queen Mine, Bisbee, Arizona. Widely distributed with copper 
ores. Not so common as malachite. 

Name. Named in allusion to its color. 
Use. An important ore of copper. 

Aurichalcite. 

A basic carbonate of zinc and copper, 2(Zn,Cu)CO 3 .3(Zn,Cu)(OH) 2 . 
In acicular crystals, forming drusy incrustations. H= 2. G. = 
3.6. Pearly luster. Color pale green to blue. Infusible. Soluble 
in hydrochloric acid with effervescence. Solution turns blue with 
ammonia in excess. Fused in R. F. on charcoal with sodium car- 
bonate gives a nonvolatile coating of zinc oxide (yellow when hot, 
white when cold). Water in C. T. A rare mineral, found in the 
oxidized zones of copper veins. 

Gay-Lussite. 

A hydrous carbonate of calcium and sodium, CaCO 3 .Na2CO 3 .5H 2 O. 
Monoclinic. In rude crystals with uneven surfaces. Often wedge- 



220 MANUAL OF MINERALOGY 

shaped. Prismatic cleavage. H. = 2-3. G. = 1.99. Vitreous lus- 
ter. Colorless, white, gray. Fusible at 1.5, giving yellow flame 
of sodium. Gives alkaline reaction after ignition. Effervesces in 
acids. Concentrated hydrochloric acid solution gives precipitate of 
calcium sulphate with sulphuric acid. A rare species, found in salt- 
lake deposits at Merida, Venezuela, and near Ragtown, Nevada. 

Other rarer species in this division include hydrozincite, 
ZnC0 3 .2Zn(OH) 2 ; trona, Na 2 C0 3 .HNaC0 3 .2H 2 0; hydromag- 
nesite, 3MgC0 3 .Mg(OH) 2 .3H 2 0. 

SILICATES. 

The silicates form the largest single section of the Chemical 
Classification of Minerals. They may be divided into (1) An- 
hydrous Silicates, (2) Hydrous Silicates. 

ANHYDROUS SILICATES. 

This section may be subdivided into (1) Disilicates, Poly sili- 
cates, being salts of di silicic acid, H 2 Si 2 6 , or polysilicic acid, 
H 4 Si 3 8 ; (2) Metasilicates, being salts of metasilicic acid, H 2 Si0 3 ; 
(3) Orthosilicates, being salts of orthosilicic acid, H 4 Si0 4 ; (4) Sub- 
silicates, including various basic species. 

1. DISILICATES, POLYSILICATES. 

The only representative of the disilicates of sufficient impor- 
tance to warrant mention here is the rare lithium mineral, petal- 
ite, LiAl(Si 2 6 ) 2 . 

THE FELDSPAR GROUP. 

The feldspars form one of the most important of mineral 
groups. They are polysilicates of aluminium with either potas- 
sium, sodium and calcium and rarely barium. They may belong 
to either the monoclinic or the triclinic systems but with the 
crystals of the different species resembling each other closely in 
angles, habits of crystallization, and methods of twinning. They 
all show cleavages in two. directions which make an angle of 90, 
or closely 90, with each other. Hardness is about 6 and spe- 
cific gravity 2.6. 



ORTHOCLASE 



221 



MONOCLINIC SECTION. 

Orthoclase. Potash Feldspar. 

Composition. Potassium-aluminium silicate, KAlSi 3 8 = 
Silica 64.7, alumina 18.4, potash 16.9. Soda sometimes re- 
places a portion of the potash. 

Crystallization. Monoclinic. Crystals are usually prismatic 
in habit and have as prominent forms ; clinopinacoid, base, prism, 
with often smaller orthodomes (Figs. 288, 289 and 290). Fre- 



m 



Fig. 289. 





Fig. 288. 



Fig. 290. 



quently twinned; Carlsbad with clinopinacoid as twinning plane 
(Fig. 291); Baveno with clinodome as twinning plane (Fig. 292); 
Manebach with base as twinning plane (Fig. 293). 




Fig. 291. 
Carlsbad Twin. 



Fig. 292. 
Baveno Twin. 



Fig. 293. 
Manebach Twin. 



Structure. Usually crystallized or coarsely cleavable to granu- 
lar; more rarely fine-grained, massive and cryptocrystalline. 



222 MANUAL OF MINERALOGY 

Physical Properties. Two prominent cleavages (one parallel 
to base, perfect: the other parallel to clinopinacoid, good), mak- 
ing an angle of 90 with each other. H. = 6-6.5. G. = 2.5-2.6. 
Luster vitreous. Colorless, white, gray, flesh-red, more rarely 
green. Streak white. 

Varieties. Common feldspar is the usual opaque variety. 
Adularia is white or colorless and translucent to transparent. 
Some adularia shows an opalescent play of colors, and is called 
moonstone. Most of the moonstones, however, belong to the 
members of the plagioclase feldspar series. Sanidine, or glassy 
feldspar, is a variety occurring in glassy, often transparent, 
phenocrysts in eruptive rocks. 

Tests. Difficultly fusible (5). Insoluble in acids. When 
mixed with powdered gypsum and heated on platinum wire gives 
the violet flame of potassium. Usually to be recognized by its 
color, hardness and cleavage. Distinguished from the other 
feldspars by its right-angle cleavage and the lack of striations 
on the best cleavage surface. 

Alteration. When acted upon by waters carrying carbon 
dioxide in solution, orthoclase alters, forming a soluble carbonate 
of potassium and leaving as a residue either a mixture of kaolin 
(H4Al 2 Si 2 9 ) and quartz (Si0 2 ), or of muscovite (H 2 K(AlSi0 4 ) 3 ) 
and quartz. Kaolin forms the chief constituent of clays and 
has been derived in this manner. 

Occurrence. One of the most common of minerals. Widely dis- 
tributed as a prominent rock constituent, occurring in all types of 
rocks; igneous, in granites, syenites, porphyries, etc.; sedimentary, 
in certain sandstones and conglomerates; metamorphic, in gneisses. 
Also in large crystals and cleavable masses in pegmatite veins, asso- 
ciated chiefly with quartz, muscovite and albite. These veins are 
to be found where granite rocks abound. Large veins of this char- 
acter from which feldspar is quarried in considerable amounts occur 
in the New England and Middle Atlantic states, chiefly in Maine, 
Connecticut, New York, Pennsylvania and Maryland. 

Name. The name orthoclase refers to the right-angle cleavage 
possessed by the mineral. Feldspar is derived from the German 
word j 'eld, field. 



MICROCLINE 223 

Use. Orthoclase is chiefly used in the manufacture of porce- 
lain. It is ground very fine and mixed with kaolin, or clay, and 
quartz. When heated to high temperature the feldspar fuses 
and acts as a cement to bind the material together. Fused 
feldspar also furnishes the major part of the glaze on porcelain 
ware. 

A rare barium feldspar, hyalophane (K 2 ,Ba)Al 2 Si40 w , belongs 
here. 

TRICLINIC SECTION. 

Microcline. 

Composition. Like orthoclase, KAlSi 3 8 = Silica 64.7, alu- 
mina 18.4, potash 16.9. 

Crystallization. Triclinic. Axial lengths and angles only 
slightly different from those of orthoclase. Ordinarily the crys- 
tals of the two species cannot be told apart except by very 
accurate measurements or a microscopical examination. Micro- 
cline crystals are usually twinned according to the same laws 
as orthoclase. Also microscopically twinned according to the 
albite and pericline laws, characteristic of the triclinic feldspars. 
A thin section of microcline under the microscope in polarized 
light usually shows a characteristic grating structure, caused by 
the crossing at nearly right angles of the twin lamellae formed 
according to these triclinic twinning laws. Orthoclase, being 
monoclinic, could not show such twinning. 

Structure. In cleavable masses or in crystals. 

Physical Properties. Cleavage parallel to base and brachy- 
pinacoid, with angle of 89 30' (orthoclase would have 90). 
H. = 6-6.5. G. = 2.54-2.57. Vitreous luster. Color white 
to pale yellow. Also sometimes green (Amazon stone) or red. 
Transparent to translucent. 

Tests. Same as for orthoclase. The two species only to be 
distinguished from each other by careful examination (see above) . 

Occurrence. Same as for orthoclase. Much that passes as ortho- 
clase in reality is microcline. Occurs with a green color in the Ural 
Mts. and at Pike's Peak, Colorado, and is known as Amazon stone. 



224 MANUAL OF MINERALOGY 

Name. Microcline is derived from two Greek words meaning 
little and inclined, referring to the slight variation of the cleavage 
angle from 90. 

Use. Same as for orthoclase. Amazon stone is at times 
polished and used as an ornamental material. 

THE PLAGIOCLASE FELDSPARS. ALBITE-ANORTHITE 

SERIES. 

The triclinic soda-lime feldspars embrace a series of isomor- 
phous minerals varying in composition from albite, NaAlSi 3 8 , to 
anorthite, CaAl 2 Si 2 8 . These two molecules can replace each 
other in any proportion, and as a consequence a practically com- 
plete series may be found from the pure soda feldspar, and then 
with gradually increasing amounts of the anorthite molecule, 
to the pure lime feldspar. Definite names have been given to 
various mixtures of these two molecules, the more important 
being listed below: 

Albite, NaAlSi 3 8 . 

Oligoclase, 3NaAlSi 3 8 .lCaAl 2 Si 2 8 . 

Andesine, lNaAlSi 3 8 .lCaAl 2 Si 2 8 . 

Labradorite, lNaAlSi 3 8 .3CaAl 2 Si 2 8 . 

Anorthite, CaAl 2 Si 2 8 . 

These triclinic feldspars crystallize in forms closely resembling 
those of the monoclinic orthoclase, and the axial lengths and in- 
clinations are also closely the same. This similarity in the crys- 
tal structure between the monoclinic and triclinic feldspars is 
best shown by a comparison of the cleavage angles of the different 
species, that of orthoclase being 90, of albite 86 24', and of 
anorthite 85 50'. The triclinic feldspars are often known as 
the plagioclase feldspars, because of their oblique cleavage. 

The crystals of the plagioclase feldspars are frequently twinned 
according to the various laws governing the twins of orthoclase, 
i.e., the Carlsbad, Baveno and Manebach laws. They are also 
practically always twinned according to one or both of two laws, 
known as the albite and pericline laws. The twinning plane 
in the albite law is the brachypinacoid, which corresponds to 
the clinopinacoid in orthoclase. The angle between the basal 



ALBITE 



225 



plane and this twinning plane is not 90, but about 86; so that 
if one imagines a triclinic feldspar crystal cut in two along this 
plane and one-half revolved 180 from its original position 
upon an axis perpendicular to the plane, there would then be 
formed a shallow trough along the upper surface of the crys- 
tal, because the basal planes of the two adjacent halves would 
not lie in the same plane, but rather slope at a slight angle 
toward each other. This sort of twinning is commonly repeated 
many times in a single crystal, and gives rise to thin lamellae, each 
one in twin position in respect to those on either side (see Figs. 
296 and 297). Consequently a basal plane or cleavage surface 
of such a twinned crystal will be crossed by a number of parallel 
groovings or striations (Fig. 298). Many times these striations 
are so fine as not to be visible to the unaided eye, but also at 
times they are coarse and easily seen. The presence of these 
striation lines upon the better cleavage surface of a feldspar is 
one of the best proofs that it belongs to the plagioclase series. 
In the pericline law the twinning axis is the b crystallographic 
axis, and when this results in polysynthetic twins the consequent 
striations are to be seen on the brachypinacoid. 

Albite. Soda-feldspar. 

Composition. Sodium-aluminium silicate, NaAlSi 3 8 = Silica 
68.7, alumina 19.5, soda 11.8. Calcium is usually present in 
small amount in the form of the anorthite molecule, CaAl 2 Si 2 8 . 

Crystallization. Triclinic. Usually in tabular crystals paral- 






Fig. 294. Fig. 295. Fig. 296. Albite Twin. 

lei to brachypinacoid (Fig. 294). Sometimes elongated parallel 
to 6 crystal axis (Fig. 295). Twinning very common, according 



226 MANUAL OF MINERALOGY 

to the albite law (see above) and evidenced by fine striation lines 
on the better cleavage surface (Figs. 297 and 298). Twinning 
according to the other laws frequent. 





Fig. 297. Fig. 298. Albite Twinning. 

Structure. Commonly massive, either lamellar with lamellae 
often curved or in cleavable masses. Distinct crystals rare. 

Physical Properties. Perfect cleavage parallel to base; good 
cleavage parallel to brachypinacoid. Cleavage angle 86 24'. 
H.= 6. G.= 2.62. Vitreous luster; sometimes pearly on cleav- 
age surface. Colorless, white, gray. Transparent to opaque. 

Tests. Fusible at 4-4.5, giving yellow flame (sodium). In- 
soluble in acids. Characterized by its hardness, white color, 
cleavage, frequently curved lamellar structure, striations on 
better cleavage .surface, etc. 

Occurrence. Like orthoclase, a widely distributed and important 
rock-making mineral. It occurs in all classes of rocks, but particu- 
larly in those of igneous origin, such as granites, syenites, porphy- 
ries arid felsite lavas. Found commonly, also, in pegmatite veins. 
Notable localities for albite are to be found in Switzerland and the 
Tyrol; in the United States at Paris, Maine; Chesterfield, Mas- 
sachusetts; Haddam and Branch ville, Connecticut; Amelia Court 
House, Virginia, etc. 

Name. From the Latin albus, white, in allusion to its color. 

Use. Has the same uses as orthoclase, but not so commonly 
employed. Some varieties, when polished, show an opalescent 
play of colors and are known as moonstones. Other members 



OLIGOCLASE 227 

of the plagioclase series and orthoclase show at times this same 
effect. The stones are usually cut in round or oval shapes and 
are valued up to $3 a carat. The finest moonstones come from 
Ceylon, but they are chiefly orthoclase. 

Oligoclase. 

Composition. Intermediate between albite and anorthite, 
chiefly near 3NaAlSi 3 8 .lCaAl 2 Si 2 8 . 

Crystallization. Triclinic. Like albite. 

Structure. Usually massive, cleavable to compact. Crystals 
rare. 

Physical Properties. Cleavage in two directions at 86 32'. 
One cleavage (parallel to base) is better than the other, and on 
this parallel striation lines due to twinning are commonly to be 
seen. H. = 6. G. = 2.66. Vitreous to pearly luster. Color usu- 
ally whitish with faint tinge of grayish green, also reddish white, 
etc. Translucent to opaque. 

Tests. Fusible at 4-4.5. Insoluble in hydrochloric acid. 
To be told from albite only by a test for calcium. Briefly, the 
test is made as follows: Fuse powdered mineral with sodium 
carbonate; dissolve fusion in hydrochloric acid and evaporate 
to dryness, moisten residue with water and a little nitric acid, 
boil and then filter off insoluble silica; to filtrate add ammonium 
hydroxide in excess, filter off precipitate of aluminium hydrox- 
ide; in filtrate get precipitate of calcium oxalate upon addition 
of ammonium oxalate. To be positively distinguished from an- 
desine and labradorite only by a chemical analysis or an optical 
examination. 

Occurrence. Like albite, but not so common. Found in various 
localities in Norway, notably at Tvedestrand, where it contains in- 
clusions of hematite, which give the mineral a golden shimmer and 
sparkle. Such feldspar is called aventurine oligoclase, or sunstone. 
Occurs in the United States at Fine and Macomb, St. Lawrence 
County, New York; Danbury and Haddam, Connecticut; Bakers- 
ville, North Carolina, etc. 

Name. Derived from two Greek words meaning little and 
fracture. 



228 MANUAL OF MINERALOGY 

Use. Occasionally used as an ornamental material, in the 
varieties sunstone and moonstone. 

Andesine. 

Composition. Intermediate between albite and anorthite, 
corresponding chiefly to lNaAlSi 3 8 .lCaAl 2 Si 2 8 . 

Crystallization. Triclinic. Like albite. 

Structure. In cleavable masses. Crystals rare. 

Physical Properties. Cleavage in two directions at 86 14'. 
One cleavage (parallel to base) better than the other, and on this 
parallel striation lines due to twinning are commonly to be seen. 
H. = 6. G.= 2.69. Vitreous to pearly luster. Color white, 
gray, greenish, yellowish, flesh-red. Often exhibits a beautiful 
play of colors, due partly to the intimate twinning and partly to 
inclusions. 

Tests. Same as for oligoclase. To be positively distinguished 
from oligoclase and labradorite only by a chemical analysis or 
an optical examination. 

Occurrence. Same as for albite, but less common. More fre- 
quently found in somewhat more basic igneous rocks, i.e., those 
containing less silica and more lime and magnesia. 

Name. Occurs in a rock called andesite, found in the Andes 
Mountains. 

Labradorite. 

Composition. Intermediate between albite and anorthite, 
corresponding chiefly to lNaAlSi30 8 .3CaAl 2 Si208. 

Crystallization. Triclinic. Like albite. 

Structure. In cleavable masses. Crystals rare. 

Physical Properties. Cleavage in two directions at 86 5'. 
One cleavage (parallel to base) better than the other, and on this 
parallel striation lines due to twinning are commonly" shown. 
H. = 6. G. = 2.73. Vitreous luster. Usually gray, brown or 
greenish; sometimes colorless or white. Often shows a beautiful 
play of colors, due in part to the intimate twinning structure, 
in part to inclusions. Transparent to ODaque. 

Tests. Same as for oligoclase. 



LEUCITE 229 

Occurrence. Like albite, but more commonly in the darker 
colored basic igneous rocks, and usually associated with pyroxene 
or amphibole. Found on the coast of Labrador in large amounts, 
associated with hypersthene and magnetite, and when polished 
showing a fine iridescent play of colors. 

Use. As an ornamental stone. 

Anorthite. 

Composition. Calcium-aluminium silicate, CaAl 2 Si 2 8 = Silica 
43.2, alumina 36.7, lime 20.1. Soda is usually present, in small 
amount, in the albite molecule, NaAlSi 3 8 . 

Crystallization. Triclinic. Crystals usually prismatic paral- 
lel to vertical axis. Twinning common according to albite and 
pericline laws (see above). . 

Structure. Massive cleavable. Crystals rare. 

Physical Properties. Cleavage in two directions at 85 50'. 
One cleavage (parallel to base) better than the other. H.= 6. 
G. = 2.75. Vitreous to pearly luster. Color white, grayish, 
reddish. Transparent to opaque. 

Tests. Fusible at 4.5. Dissolves slowly in hydrochloric acid 
and yields a silica jelly upon evaporation. Gives a strong test 
for calcium (see under oligoclase) and only a slight yellow flame 
(sodium). 

Occurrence. A rock-making mineral, particularly in the dark- 
colored basic igneous rocks. Associated with various calcium and 
magnesium silicates. Found in the lavas of Mount Vesuvius; of 
Japan, etc. 

Name. Derived from the Greek word meaning oblique, be- 
cause of its triclinic crystallization. 

2. METASILICATES. 
Leucite. 

Composition. A metasilicate of aluminium and potassium, 
KAl(Si0 3 ) 2 = Silica 55.0, alumina 23.5, potash 21.5. 

Crystallization. Isometric. Trapezohedral habit (Fig. 299). 
Other forms rare. Strictly isometric only at temperatures of 




230 MANUAL OF MINERALOGY 

500 C. or over. On cooling below this temperature it under- 
goes an internal molecular rearrangement to that of some other 
crystal system, but the external form does 
not. change. It is formed in lavas at 
high temperatures and is then isometric 
in internal structure as well as outward 
form. 

Structure. Usually in distinct crys- 
tals, also in disseminated grains. 

Physical Properties. H. = 5.5-6. 
Fi 299 G. = 2.5. Vitreous to dull luster. Color 

white to gray. Translucent to opaque. 
Tests. Infusible. Decomposed by hydrochloric acid with 
the separation of silica but without the formation of a jelly. 
Addition of ammonia to the solution gives precipitate of alu- 
minium hydroxide. When mixed with powdered gypsum and 
fused gives violet potassium flame (best observed through a 
blue glass). 

Occurrence. A rather rare mineral, occurring almost wholly in 
lavas. Found in rocks in which the amount of potassium in the 
magma was in excess of the amount necessary to form feldspar. Is 
not observed, therefore, in rocks that show quartz. Chiefly found 
in the rocks of central Italy; notably as phenocrysts in the lavas 
of Vesuvius. Pseudomorphs after leucite are found in syenites of 
Arkansas, Montana, Brazil, etc. 

Name. From a Greek word meaning white. 

Pollucite, H 2 Cs2Al 2 (Si03) 6 , is a rare mineral that belongs in the 
same group as leucite. 

PYROXENE GROUP. 

The Pyroxene Group includes a series of related metasilicates 
which have calcium, magnesium and ferrous iron as the im- 
portant bases, also manganese and zinc. Further certain mole- 
cules contain the alkalies and aluminium and ferric iron. They 
may belong to either the orthorhombic, monoclinic or triclinic 
systems, but the crystals of the different species are closely 
similar in many respects. 



PYROXENE 281 

ORTHORHOMBIC SECTION. 
Enstatite, Bronzite, Hypersthene. 

A group of orthorhombic members of the pyroxene group, en- 
statite being magnesium metasilicate, MgSiO 3 ; bronzite, the same as 
enstatite, with small amounts of iron replacing the magnesium; 
hypersthene, an iron-magnesium metasilicate, (Mg,Fe)SiOs. Dis- 
tinct crystals rare. Usually foliated massive with good cleavage; 
fibrous, etc. Color from white in enstatite to green and brown with 
increase in iron. Rock-making minerals, occurring like the mono- 
clinic pyroxenes but much rarer. Found in basic igneous rocks, 
such as peridotite, gabbro, etc. 

Pyroxene. 

Composition. Pyroxene is a metasilicate, varying in its com- 
position. It contains as bases chiefly calcium and magnesium, 
with smaller amounts of ferrous iron. In some varieties, how- 
ever, molecules are introduced in which are the alkalies (chiefly 
sodium), aluminium and ferric iron. The more important varie- 
ties of pyroxene with the formulas assigned to them follow. 

Diopside, CaMg(Si0 3 ) 2 . 

Common pyroxene, Ca(Mg,Fe)(Si0 3 ) 2 . 

Augite, CaMg(Si0 3 ) 2 with MgAl 2 Si0 6 and NaAlSi 2 6 ; with 
iron isomorphous with both the magnesium and the alu- 
minium. 

These varieties form an isomorphous series, and all gradations 
between them appear. Other varieties of less common occur- 
rence are hedenbergite, CaFe(Si0 3 ) 2 ; schefferite, a manganese 
pyroxene; jeffersonite, a manganese-zinc pyroxene. 

Crystallization. Monoclinic. Crystals prismatic in habit; 
prism faces make angles of 87 and 93 with each other. The 
prism zone commonly shows the prism faces truncated by the 
faces of both vertical pinacoids, so that the crystals show, when 
viewed parallel to the vertical axis, a rectangular cross section 
with truncated corners. The interfacial angles in the prism 
zone are either exactly or very closely 90 and 45. The ter- 
minations vary, being made up frequently of a combination of 



232 



MANUAL OF MINERALOGY 



the basal plane with pyramids both in front and behind (Figs. 
300-302). 






Fig. 300. 



Fig. 301. 



Fig. 302. 



Structure. In crystals. Often lamellar. Coarse to fine gran- 
ular. 

Physical Properties. Prismatic cleavage sometimes good, 
often interrupted. Sometimes basal parting observed, often 
shown by twinning lamellae (see Fig. A, pi. X). H. = 5-6. 
G.= 3.2-3.6. Vitreous luster. Color varying from white and 
light green in diopside, to green in pyroxene, through dark green 
to black in augite. Color deepens with increase in the amount 
of iron present. Transparent to opaque. 

Tests. Fusible from 4 to 4.5. Insoluble in hydrochloric acid. 
To test for bases : fuse with sodium carbonate ; dissolve in nitric 
acid; evaporate to dryness; notice the formation of silica jelly; 
moisten residue with water and hydrochloric acid; boil and 
filter from insoluble silica; add ammonium hydroxide in excess, 
precipitate of aluminium and ferric hydroxide; to boiling filtrate 
add ammonium oxalate, precipitate of calcium oxalate; to filtrate 
add sodium phosphate, precipitate of ammonium magnesium 
phosphate. Recognized usually by its characteristic crystals. 

Occurrence. The pyroxenes are common and important rock- 
making minerals, being found chiefly in the dark colored igneous 
rocks, especially those whose magmas were rich in iron, calcium and 
magnesium. They are seldom to be found in rocks that contain 
much quartz. Augite is found in basaltic lavas, and in the dark 



PLATE X. 







A. Pyroxene showing Twinning Lamellae due to Basal Parting. 
B Spodumene Crystal from Huntington, Massachusetts. 
C Garnet Crystals in Mica-Schist. 



SPODUMENE 233 

colored intrusions known generally as trap, in gabbros and perido- 
tites. Diopside and common pyroxene are found sometimes in 
syenites and similar rocks; also as metamorphic minerals in impure 
recrystallized dolomitic limestones. Common pyroxene also occurs 
in some gneisses. In the limestones, pyroxene is often associated 
with tremolite, scapolite, vesuvianite, garnet, titanite, phlogopite, 
etc. In igneous rocks it is found with orthoclase, the plagioclase 
feldspars, nephelite, chrysolite, leucite, amphibole, magnetite, etc. 
Some of the notable localities, particularly for fine crystals, are the 
following: For diopside. Ala, Piedmont; Traversella; Nordmark, 
Sweden; in various localities in Orange County, New York; for 
augite, in the lavas of Vesuvius ; at Fassathal, Tyrol ; Bilin, Bohemia ; 
hedenbergite from Sweden and Norway; schefferite from Sweden; 
jeffersonite from Franklin, New Jersey. 

Names. The name pyroxene, stranger to fire, is a misnomer, 
and was given to the mineral because it was thought that it did 
not occur in igneous rocks. Diopside comes from two Greek 
words meaning double appearance. Augite comes from a Greek 
word meaning luster. 

Use. Clear green diopside or common pyroxene is occasion- 
ally used as a gem material. 

^Egirite or Acmite. 

A soda-ferric iron pyroxene, NaFe"'(SiO 3 ) 2 . Monoclinic. Slender 
prismatic crystals, often with steep terminations. Faces often im- 
perfect. Imperfect prismatic cleavage with 93 angle. H. = 6-6.5. 
G. = 3.5-3.55. Vitreous luster. Color brown or green. Trans- 
lucent to opaque. Fusible at 3.5, giving yellow sodium flame. 
Fused globule slightly magnetic. A comparatively rare rock-mak- 
ing mineral found chiefly in nephelite-syenite and phonolite. 

Spodumene. 

Composition. Lithium-aluminium metasilicate, LiAl(SiO s )2 = 
Silica 64.5, alumina 27.4, lithia 8.4. Usually has a small amount 
of sodium replacing the lithium. 

Crystallization. Monoclinic. Prismatic crystals, flattened 
frequently parallel to the orthopinacoid. Deeply striated ver- 
tically (see Fig. B, pi. X). Crystals usually coarse and with 
roughened faces. Sometimes very large. 

Structure. In crystals or cleavable masses. 



234 MANUAL OF MINERALOGY 

Physical Properties. Perfect prismatic cleavage. H. = 6.5- 
7. G. = 3.18. Vitreous luster. Color white, gray, pink, yel- 
low, green. Transparent to translucent when unaltered. 

Tests. Fusible at 3.5, throwing out fine branches at first, and 
then fusing to a clear glass. Gives a crimson flame (lithium). 
Insoluble in acids. 

Varieties. Ordinary. Color white or gray, sometimes pink. 
Commonly in flattened prismatic crystals, often very large. 
Frequently altered to other minerals. 

Hiddenite. A clear, transparent variety ranging in color from 
yellow-green to deep emerald. Found in small striated and 
etched crystals. 

Kunzite. A transparent variety ranging from pale pink to 
deep amethystine purple. Has been found in flattened crystals 
8 to 10 inches in length, 5 to 6 in breadth. 

Alteration. Spodumene very easily alters to other species, 
becoming dull and opaque. The alteration products include 
albite, eucryptite (LiAlSi0 4 ), muscovite, microcline. 

Occurrence. A comparatively rare species, but found occasion- 
ally in very large crystals in pegmatite veins. Occurs at Goshen, 
Chesterfield, Chester, Huntington and Sterling, Massachusetts; 
Branchville, Connecticut; Etta tin mine, Pennington County, South 
Dakota, in crystals measuring many feet in length. Hiddenite 
occurs with emerald beryl at Stony Point, Alexander County, 
North Carolina. Kunzite is found with pink beryl in San Diego 
County, California. 

Names. Spodumene comes from a Greek word meaning ash 
colored. Hiddenite is named for Mr. W. E. Hidden; kunzite for 
Dr. G. F. Kunz. ) 

Use. The varieties hiddenite and kunzite furnish very beauti- 
ful gem stones but are limited in their occurrence. 

Jadeite. 

A sodium-aluminium metasilicate, NaAl(SiO 3 )2. Massive, gran- 
ular to closely compact. H. = 6.5-7. G. = 3.33-3.35. Vitreous 
luster. Color white, gray to light green. Translucent to opaque. 
Very tough. Fuses at 2.5, coloring the flame yellow (sodium). 
Forms in part the material known as jade and highly prized by 
oriental peoples as an ornamental material. Made into finely carved 



PECTOLITE 235 

ornaments and utensils, and when of fine color and translucent com- 
mands a high price. Found chiefly in Upper Burmah, in southern 
China and in Thibet. 

Wollastonite. 

Composition. Calcium metasilicate, CaSi0 3 = Silica 51.7, 
lime 48.3. 

Crystallization. Monoclinic. Usually in tabular crystals, 
with either base or orthopinacoid prominent. 

Structure. Commonly massive, cleavable to fibrous; also 
compact. 

Physical Properties. Perfect cleavage parallel to orthopina- 
coid. H. = 5-5.5. G. = 2.8-2.9. Vitreous luster, pearly on 
cleavage surfaces. Sometimes silky when fibrous. Colorless, 
white or gray. Translucent to opaque. 

Tests. Fusible at 4 to a white, almost glassy globule. De- 
composed by hydrochloric acid, with the separation of silica but 
without the formation of a jelly. Filtered solution with ammo- 
nium hydroxide and ammonium carbonate gives white precipi- 
tate of calcium carbonate. 

Occurrence. Commonly found in crystalline limestones which 
have been metamorphosed either through the heat and pressure 
attendant upon the intrusion into them of igneous rocks or upon 
movements of the earth's crust. An impure limestone, containing 
quartz for instance, under these conditions will become crystalline, 
and new minerals, such as wollastonite, be formed. Associated with 
calcite, diopside, lime garnet, tremolite, lime feldspars, vesuvianite, 
epidote, etc. May at times be so plentiful as to constitute the chief 
mineral of the rock mass. Such wollastonite rocks are found in 
California, the Black Forest, Brittany, etc. More rarely found in 
feldspathic schists. 

Pectolite. 

Composition. HNaCa 2 (Si0 3 ) 3 = Silica 54.1, lime 33.8, soda 
9.3, water 2.7. 

Crystallization. Monoclinic. Crystals usually elongated 
parallel to the ortho-axis. 

Structure. Usually in aggregates of acicular crystals. Fre- 
quently radiating, with fibrous appearance. Sometimes com- 
pact. 



236 MANUAL OF MINERALOGY 

Physical Properties. Perfect cleavage parallel to the ortho- 
pinacoid. H. = 5. G. = 2.7-2.8. Vitreous to pearly luster. 
Colorless, white or gray. 

Tests. Fuses quietly at 2.5-3 to a glass; colors flame yellow 
(sodium). Decomposed by hydrochloric acid, with the separa- 
tion of silica but without the formation of a jelly. Filtered solu- 
tion with ammonium hydroxide and ammonium carbonate gives 
white precipitate of calcium carbonate. Water in C. T. 

Occurrence. A mineral of secondary origin similar in its occur- 
rence to the zeolites. Found lining amygdaloidal cavities in basalt, 
associated with various zeolites, phrenite, calcite, etc. Found at 
Bergen Hill and West Paterson, New Jersey. 



TRICLINIC SECTION. 
Rhodonite. 

Composition. Manganese metasilicate, MnSi0 3 = Silica 45.9, 
manganese protoxide 54.1. Iron, calcium and sometimes zinc 
replace a part of the manganese. 

Crystallization. Triclinic. Crystals 
commonly tabular parallel to base (Fig. 
303) . Crystals often rough with rounded 




Structure. Commonly massive, cleav- 
able to compact; in embedded grains. 
Fig ' nice' N?w a jSy Fur ~ Physical Properties. Prismatic cleav- 
age at about 92. H. = 6-6.5. G. = 3.63. 
Vitreous luster. Color rose-red, pink, brown. .Translucent to 
opaque. 

Tests. Fusible (3-3.5) to a nearly black glass. Insoluble in 
hydrochloric acid. In 0. F. gives clear reddish violet color to 
borax bead. 

Occurrence. Found at Langban, Sweden, with iron ore; found 
in large masses near Ekaterinburg, Urals; from Broken Hill, New 
South Wales. A zinciferous variety, known as foivlerite, occurs in 
good-sized crystals in limestone with franklinite, willemite, zincite, 
etc., at Franklin Furnace, New Jersey. 



AMPHIBOLE 237 

Name. Derived from the Greek word for a rose, in allusion 
to the color. 

Use. Sometimes polished for use as an ornamental stone. 
Obtained chiefly from the Urals. 

AMPHIBOLE GROUP. 

The minerals of the Amphibole Group crystallize in either the 
orthorhombic, monoclinic or triclinic systems, but the crystals 
of the different species are closely similar in many respects. 
Chemically they form a series parallel to that of the Pyroxene 
Group (page 230), being metasilicates with calcium, magnesium 
and ferrous iron as important bases, and also with manganese 
and the alkalies. Certain molecules that are present in some 
varieties contain aluminium and ferric iron. 

ORTHORHOMBIC SECTION. 
Anthopyllite. 

An orthorhombic amphibole, corresponding to the orthorhombic 
pryoxene group, enstatite bronzite hy persthene. An iron-mag- 
nesium metasilicate, (Mg,Fe)SiO3. Rarely in distinct crystals. 
Commonly lamellar or fibrous. Perfect prismatic cleavage. Color 
gray to various shades of green and brown. A comparatively rare 
mineral, occurring in mica-schist, etc. 

Amphibole. 

Composition. The amphiboles consist of a series of minerals 
analogous in many ways to the pyroxenes. They are chiefly 
metasilicates of calcium and magnesium with ferrous iron re- 
placing the magnesium. Other molecules are at times intro- 
duced, in which are the alkalies, aluminium and ferric iron. 
The more important varieties of amphibole with the formulas 
assigned to them follow. 

Tremolite, CaMg 3 (Si0 3 )4. 

Actinolite, Ca(Mg,Fe) 3 (Si0 8 )4. 

Hornblende, CaMg 3 (SiO,) 4 with NasAl,(SiOOi and Mg 2 Al 4 - 
(Si0 6 )2. Ferrous iron is isomorphous with the magnesium and 
ferric iron with the aluminium. 



238 



MANUAL OF MINERALOGY 



These varieties form an isomorphous series and all gradations 
between them occur. 

Crystallization. Monoclinic. Crystals prismatic in habit; 
the prism faces make angles of 55 and 125 with each other 
(compare the 87 and 93 angles of pyroxene). The prism zone 
shows, in addition to the prism faces, usually those of the 
clinopinacoid and sometimes also those of the orthopinacoid. 





Fig. 304. 



Fig. 305. 



Prism zone frequently vertically striated and imperfectly de- 
veloped. When the prism faces are distinct, the cross section 
of the crystal, when viewed in a direction parallel to the vertical 
axis, does not have the rectangular shape .shown by the crystals 
of pyroxene. The termination of the crystals is almost always 
formed by the two faces of a low clinodome (Figs. 304 and 305). 

Structure. In crystals. Often bladed and frequently in radi- 
ating columnar aggregates. Sometimes in silky fibers. Coarse 
to fine granular. Compact. 

Physical Properties. Perfect prismatic cleavage at angle of 
125, often yielding a splintery surface. H. = 5-6. G. = 3-3.3. 
Vitreous luster. Often with silky sheen in the prism zone. Color 
varying from white and light green in tremolite, to green in 
actinolite, through dark green to black in hornblende. Color 
deepens with increase in the amount of iron present. Trans- 
parent to opaque. 

Tests. Fusible 3-4. Chemical tests same as for pyroxene, 
which see. Told from pyroxene by its better prismatic cleavage, 



AMPHIBOLE 239 

by the difference in the prismatic angle and by the characteristic 
presence on the crystals of the low clinodome. 

Occurrence. Amphibole is an important and widely distributed 
rock-making mineral, occurring both in igneous and mctamorphic 
rocks, being particularly characteristic, however, of the latter. The 
fact that amphibole frequently contains hydroxyl and fluorine in- 
dicates that, in some degree, it is often of pneumatolytic origin. 
Tremolite is most frequently found in impure, crystalline, dolomitic 
limestones, where it has been formed during the crystallization of 
the rock, while undergoing metamorphism. Actinolite commonly 
occurs in the crystalline schists, being often the chief constituent of 
green-colored hornblende-schists and greenstones. Frequently the 
amphibole of such rocks has had its origin in the pyroxene contained 
in the igneous rock from which the metamorphic type has been 
derived. Common hornblende is found in igneous rocks, such as 
granites, syenites, diorites, gabbros, and in some peridotites; it 
rarely occurs in the dark traps and basalts. It also occurs in the 
metamorphic rocks, such as gneisses and hornblende schists. 

Notable localities for the occurrence of crystals are: tremolite 
from Campolongo, Tessin; from Russell, Gouverneur, Amity, Pierre- 
pont, De Kalb, etc., New York; actinolite from Greiner, Zillerthal, 
Tyrol; hornblende from Bilin, Bohemia; Monte Somma, Italy. 
Actinolite frequently comes fibrous, and is the material to which 
the name asbestos was originally given. Has been found in the 
metamorphic rocks in various states along the Appalachian Moun- 
tains. Nephrite is a tough, compact variety of actinolite which 
supplies much of the material known as jade (see also under jadeite). 
A famous locality for its occurrence is in the Kuen Lun Mountains, 
on the southern border of Turkestan. 

Names. Tremolite is derived from the Tremola Valley near 
St. Gothard. Actinolite comes from two Greek words meaning 
a ray and stone, in allusion to its frequently somewhat radiated 
structure. 

Uses. The fibrous variety is used to some extent as asbestos 
material. The fibrous variety of serpentine furnishes more 
and usually a better grade of asbestos. The compact variety, 
nephrite, is used largely for ornamental material by oriental 
peoples and is called jade. 

Among the other rarer monoclinic members of the Am- 
phibole Group are glaucophane, NaAl(Si0 3 )j.(Fe,Mg)SiOj; 



240 



MANUAL OF MINERALOGY 



riebeckite, 2NaFe(Si0 3 ) 2 .FeSi0 3 ; crocidolite, NaFe(Si0 3 ) 2 .FeSi0 3 ; 
arfvedsonite, Na 8 (Ca,Mg) 3 (Fe,Mn) 14 (Al,Fe) 2 Si2i045. 

TRICLINIC SECTION. 

The only member of the Triclinic Section of the Amphibole 
Group is the rare mineral cenigmatite, Na 4 Fe 9 AlFe" / (Si,Ti) I 20 38 . 



Beryl. 

Composition. Be 3 Al 2 Si 6 Oi 8 . Analyses show a small amount 
of water. Small amounts of the alkali oxides, often in part 
consisting of caesium oxide, frequently replace the beryllium 
oxide. 

Crystallization. Hexagonal. Strong prismatic habit. Fre- 
quently vertically striated and grooved. Forms usually present 



Fig. 306. 



Fig. 307. 



consist only of prism of first order and base (Fig. 306). Small 
pyramid faces of both the first and second orders sometimes 
occur, but the pyramid faces are rarely prominent (Fig. 307). 
Dihexagonal forms quite rare. Crystals frequently of consider- 
able size with rough faces. 

Structure. In crystals. Also massive, with indistinct colum- 
nar structure or granular. 

Physical Properties. H. = 7.5-8. G. = 2.75-2.8. Vitreous 
luster. Color commonly bluish green or light yellow; may 
be deep emerald-green, golden yellow, pink, white or colorless. 
Transparent to subtranslucent. Frequently the larger, coarser 



BERYL 241 

crystals show a mottled appearance due to the alternation of 
clear transparent spots with cloudy, almost opaque portions. 

Tests. B. B. whitens and fuses with difficulty at 5-5.5 to an 
enamel. Yields a little water on intense ignition. Insoluble in 
acids. Recognized usually by its hexagonal crystals, its hard- 
ness, color, etc. 

Varieties. Ordinary Beryl. In coarse translucent to opaque 
crystals or masses, usually of a pale greenish blue or yellow color. 
Sometimes in very large crystals; one from Graf ton, New Hamp- 
shire, measured over 4 feet in length with a diameter between 
20 and 30 inches, weight 2900 pounds. 

Aquamarine. Name given to the pale greenish blue trans- 
parent stone. Used as a gem. 

Golden Beryl. A deep golden yellow variety, which, when 
clear, is used as a gem. 

Rose Beryl. A variety varying in color from pale pink to 
deep rose. Beautiful gem material from Madagascar has been 
named morganite. 

Emerald. The true emerald is the deep green transparent 
beryl and is among the most highly prized of gems. The color 
is due to small amounts .of chromium. 

Occurrence. Beryl, although containing the rare element beryl- 
lium, is a rather common and widely distributed mineral. It occurs 
usually as an accessory mineral in pegmatite veins. It is also found 
in clay-slate and mica-schist. Emeralds of gem quality occur in a 
dark bituminous limestone at Musa, 75 miles northwest of Bogota, 
United States of Colombia. This locality has been worked almost 
continually since the middle of the sixteenth century, and has fur- 
nished the greater part of the emeralds of the world. Another 
famous locality for emeralds is in Siberia on the river Takovaya, 
45 miles east of Ekaterinburg. They occur in a mica-schist asso- 
ciated with phenacite, chrysoberyl, rutile, etc. Rather pale emeralds 
have been found in small amount from Alexander County, North 
Carolina, associated with the green variety of spodumene, hiddenite. 
Beryl of the lighter aquamarine color is much more common, and 
is found in gem quality in Brazil, Siberia, and many other localities. 
In the United States they have been found in various places in Maine, 
New Hampshire, Massachusetts, Connecticut, North Carolina, Colo- 
rado, etc. The golden beryl has been found in Maine, Connecti- 
cut, North Carolina and Pennsylvania; also in Siberia and Ceylon. 



242 MANUAL OF MINERALOGY 

The rose-colored beryl has been found in San Diego County, Cali- 
fornia, associated with pink tourmaline and the pink spodurnene, 
kunzite. A similar occurrence in Madagascar has furnished mag- 
nificent rose-colored stones (morganite). 

Use. Used as a gem stone of various colors. The emerald 
ranks as one of the most valuable of stones, at times being of 
much greater value than the diamond. Perfect and deeply 
colored stones have been sold as high as $1000 per carat. 
Aquamarines range in value from $1 to $15 a carat. Golden 
beryls bring from $1 to $10 a carat. The rose beryl is valued 
from $5 to $20 a carat. 

lolite. Cordierite. 

A complex silicate of magnesium, ferrous iron and aluminium. 
Orthorhombic. Usually in short pseudohexagonal twinned crys- 
tals; as embedded grains; massive. Vitreous luster. Color differ- 
ent shades of blue. Most commonly altered into some form of 
mica, becoming opaque and of various shades of grayish green. 
Found as an accessory mineral in granite, gneiss (cordierite gneiss), 
schists, etc. 

3. ORTHOSILICATES. 

Nephelite. 

Composition. Sodium-aluminium silicate, approximately 
NaAlSi0 4 . There is always a few per cent of potash present, 
sometimes also lime, replacing the soda. 

Crystallization. Hexagonal. Rarely in small prismatic crys- 
tals with basal plane; sometimes shows pyramidal planes. 

Structure. Almost invariably massive, compact, and in em- 
bedded grains. Massive variety often called elceolite. 

Physical Properties. Distinct cleavage parallel to prism. 
H. = 5.5-6. G. = 2.55-2.65. Vitreous luster in the clear crys- 
tals to greasy luster in the massive variety. Colorless, white 
or yellowish. In the massive variety gray, greenish and reddish. 
Transparent to opaque. 

Tests. Fusible at 4 to a colorless glass. B. B. gives strong 
yellow flame of sodium. Readily soluble in hydrochloric acid 
and on evaporation yields a silica jelly. 



LAZURITE 243 

Alteration. Easily alters into various other minerals, such as 
the zeolites, natrolite, analcite, hydronephelite, thomsonite; also 
sodalite, muscovite, kaolin, etc v 

Occurrence. Nephelite is rarely found except in igneous rocks. 
It occurs in some recent lavas as glassy crystals, such as are found 
in the lavas of Vesuvius. The opaque, massive or coarsely crystal- 
line variety is found in the older rocks and is called elaeolite. Phono- 
lite, elseolite-syenite and nephelite-basalt are important rocks in 
which nephelite is an essential constituent. It is only to be found 
in rocks whose magmas contained an excess of soda over the amount 
required to form feldspar. It is therefore seldom found in rocks 
that contain free quartz. Extensive masses of nephelite rocks, 
elaeolite-syenites, are found in Norway. Massive and crystallized 
nephelite is found at Litchfield, Maine, associated with cancrinite. 
Found at Magnet Cove, Arkansas. 

Name. Nephelite is derived from a Greek work meaning a 
cloud, because when immersed in acid the mineral becomes 
cloudy. Elceolite is derived from the Greek word for oil, in 
allusion to its greasy luster. 

Cancrinite, H 6 Na6Ca(NaCOs) 2 Al 8 (Si04)9, is a rare mineral 
similar to nephelite in occurrence and associations. 

SODALITE GROUP. 
Sodalite. 

Composition, Na 4 (AlCl)Al 2 (SiO 4 )3. Isometric. Crystals rare, 
usually dodecahedrons. Commonly massive, in embedded grains. 
Dodecahedral cleavage. H.= 5.5-6. G.= 2.15-2.3. Vitreous lus- 
ter. Color usually blue, also white, gray, green. Transparent to 
opaque. Fusible at 3.5-4, to a colorless glass, giving a strong 
yellow flame (sodium). Soluble in hydrochloric acid and gives 
gelatinous silica upon evaporation. Nitric acid solution with silver 
nitrate gives white precipitate of silver chloride. A comparatively 
rare rock-making mineral associated with nephelite, cancrinite, etc., 
in nephelite-syenites, trachytes, phonolites, etc. Found in transpar- 
ent crystals in the lavas of Vesuvius. Similar minerals, but rarer in 
their occurrence, are hauynite, (Na2.Ca)ji(Al.NaSO 4 )Al 2 (SiO 4 )3, and 
noselite, Na 4 (NaSO 4 . Al)Al 2 (SiO 4 ) 3 . 

Lazurite. Lapis-lazuli. 

Composition, Na 4 (Al.NaS s )Al 2 (SiO 4 )3, with small amounts of the 
Bodalite and haiiynite molecules in isomorphous replacement. Iso- 



244 MANUAL OF MINERALOGY 

metric. Crystals rare, usually dodecahedral. Commonly massive, 
compact. H. = 5-5.5. G. = 2.4-2.45. Vitreous luster. Color 
deep azure-blue, greenish blue. Translucent. Fusible at 3.5, giv- 
ing strong yellow flame (sodium). Soluble in hydrochloric acid 
with slight evolution of hydrogen sulphide gas, and gives gelatinous 
silica upon evaporation. A rare mineral, occurring usually in crys- 
talline limestones as a product of contact metamorphism. Lapis- 
lazuli is usually a mixture of lazurite with small amounts of calcite, 
pyroxene, etc. It commonly contains small disseminate particles 
of pyrite. It is used as an ornamental stone, for carvings, etc. The 
best quality of lapis-lazuli comes from northeastern Afghanistan. 
Also found at Lake Baikal, Siberia, and in Chile. 

GARNET GROUP. 

Composition. The garnets are orthosilicates which conform 
to the general formula R 3 // R 2 /// (8104)3. R" may be calcium, 
magnesium, ferrous iron and manganese; R'" may be aluminium, 
ferric iron and chromium. The formulas of the chief varieties 
are given below; many of them, however, grade more or less into 
each other. 

Grossularite, 
Pyrope, 
Almandite, 
Spessartite, 
Andradite, Ca3Fe 2 (Si0 4 ) 3 . 
Uvarovite, Ca 3 (Cr,Al) 2 (Si0 4 )3. 

Crystallization. Isometric. Common forms dodecahedron 
(Fig. 308) and trapezohedron (Fig. 309), often in combination 
(Figs. 310 and 311). Hexoctahedron observed at times (Fig. 
312). Other forms rare. 

Structure. Usually distinctly crystallized; also in rounded 
grains; massive granular, coarse or fine. 

Physical Properties. H.= 6.5-7.5. G. = 3.15-4.3, varying 
with the composition. Luster vitreous to resinous. Color vary- 
ing with composition; most commonly red, also brown, yellow, 
white, green, black. White streak. Transparent to almost 
opaque. 

Tests. With the exception of uvarovite, all garnets fuse at 3 
to 3.5; uvarovite is almost infusible. The iron garnets, alman- 



GARNET GROUP 



245 




Fig. 308. 



Fig. 309. 



Fig. 310. 





Fig. 311. 



Fig. 312. 



dite and andradite, fuse to magnetic globules.' Spessartite when 
fused with sodium carbonate gives a bluish green bead (manga- 
nese). Uvarovite gives a green color to salt of phosphorus bead 
(chromium) . Andradite is somewhat difficultly soluble in hydro- 
chloric acid and gelatinizes imperfectly on evaporation. All the 
other garnets are practically insoluble in acids. All of them, 
with the exception of uvarovite, may be dissolved in hydrochloric 
acid after simple fusion and the solutions will gelatinize on evapo- 
ration. Garnets are usually recognized by their characteristic 
isometric crystals, their hardness, color, etc. It frequently re- 
quires an analysis to positively distinguish between the different 
members of the group. 

Varieties. Grossularite, Essonite, Cinnamon Stone. Calcium- 
aluminium garnet. Often contains ferrous iron replacing cal- 
cium and ferric iron replacing aluminium. Color white, green, 



246 MANUAL OF MINERALOGY 

yellow, cinnamon-brown, pale red. Name derived from the 
botanical name for gooseberry, in allusion to the light green color 
of the original grossularite. 

Pyrope. Precious garnet in part. Magnesium-aluminium 
garnet. Calcium and iron also present. Color deep red to 
nearly black. Often transparent and then used as a gem. 
Name derived from Greek, meaning firelike. Rhodolite is name 
given to a pale rose-red or purple garnet, corresponding in com- 
position to two parts of pyrope and one of almandite. 

Almandite. Precious garnet in part. Common garnet in 
part. Iron-aluminium garnet. Ferric iron replaces aluminium 
and magnesium replaces ferrous iron. Color fine deep red, trans- 
parent in precious garnet; brownish red, translucent to opaque 
in common garnet. Name derived from Alabanda, where in 
ancient times garnets were cut and polished. 

Spessartite. Manganese-aluminium garnet. Ferrous iron re- 
places the manganese and ferric iron the aluminium. Color 
brownish to garnet-red. 

Andradite. Common garnet in part. Calcium-iron garnet. 
Aluminium replaces the ferric iron; ferrous iron, manganese and 
sometimes magnesium replace the calcium. Color various 
shades of yellow, green, brown to black. Named after the 
Portuguese mineralogist, d'Andrada. 

Uvarovite. Calcium-chromium garnet. Color emerald-green. 
Named after Count Uvarov. 

Occurrence. Garnet is a common and widely distributed min- 
eral, occurring as an accessory constituent of metamorphic and 
sometimes of igneous rocks. Its most characteristic occurrence is 
in mica-schists (see Fig. C, pi. X), hornblende-schists and gneisses. 
Found in pegmatite veins, more rarely in granite rocks. Grossu- 
larite is found chiefly as a product of contact or regional metamor- 
phism in crystalline limestones. Pyrope is often found in peridotite 
rocks and the serpentines derived from them. Spessartite occurs 
in the igneous rock, rhyolite. Melanite, a black variety of andra- 
dite, occurs mostly in certain eruptive rocks. Uvarovite is found 
in serpentine associated with chromite. Garnet frequently occurs 
as rounded grains in stream- and sea-sands. 

Almandite, of gem quality, is found in northern India, Brazil, 
Australia, and in several localities in the Alps. Fine crystals, al- 



CHRYSOLITE 247 

though for the most part too opaque for cutting, are found in a mica- 
schist on the Stickeen River, Alaska. Pyrope of gem quality is 
found associated with clear grains of chrysolite (peridot) in the 
surface sands near Fort Defiance, close to the Utah-Arizona state 
line. Famous localities for pyrope gems are near Teplitz and Bilin, 
Bohemia. Grossularite is only a little used in jewelry, but essonite 
or cinnamon stones of good size and color are found in Ceylon. A 
green andradite, known as demantoid, cornes from the Urals and 
yields fine gems known as Uralian emeralds. 

Alteration. Garnet often alters to other minerals, particu- 
larly talc, serpentine and chlorite. 

Name. Garnet is derived from the Latin granatus, meaning 
like a grain. Carbuncle, an old name for garnet and other red 
stones, was derived from the Latin word carbo, coal, and is used 
at present to designate garnets cut in oval form- 
Use. Chiefly as a rather inexpensive gem stone. Sometimes 
ground and used on account of its hardness for abrading pur- 
poses, as sand for sawing and grinding stone, or for making sand- 
paper. 

CHRYSOLITE GROUP. 

Chrysolite or Olivine. Peridot. 

Composition. Orthosilicate of magnesium, with varying 
amounts of ferrous iron, (Mg,Fe) 2 Si0 4 . The ratio between the 
magnesium and iron varies widely. 

Crystallization. Orthorhombic. Crystals usually a combi- 
nation of prism, macro- and brachypinacoids and domes, pyra- 
mid and base. Often flattened parallel to either the macro- or 
brachypinacoid. 

Structure. Usually in embedded grains or in granular masses. 

Physical Properties. H. = 6.5-7. G. = 3.27-3.37. Vitre- 
ous luster. Olive to grayish green, brown. Transparent to 
translucent. 

Tests. Infusible. Rather slowly soluble in hydrochloric acid 
and yields gelatinous silica upon evaporation. After evapora- 
tion to dryness, take up residue in water with nitric acid, filter 



248 MANUAL OF MINERALOGY 

off silica, add ammonia in excess to precipitate ferric hydroxide, 
filter, add ammonium oxalate to prove absence of calcium, add 
sodium phosphate and obtain precipitate of ammonium-mag- 
nesium phosphate (test for magnesium). Distinguished usually 
by its glassy luster, green color and granular structure. 

Occurrence. A rather common rock-making mineral, varying 
from an accessory character to that of a main constituent of the rock. 
It is found principally in the dark colored ferro-magnesium igneous 
rocks such as gabbro, peridotite and basalt. A rock, known as 
dunite, is made up almost wholly of chrysolite. Found also at times 
as glassy grains in meteorites. Occasionally in crystalline dolomitic 
limestones. Associated often with pyroxene, the plagioclase feld- 
spars, magnetite, corundum, chromite, serpentine, etc. The trans- 
parent green variety, known as peridot, and used as a gem material, 
was found in ancient times in the East, the exact locality for the 
stones not being known. At present peridot is found in Upper 
Egypt, near the Red Sea, and in rounded grains associated with 
pyrope garnet in the surface gravels of Arizona and New Mexico. 
Crystals of chrysolite are found in the lavas of Vesuvius. Larger 
crystals, altered to serpentine, come from Snarum, Norway. Chryso- 
lite occurs in granular masses in the volcanic bombs in the Eifel. 
Dunite rocks are found at Dun Mountain, New Zealand, and with 
the corundum deposits of North Carolina. 

Alteration. Very readily altered to serpentine; magnesium 
carbonate, iron ore, etc., may form at the same time. 

Name. Chrysolite means golden stone. Olivine derives its 
name from the usual olive-green color of the mineral, and is 
the term usually given to the species when speaking of it as a 
rock-making mineral. Peridot is an old name for the species. 

Use. As the clear green variety, known usually as peridot, it 
has some use as a gem. A one-carat stone may be valued up 
to $5. 

Other members of the Chrysolite Group which are rarer in 
occurrence are Monticellite, CaMgSi0 4 ; fosterite, Mg 2 Si0 4 ; and 
fayalite, Fe 2 Si0 4 . Ordinary chrysolite is intermediate in com- 
position between the last two. Another member which has been 
found in the zinc deposits at Franklin Furnace, New Jersey, is 
tephroite, Mn 2 Si0 4 . 



PHENACITE 249 

PHENACITE GROUP. 
Willemite. 

Composition. Zinc orthosilicate, Zn 2 Si0 4 = Silica 27, zinc 
oxide 73, zinc 58.6. Manganese often replaces a considerable 
part of the zinc (manganiferous variety called troostite), iron 
also present at times in small amount. 

Crystallization. Hexagonal-rhombohedral ; tri-rhombohedral. 
In hexagonal prisms with rhombohedral terminations. Faces 
of third-order rhombohedrons rare. 

Structure. Usually massive to granular. Rarely crystallized 
except in variety troostite. 

Physical Properties. H. = 5.5. G. = 3.89-4.18. Vitreous 
to resinous luster. Color white, yellow-green, blue, when pure; 
with increase of manganese becomes apple-green, flesh-red and 
brown. Transparent to opaque. 

Tests. Willemite infusible, troostite difficultly fusible (4.5-5). 
Soluble in hydrochloric acid and yields gelatinous silica on evapo- 
ration. Gives a coating of zinc oxide when heated with sodium 
carbonate on charcoal; coating yellow when hot, white when 
cold; if coating is moistened with cobalt nitrate and heated again 
it turns green. Troostite will give reddish violet color to the 
borax bead in 0. F. (manganese). 

Varieties. Ordinary. White or light colored. 

Troostite. Apple-green, flesh-red or gray color. Contains a 
considerable amount of manganese. Found at Franklin Fur- 
nace, New Jersey, in quite large crystals. 

Occurrence. Found at Altenberg, near Moresnet, Belgium, and 
at Franklin Furnace, New Jersey. At the latter locality it is asso- 
ciated with franklinite and zincite, often in an intimate mixture; 
also embedded in calcite. Occurs sparingly at Merritt Mine, New 
Mexico. 

Use. A valuable zinc ore. 

Phenacite. 

Beryllium orthosilicate, Be 2 SiO 4 . Hexagonal-rhombohedral; tri- 
rhombohedral. Crystals usually rhombohedral in form, sometimes 
with short prisms. Often with complex development and fre- 



250 



MANUAL OF MINERALOGY 



quently showing the faces of the third-order rhombohedron. Pris- 
matic cleavage. H. = 7.5-8. G. = 2.96. Vitreous luster. Color- 
less, white. Transparent to translucent. Infusible and insoluble. 
A rare mineral, found associated usually with topaz, chrysoberyl, 
beryl, apatite, etc. Fine crystals are found at the emerald mines 
in the Urals, at Pike's Peak and Mount Antero, Colorado, and in 
Minas Geraes, Brazil. Occasionally cut as a gem stone. 

Dioptase, H 2 CuSi0 4 , is a rare mineral belonging in this group. 

SCAPOLITE GROUP. 

A group of minerals varying in composition by the isomor- 
phous mixture in different amounts of the two molecules, 
Ca4Al 6 Si 6 02 5 (Me) and Na 4 Al 3 Si 9 24 Cl,(Ma). When the first 
molecule (Me) alone is present, the subname of meionite is used; 
when the second molecule (Ma) represents the composition, the 
name marialite is used. Wernerite, or common scapolite } shows 
a combination of the two molecules according to the ratios of 
Me : Ma as 3 : 1 to 1 : 2; while mizzonite corresponds to the 
ratios of Me : Ma as 1 : 2 to 1 : 3. Mixtures in all proportions 
may exist. 

Wernerite. Common Scapolite. 
Composition. See above. 

Crystallization. Tetragonal; tripyramidal. Crystals usually 
prismatic. Prominent forms are prisms of the first and second 




Fig. 313. 




Fig. 314. 



orders, pyramid of first (Fig. 313). Rarely shows the faces of 
the pyramid of the third order (Fig. 314). 



VESUVIANITE 251 

Structure. Crystals are usually coarse, with rough faces and 
often large. Also massive, granular, or with faint fibrous appear- 
ance. 

Physical Properties. Imperfect prismatic cleavage. H.= 
5-6. G. = 2.68. Vitreous luster when fresh and unaltered. 
Color white, gray or pale green. Transparent to opaque. 

Tests. Fusible. Varieties containing sodium give yellow 
flame on ignition. Imperfectly decomposed by hydrochloric 
acid, yielding separated silica but without the formation of a 
jelly. 

Alteration. Easily altered into various other minerals, such 
as mica, epidote, talc, kaolin, etc. 

Occurrence. The scapolites occur in the crystalline schists, 
gneisses and amphibolites, and in many cases have probably been 
derived by alteration from plagioclase feldspars. They also charac- 
teristically occur in crystalline limestones formed through the con- 
tact metamorphic action of an intruded igneous rock. Associated 
with light colored pyroxene, amphibole, garnet, apatite, titanite, 
zircon, etc. Found in various places in Massachusetts; Orange, 
Essex, Lewis, Jefferson and St. Lawrence counties, New York; at 
Grenville, Templeton, Algona, etc., Canada. 

The other members of the group, meionite, mizzonite and 
marialite, are much rarer in occurrence. Their crystals are 
usually smaller and of better quality than those of wernerite. 
Meionite and missonite are found in limestone blocks on Monte 
Somma. 



Vesuvianite. 

Composition. A basic silicate of calcium and aluminium. 
Contains usually also iron oxides, magnesia and fluorine. For- 
mula uncertain. 

Crystallization. Tetragonal. Prismatic in habit. Often ver- 
tically striated. Common forms are prisms of first and second 
orders, pyramid of first order and base (Figs. 315 and 316). 
Some crystals show a more complex development with other 
prisms, pyramids, ditetragonal forms, etc. 



252 



MANUAL OF MINERALOGY 



Structure. In crystals, also massive, columnar, granular. 

Physical Properties. H. = 6.5. G. = 3.35-4.45. Vitreous to 
resinous luster. Usually green or brown in color; also yellow, 
blue, red. Commonly subtransparent to translucent. Streak 
white. 



771 



I 1 



Fig. 315. 




Tests. Fuses with intumescence to a greenish or brownish 
glass. Only slightly soluble in acids but gelatinizes in hydro- 
chloric acid after simple fusion. 

Occurrence. Usually to be found in crystalline limestones where 
they have been metamorphosed by the contact action of igneous 
rocks. Formed probably by the action upon impure limestone of 
hot vapors containing water and fluorine given off by the igneous 
rock. Associated with other contact minerals, such as garnet, 
pyroxene, tourmaline, chondrodite, etc. Was originally discovered 
in the ancient ejections of Vesuvius and in the dolomitic blocks of 
Monte Somma. Important localities are, Ala, Piedmont; Mon- 
zoni, Tyrol; Vesuvius; Christiansand, Norway; Achmatoosk, 
Urals; River Wilui, Siberia; in the United States, at Phippsburg 
and Rumford, Maine; near Amity, New York; Inyo County, Cali- 
fornia; in Canada at Litchfield, Pontiac County; at Grenville, 
Ontario; at Temple ton, Quebec. 



ZIRCON GROUP. 

Zircon. 

Composition. ZrSi0 4 = Silica 32.8, zirconia 67.2. 
Crystallization. Tetragonal. Crystals usually show a simple 
combination of prism and pyramid of the first order (Figs. 317 






ZIRCON 



253 



and 318). The prism of the second order and a ditetragonal 
pyramid also at times observed (Fig. 319). Base very rare. 




m 





Fig. 317. 



Fig. 318. 



Fig. 319. 



Crystal forms and axial ratio prove a close relationship between 
zircon and cassiterite and rutile. 

Structure. Usually crystallized; also in irregular grains. 

Physical Properties. H. = 7.5. G. = 4.68. Luster adaman- 
tine. Usually nearly opaque, sometimes transparent. Color 
commonly some shade of brown; also colorless, gray, green, red. 
Streak uncolored. High refractive index. 

Tests. Infusible. A small fragment when intensely ignited 
glows and gives off a white light. When fused with sodium car- 
bonate and fusion then dissolved in dilute hydrochloric acid, the 
solution will turn a piece of turmeric paper to an orange color 
(zirconium). Recognized usually by its characteristic crystals, 
color, luster, hardness and high specific gravity. 

Occurrence. Zircon is a common and widely distributed acces- 
sory mineral in all classes of igneous rocks. It is especially frequent 
in the more acid types such as granite, syenite, diorite, etc. Very 
common in nephelite-syenite. It is the first one among the silicates 
to crystallize out from a cooling magma. Found also commonly in 
crystalline limestone, in gneiss, schist, etc. Found frequently as 
rounded pebbles in stream sands; often with gold. Gem zircons 
are found in the stream sands at Matura, Ceylon. Occurs in the 
gold gravels in the Urals, Australia, etc. Found in the nephelite- 
syenites of Norway and of Litchfield, Maine. In considerable 
quantity in the sands of Henderson and Buncombe counties, North 
Carolina. . 



254 MANUAL OF MINERALOGY 

Use. When transparent serves as a gem stone, valued usu- 
ally at $10 or less per carat. It is sometimes colorless, but more 
often of a brownish and red-orange color, called hyacinth or ja- 
cinth. The colorless, yellowish or smoky stones are called jar- 
gon, because while resembling the diamond they have little value; 
and thence the name zircon. Serves as the source of zirconium 
oxide, which with other rare oxides is used in the manufacture 
of the Welsbach incandescent mantle. 

Thorite. 

Thorium silicate, ThSiO 4 , always with some water, probably from 
alteration, and sometimes uranium. Tetragonal. Crystal forms 
resemble those of zircon. Also massive. Resinous to greasy luster. 
H. = 4.5-5. G. = 4.8-5.2. Color orange-yellow, brown, black. 
Transparent to opaque. Infusible. Soluble in hydrochloric acid 
and gives gelatinous silica upon evaporation. A rare mineral, found 
chiefly in Norway, commonly altered. For uses of thorium see 
under monazite. 

DANBURITE-TOPAZ GROUP. 
Danburite. 

Composition. Calcium-boron silicate, CaB 2 (Si0 4 ) 2 . 

Crystallization. Orthorhombic. Prismatic crystals, closely 
related to those of topaz in habit. 

Structure. Commonly in crystals. 

Physical Properties. H.= 7-7.25. G.= 2.97-3.02. Vitre- 
ous luster. Colorless or pale yellow. Transparent to translu- 
cent. 

Tests. Fusible (3.5-4), giving a green flame. Insoluble in 
acids. 

Occurrence. Found in crystals at Danbury, Conn.; Russell, 
New York; eastern Switzerland; Japan. 

Topaz. 

Composition. (Al.F) 2 Si0 4 with isomorphous(A1.0H) 2 Si0 4 . 
Crystallization. Orthorhombic. In prismatic crystals termi- 
nated by pyramids, domes and basal plane (Figs. 320, 321 and 



TOPAZ 



255 



322). Often highly modified (Fig. 323). 
tically striated. 



Prism faces often ver- 





Fig. 320. 



Fig. 321. 



Fig. 322. 



Fig. 323. 



Structure. In crystalline masses; also granular, coarse or 
fine. 

Physical Properties. Perfect basal cleavage. H. = 8 (unusu- 
ally high) . G . = 3 . 52-3 . 57 . Vitreous luster. Colorless, yellow, 
yellow-brown, pink, bluish, greenish. Transparent to trans- 
lucent. 

Tests. Infusible. Insoluble. Recognized chiefly by its crys- 
tals, its basal cleavage, its hardness (8) and high specific gravity. 

Occurrence. A mineral formed through the agency of fluorine- 
bearing vapors given off during the last stages of the solidification 
of igneous rocks. Found in cavities in rhyolite lavas and granite; 
a characteristic mineral in pegmatite veins. Associated with otHer 
pneumatolytic minerals, as tourmaline, cassiterite, apatite, fluorite, 
etc.; also with quartz, mica, feldspar. Found at times as rolled 
pebbles in stream sands. Notable localities for its occurrence are 
the Nerchinsk district in Siberia in large wine-yellow crystals; from 
Adunchilon and Mursinka, Siberia, in pale blue crystals; from 
various tin localities in Saxony: from Minas Geraes, Brazil; Mino 
Province, Japan; San Luis Potosi, Mexico; Pike's Peak and Nath- 
rop, Colorado; Thomas Range, Utah; Stoneham, Maine. 

Name. Derived from the name of an island in the Red Sea 
but originally probably applied to some other species. 

Use. As a gem stone. A number of other inferior stones are 
also frequently called topaz. The color of the stones varies, 
being colorless, wine-yellow, golden brown, pale blue and pink. 
The pink color is usually artificial, being produced by gently 




256 MANUAL OF MINERALOGY 

heating the dark yellow stones ; it is permanent, however. The 
value of topaz ranges up to $10 for a one-carat stone. 

Andalusite. Chiastolite. 

Composition. Aluminium silicate, Al 2 Si0 6 = Silica 36.8, alu- 
mina 63.2. 

Crystallization. Orthorhombic. Usually in coarse, nearly 
square prisms. Closely related crystallographically to topaz. 
Structure. In crystals; massive. 

Physical Properties. H.= 7.5. G. = 3.16-3.20. Vitreous 
luster. Flesh-red, reddish brown, olive-green. Often with dark 
colored carbonaceous inclusions forming a 
cruciform design, lying parallel to the axial 
directions (variety chiastolite or made) (see 
Fig. 324). Transparent to opaque. At times 
strongly dichroic, appearing, in transmitted 
light, green in one direction and red in another. 
Tests. Infusible. Insoluble. When fine 
Fig. 324. powder is made into a paste with cobalt 

Cross Section of Chi- nitrate and intensely ignited it turns blue 

astohte Crystal, . . J 

(aluminium). 

Occurrence. Found in schists. Often impure and commonly, 
at -least partly altered. Notable localities are in Andalusia, Spain; 
the Tyrol; in water-worn pebbles from Minas Geraes, Brazil. In 
the United States at Standish, Maine; Westford, Lancaster and 
Sterling, Massachusetts; Litchfield and Washington, Connecticut; 
Delaware County, Pennsylvania. Chiastolite is found in Morihan, 
Brittany; Bimbowrie, South Australia; and Massachusetts. 

Use. When clear and transparent may serve as a gem stone. 

Sillimanite. Fibrolite. 

An aluminium silicate like andalusite, Al 2 SiO 5 . An orthorhombic 
mineral, occurring in long slender crystals without distinct termina- 
tions; often in parallel groups; frequently fibrous. Perfect pina- 
coidal cleavage. H. = 6-7. G. =3.23. Color hair-brown to pale 
green. Transparent to translucent. Infusible. Insoluble. A 
comparatively rare mineral, found as an accessory constituent of 
metamorphic rocks; gneiss, mica-schist, etc. 




DATOLITE 



257 



Cyanite. 

Composition. Aluminium silicate, like andalusite and silli- 
manite, Al 2 Si0 5 . 

Crystallization. Triclinic. Usually in long tabular crystals; 
terminations rare. 

Structure. In bladed forms. 

Physical Properties. Perfect pinacoidal cleavage. H. = 5 
parallel to length of crystals, 7 at right angles to this direction. 
G. = 3.56-3.66. Vitreous to pearly luster. Color usually blue, 
often of darker shade toward the center of the crystal. Also at 
times white, gray or green. 

Tests. Infusible. Insoluble. A fragment moistened with 
cobalt nitrate and ignited assumes a blue color (aluminium). 
Characterized by its bladed crystals, good cleavage, blue color 
and the fact that it is softer than a knife in the direction parallel 
to the length of the crystals but harder than a knife in the 
direction at right angles to this. 

Occurrence. An accessory mineral in gneiss and mica-schist, 
often associated with garnet, staurolite, corundum, etc. Notable 
localities for its occurrence are St. Gothard, Switzerland; in the 
Tyrol; Litchfield, Connecticut; Chester and Delaware counties, 
Pennsylvania; Gaston, Rutherford and Yancey counties, North 
Carolina. 

Name. Derived from a Greek word meaning blue. 



Datolite. 



Composition. A basic ortho- 
silicate of calcium and boron, 
Ca(B.OH)Si0 4 = Silica 37.6, bo- 
ron trioxide 21.8, lime 35, water 
5.6. 

Crystallization. Monoclinic. 
Habit varied. Crystals usually 
nearly equidimensional in the 
three axial directions and often 
complex in development (Fig. 
325). 




258 MANUAL OF MINERALOGY 

Structure. In crystals. Coarse to fine granular. Sometimes 
compact. 

Physical Properties. H. = 5-5.5. G. = 2.8-3. Vitreous lus- 
ter. Colorless, white, yellow. Often with faint greenish tinge. 
Transparent to translucent, rarely opaque. 

Tests. Fuses at 2-2.5 to a clear glass and colors the flame 
green (boron). Soluble in hydrochloric acid and yields gelati- 
nous silica on evaporation. Gives a little water in C. T. Char- 
acterized by its glassy luster, pale green color, and its crystals 
with many and usually irregularly developed faces. 

Occurrence. A mineral of secondary origin, found usually in 
cavities in basalt lavas and similar rocks. Associated with various 
zeolites, with calcite, prehnite, etc. Occurs associated with the 
trap rocks of Massachusetts, Connecticut and New Jersey, particu- 
larly at Westfield, Massachusetts, and Bergen Hill, New Jersey. 
Found associated with the copper deposits of Lake Superior. 

Name. Derived from a Greek work meaning to divide, allud- 
ing to the granular structure of a massive variety. 

A rare mineral belonging to the Datolite Group is gadolinite, 
Be 3 FeY 2 Si20 10 . 

EPIDOTE GROUP. 

Zoisite. 

Composition. HCa 2 Al 3 Si 3 Oi2 = Silica 39.7, alumina 33.7, lime 
24.6, water 2.0. 

Crystallization. Orthorhombic. Prismatic crystals usually 
without distinct terminations. Vertically striated. 

Structure. In crystals; also massive. 

Physical Properties. H. = 6-6.5. G. = 3.25-3.37. Vitre- 
ous luster. Color grayish white, green, pink. Transparent to 
almost opaque. 

Tests. Fuses at 3-4 with intumescence to a light colored slag. 
Yields a little water on intense ignition in C. T. 

Occurrence. Usually in crystalline schists with one of the am- 
phiboles. Thulite is a rose-pink variety. 



ALLANITE 259 

Epidote. 

Composition. Ca 2 (A1.0H)(Al,Fe) 2 (Si0 4 )3. Iron occurs in 
varying amounts isomorphous with both the aluminium and cal- 
cium. 

Crystallization. Monoclinic. Crystals are often much elon- 
gated parallel to the ortho-axis with a prominent development 
of the faces of the orthodome zone, 
giving them a prismatic aspect. </ c 

Striated parallel to the ortho-axis. \ 

Terminated usually only at one end \ r 

of the ortho-axis and most com- 
monly by the two faces of a pyra- Fig - 326 - 
mid (Fig. 326). Twinning shown at times. 

Structure. Usually coarse to fine granular. In crystals. At 
times fibrous. 

Physical Properties. Perfect basal cleavage. H. = 6-7. G. = 
3.37-3.45. Vitreous luster. Color usually pistachio-green or 
yellowish to blackish green, sometimes gray. Transparent to 
opaque. Transparent varieties often show strong dichroism, 
appearing dark green in one direction, and brown in a direction 
at right angles to the first. 

Tests. Fuses at 3-4 with intumescence to a black slag. On 
intense ignition in C. T. yields a little water. 

Occurrence. Epidote occurs commonly in the crystalline meta- 
morphic rocks; as gneiss, amphibolite and various schists. Is 
formed frequently also during the metamorphism of an impure 
limestone. Is the product of alteration of such minerals as feldspar, 
pyroxene, amphibole, biotite, scapolite, etc. Often associated with 
chlorite. Notable localities for its occurrence in fine crystals are 
Knappenwand, Unterzulzbachthal, Tyrol; Bourg d'Oisans, Dau- 
phine, the Ala Valley and Traversella, Piedmont; Prince William 
Island, Alaska; Haddam, Connecticut; Riverside, California. 

Allanite. 

A mineral similar to epidote in composition, but containing con- 
siderable amounts of the cerium metals, cerium, lanthanum and 
didymium, and sometimes with smaller amounts of yttrium and 
erbium. Composition complex and widely varying. Monoclinic, 



260 MANUAL OF MINERALOGY 

habit of crystals often similar to epidote. Commonly massive and 
in embedded grains. H. = 5.5-6. G. = 3.5-4.2. Submetallic to 
pitchy and resinous luster. Brown to pitch-black color. Fuses at 
2.5 with intumescence. Sometimes magnetic after heating. Gelati- 
nizes in acids. Occurs as a minor accessory constituent in many 
igneous rocks. Frequently associated with epidote. 




Axinite. 

Composition. Ca 7 Al4B 2 (Si04) 8 ; with varying amounts of fer- 
rous iron, manganese, magnesium and hydrogen isomorphous 
with the calcium, and ferric iron with the 
aluminium. 

Crystallization. Triclinic. Crystals 
usually thin with sharp edges but varied 
in habit (Fig. 327). 

Structure. In crystals. Massive, la- 
mellar to granular. 
Fig. 327. Physical Properties. Pinacoidal cleav- 

age. H.= 6.5-7. G.= 3.27-3.35. Vitreous luster. Color 
clove-brown, gray, green, yellow. Transparent to opaque. 

Tests. Fusible at 2.5-3 with intumescence. When mixed 
with potassium bisulphate and fluorite and the mixture heated 
on platinum wire gives a green flame (boron). 

Occurrence. Notable localities for its occurrence are Bourg 
d'Oisans in Dauphine; St. Just, Cornwall; Obira, Japan; Franklin 
Furnace, New Jersey, etc. 

Name. Derived from a Greek word meaning ax, in allusion 
to the wedgelike shape of the crystals. 

Prehnite. 

Composition. H 2 Ca 2 Al 2 Si30i 2 = Silica 43.7, alumina 24.8, 
lime 27.1, water 4.4. 

Crystallization. Orthorhombic. Distinct crystals rare. 

Structure. Reniform, stalactitic. In rounded groups of tab- 
ular crystals. 

Physical Properties. H. = 6-6.5. G. = 2.8-2.95. Vitreous 
luster. Color usually light green, passing into white. Trans- 
lucent. 



CALAMINE 



261 



Tests. Fuses at 2.5 with intumescence to an enamel. Heated 
in C. T. yields water. Slowly acted upon by hydrochloric acid 
but gelatinizes after simple fusion. 

Occurrence. As a mineral of secondary origin lining amygdaloidal 
cavities in basalt, etc. Associated with zeolites, datolite, pectolite, 
calcite, etc. Occurs in the United States at Farmington, Connecti- 
cut; Paterson and Bergen Hill, New Jersey; Somerville, Massa- 
chusetts; Lake Superior copper district. Found also in various 
European localities. 

4. SUBSILICATES. 
HUMITE GROUP. 

The three minerals, humite, Mg 3 [Mg(F,OH)] 2 [Si04]2, chondro- 
^e,-Mg 6 [Mg(F,OH)] 2 [Si0 4 ]3, and clinohumite, Mg 7 [Mg(F.OH)] 2 - 
[Si0 4 ] 4 , are closely related chemically and crystallographically. 
They are characteristically found in crystalline limestones. 
Chondrodite is the most common in occurrence. 



Ilvaite, or lievrite, HCaFe2 / 'Fe / "Si 2 09, is a rare mineral be- 
longing in this section. 

Calamine. 

Composition. Silicate of zinc, H 2 (Zn 2 0)Si0 4 = Silica 25, zinc 
oxide 67.5, water 7.5. 

Crystallization. Orthorhombic ; hemimorphic. Crystals usu- 
ally tabular parallel to the brachypinacoid. They show prism 
faces and are terminated above usually by a 
combination of macrodomes and brachy- 
domes and base, and below by a pyramid 
(Fig. 328). 

Structure. Usually in crystal groups with 
the individuals attached at their lower (pyra- 
midal) ends and lying with their brachypinacoid 
faces in common. Crystals often divergent, 
giving rounded groups with slight reentrant 
notches between the individual crystals, form- 
ing knuckle or coxcomb masses. Also mammillary, stalactitic, 
massive and granular. 




Fig. 328. 



262 MANUAL OF MINERALOGY 

Physical Properties. Prismatic cleavage. H. = 4.5-5. G.= 
3.4-3.5. Vitreous luster. Color white, sometimes with faint 
bluish or greenish shade; also yellow to brown. Transparent 
to translucent. Strongly pyroelectric. 

Tests. Fusible with difficulty at 5. Soluble in hydrochloric 
acid and yields gelatinous silica on evaporation. Fused on 
charcoal with sodium carbonate gives a nonvolatile coating of 
zinc oxide (yellow when hot, white when cold). Gives water in 
C. T. Recognized usually by the characteristic grouping of its 
crystals, but may be obscure and to be determined only by above 
tests. 

Occurrence. A mineral of secondary origin, found in the oxidized 
portion of zinc deposits, associated with smithsonite, sphalerite, 
cerussite, anglesite, galena, etc. Usually with limestone rocks. 
Occurs at Altenberg and Moresnet, Belgium; Aix-la-Chapelle, Ger- 
many; in Carinthia; Hungary; Cumberland, England; Sterling 
Hill, near Ogdensburg, New Jersey; Friedensville, Pennsylvania; 
Wythe County, Virginia; with the zinc deposits of southwestern 
Missouri. 

Name. Supposed to be derived from cadmia, a name given 
by the ancients to the silicate and carbonate of zinc. The 
mineral is called by English mineralogists hemimorphite or elec- 
tric calamine. 

Use. An ore of zinc. 

Tourmaline. 

Composition. A complex silicate of boron and aluminium, con- 
taining varying amounts of ferrous iron, magnesium, magnanese, 
calcium, sodium, potassium, lithium, hydroxyl and fluorine. 

Crystallization. Hexagonal-rhombohedral ; hemimorphic. 
Crystals usually prismatic, vertically striated. A triangular 
prism, with three faces, prominent, which with the tendency of 
the prism faces to be vertically striated and to round into each 
other gives the crystals usually a cross section like a spherical 
triangle (Fig. 329). Crystals are commonly terminated by base 
and low positive and negative rhombohedrons ; sometimes 
scalenohedrons are present. When the crystals are doubly ter- 



TOURMALINE 



263 



minated they usually show different forms at the opposite ends 
of the vertical axis (hemimorphism) (Figs. 330 and 331). 





Fig. 329. 



Fig. 330. 



Fig. 331. 



Structure. Usually in crystals. Sometimes massive com- 
pact; also coarse to fine columnar, either radiating or parallel. 

Physical Properties. Vitreous to resinous luster. Color 
varied, depending upon the composition. Common tourmaline 
with much iron is black, sometimes brown. More rarely light 
colored in fine shades of red, pink, green, blue, yellow, etc. 
Rarely white or colorless. A single crystal may show several 
different colors either arranged in concentric bands about the 
center of the crystal or in transverse layers along its length. 
Strongly pyroelectric ; i.e., when cooling from being heated to 
about 100 C. it develops positive electricity at one end of the 
crystal and negative at the other, which enables the crystal to 
attract and hold bits of paper, etc. Strongly dichroic; i.e., light 
traversing the crystal in one direction may be of quite a different 
color or shade of color from that traversing the crystal in a 
direction at right angles to the first. H. = 7-7.5; G. = 2.98-3.2. 

Tests. To be recognized usually by the characteristic rounded 
triangular cross section of the crystals; absence of prismatic 
cleavage, coal-like fracture of black variety. 

Occurrence. Tourmaline is one of the most common and charac- 
teristic minerals formed by pneumatolytic action. That is, it is a 
mineral that has been formed at high temperatures and pressures 
through the agency of vapors carrying boron, fluorine, etc. It is 
found, therefore, commonly as an accessory mineral in pegmatite 



264 



MANUAL OF MINERALOGY 



veins, or dikes, occurring with granite intrusions. Associated with 
the ordinary minerals of granite pegmatite, orthoclase, albite, quartz 
and muscovite; also with lepidolite, beryl, apatite, fluorite, etc. 
Found also as an accessory mineral in metamorphic rocks, such as 
gneisses, schists and crystalline limestones. 

The black tourmaline is of widespread occurrence as an accessory 
mineral in metamorphic rocks. The light colored gem varieties 
are found in the pegmatite dikes. Famous localities for the occur- 
rence of the gem tourmalines are the island of Elba; in the state of 
Minas Geraes, Brazil; Ural Mountains near Ekaterinburg; Mada- 
gascar; Paris and Auburn, Maine; Haddam Neck, Connecticut; Mesa 
Grande, Pala, Rincon and Ramona in San Diego County, California. 

Name. The name tourmaline comes from turamali, a name 
given to the early gems from Ceylon. 

Use. Tourmaline forms one of the most beautiful of the semi- 
precious gem stones. The color of the stones varies, the princi- 
pal shades being olive-green, pink to red and blue. Sometimes 
a stone is so cut as to show different colors in different parts. The 
green-colored stones are usually known by the mineral name, 
tourmaline, or as Brazilian emeralds. The red or pink stones 
are known as rubellite, while the rarer dark blue stones are called 
indicolite. 

Staurolite. 

Composition. A ferrous iron-aluminium silicate, HAl 6 Fe- 
Si 2 13 . 

Crystallization. Orthorhombic. Habit prismatic, showing 
usually a combination of prism with large angle (130), brachy- 





Fig. 332. Fig. 333. Fig. 334. 

pinacoid, base and macrodome (Fig. 332). Cruciform twins 
very common; of two types, (1) in which the two individuals 



APOPHYLLITE 265 

cross at nearly 90 (Fig. 333), (2) in which they cross at nearly 
60 (Fig. 334). Sometimes both types are combined in one 
crystal. 

Structure. Usually in crystals. 

Physical Properties. H. = 7-7.5. G. = 3.65-3.75. Resin- 
ous to vitreous luster, for pure and fresh material; often dull to 
earthy when altered or impure. Color red-brown to brownish 
black. Translucent to opaque. 

Tests. Infusible. Insoluble. On intense ignition in C. T. 
yields a little water. Often very impure. Recognized by its 
characteristic crystals and twins. 

Occurrence. Staurolite is an accessory mineral in metamorphic 
rocks; in crystalline schists, slates, and sometimes in gneisses. 
Often associated with garnet, cyanite, sillimanite, tourmaline. No- 
table localities for its occurrence are Monte Campini, Switzerland; 
in Brittany; Minas Geraes, Brazil; Windham, Maine; Francoriia 
and Lisbon, New Hampshire; Chesterfield, Massachusetts; Fannin 
County, Georgia. 

Name. Derived from a Greek word meaning cross, in allusion 
to its cruciform twins. 

Use. Occasionally a transparent stone from Brazil is cut as a 
gem. 

HYDROUS SILICATES. 

ZEOLITE DIVISION. 
INTRODUCTORY SUBDIVISION. 

Apophyllite. 

Composition. HyKCa/SiOs^.^^O. Usually contains a 
small amount of fluorine. 

Crystallization. Tetragonal. Usually shows a combination 
of prism of second order, pyramid of first and basal plane (Figs. 
335 and 336). Small faces of a ditetragonal prism sometimes 
observed (Fig. 337). Prism faces show vertical striations and 
have a vitreous luster, while base shows pearly luster. Crys- 
tals may resemble an isometric combination of cube and octa- 



266 



MANUAL OF MINERALOGY 



hedron, but are shown to be tetragonal by difference in luster 
between faces of prism and base. 






Fig. 335. 



Fig. 336. 



Fig. 337. 



Structure. In crystals; also massive and lamellar. 

Physical Properties. Perfect basal cleavage. H. = 4.5-5. 
G. = 2.3-3.4. Luster of base pearly, other faces vitreous. 
Color usually colorless, white or grayish; may show pale shades 
of green, yellow, rose. Usually transparent, rarely nearly 
opaque. 

Tests. Fuses easily with swelling to a white vesicular enamel. 
Colors the flame pale violet (potassium). Yields 16 per cent 
of water in C. T. Decomposed by hydrochloric acid with 
separation of silica but without the formation of a jelly. Solu- 
tion gives little or no precipitate with ammonia but gives an 
abundant white precipitate with ammonium carbonate (calcium 
carbonate) . Recognized usually by its crystals, color, luster and 
basal cleavage. 

Occurrence. Occurs commonly as a secondary mineral lining 
cavities in basalt and related rocks. Associated with various zeo- 
lites, with calcite, datolite, pectolite, etc. Found in fine crystals at 
Bergen Hill, New Jersey; Cliff Mine, Lake Superior copper district; 
Table Mountain, near Golden, Colorado; mercury mines, New Al- 
maden, California; Nova Scotia; Guanjuato, Mexico; near Bombay, 
India; Andreasberg, Harz Mountains; Faroer Islands; Iceland; 
Greenland, etc. 

Name. Apophyllite, named from two Greek words meaning 
to get leaves, because of its tendency to exfoliate when ignited. 



HARMOTONE 267 

ZEOLITES. 

The zeolites form a large family of hydrous silicates which 
show close similarities in composition and in their associations 
and mode of occurrence. They are silicates of aluminium with 
sodium and calcium as the important bases. They average 
from 3.5 to 5.5 in hardness and from 2 to 2.4 in specific gravity. 
Many of them fuse readily with marked intumescence, hence the 
name zeolite, from two Greek words meaning to boil and stone. 
They are secondary minerals found characteristically in cavities 
and veins in basic igneous rocks. 

Heulandite. 

Composition, H 4 CaAl 2 (SiO3)6.3H 2 O. Monoclinic, but crystals 
often simulate orthorhombic symmetry. Clinopinacoid prominent, 
having often a diamond shape. Perfect cleavage parallel to clino- 
pinacoid. H. = 3.5-4. G. = 2.15-2.2. Vitreous luster, except on 
clinopinacoid, which is pearly. Color white, yellow, red. Trans- 
parent to almost opaque. Fusible (3) with intumescence. Decom- 
posed by hydrochloric acid with separation of silica. Water in C. T. 
A mineral of secondary origin found in cavities of basic igneous 
rocks associated with other zeolites, calcite, etc. Found in notable 
quality in Iceland; the Faroer Islands; British India; Nova Scotia. 

Phillipsite. 

Composition, (K 2 ,Ca)Al 2 Si 4 Oi 2 .4H 2 O. Monoclinic. Crystals 
are uniformly penetration twins but often appearing to be tetragonal 
or orthorhombic in form. Cleavage parallel to base and clinopina- 
coid. H. = 4-4.5. G. = 2.2. Vitreous luster. White or reddish 
in color. Translucent to opaque. Fuses at 3 to a white enamel. 
Gelatinizes with hydrochloric acid. Water in C. T. A secondary 
mineral found in cavities of igneous rocks associated with other 
zeolites, etc. 

Harmotone. 

A barium zeolite having the composition (K 2 ,Ba)Al 2 Si4Oi2.3H 2 O. 
Monoclinic. Crystals are uniformly cruciform penetration twins. 
Perfect cleavage parallel to clinopinacoid. H. = 4.5. G. = 2.4- 
2.5. Vitreous luster. Colorless or white. Translucent. Fuses at 
3. Decomposed by hydrochloric acid with separation of silica. 
Addition of sulphuric acid to hydrochloric acid solution gives a 



268 MANUAL OF MINERALOGY 

white precipitate of barium sulphate. Water in C. T. A mineral of 
secondary origin, occurring in cavities of basic igneous rocks, asso- 
ciated with other zeolites, calcite, etc. 

Stilbite. Desmine. 

Composition. (Na2,Ca)Al 2 Si 6 Oi6.6H 2 0. 
Crystallization. Monoclinic. Uniformly in cruciform twins. 
Commonly tabular parallel to clinopinacoid. Crys- 
tals usually in sheaflike aggregates (Fig. 338). 

Structure. In crystal groups, divergent or radi- 
ated. 

Physical Properties. Perfect cleavage parallel 
to clinopinacoid. H. = 3.5-4. G. = 2.1-2.2. Vit- 
reous luster; pearly on clinopinacoid. Color white, 
yellow, brown, red. Translucent. 

Tests. Fuses with intumescence at 3. Decom- 
posed by hydrochloric acid with separation of silica 
but without the formation of a jelly. Water in 
Fig. 338. Q ,p Characterized chiefly by its cleavage, pearly 
luster on the cleavage face and common sheaflike groups of 
crystals. 

Occurrence. A mineral of secondary origin found in amygdaloidal 
cavities in basalts and related rocks. Found associated with other 
zeolites, calcite, etc. Notable localities for its occurrence are Poo- 
nah, India; IsleofSkye; Faroer Islands; Kilpatrick, Scotland; Ice- 
land; Nova Scotia. 

Name. Derived from a Greek word meaning luster. 

Laumontite. 

A zeolite with composition H4CaAl 2 Si4Oi4.2H 2 O. Monoclinic. 
In prismatic crystals with oblique terminations; columnar. Cleav- 
age parallel to prism and clinopinacoid. H. = 3.5-4. G. = 2.25- 
2.35. Vitreous to pearly luster. Color white or gray. Alters on 
exposure, becoming opaque and pulverulent. Fusible (2.5). Gelat- 
inizes in acids. Water in C. T. Found as a mineral of secondary 
origin in cavities of basic igneous rocks, associated with other zeo- 
lites, etc. 





ANALCITE 269 

Chabazite. 

Composition. Usually corresponds to (Ca,Na 2 )Al 2 Si40i2.6H 2 O 
but different analyses show considerable variation from this 
formula, so that the composition is still uncertain. 

Crystallization. Hexagonal-rhombohedral. Common form 
is the simple rhombohedron r, having nearly cubic angles. May 
show several different rhombo- 
hedrons (Fig. 339). Often in 
penetration twins. 

Structure. Usually in crys- 
tals. 

Physical Properties. H. = 
4-5. G.= 2.05-2.15. Vitreous 
luster. Color white, yellow, 
flesh-red. Transparent to trans- 
lucent. Fl - 339 - 

Tests. Fuses with swelling at 3. Decomposed by hydro- 
chloric acid with the separation of silica but without the for- 
mation of a jelly. Solution after filtering off silica gives pre- 
cipitate of aluminium hydroxide with ammonia, and in filtrate 
ammonium carbonate gives white precipitate of calcium carbo- 
nate. Gives much water in C. T. Recognized usually by its 
crystals. 

Occurrence. A mineral of secondary origin found usually with 
other zeolites, lining amygdaloidal cavities in basalt. Notable 
localities for its occurrence are the Faroer Islands; Greenland and 
Iceland; the Giant's Causeway, Ireland; at Aussig, Bohemia; in 
Nova Scotia, etc. 

Name. Chabazite is derived from a Greek word which was 
an ancient name for a stone. 

Gmelintie, (Na 2 ,Ca)Al 2 Si 4 Oi2.6H 2 0, is closely related to chaba- 
zite but rarer in occurrence. 

Analcite. 

Composition. Hydrous sodium-aluminium metasilicate, 
NaAlSi 2 6 .H 2 = Silica 54.5, alumina 23.2, soda 14.1, water 
8.2. Note similarity in composition to leucite, KAlSi 2 Oe. 



270 MANUAL OF MINERALOGY 

Crystallization. Isometric. Usually in trapezohedrons (Fig. 
340). Cubes with trapezohedral truncations also known (Fig. 
341). 





Fig. 340. Fig. 341. 

Structure. Usually in crystals, also massive granular. 

Physical Properties. H. = 5-5.5. G. = 2.27. Vitreous lus- 
ter. Colorless or white. Transparent to nearly opaque. 

Tests. Fusible at 3.5, becoming first opaque and then a clear 
glass. Colors the flame yellow (sodium). Decomposed by hy- 
drochloric acid with the separation of silica without the forma- 
tion of a jelly. Gives water in C. T. Usually recognized by its 
crystals and its vitreous luster. 

Occurrence. Commonly a secondary mineral, formed by the 
action of hot circulating waters, and is to be found deposited in the 
cavities of igneous and especially volcanic rocks. Associated with 
calcite, and various zeolites and related minerals. Fine crystals 
found at Bergen Hill, New Jersey; in the Lake Superior copper 
district; at Table Mountain, near Golden, Colorado; at Cape 
Blomidon, Nova Scotia; in the Cyclopean Islands near Sicily; in 
the Fassathal, Tyrol; on the Faroer Islands; in Iceland. 

Name. Derived from a Greek word meaning weak, in allusion 
to its weak electric power when heated or rubbed. 

Natrolite. 

Composition. Na 2 Al 2 Si30io.2H 2 0. A zeolite. 

Crystallization. Orthorhombic. Crystals usually slender 
prismatic, often acicular. Prism zone vertically striated. Some- 
times terminated by low pyramid. Crystals often appear to 
be tetragonal in symmetry. Sometimes in cruciform twins. 






MICA GROUP 271 

Structure. Usually in radiating crystal groups (see Fig. C, 
pi. II) ; also fibrous, massive, granular or compact. 

Physical Properties. Perfect prismatic cleavage. H. = 5-5.5. 
G. = 2.25. Vitreous luster. Colorless or white. Sometimes 
tinted yellow to red. Transparent to translucent. 

Tests. Easily fusible (2.5) to a clear, transparent glass giving 
a yellow (sodium) flame. Water in C. T. Soluble in hydro- 
chloric acid and gelatinizes upon evaporation. Recognized 
chiefly by its radiating crystals. 

Occurrence. A mineral of secondary origin, found lining amygda- 
loidal cavities in basalt, etc. Associated with other zeolites, calcite, 
etc. Notable localities for its occurrence are Aussig and Teplitz, 
Bohemia; Puy de Dome, France; Fassathal, Tyrol; Kapnik, Hun- 
gary; in various places in Nova Scotia; Bergen Hill, New Jersey; 
copper district, Lake Superior. 

Scolecite. 

A zeolite with composition CaAl 2 Si3Oio.3H 2 O. Monoclinic. In 
slender prismatic, twinned crystals. In radiating groups. Some- 
times fibrous. Prismatic cleavage. H. = 5-5.5. G. = 2.16-2.4. 
Vitreous luster; silky when fibrous. Colorless or white. Trans- 
parent to almost opaque. Fuses at 2.5 to a voluminous frothy slag. 
Gelatinizes in acids. Water in C. T. A mineral of secondary origin, 
found lining cavities in basic igneous rocks, associated with other 
zeolites, etc. 

Thomsonite. 

A zeolite, having the composition (Na 2 Ca)Al 2 (SiO 4 ) 2 .2|H 2 O. 
Orthorhombic but distinct crystals rare. Commonly columnar 
with radiated structure. Perfect pinacoidal cleavage. H. = 5-5.5. 
G. = 2.3-2.4. Vitreous luster. Colorless, white, gray. Transparent 
to translucent. Fuses with intumescence at 2-2.5. Soluble and 
gelatinizes in acids. Much water in C. T. Occurs in amygdaloidal 
cavities in basalt, etc., associated with other zeolites. 

MICA DIVISION. 
MICA GROUP. 

The micas form a series of complex silicates of aluminium with 
potassium and hydrogen, also often magnesium, ferrous iron, 
and in some varieties, sodium, lithium, ferric iron. More rarely 
manganese, chromium, barium, fluorine and titanium are present 



272 MANUAL OF MINERALOGY 

in small amounts. The composition of many of the micas is 
not definitely understood and the formulas assigned to them 
are only approximate. 

They crystallize in the monoclinic system but with an axial 
inclination of practically 90, so that their monoclinic sym- 
metry is not clearly seen. The crystals are usually tabular with 
prominent basal planes, and have either a diamond- or hexagonal- 
shaped outline with angles of 60 and 120. The crystals, as a 
rule, therefore, appear to be either orthorhombic or hexagonal 
in their symmetry. They are all characterized by a very perfect 
basal cleavage. 

They form an isomorphous series, and various gradations 
between the different members occur. Their isomorphism is 
further indicated by two members of the group frequently 
crystallizing together, with a parallel position, in the same 
crystal plate. Biotite occurs crystallizing in this way with 
muscovite, and muscovite with lepidolite, etc. 

The important members of the group follow: 

Muscovite, H 2 KAl3(Si0 4 ) 3 . 
Lepidolite, KLi[A1.2(OH,F)]Al(Si0 3 ) 3 . 
Biotite, (H,K) 2 (Mg,Fe) 2 Al 2 (SiO 4 )3. 

Phlogopite, H 2 KMg 3 Al(SiO 4 ) 3 ? 
Lepidomelane, (H,K) 2 Fe 3 (Fe, Al) 4 (Si0 4 ) 5 ? 

Muscovite. Common Mica. 

Composition. H 2 KAl 3 (Si0 4 ) 3 . Contains also frequently small 
amounts of ferrous and ferric iron, magnesium, calcium, sodium, 
lithium, fluorine, titanium, etc. 

Crystallization. Monoclinic with axial angle nearly 90. 
Occurs in tabular crystals with prominent base. The pres- 
ence of prism faces having angles of 60 and 120 with each 
other gives the plates a diamond-shaped outline, making them 
simulate orthorhombic symmetry. If the clinopinacoid faces 
are also present, the crystals become hexagonal in outline with 
apparently hexagonal symmetry. The prism faces are roughened 
by horizontal striations and frequently taper. 



MUSCOVITE 273 

Structure. Foliated in large to small sheets;- in scales which 
are sometimes aggregated into plumose or globular forms. Dis- 
tinct crystals comparatively rare. 

Physical Properties. Extremely perfect cleavage parallel to 
base, allowing the mineral to be split into excessively thin sheets. 
Folia flexible and elastic. H. = 2-2.5. G. = 2.76-3. Vitre- 
ous to silky or pearly luster. Transparent and almost colorless 
in thin sheets. In thicker blocks, opaque with light shades of 
brown and green. May be yellow to white. Some crystals are 
translucent when viewed perpendicular to the prism zone but 
opaque in a direction perpendicular to the base. 

Tests. Fusible at 4.5-5. Unattacked by boiling hydro- 
chloric or sulphuric acids. Characterized by its micaceous 
structure and light color. Told from phlogopite by its not being 
decomposed in sulphuric acid and from lepidolite by not giving 
a crimson flame B. B. 

Occurrence. A widespread and very common rock-making min- 
eral. Found in such igneous rocks as granite and syenite. Espe- 
cially characteristic of pegmatite veins, and found lining cavities 
in granites, where it has evidently been formed by the action of 
mineralizing vapors during the last stages of the formation of the 
rock. Muscovite is chiefly characteristic of the deep-seated igneous 
rocks, and is not found in the recent eruptive rocks. Also very 
common in metamorphic rocks, as gneiss and schist, forming the 
chief constituent in certain mica-schists. In some schistose rocks 
it occurs in the form of fibrous aggregates of minute scales having a 
silky luster, but which do not show so plainly the characters of the 
mineral. This variety is known as sericite, and is usually the prod- 
uct of alteration of feldspar. Muscovite also originates, as the 
alteration product of several other minerals, as topaz, cyanite, 
spodumene, adalusite, scapolite, etc. Finite is a name given to the 
micaceous alteration product of various minerals, and which corre- 
sponds in composition more or less closely to muscovite. 

In the pegmatite veins, muscovite occurs associated with quartz 
and feldspar, with tourmaline, beryl, garnet, apatite, fluorite, etc. 
It is found often in these veins in large blocks, which are at times 
several feet across. 

Muscovite is found in the United States in commercial deposits 
chiefly in the Appalachian and Rocky Mountain regions. The 
most productive pegmatite veins occur in North Carolina, mostly 
in Mitchell, Yancey, Haywood, Jackson and Macon counties, and 



274 MANUAL OF MINERALOGY 

in the Black Hills of South Dakota. Of less importance are the 
deposits in Colorado, Alabama and Virginia. Muscovite has been 
mined in New Hampshire, Maine and Connecticut. Large deposits 
are found in Canada in the township of Grenville, east of Ottawa, 
and in a district to the east of Quebec. Large and important 
deposits occur in India. 

Name. Muscovite was so called from the popular name of the 
mineral, Muscovy-glass, because of its use as a substitute for 
glass in Russia. Mica was probably derived from the Latin 
micare, meaning to shine. 

Use. Used chiefly as an insulating material in the manufac- 
ture of electrical apparatus. Used as a transparent material 
(isinglass) for stove doors, lanterns, etc. Scrap mica, or the 
waste material in the manufacture of sheet mica, is used in many 
ways, as in the manufacture of wall papers to give them a shiny 
luster; as a lubricant when mixed with oils; as a nonconductor 
of heat and as a fireproofing material. 



Lepidolite. 

Composition. Lithia mica, KLi[A1.2(OH.F)]Al(SiO 8 ) 3 . 

Crystallization. Monoclinic. Crystals usually in small 
plates or prisms with hexagonal outline. 

Structure. Commonly in coarse- to fine-grained scaly aggre- 
gates. 

Physical Properties. Perfect basal cleavage. H. = 2.5-4. 
G. = 2.8. Pearly luster. Color pink and lilac to grayish white. 
Translucent. 

Tests. Easily fusible (2), giving a crimson flame (lithium). 
Insoluble in acids. Characterized chiefly by its micaceous 
structure and lilac to pink color. 

Occurrence. A comparatively rare mineral, found in pegmatite 
veins, usually associated with pink and green tourmaline, cassiterite, 
amblygonite, spodumene, etc. Often intergrown with muscovite in 
parallel position. Notable localities for its occurrence are at Roznau, 
Moravia; St. Michael's Mount, Cornwall; western Maine at Hebron, 
Auburn, Norway, Paris, Rumford; Chesterfield, Massachusetts; San 
Diego County, California. 



PHLOOOPITE 275 

Name. Derived from a Greek word meaning scale. 
Use. A source of lithium compounds. 

Biotite. 

Composition. (H,K) 2 (Mg,Fe) 2 Al 2 (Si04)3. 

Crystallization. Monoclinic. In tabular or short prismatic 
crystals with prominent basal planes. Crystals rare, frequently 
pseudorhombohedral. 

Structure. Usually in irregular foliated masses; often in dis- 
seminated scales or in scaly aggregates. 

Physical Properties. Perfect basal cleavage. Folia flexible 
and elastic. H. = 2.5-3. G. = 2.95-3. Splendent luster. Color 
usually dark green and brown to black. More rarely lighter 
yellow. Thin sheets usually have a smoky color (differing from 
the almost colorless muscovite). 

Tests. Difficultly fusible at 5. Unattacked by hydrochloric 
acid. Decomposed by boiling concentrated sulphuric acid, giv- 
ing a milky solution. Characterized by its micaceous structure, 
cleavage and dark color. 

Occurrence. An important and widely distributed rock-making 
mineral, but not as common as muscovite. Occurs in igneous rocks, 
especially those in which feldspar is prominent, such as granite and 
syenite. Found also in many felsite lavas and porphyries. Less 
common in the ferromagnesium rocks. Is also present in some 
metamorphosed rocks, as gneiss and schist. Occurs in fine crystals 
in the lavas of Vesuvius. 

Phlogopite. 

Composition. A magnesium mica, near biotite, but contain- 
ing no iron, H 2 KMg3Al(Si0 4 )3(?). Usually contains about 3 per 
cent of fluorine. 

Crystallization. Monoclinic. Usually in six-sided plates or 
in tapering prismatic crystals. Crystals frequently large and 
coarse. 

Structure. In crystals or foliated masses. 

Physical Properties. Perfect basal cleavage. Folia flexi- 
ble and elastic. H. = 2.5-3. G. = 2.86. Luster vitreous to 



276 MANUAL OF MINERALOGY 

pearly. Color yellowish brown, green, white, often with copper- 
like reflections from the cleavage surface. Transparent in thin 
sheets to opaque in the mass. 

Tests. Fusible at 4.5-5. Insoluble in hydrochloric acid. 
Decomposed by boiling concentrated sulphuric acid, giving a 
milky solution. Characterized by its micaceous structure, cleav- 
age and yellowish brown color. Told from muscovite by its 
decomposition in sulphuric acid and from biotite by its lighter 
color. But it is impossible to draw a sharp distinction between 
biotite and phlogopite. 

Occurrence. Occurs as a product of metamorphism in crystalline 
magnesium limestones or dolomitic marbles. Rarely found in ig- 
neous rocks. Notable localities are in Finland; Sweden; Campo- 
longo, Switzerland; Ceylon, etc. In North America, found chiefly 
in Jefferson and St. Lawrence counties, New York; at North and 
South Burgess, Ontario, and in various localities in Quebec, Canada. 

Name. Named from a Greek word meaning firelike, in allu- 
sion to its color. 
Use. Same as for muscovite. 

Lepidomelane. 

A mica, that may be regarded as a variety of biotite, characterized 
by the large amount of ferric iron that it contains, (H,K) 2 Fe 3 (Fe,Al) 4 - 
(SiO^sC?). Monoclinic. In small hexagonal-shaped tables, or as 
an aggregate of minute scales. Perfect basal cleavage. H. = 3. 
G. = 3-3.2. Adamantine to pearly luster. Color black to green- 
ish black. Opaque or translucent in very thin laminae. Fuses at 
4.5-5 to a magnetic globule. Decomposed by hydrochloric acid. 
A comparatively rare mineral, found chiefly in pegmatitic granites 
and syenites. 

CLINTONITE GROUP. 

The minerals of this group are rare species that lie between 
the true micas and the chlorites. They resemble the micas in 
crystal forms, cleavage, etc., but differ physically in that their 
folia are brittle, and chemically in that they are basic in char- 
acter. The only species in the group that warrants description 
is margarite. 



CLINOCHLORE 277 



Margarite. 



A micaceous mineral with the composition H-jCaAhSiaO^. Mono- 
clinic but seldom in distinct crystals. Usually in foliated aggregates. 
Perfect basal cleavage. H. = 3.5-4.5 (harder than the true micas). 
G. = 3.05. Luster vitreous to pearly. Color pink, white and gray. 
Translucent. Folia somewhat brittle. Fuses at 4-4.5. Unat- 
tacked by acids. Occurs usually with corundum and apparently as 
one of its alteration products. Found in this way with the emery 
deposits of Asia Minor; on the islands of the Greek archipelago; at 
Chester, Massachusetts; Chester County, Pennsylvania; with co- 
rundum deposits in North Carolina, etc. 

CHLORITE GROUP. 

A somewhat ill-defined group of closely related micaceous 
minerals is known as the Chlorite Group or as the chlorites. 
They are so named on account of the characteristic green color 
that they show. They are silicates of aluminium with magne- 
sium, ferrous iron and hydroxyl. Ferric iron may replace the 
aluminium in small amount. Chromium and manganese may 
occur. Calcium and the alkalies, which are characteristic of 
the micas proper, are practically absent. The composition 
of these minerals is not fully understood. Their crystal forms 
are similar to those of the micas and they show a perfect basal 
cleavage. Their laminae, however, are tough and inelastic. 
Clinochlore is the most common member of the group. 

Clinochlore. Penninite. 

Composition. H 8 Mg5Al 2 Si s Oi8. See above. 

Crystallization. Monoclinic. In six-sided tabular crystals, 
with prominent basal planes. Similar in habit to the crystals 
of the mica group, but distinct crystals rare. Penninite is 
pseudorhombohedral in symmetry, otherwise it is identical with 
clinochlore. 

Structure. Usually foliated massive or in aggregates of 
minute scales; in finely disseminated particles; earthy. 

Physical Properties. Perfect basal cleavage. Folia flexible 
but not elastic. H. = 2-2.5. G. = 2.65-2.75. Vitreous to 



278 MANUAL OF MINERALOGY 

pearly luster. Color green of various shades. Rarely pale 
green, yellow, white, rose-red. Transparent to opaque. 

Tests. Difficultly fusible, 5-5.5. Unattacked by hydro- 
chloric acid. Decomposed by boiling concentrated sulphuric 
acid, giving a milky solution. Characterized by its green color, 
micaceous structure and cleavage and by the fact that the folia 
are not elastic. 

Occurrence. A common and widespread mineral, always of sec- 
ondary origin. It results from the alteration of silicates containing 
aluminium, ferrous iron and magnesium, such as pyroxene, amphi- 
bole, biotite, garnet, vesuvianite, etc. To be found where rocks, 
containing such minerals, are undergoing metamorphic change. 
The green color of many igneous rocks is due to the chlorite into 
which the ferromagnesian silicates have altered. The green color of 
many schists and slates is due to finely disseminated particles of the 
mineral. 

Name. Chlorite is derived from a Greek word meaning green, 
in allusion to the common color of the mineral. 

Serpentine. 

Composition. A magnesium silicate, H 4 Mg3Si 2 9 = Silica 44. 1 , 
magnesia 43.0, water 12.9. Ferrous iron and nickel may be 
present in small amount. 

Crystallization. Monoclinic (optically). Occurs, however, 
only in pseudomorphic crystals. 

Structure. Often in delicate fibers, which can be separated 
from each other (see Fig. D, pi. II). Usually massive, but 
microscopically fibrous and felted. 

Physical Properties. H. = 2.5-5, usually 4. G. = 2.5-2.65. 
Luster greasy, waxlike in the massive varieties, silky when 
fibrous. Color olive to blackish green, yellowish green, white. 
Color often variegated, showing mottling in lighter and darker 
shades of green. Translucent to opaque. 

Tests. Infusible. Decomposed by hydrochloric acid with the 
separation of silica but without the formation of a jelly. Fil- 
tered solution, after being oxidized with nitric acid and having 
any iron precipitated by ammonium hydroxide, and the absence 



SERPENTINE 279 

of calcium proved by addition of ammonium oxalate, gives a 
precipitate of ammonium-magnesium phosphate with sodium 
phosphate. Water in C. T. Recognized by its variegated green 
color and its greasy luster or by its fibrous structure. 

Varieties. In Crystals. Occurs in crystals as pseudomorphs 
after various magnesian silicates, principally chrysolite, pyroxene, 
amphibole. 

Precious Serpentine. Massive, translucent, of light to 
dark green color. Often mixed with white marble and shows 
beautiful variegated coloring. Frequently called verd antique 
marble. 

Ordinary Serpentine. Massive, opaque, of various shades of 
green. 

Chrysotile. The fibrous asbestiform variety, which is to be 
found in veins traversing the massive serpentine. This is the 
asbestos of commerce for the most part. 

Occurrence. A common mineral and widely distributed. Always 
as an alteration product of some magnesian silicate, especially chryso- 
lite, also pyroxene, amphibole, etc. Frequently associated with 
magnesite, chrysolite, chromite, etc. Found in both igneous and 
metamorphic rocks, sometimes in disseminated particles, sometimes 
in such quantity as to make up practically the entire rock-mass. 
Precious serpentine is found at Falun and Gulsjo, Sweden; Isle of 
Man; Cornwall, etc. The fibrous variety, chrysotile, comes from the 
Province of Quebec, Canada, just north of the Vermont line; from 
Vermont; New York; New Jersey; Grand Canyon, Arizona, etc. 

Name. The name refers to the green serpentlike cloudings 
of the massive variety. 

Use. The variety chrysotile is the chief source of asbestos. 
Fibrous amphibole (which see) is also used for the same purposes. 
The uses of asbestos depend upon its fibrous, flexible structure, 
which allows it to be woven into cloth, felt, etc., and upon 
its incombustibility and slow conductivity of heat. Asbestos 
products, therefore, are used for fireproofing and as an insulating 
material against heat and electricity. The massive mineral is 
often used as an ornamental stone and may at times be valuable 
as building material. 



280 MANUAL OF MINERALOGY 



Genthite. Garnierite. 

Nickel silicates of uncertain composition. Genthite contains mag- 
nesium, Ni 2 Mg2Si3Oio.6H 2 O(?) ; Garnierite, H 2 NiSiO 4 (?) . Amorphous, 
earthy to slightly botryoidal structure. As incrustations. H. = 
3-4. G. = 2.2-2.8. Earthy and dull luster. Color apple-green 
to white. Infusible. Difficultly decomposed by hydrochloric acid, 
giving separated silica. In O. F. color the borax bead brown. In 
C. T. blacken and give water. Genthite found with chromite at 
Texas, Lancaster County, Pennsylvania. Garnierite occurs in con- 
siderable amount, associated with serpentine and chromite, near 
Noumea, New Caledonia, and serves as an important ore of nickel. 

Talc. Steatite. Soapstone. 

Composition. A magnesium silicate, H 2 Mg 3 (Si0 3 )4 = Silica 
63.5, magnesia 31.7, water 4.8. 

Crystallization. Monoclinic. Crystals rare. Usually tabu- 
lar with rhombic or hexagonal outline. 

Structure. Foliated massive; sometimes in radiating foliated 
groups. Also compact. 

Physical Properties. Perfect basal cleavage. Thin folia 
somewhat flexible but not elastic. Sectile. H. = 1 (will make 
a mark on cloth). G. = 2.8. Pearly to greasy luster. Color 
apple-green, gray, white; in soapstone often dark gray or green. 
Translucent to opaque. Greasy feel. 

Tests. Difficultly fusible (5). Unattacked by acids. Char- 
acterized by its micaceous structure and cleavage, by its softness 
and greasy feel. To be distinguished from pyrophyllite by 
moistening a fragment with cobalt nitrate and heating intensely; 
talc will assume a pale violet color, pyrophyllite a blue color. 

Varieties. Foliated Talc. Light green or white, foliated, with 
a greasy feel. 

Steatite or Soapstone. Massive, with fine granular to crypto- 
crystalline structure. Gray to dark green colors; often impure, 
through the presence of such minerals as chlorite, tremolite, 
mica, etc. 

Pseudomorphous. Is frequently pseudomorphous after such 
minerals as enstatite, pyroxene, amphibole, chrysolite, etc. 



KAOLIN 281 

Occurrence. Talc is a mineral of secondary origin formed by 
the alteration of magnesium silicates, such as chrysolite, enstatite, 
pyroxene, amphibole, etc. Found at times in the igneous rocks, 
because of the alteration of such silicates, especially in peridotites 
and pyroxenites. Most characteristically found, however, in the 
metamorphic rocks, where it may form as soapstone, practically the 
entire rock-mass, or occur as a prominent constituent in the schistose 
rocks, as in talc-schist. In the United States, talc or soapstone 
quarries are to be found chiefly along the line of the Appalachian 
Mountains, the mineral being produced in Vermont, Massachusetts, 
Rhode Island, New York, New Jersey, Pennsylvania, Maryland, 
Virginia, North Carolina, and Georgia. Important deposits are 
located in St. Lawrence County, New York, where the talc occurs 
in the form of beds of schist interstratified with limestones. It is 
associated here with tremolite and enstatite, from masses of which 
it has evidently been derived. Large deposits of soapstone occur in 
Virginia in a narrow belt running from Nelson County northeast 
into Albemarle County. It occurs here in sheets sometimes 100 or 
more feet in thickness. There is a long series of talc and soapstone 
deposits in Vermont, located along the east side of the Green Moun- 
tains. Talc has been mined in considerable quantity in Swain 
County, North Carolina. 

Use. In the form of slabs, soapstone is used extensively for 
wash tubs, sinks, table tops, electrical switchboards, hearth- 
stones, furnace linings, etc. An especially compact variety is 
used for the tips of gas burners, for tailors' chalk, slate pencils, 
by the Chinese for carvings, etc. Talc is also used in a finely 
powdered form as a filler to give weight to paper, as a lubricant, 
for toilet powders, in paints, as a heat insulator, etc. 



Kaolin or Kaolinite. 

Composition. An aluminium silicate, H4Al 2 Si 2 9 = Silica 46.5, 
alumina 39.5, water 14. 

Crystallization. Monoclinic. In very minute, thin, rhombic 
or hexagonal-shaped plates. 

Structure. Usually in claylike masses, either compact or 
friable. 

Physical Properties. Perfect basal cleavage. H. = 2-2.5. 
G. = 2.6-2.63. Luster usually dull earthy; crystal plates 



282 MANUAL OF MINERALOGY 

pearly. Color white. Often variously colored by impurities. 
Usually unctuous and plastic. 

Tests. Infusible. Insoluble. Assumes a blue color when 
moistened with cobalt nitrate and ignited (aluminium). Recog- 
nized usually by its claylike character. 

Occurrence. Of widespread occurrence. The chief constituent 
of clay. Always a mineral of secondary origin, being derived by the 
alteration of aluminium silicates, particularly feldspar. It is found 
mixed with feldspar in rocks that are undergoing alteration; at 
times it forms entire beds where such alteration has been carried to 
completion. As one of the common products of the decomposition 
of rocks it gets into soils and being transported by water is deposited, 
mixed with quartz and other materials in lakes, etc., in the form of 
beds of clay. 

Name. Kaolin is a corruption of the Chinese, Kauling, a 
locality from which material was obtained for the manufacture 
of porcelain and which was thought to be the same as kaolin. 

Use. Used in the form of clay in making all kinds of pottery, 
stoneware, bricks, etc. The finer, purer grades of kaolin are 
used in the manufacture of porcelain, china, etc. 

Pyrophyllite. 

Composition. H 2 Al 2 (Si0 3 )4 = Silica 66.7, alumina 28.3, water 
5.0. 

Crystallization. Monoclinic (?). Not observed in crystals. 

Structure. Foliated, sometimes in radiating lamellar aggre- 
gates. Also granular to compact. Identical with talc in struc- 
ture and appearance. 

Physical Properties. Perfect basal cleavage. Folia some- 
what flexible but not elastic. H. = 1-2 (will make a mark on 
cloth). G. = 2.8-2.9. Pearly to greasy luster. Color white, 
apple-green, gray, brown. Usually opaque. Greasy feel. 

Tests. Infusible. Unattacked by acids. Characterized 
chiefly by its micaceous structure and cleavage, its softness and 
greasy feel. Only to be easily distinguished from talc by mois- 
tening a small fragment with cobalt nitrate and igniting, when 
it assumes a blue color (aluminium). Talc under the same 
conditions would become pale violet. 



TITANITE 283 

Occurrence. A comparatively rare species. Found in meta- 
morphic rocks; frequently with cyanite. Occurs in considerable 
amount in Moore and Chatham counties, North Carolina. 

Use. Quarried in North Carolina and used for the same pur- 
poses as talc. It does not command, however, as high a price 
as the best grades of talc. A considerable part of the so-called 
agalmatolite, from which the Chinese carve small images, is 
this species. 

Chrysocolla. 

Composition. Hydrous copper silicate, CuSi0 3 .2H 2 = Silica 
34.3, copper oxide 45.2, water 20.5. Varies considerably in com- 
position and often impure. 

Structure. Noncrystalline. Massive compact. Sometimes 
earthy. 

Physical Properties. H. = 2-4. G. = 2.0-2.4. Luster vit- 
reous to earthy. Color green to greenish blue; brown to black 
when impure. 

Tests. Infusible. Decomposed by hydrochloric acid with 
the separation of silica but without the formation of a jelly. 
Gives a copper globule when fused with sodium carbonate on 
charcoal. In C. T. darkens and gives water. 

Occurrence. A comparatively rare mineral occurring in the 
oxidized zones of copper veins. Associated with malachite, azurite, 
cuprite, native copper, etc. Found in the copper districts of Arizona 
and New Mexico. 

Name. Chrysocolla, derived from two Greek words meaning 
gold and glue, which was the name of a similar appearing mate- 
rial used to solder gold. 

Use. A minor ore of copper. 

Titanite. Sphene. 

Composition. Calcium titano-silicate, CaTiSi0 6 = Silica 30.6, 
titanium oxide 40.8, lime 28.6. Iron is usually present in small 
amounts. 

Crystallization. Monoclinic. Crystals varied in habit. 
Often with prominent basal plane which is steeply inclined and 



284 



MANUAL OF MINERALOGY 



which in combination with short prism and pyramid faces 
a thin wedge-shaped crystal (Figs. 342 and 343). 





Fig. 342. 



Fig. 343. 



Structure. Usually crystallized or lamellar. 

Physical Properties. Prismatic cleavage. H. = 5-5.5. G.= 
3.4-3.55. Resinous to adamantine luster. Color gray, brown, 
green, yellow, black. Transparent to opaque. 

Tests. Fusible at 4 with slight intumescence to a dark mass. 
Only slightly attacked by hydrochloric acid. Fused with sodium 
carbonate; fusion dissolved in hydrochloric acid; the solution 
when boiled with tin gives a violet color (titanium). 

Occurrence. A rather common accessory mineral in igneous rocks, 
being found as small crystals in granites, diorites, syenites, trachytes, 
phonolites, etc. Also found often in crystals of considerable size 
embedded in the metamorphic rocks, gneiss, chlorite-schist and 
crystalline limestone. Very commonly associated with chlorite. 
Also found with iron ores, pyroxene, amphibole, scapolite, zircon, 
apatite, feldspar, quartz, etc. Notable localities for its occurrence 
in crystals are Tavetsch, St. Gothard, etc., Switzerland; Ala, Pied- 
mont; Sandford, Maine; Gouverneur, Diana, Rossie, Fine, Pitcairn, 
Edenville, Brewster, etc., in New York; in various places in Ontario, 
Canada. 

Name. Sphene comes from a Greek word meaning 'wedge in 
allusion to a characteristic development of the crystals. 
Perovskite, CaTi0 3 , is a rare isometric titanate. 

NIOBATES TANTALATES. 

Columbite Tantalite. 

Composition. A niobate and tantalate of ferrous iron and 
manganese (Fe,Mn)(Nb,Ta) 2 6 which varies in composition from 
the niobate, colwnbite (Fe,Mn)Nb 2 6 , to the tantalate, tantalite 



COLUMBITE TANTALITE 



285 




Fig. 344. 



Also 



(Fe,Mn)Ta 2 6 . Often contains small amounts of tin, tungsten, 
etc. A variety, known as manganotantalite, is essentially a 
tantalite with most of the iron re- 
placed by manganese. 

Crystallization. Orthorhombic. 
Habit of crystals is short prismatic; 
often in square prisms because of 
prominent development of the verti- 
cal pinacoids. Terminated by basal 
plane, pyramids and domes; fre- 
quently complex (Fig. 344). At 
times in heart-shaped contact twins. 

Structure. Crystallized and in parallel crystal groups. 
frequently granular massive. 

Physical Properties. H. = 6. G. = 5.3-7.3, varying with 
the composition, increasing with rise in percentage of tantalum 
oxide present. Submetallic luster. Color iron-black, frequently 
iridescent. Streak dark red to black. 

Tests. Difficultly fusible (5-5.5). Fused with borax; the 
bead dissolved in hydrochloric acid; the solution boiled with 
tin gives a blue color (niobium). There is no simple test for 
tantalum. Generally when fused in 0. F. with sodium car- 
bonate gives an opaque bluish green bead. Fused with sodium 
carbonate on charcoal in R. F. yields a magnetic mass. Recog- 
nized usually by its black color, submetallic streak and high 
specific gravity. 

Occurrence. Occurs in granite rocks and in pegmatite veins, 
associated with quartz, feldspar, mica, tourmaline, beryl, spodu- 
mene, cassiterite, samarskite, wolframite, microlite, monazite, etc. 
Notable localities for its occurrence are the west coast of Greenland ; 
Bodenmais, Bavaria; llmen Mountains, Siberia; Western Australia 
(manganotantalite); Standish, Maine; Haddam, Middletown and 
Branchville, Connecticut; in Amelia County, Virginia; Mitchell 
County, North Carolina; Black Hills, South Dakota; near Canon 
City, Colorado. 

Name. The two names are derived from the acid elements 
that the minerals contain. Niobium is often called columbium. 



286 MANUAL OF MINERALOGY 

Use. Source of tantalum, which is used in making filaments 
for incandescent electric lamps. It is said that more than 
20,000 20-candle-power electric-light filaments can be made 
from one pound of tantalum. The tantalum, used for this pur- 
pose in the United States, is imported and is derived, chiefly, 
from the manganotantalite deposits of western Australia. 

There are a number of other niobates and tantalates, all of 
which are rare in occurrence. The following, however, might 
be mentioned : pyrochlore, chiefly a niobate of the cerium metals 
and calcium; microlite, essentially Ca 2 Ta 2 7 ; fergusonite, a nio- 
bate of yttrium, erbium, cerium, uranium, etc.; samarskite, a 
niobate and tantalate of ferrous iron, uranium and the cerium 
metals. 

PHOSPHATES, ETC. 

The phosphates and the related arsenates, vanadates and 
antimonates may be divided into three classes: (1) Anhydrous 
Phosphates, etc.; (2) Acid and Basic Phosphates, etc.; (3) Hydrous 
Phosphates, etc. 

1. ANHYDROUS PHOSPHATES, ETC. 
Xenotime. 

Yttrium phosphate, YPO 4 Erbium may be present in consider- 
able amount, also small amounts of cerium, silicon and thorium. 
Tetragonal. Crystal forms resemble those of zircon. In rolled 
grains. Prismatic cleavage. H. = 4-5. G. = 4.55-5.1. Vitreous 
to resinous luster. Color yellowish to reddish brown. Opaque. 
Infusible. Tests as in monazite, which see. A rare mineral which 
occurs, like monazite, as an accessory constituent in granite, gneiss 
and pegmatite veins. Found as rolled grains in the stream sands, 
particularly in Brazil. 

Monazite. 

Composition. A phosphate of the cerium metals 
(Ce,La,Di)P0 4 with usually some thorium silicate, ThSi0 4 . 

Crystallization. Monoclinic. Crystals usually small, often 
flattened parallel to the orthopinacoid. 

Structure. Usually in granular masses, frequently as sand. 
Crystals rare. 



TRIPHYLITE LITHIOPHILITE 287 

Physical Properties. H. = 5-5.5. G. = 5.2-5.3. Resinous 
luster. Color yellowish to reddish brown. Translucent to 
opaque. 

Tests. Infusible. Insoluble in hydrochloric acid. After fusion 
with sodium carbonate, dissolve in nitric acid and add solution to 
excess of ammonium molybdate solution. A yellow precipitate 
forms (test for a phosphate) . Decomposed by heating with con- 
centrated sulphuric acid; solution after dilution with water and 
filtering gives with ammonium oxalate a precipitate of the oxa- 
lates of the rare earths. 

Occurrence. A comparatively rare mineral occurring as an acces- 
sory mineral in gneissoid rocks, and as rolled grains in the sands 
derived from the decomposition of such rocks, where it has been 
preserved because of its hardness and high specific gravity. Found 
in the United States, chiefly in North and South Carolina, both in 
gneiss and in the stream sands. The bulk of the world's supply of 
monazite sand comes from the provinces of Minas .Geraes, Rio de 
Janeiro, Bahia, and Sao Paulo, Brazil. 

Name. The name monazite is derived from a Greek word 
meaning to be solitary, in allusion to the rarity of the mineral. 

Use. Monazite is the chief source of thorium oxide, which it 
contains in amounts varying from 1 to 20 per cent; commercial 
monazite usually containing between 3 and 9 per cent. Thorium 
oxide is used in the manufacture of mantles for incandescent gas 
lights. 

Triphylite Lithiophilite. 

Phosphates of lithium with ferrous iron and manganese. Tri- 
phylite corresponds to LiFePO 4 , Lithiophilite to LiMnPO 4 . The 
two molecules are isomorphous and replace each other in varying 
amounts. Orthorhombic, crystals rare. Commonly massive, cleav- 
able to compact. Cleavage parallel to base and brachypinacoid. 
H. = 4.5-5. G. = 3.42-3.56. Luster vitreous to resinous. Color 
bluish gray in triphylite to salmon-pink or clove-brown in lithio- 
philite. Translucent. Fusible at 2.5, giving red lithium flame. 
Triphylite becomes magnetic on heating in R. F. Lithiophilite gives 
in O. F. an opaque bluish green bead with sodium carbonate. Sol- 
uble in nitric acid and when the solution is added to an excess of a 
solution of ammonium molybdate gives yellow precipitate (test for 
phosphoric acid). Rare minerals occurring in pegmatite veins asso- 
ciated with other phosphates, etc. Triphylite found at Huntington, 



288 



MANUAL OF MINERALOGY 



Massachusetts; Peru, Maine; Grafton, New Hampshire; Raben- 
stein, Bavaria; Keityo, Finland. Lithiophilite found at Branch ville, 
Connecticut. 

THE APATITE GROUP. 

The Apatite Group consists of a closely related series of min- 
erals crystallizing in the pyramidal group of the hexagonal 
system. They are: 

Apatite, . Ca 4 (CaF)(P0 4 ) 3 . 

Pyromorphite, Pb 4 (PbCl)(P0 4 ) 3 . 

Mimetite, Pb 4 (PbCl) (As0 4 ) 3 . 

Vanadinite, Pb 4 (PbCl) (V0 4 ) 3 . 

Apatite. 

Composition. Fluor-apatite, Ca 4 (CaF)(P0 4 ) 3 ; more rarely 
chlor-apatite, Ca^CaClXPOOs. 

Crystallization. Hexagonal; tri-pyramidal. Crystals usually 
long prismatic in habit; sometimes short prismatic or tabular. 





Usually terminated by prominent pyramid of first order and 
frequently, a basal plane (Figs. 345 and 346). Some crystals 
show faces of the third order pyramid and have at times a very 
complex development. 

Structure. Usually crystallized; also granular massive to 
compact. 

Physical Properties. H. = 5 (can just be scratched by a 
knife). G. = 3.15. Vitreous to subresinous luster. Color 
usually some shade of green or brown; also blue, violet, colorless. 
Transparent to opaque. 



APATITE 289 

Tests. Difficultly fusible (5-5.5). Soluble in acids. Gives a 
yellow precipitate of ammonium phosphomolybdate when dilute 
nitric acid solution is added to large excess of ammonium molyb- 
date solution. Concentrated hydrochloric acid solution gives 
white precipitate of calcium sulphate when a few drops of sul- 
phuric acid are added. Recognized usually by its crystals, color 
and hardness. Distinguished from beryl by the prominent 
pyramidal terminations of its crystals and by its being softer 
than a knife. 

Variety. Phosphorite. An impure variety of apatite is known 
as phosphorite. It occurs in a compact or earthy form or in 
concretionary and nodular masses in fossiliferous rocks of different 
ages. Probably of organic origin. 

Occurrence. Apatite is widely disseminated as an accessory con- 
stituent in all classes of rocks; igneous, metamorphic and sedimen- 
tary. It is also found in pegmatite and other veins, probably of 
pneumatolytic origin. Found in titaniferous magnetites. Occa- 
sionally concentrated into large deposits or veins. In the form of 
phosphorite or phosphate rock occurs extensively as a rock strata. 

Apatite, as it exists scattered in small crystals throughout the 
rocks, slowly undergoes alteration and is gradually dissolved by 
percolating carbonated waters. Some of the phosphoric acid thus 
brought into solution goes into the sea where it is absorbed by living 
organisms ; some remains in the soil, where its presence is a necessary 
condition for fertility and from which it is absorbed by plants and 
through them goes into the bodies of animals. The large bodies of 
phosphorite are derived from organic sources, such as animal remains. 
Bone is calcium phosphate in composition. 

Apatite occurs in commercial amount in Ontario and Quebec, 
Canada. It is found there in crystals and masses enclosed in crys- 
talline calcite and in veins and irregular nests along the contact of 
the limestone with eruptive rocks. The chief deposits lie in Ottawa 
County, Quebec. Crystalline apatite occurs in large amounts along 
the southern coast of Norway, between Langesund and Arendal. 
It is found there in veins and pockets associated with a mass of 
gabbro. Nodular deposits of phosphate rock are found at intervals 
all along the Atlantic coast from North Carolina to Florida, the 
chief deposits being in the latter state. High grade phosphate 
deposits are found in western middle Tennessee. Commercial de- 
posits of phosphorite are to be found in northern Wales, in northern 
France, northern Germany, Belgium, Spain, etc. 



290 MANUAL OF MINERALOGY 

Finely crystallized apatite occurs at various localities in the Alps; 
in Alexander County, North Carolina; at Auburn, Maine, etc. 

Use. Apatite and phosphate rock are chiefly used for fer- 
tilizer purposes. They are usually ground and treated with 
sulphuric acid to render the phosphoric acid more soluble. 
Transparent varieties of apatite of fine color are occasionally 
used for gem material. The mineral is too soft, however, to 
allow of its very extensive use for this purpose. 

Pyromorphite. 

Composition. Pb 4 (PbCl) (P0 4 ) 3 = Phosphorus pentoxide 15.7, 
lead protoxide 82.2, chlorine 2.6. The phosphorus is often re- 
placed by arsenic and the species graduates into mimetite. 

Crystallization. Hexagonal; tri-pyramidal. Prismatic crys- 
^^^^SSpS^N tals with basal plane. Rarely shows 
pyramid truncations. Often in rounded 
barrel-shaped forms. Sometimes cavern- 
ous, the crystals being hollow prisms 
(Fig. 328). Frequently in parallel groups. 
Structure. Crystallized, globular, reni- 
.^.j form, fibrous and granular. 
/ Physical Properties. H. = 3.5-4. 
G. = 6.5-7.1. Resinous luster. Color 
Fig. 347. usually various shades of green, brown, 

yellow; more rarely orange-yellow, gray, white. Subtransparent 
to nearly opaque. 

Tests. Easily fusible (2). Gives a lead globule when fused 
on charcoal with sodium carbonate. When fused alone on char- 
coal gives a globule which on cooling shows crystalline structure. 
Faint white sublimate of lead chloride when heated in C. T. 
A few drops of the nitric acid solution added to ammonium 
molybdate solution gives a yellow precipitate of ammonium 
phosphomolybdate. 

Occurrence.' A mineral formed by secondary action and found 
in the upper oxidized portions of lead veins, associated with other 
lead minerals. Notable localities for its occurrence are the lead 
mines of Poullaouen, Brittany; at Ems in Nassau; in the Nerchinsk 






VANADINITE 291 

district, Siberia; Cornwall; Phoenix ville, Pennsylvania; Davidson 
County, North Carolina, etc. 

Name. Derived from two Greek words meaning fire said form 
in allusion to the crystalline form it assumes on cooling from 
fusion. 

Use. A subordinate ore of lead. 

Mimetite. 

Composition. Pb 4 (PbCl)(As0 4 ) 3 = Arsenic pentoxide 23.2, 
lead protoxide 74.9, chlorine 2.4. Phosphorus replaces the 
arsenic in part and calcium, the lead. Endlichite is a variety 
intermediate between mimetite and vanadinite. 

Crystallization. Hexagonal; tri-pyramidal. Crystals pris- 
matic, showing basal plane and at times pyramids. Usually in 
rounded barrel- to globular-shaped forms. 

Structure. In rounded crystals, mammillary crusts. 

Physical Properties. H. = 3.5. G. = 7-7.2. Resinous lus- 
ter. Colorless, yellow, orange, brown. Subtransparent to al- 
most opaque. 

Tests. Easily fusible (1.5). Gives globule of lead when 
fused with sodium carbonate on charcoal. A fragment placed 
in C. T. and heated in contact with a splinter of charcoal gives 
deposit of metallic arsenic on walls of tube. 

Occurrence. A comparatively rare mineral of secondary origin, 
occurring in the upper, oxidized portion of lead veins. Notable 
localities for its occurrence are in Cornwall, Devonshire, and Cum- 
berland, England ; Johanngeorgenstadt, Saxony; Nerchinsk, Siberia; 
Pho3nixville, Pennsylvania; Cerro Gordo, California, etc. 

Name. Derived from the Greek for imitator in allusion to its 
resemblance to pyromorphite. 
Use. A minor ore of lead. 

Vanadinite. 

Composition. Pb 4 (PbCl)(V0 4 ) 3 = Vanadium pentoxide 19.4, 
lead protoxide 78.7, chlorine 2.5. Phosphorus and arsenic some- 
times present in small amount replacing vanadium. In the 
variety endlichite the proportion of V 2 6 to As 2 6 is nearly as 1 : 1. 



292 MANUAL OF MINERALOGY 

Crystallization. Hexagonal; tri-pyramidal. Prism with base. 
Sometimes small pyramidal faces, rarely the pyramid of the 
third order. In rounded crystals; sometimes cavernous. 

Structure. In crystals and globular forms. As incrustations. 

Physical Properties. H. = 3. G. = 6.9-7.1. Adamantine 
to resinous luster. Color ruby-red, brown, yellow. Transparent 
to opaque. 

Tests. Easily fusible (1.5). Gives globule of lead on charcoal 
when fused with sodium carbonate. Gives an amber color in 
0. F. to salt of phosphorus bead (vanadium). Dilute nitric acid 
solution gives with silver nitrate a white precipitate of silver 
chloride. Endlichite would give in C. T. the reaction for arsenic 
(see under mimetite). 

Occurrence. A rare mineral of secondary origin found in the 
upper oxidized portion of lead veins. Occurs in various districts in 
Arizona and New Mexico. 

Use. Source of vanadium and minor ore of lead. Vanadium 
is obtained chiefly from other ores, such as the sulphide, patron- 
ite; the vanadate, carnotite; and a vanadium mica, roscoelite. 
Vanadium is used chiefly as a steel hardening metal. Meta- 
vanadic acid, HV0 3 , is used as a yellow pigment, known as 
vanadium bronze. Vanadium oxide is used as a mordant in 
dyeing. 



Amblygonite. 

A phosphate of lithium and aluminium, Li(AlF)PC>4, having 
hydroxyl isomorphous with the fluorine and often sodium in small 
amount replacing the lithium. Triclinic. Usually massive, cleav- 
able to compact. Perfect basal cleavage. H. =6. G. = 3.08. 
Luster vitreous, pearly on cleavage face. Color white to pale 
green or blue. Translucent. Easily fusible (2) giving a red flame 
(lithium). Insoluble in acids. After fusion with sodium carbonate 
and dissolving in nitric acid, solution with excess of ammonium 
molybdate solution gives yellow precipitate (test for phosphate). A 
rare mineral found in pegmatite veins with tourmaline, lepidolite, 
apatite, etc. Found at Montebras, France; Hebron, Paris, Auburn, 
and Peru, Maine, etc. 



SCORODITE 293 

2. ACID AND BASIC PHOSPHATES, ETC. 
Olivenite. 

An arsenate and hydroxide of copper, Cu 3 As2O 8 .Cu(OH) 2 . Ortho- 
rhombic. Prismatic, often in acicular crystals. Also reniform, 
fibrous, granular. H. =3. G. = 4.1-4.4.. Fusible at 2-2.5. Ada- 
mantine to vitreous luster. Color olive-green to blackish green; 
also shades of brown and yellow to white. Translucent to opaque. 
With sodium carbonate on charcoal gives a copper globule. When 
ignited in C. T. with splinter of charcoal gives arsenical mirror. A 
little water when heated in C. T. Found rarely in oxidized portions 
of copper veins. 

Lazulite. 

A phosphate of magnesium and aluminium, Mg(Al.OH) 2 (PO 4 ) 2 , 
with varying amounts of ferrous iron, replacing the magnesium. 
Monoclinic, usually in steep pyramids. Also massive, granular to 
compact. H. = 5-5.5. G. = 3.05-3.1. Vitreous luster. Azure- 
blue color. Translucent to opaque. Infusible. B. B. swells, loses 
its color and falls to pieces. Insoluble. A rare mineral. 

3. HYDROUS PHOSPHATES, ETC. 
Vivianite. 

Hydrous ferrous phosphate, Fe 3 P 2 O8.8H 2 0. Monoclinic. Pris- 
matic crystals, vertically striated; often in radiating groups; at 
times fibrous or earthy. Perfect pinacoidal cleavage. H. = 1.5-2. 
G. = 2.58-2.68. Vitreous to pearly luster. Colorless when un- 
altered. Blue to green when altered. Transparent when fresh to 
opaque on exposure. Fusible at 2-2.5 to a magnetic globule. 
Nitric acid solution added to an excess of ammonium molybdate 
solution gives yellow precipitate (test for phosphate). Water in 
C. T. A rare mineral of secondary origin, associated with pyrrho- 
tite, pyrite, limonite and other iron minerals. 

Erythrite or Cobalt Bloom, Co3As 2 Os.8H 2 O, is a rare secondary 
mineral which occurs as an alteration product of cobalt arsenides. 
It is usually pulverulent in structure and crimson to pink in color. 
Annabergite or Nickel Bloom, Ni 3 As 2 O 8 .8H 2 O, is a similar nickel 
compound. It is light green in color. 

Scorodite. 

A hydrous ferric arsenate, FeAsO 4 .2H 2 0. Orthorhombic, 
usually in pyramidal crystals, resembling octahedrons; also pris- 
matic. Crystals in irregular groups. Also earthy. H. = 3.5-4. 



294 MANUAL OF MINERALOGY 

G. = 3.1-3.3. Vitreous luster. Pale green to liver-brown in color. 
Translucent. Fusible at 2-2.5. Magnetic when heated in R. F. 
Heated intensely with splinter of charcoal in C. T. gives arsenical 
mirror. Water in C. T. In hydrochloric acid reacts for ferric iron. 
Occurs in oxidized portions of metallic veins with arsenopynte and 
other iron minerals 

Wavellite. 

A hydrous aluminium phosphate, (A1OH)3(PO 4 )2-5H 2 O. Ortho- 
rhombic, crystals rare. Usually in radiating globular aggregates. 
Good cleavage. H. = 3-4. G. = 2.33. Vitreous luster. Color 
white, yellow, green and brown. Translucent Infusible. In- 
soluble. Decomposed by fusion with sodium carbonate and dis- 
solved in nitric acid gives yellow precipitate (test for phosphoric 
acid) when solution is added to excess of ammonium molybdate. 
Moistened with cobalt nitrate, and then ignited assumes a blue color 
(aluminium). A rare mineral. 

Turquois. 

Composition. A hydrous phosphate of aluminium, colored 
by small amounts of a copper phosphate, H(A1.20H) 2 P0 4 with 
isomorphous H(Cu.OH) 2 P0 4 . 

Structure. Noncrystalline. Massive compact, reniform, 
stalactitic, encrusting. In thin seams and disseminated grains. 

Physical Properties. H. = 6. G. = 2.6-2.8. Waxlike lus- 
ter. Color blue, bluish green, green. Translucent to opaque. 

Tests. Infusible. Insoluble. After fusion with sodium car- 
bonate and dissolving in nitric acid, gives a yellow precipitate 
with an excess of ammonium molybdate solution (test for a 
phosphate). Gives a momentary green flame. In C. T. turns 
dark and gives water. 

Occurrence. Turquois is usually found in the form of small 
veins and stringers traversing more or less decomposed igneous 
rocks. The famous Persian deposits are found in trachyte near 
Nishapur in the province of Khorassan. In the United States it 
is found in much altered granite or granite porphyry in Mohave 
County, Arizona, and in Grant and Santa Fe counties, New Mexico. 
Turquois has also been found in Nevada, California and Colorado. 

Name. Is French and means Turkish, the original stones 
having come into Europe through Turkey. 



NITER 295 

Use. As a gem stone. It is always cut in round or oval forms 
and a one-carat stone may be valued as high as $10. Much 
turquois is cut which is veined with the various gangue materials 
and such stones are sold under the name of turquois matrix. 

NITRATES. 
Soda Niter. 

Composition. Sodium nitrate, NaN0 3 = Nitrogen pentoxide 
63.5, soda 36.5. 

Crystallization. Hexagonal-rhombohedral. Homceomor- 
phous with calcite. Has closely the same crystal constants, 
cleavage, optical properties, etc., as calcite. If a cleavage block 
of calcite is placed in a crystallizing solution of sodium nitrate, 
small rhombohedrons of the latter will form with parallel orien- 
tation on the calcite. 

Structure. Usually massive, as an incrustation or in beds. 

Physical Properties. Perfect rhombohedral cleavage. H. = 
1.5-2. G. = 2.29. Vitreous luster. Colorless or white, also 
reddish brown, gray, yellow, etc. Transparent to opaque. 
Cooling taste. 

Tests. Very easily fusible (1), giving a strong yellow sodium 
flame. After intense ignition gives an alkaline reaction on 
moistened test paper. Easily and completely soluble in water. 
Heated in C. T. with potassium bisulphate gives off red vapors 
of nitrous oxide. 

Occurrence. Because of its solubility in water it is only to be 
found in arid and desert regions. Found in large quantities in the 
district of Tarapaca, northern Chile and the neighboring parts of 
Bolivia. Occurs over immense areas as a salt (caliche) bed inter- 
stratified with sand, beds of common salt, gypsum, etc. Has been 
noted in Humboldt County, Nevada, and in San Bernardino County, 
California. 

Use. In Chile it is quarried, purified and used as a source of 
nitrates. 

Niter. 

Potassium nitrate, KN0 3 . Orthorhombic. Usually as thin en- 
crustations or as silky acicular crystals. Perfect cleavage. H. = 2. 
G. = 2.09-2.14. Vitreous luster. Color white. Translucent. 



296 MANUAL OF MINERALOGY 

Easily fusible (1) giving violet flame (potassium). After ignition 
gives alkaline reaction on moistened test paper. Heated in C. T. 
with potassium bisulphate gives red fumes of nitrous oxide. Easily 
soluble in water. Saline and cooling taste. Found as delicate 
crusts, as an efflorescence, on surfaces of earth, walls, rocks, etc. 
Found as a constituent of certain soils. Also in the loose soil of 
limestone caves. Not as common as soda niter, but produced from 
soils in France, Germany, Sweden. Obtained in India. Used 'as a 
source of nitrogen compounds. 

BORAXES. 
Boracite. 

Composition, Mg 7 Cl 2 Bi6O3o. Isometric; tetrahedral. Crystals 
usually show cube, tetrahedron and dodecahedron in some com- 
bination. Crystals usually isolated and disseminated in other 
minerals. Also massive. Vitreous luster. Colorless, white, gray, 
green. Transparent to translucent. H. =7. G. = 2.9-3.0. 
Fusible at 3 with green flame color (boron). Soluble in hydrochloric 
acid. Turmeric paper moistened with a solution of the mineral and 
then dried at 100 C. turns reddish brown (boron). Occurs asso- 
ciated with halite, anhydrite, gypsum, etc., as one of the products 
formed by the evaporation of bodies of salt water. 

Colemanite. 

Hydrous borate of calcium, Ca 2 B 6 Oii.5H 2 O. Monoclinic, in 
short prismatic crystals, highly modified. Cleavable massive to 
granular and compact. Perfect pinacoidal cleavage. H. = 4-4.5. 
G. = 2.42. Vitreous to adamantine luster. Colorless to white. 
Transparent to translucent. Fusible at 1.5. B. B. exfoliates, 
crumbles and gives green flame (boron). Water in C. T. A rare 
mineral, but occurring in considerable quantity in the salt lake de- 
posits, in the arid regions of southeastern California, in Death Valley, 
Inyo County, and in San Bernardino and Los Angeles counties. 

Borax. 

Composition. Hydrous sodium borate, Na 2 B40 7 .10H 2 = 
Boron trioxide 36.6, soda 16.2, water 47.2. 

Crystallization. Monoclinic. Prismatic crystals, sometimes 
quite large. 

Structure. In crystals and as massive cellular material or 
encrustations. 



URANINITE 297 

Physical Properties. Perfect cleavage parallel to orthopina- 
coid. H. = 2-2.5. G. = 1.75. Vitreous luster. Colorless or 
white. Translucent to opaque. Sweetish-alkaline taste. 

Tests. Easily fusible (1-1.5) with much swelling and gives 
strong yellow flame (sodium) . Readily soluble in water. Tur- 
meric paper, moistened with a dilute hydrochloric acid solution 
of the mineral, turns reddish brown when dried at. 100 C. 
Much water in C. T. 

Occurrence. Formed as a deposit from the evaporation of salt 
lakes, and as an efflorescence on the surface of the ground in arid 
regions. The deposits in Thibet have furnished large amounts of 
borax, which has been exported to Europe in the crude state, under 
the name of tincal. Found in quantity in the United States in the 
desert region of southeastern California, in Death Valley, Inyo 
County and in San Bernardino County. Occurs also in the adjacent 
parts of Nevada. Borax is associated with the other minerals 
deposited in similar manner, such as halite, gypsum, colemanite, and 
various rare borates. 

Name. Borax comes from an Arabic name for the substance. 

Use. Borax is used for washing and cleansing; as an anti- 
septic, preservative, etc., in medicine; as a solvent for metallic 
oxides in soldering and welding; and as a flux in various smelt- 
ing and laboratory operations. 

URANATES. 
Uraninite. Pitch Blende. 

Composition. An uncertain combination of the oxides of 
uranium, U0 3 and U0 2 . With small amounts of lead and the 
rare elements, thorium, yttrium, cerium, nitrogen, helium, argon, 
radium. It is the mineral in which the gas helium was first 
discovered on the earth, having been previously noted in the 
gases surrounding the sun by means of the sun's spectrum. In 
it, also, was first discovered the rare and strange substance, 
radium. 

Crystallization. Isometric. In octahedrons, also with do- 
decahedrons. Less often showing cube faces. Crystals rare. 

Structure. Usually massive and botryoidal; also in grains. 



298 MANUAL OF MINERALOGY 

Physical Properties. H. = 5.5. G. = 9-9.7 (unusually 
high). Luster submetallic to pitchlike, dull. Color black. 
Streak brownish black. 

Tests. Infusible. Imparts to the salt of phosphorus bead 
in 0. F. a yellowish green and in R. F. a green color. Soluble 
in dilute sulphuric acid with the slight evolution of helium gas. 
Characterized chiefly by its pitchy luster, its high specific gravity, 
its color and streak. 

Occurrence. Occurs either as a primary constituent of granite 
rocks or as a secondary mineral with ores of silver, lead, copper, etc. 
Found under the latter condition at Johanngeorgenstadt, Marienberg 
and Schneeberg in Saxony, at Joachimsthal and Pfibram in Bohemia, 
and Rezbdnya in Hungary. Occurs also in connection with the 
tin deposits of Cornwall, England. In the United States found in 
isolated crystals in pegmatite veins at Middletown, Glastonbury 
and Branchville, Connecticut. In the mica mines of Mitchell 
County, North Carolina. A narrow vein of it has been mined 
near Central City, Gilpin County, Colorado. 

Use. The chief interest in the mineral lies in the fact that 
it is the principal source of radium. This element exists in it 
in extremely small percentages and it is necessary to subject a 
large amount of the mineral to a chemical concentration in order 
to produce a few grains of a radium salt. Uranium, itself, 
has only a limited use. Experiments have been made looking 
toward its use in steel. In the form of various compounds it 
has a limited use in coloring glass and porcelain, in photography 
and as chemical reagents. 

SULPHATES. 

The sulphates and the related chromates may be divided into 
three divisions: (1) Anhydrous Sulphates; (2) Acid and. Basic 
Sulphates; (3) Hydrous Sulphates. 

1. ANHYDROUS SULPHATES. 
Glaub erite. 

A sulphate of sodium and calcium, Na 2 Ca(S0 4 )2. Monoclinic. 
Crystals thin, tabular parallel to base. Basal cleavage. H. = 
2.5-3. G. = 2.7-2.85. Vitreous luster. Color pale yellow or gray. 



BARITE 299 

Slightly saline taste. Fusible (1.5-2), giving yellow flame (sodium). 
After ignition, gives an alkaline reaction on moistened test paper. 
Soluble in hydrochloric acid and solution with barium chloride gives 
white precipitate of barium sulphate. A rare mineral occurring 
in the saline deposits, formed by the evaporation of salt lakes. 



BARITE GROUP. 

The Barite Group consists of the sulphates of barium, stron- 
tium, lead and calcium. They crystallize in the orthorhombic 
system with closely related crystal constants and similar habits. 
The members of the group are as follows : 

Barite, BaS0 4 . 
Cekstite, SrS0 4 . 
Anglesite, PbS0 4 . 
Anhydrite, CaS0 4 . 

Barite. Barytes. Heavy Spar. 

Composition. Barium sulphate, BaS0 4 = Sulphur trioxide 
34.3, baryta 65.7. Strontium and calcium sulphates present at 
times. 




Fig. 348. 




Fig. 350. 



Fig. 352. 

Crystallization. Orthorhombic. Crystals usually tabular 
parallel to base; often diamond shaped because of the presence 
of a short prism (Fig. 348). Both macro- and brachydomes 



300 MANUAL OF MINERALOGY 

usually present, either beveling the corners of the diamond- 
shaped crystals (Figs. 349 and 350), or if the prism faces are 
wanting, beveling the edges of the tables and forming rectan- 
gular prismatic-shaped crystals elongated parallel to either the 
brachy- or macro-axis (Figs. 351 and 352). Crystals sometimes 
quite complex. 

Structure. In crystals. In divergent groups of tabular crys- 
tals forming " crested barite." Also coarsely laminated; granu- 
lar, earthy. 

Physical Properties. Perfect cleavage parallel to base and 
prism faces. H. = 3-3.5. G. = 4.5 (heavy for a nonmetallic 
mineral). Vitreous luster; pearly at times on base. Colorless, 
white, and light shades of blue, yellow, red. Transparent to 
opaque. 

Tests. Fusible at 4, giving yellowish green barium flame. 
After ignition gives an alkaline reaction on moistened test paper. 
Fused with sodium carbonate and charcoal dust gives a residue, 
which, when moistened, produces a dark stain of silver sulphide 
on a clean silver surface. Recognized by its white color, high 
specific gravity, characteristic cleavage and crystals. 

Occurrence. Barite is a common mineral of wide distribution. 
It occurs usually as a gangue mineral in metallic veins, associated 
especially with ores of silver, lead, copper, cobalt, manganese and 
antimony. Sometimes in veins in limestone with calcite and celes- 
tite or in sandstone with copper ores. At times acts as a cement in 
sandstone. Deposited occasionally as a sinter by waters from hot 
springs. Notable localities for the occurrence of crystalline barite 
are in Westmorland, Cornwall, Cumberland, Derbyshire, and Surrey, 
England; Felsobanya and other localities, Hungary; in Saxony and 
Bohemia. In the United States at Cheshire, Connecticut; De Kalb, 
New York; Fort Wallace, New Mexico. Massive barite, occurring 
usually as veins, nests and irregular bodies in limestones, has been 
quarried in the United States in Connecticut, Virginia, North Caro- 
lina, Georgia, Tennessee, Kentucky and Missouri. 

Use. Barite is used chiefly for the production of barium 
hydroxide, employed in the refining of sugar. It is ground 
and used as a white pigment, to give weight to cloth and 
paper, etc. 



CELESTITE 



301 



Celestite. 

Composition. Strontium sulphate, SrS0 4 = Sulphur trioxide 
43.6, strontia 56.4. 

Crystallization. Orthorhombic. Crystals resemble closely 
those of barite (which see). Commonly tabular parallel to the 
base or prismatic parallel to the brachy- or macro-axis with 
prominent development of the domes (Fig. 353). Crystals which 
are elongated parallel to the brachy-axis are frequently termi- 
nated in front by four faces in nearly equal development, con- 
sisting of 2 prism faces and 2 of the macrodome (Fig. 354). 





Fig. 353. 



Fig. 354, 



Structure. Crystallized. Also radiating fibrous; sometimes 
granular. 

Physical Properties. Perfect cleavage parallel to base and 
prism. H. = 3-3.5. G. = 3.95-3.97. Luster vitreous to pearly. 
Colorless, white, often faintly blue or red. Transparent to 
translucent. 

Tests. Fuses at 3.5-4 and colors the flame crimson (stron- 
tium). After ignition gives an alkaline reaction on moistened 
test paper. Fused with sodium carbonate and charcoal dust 
gives a residue, which, when moistened, produces on a clean 
silver surface a dark stain of silver sulphide. Closely resembles 
barite and it will usually need a flame test to positively differen- 
tiate the two species. 

Occurrence. Celestite is found usually disseminated through 
limestone or in nests and lining cavities in such a rock. Associated 
with calcite, dolomite, gypsum, halite, sulphur, etc. Notable 
localities for its occurrence are with the sulphur deposits of Sicily; 
at Bex, Switzerland; Yate, Gloucestershire, England; Herrengrund, 
Hungary; Strontian Island, Put-in-Bay, Lake Erie, Mineral 



302 MANUAL OF MINERALOGY 

County, West Virginia; San Bernardino County, California. Found 
disseminated in limestones near Syracuse, New York, and in Monroe 
County, Michigan. 

Name. Derived from ccdestis in allusion to the faint blue 
color often present. 

Use. Used in the preparation of nitrate of strontium for 
fireworks. Other strontium salts used in the refining of sugar. 

Anglesite. 

Composition. Lead sulphate, PbS0 4 = Sulphur trioxide 26.4, 
lead oxide 73.6. 

Crystallization. Orthorhombic. Crystal habit often similar 
to that of barite (which see) but much more varied. Crystals 
may be prismatic parallel to all three of the crystal axes and 
frequently show many forms, with a complex development. 

Structure. Crystallized. Also massive, granular to compact. 
Frequently earthy, in concentric layers about a nucleus of 
galena. 

Physical Properties. Perfect cleavage parallel to base and 
prism. H. = 2.75-3. G. = 6.12-6.39 (unusually high). Ada- 
mantine luster when pure and crystalline, dull when earthy. 
Colorless, white, pale shades of yellow, green and blue. May 
be colored dark gray, etc., by impurities. Transparent to 
opaque. 

Tests. Easily fusible at 2.5. On charcoal with sodium car- 
bonate reduced to a lead globule with yellow to white coating 
of lead oxide. Fused with sodium carbonate and charcoal dust 
gives a residue, which, when moistened, produces on a clean silver 
surface a dark stain of silver sulphide. Recognized by its high 
specific gravity, its adamantine luster and frequently by its 
association with galena. 

Occurrence. Anglesite is a common lead mineral of secondary 
origin. It is formed through the oxidation of galena, sometimes 
directly to the sulphate as is shown by the concentric layers of angle- 
site found at times surrounding a core of unaltered galena, or some- 
times by an intermediate solution and subsequent recrystallization. 
Found in the upper, oxidized portions of lead veins, associated with 
galena, cerussite, sphalerite, smithsonite, calamine, iron oxides, etc 



CROCOITE 303 

Notable localities for its occurrence are Monte Poni, Sardinia; Is- 
land of Anglesea, England; at Leadhills, Scotland; various localities 
in Hungary, etc. Found in large amounts in Australia. Occurs in 
the United States at Phoenix ville, Pennsylvania; Carroll County, 
Maryland; Colorado; Cerro Gordo, California. 

Name. Named from the original locality on Island of Anglesea. 
Use. An ore of lead. 

Anhydrite. 

Composition. Anhydrous calcium sulphate, CaS0 4 = Sulphur 
trioxide 58.8, lime 41.2. 

Crystallization. Orthorhombic. Crystals rare; when ob- 
served are thick tabular, also prismatic parallel to the macro-axis. 

Structure. Usually in crystalline masses, with rectangular 
cleavage. Fibrous, granular. 

Physical Properties. Cleavage parallel to the three pinacoids, 
so yielding rectangular blocks. H. = 3-3.5. G. = 2.89-2.98. 
Luster vitreous to pearly. Color white with sometimes a faint 
gray, blue or red tinge. Transparent to translucent. 

Tests. Fusible at 3-3.5. After ignition gives an alkaline 
reaction on moistened test paper. Moistened with hydrochloric 
acid and ignited gives orange-red flame of calcium. Soluble in 
hot hydrochloric acid and dilute solution with barium chloride 
gives white precipitate of barium sulphate. 

Occurrence. Occurs in much the same manner as gypsum, and 
often associated with that mineral but is not nearly as common. 
Found in beds associated with salt deposits and in limestone rocks. 
Found at times in amygdaloidal cavities in basalt. Occurs at Aussee 
in Styria; at Stassfurt, Prussia; Bavaria; Hall in Tyrol; Bex, 
Switzerland; in the United States at Lockport, New York; Nash- 
ville, Tennessee. Found in large beds in Nova Scotia. 

Crocoite. 

Lead chromate, PbCrO 4 . Monoclinic. In slender prismatic crys- 
tals, vertically striated. Also granular. H. = 2.5-3. G. = 5.9- 
6.1. Adamantine luster. Color bright red. Orange-yellow streak. 
Fusible at 1.5. Fused with sodium carbonate on charcoal gives a 
lead globule. With borax gives a green bead in O. F. A rare 
mineral found in the oxidized zones of lead veins. Fine crystals 
come from Mount Dundas, Tasmania. 



304 



MANUAL OF MINERALOGY 



2. ACID AND BASIC SULPHATES. 
Brochantite. 

A basic sulphate of copper, CuSO 4 . 3 Cu(OH) 2 . Orthorhombic. 
Slender prismatic crystals, vertically striated, often acicular. Some- 
times massive reniform. Perfect pinacoidal cleavage. H. = 3.5-4. 
G. = 3.9. Vitreous luster. Emerald to blackish green in color. 
Transparent to translucent. Fusible (3.5). Copper globule when 
fused with sodium carbonate on charcoal. Hydrochloric acid solu- 
tion with barium chloride gives white precipitate of barium sul- 
phate. Water in C. T. A rare mineral found in the oxidized 
portions of copper veins. 

3. HYDROUS SULPHATES. 

Gypsum. Selenite. 

Composition. Hydrous calcium sulphate, CaS04.2H 2 = Sul- 
phur trioxide 46.6, lime 32.5, water 20.9. 

Crystallization. Monoclinic. Crystals usually tabular paral- 
lel to clinopinacoid; in diamond-shaped crystals with edges 
beveled by prism and pyramid faces (Fig. 355). Other forms 
rare. Sometimes twinned (Fig. 356). 




Fig. 355. 



Fig. 356. 



Structure. Cleavable massive; foliated; granular massive; 
sometimes with fibrous appearance. 

Physical Properties. Cleavage in three directions; perfect 
parallel to clinopinacoid, yielding easily thin folia; with con- 
choidal surface parallel to orthopinacoid; with fibrous fracture 



GYPSUM 305 

parallel to a pyramid. H. = 2 (can be scratched by the finger 
nail). G. = 2.32. Usually with vitreous luster; sometimes 
silky. Colorless, white, gray; sometimes various shades of yel- 
low, red, brown, etc., from impurities. Transparent to opaque. 

Tests. Fusible at 3-3.5. After intense ignition, residue gives 
alkaline reaction on moistened test paper. Soluble in hot dilute 
hydrochloric acid and solution with barium chloride gives white 
precipitate of barium sulphate. Much water in C. T. Charac- 
terized by its softness and its perfect pinacoidal cleavage. 

Varieties. Crystalline, In crystals or foliated masses. 

Fibrous. With coarse to fine fibrous appearance. Satin spar 
is fine fibrous with silky luster. 

Massive. Alabaster, a fine-grained variety. Rock gypsum, 
massive granular or earthy; often impure. 

Occurrence. Gypsum is a common mineral which is widely dis- 
tributed in sedimentary rocks, often as thick beds. It frequently 
occurs interstratified with limestones and shales. Usually to be 
found as a layer underlying beds of rock salt and has been deposited 
there as one of the first minerals to crystallize because of the concen- 
tration of salt waters. Occurs also as lenticular bodies or scattered 
crystals in clays and shales. Found at times in volcanic regions, 
especially where limestones have been acted upon by sulphur vapors. 
Also, is common as a gangue mineral in metallic veins. Associated 
with many different minerals, the more common ones being salt, 
anhydrite, dolomite, calcite, sulphur, pyrite, quartz. Deposits of 
gypsum of commercial importance are found in many localities in 
the United States, but the chief producers are located in New York, 
Oklahoma, Texas, Iowa, Michigan, Ohio, Virginia and Kansas. 
Gypsum is found in large deposits in Arizona and New Mexico in the 
form of wind-blown sand. 

Name. Derived from the Greek name for the species. At 
times the crystalline variety is called selenite, which comes from 
a Greek word meaning moon, probably in allusion to the moon- 
like white reflections from some varieties. 

Use. Gypsum is chiefly used for the production of plaster of 
Paris. In the manufacture of this material, the gypsum is 
ground and then heated, until a large proportion of the water 
has been driven off. This plaster, when mixed with water, 
slowly absorbs the water and so hardens or "sets." Plaster of 



306 MANUAL OF MINERALOGY 

Paris is used extensively for " staff," the material from which 
temporary exposition buildings are built, and for molds and 
casts of all kinds. Gypsum is employed in making adamant 
plaster for interior use. Serves as land plaster, for a fertilizer. 
Satin spar and alabaster are cut and polished for various orna- 
mental purposes but are restricted in their uses on account of 
their softness. 

Chalcanthite. Blue Vitriol. 

Composition. Hydrous copper sulphate, CuS0 4 .5H 2 = Sul- 
phur trioxide 32.1, cupric oxide 31.8, water 36.1. 

Crystallization. Triclinic. Crystals commonly tabular paral- 
lel to a pyramid face. 

Structure. Crystallized, also massive in stalactitic and reni- 
form structure, sometimes with fibrous appearance. 

Physical Properties. H. = 2.5. G. = 2.12-2.30. Vitreous 
luster. Color deep azure-blue. Transparent to translucent. 
Metallic taste. 

Tests. Fusible at 3. Gives copper globule when fused with 
sodium carbonate on charcoal. Soluble in water. Dilute hydro- 
chloric acid solution gives with barium chloride precipitate of 
barium sulphate. Much water in C. T. Characterized by its 
blue color and its solubility in water. 

Occurrence. A rare mineral, found at times in arid regions as a 
secondary mineral, occurring near the surface in copper veins, and 
derived from the original copper sulphides by oxidation. Often 
deposited from the waters in copper mines. 

Use. A minor ore of copper. The artificial blue vitriol is 
used in calico printing, in galvanic cells, and in various manu- 
facturing industries. 

Kalinite. Potash Alum. 

A hydrous sulphate of aluminium and potassium, K^SCV 
A1 2 (SO 4 )3.24H 2 O. Isometric; pyritohedral. Usually fibrous or mas- 
sive. H. = 2-2.5. G.= 1.75. Vitreous luster. Colorless to white . 
Transparent to translucent. Fuses at 1 with swelling and gives a 
violet flame (potassium). Easily soluble in water. Astringent taste. 
Hydrochloric acid solution with barium chloride gives a white pre- 
cipitate of barium sulphate, and with ammonium hydroxide in 



WOLFRAMITE-H UBNERITE 307 

excess gives white precipitate of aluminium hydroxide. A com- 
paratively rare mineral, which usually occurs as efflorescence on 
clays and slates, particularly those containing disseminated pyrite. 
Also at times in connection with sublimation products from vol- 
canoes. 

TUNGSTATES, MOLYBDATES. 
Wolframite-Hiibnerite. 

Composition. Tungstates of ferrous iron and manganese. 
Wolframite (Fe,Mn)W0 4 , in which the ratio of the iron to the 
manganese varies from 9:1 to 2:3. Hubnerite, nearly pure 
MnW0 4 . 

Crystallization. Monoclinic. Crystals commonly tabular 
parallel to the orthopinacoid, giving bladed forms. Prism zone 
vertically striated. 

Structure. In bladed, lamellar or columnar forms. Massive 
granular. 

Physical Properties. Perfect cleavage parallel to clinopina- 
coid. H. = 5-5.5. G. = 7.2-7.5. Submetallic to resinous lus- 
ter. Color black in wolframite to brown in hiibnerite. Streak 
from nearly black to brown. 

Tests. Fusible (3-4). Insoluble in acids. Fused with 
sodium carbonate, fusion then dissolved in hydrochloric acid, 
tin added and solution boiled gives a blue color (tungsten). In 
O. F. with sodium carbonate gives bluish green bead (manga- 
nese). Wolframite when fused with sodium carbonate in R. F. 
on charcoal gives a magnetic mass. 

Occurrence. Comparatively rare minerals, found usually with 
cassiterite and associated also with scheelite, bismuth, quartz, pyrite, 
galena, sphalerite, etc. Found in fine crystals from Schlaggenwald, 
Bohemia, and in the various tin districts of Saxony and Cornwall. 
Wolframite occurs in the United States in the Black Hills, South 
Dakota; Boulder County, Colorado; Seward Peninsula, Alaska. 
Hubnerite is found near Butte, Montana; in various localities in 
Nevada and Arizona. 

Use. Chief ores of tungsten. Tungsten is used as a harden- 
ing metal in the manufacture of tool steel. Also as a filament 
in incandescent electric lights. Sodium tungstate is used in 
fire-proofing cloth and as a mordant in dyeing. 




308 MANUAL OF MINERALOGY 

Scheelite. 

Composition. Calcium tungstate, CaW0 4 = Tungsten tri- 
oxide 80.6, lime 19.4. Molybdenum is usually present, replacing 
a part of the tungsten. 

Crystallization. Tetragonal; tri-pyramidal. Crystals usually 
simple pyramids of first order. Closely resemble isometric 
octahedrons in angles (Fig. 357). Faces of 
the pyramid of third order are small and 
rare. 

Structure. Massive granular; in crys- 
tals. 

Physical Properties. Cleavage parallel 
to pyramid of first order. H. = 4.5-5. 
G. = 6.05 (unusually high for a mineral 
with nonmetallic luster) . Vitreous to ada- 
mantine luster. Color white, yellow, green, 
brown. Usually translucent to opaque, sometimes transparent. 
Tests. Difficultly fusible (5). Decomposed by boiling hydro- 
chloric acid leaving a yellow residue of tungstic oxide, which, 
when tin is added to the solution and boiling continued, turns 
first blue then brown. Recognized by its high specific gravity 
and the test for tungsten. 

Occurrence. Occurs usually with quartz in crystalline rocks 
associated with cassiterite, topaz, fluorite, apatite, molybdenite, 
wolframite, etc. Found at times with gold. Occurs in connection 
with the tin deposits of Bohemia, Saxony and Cornwall; in quantity 
in New South Wales and Queensland. Found in the United States 
at Trumbull, Connecticut; near Randsburg, San Bernardino County, 
California; near Browns, Humboldt County, Nevada; near Dragoon, 
Cohise County, Arizona. 

Use. A subordinate ore of tungsten, wolframite (which see) 
furnishing the greater amount. Tungsten is used chiefly as a 
steel-hardening metal. 

Wulfenite. 

Composition. Lead molybdate, PbMo0 4 = Molybdenum tri- 
oxide 39.3, lead oxide 60.7. Calcium sometimes replaces the 
lead. 



WULFENITE 309 

Crystallization. Tetragonal; tri-pyramidal. Crystals usually 
square tabular in habit with prominent base. Sometimes very 
thin. Edges of tables beveled with faces of low second order 
pyramid. More rarely pyramidal in habit. Pyramid of third 
order in small faces and very rare. 

Structure. In crystals; also massive granular, coarse to fine. 

Physical Properties. H. = 4.5-5. G. = 6.05. Vitreous to 
adamantine luster. Color yellow, orange, red, gray, white. 
White streak. Transparent to subtranslucent. 

Tests. Easily fusible at 2. Gives a lead globule when fused 
with sodium carbonate on charcoal. With salt of phosphorus 
in R. F. gives green bead; in 0. F. yellowish green when hot to 
almost colorless when cold. If powdered mineral is moistened 
with concentrated sulphuric acid and evaporated almost to dry- 
ness in a porcelain crucible the residue will show a deep blue 
color on cooling (molybdenum). 

Occurrence. Found in the oxidized portion of lead veins with 
other ores of that metal, especially vanadinite and pyromorphite. 
Found in the United States in a number of places in Utah, Nevada, 
Arizona and New Mexico. 

Use. An ore of molybdenum. Molybdenum is used as a 
steel-hardening metal. In the form of ammonium molybdate 
it is used as a chemical reagent, as a fireproofing material and 
as a disinfectant. Molybdenum used also to color leather and 
rubber. 

LISTS OF MINERALS ARRANGED ACCORDING 
TO ELEMENTS. 

In the following section are given lists of the minerals that are 
of commercial importance because of some element which they 
contain. All of the minerals that could serve as a source of 
any particular element are grouped together, their relative 
importance being indicated by the type used in printing their 
names. The order in which the minerals are given in each list 
is the same as that in which they are described in the previous 
section of this book. The different elements have been treated 
in alphabetical sequence in order to facilitate ready reference 



310 MANUAL OF MINERALOGY 

to them. Each table will be followed by a brief general discus- 
sion of the occurrence of the minerals given in it and by a short 
statement as to the uses of the element derived from them. 

Aluminium. 

Cryolite, N a3 AlF 6 . Bauxite, A1 2 0(OH) 4 . 

Corundum, A1 2 3 . The Feldspars, KAlSi 3 8 , NaAlSi 3 8 , 

CaAl 2 Si 2 3 , etc. 
Gibbsite, A1(OH),. Kaolin, H4Al 2 Si 2 9 . 

Aluminium is the most common of all the metals. Unlike 
other metals, however, its occurrence, with the exception of the 
fluorides, is restricted to minerals containing oxygen. It is most 
abundantly found in the rock-making silicates, in the majority 
of which it is an essential constituent. It also occurs in large 
amount in the clays. The minerals which can be used as ores 
of the metal are, however, few in number, the only one at present 
of importance being bauxite. The enormous amounts of alu- 
minium contained in the various silicates are not yet available 
because of the difficulty and expense of extraction. 

Bauxite is produced in the United States chiefly from Arkan- 
sas, Alabama, Georgia and Tennessee. The deposits in Arkan- 
sas are found in Pulaski and Saline counties. They have an 
average thickness of 10 to 15 feet. In one district the beds lie 
directly upon a body of kaolin, which in turn rests upon a syenite 
rock-mass and it is probable that both minerals have been 
derived from its decomposition. The Alabama-Georgia district 
extends from Jacksonville, Alabama, to Carters ville, Georgia. 
The ore occurs as pockets or lenses in a clay which has been 
derived by weathering processes from a dolomite limestone. 
The bauxite is either pisolitic or clay-like in structure. 

Cryolite, imported from Greenland, has been used as an ore 
of aluminium and at present is used as a flux in the electrolytic 
process by which most of the metal is obtained. 

The usual process at present by which aluminium is extracted 
from the bauxite ores is briefly as follows : The ore is heated to 
low redness with sodium carbonate forming sodium aluminate. 
This compound is leached out by water and by passing C0 2 gas 



ANTIMONY 311 

into the solution the aluminium is precipitated as the hydroxide. 
The latter on being heated is converted into the oxide of the 
metal. The pure metal is prepared from this oxide by an elec- 
trolytic process which takes place in a bath of fused cryolite. 
The tank in which the reaction takes place is lined with carbon 
and forms the cathode, while graphite rods suspended in the 
bath serve as the anode. The metal collects in the bottom of 
the tank. 

Aluminium is valuable because of its low density and because 
it is not easily oxidized or corroded. It is a good electrical con- 
ductor and to some extent is replacing copper used for that pur- 
pose. It is used in many alloys, particularly with zinc, copper 
and nickel. It is used in small amounts in casting steel in order 
to take up any oxygen in the melt and also to prevent porosity 
in the metal. Aluminium and iron oxide are mixed in a finely 
divided state to form the material known as thermit. When 
this mixture is ignited the heat of the combustion of the alumin- 
ium is so great that it can be used in welding iron and steel. 
Sheets and tubes and castings of aluminium are used wherever a 
light weight metal is desired, for instance in the manufacture of 
certain parts of automobiles. Aluminium is used in the manu- 
facture of cooking utensils, as a substitute for lithographic stones 
and zinc plates, as powder in the manufacture of metallic paints, 
etc. It is used also in the form of salts, chiefly alum and alu- 
minium sulphate, to harden paper, in the purification of water, 
as mordants in dyeing, in baking powders, in medicine, etc. 

Antimony. 

Native Antimony, Sb. Stibnite, Sb 2 S 5 . 

Antimony occurs in a considerable number of minerals, es- 
pecially those belonging to the series known as the sulpho-salts, 
which are largely combinations of copper, lead or silver with 
antimony and sulphur. These minerals are mined, however, 
for the other metals that they contain and any antimony that 
is produced from them is in the nature of a by-product. Stib- 
nite is practically the only mineral which is mined for its anti- 
mony. This mineral has been found in the United States in a 



312 MANUAL OF MINERALOGY 

comparatively few deposits. It has been mined on a small scale 
in California, Nevada and Idaho. The greater part of the 
antimony produced in the United States is derived from anti- 
monial lead which is an alloy of the two metals derived from 
the smelting of lead ores that contain small amounts of antimony 
minerals. Considerable amounts of antimony and antimony 
ores are imported, chiefly from China, France, Italy, Mexico 
and Japan. 

Antimony is used in alloys, such as type metal (lead, antimony 
and bismuth), babbitt or anti-friction metal (antimony, tin, etc.), 
britannia metal (tin with antimony and copper), etc. Antimony 
oxide is used as a pigment and in the glazing of enameled ware. 
The sulphide is used in fireworks, in safety matches and in per- 
cussion caps. Other compounds are used in medicine and for 
various purposes in the arts. 

Arsenic. 

Native Arsenic, As. Realgar, AsS. 

Orpiment, As 2 S 3 . Arsenopyrite, FeAsS. 

Arsenic in minerals ordinarily plays the part of a nonmetallic 
element, similar to sulphur in its chemical relations. It forms 
three classes of compounds, the arsenides, the sulpharsenites 
and the arsenates. The number of minerals which contain 
arsenic is considerable but only a few can be considered as dis- 
tinctively arsenic minerals. Arsenopyrite is the only one which 
at present serves as an ore. Most of the arsenic oxide produced 
comes as a by-product in the smelting of arsenical ores for copper, 
gold, lead, etc. Large amounts of the oxide are obtained from 
the smelting of the copper ores at Butte, Mont., the mineral 
enargite, CuaAsS^ being its chief source. The oxide is also pro- 
duced at smelting plants in Washington and Utah. Arseno- 
pyrite has been mined at Brinton, Virginia. 

Metallic arsenic is used in some alloys, particularly with lead 
in shot metal. Arsenic is chiefly used, however, in the form of 
white arsenic, or arsenious oxide. This is employed in medicine, 
as a poison, as a preservative, in making Paris green (an arsenate 
and acetate of copper), as a pigment, in glass manufacture, etc. 



CADMIUM 313 

Barium. 

Witherite, BaC0 3 . Barite, BaS0 4 . 

Barite is the chief source of barium compounds. It has been 
mined in the United States in Missouri, North Carolina, Georgia, 
Kentucky and Tennessee. The mineral is ground and sometimes 
purified by washing and then used as a partial substitute for 
white lead in paint, to give weight to paper and cloth, etc. 
Barium hydroxide is used extensively in sugar refining. 

Bismuth. 

Native Bismuth, Bi. Bismuthinite, Bi 2 S 3 . 

The most important bismuth mineral is the native metal. 
Bismuth is produced, however, mostly as a by-product in the 
smelting of gold and silver ores. Only a comparatively small 
amount is obtained in the United States, chiefly from Colorado 
and Utah. 

Bismuth is used in the alloys which it forms with lead, tin and 
cadmium. These fuse at low temperatures and are used for 
safety fuses, safety plugs, etc. Various compounds of bismuth 
are used in medicine and in the arts. 

Cadmium. 

Greenockite, CdS. 

Greenockite is the only cadmium mineral of importance and 
this is very rare in occurrence. The cadmium of commerce is 
obtained from zinc ores that carry a small amount of the metal. 
Practically the entire output of cadmium in the United States 
comes from the zinc ores of the Joplin district, Missouri, which 
frequently contain some 0.3 per cent of the metal. The zinc 
ores of Silesia have for a long time been a prominent source of 
cadmium. 

Cadmium is used in various alloys, such as low-fusing alloys, 
dental amalgam, metal for stereotype plates, etc. The metal is 
used with silver in electroplating. The sulphide, CdS, is known 
as cadmium-yellow and is used extensively as a pigment. Vari- 
ous salts of cadmium find uses in the arts. 



314 MANUAL OF MINERALOGY 

Chromium. 
Chromite, FeCr0 4 with MgCr0 4 . Crocoite, PbCr0 4 . 

Chromite, or chromic iron ore, is the chief source of chromium. 
Its production in the United States is very small, coming mostly 
from Shasta County, California. It has also been found in work- 
able deposits in Pennsylvania, Maryland, North Carolina and 
Wyoming. Large amounts of the ore are imported from New 
Caledonia, Greece and Canada. 

Chromium is used as a steel-hardening metal. It gives to 
steel a superior hardness and if added in the proper proportion 
does not produce brittleness. The mineral chromite is made 
into bricks that are used as linings for metallurgical furnaces. 
Various red, orange and green pigments and dyes are made from 
chromium compounds. Chromium salts are used as mordants 
in the dyeing and printing of cloth. Chromium compounds are 
useful in tanning leather. 

Cobalt. 

Linnseite, Co 3 S 4 . Cobaltite, CoSAs. 

Smaltite, CoAs 2 . 

Cobalt is a rare element which is usually found in small 
amounts associated with nickel minerals. Much of the cobalt 
of commerce is produced from other ores as a by-product. The 
only source of cobalt at present in the United States is from the 
lead ores of southeastern Missouri, where it occurs sparingly as 
the mineral linnseite. The metal is produced from a cobaltif- 
erous manganese ore found in New Caledonia, and also from 
the silver ores of Cobalt, Canada. 

Cobalt is chiefly used in the form of the oxide as a blue pig- 
ment in making glass and pottery. 

Copper. 

Native Copper, Cu. Bornite, Cu 5 FeS 4 . 

Chalcocite, Cu 2 S. Chalcopyrite, CuFeS 2 . 

Stromeyerite, CuAgS. Tetrahedrite, Cu 8 Sb 2 S 7 . 

Covellite, CuS. Tennantite, Cu&As 2 S 7 . 



COPPER 315 

Enargite, CusAsS 4 . Chrysocolla, CuSi0 3 .2H 2 0. 

Atacamite, Cu 2 Cl(OH) 3 . Olivenite, Cu(CuOH)As0 4 . 

Cuprite, Cu 2 0. Brochantite, Cu 4 (OH)6S0 4 . 

Malachite, Cu(OH) 2 .CuC0 3 . Chalcanthite, CuS0 4 .5H 2 0. 

Azurite, Cu(OH) 2 .2CuC0 3 . 

Copper is a common and widely distributed element. It is 
found in a number of important minerals which usually occur 
in veins. Chalcopyrite is the most important ore, and in most 
cases is the only primary copper mineral in a deposit. The 
other important sulphides, bornite and chalcocite, are usually, 
although not always, the results of secondary enrichment. 
Solutions that have leached out the copper content of the upper 
portion of a copper vein will react with the unoxidized chalco- 
pyrite farther down to enrich it in respect to the amount of cop- 
per it contains and convert it into bornite and chalcocite. In 
this way copper veins often show in the upper part, just below 
the oxidized zone, a body of enriched sulphides. The veins at 
Butte, Montana, are notable examples of this. This enriched 
sulphide zone is to be observed in general when the copper veins 
traverse igneous rocks. When they lie in limestones the upper 
portion of the vein is more liable to be characterized by the 
presence of the oxidized copper ores, native copper, cuprite, 
malachite, azurite, chrysocolla, etc. Pyrite often contains small 
amounts of copper and when it occurs in large bodies becomes 
an important ore of the metal. 

Copper is produced in from fifteen to twenty of the states and 
territories of the United States. A brief description of the chief 
districts in the more productive states follows. Alaska: Three 
districts of importance have been developed; the Ketchikan 
district where the ores are contact bodies, and are composed 
chiefly of pyrrhotite, magnetite, pyrite and chalcopyrite; Prince 
William Sound district including several mines on Latouche 
Island; Copper River district where immense bodies of chal- 
cocite and azurite occur in limestone. Arizona: The most pro- 
ductive district is that of Bisbee where the ore bodies replace 
limestone and are closely associated with intrusive rocks. The 
original ores were chiefly cupriferous pyrite, but secondary en- 



316 MANUAL OF MINERALOGY 

richment has extended to great depths. Near the surface large 
bodies of oxidized ores were found. The Jerome district has 
large bodies of ore lying in an igneous rock which through shear- 
ing has been rendered almost schistose in structure. The ores 
at present are largely sulphides. Clifton-Morenci district has 
its ores occurring as contact deposits lying in limestone and 
shales into which dikes of porphyry have been intruded, and as 
disseminated bodies lying in the porphyry itself. The workable 
ores are those which have undergone secondary enrichment, and 
consist of both carbonates and sulphides. Globe district has 
deposits that occur as lenticular replacement bodies in limestone 
and as deposits in fissures in diabase. Disseminated bodies also 
occur. California: The chief districts lie in Shasta County, 
where the ores occur as replacement bodies along shear zones 
in a granite porphyry. Colorado: Most of the copper from this 
state comes as a by-product in the smelting of gold and silver 
ores and is derived chiefly from Lake, San Juan, Gilpin, Chaffee 
and Clear Creek counties. Idaho: The greater part of the out- 
put comes from the Co3ur d'Alene district. The deposit con- 
sists of disseminated bornite, chalcocite and chalcopyrite in beds 
of quartzite. Michigan: This state was for a long period the 
most important producer in the country, and still ranks with 
the leading three. The ores are unique in that they consist 
wholly of native copper. They occur on Keweenaw Peninsula, 
the rocks of which consist of a series of alternating sandstone 
conglomerate beds and basic lava flows, all inclined at a steep 
angle to the northwest. The copper is found disseminated 
through and acting as a cement in the conglomerates, and in less 
important deposits in the amygdaloidal layers of the lavas. 
Montana: The one important district, and for a number of 
years the most important copper district in the world, is at 
Butte. The ores occur as replacement veins in a granitic rock. 
The ores have been very greatly enriched by secondary action 
forming at times very large sulphide bodies. The important 
ore minerals are chalcopyrite, chalcocite and enargite. Nevada: 
The important district is at Ely, where the sulphide ores occur 
as disseminations in highly altered porphyry. New Mexico: 



GOLD 317 

The Santa Rita-Hanover and the Burro Mountain districts are 
the chief producers. Tennessee: The chief district is that of 
Ducktown. The ores occur as steeply dipping lenses in a schist 
and contain chiefly pyrrhotite, pyrite and chalcopyrite. Utah: 
The Bingham district has ores which are closely associated with 
a granitelike rock called monzonite which is intruded into a 
series of quartzites, limestones and shales. The bodies are 
either contact deposits in limestone or in large disseminated 
deposits in the monzonite. The Tintic district has ore bodies 
occurring as contact deposits, replacements in limestone and 
filling fissures, the last being the most important. The Frisco 
district has ores which consist of pyrite and chalcopyrite occur- 
ring disseminated in a monzonite. 

Important copper deposits outside of the United States are 
at Rio Tin to in Spain; in Australasia, at Mount Lyell in Tas- 
mania, at Wallaroo and Moontain, South Australia, at Mount 
Morgan in Queensland and at different localities in New South 
Wales; in Mexico at Cananea and at various districts in Sonora, 
etc.; in Canada at the Boundary district in British Columbia 
and the Sudbury district in Ontario. Chile, Japan and Germany 
also produce notable amounts of copper. 

Copper is extensively used in the form of wire, sheet and nails. 
A large amount, chiefly as wire, is used as an electrical conductor. 
It has important uses in various alloys, as brass (copper and 
zinc), bronze and bell metal (copper and tin, at times zinc also), 
Gepman silver (copper, zinc and nickel), etc. Copper sulphate, 
or blue vitriol, is used in calico printing and in galvanic cells. 

Gold. 

Native Gold, Au, with small amounts of Ag. 
Petzite, (Ag,Au) 2 Te. Krennerite, AuTe 2 . 

Sylvanite, AuAgTe 4 . Calaverite, AuTe 2 . 

By far the greater part of gold occurs as the native metal. It 
enters into only one series of compounds, the tellurides, and 
these minerals, while at times forming rich ore deposits, as at 
Cripple Creek, Colorado, are found in only a few districts. For 



318 MANUAL OF MINERALOGY 

the occurrence and associations of the gold ores see under gold, 
page 125; under calaverite, page 158; and sylvanite, page 157. 
The uses of gold for jewelry, plating and coins are well known. 
The standard gold for United States coin is composed of 9 parts 
gold and 1 part copper. The gold used in jewelry is alloyed with 
copper and silver in order to harden it. The purity of gold is 
given in carats; 24 carats being the pure metal. Most of the 
gold used is 18 carats fine or $f gold and ^ other metals. Gold 
is used as the standard of international exchange and one troy 
ounce is worth $20.67. 

Iron. 

Hematite, Fe 2 3 . Goethite, Fe 2 3 (OH) 2 . 

Magnetite, Fe 3 4 . Limonite Fe 4 3 (OH) 6 . 

Turgite, Fe 4 5 (OH) 2 . Siderite, FeC0 3 . 

Iron, next to aluminium, is the most abundant metal in the 
crust of the earth. It very rarely occurs native, being found 
chiefly in the form of oxides, sulphides and silicates. It is found 
in greater or less amount in many rocks, especially in those that 
contain the amphiboles, pyroxenes, micas or olivine. The min- 
eral species that contain iron are very numerous but the minerals 
of importance as ores number only three or four. Iron occurs 
in large amounts in the sulphides, pyrite, FeS 2 , being the most 
common of all sulphides. These, however, never serve as ores 
of the metal because of the injurious effects of the presence of 
sulphur upon the iron. The minerals used as ores are 'the 
various oxides or the carbonate. 

The various iron ores are formed under different conditions, 
and as a rule occur alone or in association with only small 
amounts of any one of the others. For discussion of the occur- 
rence of the iron ores see, therefore, under hematite, page 184; 
magnetite, page 189; limonite, page 200; and siderite, page 210. 

Hematite is by far the most important ore of iron, forming in 
the United States about nine-tenths of the ore produced. Limo- 
nite and magnetite form each about one-twentieth of the total, 
while the amount of siderite produced is almost negligible. 
Hematite ore comes chiefly from the various Lake Superior dis- 



LEAD 319 

tricts and to a much less extent from Alabama. Limonite is 
found in the Appalachian states, and magnetite in New York, 
New Jersey and Pennsylvania. Siderite is obtained from Ohio. 

Nearly one-half of the world's production of iron ore comes 
from the United States; the amount produced from Minnesota 
alone nearly if not quite equals that produced in any other 
country. Germany and Great Britain, Spain and France, are 
notable producers of iron. 

The uses of iron and steel are too well known to need dis- 
cussion. Copperas, or green vitriol, FeS0 4 .7H 2 0, is the most 
important salt of iron, being used in dyeing, in making inks, 
Prussian blue, rouge, and as a disinfectant. Rouge, Fe 2 3 , is 
used as a polishing powder and as a red paint. Considerable 
amounts of soft iron ore, known as paint ore, are ground for 
mineral paints, such as ocher, umber, sienna, etc. 

Lead. 

Galena, PbS. Vanadinite, Pb 4 (PbCl)(V0 4 ) 3 . 

Cerussite, PbC0 3 . Anglesite, PbS0 4 . 

Phosgenite, (PbCl)C0 3 . Crocoite, PrCr0 4 . 

Pyromorphite, Pb 4 (PbCl)(P0 4 ) 3 . 

Mimetite, Pb 4 (PbCl)(As0 4 ) 3 . Wulfenite, PbMo0 4 . 

Galena is the usual primary ore of lead and furnishes by far 
the greater part of the metal. Cerussite and anglesite are 
secondary minerals which occur in smaller amounts in the oxi- 
dized zone of lead deposits. Galena occurs most commonly 
associated with zinc ores, especially sphalerite, or in connection 
with silver ores. Lead, which is derived from ores that are free 
from silver, is known as "soft lead," while " desilverized" lead, 
which is obtained from silver ores, is known as "hard lead." 
Lead ores are most commonly found as replacement deposits in 
limestone rocks, either in the form of beds or irregular bodies, 
or as small masses disseminated through a stratum of the rock. 
For the associations and distribution of lead ores see under 
galena, page 139. 

Metallic lead is used in the form of sheet, pipe, etc. It is used 
to make weights, bullets and shot. It is a constituent of various 



320 MANUAL OF MINERALOGY 

alloys such as solder (lead and tin), type metal (lead and anti- 
mony), low-fusing alloys (lead, bismuth and tin). A large 
.amount of lead is used in the form of the basic carbonate, 
(Pb.OH) 2 Pb(C0 3 )2, which is known as white lead, and is very 
valuable as a paint. The oxides of lead, litharge, PbO, and 
minium, Pb 3 4 , are used in making fine grades of glass, in glaz- 
ing earthenware and as pigments. Lead chromates are used as 
yellow and red paints. Lead acetate, known as sugar of lead, 
has important uses in various industries. 

Manganese. 

Alabandite, MnS. Psilomelane, Mn0 2 , MnO, etc. 

Franklinite, (Fe,Mn,Zn)(Fe,Mn) 2 4 . 
Braunite, Mn(Mn,Si)0 3 . Wad, mixture of oxides. 

Manganite, Mn 2 (OH) 2 2 . Rhodochrosite, MnC0 3 . 
Pyrolusite, Mn0 2 . Rhodonite, MnSi0 3 . 

Manganese is an element that is widely distributed in small 
amounts. Traces of it at least are to be found in most rocks. It 
most commonly occurs in silicates, oxides and carbonates. The 
oxides are the most abundant, and practically all of the metal 
is derived from them. 

The ore deposits of manganese are ordinarily of secondary 
origin. The manganese existing in the rock-making silicates, 
through the agency of weathering processes, is changed to an 
oxide. By some process of concentration these minerals are 
often gathered together into irregular bodies lying in residual 
clays. At times the manganese oxides occur associated with 
iron oxides, and when this is the case the two are smelted to- 
gether to form directly an iron-manganese alloy used in making 
steel. Manganese minerals also frequently occur as gangue 
minerals in connection with silver ores. A manganese ore to 
be of commercial value should contain at least 40 per cent of 
metallic manganese and be low in percentages of phosphorus 
and silica. 

Manganese is obtained in the United States from the following 
materials: manganese ores, manganiferous iron ores, manganif- 



MERCURY 321 

erous silver ores, and from the residuum left from smelting the 
zinc ores of Franklin Furnace, New Jersey. Manganese ores are 
found in commercial deposits in Virginia, Georgia, Arkansas and 
California. Manganif erous iron ores are found in Virginia, and at 
various places in the Lake Superior iron-ore districts. Manga- 
nif erous silver ores are found in the Rocky Mountain and Great 
Basin regions, the principal locality being Leadville, Colorado. 
The zinc ores of Franklin Furnace, New Jersey, contain small per- 
centages of manganese, chiefly in the mineral franklinite, and in 
the smelting of them the manganese remains in the residuum from 
which it is later obtained. This is the most important source 
of manganese at present in the United States. Because of the 
small domestic production of manganese ores large amounts 
have to be imported. These come largely from India and Brazil. 

Manganese is chiefly used in the form of alloys, those with 
iron being the most important. Spiegeleisen is an alloy of iron 
and manganese containing below 20 per cent of manganese, 
while ferromanganese contains manganese ranging in amount 
from 20 to 90 per cent. These alloys are extensively used in 
the manufacture of steel. They serve to take away any oxygen 
that might be in the iron, the oxygen uniting with the manganese 
and going into the slag. They serve also to introduce carbon 
into the steel and to prevent its oxidation, and also to counteract 
the bad effects of sulphur and phosphorus. Manganese has 
also of itself a hardening influence on steel. For these reasons 
manganese steels have a wide use. 

Chemical uses of manganese compounds include the use of 
the oxide, pyrolusite, Mn0 2 , as an oxidizer in the manufacture 
of chlorine, bromine and oxygen, as a drier in paints and var- 
nishes, as a decolorizer of glass, and in the dry-cell battery. 
Potassium permanganate is used as a disinfectant. Manganese 
is used in printing calico and for coloring bricks, pottery and 
glass. 

Mercury. 

Cinnabar, HgS. 

Mercury, or quicksilver, is neither abundant nor widespread 
in its occurrence. The native metal is sometimes found and 



322 MANUAL OF MINERALOGY 

other rare minerals of mercury are occasionally noted, but 
practically the only ore of the metal is the sulphide, cinnabar. 
For the occurrence and distribution of mercury, therefore, see 
under cinnabar, page 144. 

The most important use of mercury is in the amalgamation 
process for recovering gold and silver from their ores. It is 
used in the form of an amalgam with tin in " silvering" mirrors. 
It is used in thermometers, barometers, etc. Mercury salts, 
especially calomel, are used in medicine. The sulphide is used 
as the pigment called vermilion. 

Molybdenum. 
Molybdenite, MoS 2 . Wulfenite, PbMo0 4 . 

Molybdenum is a rare element occurring chiefly as the sul- 
phide, molybdenite. More rarely wulfenite may serve as an 
ore. See under molybdenite, page 137, and under wulfenite, 
page 308, for their occurrence and distribution. Only a small 
amount of molybdenum is produced in the United States. 

Molybdenum is used to a small extent as a steel-hardening 
metal. In the form of ammonium molybdate it is used as a 
chemical reagent, as a fireproofing material, and as a disin- 
fectant. Molybdenum compounds are also used to color leather 
and rubber. 

Nickel. 

Pentlandite, (Ni,Fe)S. Chloanthite, NiAs 2 . 

Millerite, NiS. Gersdorffite, NiAsS. 

Niccolite, NiAs. Genthite, Ni 2 Mg 2 Si 3 Oi .6H 2 0(?). 

Nickeliferous Pyrrhotite. Garnierite, noumeaite, H 2 NiSi0 4 (?). 

LinnsBite, (Co,Ni,Fe) 3 S 4 . 

Nickel is a comparatively rare element, found often associated 
with cobalt. Its minerals are frequently found in small amounts 
in connection with magnesian igneous rocks, where it is com- 
monly associated with chromite. Only a few localities produce 
the metal in commercial quantities, the world's output coming 
mostly from the nickeliferous pyrrhotite ores of Sudbury, On- 



PLATINUM 323 

tario, Canada, or from the silicate (garnierite) ores of New Cale- 
donia. The production of nickel from ores mined in the United 
States is very small. 

The chief use of nickel is in various alloys. Nickel steel, con- 
taining about 3.5 per cent of nickel, has a wide use because of its 
great strength and toughness. Other alloys are German silver 
(nickel, zinc and copper) ; metal for coinage (nickel and copper) . 
Large amounts of nickel are used in nickel plating. 

Platinum. 

Native Platinum, Pt, with some iron and traces of the rare 
platinum metals. Sperrylite, PtAs 2 . 

Platinum is a rare element which usually occurs native. Its 
only known compound occurring as a mineral is the arsenide, 
sperrylite, which has been found very sparingly in two or three 
localities in association with copper and nickel ores. Platinum 
is characteristically found associated with the magnesian rocks 
called peridotites and often with chromite. The only commer- 
cial deposits of platinum so far known are placer deposits, the 
materials of which have been derived from the weathering of 
the rocks that contained the platinum in disseminated particles. 
For the occurrence and distribution of platinum see page 131. 

The uses of platinum chiefly depend upon its high fusing point 
(1700 to 1800 C.) and its resistance to chemical reagents. It 
is valuable for all sorts of laboratory apparatus, such as crucibles, 
dishes, spoons, etc. It is used in the sulphuric acid industry 
for concentrating kettles and also in the contact process for the 
manufacture of the acid in the form of finely divided platinum, 
in contact with which the acid is formed. It is largely used as 
wire to form the electrical connections with the filaments of 
incandescent electric lights. It is used in jewelry, particularly 
as the setting for diamonds, in dentistry in the making of false 
teeth, in electrical heating apparatus, for sparking plugs in ex- 
plosion motors, in the measuring of high temperatures, in elec- 
trical contacts, etc. Potassium chloro-platinate, 2KCl.PtCl 2 , is 
employed in photography. 



324 MANUAL OF MINERALOGY 

Silver. 

Native Silver, Ag. Proustite, 3Ag 2 S.As 2 S 3 . 

Argentite, As 2 S. Stephanite, 5Ag 2 S.Sb 2 S 3 . 

Stromeyerite, Ag 2 S.Cu 2 S. Polybasite, 9Ag 2 S.Sb 2 S 3 . 

Sylvanite, AgAuTe 4 . Cerargyrite, AgCl. 

Pyrargyrite, 3Ag 2 S.Sb 2 S 3 . Embolite, Ag(Cl,Br). 

It is to be noted that none of the silver minerals contain oxy- 
gen, the most important series being included in the sulphide 
and sulpho-salt "groups. Besides the distinctively silver min- 
erals listed above, several minerals of other metals contain at 
times sufficient silver to make them valuable ores of the metal. 
Most important among these are the argentiferous varieties of 
galena, chalcocite, bornite, chalcopyrite and tetrahedrite. These 
minerals form the most common ores of silver, either because of 
the small amounts of silver which they contain, or the small 
amounts of silver minerals associated with them. 

The important ores of silver can be divided into three main 
classes, namely, the siliceous ores, copper ores and lead ores. 
The siliceous ores are those ores which contain large propor- 
tions of quartz with small amounts of gold and silver minerals 
and are comparatively free from other metals. Most of them 
contain both gold and silver, the gold value being often in excess 
of the silver value. The chief districts in which this type of 
silver ore is produced are Tonopah in Nevada; the San Juan, 
Leadville and Aspen districts in Colorado; Granite, Jefferson 
and Silverbow counties in Montana; and in various districts 
in Idaho, Arizona, California, South Dakota and Utah. The 
important deposits of copper ores which contain a notable 
amount of silver are found at Butte in Montana; at the Bingham 
and Tintic districts in Utah; at the Bisbee, United Verde and 
Silver Bell districts in Arizona; in Shasta County, California; 
and at various places in Idaho, Michigan and Colorado. The 
important deposits of lead ore that produce silver are to be 
found at the Cceur d'Alene district in Idaho; at the Bingham 
and Tintic districts in Utah; at the Creede, San Juan and Lead- 
ville districts in Colorado; and at various districts in Nevada, 



TIN 325 

Montana and Arizona. For the production of these different 
classes of silver ores see Appendix II. 

The important foreign countries for the production of silver 
are Mexico, Canada and Australia. In Mexico the chief dis- 
tricts are Guanajuato, Pachuca, El Oro, Parral and Santa Eulalia; 
in Canada in the Boundary and Kootenai districts in British 
Columbia and the Cobalt district in Ontario; in Australia 
chiefly from the Broken Hill district in New South Wales. 

In connection with silver ores the following facts are of in- 
terest. Owing to the high value of silver, only a small per- 
centage of the metal in an ore is sufficient to make it valuable. 
For instance, an ore that contained only 0.34 per cent of silver 
would yield 100 ounces to the ton, which is an amount much 
larger than usual. In giving the assay value of an ore, the 
amount of silver is usually stated in ounces per ton of ore. 
Lead-silver ores are of value because in the smelting the silver 
will be taken up by the lead. Ores containing calcium car- 
bonate and iron and manganese minerals are of value because 
of the service of these materials in fluxing the ore. Zinc min- 
erals detract from the value of an ore because of the added 
difficulty in smelting caused by their presence. 

The uses of silver for coinage, for various useful and ornamental 
objects and for plating are too well known to need discussion. 
The standard silver coin for the United States contains nine 
parts of silver to one of copper. Silver salts are used in photog- 
raphy and caustic silver (AgN0 3 ) is employed in medicine. 

Tin. 

Stannite, Cu 2 S.FeS.SnS. Cassiterite, Sn0 2 . 

The only ore of tin of importance is the oxide, cassiterite. 
This is a mineral which, while occurring in small quantities in 
many localities, is found only in a comparatively few commercial 
deposits. For the occurrence and distribution of the mineral 
see page 193. The United States at present produces only a 
small amount of tin ore. 

Tin is chiefly used in the coating or "tinning" of metals, es- 
pecially iron. The tin plate thus formed is used in roofing, in 



326 MANUAL OF MINERALOGY 

various utensils, etc. An amalgam of tin and mercury is used 
in "silvering" mirrors. Various alloys are valuable, such as 
solder (tin and lead), bronze and bell metal (copper and tin). 
The artificial oxide of tin is used as a polishing powder. Stannic 
chloride is employed as a mordant in dyeing. 

Titanium. 

Ilmenite, titanic iron, FeTi0 3 Octahedrite, Ti0 2 . 

with MgTi0 3 and Fe 2 3 . Brookite, Ti0 2 . 

Rutile, Ti0 2 . Titanite, CaTiSi0 5 . 

Titanium is a rare element, but is quite widely distributed in 
small quantities. In the form of the minerals rutile and titanite 
it is present in most igneous rocks. Ilmenite is commonly 
found in the basic igneous rocks, and is often associated with 
magnetic iron ores. 

Very little titanium ore is produced in the United States. 
Rutile deposits occur in Virginia, and some of the Adirondack 
magnetite deposits contain considerable ilmenite. 

The present uses of titanium are rather limited. It has been 
used in steel and cast iron, in which it serves to eliminate the 
oxygen and nitrogen. It is also said to give a high tensile 
strength and great ductility to the steel. It is being used to 
some extent in the manufacture of electrodes for arc lights. 
The oxide is used to give a yellow color to porcelain, and to give 
a natural color to false teeth. 

Tungsten. 

Wolframite, (Fe,Mn)W0 4 . Scheelite, CaW0 4 . 
Hiibnerite, MnW0 4 . 

Tungsten is a rare acid-forming heavy metal found chiefly in 
the tungstates of iron and calcium, wolframite and scheelite. 
For the occurrence and distribution of these minerals see under 
wolframite, page 307, and scheelite, page 308. 

The most important use to which tungsten is put is as a steel- 
hardening metal. Tungsten steels hold their temper at high 
temperatures and are therefore valuable for the making of high- 



ZINC 327 

speed tools, etc. Because of its high fusing point metallic 
tungsten is used as a filament in incandescent electric lights. 
Sodium tungstate is used in fireproofing cloth and as a mordant 
in dyeing. Calcium tungstate is used as the luminous screen in 
X-ray apparatus. 

Vanadium. 

Roscoelite, H 8 K 2 (Mg,Fe)(Al,V) 4 (Si0 3 )2(?). 
Vanadinite,Pb 4 (PbCl)(V04)3.Carnotite,K(U0 2 ) 2 (V04) 2 .3H 2 0(?). 

Vanadium is an acid-forming metal which is known in a num- 
ber of very rare minerals. The three listed above are the only 
ones which occur in sufficient quantities in the United States to 
be available for ores. Roscoelite is a green micaceous mineral 
containing about 2 per cent of metallic vanadium. It is found 
in a soft sandstone near Placerville, Col. Carnotite is a sulphur- 
yellow pulverulent mineral of doubtful composition which is 
found in sandstones in several districts in Colorado and Utah, 
near the boundary line between the two states. Vanadinite is 
a secondary lead mineral which is found sparingly in the oxi- 
dized zones of certain lead deposits in Arizona and New Mexico. 
All of these ores are low grade, and are worked only in a small 
way and at intervals. The chief supply of vanadium ores at 
present comes from Peru, where there are large deposits of an 
impure carbonaceous sulphide of vanadium, known as patronite. 

Vanadium is used chiefly in steel, and is said to give it great 
tensile and elastic strength. Metavanadic acid, HV0 3 , is used 
as a yellow pigment, known as vanadium bronze. Vanadium 
oxide serves as a mordant in dyeing. 

Zinc. 

Sphalerite, ZnS. Smithsonite, ZnC0 3 . 

Zincite, ZnO. Willemite, Zn 2 Si0 4 . 

Franklinite, (Fe,Zn,Mn) (Fe,Mn) 2 3 . 

Calamine, (ZnOH) 2 SiO. 

The sulphide, sphalerite, is the one common primary ore of 
zinc. The carbonate, smithsonite, and the silicate, calamine, 
are usually associated with sphalerite deposits as secondary 



328 MANUAL OF MINERALOGY 

minerals. The three minerals, zincite, franklinite and willemite, 
are found in unique deposits at Franklin Furnace, New Jersey. 
Together with a large number of rare and unusual minerals they 
form anticlinal beds lying intercalated in a limestone series. In 
general sphalerite, the chief ore of zinc, is found in irregular 
replacement deposits in limestone. It is very frequently inti- 
mately associated with lead minerals. For its occurrence and 
distribution see page 142. 

Metallic zinc, or spelter, as it is called, is chiefly used for gal- 
vanizing iron, as an alloy with copper in brass, and in storage 
and telegraph batteries. Zinc dust or zinc shavings are used to 
precipitate gold from its solution in the cyanide process. Large 
amounts of zinc oxide, or zinc white, are used as a white paint 
which is even more permanent than lead paints. Zinc chloride 
is used as a wood preservative. 



OCCURRENCE AND ASSOCIATION OF MINERALS. 

Although minerals are found in many modes of occurrence, 
and in an almost endless variety of associations, there are, how- 
ever, certain frequent and important ways in which they occur 
that should be pointed out. An understanding of the condi- 
tions under which a particular mineral is usually formed, together 
with a knowledge of what other minerals are characteristically 
associated with it, is of the greatest value. On the following 
pages is given, therefore, a brief discussion of the more important 
modes of mineral occurrence, and of the more common associa- 
tions observed. 

Rocks and Rock-making Minerals. 

Since by far the greater part of minerals occur as rock con- 
stituents a short description of the more important rock types 
and of the common rock-making minerals will be given first. 
Only the barest outline of the subject can be given here and for 
more detailed information the reader is referred to one of the 
textbooks which treat more particularly of petrology. 



IGNEOUS ROCKS 329 

Rocks may be divided into three main divisions, namely: 
I. Igneous. 
II. Sedimentary. 
III. Metamorphic. 

I. Igneous Rocks. 

Igneous Rocks, as the name indicates, are those which have 
been formed by the cooling and consequent solidification of a 
once hot and fluid mass of rock material. This liquid mass 
is known as a rock magma. A magma, in a measure, is like 
a solution containing in a dissociated condition the elements 
which, when the mass cools sufficiently, unite to form the various 
minerals that go to make up the resulting rock. The elements 
which form the chief constituents of the magmas of igneous 
rocks are oxygen, silicon, aluminium, iron, calcium, magnesium, 
sodium and potassium, named in the order of their abundance. 
When a magma cools these elements unite to form various 
mineral molecules, which, when the point of supersaturation 
is reached, crystallize out to form the minerals of the rock. 
Certain compounds under similar conditions crystallize out 
of the fluid mass earlier than do others. In most igneous 
rocks a more or less definite order of crystallization for their 
mineral constituents can be determined. In general the more 
basic minerals or those which contain the smaller amounts of 
silica, which is the acid element in igneous rocks, are observed 
to crystallize first and the more acid minerals last. Among the 
commoner rock-making minerals the following would be the 
usual order of crystallization; iron oxides like magnetite first, 
then the ferro-magnesian minerals like pyroxene, next the 
plagioclase feldspars, then orthoclase and lastly quartz. 

The type of minerals to be found in any igneous rock would 
depend chiefly upon the chemical composition of the original 
magma. If the magma was acid in character, i.e., had a high 
percentage of silica, the resulting rock would contain the more 
acid minerals and an abundance of free quartz. It would 
usually be light in color. If, on the other hand, the magma had 



330 MANUAL OF MINERALOGY 

a low percentage of silica, or in other words was basic in char- 
acter, the resulting rock would contain the more basic minerals 
and would not show free quartz. It would also in general be 
dark in color. 

In addition to the wide variation in. chemical and mineral 
composition shown by igneous rocks there is also a variation in 
their physical structure. This is dependent upon the mode of 
origin of the rock. If a rock has been formed from a magma 
buried at a considerable depth in the crust of the earth it must 
have cooled very slowly and taken a long period of time for its 
gradual crystallization and solidification. Under these condi- 
tions the mineral particles have had the opportunity, because 
of the slowness of crystallization, to grow to considerable size. 
A rock having such a deep-seated origin has, therefore, a coarse- 
grained structure and the various minerals that go to form the 
rock can in general be differentiated and recognized by the 
unaided eye. Such rocks are commonly termed plutonic. 

On the other hand, if, by volcanic forces, the magma, has been 
extruded upon the surface of the earth or intruded in the form 
of dikes into the rocks lying close to the surface, its subsequent 
cooling and solidification go on quite rapidly. Under these con- 
ditions the mineral particles have little chance to grow to any 
size and the resulting rock is fine-grained in character. In some 
cases, indeed, the cooling has been too rapid to allow the separa- 
tion of any minerals and the resulting rock is like a glass. Ordi- 
narily the mineral constituents of such a rock are only to be 
definitely recognized by a microscopic examination of a thin 
section of the rock. Such igneous rocks are known as volcanic 
rocks. 

An igneous rock, because of the mode of its formation, con- 
sists of crystalline particles which may be said to interlock with 
each other. In other words, it is a solid mass, and each mineral 
particle is intimately and firmly embedded in the surrounding 
particles. This structure will enable one ordinarily to distin- 
guish an igneous from a sedimentary rock, the latter being com- 
posed of grains which do not interlock with each other but stand 
out, more or less, by themselves. A sedimentary rock is not 



PLUTONIC, COARSE-GRAINED ROCKS 331 

so firm and coherent as an igneous rock. Further the texture 
of an igneous rock is the same in all directions and it forms a 
fairly uniform and homogeneous mass. This characteristic will 
enable one to distinguish an igneous from a metamorphic rock, 
since the latter shows a more or less definite parallel arrange- 
ment of its minerals and a banded structure. 

Because of the almost infinite variation possible in the chemi- 
cal composition of their magmas, and because of the various 
conditions under which they may form, igneous rocks show like- 
wise a wide variation in character. The more common and 
important types, however, are very briefly described below. 

Plutonic, Coarse-grained Rocks. 

1. Granite. A granite is a medium- to coarse-grained, light- 
colored rock having an even texture and consisting chiefly of 
quartz and a feldspar. Frequently both orthoclase and a 
plagioclase feldspar,' and usually also small amounts of mica or 
hornblende are present. The feldspars can be recognized by 
their color and cleavage. Frequently the orthoclase is colored 
flesh-color or red, while the soda-lime feldspar is usually white. 
The quartz is recognized by its glassy luster and conchoidal 
fracture. It is usually white or smoky-gray in color and is 
found in irregular grains filling up the interstices between the 
other minerals. The mica, which may be either muscovite or 
biotite, is to be recognized by its cleavage. Granite is a common 
rock type. 

2. Syenite. A syenite is a medium- to coarse-grained light- 
colored rock with an even texture and much like a granite in 
appearance. It is to be distinguished from granite, however, by 
the fact that it contains little or no quartz. Its chief minerals 
are the feldspars, with more or less hornblende, mica or pyroxene. 
A variety, known as nephelite-syenite, is characterized by the 
presence of considerable amounts of nephelite. Another variety, 
called anorthosite, is composed chiefly of labradorite. The 
feldspars, mica and hornblende may be distinguished as de- 
scribed under granite. The pyroxene resembles hornblende in 
appearance, but does not show as good a prismatic cleavage. 



332 MANUAL OF MINERALOGY 

Nephelite is recognized by its lack of a distinct cleavage and its 
oily and greasy luster. Syenites are not very common. 

3. Diorite. Diorite is a medium- to coarse-grained dark gray 
or greenish colored rock having an even texture and consisting 
chiefly of hornblende and a feldspar, in which the hornblende 
predominates. Often fine grains of iron ore may be observed, 
and frequently considerable amounts of biotite. It is a common 
rock type. 

4. Gabbro. Gabbro is a medium- to coarse-grained dark gray 
to greenish black rock with an even texture composed chiefly 
of. pyroxene and a feldspar. It is closely similar to diorite, the 
distinction lying in the fact that it contains pyroxene instead 
of amphibole. These two minerals, as they occur in these rocks, 
cannot always be told apart by a megascopic examination. 
The pyroxene is usually in small crystal grains with rather poor 
prismatic cleavages which are at nearly right angles to each 
other. Hornblende is more liable to be in longer prismatic 
crystals and shows better cleavages, the angle of which is about 
125. It is a common rock. 

5. Dolerite. This is a name given to those varieties of diorite 
and gabbro which are too fine-grained in character to enable 
one to tell megascopically whether the dark-colored mineral 
which they contain is hornblende or pyroxene. 

6. Peridotite. A peridotite is a medium- to coarse-grained 
dark green to black rock with an even texture which consists 
wholly of ferromagnesian minerals. These are chiefly olivine, 
pyroxene and hornblende. As one or the other of these minerals 
predominates, various variety names are used, such as dunite for 
an olivine rock and pyroxenite and hornblendite for respectively 
pyroxene and hornblende rocks. Common accessory minerals 
found in these rocks are ilmenite, chromite and garnet. The 
peridotites are not very common in their occurrence. 

Volcanic, Fine-grained Igneous Rocks. 

Because of their very fine-grained structure volcanic rocks 
cannot in general be readily told apart. A number of different 
types are recognized, the distinction between them being based, 



VOLCANIC, FINE-GRAINED IGNEOUS ROCKS 333 

however, chiefly upon microscopic study. In the field only an 
approximate classification, depending upon whether the rock 
is light or dark in color, can be made. A brief description of 
these two types of volcanic rocks follows. 

1. Felsite. This is a dense fine-grained rock type with a stony 
texture an,d includes all colors except dark gray, dark green or 
black. These rocks may, by the aid of a lens, still show a very 
fine-grained structure or their mineral constituents may occur 
in such small particles as to give them a dense and homogeneous, 
often a flinty, appearance. By microscopic study the felsites 
have been divided into the following groups; rhyolite, consisting 
chiefly of alkaline feldspars and quartz; dacite, lime-soda feld- 
spars and quartz; trachyte, alkaline feldspars with little or no 
quartz; andesite, soda-lime feldspars with little or no quartz; 
phonolite, alkaline feldspars and nephelite. As a rule these 
varieties are not to be distinguished from each other in the field. 
The felsites are widespread in their occurrence, being found as 
dikes and sheets intruded into the upper part of the earth's crust 
or as lava flows which have been poured out upon the earth's 
surface. 

2. Basalt. The basalts are dense fine-grained rocks that are 
of very dark color, green or black. They are composed of micro- 
scopic grains of a soda-lime feldspar with pyroxene, iron ore, 
often more or less olivine and at times biotite or hornblende. 
These rocks are formed under the same conditions as the felsites 
and are to be found occurring in the same ways. 

3. Glassy Rocks. Some of the volcanic rocks have cooled 
so rapidly that they are wholly or in part made up of a glassy 
material in which the different elements have not had the neces- 
sary opportunity to group themselves into definite minerals. 
If the entire rock is composed of glass it is called obsidian, when 
it has a bright and vitreous luster; pitchstone when its luster is 
dull and pitchy; perlite if it is made up of small spheroids; and 
pumice if it has a distinctly cellular structure. These rocks 
may also have distinct crystals of various minerals embedded 
in the glass, in which case they are known as glass porphyries (see 
below for a definition of a porphyry) or vitrophyres. 



334 MANUAL OF MINERALOGY 

Porphyries. Igneous rocks at times show distinct crystals of 
certain minerals which lie embedded in a much finer-grained 
material. These larger crystals are known as phenocrysts, and 
the finer-grained material as the groundmass of the rock. Rocks 
exhibiting such a structure are known as porphyries. The 
phenocrysts may vary in size from crystals an inch or more 
across down to quite small individuals. The groundmass may 
also be composed of fairly coarse-grained material or its grains 
may be microscopic in size. It is the distinct difference in size 
existing between the phenocrysts and the particles of the ground- 
mass that is the distinguishing feature of a porphyry. This 
peculiar structure is due to certain conditions prevailing during 
the formation of the rock which permitted some crystals to grow 
to considerable size before the main mass of the rock consolidated 
into a finer- and uniform-grained material. The explanation of 
the reasons why a certain rock should assume a porphyritic 
structure would involve a more detailed discussion than it is 
expedient to give in this place. Any one of the above described 
types of igneous rocks may have a porphyritic variety, such as 
granite-porphyry, diorite-porphyry, felsite-porphyry, etc. Por- 
phyritic varieties are more liable to occur in connection with 
volcanic rocks, and they are also found most frequently in the 
case of the more acid types. 

II. Sedimentary Rocks. 

Sedimentary rocks are secondary in their origin, the materials 
of which they are composed having been derived from the decay 
and disintegration of some previously existing rock mass. They 
have been formed by a deposition of sediments in a body of 
water. They may be divided into two classes, depending upon 
whether their origin has been mechanical or chemical in its 
nature. In the case of the sedimentary rocks of a mechanical 
origin, their constituent particles have been derived from the 
disintegration of some rock mass, and have been transported 
by streams into a large body of quiet water, where they have 
been deposited in practically horizontal layers. Sedimentary 



SEDIMENTARY ROCKS 335 

rocks of chemical origin have had the materials of which they 
are composed dissolved by waters circulating through the rocks 
and brought ultimately by these waters into a sea, where through- 
some chemical change they are precipitated upon its floor, also 
in horizontal layers. These horizontal beds of sediments are 
ultimately consolidated into the masses known as sedimentary 
rocks. 

Sedimentary rocks are therefore characterized by a parallel 
arrangement of their constituent particles into layers and beds 
which are to be distinguished from each other by differences in 
thickness, size of grain and often in color. It is to be noted, 
further, that sedimentary rocks in general are composed of an 
aggregate of individual mineral particles, each of which stands 
out in a way by itself and does not have that intimate inter- 
locking relation with the surrounding particles which is to be 
seen in the minerals of an igneous rock. In all the coarser- 
grained sedimentary rocks there is some material which, acting 
as a cement, surrounds the individual mineral particles and binds 
them together. This cement is usually either silica, calcium 
carbonate or iron oxide. The chief minerals to be found in 
sedimentary rocks are quartz and a carbonate, calcite or dolo- 
mite. These give rise to the two chief types of sedimentary 
rocks, the sandstones and the limestones. A brief description 
of these rocks follows. 

1. Sandstone. Sandstones are mechanical in their origin, 
being formed by the consolidation into rock masses of beds of 
sand and gravel. Usually the constituent grains are rounded 
and water-worn, but at times they may be more or less angular 
in shape. With the variation in the size of the mineral particles 
the rocks themselves vary in their grain. Coarse-grained sand- 
stones formed from gravels are known as conglomerates. The 
cement which serves to bind the sand grains together may be 
deposited silica, a carbonate, usually calcite, an iron oxide, 
hematite or limonite, or fine-grained argillaceous or claylike 
material. The color of the rock will depend in large measure 
upon the character of the cement. The rocks which have silica 
or calcite as their binding material are light in color, usually pale 



336 MANUAL OF MINERALOGY 

yellow, buff, white to gray, while those that contain an iron 
oxide are red to reddish brown. It is to be noted that when a 
sandstone breaks it is usually the cement that is fractured, while 
the individual grains remain unbroken, so that the fresh surfaces 
of the rock have a granular appearance and feeling. The chief 
mineral of sandstones is quartz, but at times a rock may contain 
notable amounts of feldspar and is then termed an arkose. 
Graywacke is a sandstone, usually of a gray color, which in addi- 
tion to quartz and feldspar contains particles of other rocks and 
minerals. 

2. Shale. The shales are very fine-grained sedimentary rocks 
which have been formed by the consolidation of beds of mud, 
clay or silt. They have usually a thinly laminated structure. 
Their color is commonly some tone of gray, although they may 
be white, yellow, brown, green to black. They are composed 
chiefly of kaolin, mica, etc., but are too fine-grained to permit 
the recognition of their mineral constituents by the eye alone. 
By the introduction of quartz and an increase in the size of 
grain they grade into the sandstones. 

3. Limestone. The limestones are carbonate rocks composed 
usually chiefly of calcite, although dolomite may also be at times 
an important constituent. The carbonate has in the great 
majority of cases been extracted from the sea water by the 
agency of minute organisms and then deposited in beds which 
ultimately are consolidated into rock. These rocks are usu- 
ally fine- and even-grained in structure and sometimes quite 
dense. Some limestones are quite pure calcite, while others con- 
tain clay like materials and various oxides as impurities. The 
color of a limestone is usually gray, although it may be white, 
yellow, brown to almost black. It is a soft rock, to be easily 
scratched by a knife. It will effervesce readily in any common 
acid. In the case of limestones composed of dolomite, however, 
the acid needs to be heated. Oolite, or oolitic limestone, is a vari- 
ety which consists of an aggregate of small spherical concretions. 
Chalk is a very fine-grained friable limestone composed of shells 
of minute sea animals known as foraminifera. Travertine is a 
deposit of calcium carbonate formed by springs. A fine example 



METAMORPHIC ROCKS 337 

exists in the deposits formed by the Mammoth Hot Springs, 
Yellowstone Park. Marl is a loose, earthly material composed 
of a carbonate mixed with clay in variable amount. 

III. Metamorphic Rocks. 

Metamorphic rocks are rocks which have undergone some 
chemical or physical change subsequent to their original forma- 
tion. This change has been brought about by means of high tem- 
perature and pressure aided by the action of water and other 
chemical agents. The changes involve the formation of new 
minerals, the adding or subtracting of chemical constituents and 
a physical readjustment of the mineral particles to conform to 
the existing pressure. The original rock from which a metamor- 
phic rock has been derived may be either igneous or sedimentary. 
As these rocks become involved in movements of the earth's crust, 
they are subjected to extreme pressures accompanied usually 
by high temperatures. The result will be frequently to trans- 
form the existing minerals into others more stable under the 
new conditions. The physical structure of the rock will also 
ordinarily be changed during the process. Because of the pres- 
sure to which the rock is subjected the mineral particles will be 
more or less broken and flattened and rearranged in parallel 
layers. This banded or laminated character given by the 
parallel arrangement of its minerals is the most striking pecu- 
liarity of a metamorphic rock. Because of this structure a 
metamorphic rock can be distinguished from an igneous rock. 
Further, in the great majority of cases a metamorphic rock has 
a crystalline structure which distinguishes it from a sedimentary 
rock. There are, of course, all gradations from a typical meta- 
morphic rock into an unaltered sedimentary rock on the one 
hand and into an unaltered igneous rock on the other. The 
most common types of metamorphic rocks are briefly described 
below. 

1. Gneiss. When the word gneiss is used alone it usually 
refers to a metamorphic rock composed essentially of quartz, 
feldspar and a mica. The quartz and feldspar occur together 
in layers which are separated from each other by thin drawn-out 



338 MANUAL OF MINERALOGY 

bands of 'mica. A gneiss has usually a light color, although 
this is not necessarily so. Various varieties of gneiss have re- 
ceived distinctive names, most of which are self-explanatory, like 
banded-gneiss, lenticular-gneiss, biotite-gneiss, hornblende-gneiss, 
granite-gneiss, diorite-gneiss, etc. Gneiss is a very common rock 
type, especially in regions in which the oldest rocks, those of 
the Archaean age, are found. Gneisses have been more com- 
monly derived by the metamorphism of igneous rocks, mostly 
granites, but may have been formed from sedimentary rocks as 
well. 

2. Mica-schist. Mica-schist is a rock composed essentially 
of quartz and a mica, usually either muscovite or biotite. The 
mica is the prominent mineral, occurring in irregular leaves and 
in foliated masses. The mica plates all lie with their cleavage 
planes parallel to each other and give to the rock a striking lam- 
inated or " schistose" structure. The mica-schists frequently 
carry characteristic accessory minerals, such as garnet, stauro- 
lite, cyanite, epidote, hornblende, etc. They may have been 
derived from either an igneous or a sedimentary rock. Next to 
the gneisses, they are the most common metamorphic rocks. 

3. Quartzite. As its name indicates, a quartzite is a rock 
composed essentially of quartz. It is a firm, compact rock 
which breaks with an uneven, splintery or conchoidal fracture. 
It is usually light in color. Quartzite has been derived from 
a sandstone by intense metamorphism. It is a common and 
widely distributed rock. 

4. Slate. Slates are exceedingly fine-grained rocks which 
have a remarkable cleavage which permits them to be split into 
thin and broad sheets. Their color is commonly gray to black, 
but may be green, yellow, brown, red, etc. They have been 
formed commonly by the metamorphism of shales. Their 
characteristic slaty cleavage may or may not be parallel to the 
bedding planes of the original shales. They are quite common 
in occurrence. 

5. Various Schists. There are various other kinds of schistose 
rocks, which are chiefly derived by the metamorphism of the 
ferromagnesian igneous rocks. The most important types are 



THE COMMON ROCK-MAKING MINERALS 339 

talc-schist, chlorite-schist, amphibolite or hornblende-schist. They 
each are characterized, as their names indicate, by the prepon- 
derance of some metamorphic ferromagnesian mineral. 

6. Marble. A marble is a metamorphosed limestone. It is 
a crystalline rock composed of grains of calcite, or more rarely 
dolomite. At times the individual grains are so small that they 
cannot be distinguished by the eye, and again they may be quite 
coarse and show clearly the characteristic cleavage of the min- 
eral. Like limestone, a marble is characterized by its softness 
and its effervescence with acids. When pure, marble is white in 
color, but it may show a wide range of color, due to various im- 
purities that it contains. It is a rock which is found in many 
localities and at times in thick and extensive beds. 



The Common Rock-making Minerals. 

Although many minerals are found as rock constituents, those 
which can be termed common and characteristic rock-making 
minerals are comparatively few in number. The following list 
gives the names of these minerals, with a brief statement in each 
case of the types of rocks in which, they most commonly occur. 

1. Quartz. Quartz, Si0 2 , is a very common and widely dis- 
tributed rock-making mineral. It is found in all the light- 
colored, acid, igneous and metamorphic rocks. It is the chief 
constituent of sandstones and quartzites. It is to be recognized 
by its hardness (7), its vitreous luster, lack of cleavage and con- 
choidal fracture. When it occurs in igneous rocks it often has 
a gray or smoky color. 

2. The Feldspars. The feldspars include orthoclase and 
microcline, KAlSi 3 8 , albite, NaAlSi 3 8 , anorthite, CaAl 2 Si 2 8 , 
and various mixtures of these last two as oligoclase (3 albite to 
1 anorthite), andesite (1 albite to 1 anorthite) and labradorite 
(1 albite to 3 anorthite). They are very common rock-making 
minerals and are found in a great variety of rock types. They 
are characteristic of most igneous rocks, and frequently con- 
stitute a large proportion of them. They are found in the 
gneisses and to a less extent in some sandstones. They are to 



340 MANUAL OF MINERALOGY 

be distinguished by their two cleavages at right angles or nearly 
so, their vitreous luster and their hardness (6). It frequently 
is difficult, if not impossible, to tell the kind of feldspar present 
in a rock by inspection alone. Under favorable conditions 
twinning striations may be observed on the best cleavage face, 
which would indicate that the feldspar belonged to the plagio- 
clase group (see page 225) and could not be orthoclase. 

3. Nephelite. Nephelite is a silicate whose composition is 
essentially NaAlSi0 4 . It is restricted in its occurrence, being 
found only in certain igneous rocks, such as the nephelite sye- 
nites, which are low in percentages of silica. It is often mistaken 
for quartz, but the two minerals are practically never found to- 
gether. It is best determined by a chemical test. Unlike most 
rock-making minerals, it is readily soluble in hydrochloric acid 
and the solution gelatinizes on evaporation. 

4. Sodalite. Sodalite, Na 4 (AlCl)Al 2 (Si0 4 ) 3 , is similar in its 
occurrence to nephelite, with which it is commonly associated. 
It may be greenish gray or white in color, but is usually blue. 
Haiiynite and noselite are similar but rare species which occur 
in the same way. 

5. Leucite. Leucite has the composition KAl(Si0 3 ) 2 . It is 
a rare rock-making mineral found chiefly in rather basic lavas. 
It is commonly in the form of phenocrysts which show trape- 
zohedral forms. It is white to gray in color with a dull vitreous 
luster. 

6. The Micas. The micas are common rock-making min- 
erals. They may be divided into two classes : the light colored 
micas which are chiefly muscovite, and the dark colored micas 
consisting mostly of biotite. They are to be determined by 
their micaceous structure, eminent cleavage and the elasticity 
of their leaves. Muscovite is found in granites and syenites 
and other igneous rocks. It is especially common in the meta- 
morphic rocks, particularly the gneisses and schists. Biotite is 
found in many igneous rocks such as the granites, syenites and 
felsites. It occurs also in the gneisses and schists. 

7. The Pyroxenes. The pyroxenes form an important series 
of rock-making minerals which, although the different members 



THE COMMON ROCK-MAKING MINERALS 341 

vary considerably in composition, are closely related crystallo- 
graphically. The important types are hypersthene, (Mg,Fe)Si0 3 , 
diopside, CaMg(Si0 3 ) 2 , common pyroxene, Ca(Mg,Fe)(Si0 3 ) 2 , 
augite, Ca(Mg,Fe)(Si0 3 ) 2 with (Mg,Fe)(Al,Fe) 2 Si0 6 as well, and 
segirite, NaFe(Si0 3 ) 2 . The pyroxenes are characteristically 
found in igneous rocks, particularly those that contain large 
amounts of lime, iron and magnesia, such as basalt, gabbro, 
peridotite, etc. Diopside and common pyroxene are at times 
found in metamorphic limestones. The pyroxenes vary in color 
from white through green to black. They occur usually in 
small grains or in short prisms. If they show distinct crystal 
outlines, they can be told by the square cross section of their 
prisms. They have a rather poor cleavage. 

8. The Amphiboles. The amphiboles or hornblendes are 
calcium, magnesium, iron metasilicates which closely resemble 
the pyroxenes in their chemical composition. The most im- 
portant members of the group are tremolite, CaMg 3 (Si0 3 ) 4 , 
actinolite, Ca(Mg,Fe) 3 (Si0 3 ) 4 , common hornblende, Ca(Mg,Fe) 3 
(Si0 3 ) 4 , with a molecule containing aluminium and ferric iron 
besides, and arfvedsonite, which contains chiefly soda, lime and 
iron protoxide. The amphiboles are particularly characteristic 
of the metamorphic rocks, but are found in the igneous rocks as 
well. Tremolite is most commonly found in crystalline meta- 
morphosed limestones, actinolite in schists, hornblende in 
granites, syenites and diorites, and also in gneisses and horn- 
blende schists. The amphiboles commonly occur in bladed 
prismatic crystals with a good prismatic cleavage. The cleav- 
age angle is broad, having a value of about 125. They vary 
in color from white through green to black, but are most 
commonly green. 

9. Chrysolite, or Olivine. Chrysolite, or olivine, as it is more 
commonly termed when spoken of as a rock constituent, is an 
orthosilicate of magnesium and ferrous iron (Mg,Fe) 2 Si0 4 . It is 
a characteristic constituent of the ferromagnesian igneous rocks 
such as gabbros, peridotites and basalts. It is almost the only 
mineral present in the igneous rock known as dunite. It is usually 
green in color, with a vitreous luster and granular structure. 



342 MANUAL OF MINERALOGY 

10. Kaolin. Kaolin is a silicate of aluminium, H4Al 2 Si 2 9 , 
which is always secondary in its origin. It is formed by the 
weathering of some aluminium silicate, usually a feldspar. It 
may occur in quite pure masses where feldspathic rocks have 
been entirely altered, but is most commonly found, however, in 
an impure state in clay, and in the rocks formed from claylike 
materials such as shales, slates, etc. When pure it is often friable 
or mealy in structure, although at times it is compact. It varies 
in color from white to yellow, brown, red, etc., depending upon 
the amount and character of the foreign material mixed with it. 

11. Chlorites. The chlorites are a group of green-colored 
micaceous minerals of which clinochlore is the most common 
member. In composition they are hydrous silicates of alumin- 
ium and magnesium. They are always secondary in their 
origin. They are frequently formed by the alteration of the 
ferromagnesian minerals occurring in igneous rocks. The green 
color of such rocks is usually due to the presence of chlorite. 
They are also common in the chlorite-schists, in green slates, etc. 
They are to be recognized by their green color, micaceous structure, 
perfect cleavage, and by the fact that their leaves are not elastic. 

12. Serpentine. Serpentine, H 4 Mg 3 Si 2 9 , is also a secondary 
mineral formed by the alteration of some original ferromagnesian 
mineral, such as pyroxene, amphibole, and especially olivine. It 
occurs, therefore, in altered igneous rocks and in metamorphic 
rocks. It may occur in disseminated particles or in rock masses, 
of which it is the chief mineral. It is usually of some shade of 
green in color and has an oily or waxy luster. It is usually mas- 
sive in structure, but may become coarsely fibrous in the variety 
known as chrysotile. 

13. Talc. Talc, H 2 Mg 3 (Si0 3 )4, is similar in its origin and oc- 
currence to serpentine. It is found at times in altered igneous 
rocks, but is more characteristic of metamorphic rocks where 
it may occur in large beds as soapstone. It is characterized 
by its extreme softness (1), greasy feel and also frequently by 
its foliated structure. 

14. Calcite. Calcite, CaC0 3 , is a common and widely dis- 
tributed rock-making mineral found chiefly in the sedimentary 



ACCESSORY ROCK-MAKING MINERALS 343 

and metamorphic rocks. Such rocks as the limestones, marbles 
and chalks are composed almost entirely of the mineral. It is 
to be told by its softness (3), its rhombohedral cleavage and its 
ready effervescence in cold acids. 

15. Dolomite. Dolomite, CaMg(C0 3 )2, is found in the same 
way as calcite but less commonly. The two minerals are usually 
associated with each other and form dolomite marbles and 
dolomitic limestones. Its physical properties are practically 
the same as those of calcite. It will only effervesce, however, 
in hot acids. 

Accessory Rock-making Minerals. 

In addition to the more important and common rock-making 
minerals that have been described in the preceding pages, there 
is a group of minerals which are characteristically found as rock 
constituents but in a minor way. They occur usually only as 
small and scattered crystals in the rock and seldom become one 
of its prime constituents. These minerals are known as acces- 
sory rock-making minerals. The occurrences of the more im- 
portant of them are briefly described below. 

1. Garnet. Garnet is a common accessory mineral, being par- 
ticularly characteristic of the metamorphic rocks. It is found 
frequently in mica-schists, hornblende-schists, gneisses and meta- 
morphosed limestones. More rarely it is found in igneous rocks. 
It occurs in small irregular grains or frequently in fair-sized 
definitely shaped crystals. It is usually red or brown in color. 
For the different varieties of garnets and their distinguishing 
features, see p. 245. 

2. Epidote. Epidote is formed by the alteration of silicates 
containing lime, iron and aluminium. It is also characteristic 
of metamorphosed limestones. It may be associated with 
chlorite, calcite, etc. It is usually found in bladed crystalline 
masses and has a characteristic yellow-green color, is hard and 
has one good cleavage. 

3. Staurolite. Staurolite is found in metamorphic rocks, such 
as the mica-schists and slates. Sometimes it is a constituent of 
gneiss. It is associated with mica, quartz, garnet, cyanite, etc 



344 MANUAL OF MINERALOGY 

It is characterized by a brown color, hardness (7) and prismatic 
orthorhombic crystals which may show cross-shaped twins. 

4. Cyanite. Cyanite, Al 2 Si0 5 , is a rather rare accessory min- 
eral which is found in gneisses and mica-schists. It is associated 
with muscovite, quartz, garnet, staurolite, etc. It is to be dis- 
tinguished by its bladed structure, one good cleavage, blue color 
and by the fact that it is distinctly harder in the direction parallel 
to the length of the crystals than in the direction at right angles 
to this. 

5. Zircon. Zircon, ZrSi0 4 , is a rather rare mineral which 
usually occurs in minute crystals scattered throughout a rock 
mass. It is found in granites, syenites, crystalline limestones, 
chloritic schists, etc. It is to be distinguished by its usually 
brown color, hardness (7.5) and tetragonal crystallization. 

6. Titanite. Titanite or sphene, CaTiSi0 5 , is a compara- 
tively rare mineral found as an accessory constituent in granite, 
syenites, gneiss, mica- and chlorite-schists and crystalline lime- 
stones. It occurs as microscopical crystals in many igneous 
rocks. 

7. Magnetite. Magnetite, Fe 3 ()4, is widespread in its occur- 
rence as a rock constituent. It is found in all kinds of igneous 
rocks, usually in small disseminated grains. It is also charac- 
teristic of the crystalline schists and gneisses. Ordinarily it 
occurs in comparatively small amounts and would be classed as 
an accessory mineral but at times it becomes a prime constituent 
of the rock and may be segregated into almost pure bodies of 
the mineral. It is characterized by its metallic luster, black 
color and streak and its strong magnetic properties. 

8. Ilmenite. Ilmenite or titanic iron, FeTi0 3 , is a common 
accessory mineral occurring in the same way as magnetite and 
frequently found associated with it. It is most commonly found 
in the gabbros and related rocks. It is difficult to tell it frpm 
magnetite by simple inspection. 

9. Hematite. Hematite, Fe 2 3 , is found as an accessory min- 
eral in the feldspathic igneous rocks such as granite. It occurs 
also in the crystalline schists. It is common in the sedimentary 
and metamorphic rocks and at times forms large bodies of almost 



PEGMATITE DIKES AND VEINS 345 

pure mineral. It is the red pigment in many rocks and soils 
and forms the cementing material in many sandstones. It is 
to be recognized by its red streak. 

10. Pyrite. Pyrite, FeS 2 , is found in small disseminated crys- 
tals in all classes of rocks. It is characterized by its pale brass 
color, metallic luster, hardness (6), black streak and frequently 
also by its isometric crystal forms. 

11. Apatite. Apatite, Ca 4 (CaF)(P0 4 ) 3 , is found in crystals of 
considerable size in metamorphosed limestones. It is also com- 
mon in microscopic crystals in all varieties of igneous rocks, and 
in many metamorphic ones. 

In addition to the minerals listed above, the following, more 
rare in their occurrence, are at times found -as accessory rock 
constituents; rutile, iolite, scapolite, andalusite and sillimamte. 

Pegmatite Dikes and Veins. 

In connection with the deep-seated, coarse-grained igneous 
rocks, especially the granites, we frequently find*' mineral de- 
posits which are known as pegmatite dikes or veins. These 
bodies have the general shape and character of an igneous dike 
or a broad mineral vein although in certain respects they differ 
markedly from either of these. They are to be found running 
through the main mass of the igneous rock or filling fissures in 
the other surrounding rocks. They are composed chiefly of 
the same minerals as occur in the igneous rock, but usually in 
very coarse crystallizations. A granite pegmatite is therefore 
made up principally of quartz, feldspar and mica. The quartz 
and feldspar crystals may be several feet in length and the mica 
plates are at times more than a foot across. In addition to the 
coarseness of the crystallization of the minerals, these veins 
possess other peculiar features. The minerals of a pegmatite 
vein, for instance, have not apparently been deposited in the 
definite order that prevailed in the igneous rock mass, but their 
crystals have grown more nearly simultaneously. These veins 
will also at times show a ribboned or banded structure where 
the different minerals occur in distinct layers which lie parallel 



346 MANUAL OF MINERALOGY 

to the walls of the deposit. Their minerals are also commonly 
quite irregularly distributed through the mass, so that at times 
the vein is composed chiefly of feldspar and again becomes nearly 
pure quartz. Frequently, along the central portion of the dike, 
cavities and openings will be observed into which crystals of 
the different minerals project. These characteristics point to 
a somewhat different origin for the pegmatite veins from that 
of the igneous rock with which they are associated. 

No extended and detailed discussion of the theory of the origin 
of pegmatite veins can be given here, but it may be briefly sum- 
marized as follows. Pegmatite veins are formed during the 
last stages of the cooling and solidification of a plutonic igneous 
rock. As an igneous magma cools and slowly solidifies, it shrinks 
somewhat in volume and various cracks and fissures open up 
throughout the mass. The pressure due to the weight of the 
rock forces any still fluid material from the interior of the mass 
up through these cracks and also into any fissures that may exist 
in the surrounding rocks. The filling up of these fissures both 
in the igneous rock itself and in the neighboring rocks consti- 
tutes a pegmatite vein. As a magma cools and its minerals 
crystallize, large amounts of water vapor are frequently set free 
so that the residue of the still fused rock material must contain 
much higher percentages of water than the original magma. 
Consequently it becomes in its character and behavior more 
like a solution than a fused mass. This would account for the 
peculiar features observed in pegmatite veins which differentiate 
them from ordinary igneous deposits. 

The minerals found in pegmatite veins may be divided into 
three general divisions. ' First come those minerals which form 
the main mass of the deposit and which, as stated above, are the 
same as the prominent minerals of the igneous rock with which 
the pegmatite dike is associated. These are commonly quartz, 
a feldspar which is usually either orthoclase or microdine, but 
may be albite, and a mica which may "be either muscovite or 
bidtite. Garnet is also at times in a smaller way a characteristic 
constituent. Second comes a series of rare minerals which are, 
however, quite commonly observed in pegmatite deposits, and 



CONTACT METAMORPHIC MINERALS 347 

which are characterized by the presence in them of fluorine, 
boron or hydroxyl. Their presence in the veins indicates also 
that gases under high pressures have been instrumental in their 
formation. The minerals of this type include beryl, tourmaline, 
apatite &ndfluorite. A third class of minerals found in pegmatite 
veins includes species containing rare elements such as lithium, 
molybdenum, tin, niobium and tantalum, the rare earths, etc. 
These are minerals which are rarer still in their occurrence, but 
when they do occur are usually to be found in pegmatite deposits. 
The most important members of this group are molybdenite, 
lepidolite, spodumene, triphylite, columbite, cassiterite and'monazite. 
Because of the frequent occurrence in pegmatite veins of the 
rare minerals mentioned above, some of which are often found 
finely colored and well crystallized, these deposits are of particu- 
lar interest to students of mineralogy. Pegmatite veins are also 
of commercial importance, for it is from them that most of the 
feldspar and mica used in' the arts are obtained. Many beautiful 
gem stones, such as beryl and tourmaline, are also found in them. 
Pegmatite veins are widely distributed in their occurrence, being 
almost universally found wherever plutonic igneous rocks are 
exposed. Important districts for pegmatite veins in the United 
States include the New England states, the Black Hills in South 
Dakota and Southern California. 

Contact Metamorphic Minerals. 

When an igneous rock magma is intruded into the earth's crust, 
it causes through the attendant heat and pressure a greater or 
less alteration in the surrounding rock. This alteration, or 
rnetamorphism, of the rocks lying next to an igneous intrusion 
usually consists partly in the development of new and charac- 
teristic mineral species. The minerals that are formed under 
these conditions are known as contact metamorphic minerals, 
since they are produced by a metamorphic change and are to 
be found at or near the contact line between the rock in which 
they lie and an igneous rock. Any rock into which an igneous 
mass is intruded will be affected in a greater or less degree, the 



348 MANUAL OF MINERALOGY 

amount and character of the change depending chiefly upon the 
size of the intruded mass and upon the chemical and physical 
character of the surrounding rock. The most striking and im- 
portant contact metamorphic changes take place when the 
igneous rock is intruded into impure limestones. When, a pure 
limestone is affected, it is recrystallized and converted into a 
marble, but without any development of new species. But, on 
the other hand, in the case of an impure limestone the heat and 
pressure caused by the igneous intrusion will serve to develop 
new and characteristic minerals in the rock. An impure lime- 
stone will ordinarily contain, besides the calcium carbonate of the 
rock, varying amounts of quartz, clay, iron oxide, etc. Under 
the influence of the heat and pressure these materials will com- 
bine with the calcium carbonate to form new minerals. For 
instance, the calcite and quartz may react together to form 
wollastonite, CaSi0 3 . If the limestone contains dolomite, the 
reaction of this mineral with quartz ' may produce pyroxene, 
(Ca,Mg)Si0 3 . If clay is present, aluminium will enter into the 
reaction and such minerals as spinel, MgAl 2 4 , and grossularite, 
Ca 3 Al 2 Si 3 Oi2, may result. If any carbonaceous materials are 
present, the effect of the metamorphism may convert them into 
graphite. The common contact metamorphic minerals found 
in limestone are as follows: graphite, spinel, corundum, wollas- 
tonite, tremolite, pyroxene and the lime garnets, grossularite and 
andradite. 

As mentioned in a preceding paragraph, an igneous rock in 
cooling often gives off large amounts of mineralizing vapors. 
These consist largely of water vapor, but often include boron 
and fluorine gases. Under the influence of these vapors, other 
minerals are often formed in the contact zone of a limestone. 
These particular minerals are commonly spoken of as pneumato- 
lytic minerals, since they are formed, partly at least, through the 
agency of mineral gases. They consist chiefly of calcium and 
aluminium silicates which contain hydroxyl, fluorine or boron. 
The most common of the pneumatolytic contact minerals are 
chondrodite, vesuvianite, scapolite, phlogopite, tourmaline and 
fluorite. 



VEINS AND VEIN MINERALS 349 

Veins and Vein Minerals. 

Most of the important mineral deposits, especially those that 
furnish the valuable metals, are found in what are known as 
veins. A brief discussion of veins and vein minerals follows. 

The rocks of the earth's crust have many openings existing 
within them. These openings vary in size from microscopic 
cracks to cavities of considerable extent. The openings may be 
irregular and discontinuous or they may be in the form of fissures 
which are continuous for greater or less distances. Below a 
certain inconsiderable depth, these openings are largely filled by 
water. This underground water, as it is termed, slowly circu- 
lates through the rocks by means of the openings in them. 
Through a large part of its circulation, the water must exist at a 
high temperature and pressure, and under these circumstances 
becomes a strong solvent and active chemical agent. Under- 
ground water in general descends slowly through the smaller 
openings in the rocks, and then gradually finding its way into 
the bigger openings will at last enter some larger fissure and 
changing its course will begin to ascend. On its passage through 
the rocks, it will have dissolved their more soluble 'constituents, 
and when it ultimately enters the larger fissures and commences 
to rise will be carrying considerable amounts of dissolved mineral 
material. The igneous rocks in particular are important factors 
in furnishing underground waters with mineral constituents 
partly because of the <effect of their heat upon its activity, and 
partly because they give off in the form of vapors a large amount 
of mineral material which ultimately gets into the underground 
circulation. When these mineral laden waters commence to rise 
in the larger fissures, they slowly come into regions of lower pres- 
sure and temperature. Under these changing conditions, the 
water will not be able to retain all its mineral constituents in 
solution, and their points of saturation being reached various 
minerals will begin to crystallize out and be deposited on the walls 
of the fissure. In time, if the process continues, the fissure may 
be completely filled from wall to wall with minerals deposited 
in this way. Such a filled fissure is known as a mineral vein. 



350 MANUAL OF MINERALOGY 

Evidence tha.t the minerals of a vein have been deposited from 
solution is given by the following facts. Often a mineral vein 
shows a distinctly banded or ribboned structure. That is, the 
different minerals occur in more or less regular layers which lie 
parallel to the walls. This shows that the various minerals have 
not been deposited simultaneously, but in a definite order of 
succession. Again, frequently it will be observed that the vein 
material has not completely filled the fissure, but that there are 
openings left along its central line. These openings are termed 
vugs and are often lined with crystallized minerals. These con- 
ditions cannot be easily explained except on the assumption that 
the contents of a mineral vein have been deposited from solution. 

The shape and general physical character of a vein depends 
upon the type of fissure its minerals have been deposited in, and 
the type of fissure in turn depends upon the character of the rock 
in which it lies and the kind of force which originally caused its 
formation. In a firm homogeneous rock, like a granite, a fissure 
will be fairly regular and clean cut in character. It is liable to 
be comparatively narrow in respect to its horizontal and vertical 
extent and reasonably straight in its course. On the other hand, 
if a rock that is easily fractured and splintered, like a slate or 
a schist, is subjected to a breaking strain, we are more liable to 
have formed a zone of narrow and interlacing fissures, rather 
than one straight crack. In an easily soluble rock like a lime- 
stone, a fissure will often be extremely irregular in its shape and 
size due more or less to a solution of its walls by the waters that 
have flowed through it. 

A typical vein consists of a mineral deposit which has filled a 
fissure solidly from wall to wall, and shows sharply defined 
boundaries. There are, however, many variations from this 
type. Frequently, as observed above, irregular openings termed 
vugs may occur among the vein minerals. It is from these vugs 
that we obtain many of our crystallized mineral specimens. 
Again, the walls of a vein may not be sharply defined. The min- 
eralizing waters that filled the fissure may have acted upon the 
wall rocks and partially dissolving them may have replaced them 
with the vein minerals. Consequently we may have almost a 



VEINS AND VEIN MINERALS 351 

complete gradation from the unaltered rock to the pure vein 
filling, and with no sharp line of division between. Some de- 
posits have been largely formed by the deposition of vein min- 
erals in the wall rocks. Such deposits are known as replacement 
deposits. They are more liable to be found in the soluble rocks 
like limestones. There is every gradation possible from a true 
vein with sharply defined walls to a replacement deposit with 
indefinite boundaries. 

The mineral contents of a vein depend chiefly upon the chemi- 
cal composition of the waters from which its minerals have 
crystallized. There are many different sorts of veins, and many 
different mineral associations are observed in them. There are, 
however, certain minerals and associations that are more frequent 
in their occurrence to which attention should be drawn. The 
sulphides form perhaps, the most characteristic chemical group 
of minerals to be found in veins. The following minerals are 
very common vein minerals, pyrite, FeS 2 , chalcopyrite, CuFeS 2 , 
galena, PbS, sphalerite, ZnS, chalcocite, Cu 2 S, bornite, Cu 5 FeS 4 , 
marcasite, FeS 2 , arsenopyrite, FeAsS, stibnite, Sb 2 S 3 , tetrahedrite, 
Cu 8 Sb 2 S 7 , etc. In addition to these, which in large part com- 
prise our ore minerals, certain nonmetallic minerals are also 
commonly to be observed. These being of no particular com- 
mercial value are called gangue minerals (gangue is from gang, 
a vein) . They include the following : quartz, Si0 2 , cakite, CaC0 3 , 
dolomite, CaMg(C0 3 ) 2 , siderite, FeC0 3 , barite, BaS0 4 , fluorite, 
CaF 2 , rhodochrosite, MnC0 3 , etc. 

While comparatively few positive statements concerning the 
associations of vein minerals can be made, the following points 
are of interest. 

1. Gold-bearing Quartz Veins. Native gold is most com- 
monly found in quartz veins. It may occur alone in the quartz 
either in nests or in finely disseminated particles, or it may 
occur in connection with certain sulphides in the veins. The 
most common sulphides found in such connections are pyrite, 
chalcopyrite and arsenopyrite. 

2. Gold- and Silver-bearing Copper Veins. The gold and 
silver content of these veins is associated with the various copper 



352 MANUAL OF MINERALOGY 

sulphides. Frequently the amount of the precious metals is 
quite small. The chief minerals 'are chalcopyrite, tetrahedrite, 
bornite, chalcocite, pyrite and various rarer silver minerals. 

3. Silver-bearing Lead Veins. Silver and lead minerals are 
very commonly associated with each other. These veins contain 
such minerals as galena, argentite, tetrahedrite, sphalerite, pyrite, 
calcite, dolomite, rhodochrosite, etc. 

4. Lead-zinc Veins. Lead and zinc minerals often occur to- 
gether particularly in deposits that lie in limestones. The chief 
minerals of such deposits are galena, sphalerite, marcasite, 
chalcopyrite, smithsonite, calamine, cerussite, calcite, dolomite. 

5. Copper-iron Veins. Copper and iron sulphides are quite 
commonly associated with each other, the prominent minerals 
of such veins being pyrite, chalcopyrite, chalcocite, bornite, 
tetrahedrite, enargite, etc. 

Primary and Secondary Vein Minerals. Secondary 
Enrichment. 

In many mineral veins, it is obvious that certain minerals 
belong to the original vein deposit while certain others have been 
formed subsequently. These two classes of minerals are known 
respectively as Primary and Secondary Minerals. The primary 
vein minerals are those which were originally deposited by the 
ascending waters in the vein fissure. The primary metallic vein 
minerals are comparatively few in number, the more important 
being pyrite, chalcopyrite, galena and sphalerite. The second- 
ary vein minerals have been formed from the primary minerals 
by some subsequent chemical reaction. This change is ordi- 
narily brought about through the influence of oxidizing waters 
which coming from the surface of the earth descend through the 
upper portions of the vein. Under these conditions, various new 
minerals are formed, many of them being oxidized compounds. 
As the descending waters lose their oxygen content within a 
comparatively short distance of the earth's surface, the secondary 
minerals are only to be found in the upper part of a vein. To- 
gether with the formation of these secondary minerals, there is 



VEIN MINERALS 353 

frequently a downward migration of the valuable metals in the 
vein. This is brought about by the solution of the minerals in 
the uppermost portion of the vein and a subsequent reprecipi- 
tation a little farther down. As the surface of the earth is 
gradually lowered by erosion, the upper part of a vein is con- 
tinually being worn away. But the metallic content of the 
uppermost part of the vein is always being carried downward 
by the descending oxidizing waters. In this way, the metallic 
content of the upper part of many veins has been notably en- 
riched since there is concentrated in this short space most of the 
original contents of hundreds, perhaps thousands, of feet of the 
vein which have been slowly worn away by the general erosion 
of the country. Consequently the zone of the secondary vein 
minerals is also frequently a zone of secondary enrichment. 
This is an important fact to be borne in mind since, because of 
it, the upper two or three hundred feet of a vein are ordinarily 
the richest portion of a deposit. The ore below that depth grad- 
ually reverts to its original unaltered and unenriched character 
and may frequently prove too low in value to warrant its being 
mined. The prevalent idea that the ore of a vein must increase 
in value with increasing depth is not true in the great majority 
of cases. 

It will be of interest to consider the more important primary 
vein minerals and the secondary minerals that are commonly 
formed from them. 

1. Iron Minerals. The common primary vein iron mineral is 
pyrite, FeS 2 . Marcasite, FeS 2 , while not so common in occur- 
rence is also a primary mineral. When oxidized, these minerals 
yield ordinarily the hydrated oxide limonite, Fe 4 3 [OH] 6 . The 
upper portion of a vein that Was originally rich in pyrite will 
often show a cellular and rusty mass of limonite. This limonite 
deposit near the surface is commonly termed gossan. The yel- 
low rusty character of the outcrop of many veins enables one 
frequently to locate them and to trace them across the country. 

2. Copper Minerals. The one common primary copper min- 
eral is chalcopyrite, CuFeS 2 . At times, some of the other sul- 
phides may be primary in their origin, but this is not generally 



354 MANUAL OF MINERALOGY 

the case. The secondary formation of bornite and chalcocite 
may be explained as follows. The copper sulphide existing in 
the original chalcopyrite is oxidized by the descending waters at 
the surface to copper sulphate which is then dissolved and carried 
farther down the vein. Here it comes in contact with unaltered 
chalcopyrite and a reaction takes place which enriches the sul- 
phide, changing it to bornite, Cu 5 FeS 4 . Later, more copper 
sulphate in solution comes in contact with the bornite and a 
further enrichment takes place with the formation of chalcocite, 
Cu 2 S. In each case, there is an interchange of metals, the iron 
in the original sulphide going into solution as a sulphate thus 
taking the place of the copper which has been precipitated. If 
the copper deposit lies in limestone rocks, we commonly find the 
various carbonates and oxides of copper also formed in the upper 
parts of the deposit. The secondary copper minerals therefore 
include chalcocite , Cu 2 S, bornite, Cu 5 FeS 4 , native copper, Cu, cu- 
prite, Cu 2 0, malachite, (Cu.OH) 2 C0 3 , azurite, Cu(Cu.OH) 2 (CQ 3 ) 2 , 
chrysocolla, CuSi0 3 .2H 2 0, chalcanthite, CuS0 4 .5H 2 0. 

3. Lead Minerals. The one primary lead mineral is galena, 
PbS. The secondary minerals of lead are all oxidized compounds 
and include the following: cerussite, PbC0 3 , anglesite, PbS0 4 , 
pyromorphite, Pb 4 (PbCl)(P0 4 ) 3 , wulfenite, PbMo0 4 . 

4. Zinc Minerals. Sphalerite, ZnS, is the only common prim- 
ary zinc mineral. The chief secondary minerals are smithsonite, 
ZnC0 3 , and calamine, H 2 (Zn 2 0)Si0 4 . 

5. Silver Minerals. Probably most of the sulphide minerals 
of silver are primary in their origin. The following minerals are 
usually secondary, although native silver at times appears pri- 
mary; native silver, Ag, cerargyrite, AgCl, embolite, Ag(Cl,Br), etc. 

Lists of Minerals Arranged According to Systems 
of Crystallization. 

In the following tables the minerals which are described in this 
book are listed according to the system of crystallization to which 
they belong. The order in which they are given is according to 
the chemical classification adopted in this book. 



LISTS OF MINERALS 



355 



ISOMETRIC SYSTEM: NORMAL CLASS. 
Elements. 



1. Diamond, C. 

2. Gold, Au. 

3. Silver, Ag. 



1. Galena, PbS. 

2. Argentite, Ag 2 S. 

3. Pentlandite, (Ni,Fe)S. 



4. Copper, Cu. 

5. Platinum, Pt. 

6. Iron, Fe. 



Sulphides. 

4. Bornite, Cu 5 FeS 4 . 

5. Linnaeite, Co 3 S 4 . 



1. Halite, NaCl. 

2. Sylvite, KC1. 

3. Cerargyrite, AgCl. 



Chlorides, etc. 

4. Embolite, Ag(Cl,Br). 

5. Fluorite, CaF 2 . 



1. Senarmontite, Sb 2 3 . 

2. Cuprite, Cu 2 0. 



Oxides. 

4. Gahnite, ZnAl 2 4 . 

5. Magnetite, Fe 3 O 4 . 



Spinel Group, R"R'" 2 4 



or R"O.R'" 2 3 . 
3. Spinel, MgAl 2 4 . 



6. Franklinite, (Fe,Mn,Zn) 

(Fe, Mn) 2 4 . 

7. Chromite, (Fe,Mg)Cr 2 4 . 



Silicates. 



1. Leucite, KAl(Si0 3 ) 2 . 

2. Analcite,NaAl(Si0 3 ) 2 .H 2 0. 

3. Sodalite, 

Na 4 (AlCl)Al 2 (Si0 4 ) 3 . 

4. Lazurite, 

Na 4 (Al.NaS 3 )Al 2 (Si0 4 ) 3 . 



5. Garnet Group, R 3 R 2 (Si0 4 ) 3 . 
Grossularite, Ca 3 Al 2 (Si0 4 ) 3 . 
Pyrope, M g3 Al 2 (Si0 4 ) 3 . 
Almandite, Fe 3 Al 2 (Si0 4 ) 3 . 
Spessartite, Mn 3 Al 2 (Si0 4 ) 3 . 
Andradite, Ca 3 Fe 2 (Si0 4 ) 3 . 
Uvarovite, 
Ca 3 (Cr,Al) 2 (Si0 4 ) 3 . 



Uranate. 
1. Uraninite, U0 3 and U0 2 with Th, Y, Ce, Pb, He, Ra. 



356 MANUAL OF MINERALOGY 

ISOMETRIC SYSTEM: PYRITOHEDRAL CLASS. 
Sulphides, etc. 



1. Pyrite,FeS 2 . 

2. Smaltite, CoAs 2 . 

3. Chloanthite, NiAs 2 . 



4. Cobaltite, CoAsS. 

5. Gersdorffite, NiAsS. 

6. Sperrylite, PtAs 2 . 



Sulphate. 

1. Kalinite, Alum, KA1(S0 4 ) 2 .12H 2 0. 

ISOMETRIC SYSTEM: TETRAHEDRAL CLASS. 
Sulphides, etc. 



1. Sphalerite, ZnS. 

2. Tiemannite, HgSe. 



3. Alabandite, MnS. 



Sulphantimonites, Sulpharsenites. 



1. Tetrahedrite, 

Cu 8 Sb 2 S 7 = 4Cu 2 S.Sb 2 S 3 . 



2. Tennantite, 



Cu8As 2 S 7 =4Cu 2 S.As 2 S 3 . 



Borate. 

1. Boracite, Mg 7 Cl 2 B 16 30 . 

TETRAGONAL SYSTEM: NORMAL CLASS. 
Sulphide. 

1. Stannite, Cu 2 FeSnS 4 . 

Oxides and Closely Related Silicates and Phosphates. 



1. Octahedrite, Ti0 2 . 

2. Cassiterite,Sn0 2 orSnSn0 4 . 

3. Rutile, Ti0 2 or TiTi0 4 . 



4. Zircon, ZrSi0 4 . 

5. Thorite, ThSi0 4 . 

6. Xenotime, YP0 4 . 



Carbonate. 

1. Phosgenite, (PbCl) 2 C0 3 . 

Silicates. 



1. Vesuvianite, Complex 

Ca,Mg,Na,Al,Fe silicate. 



2. Apophyllite, 



H 7 KCa 4 (Si0 3 ) 8 .4iH,0 



LISTS OF MINERALS 357 

TETRAGONAL SYSTEM: TRI-PYRAMIDAL CLASS. 

Silicate. 
1. Wernerite or Scapolite, CaiAUSiAj with NjuAla 

Tungstate and Molybdate. 

1. Scheelite, CaW0 4 . | 2. Wulfenite, PbMo0 4 . 

TETRAGONAL SYSTEM: SPHENOIDAL CLASS. 

Sulphide. 
1. Chalcopyrite, CuFeS 2 . 

HEXAGONAL SYSTEM: NORMAL CLASS. 
Sulphides. 



1. Molybdenite, MoS 2 . 



3. Pyrrhotite, Fe n S, 



2. Covellite, CuS. 

Silicates. 



1. Beryl, Be 3 Al 2 (Si0 3 )6 with 
some [OH]?. 



2. Nephelite, NaAlSi0 4 . 
(Approx.) 



HEXAGONAL SYSTEM: HEMIMORPHIC CLASS. 
Sulphides, etc. 

1. Greenockite, CdS. | 2. Niccolite, NiAs. 

Oxide. 

1. Zincite, ZnO with MnO. 

HEXAGONAL SYSTEM: TRI-PYRAMIDAL CLASS. 

Phosphates, etc. 

Apatite Group. 



1. Apatite, Ca 4 (CaF)(P0 4 ) 3 . 

2. Pyromorphite, 

Pb 4 (PbCl)(P0 4 )3. 



3. Mimetite, 



Pb 4 (PbCl)(As0 4 ) 3 . 



4. Vanadinite, 



Pb 4 (PbCl)(V0 4 ) 3 . 



358 



MANUAL OF MINERALOGY 



HEXAGONAL SYSTEM: RHOMBOHEDRAL CLASS. 
NORMAL DIVISION. 

Elements. 



4. Bismuth, Bi. 

5. Tellurium, Te. 



1. Graphite, C. 

2. Arsenic, As. 

3. Antimony, Sb. 

Sulphides, Sulphantimonites, Sulpharsenites. 



1. Millerite, NiS. 

2. Pyrargyrite, 



3. Proustite, 

AgsAsSs or 3Ag 2 S.As 2 S 3 . 



Ag 3 SbS 3 or 3Ag 2 S.Sb 2 S 3 . 

Oxides, Hydroxides. 



1. Corundum, A1 2 3 . 

2. Hematite, Fe 2 3 . 



1. Calcite, CaC0 3 . 

2. Dolomite, CaMg(C0 3 ) 2 

(tri-rhombohedral) . 

3. Magnesite, MgC0 3 . 



3. Brucite, Mg(OH) 2 . 



Carbonates. 
Calcite Group. 

4. Siderite, FeC0 3 . 

5. Rhodochrosite, MnC0 3 . 

6. Smithsonite, ZnC0 3 . 



1. Tourmaline, 

R,Al,(B.OH) l Si40 1 , 

(hemimorphic). 



Silicates. 

2. Chabazite, 

(Ca,Na 2 )Al 2 Si 4 12 .6H 2 0?. 



Nitrate. 
1. Soda-niter, NaN0 3 . 

HEXAGONAL SYSTEM: RHOMBOHEDRAL CLASS. 
TRI-RHOMBOHEDRAL DIVISION. 

Titanate. 

1. Ilmenite, FeTi0 3 . 

Silicates. 

1. Willemite, Zn 2 Si0 4 . | 2. Phenacite, Be 2 Si0 4 . 



LISTS OF MINERALS 359 

HEXAGONAL SYSTEM: RHOMBOHEDRAL CLASS. 
TRAPEZOHEDRAL DIVISION. 

Sulphide. 
1. Cinnabar, HgS. 

Oxide. 

1. Quartz, Si0 2 . 

ORTHORHOMBIC SYSTEM. 

Element. 
1. Sulphur, S. 



Sulphides, etc. 



1. Stibnite, Sb 2 S 3 . 

2. Bismuthinite, Bi 2 S 3 . 

3. Chalcocite, Cu 2 S. 



4. Stromeyerite, CuAgS. 

5. Marcasite, FeS 2 . 

6. Arsenopyxite, FeAsS. 



Sulphantimonites, etc. 



1. Bournonite, (Pb,Cu 2 ) 3 Sb 2 S 6 
or 3(Pb,Cu 2 )S.Sb 2 S 3 . 



2. Stephanite, Ag 6 SbS 4 or 
5Ag 2 S.Sb 2 S 3 . 



Sulpharsenate. 

1. Enargite, CuaAsS 4 or 3Cu 2 S.As 2 S 6 . 

Chlorides. 

1. Atacamite, Cu 2 Cl(OH) 3 . | 2. Carnallite, KMgCL.6HA 

Oxides, Hydroxides. 



1. Chrysoberyl, BeAl 2 4 . 

2. Brookite, Ti0 2 . 

3. Diaspore, A1 2 2 (OH) 2 . 

4. Goethite, Fe 2 2 (OH) 2 . 



5. Manganite, Mn 2 2 (OH) 2 . 

6. Pyrolusite, Mn0 2 with 

about2%H 2 0. (Pseudo- 



morphous.) 



Carbonates. 
Aragonite Group. 



1. Aragonite, CaC0 3 . 

2. Strontianite, SrC0 3 . 



3. Witherite, BaCO,. 

4. Cerussite, PbCO,. 



360 



MANUAL OF MINERALOGY 



1. Enstatite, Bronzite, 

Hypersthene, 
MgSi0 3 ,(Mg,Fe)Si0 3 . 

2. Anthophyllite,(Mg,Fe)Si0 3 . 

3. lolite, 



Silicates. 

9. Prehnite, H 2 Ca2Al 2 (Si04) 3 . 

10. Calamine, 

H 2 (Zn 2 0)Si0 4 (hemimor- 
phic). 

11. Staurolite, 



(Mg,Fe)4Al 6 (A1.0H) 2 (Si 2 7 ) 5 . 

4. Chrysolite, (Mg,Fe) 2 Si0 4 . 

5. Danburite, CaB 2 (Si0 4 ) 2 . 

6. Topaz, (Al(F.OH)) 2 Si0 4 . 

7. Andalusite, (A10)AlSi0 4 . 

8. Zoisite, 

Ca(A1.0H)Al 2 (SiO 4 ) 3 



(Mg,Fe)(A1.0H)(A10) 4 (Si0 4 )f. 

12. Sillimanite, Al 2 Si0 6 . 

13. Natrolite, 

Na 2 Al 2 Si 3 10 .2H 2 0. 

14. Thomsonite 

(Na 2 ,Ca)Al 2 (Si0 4 ) 2 .2|H 2 0. 



Niobate, Tantalate. 
1. Columbite-tantalite, (Fe,Mn)(Nb,Ta) 2 6 . 



Phosphates, etc. 



1. Triphylite-lithiophilite, 

Li(Fe,Mn)P0 4 . 

2. Olivenite, Cu(Cu.OH)As0 4 . 



3. Scorodite, FeAs0 4 .2H 2 0. 

4. Wavellite, 

(A1.0H) 3 (P0 4 ) 2 .5H 2 0. 



1. Barite, BaS0 4 . 

2. Celestite, SrS0 4 . 

3. Anglesite, PbS0 4 . 



Nitrate. 
1. Niter, KN0 3 . 

Sulphates. 

4. Anhydrite, CaS0 4 . 

5. Brochantite, Cu 4 (OH) 6 S0 4 . 



MONOCLINIC SYSTEM. 
Sulphides, Tellurides. 



1. Realgar, AsS. 

2. Orpiment, As 2 S a . 



3. Sylvanite, AuAgTe 4 . 

4. Calaverite, AuTe. 



LISTS OF MINERALS 



361 



Sulphantimonite. 

1. Polybasite, Ag 9 SbS 6 . 

Fluoride. 
1. Cryolite, Na 3 AlF 6 . 

Hydroxide. 

1. Gibbsite, A1(OH) 3 . 



Carbonates. 



1. Malachite, (Cu.OH) 2 C0 3 . 

2. Azurite,Cu(Cu.OH) 2 (C0 3 ) 2 . 

3. Aurichalcite, 
2(Zn,Cu)C0 3 .3(Zn,Cu) (OH) 2 . 



4. Gay-Lussite, 



Na 2 C0 3 .CaC0 3 .5H 2 0. 



Silicates. 



1. Orthoclase, KAlSi 3 O a . 

2. Pyroxene Group, R"Si0 3 

(R = Ca,Mg,Fe). 

3. ^Egirite, NaFe(Si0 3 ) 2 . 

4. Jadeite, NaAl(SiO 3 ) 2 . 

5. Spodumene, LiAl(Si0 3 ) 2 . 

6. Wollastonite, CaSi0 3 . 

7. Pectolite, HNaCa 2 (Si0 3 ) 3 . 



8. Amphibole Group, 

R"Si0 3 (R = Ca,Mg,Fe). 

9. Datolite, Ca(B.OH)Si0 4 . 

10. Epidote, 

Ca 2 (A1.0H)Al 2 (SiC>4) 3 . 

11. Allanite, 
Ca 2 (A1.0H) (Al,Fe,Ce,La,Di), 

(Si0 4 ) 3 . 



1. Heulandite, 

H 4 CaAl 2 (Si0 3 ) 6 .3H 2 0. 

2. Harmotome, 

(K 2 ,Ba)Al 2 Si 5 ]4 .5H 2 0. 

3. Stilbite, 

(Na 2 ,Ca)Al 2 Si 6 16 .6H 2 0. 



Hydrated SiUcates. 

4. Laumontite, 

H 4 CaAl 2 Si 4 14 .2H 2 0. 

5. Scolecite, 

CaAl 2 Si 3 0, .3H 2 0. 



362 MANUAL OF MINERALOGY 



Foliated, Micaceous Silicates. 



1. Muscovite, H 2 KAl 3 (Si0 4 ) 3 . 

2. Lepidolite, 
KU(A1.2(OH,F))Al(SiOa)i. 

3. Biotite, 

(H,K) 2 (Mg,Fe) 2 Al 2 (Si0 4 ) 3 .' 

4. Phlogopite, 



6. Margarite, H 2 CaAl 4 Si 2 ]2 . 

7. Clinochlore, Chlorite, 

H 8 Mg 5 Al 2 Si 3 18 . 

8. Serpentine, H 4 Mg 3 Si 2 9 . 

9. Kaolin, H4Al 2 Si 2 9 . 
10. Talc, H 2 Mg 3 (Si0 3 )4. 



H 2 KMg 3 Al(Si0 4 ) 3 ?. I 11. Pyrophyllite, H 2 Al 2 (Si0 3 ) 4 . 

5. Lepidomelane, 

(H,K) 2 Fe 3 (Fe,Al) 4 (Si0 4 ) 5 ?. 

Titanosilicate. 
1. Titanite, CaTiSi0 8 . 



Phosphates. 



1. Monazite, (Ce,La,Di)P0 4 

with ThSi0 4 . 

2. Lazulite, 

Mg(A1.0H) 2 (P0 4 ) 2 . 



3. Vivianite, 



Fe 3 (P0 4 ) 2 .8H 2 0. 



Borates. 



1. Colemanite, 



Ca 2 B 6 On.5H 2 0. 



2. Borax, Na 2 B 4 7 .10H 2 0. 



Sulphates, Chromates. 



1. Glauberite, Na 2 Ca[S0 4 ] 2 . 

2. Crocoite, PbCr0 4 . 



3. Gypsum, CaS0 4 .2H 2 0. 



Tungstates. 
1. Wolframite, FeW0 4 . | 2. Hubnerite, MnW0 4 . 



LISTS OF MINERALS 



363 



TRICLINIC SYSTEM. 
Silicates. 



1. Microcline, KAlSi 3 8 . 

Plagioclase Feldspars. 

2. Albite, NaAlSi 3 8 . 

3. Oligoclase, 3 Albite, 1 An- 

orthite. 

4. Andesine, 1 Albite, 1 An- 

orthite. 



5. Labradorite, 1 Albite, 3 An- 

orthite. 

6. Anorthite, CaAl 2 Si 2 8 . 

7. Rhodonite, MnSi0 3 . 

8. Cyanite, Al 2 Si0 5 . 

9. Axinite, Ca 7 Al 4 B 2 (Si0 4 ) 8 . 



Phosphate. 
1. Amblygonite, Li(AlF)P0 4 . 

Sulphate. 
1. Chalcanthite, CuS0 4 .5H 2 0. 



AMORPHOUS OR MASSIVE MINERALS. 
Oxides, Hydroxides. 



1. Opal, Si0 2 , generally with 3 

to 9% H 2 0. 

2. Turgite, Fe 4 O 5 (OH) 2 . 

3. Limonite, Fe 4 3 (OH) 6 . 



4. Bauxite, A1 2 0(OH) 4 . 

5. Psilomelane, Mn0 2 with 

MnO, BaO, CoO, H 2 0, 
etc. 



Silicates. 



1. Genthite, Garnierite, 
Ni,Mg, silicates. 



2. Chrysocolla, CuSi0 3 .2H 2 0. 



Phosphate. 
1. Turquois, H(A1.20H) 2 P0 4 with H(Cu.OH) 2 P0 4 . 



V. DETERMINATIVE MINERALOGY. 

INTRODUCTION. 

Determinative Tables for minerals are of two kinds: (1) those 
which rely chiefly upon chemical tests, and (2) those which make 
use solely of physical tests. Obviously, since the chemical com- 
position of a mineral is its most fundamental property, those 
tables which emphasize chemical tests are much the more satis- 
factory. On the other hand, the tables which depend wholly 
upon physical tests have distinct limitations beyond which it is 
impossible to use them. These latter tables have, however, the 
important advantages that their tests are simpler, more readily 
and quickly performed, and do not require the equipment of a 
laboratory. For these reasons physical determinative tables 
probably have a wider use, in spite of their limitations, than those 
that involve chemical tests. 

The character and purpose of this book forbid the inclusion of 
elaborate chemical tables and require instead the introduction 
of physical tables of as simple a form as possible. Such tables 
must, however, be used with a thorough understanding of their 
nature and their inherent disadvantages. Many of the physical 
properties of minerals are not entirely fixed in their character. 
Color, for instance, is frequently an extremely variable property. 
Hardness, while more definite, may vary to a slight extent, and 
by a change in the structure of a mineral may appear to vary 
much more widely. Cleavage is a property which may often 
be obscured by the physical condition of the mineral. Conse- 
quently in making a determination of a mineral by means of its 
physical properties alone, it is necessary to have a fairly typical 
specimen and one which is of sufficient size to enable its charac- 
ters to be definitely seen. Often, moreover, it will be impossible 
by the aid of such tables to positively differentiate between two 

364 



DETERMINATIVE MINERALOGY 365 

or three similar species. Frequently, however, in such cases the 
descriptions of these possible minerals given in Section IV will 
enable one to make a definite decision. Moreover, the tables 
that follow, used in connection with the chemical tests given 
under the description of minerals in Section IV, together with 
the more detailed explanations of the various tests to be found in 
Section III, may serve as a substitute for more elaborate chemical 
tables. 

The Determinative Tables given beyond have been made as 
brief and simple as possible. Only the common species or those 
which, while rarer in occurrence, are of economic importance 
have been included. The chances of having a mineral to deter- 
mine that is not included in these tables are small, but it must 
be borne in mind that there is such a possibility. The names 
of the minerals have been printed in three different styles of . 
type, as (see page 373) CHALCOCITE, ARGENTITE and stephanite, in 
order to indicate their relative importance and frequency of 
occurrence. Whenever it was felt that difficulty might be ex- 
perienced in correctly placing a mineral, it has been included in 
the two or more possible divisions. Usually, however, for the 
sake of brevity, the detailed description of such a mineral has 
been printed in full only upon one page. 

On page 369 will be found a General Classification of the 
tables. The proper division in which to look for a mineral is to 
be determined by means of the tests indicated there. The tables 
are divided into two main sections depending upon the luster of 
the minerals in them. The first division includes those minerals 
which have a Metallic or Submetallic Luster. By that is meant 
those minerals which on their thinnest edges remain opaque 
and which consequently will give black or dark-colored " streaks" 
when they are rubbed across a piece of unglazed porcelain, the 
so-called streak plate. Nonmetallic minerals are those which 
are transparent upon their thinnest edges, and which therefore 
give either a colorless or a light-colored streak. It is to be 
noted that the color of the streak cannot always be foretold 
from the color of the mineral itself. Frequently a dark-colored 
mineral will be found to give a light-colored streak. 



366 MANUAL OF MINERALOGY 

The tables are next subdivided according to hardness. The 
tests used in the General Classification are: (1) minerals that are 
soft enough to leave a mark when rubbed across a piece of paper; 
(2) minerals that can be scratched by the finger nail; (3) those 
that can be cut by a cent; (4) minerals that are softer than the 
steel of the blade of an ordinary pocket knife; (5) and (6) min- 
erals that are harder than a knife but can or cannot be scratched 
by quartz. In applying the tests for hardness, certain precau- 
tions should be observed. Before deciding upon the relative 
hardness of a mineral, it is well to try the test if possible in two 
ways. For instance, if a mineral is apparently scratched by the 
edge of a cent make sure on the other hand that the cent cannot 
be scratched by the mineral. Further, the cent and the knife 
blade used in making the tests should be bright and clean, other- 
wise the rubbing off of a layer of dirt or tarnish might be mis- 
taken for a scratch. In the tables themselves, the hardness 
of the minerals is given in terms of the Scale of Hardness, see 
page 61. The possession of specimens of the minerals of this 
scale, so that the hardness of a mineral could be closely deter- 
mined, would frequently be of great assistance in the use of the 
tables. Lastly, it is to be remembered that the physical con- 
dition of a mineral may apparently change its hardness. For 
instance, minerals that occur at times in pulverulent or fibrous 
forms will under these conditions appear to be much softer than 
when in their more usual form. Also the chemical alteration 
of a mineral will commonly change its hardness. 

The minerals with nonmetallic luster are, in general, further 
subdivided according to whether they show a prominent cleavage 
or not. This-will frequently be a difficult decision to make. It 
will require some practice and experience before one can always 
make the determination rapidly and accurately. Note that the 
minerals are divided according to whether they show a prominent 
cleavage or not. Minerals in which the cleavage is imperfect 
or ordinarily obscure are included with those that have no cleav- 
age. It will always be best, if it is possible, to actually try to 
produce a cleavage upon the specimen rather than to judge from 
its appearance alone. If a mineral shows a cleavage, the num- 



DETERMINATIVE MINERALOGY 367 

her of the cleavage planes, their relations to each other and to 
any crystal forms present, etc., are to be noted. As far as pos- 
sible, the minerals in which the cleavage may become obscure, 
because of certain conditions of structure, have been included 
in both divisions. 

The minerals which fall in any one of the different divisions 
of the tables have been arranged according to various methods. 
In some cases, those that possess similar cleavages have been 
grouped together; frequently color determines their order, etc. 
The column farthest to the left will indicate the method of 
arrangement used in each section. Most of the different prop- 
erties listed and the more general facts included under the 
headings, Crystallization and Structure and Remarks, need no 
especial explanation. A few words, however, may be said con- 
cerning the column headed Specific Gravity. For a discussion 
of specific gravity and the methods for its accurate determina- 
tion, see page 62. If the specimen to be determined is of suffi- 
cient size and is pure, its approximate specific gravity can be 
determined by simply weighing it in the hand. In order to do 
this, however, will require some experience. Below is given a 
list of common minerals which show a wide range of specific 
gravity. By experimenting with specimens of these, one can 
become quite expert in the approximate determination of the 
specific gravity of any mineral. 

Halite, 2.14 Limonite, 3.80 Cerussite, 6.51 

Gypsum, 2.32 Corundum, 4.03 Cassiterite, 6.95 

Orthoclase, 2.56 Chalcopyrite, 4.20 Galena, 7.50 

Calcite, 2.72 Barite, 4.48 Cinnabar, 8.10 

Fluorite, 3.18 Pyrite, 5.03 Copper, 8.84 

Topaz, 3.53 Chalcocite, 5.75 Silver, 10.60 

When the subdivisions of the tables are studied, the following 
interesting and important facts are to be noted. The majority 
of the minerals with metallic luster are sulphides. Most of them 
are softer than a knife. The only sulphides that are harder.than 
a knife are Pyrite, Marcasite and Arsenopyrite. The greater 
part of minerals with metallic or submetallic luster that are 



368 MANUAL OF MINERALOGY 

harder than a knife are oxygen compounds of iron. Among the 
minerals with nonmetallic luster, it is to be noted that those 
which are harder than a knife are, with very few exceptions, 
either silicates or oxides. Comparatively few silicates are to be 
found among the minerals of nonmetallic luster which are softer 
than a knife. It is to be further noted that the majority of such 
silicates contain water in some form. On the other hand, 
the greater part of the carbonates, sulphates, phosphates, etc., 
are to be found in these sections. 



GENERAL CLASSIFICATION OF THE 
TABLES. 

A. METALLIC OR SUBMETALLIC LUSTER. 
I. Very Soft. Will Readily Leave a Mark on Paper, 

p. 370. 
II. Can be Scratched by a Knife, but Will not Readily 

Leave a Mark on Paper, p. 372. 
III. Cannot be Scratched by a Knife, p. 382. 

B. NONMETALLIC LUSTER. 

I. Minerals which Give a Definitely Colored Streak, 

p. 386. 
U. Minerals which Give a Colorless Streak. 

1. Can be scratched by the finger nail, p. 392. 

2. Cannot be scratched by the finger nail, but can 

be scratched by a cent. 
a. Show a prominent cleavage, p. 396. 
6. Do not show a prominent cleavage. 

1. A small splinter is fusible in the 

candle flame. 

a. Readily soluble in water; yield a 

taste, p. 398. 

b. Insoluble in water, p. 400. 

2. Infusible in the candle flame, p. 400. 

3. Cannot be scratched by a cent, but can be 

scratched by a knife. 

a. Show a prominent cleavage, p. 402. 

b. Do not show a prominent cleavage, p. 410. 

4. Cannot be scratched by a knife, but can be 

scratched by quartz. 
a. Show a prominent cleavage, p. 414. 
6. Do not show a prominent cleavage, p. 420. 

5. Cannot be scratched by quartz. 

a. Show a prominent cleavage, p. 426. 

b. Do not show a prominent cleavage, p. 428. 

369 



METALLIC OR 
I. Very soft. Will readily 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Black. 


Iron-black. 


2-2.5. Marks 
paper easily. 


F. Splintery. 


4.7 


Steel-gray to 
iron-black. 


1-1.5. Marks 
paper easily. 


One perfect C. 


2.2 


Gray-black. 


Blue-black or 
lead-gray. 


1-1.5. Marks 
paper easily. 


One perfect C. 


4.7 


2. Marks paper 
easily. 


One perfect C. 


4.5 


2.5. Marks paper 
with difficulty. 


Perfect cubic C. 


7.6 


Bright red. 


Red to vermil- 
ion. 


Marks paper with 
difficulty. 




8.1 


Red-brown. 


Red-brown. 


Vlarks paper eas- 

ly. 




5.2 


Yellow-brown 


Yellow- 
brown. 


Marks paper eas- 

ly. 




3.6-4.0 



See also covellite, p. 377, and argentite, p. 373, 



370 



SUBMETALLIC LUSTER, 
leave a mark on paper. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Usually radiating fibrous or 
splintery. 


Distinguished from other minerals 
of this group by its structure. 


PYROLUSITE. 

Mn0 2 . 


Rhombohedral. Micaceous. 


May be in hexagonal-shaped leaves. 
Told irom molybdenite by the 
brown tinge to its black color. 
Greasy feel. 


GRAPHITE. 
C. 


Hexagonal. Micaceous. 


May be in hexagonal-shaped leaves. 
Told from graphite by the blue 
tinge to its black color and its 
higher specific gravity. Greasy feel. 


Molybdenite. 
MoS 2 . 


Orthorhombic. B 1 a d e d 
structure or in slender radi- 
ating crystals. 


Characterized by its long and 
bright cleavage faces. Fuses in the 
candle flame. 


STIBNITE. 

Sb 2 S 3 . 


In cubic crystals or cleavage 

masses. 


See p. 375. 


GALENA. 
PbS. 


Earthy. 


The earthy form of cinnabar is not 
common. 


CINNABAR. 

HgS. 


Earthy. 


The earthy form of hematite is 
often known as red ochre or paint 
ore. 


HEMATITE. 
Fe 2 3 . 


Earthy. 


The earthy form of limonite is 
often known as yellow ochre. 


LIMONITE. 

Fe 4 O 3 (OH) 8 . 



which may leave a slight mark on paper. 



371 



METALLIC OR 
II. Can be scratched by a knife, 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Soft black. 


Iron-black. 


2-2.5. Very soft. 
Will mark paper. 


F. Splintery. 


4.7 


Black, with 
sometimes a 
brown tinge. 


Iron-black. 


5-6. U. harder 
than knife. 


F. Irregular. 


4.3 


Gray-black. 


Steel-gray on fresh 
surface, tarnishing 
to dead black on 
exposura. 


2.5-3. 


F. Irregular. 


5.7 


Black, with 
sometimes a 
brown tinge. 


Steel-gray, some- 
times tarnishes to 
dead black on ex- 
posure. 


3-4. 


F. Irregular. 


4.7-5.0 


Black. 


Gray-black. 


3. 


C. Perfect prismatic. 
F. Uneven. 


4.4 


2-2.5. 


F. Uneven. 


7.3 


2-2.5. 


F. Uneven. 


6.2 


2-3. 


F. Uneven. 


6-6.2 


2.5-3. 


F. Uneven. 


6.2-6 3 


2-3. 


F. Fibrous 


5.5-6 



372 



SUBMETALLIC LUSTER. 

but will not readily leave a mark on paper. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Usually radiating fibrous or 
splintery. 


Usually to be told by its struc- 
ture and soft black streak. 


PYROLUSITE. 

Mn0 2 . 




See p. 385. 


Psilomelane. 
MnO 2 with MnO, etc. 


Orthorhombie. Compact 
massive. 


Often associated with other cop- 
per ores, such as bornite, chalco- 
pyrite, malachite, etc. 


CHALCOCITE 

(Copper Glance). 


Isometric, tetrahedral. 
Massive or in tetrahedral 
crystals. 


Often associated with chalcopy- 
rite, pyrite, silver ores, etc. 


TETRAHEDRITE 

(Gray Copper). 
4Cu 2 S.Sb 2 S 3 . 


Orthorhombie. In bladed 
masses, showing long cleav- 
age faces. More rarely in 
stout prismatic crystals. 


A rare mineral, found usually 
with other copper minerals. 


Enargite. 
SCuzS.ASjSs. 


Isometric. Usually irregu- 
lar massive or earthy. At 
times in small isometric 
crystals, commonly cubes. 


Distinguished by being easily 
sectile, i.e., it can be cut with a 
knife, like lead. Bright steel- 
;ray on fresh surface but tarnish- 
ing to a dull gray-black on expos- 
ure. 


Argentite. 
Ag 2 S. 


Orthorhombie. In small ir- 
regular masses, often earthy. 
At times in stout six-sided 
prismatic crystals. 


A rare mineral. Bright 
G steel-gray on a fresh sur- 
tg face but tarnishing to a 
c dull gray-black on expos- 

1 ure ' 


Stephanite. 
5A g2 S.Sb 2 S,. 


Monoclinic. Often in thin 
six-aided crystal plates with 
triangular markings on top. 
Also massive and earthy. 


A rare mineral. 

a 
>> 

1 


Polybasite. 
9(Ag,Cu) 2 S.Sb,S,. 


Irregular massive. 


| A rare mineral. To be 
positively told only by 
~ chemical tests. 


Stromeyrite. 
CuAgS. 


In fibrous, feather-like 
masses. 


cr 
$ Characterized usually by 
J| its fibrous structure. 


Jamesonite 
(Feather ore). 
2PbS.Sb 2 S,. 

1 



373 



METALLIC OR 
II. Can be scratched by a knife, but will 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Black. 


Gray-black. 


2.5-3. 


F. Uneven. 


5.8 


4. 


F. Uneven. 


4.4 


Gray-black. 


Blue-black or 
lead-gray. 


Will leave a mark 
on paper. 


One perfect cleavage. 


4.5 


6.4 


2.5. Marks paper 
with difficulty. 


Perfect cubic cleavage. 


7.6 


Tin-white, tar- 
nishing to dark 
gray. 


3.5. 


One good cleavage but 
seldom seen. 


5.7 


Tin-vvhite. 


3-3.5. 


One good cleavage seen 
in the more coarsely 
crystallized type. 


6.6 


2-2.5. 


Perfect prismatic 
cleavage in 3 direc- 
tions. 


6.1-6.3 



374 



SUBMETALLIC LUSTER. 

not readily leave a mark on paper. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Orthorhombic. In stout six- 
sided prismatic crystals. 
Often twinned with reen- 
trant angles, giving a " cog- 
wheel " effect. Also mas- 
sive granular. 


Commonly'called " cog-wheel ore" 
because of the characteristic group- 
ing of its crystals. Easily fusible 
in the candle flame. Not to be 
positively identified when massive 
except by chemical tests. 


Bournonite. 
2PbS.Cu 2 S.Sb,S,. 


Tetragonal. Irregular mas- 
sive. 


Decrepitates violently in the can- 
dle flame. Sometimes shows a 
bluish tarnish. 


Stannite 
(Tin Pyrites). 
Cu 2 S.FeS.SnS 2 . 


Orthorhombic. Bladed 
structure or in slender radi- 
ating crystals. 


Characterized by its long bright 
cleavage faces. Fuses easily in the 
candle flame. 


STIBNITE. 

Sb 2 S 3 . 


Orthorhombic. In long 
slender crystals, often radi- 
ating. Frequently bladed. 


Fuses in candle flame. A rare 
mineral. To be positively told 
from stibnite only by a test for bis- 
muth. 


Bismuthinite. 
Bi 2 S 3 . 


Isometric. Crystallized or 
(cleavable) granular. 


If a small fragment is held in a 
candle flame it does not fuse but is 
slowly reduced and small globules 
of metallic lead collect upon the 
surfaces. 


GALENA. 

PbS. 


Rhombohedral. Usually 
fine granular, often with bot- 
ryoidal structure. 


Tarnishes more readily than the 
other similar minerals. Heated in 
the candle flame does not fuse but 
gives off a white smoke and yields 
a strong garlic odor. A rare min- 
eral. 


Arsenic. 

As. 


Rhombohedral. Usually 
fine granular. 


Usually bright in luster. Heated 
in candle flame does not fuse read- 
ily, gives off a white smoke but no 
odor. A rare mineral. 


Antimony. 
Sb. 


Rhombohedral. In cleav- 
able masses. 


Characterized by bright luster and 
prominent cleavage. Heated in 
candle flame fuses very easily. A 
rare mineral, often associated with 
the gold and silver tellurides. See 
under sylvanite, below. 


Tellurium. 
Te. 



375 



METALLIC OR 
II. Can be scratched by a knife, but will 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Gray-black. 


Tin-white. 


1.5-2. 


One perfect C. 


8-8.7 


2.5. 


F. Uneven. 


9.3 


Black. 


Usually pale cop- 
per-red. See p. 382. 


5-5.5. 


F. Uneven. 


7.5 


Brownish bronze 
but when exposed 
to the air rapidly 
takes on a purple 
tarnish. 


3. 


F. Uneven. 


4.9-5 4 


Brownish bronze. 


4. 


F. Uneven. 


4.6 


3.5-4. 


C. Octahedral. 


4.9 


Brass-yellow. 


3.5. 


F. Uneven. 


4.2 


Brass-yellow, al- 
most greenish 
when in very 
slender crystals. 


3-3.5. 


F. Uneven. 
C. Rhombohedral 
but seldom seen. 


5.6 


Indigo-blue, may 
tarnish to blue- 
black. 


1.5-2. 


Perfect basal C. 


4.6 



See also wolframite, p. 379, which may give nearly a black streak. 

376 



SUBMETALLIC LUSTER. 

not readily leave a mark on paper. (Continued.) 



Crystallization and. 
Structure. 


Remarks. 


Name and 
Composition. 


Monoclinic. In thin lath- 
shaped crystals. Often as 
thin coatings on surfaces of 
rock arranged like ancient 
forms of writing. 


Fuses very easily in candle flame. 
A rare mineral. Often to be posi- 
tively told from tellurium and the 
other similar tellurides only by 
chemical tests (see p. 157) . 


Sylvanite. 
AuAgTe 4 . 


Monoclinic. In irregular 
small masses or in thin, 
deeply striated lath-shaped 
crystals. 


Easily fusible in candle flarr.e. 
Takes on at times a faint yellow 
color. A very rare mineral. Told 
from tellurium and sylvanite by its 
lack of cleavage, but for positive 
identification may need chemical 
tests. 


Calaverite. 
AuTe 2 . 


Hexagonal, hemimorphic. 
Massive. 


See p. 383. 


Niccolite. 
NiAs. 


Isometric. Massive. 


Recognized usually by its promi- 
nent purple tarnish. Associated 
with other copper ores, chiefly 
chalcocite and chalcopyrite. 


BORNITE. 

Cu 5 FeS 4 . 


Hexagonal. Massive. 


Recognized usually by its charac- 
teristic color. Small fragments 
often magnetic. Often associated 
with chalcopyrite and pyrite. 
Frequently carries nickel. 


PYRRHOTITE. 
Feats*. 


Isometric.' Granular. 


A rare mineral resembling closely 
pyrrhotite, with which it is inti- 
mately associated. Distinguished 
from pyrrhotite by its cleavage. 


Pentlandite. 

(Ni.Fe)S. 


Tetragonal, sphenoidal. Us- 
ually massive. Sometimes 
in small tetrahedral-shaped 
crystals. 


Usually recognized by its color and 
softness. Associated with pyrite, 
chalcocite, bornite, etc. 


CHALCOPYRITE 

(Copper Pyrites). 


Rhombohedral. In radiat- 
ing groups of hair like crys- 
tals. 


Commonly called capillary pyrites 


Millerite. 

NiS. 


Hexagonal. In platy masses 
or in thin six-sided platy 
crystals. 


A rare mineral. Characterized 
chiefly by its color. Tarnishes 
to blue-black on exposure. Mois- 
tened with a drop of water turns 
purple. 


Covellite. 
CuS. 



377 



METALLIC OR 
II. Can be scratched by a knife, but will 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 




Steel-gray to iron- 
black. 


4. 


One good C. 
F. Splintery. 


4.3 


Dark-brown 
to black. 






F. Uneven. 


4.3 




Iron-black to 
brownish black. 


5.5. Scratched by 
knife with diffi- 














culty if at all. 


One good C. 


7.2-7.5 








F. Uneven. 





See also psilomelane and tetrahedrite, p. 373, which may give brown-black streaks. 













Light to dark 
brown. 


Dark brown to 
coal-black. 


3.5-4. 


Perfect C. in six direc- 
tions (dodecahedral). 


4.1 


Red-brown. 
Indian-red. 


Dark brown to 
steel-gray to 
black. 


5.5-6.5. Softer in 
some earthy vari- 
eties but usually 
harder than a 
knife. 


F. Uneven or fibrous. 


5.2 


F. Splintery. 


4.1 


Deep red to black. 


2.5. 


C. Rhombohedral. 
F. Conchoidal. 


5.8 


Red-brown to 
deep red. Ruby- 
red in transparent 
variety. 


3.5-4. 


F. Uneven. 


6.0 



378 



SUBMETALLIC LUSTER. 

not readily leave a mark on paper. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Orthorhombic. In radiating 
fibrous or crystalline masses. 
Sometimes in distinct pris- 
matic crystals, often grouped 
in bundles. 


Often closely resembles pyrolusite, 
with which it is frequently associ- 
ated, but is to be distinguished 
rom the latter by its greater hard- 
ness and dark-brown streak. 


MANGANITE. 
MnO(OH) = 
MnAi.HjO. 


Usually in granular masses. 


See p. 385. 


CHROMITE 
[Chromic Iron). 

FeO.CrjOs. 


Monoclinic. In bladed 
masses. Granular to mas- 
sive. 


Characterized by bladed structure 
showing good cleavage parallel to 
ength of crvstal. As the amount 
of manganese contained in the min- 
eral increases it becomes browner 
in color and streak and graduates 
toward hubnerite, MnWO 4 . 


Wolframite. 
(Fe. Mn)WO 4 . 


Isometric, tetrahedral. 
Usually cleavable granular. 


VIost sphalerite is nonmetallic and 
strongly resinousin its luster. With 
increase in the amount of iron pres- 
jnt it becomes dark brown to 
black. The darker varieties can 
often be told by scratching a cleav- 
age surface with a knife and noting 
the reddish mark left. The color 
of the streak is always much 
lighter than the color of the speci- 
men. 


SPHALERITE 

(Zinc Blende, Black 
Jack, etc.). 

(Zn.Fe)S. 




See p. 385. 


HEMATITE. 
FezOa. 




See p. 385. 


Turgite. 
Fe 4 0<(OH) 2 = 
2FeA.H 2 0. 


Rhombohedral. Irregular 
massive. 


The dark Ruby Silver, showing 
dark ruby color in thin splinters. 
See p. 387. 


Pyrargyrite. 
3A g2 S.Sb 2 S 3 . 


Isometric. Massive or rarely 
in isometric crystals, cubes 
or octahedrons. Sometimes 
in very slender crystals 
(chalcotrichite or plush cop- 
per). 


Characterized by its submetallic 
luster and red streak. Associated 
with other copper minerals, espe- 
cially malachite and native copper. 


CUPRITE. 
Cu 2 O. 



379 



METALLIC OR 
II. Can be scratched by a knife, but will 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Yellow- 
brown. Yel- 
low ocher. 


Dark brown to 
black. 


5-5.5. Softer in 
some varieties but 
usually harder 
than a knife. 


F. Splintery. 


3.6-4.0 


One good C. 
F. Splintery. 


4.3 


Dark red. 


Dark red to ver- 
milion. 


2-2.5. Some 
earthy varieties 
are soft enough to 
mark paper. 


F. Uneven. 
Prismatic C., seldom 
seen. 


8.1 


Copper-red, 

shiny. 


Copper-red, 
black tarnish. 


2.5-3. 


F. Hackly. 


8.8 


Silver-white, 
shiny. 


Silver-white, gray 
to black tarnish. 


2.5-3. 


F. Hackly. 


10.5 


Gray, shiny. 


Whitish, or steel- 
gray. 


4-4.5. 


F. Hackly. 


14-19 


Silver-white, 
shiny. 


Silver-white with 
a reddish tone. 


2-2.5. 


Perfect basal and 
rhombohedral C. 


9.8 


Gold-yellow, 
shiny. 


Gold-yellow. 


2.5-3. 


F. Hackly. 


19 


Olive-green. 


Iron-black with a 
brown tarnish. 


3.5-4. 


C. Cubical. 


3.9 



380 



SUBMETALLIC LUSTER. 

not readily leave a mark on paper, (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 




See p. 387. 


LIMONITE 

(Bog Iron Ore). 
Fe 4 3 (OH) 6 = 
2Fe 2 3 .3H 2 0. 




See p. 387. 


Goethite. 
FeO(OH) = 
Fe 2 3 .H 2 O. 


Rhombohedral. Usually 
fine granular or earthy. 


Usually impure and of a dark-red or 
brown color. When pure is trans- 
lucent to transparent and of a bright 
red color. Very heavy. 


CINNABAR. 
HgS. 


Isometric. Usually in irreg- 
ular grains. May be in 
branching crystal groups or 
in rude isometric crystals. 


A metal. Malleable. Very heavy. 


COPPER. 
Cu. 


A metal. Malleable. Very heavy. 


SILVER. 
Ag. 


Isometric. Irregular grains 
or nuggets. 


A metal. Malleable. Very heavy. 
Unusually hard for a metal. Very 
rare. 


Platinum. 
Pt. 


Rhombohedral. In cleav- 
able granular masses. 


A metal. Sectile. When ham- 
mered out is at first malleable but 
soon breaks up into small pieces. 
Easily fusible in the candle flame. 
A rare mineral. 


Bismuth. 
Bi. 


Isometric. In irregular 
grains, nuggets, leaves, etc. 


A metal. Malleable. Very heavy. 


GOLD. 
Au. 


Isometric, tetrahedral. In 
granular cleavable masses. 


A rare mineral. Characterized by 
its brown tarnish, olive- green 
streak and cubical cleavage. 


Alabandite. 
MnS. 



381 



METALLIC OR 
III. Cannot be scratched 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 

6-6.2 


Black. 


Silver or tin white. 


5.5-6. 


F. Uneven. 


5.5-6. 


F. Uneven. 


5.5-6 


p.5. 


F. Uneven. 


5.5 


5.5. 


F. Uneven. 


4.9 


Usually pale cop- 
per-red. Some- 
times almost sil- 
ver-white with 
pink tone. 


5-5.5. 


F. Uneven. 


7.5 


Pale brass-yellow. 


6-6.5 


F. Uneven. 


5.0. 


Pale yellow to al- 
most white. 
Yellowish tarnish. 


6-6.5 


F. Uneven. 


4.9 


Black. 


6. 


F. Uneven. At times 
shows octahedral part- 
ing. 


5.18 



382 



SUBMETALLIC LUSTER, 
by a knife. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Orthorhombic. Massive 
granular. Sometimes in 
crystals. 


Vhen crystallized is commonly 
ound in diamond-shaped tabular 
crystals with striations running 
>arallel to the shorter diagonal of 
he diamond. Sometimes in fan- 
shaped twins. 


ARSENOPYRITE 

Mispickel). 
FeAsS. 


Isometric, pyritohedral. 
Massive. 


Rare minerals found with other co- 
)alt and nickel species. 


Smaltite- 
Uhloanthite. 
CoAs2-NiAs2. 


Isometric, pyritohedral. 
Usually massive. 


Flare minerals found with other co- 
salt and nickel species. Cobaltite 
shows a faint reddish tone to its 
silver color. 


Cobaltite- 
Gersdorffite. 
CoAsS-NiAsS. 


Isometric. In fine granular 
masses or in small octahe- 
dral crystals. 


A rare mineral. 


Linnseite. 

(Co,Ni) 3 S 4 . 


Hexagonal, hemimorphic. 
Massive. 


Recognized chiefly by its color and 
streak. A rare mineral found with 
other nickel and cobalt ores. 


Niccolite. 
NiAs. 


Isometric, pyritohedral 
Massive granular. Often in 
striated cubes, octahedrons 
pyritohedrons, etc. 


Most common sulphide. Will 
strike fire with steel. 


PYRITE 

(Iron Pyrites). 
FeS 2 . 


Orthorhombic. Often in ra- 
diating fibrous masses. In 
crystal groups. 


Found in nodules and stalactites 
Not nearly so common as pyrite 
Usually distinguished from pyrite 
by its lighter color and character- 
istic crystals, but it may require a 
chemical test to positively differ- 
entiate them (seep. 156). 


MARCASITE 
(White Iron Py- 
rites). 
FeSj. 


Isometric. Usually coarse to 
fine granular. At times in 
crystals, usually octahe 
drons. 


Strongly magnetic. No other min 
eral exhibits this property as 
strongly. 


MAGNETITE. 
Fe 3 0<. 



383 



METALLIC OR 
III. Cannot be scratched 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Very dark 
brown to 
black. 


Black. 


5.5. 


F. Uneven. 


9-9.7 


5.5-6 


F. Uneven. 


4.3 


Black. 


5-6. 


F. Uneven. 


4.3 


6. 


F. Uneven. 


5.3-7.0 


Dark brown. 


Iron-black to 
brownish black. 


5.5-6. 


One good C. 
F. Uneven. 


7.2-7.5 


F. Uneven. 


4.6 


F. Uneven. 


5.1 


Red-brown. 
Indian-red. 


Dark brown to 
steel-gray to 
black 


5.5-6.5. 
Softer in some 
earthy varieties. 


F. Uneven or fibrous. 


5.2 


F. Splintery. 


4.1 



384 



SUBMETALLIC LUSTER, 
by a knife. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Isometric. Massive eranu- 


Characterized bv its black color 


Uraninite 



Rarely in octahedral crys- 
tals. 


mineral in which the rare elements 
helium and radium have been 
found. 


^irncn oienae;. 
Uncertain composi- 
tion. Chiefly oxidea 
of uranium. 


Rhombohedral. In grains as 
sand; massive granular; platy 
crystals. 


Sometimes slightly magnetic. 
Often associated with magnetite. 


ILMENITE 
(Titanic Iron). 
FeTi0 3 with FejOs. 
Sometimes much 
Mg. 


Compact massive, some- 
times stalactitic or botryoi- 
dal. 


Dull-black luster. Often associ- 
ated with other manganese ores 
rom which it is told by its greater 
lardness. 


Psilomelane. 
Uncertain composi- 
tion. MnO 2 with 
MnO, H 2 0, BaO, 
K 2 O, etc. 


Orthorhombic. Granular or 
in stout prismatic crystals. 


Black shiny luster on fresh surface. 
Sometimes takes on a slight bluish 
tarnish. 


3olumbite- 
Tantalite. 
(Fe,Mn)Nb 2 O e 
with (Fe,Mn)Ta 2 O. 


In bladed masses. 


See p. 379. 


Wolframite. 
(Fe,Mn)WO 4 . 


Isometric. Usually in granu- 
lar masses. Rarely in small 
octahedral crystals. 


Characterized often by a pitchy 
luster and accompanied frequently 
by traces of a yellow oxidation 
product. 


CHROMITE. 
(Chromic Iron). 
FeCr 2 4 . 


Isometric. Granular or in 
octahedral crystals. 


Occurs at Franklin Furnace, N. J., 
usually in intimate association with 
zincite (red) and willemite (green). 


FRANKLINITE. 
(Fe.Zn.Mn)O 
(Fe,Mn) 2 O 8 . 


Rhombohedral. Radiating, 
reniform, crystallized, mica- 
ceous. 


Recognized usually by its red- 
brown streak. When in fibrous 
mammillary forms cannot be posi- 
tively told from the rare mineral 
turgite except by proving the ab- 
sence of water in its composition by 
heating in a closed tube. 


HEMATITE. 

FejOs. 


Radiating reniform and sta- 
lactitic. 


A rare mineral usually associated 
with limonite. For positive iden- 
tification see above. 


Turgite 
(Hydro-hematite). 
Fe 4 O 6 (OH) 2 = 
2Fe2O3.H 2 O. 



385 



METALLIC OR 
III. Cannot be scratched 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 








F. Splintery. 


3.6-4.0 


Va11<->_ 










brown. 


black. 


Softer in some 
earthy varieties. 


One good C. 
F. Splintery. 


4.3 



NONMETALLIC 
I. Give a definitely 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Dark red. 


Dark red to ver- 
million. 


2-2.5. 


F. Uneven. 


8.1 


Red-brown. 
Ruby-red when 
transparent. 


3.5-4. 


F. Uneven. 


6.0 


Red-brown. 
Indian-red. 


Dark brown to 
steel-gray, to 
black. 


5.5-6.5. 


F. Splintery. 


5.2 


4.1 


Deep red to black. 


2.5. 


F. Conchoidal. 


5.8 


Bright red. 


Ruby-red. 


2-2.5. 


F. Conchoidal. 


5.5 



386 



SUBMETALLIC LUSTER. 

by a knife. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Radiating fibrous in mam- 
millary or stalactitic forms. 


Characterized by its streak and 
structure. Not always to be posi- 
tively told from the rarer mineral 
goethite, except by an estimation of 
the water present. Limonite con- 
tains 15%, goethite 10% of water. 


LIMONITE 

(Bog Iron Ore). 
Fe 4 O 3 (OH)8= 
2Fe 2 O 3 .3H 2 O. 


Orthorhombic. Radiating 
fibrous in mammillary or 
stalactitic forms. Some- 
times in groups of slender 
radiating crystals. More 
rarely in distinct prismatic 
crystals. 


Told definitely from limonite if it 
shows cleavage or any crystal struc- 
ture. Otherwise to be distin- 
guished only as described above. 


Goethite. 
FeO(OH) = 
Fe 2 3 .H 2 0. 



LUSTER, 
colored streak. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Rhombohedral. Usually 
fine granular or earthy. 


See p. 381. 


CINNABAR. 

HgS. 


Usually massive. 


See p. 379. 


CUPRITE 
(Ruby Copper). 
Cu 2 0. 


Reniform, crystalline, mica- 
ceous, earthy. 


See p. 385. 


HEMATITE. 

Fe 2 3 . 


Reniform and stalactitic. 


See p. 385. 


Turgite. 
Fe 4 O 8 (OH) 2 = 
2Fe 2 3 .H 2 0. 


Rhombohedral. Irregular 
massive. Rarely in crystals. 


The dark " ruby silver " showing 
dark ruby-red color in thin splin- 
ters. A rare mineral associated 
with proustite, stephanite, polybas- 
site, argentite, etc. Easily fusible 
in the candle flame. 


Pyrargyrite. 
3Ag 2 S.Sb 2 S,. 


Rhombohedral. Irregular 
massive. Rarely in crystals. 


The light " ruby silver." Charac- 
terized by its color and adamantine 
luster. Rare, with associations 
like those of pyrargyrite. Easily 
Fusible in the candle flame. 


Proustite. 
SAgzS-AszS,. 



387 



NONMETALLIC 
I. Give a definitely 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Yellow- 
brown. 


Dark brown to 
black. 


5-5.5? Softer in 
some varieties but 
usually harder 
than a knife. 


F. Splintery. . 


3.6-4.0 


One good C. 
F. Splintery. 


43 


Brown. 


Dark brown. 


5.5. 


One good C. 
F. Uneven. 


7 2-7.5 


Light brown. 


Light to dark 
brown. 


3.5 


Perfect C. In 6 direc- 
tions (dodecahedral). 


4.0 


Light orange 
to dark 
brown. 


Orange-yellow, 
brown, black. 


4.5-5. 


Prismatic C. 


4.8-5 2 


Light 
brown. 


Brown to black. 


6-7. 


F. Uneven. 


6.8-7.1 


Light 
brown. 


Reddish brown to 
black. 


6-6.5. 


F. Uneven. 
C. Not prominent. 


4.2 


Orange-yel- 
low. 


Deep red to or- 
ange-yellow. 


4-4.5. 


C. Basal. 


5.5 


Bright red. 


2.5-3. 


F. Uneven. 


5 9-6.1 


Deep red. 


1.5-2. Can be 
scratched by fin- 
ger nail. 


F. Conchoidal. One 
C., not prominent. 


3.5 



388 



LUSTER. 

colored streak. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Mammillary or stalactitic. 


See p. 387. 


LIMONITE 

(Bog Iron Ore). 
Fe 4 O 3 (OH)= 
2Fe 2 3 .3H 2 0. 


Mammillary or stalactitic. 
Radiating groups of 
slender crystals. 


See p. 387. 


Goethite. 
FeO(OH) = 
Fe 2 O 3 .H 2 O. 


Monoclinic. In b 1 a d e d 
masses. 


See p. 379. 


Wolframite. 
(Fe,Mn)WO 4 . 


Isometric; tetrahedral. In 
granular cleavable masses or 
in rounded crystals. 


Characterized by its resinous luster 
and perfect cleavage. See p. 379. 


SPHALERITE. 

ZnS. 


Tetragonal. In prismatic 
crystals; also massive, com- 
pact. 


A rare mineral. 


Thorite. 
ThSiO 4 . 


Tetragonal. In irregular 
masses; in compact fibrous 
reniform structure; in rolled 
grains. Rarely in prismatic 
crystals. Commonly 
twinned. 


Very heavy. Usually opaque to 
translucent. Occurs as rolled grains 
in sand; in pegmatite veins and in 
granite rocks. 


CASSITERITE 

(Tin Stone). 
SnO 2 . 


Tetragonal. In prismatic 
crystals vertically striated; 
often slender acicular. Fre- 
quently twinned. 




RUTILE. 
TiO 2 . 


Hexagonal ;hemimorphic. 
Granular cleavable, 


Characterized by its color, streak 
and cleavage. Found at Franklin 
Furnace, N. J., often intimately as- 
sociated with franklinite (black) 
and willemite (green). 


ZINCITE. 
(Zn.Mn)O. 


Monoclinic. In long slender 
crystals, often in interlacing 
groups. 


Characterized by its color and 
high luster. Decrepitates in the 
candle flame. 


Crocoite. 
PbCrO 4 . 


Monoclinic. Crystallized or 
earthy. 


Easily fusible in the candle flame. 
Characterized by its color and 
when in crystals by its resinous 
luster. 


Realgar. 

AsS. 



NONMETALLIC 
I. Give a definitely 



Streak. 


Color. 


Hardness. 


Cleavage and 
Fracture. 


Spec. 
Grav. 


Pale yellow. 


Lemon-yellow. 


1.5-2. Can be 
scratched by fin- 
ger nail. 


One prominent C. 


3.5 


Pale yellow. 


1.5-2.5. 


F. Conchoidal or un- 
even. 


2.0 


Light yellow- 
green. 


Blackish, 
olive-green, 
brown. 


3. 


F. Uneven. 


4.4 


Light green. 


Dark emerald- 
green. 


3-3.5. 


One good C. 


3.7 


3.5-4. 


One good C., not com- 
monly seen. 


3.9 


Bright green. 


3.5-4 


One good C., rarely 
seen. 


3.9-4.0 


Light blue. 


Intense azure-blue. 


3.5-4. 


F. Conchoidal or un- 
even. 


3.7 


2.5. 


F. Conchoidal. 


2.2 


Very light 
blue. 


Light green to tur- 
quois blue. 


2-4. 


F. Uneven. 


2.0-2.4 


Grayish blue. 


Very dark blue. 
Bluish green. 


1.5-2. 


One good C. 


2.6-2.7 



See also lazurite, p. 415, which may give a very light blue streak. 



390 



LUSTER. 

colored streak. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Monoclinic. In cleavable 
masses. 


Easily fusible in the candle flame. 
Characterized by its cleavage, 
color and resinous luster. 


Orpiment. 

AszSs. 


Orthorhombic. In crystals. 
Granular crystalline. 
Earthy. 


iurns with a blue flame giving a 
trong odor of sulphur dioxide. A 
>oor conductor of heat. A mass 
leld in the hand close to the ear 
will be heard to crackle on account 
of the irregular expansion due to the 
heat of the hand. Often earthy 
and impure. 


SULPHUR. 


Orthorhombic. In aggre- 
gates of small crystals. 


Characterized by its color and 
small prismatic crystals. 


Olivenite. 
Cu(Cu.OH)AsO 4 . 


Orthorhombic. In granular 
cleavable masses or in small 
prismatic crystals. 


Characterized by its dark green 
color and good cleavage. 


Acatamite. 
Cu 2 Cl(OH),= 
CuCl 2 .3Cu(OH),. 


Orthorhombic. In small 
prismatic crystals or in gran- 
ular masses. 


Characterized by its green color 
and slender prismatic crystals. 


Brochantite. 
CuS0 4 .3Cu(OH) t . 


Monoclinic. Radiating fi- 
brous, mammillary. 


Characterized by its bright green 
color and radiating fibrous struc- 
ture. Effervesces when a drop o 
cold acid is placed on the specimen 


MALACHITE. 

CuC0 3 .Cu(OH) 2 . 


Monoclinic. In small crys- 
tals, often in groups. Radi- 
ating fibrous, mammillary. 


Characterized by its intense blue 
color. Effervesces when a drop o 
cold acid is placed on the specimen 


AZURITE. 
2CuC0 3 .Cu(OH)i. 


Triclinic. In crystals. Mas- 
sive, stalactitic. Sometimes 
with fibrous appearance. 


Soluble in water. Metallic taste 
Characterized by color. Product 
of oxidation of copper sulphides. 


Chalcanthite. 
(Blue Vitriol). 
CuSO 4 .5H 2 O. 


Massive and amorphous. 


Characterized by its structure am 
color. Associated with other cop- 
per minerals. 


CHRYSOCOLLA. 
CuSiO,.2H 2 0. 


Monoclinic. Usually in pris- 
matic crystals. 


Characterized by its color and 
streak. 


Vivianite. 
Fe 3 (P0 4 ),.8H 2 0. 



and lepidomelane, p. 393, which may give a light green streak. 



391 



NONMETALLIC 

II. Give a 

1. Can be scratched 



Cleavage and 
Fracture. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


Perfect cleavage in 
one plane. 
The Micas or re- 
lated micaceous 
minerals, which 
possess such a 
perfect cleavage 
that they can be 
split into exceed- 
ingly thin sheets. 
Sometimes they oc- 
cur as aggregates of 
minute scales when 
the micaceous 
structure may not 
be readily appar- 
ent. 


Pale brown, green, 
yellow, white. 


Vitreous, pearly. 


2-2.5. 


2.8 


Usually dark 
brown, green to 
black. May be 
yellow. 


Vitreous. 


2.5-3. 


3.0 


Yellowish brown, 
green, white. 


Vitreous, pearly. 


2.5-3. 


2.8 


Black, greenish 
black. 


Adamantine to 
pearly. 


3. 


3-3.2 


Green of various 
shades. 


Vitreous, pearly. 


2-2.5. 


2.7 


White apple- 
green, gray. 
When impure as in 
soapstone, dark 
gray, dark green 
to almost black. 


Pearly, greasy. 


Very soft. Will 
leave a mark on 
cloth. 


2.8 


White, gray 
green. 


Pearly, vitreous. 


2.5. 


2.4 



392 



LUSTER. 

colorless streak, 
by the finger nail. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Monoclinic. In foliated 
masses; in tabular crystals 
with hexagonal or diamond- 
ehaped outlines: in scales. 


The common mica or ising-glass. 
Characterized by its micaceous 
structure, its perfect cleavage, the 
elasticity of its leaves and its light 
solor. While in the mass it may be 
brown or green, the thin sheets are 
colorless. 


MUSCOVITE 

(Potash Mica). 
H 2 KAl 3 (SiO 4 ),. 


Monoclinic. In irregular foli- 
ated masses. Six-sided tab- 
ular crystals rare. 


The common dark green or black 
mica. Even in thin sheets it shows 
a smoky color. Sheets are flexible 
and elastic.' 


BIOTITE. 

(H,K) 2 (Mg,Fe), 
(Al,Fe)(Si0 4 ),. 


Monoclinic. In irregular foli- 
ated masses. Often in six- 
sided tabular crystals, fre- 
quently large. 


Jsually a light- though sometimes 
a dark-colored mica. Often shows 
a coppery-like reflection from the 
cleavage surface. Occurs kt crys- 
talline limestone. 


PHLOGOPITE. 

(H,K) 3 (Mg,Fe) s 
(Al,Fe)(Si0 4 ) 3 . 


Monoclinic. Usually in 
masses of small irregular 
scales. 


Characterized by its micaceous 
structure and its shining black 
color. 


Lepidomelane. 
(H,K) 2 Fe 2 (Fe,Al), 
(Si0 4 ) 3 ?. 


Monoclinic. Usually in ir- 
regular foliated masses, at 
times in compact masses of 
minute scales. 


Characterized by its green color 
and by the fact that thin sheets are 
flexible but not elastic. 


CLINOCHLORE, 

Penninite 
(Ripidolite, Chlo- 
rite). 
H.jMg^SiA,. 


V 

Monoclinic. Foliated or 
compact. 


Characterized by their greasy feel 
softness, frequently distinctly foli- 
ated or micaceous structure. Can- 
not be positively told apart by phys- 
ical tests. See p. 280. 


TALC 

(Steatite, 
Soapstone). 
H 2 M gs (Si0 3 ) 4 . 


PYROPHYLLITE 
H 2 Al 2 (SiO 3 )<. 


Rhombohedral. Commonly 
foliated massive. At times 
in broad tabular crystals. 


Luster on cleavage surface pearly 
elsewhere vitreous. S e e t i 1 e 
Transparent to translucent. Can 
be split with some difficulty into 
thin sheets which are somewha 
flexible but not elastic. 


Brucite. 
Mg(OH),. 



393 



NONMETALLIC 

II. Give a 

1. Can be scratched 



Cleavage and 
Fracture. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


Perfect pinacoidal 
C. Two other 
cleavages not so 
prominent. 


Colorless, white, 
gray. Sometimes 
colored by impur- 
ities. 


Vitreous. 


2. 


2.3 


One perfect C. 


Blue, bluish green 
to colorless. 


Pearly to vitreous. 


2-3. 


2.6-2.7 


Cubical C. 


Colorless or white. 


Vitreous. 


2-2.5. 


2.0 


F. Uneven. 


Pearl-gray or col- 
orless. Turns to 
pale brown on ex- 
posure to light. 


Adamantine. 


2-3. Highly sec- 
tile. 


5.8-6.0 


F. Uneven. 


Green or yellow. 


Adamantine. 


2-3. Highly sec- 
tile. 


5.8 


F. Uneven. 


Pale yellow. 


Resinous. 


1.5-2.5. 


2.0 


F. Uneven. 
Rhombohedral C. 
Seldom seen. 


Colorless or 
white. 


Vitreous. 


1.5-2. 


2.3 


F. Conchoidal. 
C. Prismatic, sel- 
dom seen. 


2.1 



See also kaolinite, bauxite, and greenockite p 401, which on account 



394 



LUSTER, 
colorless streak, 
by the finger nail. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Monoclinic. In granular 
masses or cleavable crystal- 
line. 


Characterized by its one perfect 
cleavage, and two others, one giv- 
ing a conchoidal surface and the 
other a silky surface, and by its 
softness. 


GYPSUM 

(Alabaster). 
CaS0 4 .2H 2 0. 


Monoclinic. 


See p. 391. 


Vivianite. 
Fe 3 (PO 4 )28H 2 O. 


Isometric. 


See p. 397. 


Sylvite 
KC1. 


Isometric. In irregular 
masses. Rarely in rude 
crystals. 


Commonly known as horn-silver, 
because it can be cut with a knife 
like horn and because in thin plates 
it is translucent. More common 
than the other halogen salts of sil- 
ver but to be distinguished from 
them only by chemical tests. 


CERARGYRITE 

(Horn Silver). 
AgCl. 


Isometric. In irregular 
masses. Rarely in rude crys- 
tals. 


Like cerargyrite. To be distin- 
guished from it only by chemical 
tests. 


Embolite. 
Ag(Cl.Br). 


Orthorhombic. Crystal- 
lized. Granular. Earthy. 


Burns with a blue flame giving a 
strong odor of sulphur dioxide. 
Often earthy and impure. See also 
p. 391. 


SULPHUR. 

S. 


Saline crusts. 


Rare minerals. Readily soluble in 
water; cooling and salty tastes. 
Readily fusible in the candle flame. 


SODA NITER. 
NaNO s . 


Usually in thin crusts, silky 
tufts and delicate acicular 
crystals. 


Niter. 
KNO,. 



of their earthy structure may appear to be softer than the finger nail. 



395 



NONMETALLIC 

II. Give a 

2. Cannot be scratched by the finger nail, 

a. Show a 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


Cleavage in one 
plane. 

See also the miner- 
als of the mica 
group, p. 393, which 
may at times be 
harder than the fin- 
ger nail. 


Lilac, grayish, 
white. 


Pearly. 


2.5-4 


2.8-2.9 


Pink, gray, white 


Pearly. 


3.5-4.5 


3.0 


Blue, bluish green 
to colorless. 


Pearly to vitreous. 


3 


2.6-2.7 


Colorless or white. 


Vitreous to resi- 
nous. 


3.5 


4.3 


Cubic. 

i 


Colorless, white, 
red, blue. 


Vitreous. 


2.5 


2.1 


Colorless or white. 


Vitreous. 


2-2.5 


2.0 


Jin 3 directions 
at right angles 
to each other 
but with vary- 
J ing degrees of 
ease. 
c 


Colorless, white, 
blue, gray, red. 


Vitreous, pearly. 


3-3.5. 


2.9 


U In 3 directions 
not at right 
angles to each 
other, giving 
rhombohe- 
drons. 


Colorless, white 
and variously 
tinted. 


Vitreous. 


3 


2.7 


Colorless, white, 
pink, etc. 


Vitreous, pearly. 


3.5-4 


2.8 



396 



LUSTER. 

colorless streak. 

but can be scratched by a cent. 

prominent cleavage. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Monoclinic. In masses of 
small irregular scales. 
Rarely in six-sided prismatic 
crystals. 


Characterized by its lilac color. 
Always in very small sheets or 
scales. A rare mineral often asso- 
ciated with colored tourmalines. 


Lepidolite 
(Lithia Mica). 
LiK(AJ(OH,F) 2 ) 
Al(SiO,) 8 . 


Monoclinic. Usually in ir- 
regular foliated masses. 


Folia somewhat brittle. Charac- 
terized by its color. A rare min- 
eral. 


Margarite. 
H 2 CaAl 4 Si,Oi,. 


Monoclinic. Prismatic crys- 
tals, often in stellate groups. 
At times divergent, fibrous 
or earthy. 


A rare mineral. 


Vivianite. 
Fe 3 (PO4) 2 .8H,O. 


Usually massive with radia- 
ting structure. 


Cleavage rarely prominent. See p. 
411. 


WITHERITE. 
BaCOj. 


Isometric. In granular 
cleavable masses or in cubic 
crystals. 


Common salt. Characterized by 
its salty taste. Fusible in the can- 
dle flame. Highly diathermous. 
Compare sylvite, below. 


HALITE 

(Common Salt). 

NaCl. 


Isometric. Same as for hal- 
ite. Crystals frequently 
show octahedral truncations. 


A rare mineral closely resembling 
halite. To be distinguished from 
it by its more bitter taste and its 
greater softness (can usually be 
scratched by the finger nail). 


Sylvite. 
KC1. 


Orthorhombic. In granular 
cleavable masses. 


Characterized chiefly by its cleav- 
age. If hi a form where this does 
not show it wijl require chemical 
tests to determine it. 


ANHYDRITE. 
CaS0 4 . 


Rhombohedral. In fine- to 
coarse-grained cleavable 
masses. Whan crystallized 
shows prismatic, rhombo- 
hedral and scalenohedral 
forms. 


Effervesces readily when a drop of 
cold acid is placed upon it. Char- 
acterized by its perfect rhombo- 
hedral cleavage and crystal forms. 
Clear varieties show strong double 
refraction. Occurs in large masses 
as limestone and marble. Crystal 
faces may be harder than a cent. 


CALCITE. 
CaCO,. 


Rhombohedral 


See p. 407. 


DOLOMITE. 

CaMg(CO,),. 



397 



NONMETALLIC 

II. Give a 

2. Cannot be scratched by the finger nail, 

a. Show a 



Cleavage and 
Fracture. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


In 3 directions 
giving tabular 
diamond-shaped 
cleavage blocks. 


Colorless, white, 
blue, yellow, red. 


Vitreous, pearly. 


3-3.5 


4.5 


Colorless, white, 
blue, red. 


Vitreous, pearly. 


3-3.5 


3.9 


Colorless or white. 
Gray and brown 
when impure. 


Adamantine. 


3 


6.3 



6. Do not show a 
1. A small splinter is 

a. Readily soluble in water; 



F. Conchoidal. 


Colorless, white, 
red. 


Vitreous, greasy. 


2.5 


1.6 


F. Conchoidal. 
One good C. sel- 
dom seen. 


Colorless or white. 


Vitreous. 


2-2.5 


1.7 


F. Conchoidal. 


Colorless or white. 


Vitreous. 


2-2.5 


1.7 



See also halite, p. 397, which may exist in forms in which its cleavage is 



398 



LUSTER. 

colorless streak. 

but can be scratched by a cent. 

prominent cleavage. (Continued.} 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Orthorhombic. In aggregates 
of platy crystals or in tabular 
orthorhombic crystals with 
rectangular or diamond- 
shaped outlines. Crystal 
edges frequently beveled by 
other faces. At times granu- 
lar. 


Characterized by its unusual 
weight for a nonmetallic mineral, 
its platy structure, cleavage and 
pearly luster on basal cleavage. 
At times to be told from celestite 
and anglesite only getting a green 
flame (test for barium). 


BARITE, 

Barytes. 
(Heavy Spar). 
BaSO 4 . 


Orthorhombic. In granular 
platy masses or in tabular 
crystals like those of barite. 
At times in long prismatic- 
like crystals with blunt ter- 
minations. 


Very similar in appearance to ba- 
rite. Frequently can only be told 
from barite and anglesite by get- 
ting a crimson flame color (test for 
strontium). 


CELESTITE. 

SrSO 4 . 


Orthorhombic. Usually 
earthy and impure. At 
times in small crystals re- 
sembling those of barite and 
celestite. 


Characterized by its weight. Usu- 
ally associated with galena as an 
alteration product in concentric 
layers around an unaltered core of 
galena. Will often need a test for 
lead for its positive identification. 


ANGLESITE. 

PbS0 4 . 



prominent cleavage. 
fusible in the candle flame. 

yield a taste. 



Orthorhombic. Commonly 
massive, granular. 


A rare mineral. In the candle 
flame swells, then fuses. Bitter 
salty taste. 


Carnallite. 
MgCl 2 .KCl.flH 2 O. 


Monoclinic. In crusts, often 
impure. Rarely in prismatic 
crystals. 


A comparatively rare mineral. 
Found only in dry countries. In 
candle flame swells and then fuses. 
Sweetish-alkaline taste. 


BORAX. 
Na2B 4 O 7 .10H 2 O. 


Usually fibrous or massive 
or in mealy or solid crusts. 


Easily fusible with frothing in can- 
dle flame. A rare mineral. As- 
tringent taste. 


Kalinite 
(Potash Alum). 
KA1(SO 4 ) 2 .12H 2 O. 



obscure, and chalcanthite, p. 390, which may give a nearly colorless streak. 



NONMETALLIC 

n. Give a 

2. Cannot be scratched by finger nail, 

b. Do not show a 
1. A small splinter is fusible 

b. Insoluble in 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Colorless or white. 


Vitreous to greasy. 


F. Uneven. 
C. In one direc- 
tion, seldom seen. 


3-3.5 


2.9 


Adamantine. 


F. Conchoidal. 


3-3.5 


6.5 


'Colorless, yellow, 
orange, brown. 


Resinous. 


F. Uneven. 


3-3.5 


7.0-7.2 



See also vanadinite below, 



2. Infusible 



Colorless or white. 
See also bauxite, 
wavellite and ser- 
pentine below, 
which may be 
nearly white. 


Vitreous to resi- 
nous. 


F. Uneven. 


3-3.5 


4.3 


Pearly, dull. 


F. Earthy. 


2-2.5 


2.6 


Honey-, citron- or 
orange-yellow. 


Adamantine, resi- 
nous, earthy. 


F. Uneven. 


3-3.5 


4.9-5.2 


Yellow, brown, 
gray, white. 


Dull, earthy. 


F. Uneven. 


3 


2.5 


Ruby-red, brown, 
yellow. 


Resinous. 


F. Uneven. 


2 


6.9-7.1 



400 



LUSTER. 

colorless streak. 

but can be scratched by a cent. 

prominent cleavage. 
in the candle flame. 

water. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Monoclinic. Massive. 


Characterized by its peculiar trans- 
lucent appearance, like that of par- 
affine. Its fine powder practically 
disappears when placed in water 
but is insoluble. 


CRYOLITE. 

Na 3 AlF 6 . 


Orthorhombic. In granular 
masses; platy crystals often 
crossing each other to form a 
lattice-like effect. 


When fused in the candle flame is 
slowly reduced showing globules 
of lead on surface of fragment. 
Heavy. Effervesces when a drop 
of cold acid is placed upon it. 
Associated usually with galena. 


CERUSSITE. 
PbCO 3 . 




See p. 413. 


Mimetite. 
Pb 4 (PbCl)(AsO 4 )3. 



which may fuse slightly. 



in the candle flame. 



Often massive with radiat- 
ing structure. 


See p. 411. 


WITHERITE. 
BaCOj. 


Generally clay-like, com- 
pact or mealy. 


Often impure. When breathed upon 
gives an argillaceous odor. Will 
adhere to a dry tongue. The basis 
of most clays. 


KAOLINITE. 

H 4 Al 2 Si 2 0,. 


Hexagonal, hemimorphic. 
Usually in form of powder. 
Rarely in crystals. 


A rare mineral. Characterized by 
its color and pulverulent form. 
Often as a coating on sphalerite. 


Greenockite. 
CdS. 


In rounded grains. Also 
earthy, clay-like. 


A rare mineral. Often impure. 


Bauxite. 
A1 2 O(OH) 4 . 


Hexagonal, pyramidal. In 
slender prisms. Sometimes 
in cavernous crystals and 
also in rounded barrel-shaped 
forms. 


Characterized by its color and 
crystals. Compare mimetite, 
above and pyromorphite, p. 413. 


Vamu Unite. 
Pb^PbClHVO*)!. 



401 



NONMETALLIC 

II. Give a 

2. Cannot be scratched by the finger nail, 

b. Do not show a 
2. Infusible 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Yellow, green, 
white, brown. 


Vitreous, pearly. 


F. Uneven. One 
C., not prominent. 


3-4 


2.3 


Olive to blackish- 
green, yellow-green, 
white. 


Greasy-, wax-like. 


F. Uneven. 


3.5-5 


2.6 


Pale to deep green. 


Dull to resinous. 


F. Uneven. 


3-4 


2.2-2.8 



Some varieties of anglesite, p. 399, anhydrite, p. 397, and vivianite, p. 397, do not show 

3. Cannot be scratched by a cent 

a. Show a 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


C. Pinacoidal. 


Blue, usually 
darker at center of 


Vitreous, pearly. 


5-7 


3.6 


5 


crystal. At times 








1 


white, gray or 








O 


green. 








$ 
>,C. Basal. 


Light blue, green, 


Resinous. 


4.5-5 


3.5 


Ctf "rt 


gray, salmon to 








i 


clove-brown. 








y 

g C. Pinacoidal. 


White, yellow, 


Pearly, vitreous. 


3.5-4 


2.1-2.2 


1 


brown, red. 









402 



LUSTER. 

colorless streak. 

but can be scratched by a cent. 

prominent cleavage. 

in the candle flame. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Usually in radiating hemi- 
spherical, globular forms. 


Characterized by its structure. 


Wavellite. 
(A1.0H) 3 (PO 4 ) 2 
5H 2 O. 


Massive. Fibrous. 


See p. 415. 


SERPENTINE. 

H 4 Mg 3 Si 2 9 . 


Massive and amorphous, at 
times as an incrustation with 
botryoidal or stalactitic sur- 
face; earthy. 


A rare mineral. Characterized 
chiefly by its color. 


Genthite 
(Garnierite). 
Nickel, magnesium 
silicate. 



a distinct cleavage and might be expected to be included in the above group. 

but can be scratched by a knife. 

prominent cleavage. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Triclinic. In bladed s t r u c- 
ture with prominent cleavage 
plane. 


Characterized by its color and the 
Fact that it can be scratched by a 
knife in a direction parallel to 
length of crystal but not in a direc- 
tion at right angles to this. 


CYANITE. 

Al 2 SiO 6 . 


Commonly massive cleav- 
able. 


Rare species. Triphyllite is essen- 
tially LiFePO 4 and lithiophyllite 
LiMnPO 4 . 


Triphyllite- 
Lithiophyllite. 
Li(Fe,Mn)PO 4 . 


Monoclinic. Commonly in 
sheaf-like aggregates of crys- 
tals or in flat tabular crys- 
tals. 


Characterized by the grouping of 
its crystals into a radiating sheaf- 
like aggregate and by the pearly 
luster of the cleavage face. 


STILBITE. 
H.(Ca,N ai )Al, 
(SiO 8 ),.4H,O. 



403 



NONMETALLIC 

II. Give a 

3. Cannot be scratched by a cent, 

a. Show a 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


C. Basal. 


Colorless, 
white, pale 
green, yellow, 
rose. 


Pearly, vitreous. 


4.5-5 


2.3-2.4 


C. Pinacoidal. 


White, yellow, 
red. 


Pearly, vitreous. 


3.5-4 


2.2 


g .C. Pinacoidal, 
J5 2 often not prom- 
& -* inent. 
Jo. 
| 

.as 


White, 
colorless. 

i 

* 


Vitreous. 


4.5 


2.4-2.5 


<D = 

?' C. Pinacoidal. 

C"5 


3 Colorless, 
w white. 

B 


Vitreous. 


4-4.5 


2.4 


1 
fl^C. Pinacoidal, 
q seldom seen. 


8 Colorless, 
t white. 


Vitreous to resi- 
nous. 


3.5 


4.3 


C. Pinacoidal. 


& Colorless, 
white, gray. 


Vitreous, pearly. 


5-5.5 


2.8-2.9 


C. Pinacoidal, 
also basal but 
seldom seen. 


Colorless, 
white, gray. 


Vitreous, pearly. 


4.5-5 


2.7-2.8 


C. In two di- 
rections. 
C. Prismatic. 


Colorless, 
white. 


Vitreous. 


5-5.5 


2.2 



404 



LUSTER. 

colorless streak. 

but can be scratched by a knife. 

prominent cleavage. (Continued.} 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Tetragonal. In prismatic 
crystals with square cross- 
section. Often resemble a 
combination of cube and oc- 
tahedron. 


Pearly luster on basal plane (cleav- 
age face), vitreous luster on other 
faces. Prism faces usually verti- 
cally striated. A zeolite found 
lining cavities in igneous rocks. 


APOPHYLLITE. 
H 7 KCa 4 (Si0 3 ), 
4*H 2 0. 


Monoclinic. Crystals often 
tabular parallel to cleavage 
plane (surface of pearly lus- 
ter). 


Pearly luster on cleavage face, 
elsewhere vitreous. A rare zeo- 
lite found lining cavities in igneous 
rocks. 


Heulandite. 
H 4 (Ca,Na,)Al, 
(SiO^.SHjO. 


Monoclinic. Crystals usu- 
ally like square prisms ter- 
minated by 4 pyramid faces, 
the latter faces striated. At 
times in cruciform penetra- 
tion twins. 


Characterized by its crystals, see 
p. 267. A rare zeolite found lining 
cavities in igneous rocks. 


Harmotone. 
(Ba,K 2 )Al 2 Si 6 M 
5H 2 O. 


Monoclinic. In crystalline or 
granular crystalline masses. 


Decrepitates violently in the can- 
dle flame. A rare mineral. 


Colemanite. 
CajBjOn.SHjO. 


Usually massive with .radi- 
ating structure. 


Seep. 411. 


WITHERITE. 

BaCO 3 . 


Monoclinic. Usually cleav- 
able massive to fibrous. 
Also compact. Rarely in 
tabular crystals. 


Associated with crystalline lime- 
stone. 


WOLLASTONITE. 
CaSiOj. 


Monoclinic. Commonly in 
close radi tin? aggregates of 
acicular crystals Fibrous 
massive. 


Characterized by its radiating 
structure. A rare mineral. 


Pectolite. 
HNaCMSiO,),. 


Orthorhombic. In slender 
to acicular prismatic crystals 
terminated by 4 low pyra- 
mid faces. Prism faces ver- 
tically striated. Often in 
radiating groups. 


Characterized chiefly by its struc- 
ture. A zeolite found lining cavi- 
ties in igneous rocks. 


NATROLITE. 

NasAKAlO) 
(Si6,),.2H,0. 



405 



NONMETALLIC 

II. Give a 

3. Cannot be scratched by a cent, 

a. Show a 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


C. Prismatic 
making angles 
of 55 and 125. 

5!. 


White, green, 
black. 


Vitreous, pearly. 


5-6 


3.0-3.3 


J.fc. Prismatic 
u "o making angles 
|of 54 and 126. 


Gray, clove- 
brown, green. 


Vitreous, pearly. 


5-6 


3.1 


OT3 

> C. Prismatic, 
*"* 2 rather poor at 
.9-| 90 angles. 

tP 
.3 

v o 

3| 
1 


White, green, 
black. 


Vitreous. 


5-6 


3.1-3.5 


C. Prismatic 
with nearly 90 
angles. 


Rose-red, pink, 
brown. 


Vitreous. 


5-6 


3.6 


^ In 3 directions 
not at right an- 
^ gles to each 
other, giving 
rhombohe- 
9 drons. 

1 


Colorless, white 
and variously 
tinted. 


Vitreous. 


3 


2.7 


Colorless, white, 
pink, etc. 


Vitreous, pearly. 


3.5-4 


2.8 



406 



LUSTER. 

colorless streak. 

but can be scratched by a knife. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Monoclinic. In slender pris- 
matic crystals, showing prom- 
inent cleavage, giving fre- 
quently a bladed appearance. 
When terminated the crys- 
tals usually show 2 low dome 
faces. Sometimes fibrous, 
asbestiform. 


Tremolite, CaMg 3 Si 4 O 12 , is white, 
gray, violet; ActinoJite, 
Ca(Mg,Fe) 4 Si 4 O 12) green of various 
shades; Amphibole or Horn- 
blende, CaMg 3 Si 4 O 12 with NajAlj 
Si 4 O 12 and Mg 2 Al 4 Si 4 O 12 , is green to 
black. The group is characterized 
chiefly by its broad angle cleavage. 
Found in metamorphic rocks. 


AMPHIBOLE 
GROUP. 

Essentially calcium, 
magnesium metasil- 
icates. 


Orthorhombic. Lamellar or 
fibrous. 


Seep. 419. 


Anthophyllite. 
(Mg,Fe)Si0 3 . 


Monoclinic. In stout pris- 
matic crystals with rectan- 
gular cross-section. When 
terminated they usually 
show more than 2 faces at 
ends. Often in granular crys- 
talline masses. 


Diopside, CaMgSi 2 O 6 , is colorless, 
white, pale green; Pyroxene, 
Ca(Mg,Fe)Si 2 O 6 , light to dark 
green; A u g i t e, CaMgSi 2 O with 
MgAl 2 SiO 6 and NaAlSi 2 O 6 , is 
greenish black to black. Charac- 
terized by the rectangular cross- 
section of its crystals and the rather 
poor prismatic cleavage at right 
angles. Shows at times a basal 
parting. Found in igneous rocks. 


PYROXENE 
GROUP. 

Essentially calcium, 
magnesium metasil- 
cates. 


Triclinic. Usually massive, 
cleavable to compact, in 
embedded grains; in large 
rough crystals with rounded 
edges. 


Characterized by its color. 


Rhodonite. 
MnSiO,. 


Rhombohedral. In granular 
cleavage masses or crystal- 
lized. 


See p. 397. 


CALCITE. 

CaCO,. 


Rhombohedral. In fine- to 
coarse-grained cleavable 
masses. Often in strongly 
curved rhombohedral crys- 
tals. 


Will not effervesce when a drop of 
cold hydrochloric acid is placed 
upon it. Characterized by its 
rhombohedral cleavage, by its 
rounded rhombohedral crystals 
and its frequently pink or flesh 
color. Pearly luster on curved 
crystal faces. Occurs in iarge 
masses as dolomite limestone and 
marble. Frequently associated 
with lead and zinc minerals. 


DOLOMITE. 

CaMg(CO,) 2 . 



407 



NONMETALLIC 

II. Give a 

3. Cannot be scratched by a cent, 

a. Show a 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


In 3 directions not 
at right angles to 
each other, giving 
rhombohedrons. 


White, yellow, 
gray, brown. 


Vitreous. 


3.5-4 


3.0-3.1 


Light to dark 
brown. 


Vitreous, pearly. 


3.5-4 


3.8 


Pink, rose-red, 
dark red, brown. 


Vitreous, pearly. 


3.5-4.5 


3.5-3.6 


Brown, green, 
blue, pink, white. 


Vitreous. 


5 


4.3 


White, yellow, 
flesh-red. 


Vitreous. 


4-5 


2.1 


In 3 directions at 
right angles to each 
other but with 
varying degrees of 
ease. 


Colorless, white, 
blue, gray, red. 


Vitreous, pearly. 


3-3.5 


2.9 


In 3 directions giv- 
ing tabular dia- 
mond-shaped cleav- 
age blocks. 


Colorless, white, 
blue, yellow, red. 


Vitreous, pearly. 


3-3.5 


4.5 


C. Octahedral. 


Colorless, violet, 
green, yellow, 
pink. Usually has 
a fine color. 


Vitreous. 


4 


3.1 


C. Perfect in 6 di- 
rections, dodeca- 
hedral. 


Yellow, brown, 
white. 


Strongly resinous. 


3.5-4 


4.0 


Dodecahedral C., 
more or less dis- 
tinct. 


White, gray, blue, 
green. 


Greasy, vitreous. 


5.5-6 


2.1-2.3 



Note. Apatite, p. 413, may show somewhat imperfect cleavage. 

408 



LUSTER. 

colorless streak. 

but can be scratched by a knife. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Rhombohedral. In granu- 
lar cleavable masses. 


A rare mineral. 


Magnesite. 
MgC0 3 . 


Rhombohedral. In cleav- 
able masses or in small 
rhombohedral crystals. 


After being heated in the candle 
flame a fragment is attracted by a 
magnet. 


SIDERITE. 

FeC0 3 . 


Rhombohedral. In cleav- 
able masses or in small 
rounded rhombohedral crys- 
tals. 


Characterized by its color, cleav- 
age and softness. 


RHODOCHRO- 
SITE. 
MnCO 3 . 


Rhombohedral. Usually in 
botryoidal or honey-combed 
masses. 


See p. 411. 


SMITHSONITE. 
ZnCO 3 . 


Rhombohedral. In small 
rhombohedral crystals with 
nearly cubic angles. 


A zeolite found lining cavities in 
igneous rocks. 


CHABAZITE. 

(Ca,Na2)Al 2 
(Si0 3 ) 4 6H 2 0. 


Orthorhombic. In granular 
cleavable masses. 


See p. 397. 


Anhydrite. 
CaSO 4 . 


Orthorhombic. In tabular 
crystals and lamellar masses. 


See p. 399. 


BARITE, 

Barytes 
(Heavy Spar). 
BaSO 4 . 


Isometric. In cubic crystals, 
often in interpenetration 
twins. 


Characterized by its crystals, color 
and cleavage. The bluish green 
variety shows fluorescence, i.e. ap- 
pears green by transmitted and 
blue by reflected light. 


FLUORITE. 

CaF 2 . 


Isometric, tetrahedral. In 
cleavable masses or small 
ronnded crystals. 


Characterized by its color, luster 
and cleavage. 


SPHALERITE. 

ZnS. 


Isometric. Massive or in 
embedded grains. 


Frequently blue in color. A rock- 
making mineral, never associated 
with quartz. Usually opaque to 
translucent. 


Sodalite. 
Na 4 (AlCl)Al, 
(Si0 4 ),. 



409 



NONMETALLIC 

II. Give a 

3. Cannot be scratched by a cent, 

6. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


>> Colorless, 
pale green, 
ti yellow. 
A 

.a 

ifl 


Vitreous. 


F. Uneven. 


5-5.5 


2.9-3.0 




5 White, pale 
A green, blue. 


Vitreous. 


F. Uneven. C. 
prismatic, seldom 
seen. 


4.5-5 


3.4 


.- White, gray, 
oj ; light green, 
".2 darker green 
gj "8 or brown. 

if 


Vitreous to dull. 


F. Uneven. C. 
prismatic, seldom 
seen. 


5-6 


2.7 


^| Colorless or 
i f white. 

S 

*! 


Vitreous. 


F. Uneven. 


3.5-4 


2.9 


o 
1J2 Colorless or 
J white. 
.a 

Rj 


Vitreous. 


F. Uneven. 


5-5.5 


2.3 


|| 

13 Colorless or 
^ white. 

s 


Vitreous to 
resinous. 


F. Uneven. 


3.5 


4.3 


J5 Colorless or 
.0 white. 

6 


Vitreous, pearly. 


Pinacoidal C., 
may be obscure. 


4.5-5 


2.7-2.8 


g Colorless or 
white. 


Vitreous. 


Prismatic C., may 
be obscure. 


5-5.5 


2.2 


Brown, green, 
fblue, pink, 
g white. 

H 


Vitreous. 


F. Uneven. 
Rarely shows 
rhombohedral C. 


5 


43 


Gray, brown 
p green, yel- 
low. 


Resinous, ada- 
mantine. 


F. Uneven. Pris- 
matic C., seldom 
prominent. 


5-5.5 


3 4-3.5 



410 



LUSTER. 

colorless streak. 

but can be scratched by a knife. 

prominent cleavage. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Monoclinic. Usually in crys- 
tals developed with nearly 
equal dimensions in all di- 
rections and many faces. 


Characterized by its luster and 
crystals. Usually transparent. 
Occurs with the zeolites, lining cav- 
ities in igneous rocks. 


DATOLITE. 
Ca(B.OH)SiO 4 . 


Orthorhombic. Often in ra- 
diating crystal groups. Also 
stalactitic, mammillary. 


Characterized by its structure. 
Pyroelectric. 


CALAMINE. 
(Zn.OH) 2 SiO,. 


Tetragonal. In prismatic 
crystals, granular or mas- 
sive. 


Often altered. 


SCAPOLITE. 
Ca 4 Al 6 Si 6 Oi 8 with 
Na 4 Al 3 Si 9 O34Cl. 


Orthorhombic. Frequently 
in radiating groups of acicular 
crystals. 


Effervesces in cold acids. Falls 
to powder in candle flame. 


ARAGONITE. 

CaCO 3 . 


Isometric. In crystals, usu- 
ally trapezohedrons. 


Characterized by its crystals and 
its glassy luster. A zeolite found 
lining cavities in igneous rocks. 


ANALCITE. 
NaAl(SiO 3 ) 2 H,O. 


Orthorhombic. Often in 
masses with radiating struc- 
ture; granular; rarely in hex- 
agonal pyramidal crystals. 


Heavy. When a fragment is placed 
in cold hydrochloric acid there is a 
brisk effervescence for a moment 
and then the action ceases. 


WITHERITE. 

BaCO 3 . 


In radiating acicular crys- 
tals. 


See p. 405. 


Pectolite. 
HNaCa2(SiO 3 ) 3 . 


Radiating prismatic. 


See p. 405. 


Natrolite. 
NajAKAlO) 
(SiO 3 ),.2H,O. 


Rhombohedral. In rounded 
botryoidal forms. Often in 
honey-combed masses. 


Harder than most carbonates. A 
fragment effervesces when placed 
in cold hydrochloric acid. 


SMITHSONITE. 

ZnCO 3 . 


Monoclinic. In thin crystals 
with sharp edges, wedge- 
shaped. 


Characterized by its crystals. 


TITANITE 

(Sphene). 
CaTiSiO. 



411 



NONMETALLIC 

II. Give a 

Cannot be scratched by a cent, 

b. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Yellowish to 
. reddish 
^ brown. 

3 


Resinous, vitre- 
ous. 


F. Uneven. Pris- 
matic C., seldom 
prominent. 


4-5 


5.0 


j Yellowish to 
i-g. reddish 
S 3 brown. 


Resinous. 


F. Uneven. 


5-5.5 


5.2-5.3 


! | White, yel- 
ls T5 low, green, 
'g | brown. 


Vitreous, ada- 
mantine. 


F. Uneven. 


4.5-5 


6.0 


|| Usually a 
3* brilliant 
pj a shade of yel- 
3 low or orange. 
Also red, 
8 gray, green. 



Vitreous to ada- 
mantine. 


F. Uneven. 


4.5-5 


6.0 



a'i Colorless, 
* yellow, or- 
^ 8 ange, brown. 


Resinous. 


F. Uneven. 


3.5 


7.0-7.2 


Yellow, 
brown, gray, 
white. 


Dull, earthy. 


F. Uneven. 


3 


2.5 


White, green, 
black. 


Vitreous. 


F. Uneven. 
Rather poor pris- 
matic C., at 90 
angles. 


5-6 


3.1-3.5 


So Green, blue, 
>, violet, brown, 
5| colorless. 


Vitreous, greasy. 


F. Uneven. 


5 


3.1 


Green, 
brown, 
yellow, gray. 


Resinous. 


F. Uneven. 


3.5-4 


6.5-7.1 



412 



LUSTER. 

colorless streak. 

but can be scratched by a knife. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Tetragonal. In prismatic or 
pyramidal crystals. In 
rolled grains. 


A rare mineral. Heavy. 


Xenotime. 
YPO 4 . 


Monoclinic. In small crys- 
tals or as rolled grains. 


A rare mineral. Heavy. 


MONAZITE. 
(Ce,La,Di)P0 4 
often with ThSiO 4 . 


Tetragonal. In octahedral- 
like crystals. Massive, 
granular. 


A rare mineral. Heavy. 


Scheelite. 
CaW0 4 . 


Tetragonal. Usually in very 
thin square tabular crystals. 
Less frequently octahedral 
in habit. Also granular 
massive. 


Characterized by its crystals and 
color. Heavy. 


Wulfenite. 
PbMoO 4 . 


Hexagonal. In small pris- 
matic crystals. Prism faces 
often curved, giving barrel 
shapes. In granular masses. 


A rare mineral. Heavy. Fuses 
slowly in candle flame. 


Mimetite. 
Pb 4 (PbCl)(As0 4 ) a . 




See p. 401. 


Bauxite. 
A1 2 0(OH) 4 . 


Monoclinic. In stout rec- 
tangular crystals with rec- 
tangular cross-section. 


See p. 407. 


PYROXENE 
GROUP. 

Essentially calcium 
and magnesium sili- 
cates. 


Hexagonal. In prismatic 
crystals, often large, usually 
with prominent pyramid 
planes. Also massive. 


Characterized by its crystals. 


APATITE. 
Ca 4 (CaF)(PO 4 ),. 


Hexagonal. In small crys- 
tals. Often in rounded barrel- 
shaped forms. Crystals at 
times cavernous. Often 
globular and botryoidal. 


Characterized chiefly by its struc- 
ture and color. Heavy. 


PYROMOR- 
PHITE. 
Pb 4 (PbCl)(P0 4 ),. 



413 



NONMETALLIC 

II. Give a 

3. Cannot be scratched by a cent, 

b. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Yellow, 
. green, white, 
brown. 


Vitreous, pearly. 


F. Uneven. One 
C., not prominent. 


3-4 


2.3 


3 
Olive to 
g blackish 
j8 green, yellow- 
g green, white. 

si 


Greasy, waxlike. 


F. Uneven. 


3.5-5 


2.6 


-2 
0$;s Yellow-green, 
t^a white, color- 
s' |j less, blue, 
6 gray, brown. 

l| 


Vitreous. 


F. Uneven. May 
show fairly good 
C. 


5.5 


4.0-4.1 


1 

J White, gray, 
. blue, green. 

9 




Greasy, vitreous. 


F. Conchoidal. 
Dodecahedral C., 
seldom seen. 


5.5-6 


2.1-2.3 


1 

Deep azure- 
blue, green- 
" ishblue. 


Vitreous. 


F. Uneven. 


5-5.5 


2.4 



NONMETALLIC 

II. Give a 

4. Cannot be scratched by a knife, 

a. Show a 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


8, C. Basal. 


> 

? 


White to pale 
green or blue. 


Vitreous to greasy. 


6 


3.0 


1 

g C. Pinacoidal. 

O 


Colorless, white, 
gray. 


Vitreous, pearly. 


5-5.5 


2.8-2.9 



414 



LUSTER. 

colorless streak. 

but can be scratched by a knife. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Usually in radiating hemi- 
spherical, globular forms. 


Characterized by its structure. 


Wavellite. 
(A1.0H) 3 (P0 4 ) 2 
5H 2 O. 


Massive. Fibrous in the as- 
bestos variety. 


Characterized by its massive 
structure, mottled green color and 
frequently by the presence of veins 
of finely fibrous material, known as 
chrysotile or asbestos. 


SERPENTINE. 
H 4 Mg 3 Si 2 9 . 


Massive and in disseminated 
grains. 


See p. 423. 


WILLEMITE. 

Zn 2 SiO 4 . 
Troostite. 
(Zn,Mn) 2 SiO 4 . 


Massive or in embedded 
grains. 


See p. 409. 


Sodalite. 
Na 4 (AlCl)Al 2 
(Si0 4 ) 3 . 


Usually massive. 


Characterized by its color. 


Lazurite 
(Lapis-Lazuli). 
(Na 2 ,Ca) 2 (Al.NaS,) 
Alj(SiO 4 ),. 



LUSTER. 

colorless streak. 

but can be scratched by quartz. 

prominent cleavage. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Usually cleavable to com- 
pact massive. 


A rare mineral. Usually found 
with lepidolite, tourmaline, etc. 


Amblygonite. 
Li(AlF)PO 4 . 


Usually cleavable massive 
to fibrous. 


See p. 405. 


WOLLASTONITE. 
CaSiO,. 



415 



NONMETALLIC 
II. Give a 

4. Cannot be scratched by a knife, 

a. Show a prominent 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


. C. Pinacoidal 


White, gray, pale 
lavender, yellow- 


Pearly, vitreous. 


6.5-7 


3.4 


1 


ish, greenish. 








3 










C. Pinacoidal 


Grayish white, 


Vitreous, pearly. 


6-6.5 


3.3 


5 


green, pink. 








1 










2 C. Pinacoidal 


Hair- brown, gray, 


Vitreous. 


6-7 


3.2 


1 


grayish green. 








1 

$ 










C. Basal. 


Yellowish to 


Vitreous. 


6-7 


3 4 


t* 


Dlackish green to 










gray. 








a C. Pinacoidal. 


Blue, usually 
darker at center of 
crystal. At times 
gray or green. 


Vitreous, pearly. 


5-7 


3.6 


Cleavage in 
two directions. 


Colorless, white. 


Vitreous. 


5-5.5 


2.2 


C. Prismatic. 










C. Basal and 
pinacoidal 


Colorless, white, 
gray, cream, red, 


Vitreous, pearly. 


6 


2.6 


.2 making a 90 


green. 








ft angle. 










A 











416 



LUSTER. 

colorless streak. 

but can be scratched by quartz. 

(Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Orthorhombic. In thin tab- 
ular crystals or scales. 
Bladed or foliated structure. 


Pearly luster on cleavage face, else- 
where vitreous. Often associated 
with corundum, chlorite, marga- 
rite, etc. 


Diaspore. 
AIO(OH). 


Orthorhombic. In prismatic 
crystals, deeply striated ver- 
tically and seldom distinctly 
terminated. Also massive, 
columnar to compact. 


Pearly luster on cleavage face, else- 
where vitreous. 


Zoisite. 
Ca 2 (Al.OH)AI 2 
(Si0 4 ),. 


Orthorhombic. Commonly 
in long slender unterminated 
crystals. Often in close par- 
allel groups. Fibrous, co- 
lumnar. 


In schistose rocks. 


Sillimanite 
(Fibrolite). 
Al 2 SiO 6 . 


Monoclinic. In slender pris- 
matic crystals, striated par- 
allel to length of crystal. 
Also fibrous, granular. 


Characterized by its olive-green 
color. When transparent shows di- 
chroism; i.e., in transmitted light 
ippears green in one position and 
brown in another. In metamorphic 
rocks; often in crystalline lime- 
stones. 


EPIDOTE. 

CMAl.OH) 
(Al,Fe) 2 (SiO 4 ) 3 . 


Bladed. 


See p. 403. 


CYANITE. 
AljSiOfi. 


Radiating prismatic. 


See p. 405. 


NATROLITE. 
Na 2 Al(AlO) 
(Si0 3 ) 3 .2H 2 0. 


Monoclinic. In cleavable 
masses or in irregular grains 
as a rock constituent. May 
be in crystals, see Figs. 269- 
271, p. 221. 


Orthoclase is monoclinic while mi- 
crocline is triclinic. Ordinarily 
they can only be told apart by a 
microscopic examination. The 
green amazon stone is usually mi- 
crocline. Characterized by its 2 
cleavage planes at righ angles; the 
:>asal cleavage is the better. 
Found as a prominent constituent 
of granite rocks and pegmatite 
veins, associated with quartz and 
mica. 


ORTHOCLASE, 

Microcline 
(Potash Feldspar). 
KAlSi,0,. 



417 



NONMETALLIC 

II. Give a 

4. Cannot be scratched by a knife, 

a. Show a prominent 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


C. Basal per- 
fect. C. Pina- 
coidal not so 
distinct. The 
two make an- 
gles with each 
other varying 
from 85 50' to 
86 24'. 


Colorless, white, 
gray, greenish, 
bluish, reddish. 
Often exhibit a 
beautiful play of 
color on the cleav- 
age surfaces. 


Vitreous, pearly. 


6 


2.6-2.7 


J C. Prismatic. 

1 
.a 


White, gray, pink, 
emerald-green 


Vitreous. 


6.5 


3.2 


fi C. Prismatic 
g making angles 
3 of 5$ and 125. 


White to green to 
black. 


Vitreous, pearly. 


5-6 


3.0-3.3 


C. Prismatic. 
Perfect at an- 
gles of 54 and 
126. 


Gray, clove- 
brown, green. 


Vitreous, pearly. 


5.5-6 


3.1 


C. Prismatic. 
Not very per- 
fect at angles 
nearly 90. 


Greenish to brown- 
ish black. 


Vitreous. 


6-6.5 


3.5 


C. Prismatic. 
Rather poor at 
90 angles. 


White to green to 
black. 


Vitreous. 


5-6 


3.1-3.5 



418 



LUSTER. 

colorless streak. 

but can be scratched by quartz. 

cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Triclinic. In cleavable 
masses or in irregular grains 
as a rock constituent. Al- 
bite may be in thin tabular 
crystals or with a curved 
lamellar structure. 


Albite = NaAlSi 3 O 8 ; Oligoclase = 
3NaAlSi 3 8 lCaA! 2 Si 2 O 8 ; Andesine 
= !NaAlSi 3 O 8 lCaAl 2 Si 2 O 8 ; Lab 
radorite = lNaAlSi 3 O 8 3CaAl 2 Si 2 O 8 
Anorthite = CaAl 2 Si 2 O 8 . Charac 
terized b., a perfect basal cleavage 
and a pinacoidal cleavage not so 
distinct; the two making an angle 
with each other of nearly 90 
Often on the best cleavage surface 
will be seen a series of fine parallel 
striation lines due to intimate 
twining. Often they show a fine 
play of colors on cleavage surfaces, 
>ale blue in albite and oligoclase; 
>right blue, green, gold, etc., hi an- 
desite and labradorite. Rock con- 
stituents; albite and oligoclase in 
the light colored granitic rocks; the 
others in the darker colored, more 
>asic igneous rocks. 


THE 
PLAGIOCLASE 
FELDSPARS. 

Combinations in 
varying amounts of 
NaAlSi 3 8 , the Al- 
bite molecule, and of 
CaAl 2 Si 2 O 8 , the An- 
orthite molecule. 


Monoclinic. In flattened 
prismatic crystals, vertically 
striated; sometimes very 
large. Also massive, cleav- 
able. 


jilac to pink called kunzite. Green 
s called hiddenite. Often alters to 
other minerals with a dull gray 
color. Not common. 


SPODUMENE. 
(Li,Na)Al(SiO 3 ) 2 . 


Monoclinic. In slender pris- 
matic crystals, showing 
prominent cleavage. 


See p. 407. 


AMPHIBOLE 
GROUP. 


Orthorhombic. Commonly 
lamellar or fibrous massive; 
fibers often very slender. 
Also in aggregates of prisms. 
Distinct crystals rare. 


Characterized by its cleavage an- 
;le. Sometimes fibrous (asbesti- 
orm. Not common. An ortho- 
hombic amphibole. 


Anthophyllite. 
(Mg,Fe)SiO,. 


Monoclinic. Long prismatic 
crystals, vertically striated. 
Acute terminations charac- 
teristic. Also in groups of 
acicular crystals. Fibrous. 


A. rare mineral. 


Acmite 
(^girite). 
NaFe(SiO,)j. 


Monoclinic. In stout pris- 
matic crystals with rectan- 
gular cross-section. 


See p. 407. 


PYROXENE 
GROUP. 



419 



NONMETALLIC 

II. Give a 

4. Cannot be scratched by a knife, 

a. Show a prominent 



Cleavage. 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


| Enstatite has 
5 fair prismatic 
I, C.,at90. 
JHypersthene 
has perfect 
g pinacoidal C. 




Gray-brown, 
green, bronze- 
brown, black. 


Pearly, bronze- 
like. 


5.5-6.5 


3.2-3.3 


& C. Prismatic 
at nearly 90. 


Rose-red, pink, 
brown. 


Vitreous. 


5-6 


3.6 


C. Basal and 
pyramidal. 


Yellow, brown, 
blue, black. 


Adamantine. 


5.5-6 


3.8-3.9 


Dodecahedral 
C., seldom 
seen. 


White, gray, blue, 
green. 


Greasy, vitreous. 


5.5-6 


2.1-2.3 



b. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Colorless or 
white. 


Vitreous. 


F. Uneven. 


5-5.5 


2.3 


-Gray, white. 
2 J2 colorless. 

gl 

'J9f*> 


Vitreous to dull. 


F. Uneven. 


5.5- 


2.5 


*T3 

J* Colorless, pale 
<D green, yellow. 

o 1 


Vitreous. 


F. Uneven. 


5-5.5 


2.9-3.0 


"3 o 
^Colorless. 
S3 white, to pale 
JJ yellow. 


Vitreous. 


F. Uneven. 


7 


3.0 


50 White, gray, 
light to dark 
green, brown. 


Vitreous to dull. 


F. Uneven. Pris- 
matic C., seldom 
seen. 


5-6 


2.7 



420 



LUSTER. 

colorless streak. 

but can be scratched by quartz. 

cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Orthorhombic. Crystals 
usually prismatic but rare. 
Commonly massive, fibrous 
or lamellar. 


Enstatite is light colored; with in- 
crease of iron, bronzito, is olive- 
green to brown, often with bronze- 
like reflections; hypersthene, rich 
in iron, is dark green to almost 
black. An orthorhombic pyroxene. 


ENSTATITE 
(Bronzite). 
MgSiO 3 . 
Hypersthene. 
(Fe,Mg)Si0 3 . 


Triclinic. Usually massive, 
cleavable to compact. 


See p. 407. 


RHODONITE. 
MnSiO 3 . 


Tetragonal. In pyramidal 
crystals. At times tabular 
with promin nt basal plane. 


A rare mineral. 


Octahedrite 
(Anatase). 
TiO 2 . 


Isometric. Massive or in 
e-n bedded grains. Rarely in 
dodecahedral crystals. 


Frequently blue. A rock-making 
mineral, never associated with 
quartz. Opaque to translucent. 


Sodalite. 
Na 4 (AICl)Al, 

(SiO 4 ) s . 



prominent cleavage. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


In trapezohedrons. 


See p. 411. 


ANALCITE. 

NaAl(SiO,) 2 H 2 O. 


Isometric. In trapezohe- 
drons. 


Characterized by its crystals. 
Usually gray in color and -with a 
dull luster. Translucent to opaque. 
Found as phenocrysts in basic 
igneous rocks, never with quartz. 


LEUCITE. 
KAl(SiO,) 2 . 


Monoclinic. Usually crys- 
tallized. 


See p. 411. 


DATOLITE. 
Ca(BOH)SiO 4 . 


Orthorhombic. In prismatic 
crystals. 


See p. 429. 


Danburite. 
CaB 2 (Si0 4 ),. 


Tetragonal. Prismatic crys- 
tals, granular or massive. 


Often altered. Opaque to translu- 
cent. 


SCAPOLITE. 
Ca 4 AUSijO 26 with 
Na 4 Al,Si,0, 4 Cl. 



421 



NONMETALLIC 

II. Give a 

4. Cannot be scratched by a knife, 

b. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Colorless, 
gray, greenish, 


Greasy, vitreous. 


F. Uneven. Pris- 
matic C., seldom 
seen. 


5.5-6 


2.6 


Apple-green, 
gray, white. 


Vitreous. 


F. Uneven. 


6-6.5 


2.9 


d. 










S 










3 Yellow- 


Vitreous. 


F. Uneven. May 


5.5 


4-4.1 


jj 3 green, white, 




show fairly good 






-^ colorless, 




C. 






*/ blue, gray, 










* brown. 










5* 










-S3 ' 










o"c3 Olive to 


Vitreous. 


F. Uneven. C., 


6.5-7 


3.3 


^"i grayish- 




rarely seen. 






jd green, brown. 










jj ^ Green, 


Vitreous. 


F. Uneven. 


7-7.5 


3-3.1 


O a brown, blue, 










<u red, pink, 
a white, black. 










! 










i 

1 Green, 


Vitreous, resinous. 


F. Uneven. 


6.5 


3.4 


_ brown, yel- 










M low, blue, 










red. 










White to 
green to 


Vitreous. 


F. Uneven. 
Rather poor pris- 


5-6 


3.1-3.4 


black. 




matic C., at 90 










angles. 






Clove-brown, gray, 


Vitreous. 


F. Conchoidal. 


6.5-7 


3.3 


green, yellow. 




Pinacoidal C., not 










prominent. 







422 



LUSTER. 

colorless streak. 

but can be scratched by quartz. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Hexagonal. Usually mas- 
sive. Rarely in small prisms. 


A rock-making mineral. Com- 
monly found in igneous rocks which 
do not contain quartz. Usually 
opaque to translucent with a greasy 
luster. 


NEPHELITE. 
NaAlSiO 4 . 


Orthorhombie. Reniform, 
globular and stalactitic with 
crystalline surface. In groups 
of tabular crystals, often bar- 
rel-shaped. Distinct crys- 
tals rare. 


Characterized by its structure and 
pale green color. Translucent. 


PREHNITE. 
HzCasAlzlSiO,),. 


Massive and in disseminated 
grains. Rarely in hexagonal 
prismatic crystals. 


Characterized by its color and 
franular structure. Associated at 
'ranklin with red zincite and black 
franklinite. Troostite is brown or 
gray in color. 


WILLEMITE. 

Zn 2 SiO 4 
Troostite. 
(Zn,Mn) 2 SiO 4 . 


Orthorhombie. Usually 
granular either in masses or 
disseminated. 


Characterized usually by its green 
color, glassy luster and granular 
structure. Occurs in basic igneous 
rocks. 


CHRYSOLITE 

(Olivine, Peridot). 
(Mg,Fe) 2 SiO 4 . 


Hexagonal, rhombohedral. 
Usually in slender prismatic 
crystals. 


See p. 431. 


TOURMALINE. 

A complex boron sil- 
icate containing 
chiefly Al, Fe, Mg, 
Mn, alkalies, F and 
OH. 


Tetragonal. In square pris- 
matic crystals terminated 
usually by base and pyramid. 
Often columnar. Granular 
massive. 


Usually green or brown in color. 
Transparent to translucent. Often 
occurs in crystalline limestones. 


VESUVIANITE 

(Idocrase) 
Ca 6 (Al(OH,F)) 
(Al,Fe) 2 (SiO 4 ) 6 . 


Monoclinic. In stout pris- 
matic crystals with rectan- 
gular cross-section. 


See p 407. 


PYROXENE 
GROUP. 


Triclinic. Crystals with 
acute edges, wedge-shaped. 
Also lamellar, lamellae often 
curved. 


Characterized by its crystal habit. 
Transparent to translucent. Not 
common. 


Axinite. 
Ca7Al 4 B 2 (Si0 4 ) 8 . 



423 



NONMETALLIC 

II. Give a 

Cannot be scratched by a knife, 

b. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Red-brown to 
brownish 
black. 


Resinous, vitreous, 
dull when altered. 


F. Uneven. 


7-7.5 


3.8 


Reddish 
brown, flesh- 
red, olive- 
green. 


Vitreous, dull 
when altered. 


F. Uneven. C. 
seldom prominent. 


7.5 
Softer when al- 
tered. 


3.2 


Brown, gray, 
green, yellow. 


Resinous, adaman- 
tine. 


F. Uneven. Pris- 
matic C. seldom 
prominent. 


5-5.5 


3.4-3.5 


Yellowish to 
g reddish brown. 


Resinous. 


F. Uneven. 


5-5.5 


5.2-5.3 


w Brown to 
black. 


Adamantine. 


F. Uneven. 


6-7 


6.8-7.1 


Reddish 
>> brown to black. 

y 


Adamantine. 


F. Uneven. C. 
not prominent. 


6-6.5 


4.2 


Hair-brown to 
black. 


Adamantine. 


F. Uneven. 


6. 


4.0 


Brown to pitch- 
black. 


Pitchy or resinous. 


F. Uneven to con- 
choidal. 


5.5-6 


3.5-4.2 


Blue, rarely 
colorless. 


Vitreous. 


F. Conchoidal. 
C. Pinacoidal not 
prominent. 


7-7.5 


2.6 



424 



LUSTER. 

colorless streak. 

but can be scratched by quartz. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Orthorhombic. In pris- 
matic crystals. 


See p. 433. 


STAUROLITE. 
(A1O)<(A1.OH) 
Fe(SiO<) 2 . 




See p. 431. 


Andalusite 
(Chiastolite). 
Al 2 SiO 6 . 


Monoclinic. Wedge-shaped 
crystals. 


Seep. 411. 


TITANITE 
(Sphene). 
CaTiSiOj. 


Monoclinic. Granular. 


A rare mineral. Heavy. 


MONAZITE. 
(Ce, La, Di)PO 4 
often with ThSiO 4 . 


In irregular masses; in rolled 
grains. 


See p. 431. 


CASSITERITE. 
(Tin Stone) SnO,. 


Tetragonal. In prismatic 
crystals vertically striated; 
often slender acicular. Crys- 
tals frequently twinned. 


Usually gives a light brown streak. 
Usually opaque to translucent. 


RUTILE. 
TiO 2 . 


Orthorhombic. Only in 
crystals. Habit varied; tab- 
ular; prismatic; resembling 
hexagonal pyramids, etc. 


A rare mineral. 


Brookite. 
TiO 2 . 


Monoclinic. Massive and in 
embedded grains. Crystals 
often tabular. 


A rare mineral. 


Allanite. 
R 2 "(R.OH)R 2 '" 
(SiO,),. 
R"=Ca and Fe. 
R" =Al,Fe,Ce,La 
Di. 


Orthorhombic. In em- 
bedded grains; also massive, 
compact. In six-sided pris- 
matic crystals. 


Transparent to translucent. Most 
commonly found altered with foli- 
ated structure, a grayish green 
color, and softer than a knife. 


lolite 
(Cordierite). 
H 2 (Mg,Fe) 4 
Al s Si 10 O n . 



425 



NONMETALLIC 

II. Give a 

4. Cannot be scratched by a knife, 

6. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Deep azure- 
blue, greenish 
blue. 


Vitreous. 


F. Uneven. 


5-5.5 


3.0-3 1 


Azure-blue. 

5 


Vitreous. 


F. Uneven. 


5-5.5 


2.4 


Blue, green, 
white, gray. 


Greasy, vitreous. 


F. Conchoidal. 
Dodecahedral C. 
seldom seen. 


5.5-6 


2.1-2.3 



Pink to red. See tourmaline, p. 423. 

Black. The following minerals may be almost or quite black; cassiterite, 

NONMETALLIC 

II. Give a 

5. Cannot be scratched 

a. Show a 



Cleavage 


Color. 


Luster. 


Hardness. 


Spec. 
Grav. 


Perfect basal C. 


Colorless, yellow, 
pink, bluish, green- 
ish. 


Vitreous. 


8 


3.5 


C. Pinacoidal. 


Hair-brown, gray, 
grayish green. 


Vitreous. 


6-7 


3.2 


C. Prismatic. 


White, gray, pink, 
emerald-green. 


Vitreous. 


6.5-7 


3.2 


C. Octahedral. 


Colorless, yellow, 
red, blue, gray, 
black. 


Adamantine. 


10 


3.5 



See also corundum, p. 429, which may sho'w a parting resembling cleavage. 

426 



LUSTER. 

colorless streak. 

but can be scratched by quartz. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Usually massive. 


Characterized by its color. 


Lazurite 
(Lapis- Lazuli). 
(Na 2 ,Ca) 2 (Al.N a S 3 ) 
Al 2 (SiO 4 ) 3 . 


Usually in pyramidal crys- 
tals. 


A rare mineral. Characterized by 
its color. Told from lazurite by its 
crystals. Opaque. 


Lazulite. 
(Mg,Fe)(Al.OH) 2 
(P0 4 ) 2 . 


Massive. 


See p. 421. 


SODALITE. 

Na 4 (AlCl)Al 2 
(Si0 4 ) 3 . 



rutile, brookite, allanite, p. 425; pyroxene and tourmaline, p. 423. 

LUSTER, 
colorless streak, 
by quartz. 

prominent cleavage. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Orthorhombic. In prismatic 
crystals, terminated by base, 
pyramids and domes. Also 
coarse to fine granular. 


Characterized by its crystals, hard- 
ness and cleavage. 


TOPAZ. 

(AlF) 2 SiO 4 
(OH) iso. with F. 


Orthorhombic. Commonly 
in long slender crystals. 


See p. 417. 


Sillimanite 
(Fibrolite). 
Al 2 SiO 6 . 


Monoclinic. 


See p. 419. 


SPODUMENE. 

(Li,Na)Al(SiO,) 2 . 


Isometric. In octahedral 
crystals, faces usually rough 
and curved. In irregular 
rounded pieces. 


Characterized by its extreme hard- 
ness. Hare. 


Diamond. 
C. 



427 



NONMETALLIC 

II. Give a 

5. Cannot be scratched 

6. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Colorless, 
white, 
smoky, ame- 
thyst. Vari- 
ously colored 
when impure. 

fs 


Vitreous, greasy. 


F. Conchoidal 


7 


2.6 


o u Colorless, 
gjj'S white to pale 
, "S yellow. 

Is 
i 


Vitreous. 


F. Uneven. 


7 


3.0 


8 " 

.S 32 White, color- 
Q less. 


Vitreous. 


F. Conchoidal. 


7.5-8 


2.9 


White, gray, 
blue, yellow, 
brown, green, 
pink, red. 


Adamantine to 
vitreous. 


F. Uneven. 


9 


4.0 


Lavender, 
blue, green, 
brown, red, 
fl . black. 


Vitreous. 


F. Conchoidal. 


8 


3.5-3.8 


j^ Bluish green, 
g green, yellow, 
pink, colorless. 
5 

r 

>> 
i 


Vitreous. 


F. Conchoidal, 
uneven. 


7-7.5 


2.7 


IB 

Yellowish to 
emerald- 
green. 


Vitreous. 


F. Conchoidal, 
uneven. C. not 
Drominent. 


8.5 


3.6-3.8 



428 



LUSTER. 

colorless streak, 
by quartz. 

prominent cleavage. 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Rhombohedral, trapezohe- 
dral. Irregular massive; in 
embedded grains; as pebbles, 
sand. Crystals usually show 
hexagonal prism terminated 
by what appears to be a hex- 
agonal pyramid. Prism 
faces are striated horizon- 
tally. Crystals frequently 
tapering. 


Characterized by its crystals; its 
conchoidal fracture and vitreous 
luster. For description of varieties 
see pp. 175-177. Transparent to 
translucent. Most common min- 
eral. 


QUARTZ. 

SiO 2 . 


Orthorhombic. In prismatic 
crystals, resembling those of 
topaz. Also disseminated in 
indistinct crystals and irreg- 
ular masses. 


Characterized by its crystals. 
Distinguished from topaz by its 
lack of cleavage. Transparent to 
translucent. A rare mineral. 


Danburite. 
CaB 2 (Si0 4 ) 2 . 


Rhombohedral. In small 
rhombohedral crystals. 


A rare mineral. 


Phenacite. 
Be 2 SiO 4 . 


Hexagonal, rhombohedral. 
In irregular masses showing 
at times an almost cubic 
structure owing to a rhombo- 
hedral parting. In rude 
prisms, often barrel-shaped. 


Characterized by its extreme hard- 
ness. Ruby = red; sapphire = blue; 
various other colors. Emery is im- 
pure corundum usually with magne- 
tite. May show rhombohedral 
parting with nearly 90 angles. 


CORUNDUM. 

A1 2 3 . 


Isometric. In octahedrons; 
sometimes twinned. 


Characterized by its crystals and 
its hardness. Ruby spinel when 
red. 


SPINEL. 
MgAl 2 4 . 


Hexagonal. Usually in pris- 
matic crystals with basal 
plane; pyramid faces rare. 
Sometimes deeply furrowed 
vertically. Crystals at times 
large. Also irregular, mas- 
sive. 


Often shows a mottling of color due 
to alternation of transparent and 
opaque spots. Crystals very char- 
acteristic. Most common color = 
blue-green, known as aqua-marine; 
also deep green as emerald; yellow 
as golden beryl; pink as morganite. 
Found in pegmatite veins. 


BERYL. 

Be 3 Al 2 (Si0 3 ) 8 iH 2 0. 

> 


Orthorhombic. In tabular 
crystals which are frequently 
twinned giving hexagonal 
shapes. 


A rare mineral. Characterized by 
its hardness. 


Chrysoberyl 
(Alexandrite). 
BeAl 2 O 4 . 



429 



NONMETALLIC 

H. Give a 

5. Cannot be scratched 

b. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Green, 
brown, blue, 
M red, pink, 
S white, black. 

d. 
^r 

if 


Vitreous. 


F. Uneven. 


7-7.5 


3.0-3.1 


S-s " 
aj Green, gray, 
*| white. 

fS 

5^ 


Vitreous. 


F. Splintery. C., 
prismatic at 
nearly 90 angles, 
not prominent. 


7 


3.3 


3 
If Olive to gray 
J2 iah green, 
iB.a brown, 
g aJ 


Vitreous. 


F. Uneven. C. 
rarely seen. 


6.5-7 


3.3 


1 flreen, 
-^ brown, yel- 
o low, blue, 
o red. 


Vitreous, resinous. 


F. Uneven. 


6.5 


3.4 


J Dark green. 


Vitreous. 


F. Conchoidal, 
uneven. 


7.5-8 


4.5 


Reddish brown 
to black. 

I , ; 


Adamantine. 


F. Uneven. C. 
not prominent. 


6-7 


6.8-7.1 


J Reddish 
O brown, flesh- 
red, olive- 
green. 


Vitreous, dull 
when altered. 


F. Uneven. C. 
seldom prominent. 


7.5 


3.2 



430 



LUSTER, 
colorless streak, 
by quartz. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Rhombohedral. Usually in 
slender prismatic crystals, 
striated vertically. Cross- 
section usually resembles a 
spherical triangle. When 
terminated usually shows 
base and rhombohedrons. 
Often in slender radiating 
crystals. 


Widely various in color. Most com- 
monly black. Of the lighter colors 
jjreen is most frequent. ^Character- 
:zed by its crystal * structure. 
Crystals exhibit pyro-electricity; 
i.e., after being heated they will 
attract and hold small pieces of tis- 
sue paper, etc., A candle flame may 
be used. Found in pegmatite veins 
and metamorphic rocks. 


TOURMALINE. 

A complex boron sil- 
icate containing 
chiefly Al.Fe.Mg, 
Mn, alkalies F and 
(OH). 


Always massive, usually 
closely compact. 


Translucent. A rare mineral. 


Jadeite 
(Jade). 
NaAlSi 2 O. 


Orthorhombic. Usually 
granular. 


See p. 423. 


CHRYSOLITE 

(Olivine, Peridot). 
(Mg,Fe) 2 SiO 4 . 


Tetragonal. 


See p. 423. 


Vesuvianite 
(Idocrase). 
Ca 6 (Al(OH,F)) 
(Al,Fe) 2 (Si0 4 ) 5 . 


Isometric. Usually in octa- 
hedrons. Sometimes 
twinned. 


Characterized by its. crystals and 
hardness. A variety of spinel; see 
p. 429. 


Gahnite 
(Zinc Spinel). 
ZnAl 2 O 4 . 


Tetragonal. In irregular 
masses; in compact fibrous, 
reniform structure; in rolled 
grains. Rarely in prismatic 
crystals, twins. 


Very heavy. Usually opaque to 
translucent. Often gives a light- 
brown streak. Usually to be 
scratched by quartz with difficulty. 
Occurs as rolled grains in sand, in 
pegmatite veins and in granite 
rocks. 


CASSITERITE 

(Tin Stone). 
SnO 2 . 


Orthorhombic. In coarse 
prismatic crystals with 
nearly square cross-section. 


Often soft on surface due to altera- 
tion. Frequently a cross-section of 
a crystal will show a dark-colored 
cross due to a regular arrangement 
of impurities in the interior of crys- 
tal. Occurs in rnetamorphic rocks, 
usually clay slates. 


Andalusite 
(Chiastolite). 
Al 2 SiO s . 



431 



NONMETALLIC 

II. Give a 

5. Cannot be scratched 

6. Do not show a 



Color. 


Luster. 


Cleavage and 
Fracture. 


Hardness. 


Spec. 
Grav. 


Clove-brown, 


Vitreous. 


F. Conchoidal. 


6.5-7 


3.3 


green, yellow, 




C. Pinacoidal, 






gray. 




not prominent. 






Red-brown 
to brownish 


Resinous, vitreous. 
Dull when altered. 


F. Uneven. 


7-7.5 


3.7 


d black. 










jg'3 Brown, red, 
o.S gray, green, 
jg colorless. 


Adamantine. 


F. Conchoidal. 
C. prismatic not 
prominent. 


7.5 


4.7 


w > 










sS 

S3 a Usuallv 


Vitreous. 


F. Uneven. 


6.5-7.5 


3.1-4.3 


$ brown to red. 










jj? 02 Also various 










shades of yel- 










-S low, green, 










u pink, etc. 


' 









Yellow minerals, see corundum, beryl, p. 429, axinite and garnet above. 
Pink to red minerals, see corundum, spinel, boryl, p. 429, tourmaline, p. 431, and 
garnet above. 

Black mineral, see tourmaline, p. 431. 



432 



LUSTER, 
colorless streak, 
by quartz. 

prominent cleavage. (Continued.) 



Crystallization and 
Structure. 


Remarks. 


Name and 
Composition. 


Triclinic. 


See p. 423. 


Axinite. 
Ca 7 Al 4 B 2 (Si0 4 ) 9 . 


Orthorhombic. In prismatic 
crystals; very commonly in 
cruciform penetration twins. 


Characterized by its crystals. May 
ae altered to earthy material in 
which case it can be softer than a 
knife. Opaque to translucent. 
Occurs in mica schist. 


STAUROLITE. 

(AlO) 4 (Al.OH)Fe 

(SiO 4 ) 2 . 


Tetragonal. Usually in 
small prisms terminated by 
pyramid of the same order. 
As rolled grains in sand. 


Characterized by its crystals. 
Usually opaque. 


ZIRCON. 
ZrSiO 4 . 


Isometric. Commonly as 
dodecahedrons trapezohe- 
drons or a combination of the 
two. In rolled grains. 


Grossularite=Ca 3 Al 2 (SiO4)3. usu- 
ally light yellow or green. Pyrope 
= M g3 Al 2 (Si0 4 ) ? , deep red. Al- 
mandite = Fe 3 Al 2 (SiO 4 ) 3 , brown to 
red. Spes?artite = Mn 3 Al 2 (SiO4) 3) 
red. Andradite = Ca 3 Fe 2 (SiO 4 ) 3 , 
green, yellow, brown, to black. 
Uvarovite = Ca 3 Cr 2 (SiO 4 ) 3 , emer- 
ald-green. Characterized by crys- 
tal shape and commonly its red 
color. An accessory rock mineral. 
Commonly in metamorphic rocks. 
As sand. 


GARNET. 

R" 3 R'" 2 (SiO 4 ) 3 . 
R" = Ca.Mg.Fe.Mn 
R'" = Al.Fe.Cr. 



433 



INDEX TO DETERMINATIVE TABLES. 



Acmite, 419 
Actinolite, 407 
Alabandite, 381 
Albite, 419 
Allanite, 425 
Amblygonite, 415 
Amphibole, 407, 419 
Analcite, 411, 421 
Anatase, 421 
Andalusite, 425, 431 
Andesine, 419 
Anglesite, 399 
Anhydrite, 397, 409 
Anorthite, 419 
Anthophyllite, 407, 

419 

Antimony, 375 
Apatite, 413 
Apophyllite, 405 
Aragonite, 411 
Argentite, 373 
Arsenic, 375 
Arsenopyrite, 383 
Atacamite, 391 
Augite, 407 
Axinite, 423, 433 
Azurite, 391 

Barite, 399, 409 
Bauxite, 401, 413 
Beryl, 429 
Biotite, 393 
Bismuth, 381 
Bismuthinite, 375 
Borax, 399 
Bornite, 377 
Bournonite, 375 
Brochantite, 391 
Bronzite, 421 



Brookite, 425 
Brucite, 393 

Calamine, 411 
Calaverite, 377 
Calcite, 397, 407 
Carnallite, 399 
Cassiterite, 389, 425, 

431 

Celestite, 399 
Cerargyrite, 395 
Cerussite, 401 
Chabazite, 409 
Chalcanthite, 391 
Chalcocite, 373 
Chalcopyrite, 377 
Chloanthite, 383 
Chromrte, 379, 385 
Chrysoberyl, 429 
Chrysocolla, 391 
Chrysolite, 423, 431 
Cinnabar, 371, 381, 

387 

Clinochlore, 393 
Cobaltite, 383 
Colemanite, 405 
Columbite, 385 
Copper, 381 
Corundum, 429 
Covellite, 377 
Crocoite, 389 
Cryolite, 401 
Cuprite, 379, 387 
Cyanite, 403, 417 

Danburite, 421, 429 
Datolite, 411, 421 
Diamond, 427 
Diaspore, 417 
434 



Diopside, 407 
Dolomite, 397, 407 

Embolite, 395 
Enargite, 373 
Enstatite, 421 
Epidote, 417 

Fluorite, 409 
Franklinite, 385 

Gahnite, 431 
Galena, 371, 375 
Garnet, 423 
Garnierite, 403 
Genthite, 403 
Gersdorffite, 383 
Goethite, 381, 387, 

389 

Gold, 381 
Graphite, 371 
Greenockite, 401 
Gypsum, 395 

Halite, 397 
Harmotone, 405 
Hematite, 371, 379, 

385, 387 
Heulandite, 405 
Hornblende, 407 
Hypersthene, 421 

Ilmenite, 385 
lolite, 425 

Jadeite, 431 
Jamesonite, 323 

Kaolinite, 401 



INDEX 



435 



Kalinite, 399 

Labradorite, 419 
Lazulite, 427 
Lazurite, 415, 427 
Lepidolite, 397 
Lepidomelane, 393 
Leucite, 421 
Limonite, 371, 381, 

387, 389 
Linnseite, 383 
Lithiophyllite, 403 

Magnetite, 383 
Magnesite, 409 
Malachite, 391 
Manganite, 379 
Marcasite, 383 
Margarite, 397 
Microcline, 417 
Millerite, 377 
Mimetite, 401, 413 / 
Molybdenite, 371 
Monazite, 413, 425 
Muscovite, 393 

Natrolite, 405, 411, 

417 

Nephelite, 423 
Niccolite, 377, 383 
Niter, 395 

Octahedrite, 421 
Oligoclase, 419 
Olivenite, 391 
Olivine, 423, 431 
Orpiment, 391 
Orthoclase, 417 

Pectolite, 405, 411 
Pentlandite, 377 
Phenacite, 429 



Phlogopite, 393 
Platinum, 381 
Plagioclase'Feldspars, 

419 

Polybasite, 373 
Prehnite, 423 
Proustite, 387 
Psilomelane, 373, 385 
Pyrargyrite, 379, 387 
Pyrite, 383 
Pyrolusite, 371, 373 
Pyromorphite, 413 
Pyrophyllite, 393 
Pyrrhotite, 377 
Pyroxene, 407, 413, 

419, 423 

Quartz, 429 

Realgar, 389 
Rhodochrosite, 409 
Rhodonite, 407, 421 
Rutile, 389, 425 

Scapolite, 411, 421 
Scheelite, 413 
Serpentine, 403, 415 
Siderite, 409 
Sillimanite, 417, 427 
Silver, 381 
Smalltite, 383 
Smithsonite, 409, 411 
Sodalite, 409, 415, 

421, 427 
Soda Niter, 395 
Sphalerite, 379, 389, 

409 

Spinel, 429 
Spodumene, 419, 427 
Stannite, 375 
Staurolite, 425, 433 



Stephanite, 373 
Stibnite, 371, 375 
Stilbite, 403 
Stromeyerite, 373 
Sulphur, 391, 395 
Sylvanite, 377 
Sylvite, 395, 397 

Talc, 393 
Tantalite, 385 
Tellurium, 375 
Tetrahedrite, 373 
Thorite, 389 
Titanite, 411, 425 
Topaz, 427 
Tourmaline, 423, 431 
Tremolite, 407 
Triphyllite, 403 
Turgite, 379, 385, 387 

Uraninite, 385 

Vanadinite, 401 
Vesuvianite, 423, 431 
Vivianite, 391, 395, 
397 

Wavellite, 403, 415 
Willemite, 415, 423 
Witherite, 397, 401, 

405, 411 
Wolframite, 379, 385 

389 

Wollastonite, 405,415 
Wulfenite, 413 

Xenotine, 413 

Zincite, 389 
Zircon, 433 
Zoisite, 417 



APPENDIX I. 



LIST OF MINERALS SUITABLE FOR A SMALL 
MINERAL COLLECTION. 

For the convenience of those who desire to possess a small 
but representative mineral collection the following list is given. 
The names of the more important species are printed in black- 
face type, and the names of other desirable but less important 
minerals in ordinary type. The first list includes 59 names, 
while the complete list numbers 109. 



Graphite 

Sulphur 

Gold in quartz 

Silver 

Copper 

Orpiment 

Stibnite 

Molybdenite 

Galena 

Argentite 

Chalcocite 

Sphalerite 

Cinnabar 

Millerite 

Niccolite 

Pyrrhotite 

Bornite 

Chalcopyrite 

Pyrite 

Marcasite 

Arsenopyrite 

Tetrahedrite 

Halite 

Fluorite 

Cryolite 

Quartz (several 

varieties) 
Opal 
Cuprite 
Zincite 
Corundum 
Hematite 
Spinel 
Magnetite 
Franklinite 
Chromite 
Cassiterite 
Rutile 



Pyrolusite 

Manganite 

Limonite 

Brucite 

Calcite 

Dolomite 

Siderite 

Rhodochrosite 

Smithspnite 

Aragonite 

Witherite 

Strontianite 

Cerussite 

Malachite 

Azurite 

Orthoclase 

Albite 

Oligoclase 

Labradorite 

Leucite 

Pyroxenes (several 
varieties) 

Spodumene 

Pectolite 

Rhodonite 

Amphibole (sev- 
eral varieties) 

Beryl 

Garnet 

Chrysolite 

Willemite 

Scapolite 

Vesuvianite 

Zircon 

Topaz 

Andalusite 

Cyanite 

Datolite 



Epidote 
Prehnite 

Calamine 

Tourmaline 

Staurolite 

Apophyllite 

Heulandite 

Stilbite 

Chabazite 

Analcite 

Natrolite 

Muscovite 

Lepidolite 

Biotite 

Phlogopite 

Clinochlore 

Serpentine 

Talc 

Kaolinite 

Chrysocolla 

Titanite 

Columbite 

Monazite 

Apatite 

Pyromprphite 

Mimetite 

Vanadinite 

Turquois 

Uraninite 

Barite 

Celestite 

Anglesite 

Anhydrite 

Wolframite 

Scheelite 

Wulfenite 



436 



APPENDIX II. MINERAL STATISTICS. 

INTRODUCTION. 

Brief statistics relative to the amount and value of the pro- 
duction of the different economic minerals and metals are pre- 
sented below. The figures have been taken from the bulletin 
of the United States Geological Survey entitled Mineral Re- 
sources of the United States for 1915. Unless otherwise stated 
all statistics refer to productions from the United States. It 
should be noted that because of the European war the condi- 
tions affecting mineral production during 1915 were abnormal 
in several respects. In the case of many metals there was a 
marked increase in the amounts produced and the prices obtained 
were exceptionally high. 

SUMMARY OF THE MINERAL PRODUCTION 
OF THE UNITED STATES FOR 1915. 

Metals. 

Pig Iron $401,409,604 Zinc $113,617,000 

Silver 37,397,300 Mercury 1,826,912 

Gold 101,035,700 Aluminum 17,985,500 

Copper 242,902,000 

Lead 47,660,000 Total $993,000,000 

Nonmetals. 

Bituminous Coal. $502,037,688 Sand (Molding, etc.) $21,514,977 

Anthracite Coal. . 184,653,498 Slate 4,958,915 

Natural Gas 101,312,381 Stone. 74,595,352 

Petroleum 179,462,890 Borax 1,677,099 

Clay Products.. 163,120,232 Gypsum 6,596,893 

Cement 75,155,102 Phosphate Rock. . . 5,413,449 

Ume 14,336,756 Pyrite 1,674,933 

437 



438 APPENDIX 



Nonmetals (Continued) 

Sulphur $5,954,236* Glass Sand $1,606,640 

Salt 11,747,686 Graphite 429,631 

Mineral Paints . . 15,514,059 Mica 428,769 

Asphalt 5,242,073 Mineral Waters 5,138,794 

Bauxite 1,514,834 Quartz 273,553 

Feldspar. . . ' 629,356 Talc 1,891,582 

Gems 170,431 Tungsten Ores 4,100,000 



Total $1,393,565,098 

Total value of all mineral products = $2,393,831,951. 
* 1914. 

Aluminium. 

The production of bauxite, the ore of aluminium, in 1915 had 
a value of $1,514,834. The consumption of the metal totaled 
99,806,000 pounds. Its price varied from 19 to 60 cents per 
pound. 

Antimony. 

Only a small amount of antimony ore is mined in the United 
States. The domestic source of the metal is largely confined 
to the smelting of antimonial lead ores where it is obtained in 
the nature of a by-product. The total value of the antimony 
produced during 1915, was $2,100,000. 

Apatite, see Phosphate Rock. 

Arsenic. 

Arsenic, chiefly in the form of the oxide, is produced by only a 
few companies in the United States and the total production is 
comparatively small. It is practically all obtained as a by- 
product from the smelting of ores that contain small amounts 
of the metal. A large part of the production comes from the 
smelting of the copper ores at Butte, Montana, which contain 
arsenic in the form of the mineral enargite. The amount of 
arsenic oxide, or white arsenic, produced in 1915 was 5,498 tons 
with a value of $302,116. 



APPENDIX 



439 



Asbestos. 

The amount of asbestos produced is small, amounting to 
$76,952 worth in 1915. Imports for the same year had a value 
of $1,981,483. 

Barite. 

The value of the barite produced in 1915 was $381,032. The 
largest amount came from Missouri. 

Bauxite, see Aluminum. 

Bismuth. 

Little bismuth was produced in 1915. Imports of the metal 
reached the value of $108,288. 

Borax. 

A considerable amount of the borates produced in the United 
States comes from the mineral colemanite. All the borates 
mined are grouped together, however, under the title borax. 
The value of the production for 1915 was $1,677,099. 

Calcite. 

Following are the .statistics for the production of Portland 
Cement for 1915. 





Quantity in 
Barrels. 


Value of 
Shipments. 


Pennsylvania 


28,648,941 


$20,252,961 


Indiana 


8,145,401 


7,336,821 


Kansas 


3,580,287 


2,826,443 


California 


4,503,306 


6,338,918 


Illinois 


5,156,869 


4,884,026 


Missouri 


4,626,771 


4,007,679 


New Jersey 


1,579,173 


1,473,499 


Michigan 


4,765 294 


4,454,608 


New York 


5,043,889 


4,039,215 


Iowa 


4,559,630 


4,119,952 


Ohio 


1,948,826 


1,917,920 


Texas 


1,939,363 


2,518,233 


Washington 


1,496,216 


1,790,499 


12 other states 


9,920,941 


8,795,900 


Total 


85,914,907 


$74,756,674 









Total production of cement of all classes for 1915 had a value 

of $74,285,248. 



440 



APPENDIX 



The value of the production of limestone for the year 1915 
follows: 



Illinois $2,864,103 

Indiana 4,204,092 

Missouri 1,927,534 

New York 3,018,871 

Michigan 1,828,766 



Ohio $4,4051590 

Pennsylvania 6,367,446 

Virginia 1,534,545 

Other states 9,078,919 

Total ,$35,229,866 



Cement, see above. 

Chromite. 

The production and imports of chromite for the year 1915 
follow. Chromite wholly from California, 3,281 tons; value 
$36,744. Imported, chiefly from New Caledonia, British South 
Africa, Portuguese Africa and Canada, 76,455 tons; value 
$780,061. 

Clay. 

The total value of the various kinds of clay produced in 1915 
was $3,971,941. The value of kaolin produced was $241,520. 
The value of kaolin imported during 1915 was $1,152,778. The 
total value of all brick and tile products was $125,794,844; that 
of pottery products was $37,325,388. 

' Copper. 

The amounts of copper produced in the years 1905, 1910 and 
1915 follow: 





1905. 


1910. 


1915. 


Alaska 


Pounds. 

4,900,866 


Pounds. 

4,311,026 


Pounds. 

70,695,286 


Arizona 


235,908,150 


297,250,538 


432,467,690 


California 


16,697,489 


45,760,200 


37 658 444 


Colorado 


9,404,830 


9,307,497 


7 272 178 


Idaho 


7,321,585 


6,877,515 


6 217 728 


Michigan 


230,287,992 


221,462,984 


238,956,410 


Montana 


314,750,582 


283,078,473 


268,263,040 


Nevada . . 


413,292 


64,494,640 


67,757,322 


New Mexico 
Tennessee . 


5,334,192 


3,784,609 
16,691,777 


62,817,234 
18,205,308 


Utah 


58,153,393 


125,185,455 


175,177,695 


Other states 


18,735,472 


2,944,795 


2,521,192 


Total 


901,907,843 


1,080,159,509 


1,388,009,527 



APPENDIX 



441 



Note. Practically the entire production of Michigan is 
from native copper; that of the other states is from various other 
ores. 

The value of copper varies quite widely from year to year. 
One pound was worth about 16.75 c. in 1900; 15.63 c. in 1905; 
13 c. in 1910; 17.47 c. in 1915. 

The United States furnished in 1913 approximately one-half 
of the total world's production. Statistics are not available 
for subsequent years. Other countries that have produced 
notable amounts of copper are Mexico, Spain, Portugal, Japan, 
Australasia, Chile, Canada, Germany. 

Corundum. 

The production of corundum for abrasive purposes is practi- 
cally negligible. Since 1898, when the production was valued 
at $275,064, it has rapidly fallen until in 1915 the only corundum 
produced was in the form of emery with a total value for the 
year of $31,131. Considerable amounts of emery are imported, 
the value for 1915 being $271,649. The decline hi the domestic 
production of corundum is due in large part to the manufacture 
of the artificial abrasives, carborundum and alundum. The 
value of such materials produced in 1915 was $2,248,778. For 
the production of corundum as sapphire, see under gem stones. 

Feldspar. 

The amount of feldspar sold hi 1915 was as follows: 





Quantity. 


Value. 


Connecticut . 


Tons. 

13,510 


$73,124 


Maine 


27,878 


191,456 


Maryland 


12,485 


36,861 


New York 


17,375 


65,988 


Pennsylvania 


15,830 


120,984 


Other states 


26,691 


140,943 








Total 


113,769 


$629,356 









442 



APPENDIX 



Fluorite, Fluorspar. 

The production of fluorite during 1915 was as follows: 
Colorado, New Hampshire and New Mexico, $10,562; Illinois, 
and Kentucky, $753,913. 

Garnet. 

The value of garnet produced for an abrasive during 1915 was 
$139,584. 

Gem Stones. 

The value of the gems and ornamental stones produced in the 
United States for 1915 was $170,431. More than 20 different 
minerals contributed to this total, the majority of them being 
found in small amounts, however. The values of the produc- 
tion of the more important stones follow: Sapphire, $88,214; 
Tourmaline, $10,969; Turquoise and turquoise matrix, $11,691. 



Gold. 

The values of the gold production in the years 1905, 1910 and 
1915 are given below. 





1905. 


1910. 


1915. 


Alaska 


$15,630,000 


$16,126,749 


$16 710 000 


Arizona 


2,799,214 


3,149,366 


4,555 900 


California. . . ... 


18,898,545 


19,715,440 


22,547,400 


Colorado 


25,023,973 


20,507,058 


22,530,800 


Idaho 


1,075,618 


1,096,842 


1,170,600 


Montana. ... . . 


4,794,083 


3,730,486 


4,978,300 


Nevada 


5 269 819 


18 878 864 


11,883,700 


Oregon. . 


1 405 235 


679 488 


1 867 100 


South Dakota 
Utah 


6,989,492 


5,402,257 


7,403,500 
3,907,900 


Other states 


6,274,102 


5,647,228 


3,483,500 


Total . . . 


$88,159,881 


$94,933 778 


$101,035,700 











APPENDIX 



443 



The gold production of the leading countries for the year 1915 
follows : 

United States. . . . $101,035,700 Africa $217,639,599 

Canada 18,936,971 Japan 5,385,917 

Mexico 6,559,275 China 2,804,692 

Russia 28,586,392 India 11,522,457 

Australasia 49,397,797 

Total including all other countries $470,466,214 



Graphite. 

The production of natural graphite hi 1915 was as follows: 





Quantity. 


Value. 


Alabama 


Pounds. 
3,474,800 


$204,572 


6 other states 


5,961,200 


225,059 








Total 


9,436 000 


$429,631 









Artificial graphite produced hi 1915 amounted to 2,542 tons; 
value, $99,633. 
Ceylon produced graphite in 1913 with a value of $2,935,529. 



Gypsum. 

The value of the gypsum produced in the various states for 
1915 follows: 



California $113,863 

Iowa 1,278,128 



Oklahoma and Texas $814,109 
Utah 75,835 



Kansas 

Michigan 686,309 

New York 1,267,706 

Ohio 772,520 



250,014 Wyoming 103,110 

Other states 1,235,299 



Total...: $6,596,893 



444 



APPENDIX 



Iron. 

The production in long tons of the different iron ores by 
states is given in the following table for 1915. 





Hematite. 


Limonite. 


Magnetite. 


Alabama 
Michigan . . . 


4,374,309 
12,514,516 


935,045 




Minnesota 


33 464,660 






New Jersey 






415,234 


New York 


71,207 




927,638 


Pennsylvania 




22,552 


340,757 


Tennessee 


181,509 


100,469 


2,207 


Virginia 


38,506 


309,536 




Wisconsin 


1,095,388 






Other states 


486, 163 


142,291 


101,048 










Total 


52,227,324 


1,488,709 


1,807,002 



Total of all ores = 55,526,490 tons. 



Production of Lake Superior District by ranges in long tons. 





Marquette. 


Menominee. 


Gogebic. 


Vermilion. 


Mesabi.* 


1880 


1,384,010 


524,735 








1885 


1,430,862 


690,435 


" 119,590' 


"'227,675' 




1890 


2,863,848 


2,274,192 


2,914,081 


891,910 




1895 


1,982,080 


1,794,970 


2,625,475 


1,027,103 


' 2,839,350' 


1900 


3,945,068 


3,680,738 


3,104,033 


1,675,949 


8,158,450 


1905 


3,772,645 


4,472,630 


3,344,551 


1,578,626 


20,156,566 


1910 


4,631,427 


4,983,729 


4,746,818 


1,390,360 


30,576,409 


1915 


3,817,892 


4,665,465 


4,996,237 


1,541,645 


30,802,409 


Total to end of 












1915 


116,266,083 


98,253,341 


87,900,570 


37,942,442 


369,658,988 



The Mesabi District first shipped ore in 1892. 



Total for Lake Superior District to end of 1915 = 713,213,051 
tons. 



APPENDIX 445 

Kaolin, see Clay. 
Lead. 

The production of lead in 1915 follows: 

Short Tons. 

Colorado 32,352 

Idaho 160,680 

Missouri e 195,634 

Utah 106,105 

Other states 42,241 

Total 537,012 

Its various uses were divided in 1909 as follows: 

Short Tons. 

White lead and oxides 134,138 

Pipe 52,914 

Sheet 23,421 

Shot 36,433 

Other purposes 104,094 

The average price of lead for 1915 was 4.7 cents per pound. 

Limestone, see Calcite. 
Magnesite. 

The production of magnesite for 1915 amounted to 30,499 tons, 
valued at $274,491. The imports of the mineral were valued at 
$487,211. 

Manganese. 

The United States produces only small amounts of manganese 
ores. The output comes from Georgia, California, Virginia, 
Arkansas, etc., and was valued in 1915 at $113,309. A larger 
amount of manganiferous ores, in which the manganese is saved 
as a by-product, was produced. The imports of manganese 
ores were valued at $2,655,980. 



446 APPENDIX 

Mercury. 

The production of mercury (quicksilver) for 1915 was as 
follows : 

California, 14,283 flasks (75 Ibs. each); value, $1,174,881 
Arizona, Oregon, Texas, 4,423 flasks " 442,120 

Nevada, 2,327 " 209,911 

Mica. 

The total value of the mica produced during 1915 was $428,769. 
Importations during the same year were valued at $692,269. 

Monazite. 

There has been no domestic production of monazite since 1910. 
The importations of monazite, thorium oxide and thorium 
nitrate for 1915 had a value of $332,073. 

Nickel. 

No nickel ores are known to have been mined in the United 
States in recent years. The value of the nickel ore and matte 
imported during 1915 was $7,629,686. 

Phosphate Rock. 

The production of phosphate rock during 1915 was as follows: 

Value. 

Florida $3,762,239 

Tennessee 1,327,747 

South Carolina 310,850 

Other states. 12,613 

Total $5,413,449 

Platinum. 

The value of the platinum produced in the United States is 
small, being $23,500 in 1915. Russia produced 200,450 ounces 
in 1905, 275,000 ounces in 1910, and 124,000 ounces in 1915. 
Other sources at present are negligible. The value of importa- 



APPENDIX 



447 



tions into the United States of unmanufactured and manu- 
factured platinum in 1915 amounted to more than $2,412,008. 
The price of platinum has been steadily rising. Platinum in 
ingots at New York during 1915 varied from $38.00 to $85.50 
per ounce. 

Potash Salts. 

The value of potash salts produced in the United States in 
1915 was $342,000. The value of the various salts imported 
during 1915 was $3,765,224. 

Pyrite. 

The production of pyrite by states for 1915 follows: 





Long Tons. 


Value. 


California 


132,270 


$496,111 


Illinois and Indiana 
Ohio 


15,821 
10,857 


25,556 
27,404 


Virginia 


145,050 


729,644 


Wisconsin 


13,985 


43,354 


Other states . 


76,141 


352,864 








Total.... 


394,124 


$1,674,933 



Average price per ton = $4.25. 

Quartz. 

Pure crystalline quartz, used for pottery, scouring soaps, 
paints, etc., brings about $2.00 to $3.50 per ton in its crude form. 
The purer varieties of quartzite and sandstone, used for the same 
purposes, are worth from $1.00 to $2.00 a ton. The total pro- 
duction of quartz for these purposes, and including that used as 
a flux or for abrading purposes for 1915, had a value of $273,553. 
The value of the sandstone production in the United States for 
the same year was $6,095,800. Sand, used for glass, moulding, 
building, etc., was produced from a great number of states, 
Pennsylvania, Ohio, New York, Illinois, New Jersey, Indiana 
and Michigan leading in the order named and had a total value, 
in 1915, of $23,121,617. 



448 



APPENDIX 



Rutile, see Titanium. 
Salt. 

The production of salt in the different important states for 
1915 follows: 





Quantity. 


Value. 


California 


(In barrels of 280 
Ibs.) 

1 048 457 


$694 070 


Kansas 


3,765,164 


1,035,879 


Michigan 


12 588,788 


4 304 731 


New York 


11,217,471 


2 976 405 


Ohio 


5,880,243 


1 462 192 


Texas . . . 


444,978 


345,944 


Utah 


394,850 


266,334 


West Virginia : 


232,239 


115,143 


Other states 


2,659,306 


546,988 








Total 


38,231,496 


$11 747 686 









Silver. 

The amounts and values of the silver production for the years 
1905, 1910 and 1915, are given below: 





19 


05. 


19 


10. 


19 


15. 




Ounces. 


Commer- 
cial Value. 


Ounces. 


Commer- 
cial Value. 


Ounces. 


Commer- 
cial Value. 


Arizona 


2,605,712 


$1,573,850 


2,566,528 


$1,385,925 


5,665,672 


$2,826,500 


Colorado 


11,499,307 


6,945,581 


8,509,598 


4,595,183 


7,199,745 


3,591,900 


Idaho 
Montana . ... 
Nevada 
Utah 
Other states.'. 


8,679,093 
13,231,300 
6,482,081 
11,036,471 
2,738,522 


5,242,172 
7,991,705 
3,915,177 
6,666,028 
1,543,926 


7,369,742 
12,162,857 
12,479,871 
10,466,971 
3,847,942 


3,979,661 
6,567,942 
6,739,130 
5,652,164 
2,183,190 


13,042,466 
14,423,173 
14,453,085 
13,073,471 
7,103,463 


6,506,800 
7,195,600 
7,210,500 
6,522,200 
3,543,800 


Total 


56,272,496 


$33,988,587 


57,598,509 


$31,103,195 


74,961,075 


$37,397,300 



Two thirds of the world's total production of silver comes 
from Mexico, United States and Canada, arranged in the order 
of their importance. 



APPENDIX 449 

The commercial value of silver varies quite widely from year 
to year. An ounce was valued in 1900 at 61.6 c., in 1905 at 
60.4 c., in 1910 at 49.3 c., and in 1915 at 51.9 c. 

Soapstone, see Talc. 
Sulphur. 

The value of the sulphur produced in 1914, chiefly from 
Louisiana and Texas was $5,954,236. The value of the imports 
for the same year was $477,937. 

Talc and Soapstone. 

The production of talc and soapstone for 1915 follows. 

New Jersey and Vermont $409,652 

Pennsylvania $56,466 Virginia 504,742 

New York 864,843 Other states 34,758 

North Carolina 21,501 Total $1,891,582 

Tin. 

The domestic production of tin is negligible. The value of 
the imports of the metal for 1915 was $38,854,597. 

Titanium. 

Very little rutile is produced hi the United States. The 
localities in Nelson County, Virginia, are the only ones that have 
been worked recently. The value of the rutile produced from 
them in 1915 was $27,500. The value of the mineral varies 
according to purity from $40 to $150 per ton. 

Tourmaline, see Gem Stones. 
Tungsten. 

The total value of tungsten concentrates produced during 
1915 was $4,100,000. These come chiefly from California and 
Colorado. 



450 APPENDIX 

Turquoise, see Gem Stones. 
Zinc. 

The production of zinc in the United States for 1915 is given 
below. 

Short Tons. 

Colorado 52,297 

Kansas 14,365 

Missouri 136,300 

Montana 93,573 

New Jersey 116,618 

Wisconsin '. 41,403 

Other states 231,935 

Total 586,491 

The world's production of spelter by countries for 1913 follows: 

Short Tons. 

Belgium 217,928 

France and Spain 78,289 

Germany 312,075 

Great Britain 65,197 

United States 346,676 

Total 1,093,635 



INDEX. 



Note. Names of mineral species are printed in heavy-faced type; synonyms and 
variety names in italics; general matter in light-faced type. 



A. 

Accessory rock-making min- 
erals, 343. 

Acicular structure, 57. 
Acid potassium sulphate, 92 
Acmite, 233. 
Actinolite, 237. 
Adamantine luster, 66. . 
Adularia, 222. 
.ffigirite, 233. 
.ffinigmatite, 240. 
Agalmatolite, 283. 
Agate, 176. 
Alabandite, 144. 
Alabaster, 305. 
Albite, 225. 
Alexandrite, 193. 
Allanite, 259. 
Almandite, 244. 
Altaite, 140. 
Aluminium, tests for, 95. 
Aluminium minerals, 310. 
Amalgam, 131. 
Amazon stone, 223. 
Amblygonite, 292. 
Amethyst, 176. 
Ammonium carbonate, 93. 
Ammonium hydroxide, 93. 
Ammonium molybdate, 93. 
Ammonium oxalate, 93. 
Ammonium sulphocyanite, 93. 
Amorphous minerals, 363. 
Amphibole, 237. 
Amphibole Group, 237. 



Analcite, 269. 
Anatase, 196. 
Andalusite, 256. 
Andesine, 228. 
Andesite, 333. 
Andradite, 244. 
Anglesite, 302. 
Anhydrite, 303. 
Ankerite, 209. 
Annabergite, 293. 
Anorthite, 229. 
Anthophyllite, 237. 
Antimony, 124. 
Antimony minerals, 311. 
Antimony, tests for, 95. 
Apatite, 288. 
Apatite Group, 288. 
Apophyllite, 265. 
Aquamarine, 241. 
Aragonite, 2141 
Aragonite Group, 213. 
Arfvedsonite, 246. 
Argentite, 138. 
Arkose, 336. 
Arsenic, 123. 
Arsenic minerals, 312. 
Arsenic, tests for, 96. 
Arsenopyrite, 156. 
Asbestos, 279. 
Asterism, 68. 
Atacamite, 172. 
Augite, 231. 
Aurichalcite, 219. 
Aventurine, 176. 
Axinite, 260. 
Azurite, 219. 



451 



452 



INDEX 



B. 

Balas ruby, 188. 
Banded structure, 59. 
Barite, 299. 
Barite Group, 299. 
Barium chloride, 93. 
Barium hydroxide, 93. 
Barium minerals, 313. 
Barium, tests for, 96. 
Barytes, 299. 
Basalt, 333. 
Bauxite, 201. 
Bead tests, 90. 
Beam balance, 64. 
Beryl, 240. 
Biotite, 275. 
Bismuth, 124. 
Bismuthinite, 136. 
Bismuth minerals, 313. 
Bismuth, tests for, 97. 
Black-band ore, 211. 
Blackjack, 142. 
Blowpipe, 80. 
Blowpipe flame, 82. 
Blue vitriol, 306. 
Bog-iron ore, 200. 
Boracite, 296. 
Borax, 296. 
Borax, 92. 
Bornite, 148. 
Boron, tests for, 97. 
Sort, 117. 

Botryoidal structure, 58. 
Boulangerite,' 160. 
Bournonite, 160. 
Brachy-axis, 47. 
Brachydome, 48. 
Brachypinacoid, 48. 
Braunite, 193. 
Brazilian emerald, 264. 
Brittle, 62. 
Brochantite, 304. 
Bromyrite, 170. 
Bronzite, 231. 



Brookite, 196. 
Brown hematite, 200. 
Brucite, 202. 

C. 

Cadmium minerals, 313. 
Cairngorm stone, 176. 
Calamine, 261. 
Calaverite, 158. 
Calcite, 204. 
Calcite Group, 203. 
Calcium, tests for, 98. 
Cancrinite, 243. 
Capillary pyrites, 146. 
Capillary structure, 57. 
Carbonado, 117. 
Carbon, tests for, 99. 
Carborundum, 184. 
Carbuncle, 247. 
Carnallite, 173. 
Carnelian, 176. 
Cassiterite, 193. 
Cat's eye, 176, 193. 
Celestite, 301. 
Cerargyrite, 169. 
Cerussite, 217. 
Chabazite, 269. 
Chalcanthite, 306. 
Chalcedony, 176. 
Chalcocite, 141. 
Chalcopyrite, 150. 
Chalcotrichite, 179. 
Chalk, 206, 336. 
Chalybite, 210. 
Chemical formula, 75. 
Chemical groups, 74. 
Chessylite, 219. 
Chiastolite, 256. 
Chloanthite, 154. 
Chlorine, tests for, 99. 
Chlorite Group, 277. 
Chlorophane, 171. 
Chlorospinel, 188. 
Chondrodite, 261. 



INDEX 



453 



Chromite, 191. 
Chromium minerals, 314. 
Chromium, tests for, 99. 
Chrysoberyl, 192. 
Chrysocolla, 283. 
Chrysolite, 247. 
Chrysoprase, 176. 
Chrysotile, 279. 
Cinnabar, 144. 
Cinnamon stone, 245. 
Classification of minerals, 114. 
Clay ironstone, 211. 
Cleavage, 3, 59. 
Clino-axis, 50. 
Clinochlore, 277. 
Clinodome, 52. 
Clinohumite, 261. 
Clinopinacoid, 53. 
Clintonite Group, 276. 
Closed tube test, 87. 
Coatings on charcoal, 86. 
Cobalt bloom, 293. 
Cobaltite, 154. 
Cobalt minerals, 314. 
Cobalt nitrate, 93, 
Cobalt, tests for, 99. 
Cogwheel ore, 160. 
Colemanite, 296. 
Coloradorite, 144. 
Color of minerals, 67. 
Columbite, 284. 
Columnar structure, 58. 
Compact structure, 58. 
Concentric structure, 58. 
Conchoidal fracture, 60. 
Conglomerate, 335. 
Constancy of interfacial angles, 5. 
Contact metamorphic minerals, 

347. 

Copper, 130. 
Copper glance, 141. 
Copper minerals, 314. 
Copper nickel, 147. 
Copper pyrites, 150. 
Copper, tests for, 99. 



Cordierite, 242. 
Corundum, 181. 
Covellite, 145. 
Crocidolite, 240. 
Crocoite, 303. 
Cryolite, 172. 
Crystal combinations, 13. 
Crystal, defined, 1. 
Crystal distortion, 14. 
Crystal form, 12. 
Crystal habit, 13. 
Crystallized structure, 57. 
Crystallographic axes, 9. 
Cube, 18. 
Cuprite, 179. 
Cyanite, 257. 
Cymophane, 193. 

D. 

Dacite, 333. 

Danburite, 254. 

Datolite, 257. 

Deltoid dodecahedron, 29. 

Demantoid, 247. 

Dendritic structure, 57. 

Desmine, 268. 

Determinative Mineralogy, 364. 

Determinative Tables, 369. 

Diamond, 116. 

Diaspore, 198. 

Dimorphism, 80. 

Diopside, 231. 

Dioptase, 250. 

Diorite, 332. 

Diploid, 25. 

Divergent structure, 57. 

Dodecahedron, 19. 

Dolerite, 332. 

Dolomite, 208. 

Double refraction, 71. 

Drusy structure, 57. 

Dry-bone ore, 212. 

Dry reagents, 92. 

Dunite, 332. 



454 



INDEX 



E. 

Earthy structure, 58. 
Elceolite, 242. 
Elastic, 62. 
Electric calamine, 262. 
Electrum, 125. 
Elements, 115. 
Elements, list of, 94. 
Embolite, 169. 
Emerald, 241. 
Emery, 182. 
Enargite, 165. 
Endlichite, 291. 
Enstatite, 231. 
Epidote, 259. 
Erubescite, 149. 
Erythrite, 293. 
Essonite, 245. 
Eucryptite, 234. 

F. 

Fahlore, 162. 
Famatinite, 165. 
Fayalite, 248. 
Feather ore, 159. 
Feldspar Group, 220. 
Felsite, 333. 
Fergusonite, 286. 
Fibrolite, 256. 
Fibrous fracture, 60. 
Fibrous structure, 58. 
Filiform structure, 57. 
Flame tests, 88. 
Flexible, 62. 
Flint, 177. 
Flos ferri, 215. 
Fluorine, tests for, 100. 
Fluorite, 170. 
Fluor spar, 170. 
Foliated structure, 58. 
Fosterite, 248. 
Fracture, 60. 
Franklinite, 191. 
Fusion, 83. 



G. 

Gabbro, 332. 
Gadolinite, 258. 
Gahnite, 189. 
Galena, 139. 
Galenite, 139. 
Gangue minerals, 351, 
Garnet, 244. 
Garnierite, 280. 
Gay Lussite, 219. 
Genthi^e, 280. 
Geocronite, 160. 
Geode, 59. 
Gersdorffite, 154. 
Geyserite, 178. 
Gibbsite, 203. 
Glauberite, 298. 
Glaucophane, 239. 
Globular structure, 58. 
Gmelinite, 269. 
Gneiss, 337. 
Goethite, 199. 
Gold, 125. 
Golden beryl, 241. 
Gold minerals, 317. 
Gold, tests for, 101. 
Goniometers, 6. 
Gossan, 153. 
Granite, 331. 
Granular structure, 58. 
Graphite, 120. 
Gray copper, 162. 
Graywacke, 336. 
Greasy luster, 66. 
Greenockite, 146. 
Grossularite, 244. 
Groundmass, 334. 
Gypsum, 304. 



H. 

Hackly fracture, 60. 

Halite, 166. 

Hardness of minerals, 60. 



INDEX 



455 



Harmotone, 267. 
Hausmannite, 193. 
Haiiynite, 243. 

Heavy spar, 299. 
Hedenbergite, 231. 
Hematite, 184. 
Hemimorphite, 262. 
Hessite, 140. 
Heulandite, 267. 
Hexahedron, 18. 
Hexagonal axes, 37. 
Hexagonal minerals, 357. 
Hexagonal prisms, 38. 
Hexagonal pyramids, 39, 40. 
Hexagonal symmetry, 38. 
Hexagonal system, 37. 
Hexakistetrahedron, 29. 
Hexoctahedron, 23. 
Hiddenite, 234. 
Hornblende, 237. 
Hornblendite, 332. 
Horn silver, 169. 
Horseflesh ore, 149. 
Hiibnerite, 307. 
Humite, 261. 
Hyacinth, 254. 
Hyalite, 178. 
Hyalophane, 223. 
Hydrargillite, 203. 
Hydrochloric acid, 93. 
Hydrogen sodium phosphate, 93. 
Hydrohemalite, 198. 
Hydromagnesite, 220. 
Hydrozincite, 220. 
Hypersthene, 231. 

I. 

Ice, 181. 

Iceland spar, 206. 

Igneous rocks, 329. 

Ilmenite, 186. 

Ilvaite, 261. 

Index of refraction, 69. 

Indices, 12. 



Indicolite, 264. 
Infusorial earth, 
lodyrite, 170. 
lolite, 242. 
Iridescence, 68. 
Iridium, 133. 
Iridosmine, 133. 
Iron, 133. 
Iron minerals, 318. 
Iron pyrites, 151. 
Iron, tests for, 101. 
Irregular fracture, 60. 
Isometric angles, 30. 
Isometric axes, 16. 
Isometric minerals, 355. 
Isometric symmetry, 17. 
Isometric system, 16. 
Isomorphism, 77. 
Isomorphous groups, 79. 

J. 

Jacinth, 254. 
Jadeite, 234. 
Jamesonite, 159. 
Jargon, 254. 
Jasper, 177. 
Jeffersonite, 231. 
Jolly balance, 64. 

K. 

Kainite, 168. 
Kalinite, 306. 
Kaolin, 281. 
Kaolinite, 281. 
Kidney ore, 185. 
Krennerite, 159. 
Kunzite, 234. 

L. 

Labradorite, 228. 
Lamellar structure, 58- 
Lapis-lazuli, 243. 
Laumontite, 268. 



456 



INDEX 



Lazulite, 293. 
Lazurite, 243. 
Lead, 131. 
Lead minerals, 319. 
Lead, tests for, 102. 
Lepidolite, 274. 
Lepidomelane, 276. 
Leucite, 229. 
Lievrite, 261. 
Limestone, 206, 336. 
Limonite, 200. 
Linnseite, 149. 
Lithiophilite, 287. 
Lithium, test for, 103. 
Litmus paper, 92. 
Lodestone, 189. 
Luster, 65. 

M. 

Macro-axis, 47. 
Macrodome, 48. 
Macropinacoid, 48. 
Magnesite, 209. 
Magnesium, tests for, 103. 
Magnetic pyrites, 147. 
Magnetite, 189. 
Malachite, 218. 
Malleable, 62. 
Mammillary structure, 58. 
Manganese minerals, 320. 
Manganese, tests for, 104. 
Manganite, 199. 
Manganotantalite, 285. 
Marble, 206, 339.. 
Marcasite, 155. 
Margarite, 277. 
Marialite, 250, 251. 
Marl, 337. 

Massive minerals, 363. 
Massive structure, 59. 
Meionite, 250, 251. 
Melaconite, 181. 
'Melanile, 246. 
Menaccanite, 186. 



Meneghinite, 160. 
Mercury, 131. 
Mercury minerals, 321. 
Mercury, tests for, 104. 
Metacinnabarite, 144. 
Metallic luster, 66. 
Metamorphic rocks, 337. 
Mica Group, 271. 
Mica-schist, 338. 
Micaceous structure, 58. 
Microcline, 223. 
Microcosmic salt, 92. 
Microlite, 286. 
Milky quartz, 176. 
Millerite, 146. 
Mimetite, 291. 
Mispickel, 156. 
Mizzonite, 250, 251. 
Molybdenite, 137. 
Molybdenum minerals, 322. 
Molybdenum, tests for, 104. 
Monazite, 286. 
Monoclinic axes, 50. 
Monoclinic minerals, 360. 
Monoclinic prism, 52. 
Monoclinic pyramid, 51. 
Monoclinic symmetry, 51. 
Monoclinic system, 50. 
Monticellite, 248. 
Moonstone, 222, 226. 
Morganite, 241. 
Muriatic acid, 93. 
Muscovite, 272. 

N. 

Nagyagite, 159. 
Natrolite, 270. 
Nephelite, 242. 
Niccolite, 147. 
Nickel bloom, 293. 
Nickel minerals, 322. 
Nickel, tests for, 104. 
Niobium, tests for, 105. 
Niter, 295. 



INDEX 



457 



Nitric acid, 93. 
Nonmetallic luster, 66. 
Noselite, 243. 

O. 

Obsidian, 333. 
Octahedrite, 196. 
Octahedron, 18. 
Oligoclase, 227. 
Olivenite, 293. 
Olivine, 247. 
Onofrite, 144. 
Onyx, 177. 
Oolite, 336. 
Opal, 178. 
Opalescence, 68. 
Open tube test, 86. 
Orpiment, 134. 
Ortho-axis, 50. 
Orthoclase, 221. 
Orthodome, 52. 
Orthopinacoid, 53. 
Orthorhombic axes, 46. 
Orthorhombic minerals, 359. 
Orthorhombic prism, 47. 
Orthorhombic pyramid, 47. 
Orthorhombic symmetry, 46. 
Orthorhombic system, 47. 
Oxidizing flame, 84. 
Oxygen, tests for, 105. 

P. 

Palladium, 133. 

Parameters, 10. 

Parting, 59. 

Peacock ore, 149. 

Pearl spar, 209. 

Pearly luster, 66. 

Pectolite, 235. 

Pegmatite dike, 345. 

Penninite, 277. 

Pentagonal dodecahedron, 25. 

Pentlandite, 144. 



Percentage composition, 76. 
Peridot, 247. 
Peridotite, 332. 
Perlite, 333. 
Perovskite, 284. 
Petalite, 220. 
Petzite, 140. 
Phenacite, 249. 
Phenocryst, 334. 
Phillipsite, 267. 
Phlogopite, 275. 
Phonolite, 333. 
Phosgenite, 218. 
Phosphorescence, 68. 
Phosphorite, 289. 
Phosphorus, tests for, 106. 
Picotite, 188. 
Pitch blende, 297. 
Pitchstone, 333. 
Plagioclase feldspars, 224. 
Plagionite, 160. 
Platinum, 131. 
Platinum minerals, 323. 
Platinum, tests for, 106. 
Play of colors, 68. 
Pleonaste, 188. 
Plumose structure, 58. 
Plutonic rocks, 330, 331. 
Pneumatolytic minerals, 348. 
Polarized light, 72. 
Polianite, 198. 
Pollucite, 230. 
Polybasite, 164. 
Polyhalite, 168. 
Porphyry, 334. 
Potash alum, 306. 
Potash feldspar, 221. 
Potassium iodide and sulphur 

mixture, 92. 

Potassium ferricyanide, 93. 
Potassium ferrocyanide, 93. 
Potassium, tests for, 106. 
Prehnite, 260. 
Primary vein minerals, 352. 
Proustite, 161. 



458 



INDEX 



Pseudomorphs, 15. 
Psilomelane, 203. 
Pumice, 333. 
Purple copper ore, 148. 
Pyrargyrite, 161. 
Pyrite, 151. 
Pyritohedral class, 24. 
Pyritohedron, 25. 
Pyrochlore, 286. 
Pyroelectricity, 72. 
Pyrolusite, 196. 
Pyromorphite, 290. 
Pyrope, 244. 
Pyrophyllite, 282. 
Pyroxene, 231. 
Pyroxene Group, 230. 
Pyroxenite, 332. 
Pyrrhotite, 147. 

Q. 

Quartz, 174. 
Quartzite, 338. 
Quicksilver, see Mercury. 

R. 

Radiated structure, 57. 
Realgar, 134. 
Red copper ore, 179. 
Reducing flame, 84. 
Refraction of light, 68. 
Reniform structure, 58. 
Replacement deposits, 351. 
Resinous luster, 66. 
Reticulated structure, 57. 
Rhodochrosite, 211. 
Rhodolite, 246. 
Rhodonite, 236. 
Rhombohedral class, 41. 
Rhombohedral minerals, 358. 
Rhombohedron, 42. 
Rhyolite, 333. 
Riebeckite, 239. 
Rock crystal, 175. 



Rock-making minerals, 339. 
Rock salt, 166. 
Rose beryl, 241. 
Rose quartz, 176. 
Rubellite, 264. 
Rubicelle, 188. .'._ 
Ruby, 182. 
Ruby copper, 179. 
Ruby silvers, 161. 
Rutile, 195. 

S. 

SdU, 166. 

Salt of phosphorus, 92. 
Samarskite, 286. 
Sandstone, 335. 
Sanidine, 222. 
Sapphire, 182. 
Satin spar, 305. 
Scalenohedron, 42. 
Scale of fusibility, 84. 
Scale of hardness, 61. 
Scapolite Group, 250. 
Schoelite, 308. 
Schefferite, 231. 
Schist, 338. 
Scolecite, 271. 
Scorodite, 293. 
Secondary enrichment, 352. 
Secondary vein minerals, 352. 
Sectile, 62. 

Sedimentary rocks, 334. 
Selenite, 304. 
Serpentine, 278. 
Shale, 336. 
Siderite, 210. 
Silicon, tests for, 107. 
Silky luster, 66. 
Sillimanite, 256. 
Silver, 129. 
Silver glance, 138. 
Silver minerals, 324. 
Silver nitrate, 93. 
Silver, tests for, 108. 



INDEX 



459 



Slate, 338. 
Smaltite, 154. 
Smithsonite, 212. 
Smoky quartz, 176. 
Soapstone, 280. 
Soda-feldspar, 225. 
Sodalite, 243. 
Soda niter, 295. 
Sodium carbonate, 92. 
Sodium, tests for, 109. 
Spathic iron, 210. 
Specific gravity, 62. 
Specular hematite, 185. 
Sperrylite, 154. 
Spessartite, 244. 
Sphalerite, 142. 
Sphene, 283. 
Sphenoid, 35. 
Sphenoidal class, 35. 
Spinel, 187. 
Spinel Group, 187. 
Spodumene, 233. 
Stalactitic structure, 58. 
Stannite, 151. 
Staurolite, 264. 
Steatite, 280. 
Stellated structure, 58. 
Stephanite, 163. 
Stibnite, 135. 
Stilbite, 268. 
Stromeyerite, 142. 
Strontianite, 216. 
Strontium, tests for, 109. 
Structure of minerals, 57. 
Sublimates in closed tube, 88. 
Sublimates in open tube, 87. 
Sublimates on charcoal, 86. 
Submetallic luster, 67. 
Sulphides, 133. 
Sulphur, 122. 
Sulphuric acid, 93. 
Sulphur, tests for, 109. 
Syenite, 331. 
Sylvanite, 157. 
Sylvite, 168. 



Symmetry, 7. 
Symmetry axis, 7. 
Symmetry center, 8. 
Symmetry plane, 7. 

T. 

Tabular structure, 58. 
Talc, 280. 
Tantalite, 284. 
Tarnish, 68. 
Tellurium, 123. 
Tellurium, tests for, 110. 
Tenacity of minerals^ 62. 
Tennantite, 162. 
Tenorite, 181. 
Tephroite, 248. 
Test papers, 92. 
Tetragonal axes, 31. 
Tetragonal combinations, 34. 
Tetragonal minerals, 356. 
Tetragonal prisms, 32. 
Tetragonal pyramids, 32, 33. 
Tetragonal system, 31. 
Tetragonal symmetry, 31. 
Tetragonal trisoctahedron, 20 
Tetrahedral class, 27. 
Tetrahedrite, 162. 
Tetrahedron, 28. 
Tetrahexahedron, 19. 
Thomsonite, 271. 
Thorite, 254. 
Thulite, 258. 
Tiemannite, 144. 
Tiger's eye, 176. 
Tin minerals, 325. 
Tin stone, 193. 
Tin, tests for, 111. 
Titanic iron' ore, 186. 
Titanite, 283. 
Titanium minerals, 326. 
Titanium, tests for, 111, 
Topaz, 254. 
Tourmaline, 262. 
Trachyte, 333. 



460 



INDEX 



Trapezohedral class, 45. 
Trapezohedron, 20. 
Travertine, 206, 336. 
Tremolite, 237. 
Triclinic axes, 54. 
Triclinic domes, 55. 
Triclinic minerals, 363. 
Triclinic pinacoids, 56. 
Triclinic prisms, 55. 
Triclinic pyramids, 55. 
Triclinic symmetry, 55. 
Triclinic system, 54. 
Trigonal trisoctahedron, 22. 
Trimorphism, 80. 
Triphylite, 287. 
Tripolite, 178. 
Tri-rhombohedral class, 45. 
Trisoctahedron, 22. 
Tristetrahedron, 29. 
Trona, 220. 
Troostite, 249. 
Tungsten minerals, 326. 
Tungsten, tests for, 111. 
Turgite, 198. 
Turmeric paper, 92. 
Turquois, 294. 
Twin crystals, 15. 

U. 

Uneven fracture, 60. 
Uralian emeralds, 247. 
Uraninite, 297. 
Uranium, tests for, 112. 
Uvarovite, 244. 

V. 

Vanadinite, 291. 
Vanadium minerals, 327. 
Vanadium, tests for, 112. 
Variegated copper ore, 149. 



Veins and vein minerals, 349, 
Verd antique marble, 279. 
Vesuvianite, 251. 
Vitreous luster, 66. 
Vitrophyre, 333. 
Vivianite, 293. 
Volcanic rocks, 330, 332. 

W. 

Warrenite, 160. 
Water, tests for, 101- 
Wavellite, 294. 
Wernerite, 250. 
Wet reagents, 92. 
White iron pyrites, 155. 
Willemite, 249. 
Witherite, 215. 
Wolframite, 307. 
Wollastonite, 235. 
Wulfenite, 308. 
Wurtzite, 148. 

X. 
Xenotime, 286. 

Y. 

Yellow copper ore, 150. 

Z. 

Zeolites, 267. 
Zinc blende, 142. 
Zincite, 180. 
Zinc minerals, 327. 
Zinc, tests for, 112. 
Zinkenite, 160. 
Zircon, 252. 
Zoisite, 258. 



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