Field Book _of_
Common Rocks
_and_ Minerals
For identifying the Rocks and Minerals of the United States and
interpreting their Origins and Meanings
By
Frederic Brewster Loomis
Late Professor of Mineralogy and Geology
in Amherst College
With 47 Colored Specimens and over 100 other Illustrations from
Photographs by W. E. Corbin and drawings by the Author
G. P. Putnam’s Sons
New York and London
FIELD BOOK
OF
COMMON ROCKS AND MINERALS
Copyright, 1923, 1948
by
Frederick Brewster Loomis
Twenty-sixth Impression
Revised 1948
All rights reserved. This book, or parts thereof, must not be
reproduced in any form without permission.
Made in the United States of America
Dedicated
TO
MY MOTHER
WHO ENCOURAGED ME WHILE A BOY TO GATHER MINERALS, ROCKS AND FOSSILS.
PREFACE
Everyone, who is alert as he wanders about this world, wants to know
what he is seeing and what it is all about. Here and there with the aid
of capable guides a few have been introduced into the sphere of that
wide and fascinating knowledge of Nature which has been so rapidly
accumulated during this and the latter part of the last century. It is a
full treasure house constantly being enriched, but unfortunately the few
who have been initiated have soon acquired a technical language and
habit, so that their knowledge and new acquisitions are communicated to
but few. The public at large, not having the language nor an interpreter
at hand, has come almost at once to a barrier which few have the time or
patience to surmount.
Latterly it has become clear that the largest progress cannot be made if
the knowledge of any branch of Science is confined to a few only. The
most rapid advances have been made where many men are interested and
enthusiastic. In no science should there be a difficult barrier between
the amateur and the professional student. All Nature is equally open for
everyone to study, and there should never be created obstacles as by the
use of terminology not easily acquired by anyone. Of late these barriers
have been in part broken down and competent students have written guides
which anyone can follow, and soon begin to know the plants, trees,
birds, insects, etc. So far no one has attempted to make the study of
minerals and rocks so direct and simple that everyone can get a start.
Most books on minerals, and practically all those on rocks are written
for school courses, and to say the least chill any enthusiasm which is
naturally aroused by the finding of interesting looking rocks or
minerals.
The purpose of this book is first of all to provide a means of
identifying minerals and rocks by such methods as are practical without
elaborate equipment or previous training: and second to suggest the
conditions under which the various minerals and rocks were formed, so
that, at the first contact, one may get a conception of the events which
have anteceded the mineral or rock which has been found. For this
purpose keys have been worked out for determining the rocks and minerals
by such obvious features as color, hardness, etc. Each mineral or rock
is introduced by a summary of its characters, then the features by which
it may be distinguished from any other similar mineral are given, after
which its mode of origin and its meanings are considered. For those
interested in the composition of the minerals, it is given in chemical
symbols with each mineral. Most classifications of minerals are based on
the composition, all the sulphides, carbonates, etc., being grouped
together, but in this book, because the popular interest and commercial
uses are primarily in the metal present, the minerals are grouped in
each case about the chief metal, all the minerals of iron being grouped
together, for instance.
A few minerals and rocks which are not strictly common have been
included such as gems and meteorites; the gems because they are of
intense interest to their owners and are often simply perfect examples
of a fairly common mineral; and such forms as meteorites because it is
important that, if one should run across one, it should be recognized,
and so not lost to the world.
The book is freely illustrated, those minerals in which color is
important for identification being illustrated in colors, and those
which are black, or in which the color is not a determining factor, are
shown in either photographic or outline figures.
In the introductory chapter there are explanations of the terms used in
describing minerals, and of the systems in which they are grouped. A
knowledge of the systems may not be a necessity, but it is a great help
in determining minerals, and is very important in understanding why the
individual minerals take the varied forms which are characteristic of
them. These systems will be better understood after a few minerals have
been gathered and examined.
It is hoped the book will help those who have already some knowledge of
rocks and minerals, and especially that it will tempt many to begin an
acquaintance with the rocks and minerals which are all about them, and
are the foundation on which our material progress is built. Rocks and
minerals have some advantages over most objects which are collected in
that they neither require special preparation before they can be kept,
nor do they deteriorate with time.
The author will appreciate corrections or suggestions as to better
presentation of the material in this book.
F. B. L.
Amherst, Mass.
CONTENTS
PAGE
Preface vii
CHAPTER
I.—An Introduction 3
II.—On the Forms and Properties of Minerals 10
III.—The Minerals 25
IV.—The Rocks 170
V.—Miscellaneous Rocks 248
Bibliography 270
Index 273
LIST OF PLATES
(AT END OF BOOK)
PAGE
Tourmaline crystals, growing amid feldspar crystals in a cavity in
granite, from Paris, Me. 279
Plate 1.—Basal forms of the isometric system 311
Plate 2.—Basal forms of the tetragonal system. Basal forms of the
orthorhombic system 312
Plate 3.—Basal forms of the monoclinic system. A cross section of
the prism with its edges beveled so that a six-sided prism
is formed (pseudo-hexagonal). Basal form of the triclinic
system. 313
Plate 4.—Basal forms of the hexagonal system 314
Plate 5.—Gold in quartz from California (_in color_) 280
Plate 6.—Native silver in calcite. Argentite, the black masses
throughout the white quartz (_in color_) 281
Plate 7.—Pyrargyrite as it appears after moderate exposure to the
light; streak at left. Crystal form of pyrargyrite.
Prousite as it appears after moderate exposure to the
light; streak at left (_in color_) 282
Plate 8.—Native copper from Michigan. Chalcopyrite in tetrahedrons
and an occasional octahedron; streak to the left (_in
color_) 283
Plate 9.—Chalcocite crystals with the bluish tarnish. Tetrahedrite
crystals; streak to left (_in color_) 284
Plate 10.—Tetrahedrons showing characteristic manner in which
tetrahedrite occurs. A cube with the edges beveled and the
corners cut in a form characteristic of cuprite 315
Plate 11.—Cuprite, the red crystals showing characteristic color,
others showing the green tarnish of malachite. Malachite
(green) and azurite (blue), the two minerals shown
together as they very commonly occur (_in color_) 285
Plate 12.—Limonite. The crystal form in which goethite is found
(_in color_) 286
Plate 13.—Hematite. Clinton iron ore, oolitic. Siderite crystals
(_in color_) 287
Plate 14.—Crystal forms of hematite. A typical crystal of
magnetite. The rhombohedron typical of siderite 317
Plate 15.—Pyrite crystals. Marcasite in concretionary form with
radiate structure (_in color_) 288
Plate 16.—The pyritohedron. The pyritohedron with certain of its
edges beveled by the cube faces, to show the relationship
of these two forms 318
Plate 17.—Galena in crystals. Pyromorphite crystals (Green) (_in
color_) 289
Plate 18.—Typical forms for cerrusite. Forms in which anglesite
occurs 319
Plate 19.—Sphalerite, some the normal yellow and some crystals
with the reddish tinge. (White is dolomite.) Zincite,
streak to the left (_in color_) 290
Plate 20.—A characteristic form in which sphalerite may occur.
Characteristic form for zincite crystals. Typical form of
crystal of willemite 320
Plate 21.—Smithsonite in yellow crystals. Franklinite in
octahedral crystals, streak to left (_in color_) 291
Plate 22.—Moss agates, showing the dendritic growth of manganitic
minerals, like manganite or pyrolusite. Crystal form of
manganite 321
Plate 23.—Crystals of green corundum in syenite, from Montana.
Typical crystal forms of corundum 322
Plate 24.—Arsenopyrite, showing crystals massed so as to be
incompletely developed. Realgar as it usually occurs in
powdery incrustations (_in color_) 292
Plate 25.—Large crystals of stibnite; the light colored face is
the one parallel to which cleavage occurs. Niccolite is a
vein in slate (_in color_) 293
Plate 26.—Cobaltite, silver color, with pink tinge. Smaltite, pink
is cobalt bloom (_in color_) 294
Plate 27.—Carnotite from Southwest Colorado. Cinnabar (_in color_) 295
Plate 28.—Cassiterite, twinned crystals. The crystal form in which
both cassiterite and rutile occur when in simple crystals.
Multiple twinning characteristic of rutile 323
Plate 29.—Crystal of spinel. Crystal forms in which dolomite
occurs 324
Plate 30.—Two intergrowing or twinned quartz crystals. Diagram of
the typical quartz crystal. A quartz crystal on which the
left hand rhombohedron is represented by small faces,
while the right hand rhombohedron has large faces 316
Plate 31.—Amethyst, not however deep enough colored for gems.
Jasper, with botryoidal surface (_in color_) 296
Plate 32.—Banded agate from Brazil (_in color_) 297
Plate 33.—Common opal from Arizona. Siliceous sinter or geyserite
from Yellowstone Park (_in color_) 298
Plate 34.—Orthoclase, a cleavage piece. Crystal forms of
orthoclase. Diagram of a multiple twin of a plagioclase
feldspar 325
Plate 35.—A group of microcline crystals from Pike’s Peak, Colo.
Labradorite, showing multiple twinning (the striation) and
the iridescent play of colors (_in color_) 299
Plate 36.—Crystal form of a pyroxene. Cross sections of a pyroxene
crystal showing the lines of intersection of two cleavage
planes. Cross sections of pyroxenes, showing typical forms
taken by crystals. Augite crystals, in crystalline
limestone (_in color_) 300
Plate 37.—Diagrams of amphibole crystals. Tremolite in silky
fibrous crystals, asbestos. Hornblende crystals in
quartzite 326
Plate 38.—The dodecahedron and the 24-sided figure characteristic
of garnets. The garnet, grossularite. The garnet,
alamandite (_in color_) 301
Plate 39.—Beryl of gem quality. Zircon in syenite (_in color_) 302
Plate 40.—Cyanite crystals in schist. A crystal of mica, showing
basal cleavage (_in color_) 303
Plate 41.—Crystal form typical of topaz. A topaz crystal from
Brazil. Crystal form typical of staurolite when simple. A
typical twin of staurolite (_in color_) 304
Plate 42.—Epidote crystals. Typical forms of epidote crystals.
Typical forms of tourmaline 327
Plate 43.—Serpentine. Chlorite (_in color_) 305
Plate 44.—The typical form of analcite. A typical natrolite
crystal. The typical crystal form of stilbite. A
sheaf-like bundle of fibrous crystals, typical of stilbite 329
Plate 45.—A group of calcite crystals. Typical forms of calcite 330
Plate 46.—Typical forms of aragonite. Typical form of the
anhydrite crystal 331
Plate 47.—A piece of gypsum looking on the surface of the perfect
cleavage, and showing the two other cleavages as lines,
intersecting at 66°. Twinning is also shown. A simple
crystal of gypsum. Twin crystals of gypsum. 332
Plate 48.—A group of barite crystals. Outline of the typical
tabular barite crystal. The six-sided double pyramid,
composed of three interpenetrating crystals, typical of
witherite and strontianite 328
Plate 49.—Apatite crystals in crystalline calcite. The ends of
apatite crystals showing common modes of termination (_in
color_) 306
Plate 50.—A group of fluorite crystals. A group of halite crystals
(_in color_) 307
Plate 51.—Sulphur crystals. Ice crystals, the top one, the end of
a hexagonal prism; the two lower figures multiple twins as
in snow flakes 333
Plate 52.—The Devil’s Tower, Wyoming, an example of igneous rock
with columnar structure, and resting on sedimentary rocks 334
Courtesy of the U. S. Geological Survey
Plate 53.—A coarse granite. Graphic granite 335
Plate 54.—Syenite. Gabbro 336
Plate 55.—Basalt-porphyry. The large white crystals are
phenocrysts of plagioclase feldspar. Basalt-obsidian 337
Plate 56.—Amgydoloid 338
Plate 57.—The north face of Scott’s Bluff, Neb., showing
sedimentary sandstones above and clays below. The type of
erosion is characteristic of arid regions 339
Courtesy of the U. S. Geological Survey
Plate 58.—Breccia. Conglomerate 340
Plate 59.—Calcareous shale. Coquina 341
Plate 60.—Foramenifera from chalk; enlarged about 25 diameters.
Encrinal limestone; fragments of the stems, arms and body
of crinoids 342
Plate 61.—Amber. Two bottles of petroleum, the left hand one with
a paraffin base, the right hand one with an asphalt base
(_in color_) 308
Plate 62.—Diatomaceous earth magnified 50 times. Two diatoms from
the above enlarged 250 times 343
After Gravelle, by the courtesy of Natural History
Plate 63.—A metamorphic rock, showing the contortion of layers due
to expansion under heat 344
Plate 64.—A conglomerate partly metamorphosed to a gneiss. A
typical gneiss 345
Plate 65.—Mica schist, with garnets. Chlorite schist (_in color_) 309
Plate 66.—Phyllite. A white marble, with black streaks due to
graphite 346
Plate 67.—Serpentine composed of serpentite, hematite, and some
calcite (_in color_) 310
Plate 68.—Claystones, simple and compound. A lime concretion,
which on splitting disclosed a fern leaf of the age of the
coal measures 347
Plate 69.—A septeria from Seneca Lake, N. Y. Pisolite from Nevada 348
Plate 70.—A geode filled with quartz crystals 349
Plate 71.—A quartz pebble from the bed of a New England brook. A
pebble of schist and granite from the foot of Mt. Toby,
Mass. 350
Plate 72.—An iron-nickel meteorite, of 23 lbs., which fell in
Claiborne Co., Tenn. An etched slice of an iron meteorite
which fell in Reed City, Osceola, Co., Mich. 351
Plate 73.—A stone meteor, about natural size, which fell in 1875
in Iowa Co., Iowa 352
FIELD BOOK OF
COMMON ROCKS AND MINERALS
CHAPTER I
AN INTRODUCTION
Why
Why should one be interested in rocks and minerals? Because the whole
world is made of rocks and minerals. They are the foundations on which
we build. From them we draw all our metals, and the extent to which we
utilize our minerals is a measure of the advance of our civilization.
Fragments of rock are the soil from which, by way of the plants, we draw
our food, and ultimately our life. The rocks make wild or gentle
scenery, one at least of the sources of pleasure. Knowledge of rocks and
minerals is then knowledge of fundamentals, of ultimate sources. Between
finding the raw materials and their present uses there are usually many
steps (so many that we forget that the beginning and end are united), as
for instance in your watch. It is made of gold, brass, steel, agate,
glass, and perhaps has luminous radium paint on the hands. It is a long
way from finding and mining gold, chalcopyrite, hematite, carnotite,
etc., through the raw materials, gold, copper, iron, etc., to the
finished watch, but the minerals are the foundations of the watch; and
it took centuries to find them and learn one by one how to use them,
from the gold 10,000 years ago down to the radium within the last fifty
years. Then too there is joy in going out into Nature’s wild and raw
places, joy in being on the foundations of the earth, joy in the
scenery, in the beauty of the minerals themselves.
But why collect the rocks and minerals? First because this is the way to
know them. Both mineral and rocks require careful examination in order
to see all those fine points by which they are distinguished. It is
often necessary to compare one with another to get in mind the
differences of form, color, streak, though with increasing familiarity
these characteristics are recognized at first sight. It is the repeated
examination which makes a rock tell the story of the country from which
it came. Our first attempts to read the story give us only the most
general facts. Nature’s book, written in the rocks, has to be read
closely, often between the lines. Until we are used to the characters in
which the words are written, we read slowly. When they look at Nature’s
book, always open, most people do not read; for they do not know their
letters. Every mineral is a letter, every rock a word, and we learn to
read as we learn the minerals and rocks, and every time we go over them
we get more facts coming out. The place where a rock or mineral occurs
is of course the relation between them, and is involved in reading the
story. No one today is a perfect reader. We are all learning to see more
in the rocks day by day. So it is important to have the rocks and
minerals where they can be handled and repeatedly examined, where we can
turn to them in our leisure moments. Don’t stop when you have learned
the name of a mineral or rock. You need more. See what it means.
Secondly, minerals have beauties of form, color, and structure, and they
do not fade. They will be as perfect in ten years as when found. We are
all naturally crows, and love to gather the objects which interest us.
It is not a bad habit, and only needs directing. Cultivate it. Have a
hobby, and minerals and rocks are a good one; for they are like
treasures in Heaven which “neither moth nor rust doth corrupt.” Not only
will they give you pleasure, but they will be a constructive education,
training the eye to see, and the mind to think straight. No one ever
regretted the time and effort spent in collecting either minerals or
rocks.
Collecting
In order to make a collection valuable two or three rules must be
observed. In the case of rocks, collect large enough samples so that
they will be characteristic, and clear in their make-up. The standard
size for rocks is 3 × 4 inches on top and one to two inches thick
according to the nature of the rock. Tiny fragments do not give the
character of the rock as well, and they are all the time getting into
confusion. Every specimen should be labeled, with at least its name and
the exact locality from which it came. Composition, structural features,
associations, and classification may be added, the more the better; for
each item adds to the information and interest of the specimen. One may
make his own labels or have printed blanks, and may put as much care and
art into the labels as desired, the more the better. One thing is very
important and that is to have a number on the label with a corresponding
one on the specimen, so that in case they should get separated, they may
be readily brought together, even by one who is not familiar with the
individual specimens. Lastly, give your collection as good a place as
possible, either in drawers, boxes or in a case. The specimens are worth
being kept in order and where they can be readily seen and compared.
Nature is systematic, and there is a reason for the order in which rocks
and minerals are taken up. It is desirable either that this order, or
some one of the orders of Nature appear in the collection. In this book
the metals are the basis of classification, all those minerals primarily
related to one of the metals being grouped together.
In collecting minerals, the size of the specimens can not be so
regularly followed, but it should be followed when collecting
non-crystalline minerals, and when possible. Crystals however are chosen
from a variety of points of view, as perfection of form, color, examples
of cleavage, twinning, etc.; so that in many cases smaller or larger
examples must appear in the collection. It is always desirable that as
many variations of a rock or mineral as possible should appear in the
collection, and in many cases examples of the matrix from which the
crystals came. When crystals are tiny, it is well to place them in
vials, that they may not be lost.
Where
Where shall we start in making a collection? Near home. Get the local
minerals and rocks first, and then range as widely as possible. The best
places are bare and exposed rocks, especially where fresh and
un-weathered surfaces are available. Quarries and where there has been
blasting along roads offer fine opportunities. Fissures and cavities in
the rocks are especially likely to have fine crystals, and in all
localities continued search will reveal a surprising number of different
minerals. The greatest variety occur in metamorphic rocks, or where
igneous rocks come in contact with other rocks, but even the sedimentary
rocks have a goodly range of minerals. All through the glaciated regions
of the northern United States lie scattered boulders brought from afar,
which will yield a surprising number of minerals and variety of rocks.
Equipment
One may start with a very simple equipment, a geologist’s or stone
mason’s hammer which can be obtained at any hardware store, being
sufficient for field work. Rocks should be broken, so as to show fresh
surfaces and to get below the disintegrating effects of weathering. At
home one should have a streak plate (a piece of unglazed porcelain), a
set of hardness minerals (see page 20), and a small bottle each of
hydrochloric and nitric acid. A pocket lens is useful in order to see
more clearly the form of small minerals. These things can be purchased
of any Naturalist’s Supply Co., like Ward’s Natural Science
Establishment, P.O. 24, Beachwood Sta., Rochester, N. Y., or the
Kny-Scheerer Corp., 483 First Ave., New York City. Success depends upon
a quick eye, and persistent hunting. When traveling, opportunities are
offered at frequent intervals to see and get new specimens.
Study Your Collection
Be sure and see the meaning in each rock and mineral. The history of the
country is revealed in its rocks and minerals. Note whether the rocks
are horizontal or folded, whether they change character from place to
place, or vertically. In going over a piece of country you may locate an
ancient mountain system now leveled, by noting a series of metamorphic
rocks, with a central core of granite, the roots of former mountains.
Don’t be afraid to draw conclusions from what you see. Later, when the
opportunity offers, look up the region in the geological folio,
bulletin, or map of that section, and check up your findings. These
geological folios and bulletins, of which there is one for nearly every
region, are a great help to collectors in suggesting where to look for
various rocks and minerals. Write to the Director of the U. S.
Geological Survey, Washington, D. C., for a catalogue of the
publications of the United States Survey, or find out from him what are
the maps or folios for the region in which you are interested. These U.
S. publications cost but little. When opportunity presents itself, visit
other collections. In them you will see some of the minerals or rocks
which have puzzled you, and there is nothing quite so satisfactory as
seeing the rocks or minerals themselves. No description can always be so
convincing. Then too you will get suggestions as to localities that you
can visit.
Literature
As your collection grows, if you find you have special interest in one
or another branch of the field, you can get books giving more details in
that line; and at the back of this book will be found a list of such
books.