:" 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 ch
