Edward Salisbury Dana.

Minerals, and how to study them. A book for beginners in mineralogy. With more than 300 illustrations online

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Online LibraryEdward Salisbury DanaMinerals, and how to study them. A book for beginners in mineralogy. With more than 300 illustrations → online text (page 1 of 23)
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THE LIBRARY

OF

THE UNIVERSITY
OF CALIFORNIA

PRESENTED BY

PROF. CHARLES A. KOFOID AND
MRS. PRUDENCE W. KOFOID




QUARTZ CRYSTAL-NORTH CAROLINA

Two fifths natural size.



MINERALS,



AND



HOW TO STUDY THEM.



A BOOK FOR BEGINNERS IN MINERALOGY.



BY
EDWARD SALISBURY DANA,

YALE UNIVERSITY, NEW HAVEN,

Author of a Text-book of Mineralogy, Sixth Edition of
Dana's System of Mineralogy, etc.



TlBKtb more tban 300 trilustratfons.



SECOND REVISED EDITION

FIRST THOUSAND.



NEW YORK
JOHN WILEY & SONS.

LONDON: CHAPMAN & HALL, LIMITED.
1896.



Copyright, 1895,

BY

EDWARD S. DANA.



ROBERT DRUMMOND, KLECTROTYPER AND PRINTER, NEW YORK.



BMTOH
SCIENCES



PEEEACE.

THE author has occupied some hours, which could not
be devoted to more serious labor, in preparing this little
book, in the hope that it might serve to encourage those
who have a desire to learn about minerals, and also to in-
crease the number of those whose tastes may lead them in
this direction. He shares with most teachers at the pres-
ent time the conviction that the cultivation of the powers
of observation is a most essential element in the education
of young people of both sexes; he believes, further, that
no subject is better fitted to accomplish this object and at
the same time to excite active interest than that of Miner-
alogy. The attempt has been made to present the whole
subject in a clear, simple, and, so far as possible, a read-
able form without too much detail and at the same time
without cheapening the science. As the understanding of
the different parts of the subject requires some preliminary
knowledge of physics and of chemistry, a little elementary
matter in these departments has been introduced.

Much attention has been given to the illustrations, most
of which have been made expressly for this book ; others
(reduced in size) are taken from the sixth edition of the

System of Mineralogy (1892); several have been borrowed

iii



iv PREFACE.

from Tschermak's Mineralogy, and one from a work by
Baumhaner. The correct representation of real crystals
and of the actual specimens from the cabinet is a difficult
matter, and in this the author has been so fortunate as to
secure the services of the skillful wood-engraver Mr. W. F.
Hopson of New Haven. Any suggestions which would
tend to give this volume greater accuracy or usefulness
will be always gratefully received.

NEW HAVEN, July 1, 1895.



TABLE OF CONTENTS.



CHAPTER PAGE

I. MINERALS AND MINERALOGY: INTRODUCTORY REMARKS. . 1
II. SOME PRELIMINARY HINTS AS TO How TO STUDY MIN-
ERALS 8

Suggestions about making a Collection 11

III. THE FORMS OP CRYSTALS AND KINDS OF STRUCTURE 14

The General Characters of Crystals 14

The Systems of Crystallization 21

I. Isometric System 22

II. Tetragonal System 31

III. Hexagonal System 36

Rhombohedral System 39

IV. Orthorhombic System 41

V. Monoclinic System. 44

VI. Triclinic System 45

Irregularities of Crystals , 48

Distorted Crystals 48

Pseudomorphs 55

Groupings or Aggregations of Crystals . 56

Twin Crystals 57

Parallel Grouping , 60

Irregular Grouping 62

Structure in General 63

IV. THE OTHER PHYSICAL CHARACTERS OF CRYSTALS 70

1 . Characters depending upon Cohesion 70

*

Cleavage 70

Fracture. 73

Hardness and Tenacity 74

v



Vi TABLE OF CONTENTS.

CHAPTER PAGE

2. Specific Gravity or Relative Density 79

3. Characters depending upon Light 88

Luster 88

Color 90

Transparency 92

Other Optical Characters 93

4. Characters depending upon Heat 95

5. Characters depending upon Magnetism 96

6. Characters depending upon Electricity 96

7. Taste and Odor 97

V. THE CHEMICAL CHARACTERS OF MINERALS 99

The Chemical Elements 100

The Chemical Formula, etc 104

Kinds of Chemical Compounds among Minerals 109

Percentage Composition 116

Classification 118

VI. THE USE OF THE BLOWPIPE 121

1. General Description of Apparatus 121

2. How to Use the Blowpipe 127

3. Examination in the Forceps 130

4. Use of the Platinum Wire 136

5. Use of Charcoal 140

6. Use of .the Closed and Open Tubes 147

7. Chemical Examination by Acids and other Reagents. 153
VII. DESCRIPTION OF MINERAL SPECIES , 158

VIII. THE DETERMINATION OF MINERALS 339

APPENDIX 365

GENERAL INDEX , 369

INDEX TO MINERAL SPECIES. ... 373



MINERALS, AND HOW TO STUDY THEM,



CHAPTER I.
MINERALS AND MINERALOGY.

WE are to learn about minerals and how to study them;
but, before we can fairly begin, we must understand clearly
what substances we may call minerals, and what specimens
have a right to a place in the collection that every one
who wishes to become a mineralogist must make.

We all know, in the first place, that minerals are the
materials out of which the earth is built, and we often hear
that division of nature to which they belong called the
Mineral Kingdom, in distinction from the Animal and
Vegetable Kingdoms, which embrace the animals and
plants which live and grow upon the earth's surface.

And here it is important to realize how little we can
know by actual contact and direct observation about this
earth, though we live upon it. It is possible, indeed,
to measure its size and shape, to find out its density as a
whole, to study its surface features and the changes which
they have undergone; but of the materials of which it is
made we can know little beyond those which form the
surface upon which we walk, The miner digs down a



2 MINERALS, AND HOW TO STUDY THEM.

little distance, and the artesian-well borer goes down still
deeper, and we may have a chance to examine the spec-
imens that their work brings up; or perhaps we can go
down with the miner and see them in place. But the
deepest mines descend to less than three quarters of a mile ;
and though this seems deep to one who is let down a shaft
in a bucket, it is but a little way compared with the whole
distance to the earth's center, which would require a journey
of nearly 4000 miles. Even the deepest artesian- well bor-
ings hardly go down to the depth of one mile.

Our knowledge, to be sure, is increased a little by the
fact that we find now on the surface of the earth rocks
made, as we have reason to believe, of materials brought
up in a molten condition from great depths below. This
is true of the lava thrown out by a volcano, and of such
igneous rocks, for example, as form the Palisades along the
Hudson River; and these occurrences give us some idea as
to what kinds of matter there are, and in what condition,
far below the surface. Further, we are able to weigh the
entire earth, too, and find what its density is; and as this
is nearly twice as great as that of the rocks on the surface,
it gives a suggestion as to the heavy nature of the mineral
material that must make up the interior.

Thus the mineralogist is limited to the study of the lit-
tle part of the crust of earth which he can reach with his
hammer; and he cannot extend his collection much be-
yond this, unless indeed he takes in some of those rare
visitors from outer space called meteorites which once
in a while tumble down to the earth, usually with a bright
light and loud explosion,



MINERALS AND MINERALOGY. 3

Now what does this study show of the hard rocky mate-
rial of which the earth, so far as we can examine it, is made
up; for example, of the sand of the seashore, the granite,
the trap, the slate and marble of the hills ?

We find, in the first place, that it in general consists of
different kinds of substances, each one having certain
peculiarities or characters of its own, by which it can
always be recognized ; and it is to each of these individual
kinds that the name MINERAL is given.

Thus, more particularly, the sand of the seashore can be
separated without much difficulty into various sorts of
grains, each kind alike in chemical substance, as the
chemist can prove in the laboratory, and with certain
characters of hardness, density, luster, and color of its own,
which enable us after a little practice to distinguish the
different kinds with comparative ease.

Most of the grains are alike clear and glassy, hard enough
to scratch glass, and as we learri to know tnem better we
call them quartz. There are also black grains; some of
these are heavy and jump to a magnet, and often they are
sorted out by the waves into little rifts on the white sand;
these are called magnetite, or magnetic iron. There are
other black grains, too, which the magnet does not attract,
perhaps some red, glassy ones which are fragments of
garnets, and, it may be, still others, depending upon where
the sand comes from, and what kind of rock has been
ground up by nature's mill and sorted out by the water to
make the sand.

If a piece of granite is taken, here too it is possible to
distinguish several kinds of mineral substances, though it



4 MINERALS, AND HOW TO STUDY THEM.

is not quite so easy to separate them. There are hard
glassy grains with irregular surface, which, like the greater
part of the sand-grains, are quartz. There are white or
yellow or pale flesh-red fragments, also hard, though not so
hard as the others, but which are sure to show one or two
smooth surfaces of fracture: these are feldspar. Then
there is the mica, more easily recognized still, which is
either nearly white and silvery, or black (and sometimes both
kinds), and which with a touch of the knife separates into
very thin scales or leaves. Besides these there may be a
little coal-black tourmaline, some bright red garnets, and
other kinds which we shall learn later. If a cavity or
open space in the granite can be found, here it is often
possible to find the same kinds of substances, only larger
and more distinct and very likely in the regular form
which are called crystals.

If, instead of a coarse-grained rock like granite, we ex-
amine a fine compact orfe such as the trap-rock of the
Palisades on the Hudson, it very probably appears all alike
to the eye ; but if we crush some of it to powder, the magnet
will pick out some magnetic iron, as from the seashore sand.
Or the skillful mineralogist may make a slice thin enough
to be transparent, so that he can study it under the micro-
scope, and then recognize a variety of different minerals.
In seams and cavities in these rocks other sorts are often
found, not like those in the solid rock.

Sometimes we find a rock, like the white marble of
Vermont, which the examination of the chemist shows to
be all of the same chemical substance, and which has
throughout the same characters of hardness, density, color,



MINERALS AND MINERALOGY. 5

and so on; then it is said to be a mineral itself, and not,
like most rocks, a mixture of a variety of different min-
erals.

These different kinds of substances, then, which make
up the rocky material of the earth so far as we can
study it, and into which we can separate the seashore
sand, the granite, and most other rocks, are called MIN-
ERALS. Each one has, first of all, a definite chemical
composition, wherever it is found. Moreover, if in the
form of a crystal, it has a shape of its own, too, by which
it may be distinguished; it has also certain characters
of hardness and density, luster, color, transparency, and
others. And because to it belong all these different char-
acters, which distinguish it from other kinds, it is called a

MINERAL SPECIES.

It is the work of the mineralogist to study these min-
erals; to learn all the different kinds; what the characters
of each are; how they are classified and how distinguished
from each other; how they occur in nature; and some-
thing about their practical uses.

All the knowledge which the many mineralogists have
learned, after long years of patient observation and study,
both in the field and the laboratory, has been arranged in
systematic form and makes up the Science of Mineralogy.

The question as to what particular minerals go together
to make the different kinds of rocks, how these are formed,
and what changes of position or of character they have
experienced all these and other similar questions are re-
ferred to the geologist. The science of the geologist, or
geology, is much broader than mineralogy: it treats of



6 MINERALS, AND HOW TO STUDY THEM.

the history of the earth and all the changes it has gone
through; the different kinds of rocks; the way the moun-
tains have been built up from them; the growth and de-
velopment of different kinds of life from the earliest times
down to the present.

It was stated at the beginning of the chapter that min-
erals belong to the MINERAL KINGDOM; but it is important
to remember that all substances mineral in nature are not
necessarily called minerals.

The mineralogist, for example, usually excludes from
his cabinet many mineral substances, such as the pearl of
the oyster-shell and the shell itself, the lime of the bones
of animals, and the opal-like form of silica secreted by
the growth of plants, as the tabasheer found in the joints
of the bamboo. In general mineral substances such as
these, which are formed immediately by the processes of
animal or vegetable life, are not called minerals.

Further, the mineralogist does not, as a rule, admit among
minerals gases like the oxygen and nitrogen which make
up the air; and of the liquids he includes only the metal
mercury, and perhaps also water.

The many beautiful kinds of salts made by the chemist
are also not called minerals. The rock salt or sodium
chloride which is mined, sometimes in fine clear cubi-
cal blocks, is the same sodium chloride which, as the
table-salt of every-day life, is so commonly used. But the
table-salt obtained from evaporating sea - water or the
brines of salt- wells, or from the solution of crude rock
salt, though when manufactured it may be formed in crys-



MINERALS AND MINERALOGY. 7

tals as fine as those found in the rocks, is not called a
mineral, because not made by nature alone. So, too, the
fine crystals of blue vitriol, or copper sulphate, made by
the chemist, do not find a place in a mineral cabinet,
though the much less fine specimens of the same material
found in some of the Arizona mines do. In the same
way, the crystals of the metals and of many interesting
compounds formed in the metallurgical process of making
iron or lead or zinc are called furnace-products, and not
minerals. These substances, however, are all very inter-
esting, and their study is a very important help to pure
mineralogy. In recent years the chemist has busied him-
self in imitating, so far as he can, the possible processes of
nature, and thus making " artificial minerals." Kecently
the diamond has been formed in minute crystals, also small
but fine clear rubies, and so, too, quartz, feldspar, mica,
and many common species.

It must be acknowledged, however, that the specimens
thus obtained in the laboratory are in most cases very
minute and much less beautiful than those of nature; for
the chemist in the laboratory has only a limited time for
his experiments, and often must use violent means, as
the great heat of a furnace./ while nature works slowly
and gently.



MINERALS, AND HOW TO STUDY THEM.



CHAPTER II.

SOME PRELIMINARY HINTS AS TO HOW TO STUDY
MINERALS.

A MINERAL, we have seen, is a substance formed by
nature alone, a solid with one or two exceptions, and one
having as a rule a definite form of its own and certain
characters of hardness, density, luster, color, and still
others, and, most important of all, a definite chemical com-
position. The first group of characters, having to do with
the form and structure and so on, are called PHYSICAL
CHARACTERS, while those depending directly upon the
composition are called CHEMICAL CHARACTERS. All of
these will be described in some detail in subsequent chap-
ters, but it is necessary first to gain a little knowledge as
to how to study minerals, where the object is to learn as
much as possible about each and to distinguish one kind
from another.

The mineralogist must first of all use his eyes and other
unaided senses in studying minerals; in other words, he
must gain all the information he can about minerals by
looking at them and handling them. If he learns to do
this wisely, he will be surprised to find how keen his
senses become and how much he can find out. But as he
gains in experience he will see that this only carries him
to a certain point, and he should always recognize the im-



HINTS ON THE STUDY OF MINERALS. 9

portance of confirming the conclusions reached by his eye
and hand by more positive tests. Often, even in the case
of the commonest species, the appearance may lead one
who depends upon it alone quite astray. The old saying
that "all is not gold that glitters," and the names ap-
plied to certain common minerals of " fool's gold," " false
galena," and others like them, express the result of experi-
ence that the senses unassisted may readily be deceived.

The trained eye of the mineralogist will show him, first
of all, the form of the mineral, as to whether it has the
regular geometrical shape of a crystal or not, or is simply
granular, fibrous, and so on. It will show him whether
it has the natural, easy, smooth fracture of many crystal-
lized substances, called cleavage, or only the fracture of
ordinary kinds. It will tell him, too, what peculiarities of
luster the surface of a mineral presents, depending upon
the way in which it reflects light, whether metallic,
glassy, greasy, or silky, and so on; also what the color is,
whether it is transparent or opaque, and many other
points.

The touch will show whether the "feel" is greasy, as is
true of a few very soft minerals, or harsh, as are the
majority. Again, a mass in the hand will often be recog-
nized at once as heavy or light as compared with familiar
substances of the same appearance. Thus the common
minerals quartz, feldspar, calcite, have nearly the same
density, and one can easily become so accustomed to them
that a piece of gypsum seems light and one of barite
(heavy spar) seems heavy. So a piece of the metal alu-
minium seems very light because we instinctively compare



10 MINERALS, Afrt> HOW TO STUDY THEM.

it with the other much denser metals which we are ac-
customed to handle.

The taste may sometimes tell, for instance, that rock
salt is in hand, while the odor is occasionally a useful
character, as the clayey odor of some minerals when
breathed upon.

But it requires some education and experience before
the senses are so on the alert that all the characters noted
are perceived at once and rightly estimated; this is what
every one should strive for; and one of the great benefits to
be derived from the study of mineralogy is that it culti-
vates and stimulates the powers of observation.

When the senses alone stop, simple tests to aid them
come in. A touch upon the smooth surface of a mineral
with the point of a knife serves to show whether it
is relatively soft or hard. The color of the powder ob-
tained by scratching with the knife or upon a plate of
rough porcelain or ground glass, called the streak, is some-
times quite different from that of the surface, and in such
cases this is a very important character.

Then come more careful tests : the determination of the
relative density or specific gravity; the use of the blow-
pipe, giving the comparative degree of fusibility; and a
number of simple chemical trials, to show the presence
of sulphur or arsenic, silver, lead or iron, barium or stron-
tium. Then follow still other tests, till we come to the re-
fined methods of the trained mineralogist with his beauti-
ful goniometer for measuring angles, the microscope and
optical instruments, the accurate chemical analysis and
other means by which most of nature's secrets may be



HINTS ON THE STUDY OF MINERALS. 11

learned and the characters of each mineral thoroughly
studied.



SOME SUGGESTIONS ABOUT MAKING A COLLECTION OF
MINERALS.

A very important matter in the study of minerals is the
student's own collection; for every one who desires to
really learn mineralogy must have a collection of his own
to examine and experiment upon. It is very desirable that
the school or college should have a larger cabinet for refer-
ence and study, but this does not take the place of the in-
dividual collection, which will be studied, arranged, labeled,
and handled over and over again till every specimen is per-
fectly familiar.

Further, the student should obtain his specimens as far
as he can by collecting for himself. No matter if he lives in
a region that does not seem at first to afford very much,
he can certainly find something that is worth keeping
until he obtains better; and occasionally he will have the
opportunity to make trips to some of the noted localities,
where he can find more and a great variety. There is
nothing more delightfully instructive and health-giving
than to spend a day in the open air, with a good hammer
in hand, a bag for the specimens, and plenty of soft paper
(and perhaps some cotton) to wrap them up in.

The hammer should be of hard steel that will not chip
on the edges; it may weigh from a pound to a pound and a
half, and the face should be square or slightly oblong and
the edges sharp, while the back has the form of a



12 MINERALS, AND HOW TO STUDY THEM.

wedge, as seen in Figure 1 (one-fourth natural size). A
cold-ghisel or two, for working into cracks or crevices,
will often be found useful; also a
small light hammer with a sharp edge
for trimming specimens. This will
often do no damage, when a blow from
a heavy hammer would shatter the
specimen and destroy it.

Do not break the crystals out of the
rock, as a rule. A detached crystal
of garnet is interesting when quite
perfect, but in general the crystal is
most interesting and instructive when
in its own home. The seller of min-
erals soon discovers this, and it is un-
fortunately not an uncommon trick
at some localities for instance in the
Alps for the local collector working
for his daily bread to exercise his
ingenuity in mounting a loose crystal

J4 natural size.

in a mass of rock in which it never
belonged, thus to increase the value of the specimen and
deceive the unwary purchaser.

The student is not advised to spend a great deal of
money in buying specimens, particularly at any one time.
Still it is less easy to collect personally now than it was
years ago, and many students may not have opportunity to
do the traveling that it requires: and even here the reward
is often small, unless at a quarry or mine where work is
being carried on all the time.



HINTS ON THE STUDY OF MINERALS. 13

Hence a little money is by no means thrown away if
judiciously expended from time to time, for it will serve to
buy a few small characteristic specimens of the common
species and pure fragments for blowpipe tests. Fine
specimens, especially of the rarer species, are now very
expensive, but sufficiently good ones of the . minerals it is
important for the student to know well may be obtained,
for very little money.*

It is better to collect small specimens rather than large,
as far as possible, such as will go in a little paper tray 2
inches square, or 2 by 3 inches, or at most 3x3. These
trays are inexpensive and are very useful for the arrange-
ment and preservation of a cabinet. If the specimens are
placed loose in a drawer, it can hardly be opened a few
times without throwing them into confusion, and sooner or
later they will be badly injured. The sizes mentioned are
the most useful, though 3x4 inches might well be added.
A depth of half an inch is sufficient for the tray, but the
drawers, if possible, should not be less than 2J or 3 inches
deep. All the specimens in a collection should be care-
fully labeled, particularly as regards the locality.

* A list of the most important minerals is given at the close of the
book, and those most useful for trial with the blowpipe are there
indicated.



14 MINERALS, AND HOW TO STUDY THEM.



CHAPTER III.
THE FORMS. OF CRYSTALS AND KINDS OF STRUCTURE.

THE principal characters of minerals, by which one
species is distinguished from another, have been briefly
alluded to in the preceding chapter. It is now necessary
to study some of these characters more fully.

First the PHYSICAL CHARACTERS will be considered.
These include the form and structure, the cleavage, frac-
ture, hardness, tenacity, elasticity; also the density; fur-
ther, the color, luster, degree of transparency, and some
few others. The present chapter is limited to a discussion
of the crystalline form and the structure in general.


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Online LibraryEdward Salisbury DanaMinerals, and how to study them. A book for beginners in mineralogy. With more than 300 illustrations → online text (page 1 of 23)