Chapter I: 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