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               THE COMMON ROCKS AND MINERALS OF MISSOURI


                              W. D. KELLER

                UNIVERSITY OF MISSOURI PRESS • COLUMBIA

  University of Missouri Press, Columbia, Missouri 65201
  ISBN 0-8262-0585-2
  Library of Congress Card Number 67-66173
  Printed and bound in the United States of America
  All rights reserved
  First Edition 1945
  Revised Editions 1948, 1961
  Reprinted 1971, 1973, 1978, 1986, 1989, 1992, 2004




                           TABLE OF CONTENTS


                                                                    Page
  INTRODUCTION                                                         5
  DETERMINATIVE KEY                                                    6
  ROCK AND MINERAL DESCRIPTION                                        10
      Limestone and Dolomite                                          10
      “Cotton Rock” Limestone                                         15
      Marble                                                          15
      Cave Onyx and Deposits                                          16
      Travertine                                                      16
      Calcite                                                         16
      Dolomite                                                        18
      Shale                                                           20
      Fire Clay                                                       24
      Plastic Fire Clay                                               26
      Flint Fire Clay                                                 26
      Diaspore                                                        27
      Burley Clay                                                     29
      Sandstone                                                       30
      Chert, Flint                                                    34
      Weathered Chert                                                 36
      “Kaoleen”                                                       37
      Tripoli                                                         37
      Agate                                                           37
      Jasper                                                          38
      Granite                                                         38
      Quartz                                                          41
      Feldspar                                                        43
      Mica                                                            44
      Porphyry, Rhyolite                                              45
      Basalt                                                          46
      Gabbro, Diabase                                                 48
      Goal                                                            49
      Pyrite, Marcasite                                               51
      Conglomerate                                                    54
      Gneiss                                                          54
      Hematite                                                        56
      Limonite                                                        57
      Paint Ore, Ochre                                                58
      Iron Band Diaspore                                              58
      Manganese Ore                                                   58
      Galena                                                          59
      Sphalerite                                                      60
      Barite                                                          61
      Gypsum                                                          63
      Meteorites                                                      64
      Gold                                                            65
      Silver                                                          65
      Diamonds                                                        65
      Uranium Minerals                                                65
  MISCELLANEOUS ROCK STRUCTURES                                       66
      Concretions                                                     66
      Geodes                                                          67
      Fossils                                                         69
      Arrow Heads, Artifacts                                          71
  THE ROCKS OF MISSOURI                                               71
  MINERALS OF MISSOURI                                                74
  GEOLOGICAL VALUES                                                   74
  INDEX                                                               76




                              INTRODUCTION


Missourians are interested in the rocks and minerals which they find on
their farms, in excavations, and while on their vacation trips. Some of
the specimens are unusual in shape or appearance, some are crystalline
and beautiful, some may be ores of economic importance, but many simply
arouse the curiosity of the finder.

Many of these specimens are received each year at the University at
Columbia, and each is usually accompanied by a request for information
on the correct name for the specimen, its composition, its commercial
value, and the manner of its formation.

Frequently the requests include questions of a broader geological
nature, or seek the recommendation of a general, easily-read book
written on rocks and minerals which may be purchased at a book store or
consulted at a library. Moreover, many persons ask how they may
determine for themselves the geological specimens which they have
collected.

This little booklet has been prepared with the intention of answering
the questions most commonly asked by citizens of the state about
Missouri rocks and minerals.

Descriptions and photographs of Missouri rock and mineral occurrences
are provided, and essential facts about the geological conditions of
their formation are simply told. A determinative key is supplied in
order that the reader may identify and name most of the common specimens
which he collects within the state (and elsewhere, also). No special
determinative equipment will be suggested, and only non-technical
language will be employed because the chief objective here is to furnish
a useful, understandable geological account of the _common_ Missouri
rocks and minerals to the average person without geological training. In
fact, for the purposes of identification no differentiation is made
between mineral and rock, although the professional geologist does
separate them in definition. For our purpose, a rock is an aggregate of
mineral particles, but a mineral is a substance (without life) having
more definite and constant properties than a rock. For those interested
further, more technical and more nearly correct definitions, with
explanations, are given at the back, on page 74.

The rarer minerals and those requiring special equipment for
determination may be sent to the Department of Geology of the University
of Missouri at Columbia for identification free of charge.[1]

Names used locally, and sometimes incorrectly from a strictly technical
sense, for rocks and minerals will follow the generally accepted names,
and both will be duplicated in the index at the back of the pamphlet to
facilitate finding either one.




                           DETERMINATIVE KEY


A rock or mineral specimen which is unfamiliar to the collector may be
identified by using the information in this booklet in either of two
ways: (1) the reader may turn through the pages and compare his specimen
with the photographs of others named there and read their descriptions
until he finds a match for his specimen; or (2), the better way, he may
classify his specimen first by the use of the determinative key which
follows and be directed thereby to the pages in the book for
confirmation of the name by the photographs, description, and discussion
of the substance. The writer recommends the second method and has
prepared this booklet on the assumption that the determinative key will
be used.

The simplest and probably the best means of separating specimens of
different rocks and minerals is on the basis of hardness, which means
_resistance to scratching_. Crushing strength is different from
hardness; therefore, in testing for hardness, do not attempt to
pulverize. Merely determine if the specimen can be scratched with the
substance indicated.

Determination of the mark or “streak” of a mineral when rubbed on a hard
white rock or unglazed porcelain is demonstrated in the photograph on
page 56.

  A. Specimens that can be scratched readily with the THUMB NAIL.
    1. Become muddy when rubbed with a wet finger.
                                                                    Page
      Shale                                                           20
      Fire Clay                                                       24
      Flint Fire Clay                                                 26
      Diaspore Clay                                                   27
    2. Crumble easily into hard sand grains.
      Sandstone                                                       30
    3. Chalky, white, porous.
      Tripoli                                                         37
      Weathered Chert                                                 36
      “Cotton Rock” Dolomite                                          15
    4. Clear and glassy, or glistening white; may split and show glassy,
        flat faces.
      Gypsum                                                          63
  B. Specimens scratched readily with a POCKET KNIFE, or IRON NAIL but
      not with the thumb nail.
    1. Loose sand grains scratched off.
      Sandstone                                                       30
    2. Granular, but grains are tightly interlocked; also “bubbles” or
        effervesces in dilute muriatic (hydrochloric) acid.
      Limestone                                                       10
      Dolomite                                                        10
      Marble                                                          15
      Formed in a cave.
      Cave Onyx                                                       16
      Travertine                                                      16
    3. Chalky white, porous.
      Weathered Chert                                                 36
    4. Black.
      Coal                                                            49
      Black Shale                                                     20
    5. Pebbles or gravel cemented together.
      Conglomerate                                                    54
    6. Powder becomes muddy when wetted.
      Hard Shale                                                      20
      Flint Fire Clay                                                 26
      Diaspore Clay                                                   27
    7. Intense red; leaves a red mark or streak when rubbed on a hard
        white rock or on unglazed porcelain.
      Hematite                                                        56
      Iron Band Diaspore                                              58
      Paint Ore                                                       58
    8. Yellow, brown, or black and leaves a yellow-to-brown mark or
        streak when rubbed on a hard white rock or on unglazed
        porcelain.
      Limonite                                                        57
      Ochre                                                           57
    9. Heavy, black, leaves a black or brownish black mark or streak
        when rubbed on a hard white rock or on unglazed porcelain.
      Manganese Ore                                                   58
    10. Heavy, with bright metallic luster, and lead-colored on a
        freshly broken surface.
      Galena                                                          59
    11. Looks like rosin, or may be ruby-colored or black, but has a
        high resinous luster on freshly broken surface.
      Sphalerite                                                      60
    12. Glassy luster; water-white, milky, honey-colored, pink, gray;
        may occur in six-sided crystals, sometimes pyramid-shaped;
        always breaks with flat glistening faces; always reacts in the
        lump with cold dilute muriatic (hydrochloric) acid.
      Calcite                                                         16
    13. Like calcite above but may have a pink, pearly luster and curved
        crystal faces; reacts with cold dilute acid when powdered but
        not readily in lump form.
      Dolomite                                                        18
    14. Opaque white, glassy or bluish, very heavy, lustrous on freshly
        broken surface; does not react with acid.
      Barite                                                          61
    15. Flaky, micaceous like “isinglass”.
      Mica                                                            44
  C. Specimens TOO HARD to be scratched readily on a fresh surface with
      a pocket knife or iron nail; weathered specimens may be slightly
      scratched.
    1. Very fine-grained throughout, compact; occurs in nodules,
        pebbles; breaks with a slick, curved, oyster-shell-like
        (conchoidal) fracture.
      Chert, if white, gray or stained yellow or red                  34
      Flint, if black                                                 34
      Agate, if banded                                                37
      Petrified Wood, if it shows the grain or bark of wood           37
    2. Granular like sandstone but extremely hard and breaks through the
        grains as readily as around them.
      Quartzite                                                       41
      Quartzitic Sandstone                                            30
    3. Fine-grained, dark green to dark gray to greenish black; occurs
        in boulders north of Missouri River and in the granite and
        porphyry country or southeastern Missouri.
      Basalt                                                          46
    4. Very fine-grained, compact, pink, red, brown, gray; usually
        “freckled” or sprinkled with grains about 1/16 inch in diameter.
      Porphyry                                                        45
      Rhyolite                                                        45
      Rhyolite Porphyry                                               45
    5. Coarse-grained (BB-shot size to considerably larger), glassy
        luster where freshly broken; pink, red, grey.
      Granite                                                         38
      Gneiss, like granite but _banded_; occurs in boulders north of the
          Missouri River                                              38
    6. Coarse-grained, dark green, dark gray, greenish-black.
      Gabbro                                                          54
      Diabase                                                         48
    7. Brassy, metallic, heavy; leaves a black to greenish black mark or
        streak when rubbed on a hard white rock or on unglazed
        porcelain.
      Pyrite                                                          51
      Marcasite                                                       51
    8. Glassy fragments breaking with rough fracture, or may occur in
        six-sided crystals; clear, water-white, milk-white, gray or
        pink; in sand grains; in granite.
      Quartz                                                          41
    9. Intense red; leaves a red mark or streak when rubbed on a hard
        white rock or on unglazed porcelain.
      Hematite                                                        56
      Iron Band Diaspore                                              58
      Paint Ore                                                       58
    10. Yellow, brown or black, but leaves a yellow to brown mark or
        streak when rubbed on a hard white rock or on unglazed
        porcelain.
      Limonite                                                        57




                     ROCK AND MINERAL DESCRIPTIONS


                         Limestone and Dolomite

Limestone is a bedded or layered rock found abundantly in Missouri in
bluffs, creek beds, hill sides, and is known to underlie the soil in
most of the south half of the state. It occurs in thin slabs, thick
layers, and in massive beds which may make a small cliff in themselves.
Limestone is soft enough to be scratched with steel. It is commonly
white to grayish, but may be stained tan, yellowish, or reddish by iron
oxide, or darkened through shades of gray to black by the presence of
very finely-divided, black carbonaceous matter. It may be
microscopically fine-grained (and then it can be used in lithographic
printing in the reproduction of very fine images), or its grains may
vary in size up to one-half inch in cross section.

    [Illustration: Limestone (dolomite) bluff near Jefferson City.]

It is determined as limestone with certainty by wetting with dilute cold
acid; then it “bubbles” or effervesces, and eventually dissolves
entirely. Ordinary or regular limestone contains the mineral calcite,
but the magnesian variety of limestone, dolomite, contains the mineral
dolomite, which does not effervesce freely in lump size in dilute acid,
but which does effervesce when _powdered_ or when treated with hot acid
or concentrated acid. The preferred acid to use is muriatic
(hydrochloric, the “not-cut” soldering acid) diluted one part of acid to
one part of water. Caution! This acid mixture should be stored in a
glass or porcelain container away from children or animals! Acid strong
enough to dissolve rock will ruin clothes, destroy flesh, and is
poisonous! Dilute sulphuric (storage battery) acid will also give the
effervescence test, and the acid of very strong vinegar will react with
limestone slowly. In making the test it should be recognized that the
limestone which acts as a cement in sandstone, or limestone impurities
in shale will also effervesce, but those minor parts of the rock will
dissolve and leave the residues of sandstone or shale, which are
insoluble.

    [Illustration: A coarse-grained limestone effervescing in dilute
    muriatic acid. (This photograph and other close-up views taken by J.
    F. Barham and Allen Barnes, University photographers.)]

    [Illustration: Solid dolomite does not effervesce in dilute acid.
    Note the white rock powder scrapings adjacent.]

    [Illustration: Dolomite powder does effervesce in dilute muriatic
    acid. Not all dolomite is this fine in grain.]

Some limestones are chemical deposits but many are consolidated
accumulations of fossil shells and shell fragments—organic limestone.
For example, a widespread limestone, the so-called Burlington limestone,
extending across central Missouri, contains many crinoid stem fragments
and plates, attesting to the abundance of crinoids living in the sea at
the time this limestone was laid down. Crinoids are sea animals which,
because of their branching structure and superficial resemblance to
plants, have been nicknamed “sea lilies.” Except for calcareous cave and
spring deposits, almost all limestone formations in Missouri contain a
few fossils of animals which lived in the ocean, and therefore Missouri
limestones are considered marine in origin. They offer evidence for the
very interesting land-sea changes which this state has undergone in the
geologic past.

    [Illustration: Limestone composed almost entirely of crinoid (marine
    animal fossil) stem plates, from near Columbia.]

Pure limestone is composed of 100% calcium carbonate (calcite mineral),
whereas pure dolomite contains 54.35% calcium carbonate and 45.65%
magnesium carbonate (dolomite mineral). Magnesium carbonate has slightly
higher acid-neutralizing properties than calcium carbonate, weight for
weight, and because analyses of limestone to be used for soil sweetening
and agricultural fertilizer purposes are commonly reported in calcium
carbonate equivalents, a dolomite or dolomitic limestone may be reported
over 100% calcium carbonate equivalent. Unless one understands the full
meaning of the report he may be bewildered by a statement of the value
over 100%.

The calcium and magnesium which form limestone (or dolomitic limestone)
in the ocean are carried there in solution by the streams which drain
the land. Rain water percolating through the ground and rocks becomes
slightly acidified with carbon dioxide (like the carbonated water in
beverages) and dissolves the calcium and magnesium from primary igneous
rocks like gabbro and basalt which are weathering, or from preexisting
limestones which primitively were derived from igneous rocks. This
calcium and magnesium in solution are responsible for the hardness of
the water. In fact, the hard water in Missouri springs, wells, and
streams is hard because it contains either or both calcium (“lime”) and
magnesium in solution.

This soluble calcium and magnesium flows on in the stream to the ocean
because of its combination with the dissolved carbon dioxide. In the
shallow parts of the ocean, as on the continental shelves where the
water is less than 600 feet deep, the limestone is deposited in layers
just like the white lime layer deposits on the bottom of the teakettle
in which hard water has been boiled. Chemical processes, temperature
changes, evaporation of the ocean water, and organisms are responsible
for most of the limestone deposition. Extensive limestone deposition is
taking place today off the coast of Florida and around the tropical
islands of the southern Pacific.

The uses of limestone are numerous. It is an excellent building stone in
either the rough, sawn, or dressed state. It is used for rubble stone,
rip-rap, railroad ballast, crushed gravel, and aggregate in concrete. It
is one of the raw materials of Portland cement. Quicklime and hydrated
lime are prepared from limestone which has been heated to drive off the
chemically combined carbon dioxide.

Limestone is added as a fluxing material in metallurgical processes. It
is the lowest priced source of alkali in chemical industry. Pulverized
limestone may be used as a filler in paints, putty, paper, or rubber;
and rock wool is made by melting and blowing a limestone having a
suitable chemical composition. Two formations develop a “spongy”
appearance (“sponge rock” or “sponge limestone”) upon weathering and are
utilized abundantly in the eastern part of the state for rock gardens
and for ornamental and decorative stone.

Many tons of limestone are used each year in Missouri as a soil
fertilizer because it neutralizes acidity, coagulates the clay,
furnishes calcium to the plants by way of the colloidal clay, and frees
other chemical elements so that they become available to the plants. No
doubt rocks other than limestone will be crushed and added to the soil
in the future, but today our attention is focussed chiefly on limestone
and dolomite.

The value of a limestone quarry for agricultural purposes depends upon
availability, amount of overburden, purity of the stone, ease of
crushing, and size of deposit. For instance, a stone of 90% purity,
which is close at hand, will probably be more valuable than one of 98%
purity which must be hauled fifteen miles. Bare hillsides or creek banks
where a crusher can be set up to handle the stone without extra lifting
are preferable for quarry sites. Usually the overburden is less in such
an exposed face. Impurities in limestone deposits may be large chert
(flint) nodules which can be hand-sorted out, sand grains, clay which
settled into and onto the stone during its accumulation, and pyrite
(fool’s gold) or other minerals of lesser importance. Clay impurities
simply act as useless extra weight which must be handled. Sand grains,
however, are hard, and will abrade and wear out crushing equipment.
Chert and fine-grained silica likewise are harder than steel and will
wear a crusher excessively. Pure limestone (calcite or dolomite mineral)
has a hardness less than that of steel and will only polish or wear the
metal slightly.

    [Illustration: Typical, intermittently-operated, farm limestone
    quarry near North Kansas City.]

It will probably pay to give some thought to this matter of crushing
when selecting a quarry site for agricultural limestone. The several
beds of stone available should be tested not only for amount, but kinds
of impurities. Samples sent in for testing must be _representative_ of
the rocks under consideration or the analytical results are meaningless.
The writer does not believe this point can be over-emphasized. Time
after time he has seen samples taken of geological deposits for testing
which no more represented the deposits than a bantam rooster picked out
of a chicken pen would represent the egg-laying or weight-production
possibilities of the flock of Plymouth Rock hens.

If five layers or beds of stone are to be properly tested, then five
samples must be taken, _one broken from each layer of solid rock in
place_. The five layers may have the same color, or look much the same,
but fine grains of sand, hardly visible without magnification, may be
abundant in some layers and not in others. If circumstances do not
permit having five different tests made, but allow only one sample to be
run, then specimens should be taken from all five beds, their sizes
being in proportion to the relative amounts expected to be quarried from
each bed, and all five specimens sent to the analyst, who can crush and
mix them.

A single grab sample taken from loose rock on a hillside, in expectation
that it will represent the rocks inside, depends as much on luck as
betting on the weather next 4th of July, a year hence. The chemist who
analyzes the limestone for calcium can usually report on the kind of
impurity if he will take the time to do it.


                        “Cotton Rock” Limestone

“Cotton rock” refers to a white to slightly gray or buff variety of
limestone which has a “soft”, somewhat chalky and porous appearance that
is suggestive of cotton. Missouri “cotton rock” is usually dolomitic.
Although the term “cotton rock” has no standing in a technical sense,
its fairly wide use indicates that the name has descriptive value.


                                 Marble

Marble, in a scientific sense, is a metamorphic rock and does not occur
as such in Missouri. However, marble has been used as a name in
commercial trade to refer to a crystalline, fairly pure limestone, which
possesses most of the useful qualities of true marble. In that sense the
“marbles” quarried near Ozora and Carthage, Missouri, are very excellent
stone. No doubt some recrystallization has occurred in connection with
the faulting in the Ozora region, and this may be interpreted as mild
metamorphism. The Carthage “marble” is quarried from beds of limestone
well developed for structural purposes. These “marbles” effervesce in
acid, of course, just as described for limestone.

In this connection it is interesting to note that the polish on
limestone or marble is not durable where exposed to the weather in the
same sense as is the polish on granite. Because limestone and marble are
softer than granite they may be cut and polished at lower cost, but
because of their ease of attack by acid, water, and abrasion they soon
become dull when used as an exterior stone. For interior decoration they
are excellent, of course. Granite contains hard minerals which happen
not to be attacked appreciably by dilute acids, and therefore it retains
a polish for a long time even where exposed to the weather.


                         Cave Onyx and Deposits

The stalactites (rock icicles) hanging from cave ceilings, stalagmites
built up from the floors, and other drip stone deposits of caves are
largely calcite, the mineral of limestone. Again, this can be recognized
by the limestone acid test (effervescence, see limestone). Cave onyx may
be banded like agate. It is then commonly called Mexican onyx. The name
travertine has also been applied to such deposits from water.


                               Travertine

Travertine is a general name for calcium carbonate deposits of varying
size, shape, color, texture, and purity which originate largely through
evaporation of spring or surface water. Its composition of calcium
carbonate, calcite mineral, is easily confirmed by effervescence in
acid, like limestone.


                                Calcite

Calcite (sometimes called “tiff” locally in south-_western_ Missouri),
the essential mineral in limestone, can be recognized by several
definite characteristics:

  1. It bubbles, “fizzes,” or _effervesces_ in dilute acid. See page 11.
  2. It is easily scratched with a knife.
  3. It breaks or cleaves into rhombohedral shapes, of which at least
          one flat, glistening side is visible on every individual grain
          in the broken surface of limestone.
  4. It has a glassy luster on crystal and cleavage faces.
  5. It crystallizes into six-sided crystal forms, which can be
          differentiated from quartz (also six-sided) by tests (1) and
          (2) above.

The one single test of calcite which is most diagnostic, and which
appeals to most persons, is number one above, effervescence of the solid
lump in dilute acid. The bubbles are filled by carbon dioxide gas which
comes from, and is freed from, the calcite by the reaction of it with
the acid. Calcite is calcium carbonate, CaCO₃.

    [Illustration: A small calcite crystal from the Joplin region.]

Many Missourians have not realized that the ordinary, everyday limestone
(fine to coarse granular), which is so abundant here, is composed of a
mineral—calcite which makes up the grains. The strikingly beautiful
calcite crystals (displayed in museums) derived from the calcite crystal
caves found in some mines in the Joplin district are accepted without
question as _mineral_ specimens of calcite, but the idea that all of the
commonplace glistening grains in the local limestone are also mineral
grains is a new thought to most persons. A pure limestone is composed
entirely of calcite. Even impure limestones which contain subordinate
amounts of quartz sand, chert, clay, or iron oxide are in the main also
calcite. Dolomite and dolomitic limestones contain the mineral dolomite.

The mineral of ordinary marble is calcite; dolomite marble contains
dolomite. The cementing material in sandstone and a common accessory
mineral in shale are calcite. It is truly a wide-spread and abundant
mineral. Even the lime deposit in the bottom of the tea-kettle, the
water heater, boiler, or automobile cooling system is calcite, or
aragonite, a twin brother to calcite.

The use of calcite in the form of limestone is treated under limestone.
As for the use of large calcite crystals, they are sold as ornaments and
curiosities. Visitors to the Missouri State Fair may recall the exhibit
of a beautiful, reconstructed crystal cave which was lined with large
calcite crystals. Calcite crystals have been shipped in car-load lots to
beautify grottos, notably some in Iowa and Illinois, and are displayed
in almost all prominent museums.

Water-white (clear), optical-quality calcite crystals, which command a
high price, are relatively rare and have not been found in Missouri.

The optical property of calcite which accounts for its high value is its
ability to separate, or refract, every single ray of light passing
through it into two widely separated, easily distinguishable rays, hence
doubling their number. This is called double refraction, and is shown by
the double image of an object viewed through the calcite. Instruments
which polarize light may contain calcite crystals. The artificial
product, “Polaroid”, is used for a similar purpose.

    [Illustration: Calcite cleavage rhomb, characteristic rhombohedral
    shape. Note the double image due to high double refraction of
    calcite.]


                                Dolomite

Dolomite mineral occurs in Missouri as a constituent of dolomitic
limestone or as a vein and cavity filling in the rocks of the Joplin
mining district and as a lining in cavities in the dolomitic limestones
of the southern and eastern parts of the state.

Dolomite when _powdered_ (by scraping the surface of the specimen, for
dolomite is softer than steel or glass) effervesces freely in cold
dilute hydrochloric (muriatic) acid, but the lump dolomite effervesces
_very slowly, if at all_. Calcite effervesces freely in the lump with
cold dilute acid. This acid test is the one certain test for dolomite,
and works with the thick-bedded formations as well as with the showy,
crystal-faced material from veins. See page 11.

Dolomite crystals have a pearly luster and are usually pale pink in the
Joplin district. Their faces are commonly curved but where broken show
glistening to pearly cleavage faces. These properties assume more
significance in mineral determination as one becomes familiar with
mineral collections, but the non-technical person can rely on the acid
test.

    [Illustration: Typical dolomite crystals from Joplin region.]

With the above information in mind, one may proceed with certainty to
identify a layer of dolomite from a quarry or hillside, or a crystal of
it in a hand specimen. First, determine that it is scratched readily
with a knife blade or iron nail. Anything too hard to be scratched by
steel is neither calcite nor dolomite. Second, scrape a small mound of
powder on the lump specimens. Third, apply one or two drops of cold
dilute acid to the lump near the powder and allow the acid to run into
the powder. If the _lump_ effervesces _freely_ the specimen is _calcite_
mineral or limestone rock. If the _lump_ does _not effervesce freely_
but the _powder does_, it is _dolomite_ mineral or dolomite rock,
dolomitic limestone. If neither lump nor powder effervesce it is neither
calcite (ordinary limestone) nor dolomite (dolomitic limestone). In the
latter case, it may be gypsum, barite, Shale, weathered chert, clay, or
fire clay, or other rock.

The composition of dolomite is calcium-magnesium carbonate, CaMg(CO₃)₂,
and when pure runs about 54½ per cent calcium carbonate and 45½ per cent
magnesium carbonate. However, dolomite is _not a mechanical mixture_ of
the two carbonates; it is a single crystalline compound wherein the
calcium and magnesium are securely interlocked within the arrangement of
the atoms. For that reason, the extraction of magnesium metal or other
magnesium compounds from dolomite is so difficult and costly that other
magnesium minerals, although not nearly so abundant and accessible to
industry as dolomite, have been processed to obtain the lightweight
metal magnesium.

The thick beds of Missouri dolomitic limestone (and some fairly pure
dolomite) have been used chiefly as agricultural stone for soil
sweetening, for building stone, gravel, and other purposes to which
rough stone is put.


                                 Shale

    [Illustration: Shale bluff at a strip mine near Columbia.]

Shale is a compressed, and layered or laminated clay or mud rock.
Consequently it will return to mud if it is wetted with water and
rubbed. This may serve as a test for shale. It may occur in thick layers
or formations, five, ten to fifty or more feet in thickness, and it
ranges downward to paper-thin partings between beds of limestone. It is
also commonly associated with coal beds. The color of shale varies from
light gray to black, or it may be tan, yellow, red, rust, purplish, or
green. It is platy, and these thin plates or laminae, piled on each
other, make up the shale bed.

    [Illustration: Hand specimen of shale shown in preceding picture.
    Note the characteristic thin layering or lamination.]

Some shales are hard, tough, and strong enough to serve as temporary
mine roofs. Hard shales are sometimes called “slate” but this name is
technically incorrect. _True slate_ is a metamorphic rock, composed
chiefly of the mineral mica in very fine flakes, and will resist the
action of water (weathering) for a long time. Therefore, it is a good
roofing material for buildings, whereas shale is composed chiefly of
clay minerals, and despite the strength and compactness of the more
“slaty” varieties soon disintegrates in water. Missouri “slaty” shale
would not serve as satisfactory roofing material.

The red “burned” shale found on burned-out coal mine dumps is called
“shale” locally. It is, of course, shale which has been fired more or
less to the condition of building brick by the hot burning waste coal.
The same original shale could be crushed, molded into brick, “burned” in
a kiln, and become a satisfactory building brick. The “burned shale” of
the coal mine dumps is used in many places as a drive-way covering.

“Soapstone” is a name applied by some persons to some soft, slippery to
greasy shales, but this name is incorrect in a technical sense. True
soapstone is a metamorphic rock (shale is sedimentary) which is composed
chiefly of the mineral talc. Soapstone occurs abundantly in certain
parts of the Appalachian Mountains but is exceedingly sparse in
Missouri.

The chief commercial uses of shale are in the manufacture of common
brick, building brick, building tile, drain tile, sewer pipe, Portland
cement, and other ceramic products. Many shale beds and occurrences are
technically suitable for these uses but have no real commercial value
because other necessary factors are lacking. In order to make brick,
tile, or cement there must be sufficient fuel available at low cost,
low-priced bulk transportation of the raw and finished products,
available labor, capital for the erection of a plant, and above all a
large near-by, dependable market for the manufactured product. The value
of a shale deposit, therefore, depends as much upon outside conditions
as upon the properties of the rock (shale) itself.

The shales of Missouri were formed from deposits of mud that settled out
in sea water which in the past covered this state. Fossil remains of
sea-living organisms which are preserved in the shale give evidence of
the marine conditions once existent here. Like the muds that are
accumulating along the Atlantic coast and in the Gulf of Mexico, where
the Mississippi River is discharging its load of silt and clay, so did
mud form layers on the bottom of geologically ancient interior seas. In
some cases sand was later washed in and covered the mud; in other cases
limestone-forming material (like off the coast of Florida today) was
deposited on top of the mud. The weight of the overlying beds and the
slow movement which raised the sea bottom up to land squeezed out the
excess water, compressed and compacted the muds into thin layers, and
brought about the shale rock which is exposed to us today.

    [Illustration: Soft, easily eroded bed of shale between two more
    resistant beds of limestone near Columbia.]

Black muds, rich in humus and other organic material, formed black
shales; red and yellow clays colored by red and yellow iron oxides (iron
rusts) formed red and yellow shales; and sandy muds were compacted into
gritty, sandy shales. All of them were derived from eroding land and
soils just as today our eroding soils contribute to the formation of
more shale now in the long, slow process of formation.

The chemical composition of an average shale is not simple, as is shown
by the subjoined composite analyses of sedimentary rocks taken from U.
S. Geological Survey Professional Paper No. 127.

                         78 shales   253 sandstones   345 limestones

  SiO₂                       58.11            78.31             5.19
  Al₃O₂                      15.40             4.76              .81
  Fe₂O₃                       4.02             1.08              .54
  FeO                         2.45              .30
  MnO                         2.44             1.16             7.89
  CaO                         3.10             5.50            42.57
  Na₃O                        1.30              .45              .05
  K₂O                         3.24             1.32              .33
  H₂O+                        3.66             1.32              .56
  H₂O-                        1.33              .31              .21
  CO₂                         2.63             5.04            41.54
  TiO₃                         .65              .25              .06
  P₃O₅                         .17              .08              .04
  SO₃                          .65              .07              .05
  Organic carbon               .80                —                —
                            (100.)           (100.)   approx. (100.)

Many persons upon learning that average shale, and even “clay dirt,” may
contain 15% alumina, Al₂O₃ (equivalent to almost 8% metallic aluminum),
become thoughtlessly and erroneously enthusiastic about aluminum ore
possibilities on their farms or properties. The aluminum is there all
right, but it is so securely combined with silica and other elements
that the cost of extraction is now greater than the price of aluminum
obtained from less abundant ores. Until chemists find a method of
extraction of the metal from ordinary clay or shale that can be carried
out at considerably less expense than is now possible, the vast
quantities of clay and shale on the earth’s surface must be considered a
distant reserve of a prohibitively high cost aluminum.

Missouri possesses a little bauxitic clay in the southeastern part of
the state but unfortunately does not contain deposits of high grade
bauxite, the chief ore of aluminum, and so does not contribute to the
aluminum production of the United States (see the discussion under
DIASPORE CLAY). Arkansas is a leading producer of bauxite, but the
geological conditions present in that bauxite locality are so different
from Missouri geology that little hope is held for finding bauxite in
Missouri, except possibly in the extreme southeastern part.


                               Fire Clay

Fire clay resembles shale in that it is also a clayey rock and becomes
muddy upon wetting and rubbing. It differs from shale at sight in that
it (fire clay) is not laminated like shale, but occurs instead in a
massive structure which is relatively uniform throughout. Fire clay
fractures naturally into blocky or irregular fragments ranging in size
from boulders to rough flakes, whereas shale weathers into layered,
platy chips.

Shales are commonly buff, yellow, reddish, greenish, or brown in
addition to gray in color, whereas good useable fire clay predominates
in white, cream, and gray to almost black (if much organic matter is
contained in it). Shale is ordinarily gritty with hard sand particles,
but most good Missouri fire clay contains only a small amount of sand.
Of course, fire clay may grade into sandstone through a sandy clay
phase, but this part would not be confused with a layered, gritty shale.

The really determining characteristic of fire clay is its resistance to
melting under high temperature. The most positive test for this property
is to heat the fire clay to a white heat in comparison with standard
preparations (Pyrometric Test Cones) whose fusion temperatures are
known. Most of Missouri fire clay will withstand a clean oxidizing heat
of over 3000° Fahrenheit without melting.

Clay minerals originate, in general, from the weathering of previously
existing silicate rocks and have therefore been called, on occasions,
“rotted rocks.” The writer has long insisted that clays, particularly
fire clays, should be thought of instead as purified or refined rocks.
The original silicate rocks and minerals, which were rich in
constituents melting at low temperatures, have been soaked, leached, and
washed by chemically active ground water and rain water until many of
the undesirable elements have been carried away, leaving a refined
material which we use and know as fire clay. Missouri possesses one of
the largest reserves of finest quality fire clay in the world. Special
bulletins on Missouri fire clay are published by the State Geologist,
Rolla, Missouri, and may be obtained from his office.

    [Illustration: Plastic fire clay. Shows typical break and naturally
    polished slicken-sided surfaces. From Mexico, Missouri.]

    [Illustration: Typical break.]

Persons who have undeveloped fire clay deposits on their property
frequently ask advice on whom to contact and how to arrange for sale of
their fire clay, with the expectation of a fair return and fair
treatment. The writer recommends in such cases that the owner of the
clay dig into his deposit to obtain a fresh, clean, _representative_
specimen of his fire clay (about one pound) and send it to one or more
of the large substantial fire brick or refractories companies operating
in Missouri. Obviously the company located nearest the deposit, or with
the lowest-cost shipping facilities, will be in a favored position to
purchase the clay. If the individual is skeptical about the
trustworthiness of the company’s report, he may send opposite parts of
the sample lumps to competitive companies. Of course, the individual may
have his clay tested by an independent laboratory at his own expense,
but this is ordinarily a useless, costly experience because a company
will duplicate those tests in its own laboratory before purchasing the
clay. If the refractories companies find the clay useful to them they
will proceed with negotiations. If the clay is of inferior quality or if
it is not needed by the particular company at _that time_, even though
of acceptable quality, usually the company will return a truthful report
at no cost to the clay owner.

The same general advice is given in regard to the development of any
mineral deposit which the holder may have. The caution about obtaining a
representative sample is especially to be emphasized. It applies to the
metallic ores, mineral water, and common rock as well as to fire clay.


                           Plastic Fire Clay

Plastic fire clay forms a sticky, soft mass when wetted and kneaded with
water, and will bond together other clays or rocks. Large plastic fire
clay deposits occur in Audrain, Callaway, and St. Louis counties, and
lesser quantities are known in Boone, Osage, Gasconade, and Phelps
counties. The larger deposits assume a blanket shape with a highly
irregular lower surface.


                            Flint Fire Clay

Flint fire clay is very fine-grained, smooth or slick, and breaks with a
shell-like (conchoidal) fracture. It varies in color from white to
black, but most flint fire clay mined is near to white. It is relatively
non-plastic—that is, does not readily slake or form a sticky mass when
worked a little in water. In fact, flint fire clay has been used locally
as road surfacing because it does not become very muddy and sticky. Of
course, it is inferior to black-top or concrete road surfaces and has
too high a commercial value now to be used extensively as road metal.

A hard, white variety of flint fire clay which breaks with numerous
conchoidal fractures in appropriate shaped fragments has been called
locally “pop-corn flint.” This clay, and other sand-free flint clay,
when crushed between one’s teeth “goes to water” in the mouth. Many clay
miners use the chewing test to establish the freedom of their clays from
gritty sand, which renders flint clay inferior in quality.

    [Illustration: Flint fire clay showing typical “slick break” and
    conchoidal fracture, from near New Florence.]

Flint fire clays occur geologically in old land depressions and in
roughly funnel-shaped pits surrounded by an enclosing layer of
sandstone, the whole lying within limestone country rock. The most
prominent flint fire clay deposits are found in Callaway, Warren,
Lincoln, Osage, Gasconade, Maries, Franklin, and Phelps counties.


                             Diaspore Clay

Diaspore clay is a harsh, usually porous, earthy type of clay which has
been found in Warren, Osage, Gasconade, Maries, Franklin, Phelps, and
Crawford counties in Missouri. Some diaspore clay is mealy, or finely
granular, some is chalky to compact, and much of it is more or less
oolitic. Oolites (oolitic structure) are small rounded bodies varying in
size from about bird shot to BB shot size, and those in diaspore may be
solid or hollow. Their hollow structure contributes to the porous
condition in diaspore clay. See page 29.

It is almost impossible to write a description of diaspore clay which
can be used to determine it because the clay has so few individual
characteristics. A person familiar with diaspore clay, however, can
recognize it at a glance. Probably diaspore clay will not be found
outside the counties listed above, and within those counties many
persons know the clay from contact with the commercial production of it.

    [Illustration: Diaspore clay, over 70% alumina, from near Belle.]

Diaspore clay occurs in old sink-hole, funnel-shaped pits which formed
in the dolomite (limestone) underlying that region. A sandstone layer
which lines the pit and commonly stands somewhat above the level of the
clay because of the sandstones superior resistance to weathering is
known as the “rim rock” of the pit. The diaspore clay may be thought of
as an extra-refined type of fire clay from which silica has been leached
during prolonged solution in swamps and ground water and the more stable
alumina (Al₂O₃) left behind as the refined product.

Pits in the diaspore region may contain from a few truck loads of clay
to over 50,000 tons of it, but a pit which produces 10,000 tons of good
clay is a valuable and not very common deposit. A small fortune falls to
the landowner who finds a large diaspore deposit (pit) on his farm, for
royalty rates at this time are not less than $1.00 per ton for first
grade, 70% Al₂O₃ clay.

Because of the high value of diaspore, a highly competitive prospecting,
leasing, mining, and brokerage business has developed in the diaspore
region. Practically all of the thrills, hopes, disappointments, and good
fortunes that are associated with oil booms are found in this business
and clay area; clay pits are only smaller in scale than wild oil
gushers. Clay scouts work in secret, mining leases are contested in
court, rumors fly fast in English, German, and German-Swiss over the
country telephones, prospecting results may be hidden, personal pressure
may be brought to influence a deal, and speedy salesmanship is employed
when an exciting find is in the offing. When the legends, traditions,
and facts of the diaspore region are collected and recorded, an
interesting and essential part of Missouri history will have been
written.

Missouri has the only locality in the entire world where relatively pure
diaspore clay is now mined in commercial quantities. Because of its
extreme resistance to fusion under very high temperatures, diaspore has
been called the “aristocrat of fire clays.” Diaspore contains a higher
percentage of aluminum than does bauxite, the chief ore of aluminum, but
because of diaspore’s extremely refractory nature it is less easily
reduced to aluminum metal than is bauxite, and therefore finds a more
specialized use in the manufacture of refractory and super-refractory
brick and tile which may even be used in furnaces to calcine aluminum
ore. Where resistance to very high temperature has been required,
diaspore super fire brick has been remarkably useful.


                              Burley Clay

    [Illustration: Burley clay. Note the oolitic structure, the “burls.”
    From a diaspore pit near Swiss.]

Burley clay is a fire clay intermediate in alumina content between flint
clay and first quality diaspore. It takes its name from the oolites
(rounded pellets of diaspore) which are scattered through a flint clay
base and which were called “burls” by the early clay miners. As the
relative number of diaspore oolites increase, an otherwise flint clay
becomes burley-flint, then typical burley, and finally grades into
second quality and first quality diaspore. Clay in any stage of the
variation may be found in some part of the diaspore region or pits. Most
of the remarks written on diaspore apply as well to burley clay.


                               Sandstone

Sandstone is a rock made of sand-size particles more or less well
cemented. It is recognized by the grains of sand which are dislodged or
scratched loose when the rock is broken, or when scraped with a piece of
steel or another hard rock. The old-fashioned grindstone is a sandstone
nicely cemented by nature.

    [Illustration: Sandstone bluff near mine entrance, Crystal City.
    (Photo courtesy of Pittsburgh Plate Glass Company.)]

Sandstone occurs in thin layers to thick massive beds and deposits which
may exceed fifty feet in thickness. In addition to possessing horizontal
bedding and parallel bedding planes, some sandstone displays beautiful,
intricate cross-bedding or cross-lamination.

The grains of sand composing the stone may be either angular or rounded.
They may sparkle in the light from reflections from their crystal faces,
or they may have dull, frosted surfaces. Sandstones are ordinarily
nearly white in color except where the grains are covered with coatings
of yellow or red iron oxide (rust).

    [Illustration: Cross-bedding in sandstone north of Fredericktown.]

    [Illustration: Sandstone in hand specimen. Magnification 4x.]

    [Illustration: Quartz sand grains. Magnification 21x.]

The grains themselves are predominantly particles of the mineral quartz,
although any rock or mineral of sand size may be present in sandstone.
The quartz (see discussion of quartz on page 41) may have been derived
from pre-existing sandstones or more directly from granite, porphyry, or
other igneous rocks in which quartz crystallized when the hot liquid
rock solidified. Today quartz grains which are weathering out of igneous
rocks and sandstones are being carried by the Missouri river and
tributaries to the Mississippi river and thence to the ocean, where
extensive deposits of sand are accumulating, probably destined to become
widespread beds of sandstone.

The grains of sand may be broken and become angular during their long
trip to the ocean, or they may become rounded by rubbing against each
other. If they exist in sand dunes, blown about by the wind before being
cemented into rock, the grains usually become somewhat rounded. Even
after sandstones are buried beneath other rocks, silica, which is
carried in solution by ground waters percolating through the sandstone,
may crystallize out on the sand grains and restore some brilliant,
angular crystal faces to the otherwise rounded grains.

Cementation of loose sand to more or less firm sandstone is due to the
presence of clay, iron oxides, or calcite (mineral of limestone) which
may be deposited with the sand. All of these cements are softer and
weaker than quartz, thereby being broken first and freeing the harder
quartz when the rock is scratched or crushed.

A variety of very hard sandstone called quartzite is one that is so
strongly cemented that it breaks through the sand grains instead of
around them as is the case with ordinary sandstone. This condition is
brought about by their being cemented with silica (chemically the same
as quartz), which makes for essentially uniform hardness throughout the
rock.

Quartzites are, as previously noted, extremely hard, and resist abrasion
and chemical weathering. Reddish quartzite boulders occur rather
abundantly north of the Missouri River in the glacial clay, sand, and
gravel which overlie the sedimentary rocks that form the bed rock or
country rock there. Locally, the hard, red quartzite boulders may be
called “red niggerheads”, although the term “niggerhead” is more often
applied to black or dark greenish black boulders of basalt (see page 48)
also present in the glacial drift. It is to be recalled that the
distinguishing hardness of quartzite is due to the hardness of the
quartz grains plus the equal hardness of the silica cement.

Asphaltic sandstone is a sandstone impregnated with a bituminous residue
from the evaporation of petroleum which once occupied the pores of the
rock. It has been reported from more than a dozen counties in western
Missouri, but the most extensive deposits are probably in Barton,
Vernon, and Lafayette counties.

Attention has been directed to the origin of sandstones from ocean
deposits of sand and from sand dunes, but it should be recognized also
that river channels and stream valleys which contain deposits of sand
(such as those on floodplains, river bottoms, and sand bars) may be
covered, and the sand consolidated to sandstone. Many years ago, even
long ago geologically, a large river, almost comparable in size to the
Missouri river, occupied a channel which is now represented by a long
narrow sandstone deposit extending from a little north of Clinton
through Warrensburg to Lexington and then east through Moberly almost to
Paris. Smaller channel sandstones are abundant in other areas in
Missouri.

The sandstones of the so-called Roubidoux formation, which occurs in
south central Missouri, commonly show well-preserved ripple marks on the
rock slabs. These marks were formed exactly as their name suggests—in
sand which was thrown into ripples by the shallow water in which it
accumulated and was covered and cemented so as to retain the ripple
forms.

    [Illustration: Ripple marks in limy sandstone.]

Sandstone is used for building stone, walks, grindstones, furnace
linings, and rock gardens. Large quantities are mined each year near
Pacific, Festus and Crystal City, Klondike, and Hermann, for the
manufacture of glass and other uses. Common glass is a cooled melt of
relatively pure silica sand, soda ash, and lime. Asphaltic sandstone is
used in road building. Sand-lime brick are made of sand. Sand is used as
a molding material for metal castings, a parting substance between brick
in kilns, and in large quantities in concrete and mortar mixtures.


                              Chert, Flint

The names chert and flint have in some regions been used for the same
hard, fine-grained rock found so abundantly in Missouri, but correct
usage employs chert for the white and gray varieties, and flint for the
black variety. Flint may be thought of as slightly impure chert, a chert
which is colored black by a small amount of pigment, usually fine
carbon, or perhaps iron sulphide, scattered through it like fine dust.

    [Illustration: Chert, fossiliferous and slightly speckled. Note
    typical sharp edges, smooth surfaces, and conchoidal fracture. From
    near Columbia.]

Chert is characterized by being harder than glass, brittle, very
fine-grained, and by breaking with a smooth, rounded or hollowed clam
shell-like (conchoidal) fracture and sharp edges. It was used by Indians
to make arrow heads. It accumulates in abundance both in stream beds as
gravel which has been more or less rounded by wear, and on the hillsides
within the soil and sub-soil. Yellow and red iron oxides may stain and
penetrate weathered chert gravel so that it becomes reddish, rusty, tan,
yellow or brown.

Chert remains abundant because of its extreme resistance to weathering.
It is so hard that stream action wears it only very slowly. Its chemical
composition is silica, SiO₂, a substance which is but little affected
chemically by ground water. Where chert has contained fine grains of
calcite scattered through it, the calcite may be removed in solution,
leaving pores, and a zone of porous, light weight, tripolitic chert,
harsh to the feel and enveloping an unaltered interior (See WEATHERED
CHERT). Not uncommonly, fossil remains of calcite which were embedded in
chert have been dissolved, leaving their hollow impressions.

Chert in Missouri originally occurs chiefly in limestone formations,
where it is found as nodules, lenses, stringers, and irregular forms in
and between the limestone beds. Chert and flint may be deposited
directly from silica in solution, or they may replace (substitute for)
wood, fossils, or older rock where silica-bearing solutions contact and
react with the replaced substance. For example, petrified wood usually
is wood which has been replaced molecule by molecule with silica. This
statement applies equally to the brightly colored petrified wood in the
Petrified Forest in Arizona and to that with comparatively drab coloring
in Missouri. Many other siliceous fossils, notably animal remains, are
replacements of calcite (limestone) by silica.

In anticipation that the reader may have difficulty understanding how
silica may go into solution if chert (silica) is hardly attacked by the
weathering process, it should be explained that silica is freed in
solution predominately during the weathering of complex
silica-combinations, silicates, rather than from uncombined silica. For
instance, feldspar and pyroxene from granite or gabbro weather in ground
water to a soil-forming clay mineral and release some silica in solution
in the ground water. After this silica is redeposited in an uncombined
form, like chert, it becomes highly insoluble.

An observation in regard to flint is that the metallic “flints” which
are used to ignite gas burners or cigarette lighters are not black
chert, SiO₂. Instead, they are special alloys containing rather uncommon
elements which possess the useful characteristic of emitting a brilliant
hot spark when harshly scratched.

Chert is the chief source of natural gravel in Missouri because it
accumulates in stream beds and on hillsides on account of its resistance
to weathering. The piles of “chats” in the Joplin region, containing
thousands of tons of crushed chert, have been used in part in road
surfacing material.


                            Weathered Chert

Weathered chert, or leached chert, is a white to gray, or yellowish,
porous, light-weight, harsh to feel, chalky-appearing rock which occurs
over much of the southern half of Missouri. It does not effervesce in
acid. Usually it occurs as a zone from a fraction of, to more than an
inch in thickness, about a denser core of hard, compact chert (flint),
or makes up an entire small rock fragment or gravel.

    [Illustration: Chert hand specimen showing quartz-lined fossil
    cavity in center, compact fresh chert in interior, and
    chalky-appearing weathered outside margins. From near Columbia.]

It develops as a relatively insoluble residue left when the more soluble
rock material in association has been leached away during the weathering
process. Its composition approaches pure silica. It has no established
use and no commercial value.


                               “Kaoleen”

“Kaoleen” is a term used locally in part of south-central Missouri to
refer to a chalky, white to tan or buff, porous weathered chert, but the
name should be dropped because it is unnecessary (use weathered chert),
confusing, and not recognized elsewhere. Most probably the term arose in
corruption of the word _kaolin_, which is the name for a true,
high-quality clay, to which the leached and weathered chert bears a
slight resemblance. Kaolin has the chemical composition of clay (hydrous
aluminum silicate), whereas “kaoleen” is impure silica. See the
discussion on Weathered Chert.


                                Tripoli

Tripoli occurs in the vicinity of Seneca, Newton County, Missouri. It is
a light-weight, porous, white to creamy, siliceous rock, which may be
scratched because of its softness. Tripoli represents the porous
insoluble residue of an earlier rock, which was composed of skeletal
insoluble silica and interstitial soluble calcium carbonate (calcite),
the latter having been dissolved away by ground water. Tripoli has a
chalky appearance but is totally unlike chalk chemically. Tripoli is
nearly pure silica, whereas chalk is calcium carbonate. Any tripoli-like
rock found in Missouri outside the region of tripoli mines is likely to
be a fragment of weathered chert which is described above.

Tripoli has been used as an abrasive, a polishing agent, a parting
material in molding sand, and a filter rock.


                                 Agate

Agate is a banded variety of chert. Although the chemical composition of
agate is SiO₂, the same as chert, a microscopically fibrous part of it
having a waxy luster or varying in color or translucency may give the
appearance to the rock that we associate with the name agate. The
mineral name chalcedony is given to the fibrous, waxy material.

Typical agates are most abundant in Missouri in the glacial and stream
gravels in the northern part of the state, although part of the Potosi
drusy quartz and chalcedony in the southeast is also prized. The large
gravel pit near LaGrange, in the northeast, has furnished many beautiful
specimens, not only of agate, but also of petrified wood and fossils.

Missouri lapidists and collectors of semi-precious stones find plenty of
interesting raw material within their own state.


                                 Jasper

Jasper is chert which is colored red or yellowish brown by iron oxides.


                                Granite

    [Illustration: Close view of a granite hand specimen. Feldspar
    predominates. Quartz appears dark in the photograph, but shows
    glistening edges and points. From Graniteville.]

Granite is a granular (coarse-grained) rock which has a glassy luster
and is too hard to be scratched appreciably by steel. It may be white to
gray, tan, brown, or pink to red in color, but pinkish to red granite
predominates in Missouri. Some black stone, referred to locally as
“black granite,” is usually a variety of gabbro. Most Missouri granite
is coarse-grained, so that the constituent mineral grains—quartz,
feldspar, and (less frequently) mica—can be readily recognized by anyone
familiar with those minerals. It makes up many of the mountains and
hills in Iron, Madison, and St. Francois counties and adjacent regions.
North of the Missouri River, or where the glacial deposits remain,
granite boulders may occur in the sandy and clayey glacial drift.

The mineral quartz is recognized in granite by its glistening, oily
luster, really more brilliant than the luster of glass, and by its
curved to irregular broken surface. Furthermore, the brilliant luster of
quartz is not dulled by exposure to weather.

The mineral feldspar, in granite, has a glassy luster on the tiny flat
cleavage faces where the individual grains are broken. Where weathered,
feldspar becomes dulled, and chalky to dusty or clayey. Fresh feldspar
may be glassy, white, buff, pink, red, in intermediate shades in color.
With the mica, it imparts most of the color to granite.

Mica is recognized by its softness and its ability to be split very
easily into tiny flakes. Other minerals may be found in granite under
the microscope, but they have little importance or significance.

    [Illustration: Granite at the “Elephant Rocks,” Graniteville. The
    large boulders now rounded by weathering are remnants of a higher
    part of the large granite body which underlies this region.
    (Photograph courtesy of Mr. Noel Hubbard).]

Granite is an intrusive igneous rock; that is, it solidified from a hot
liquid state (like lava) in a large body, beneath, or surrounded by
pre-existing rocks. Because of slow solidification a coarse-grained
texture was developed. In southeastern Missouri where granite is now
exposed at the surface (for example, the Elephant Rocks State Park at
Graniteville), that granite was covered originally by hundreds of feet
of rock at the time it solidified from a liquid. During the millions of
years which have elapsed since the granite solidified, its cover and the
upper part of the granite have been eroded away by streams and rain
after weathering to soil material. In fact, the ocean has covered the
area several times during its long geological history.

Missouri has a fine quality of granite in large quantity in southeastern
Missouri. Granite is used for building, structural and monument purposes
(see discussion under marble), for rubble stone, rip-rap, ballast,
gravel, paving blocks, crushed chicken gravel, and for other specialized
uses where favorably located. Chemical analyses of granite and porphry,
taken from Missouri Geological Survey Report, Volume VIII, 1895, follow.

                    Porphyry 6 miles east    Granite 6 miles east
                               of Ironton              of Ironton

  SiO₂                              71.88                   72.35
  Al₂O₃                             12.88                   13.78
  Fe₂O₃                              3.05                    1.87
  FeO                                1.05                    0.36
  CaO                                1.13                    0.87
  MgO                                0.33                    0.42
  K₂O                                4.46                    4.49
  Na₂O                               4.21                    4.14
  P₂O₅                               0.15                    0.13
  TiO₃                               0.22                    0.44
  Ignition loss                      0.26                    0.54

The glacial granite boulders found in central to northern Missouri also
solidified as intrusive rock in the northern United States or in Canada.
After being exposed at the surface they were picked up and carried down
by the geologically recent, continental ice sheet (glacier) that moved
down from Canada to across the northern half of Missouri. Scratches and
grooves may have been cut in some of these boulders, or flat faces
scoured and planed off as they were scraped against other hard rocks.
Quartz gravel is usually present, often in abundance, in glacial
deposits. Small specimens of native metallic copper, which come from
near Lake Superior, have been found in Missouri glacial deposits. Even
diamonds from an unknown source in the north were carried by the ice
down into the United States. The history of the glaciation is a
spectacular account of changes which our continent has undergone in the
geological past.

    [Illustration: Glacial scratches on boulder carried by the large
    glacier in northern Missouri long ago. Boulder from near Columbia.]


                                 Quartz

Quartz is a mineral of wide-spread occurrence which is characterized by
the following properties: (1) it is considerably harder than glass or
steel, (2) it has a high luster, glassy to oily, (3) it breaks with an
irregular or rough glistening fracture, and (4) it crystallizes in
six-sided crystals when it grows unobstructed. Ordinary acids do not
attack quartz, and it is relatively unaffected by chemical weathering in
Missouri. Its composition is silicon dioxide, SiO₂.

Quartz occurs in granite as the lustrous, partially rounded grains which
constitute perhaps 20% of the rock (feldspar makes up most of the more
opaque remainder which breaks with many small flat faces), and is
recognized in the small glistening grains in the porphyry. Hence it is
an important igneous rock-forming mineral.

Sandstone in Missouri is made almost entirely of quartz grains which
have been broken, worn, and more or less rounded during their long
travel history. The sandstone formation quarried and mined near Pacific
and Crystal City, named the St. Peter sandstone formation, is an
outstandingly pure quartz sandstone and therefore usable in the glass
industry. It is obvious that quartz is an important constituent of
sedimentary rocks.

    [Illustration: Lustrous, translucent quartz. The irregular fracture
    and oily luster are characteristic.]

Further, in the sedimentary dolomite formation near Potosi, fine to
coarse quartz crystals line the surfaces of cavities and pockets in the
stone. This cavity coating of quartz which reflects light brilliantly
from the many small crystal faces is called drusy quartz by the
mineralogist, but is locally and popularly known as “blossom rock.”
Thousands of pounds of “blossom rock” are sold each year for rock
gardens and various ornamental purposes.

In northeastern Missouri quartz crystals line the hollow, more or less
spherical bodies called Geodes, which vary in size from small nuts to
melons, and weather out of the so-called Warsaw formation. Other types
of hollow cavities in many Missouri rocks may contain quartz growing
inward from their walls.

Missouri chert is composed primarily of quartz in microscopically fine
grains; likewise, agate and petrified wood may contain abundant quartz.
Other varieties are rock crystal, rose quartz, amethyst, false topaz,
bloodstone, carnelian, and onyx.

Quartz crystallized in an igneous rock as the hot fluid cooled through
its “freezing” temperature interval, which was probably not below
1000°F. In the cases of the quartz in geodes, the drusy quartz, or that
in cavities within petrified wood, quartz crystals grew from ground
water solutions which must have carried very low concentrations of
silica in solution, and whose temperatures did not depart far from that
of rocks buried at various depths today. Although quartz is a very
common and abundant mineral, our specific knowledge about its transport
and deposition is surprisingly meager.

    [Illustration: Quartz crystal cluster. Crystals are six-sided. From
    Arkansas.]

Quartz crystals are used in large quantities in radio apparatus where it
is necessary to maintain very close control on the tuning of a circuit.
This use requires quartz of highest quality and crystals above minimum
size, which have never been found in Missouri and probably are not
present. Silica production from this state is in its sandstone, tripoli,
chert chats, and rock garden ornamental stone.


                                Feldspar

Feldspar is a white to pink or red mineral having a glassy luster on its
flat broken surfaces (cleavage faces). It will scratch window glass.

It is the most abundant mineral in granite and usually controls the
color of that rock; for example, the red granite at Graniteville
contains red feldspar, and the pink-gray granite in the Knoblick region
has feldspar of those colors. Small bodies or bands of very coarse
feldspar, quartz, and mica (pegmatite dikes) which cut the granite may
contain crystals of feldspar large enough to be recovered as small, hand
specimens, but otherwise it does not occur in coarse fragments. The
recognizable crystals, or phenocrysts, in the porphyry are mainly
feldspar.

    [Illustration: A large piece of feldspar showing cleavage surfaces.]

Feldspar is really a family name for a group of several minerals, all of
which are crystallized in the igneous rocks. The potassium
(potash)-containing varieties, named orthoclase and microcline, occur in
the granite and porphyry, whereas plagioclase, a calcium-sodium
(lime-soda) feldspar is in gabbro, diabase, and basalt.

Plagioclase commonly has a thin, lath shape, is a shade of gray, and
makes up the lighter colored part of the greenish to dark gray igneous
rocks. Further differences between it and orthoclase may interest the
mineralogist but are of little concern to the non-technical person.

Pulverized feldspars are used extensively in the ceramic industries, but
Missouri does not have any productive deposits. Under natural, long-time
weathering processes feldspar usually decomposes to clay which may be
used technically, but the usual fate of it is soil formation.


                                  Mica

Mica, incorrectly called isinglass, is an elastic, fairly soft, platy
mineral, which may be split into flakes of paper thinness. The
relatively clear variety is called muscovite, and the brownish black to
black variety is biotite, both being members of the mica family. They
may occur in Missouri in small grains in the igneous rocks, except that
muscovite may be present in sandstone, where it was deposited along with
the quartz sand.

Mica is used chiefly as insulating material in the electrical industry
where large sheets are required. Another use is as window or chimney
material in stoves or lanterns. Missouri has no mica which is
satisfactory for these purposes.


                 Porphyry, Rhyolite, Rhyolite Porphyry

Porphyry and granite are the two most abundant igneous rocks in
southeastern Missouri (Iron, Madison, and St. Francois counties, and
adjacent country). The porphyry there is a compact, very fine-grained,
almost glassy, hard, brittle rock that varies in color from light gray
through pink and red to dark purplish red and almost black. It always
breaks with a horny, flinty fracture. Small mineral crystals of
glistening quartz and usually reddish feldspar are generally scattered
throughout the dense background (groundmass). The crystals are commonly
about one-sixteenth of an inch in cross section and ordinarily
constitute from about ten to twenty per cent of the rock. Other names,
somewhat more specific than simple porphyry, which are applied
technically to certain phases of the rock are rhyolite, and rhyolite
porphyry.

    [Illustration: Rhyolite porphyry showing phenocrysts (light
    “freckles”) of quartz and feldspar. From near Ironton.]

The porphyry of southeastern Missouri is igneous rock which in the main
poured out as lava flows, millions of years ago. Volcanic dust or “ash”
was erupted during the same period, and layers of it, now strongly
cemented, are found in association with the flow rock.

The Missouri rhyolite porphyry has about the same chemical composition
(see page 40) as Missouri granite, but whereas granite is
coarse-grained, the porphyry has an extremely fine-grained to almost
glassy ground-mass. This difference in texture (grain size) is due to
the difference in rate of solidification. The porphyry lava flows
chilled and solidified very rapidly, thereby freezing the liquid to
glassy and extremely fine-grained rock, except for the scattered larger
crystals (phenocrysts) which had developed prior to eruption. Granite,
on the other hand, solidified very slowly under a thick cover of rock
which acted as a heat insulator, and during the long time of
solidification large or coarse grains of minerals could grow and develop
by crystallization so that a coarse-textured rock (granite) was formed.

The relative ages of the Missouri igneous rocks are of interest to
geologists and to most persons who recognize the different types within
a small area. It has been found that the prophyry was invaded by the
granitic liquid, that both the porphyry and granite were cracked after
solidification, and that liquid basalt rose and filled the cracks. Hence
the porphyry is the oldest, the granite next in age, and the basalt is
youngest. In fact, it may be mentioned in passing that some basalt and
allied dikes have been found cutting through the sedimentary sandstone,
shale, and limestone which overlie the igneous granite and porphyry and
are much younger.

Missouri porphyry has little use or value other than of bulk or crushed
stone.


                                 Basalt

Basalt is a fine-grained, dark-gray, dark-green, or greenish-black rock
which is hard enough to be scratched with difficulty by steel. It
originated by the solidification of lava. Today, basalt rock is forming
where lava at the Hawaiian volcanoes solidifies.

The relatively small amount of basalt in southeastern Missouri
solidified mostly in cracks within other rocks through which it rose.
Those occurrences—that is, fillings in nearly vertical cracks—are called
dikes. The basalt dikes in southeastern Missouri have been exposed by
the weathering and erosion of rocks which previously covered them.

    [Illustration: A dark dike of basalt in granite near Silver Mines.]

In northern Missouri, boulders of basalt may be found in deposits of
glacial clay, sand, and gravel (glacial drift), where they were left
after the melting of the great ice sheet which brought the basalt down
from ancient dikes and igneous bodies cropping out in the northern
United States and Canada. Many of the boulders have been rounded by
weathering, and their shape, together with their dark color, has
stimulated the local name “niggerhead” for them.

    [Illustration: Basalt in hand specimen.]

Basalt is a strong, tough, well-knit rock that will withstand heavy
blows from a sledge hammer, which usually rebounds upon striking. Except
for use as rubble stones, basalt has no commercial value. It weathers
characteristically to a yellowish, brownish, or reddish surface coating
of iron oxide and clay.


                           Gabbro and Diabase

Gabbro and Diabase are dark-colored, coarse-grained, hard igneous rocks,
which may be found in the granite and porphyry regions of southeastern
Missouri and as separate boulders in the glacial deposits north of the
Missouri River. Both resemble basalt, which has been described in detail
elsewhere, except that basalt is fine-grained, whereas gabbro and
diabase are coarse-grained (separate grains easily distinguished without
a magnifying glass). The layman is ordinarily not concerned with the
technical differences between gabbro and diabase, which appear about the
same. Both contain plagioclase feldspar (see FELDSPAR) and a dark green
mineral of the pyroxene family.

    [Illustration: Diabase hand specimen. From near Roselle.]

Gabbro and Diabase are sometimes called “black granite.” Their chief use
is as bulk or rubble-stone, although special varieties may be used for
building purposes.


                                  Coal

Coal is so well known that little need be written about its
distinguishing characteristics. Most of the coal in Missouri is of about
bituminous rank, although some cannel coal, which is discussed below, is
also present.

Missouri bituminous coal occurs in the northern and western parts of the
state. It contains bands of dull coal, bands of glistening “glance”
coal, the sooty “mineral charcoal,” and common mineral impurities like
calcite, gypsum, pyrite and marcasite (“sulphur”), clay minerals, and
quartz. Bituminous coal breaks with essentially a cubical fracture.

It occurs in horizontal or nearly horizontal beds or “seams,” which may
be followed considerable distances laterally without necessarily
encountering much change. Usually, a fire clay or a fire clay-like
under-clay immediately underlies the coal, but the overlying rock (the
roof) may be shale (slate? see discussion of SHALE), sandstone, or less
commonly, limestone.

    [Illustration: Bed of coal exposed by stream erosion, near
    Columbia.]

Coal originates from pre-existing plants and may be thought of as Mother
Nature’s storage cellar of “preserved” plant life. The Missouri coal
began millions of years ago as mosses, tree-like ferns, conifers, and
various plants that reproduce by spores, which flourished in great
wide-spread swamps. Insects were abundant, as is indicated by their
remains. Rain was probably plentiful and climate favorable, so that such
vegetation thrived luxuriantly. Today, fallen forest timber of the
highland disappears by oxidizing and decaying in the air; but in swamp
land the leaves, stems, pollen and woody trunks fall into and under
water and under favorable conditions decompose through bacterial and
chemical action into layers and pools of slippery, oozy, blackish humic
gel (like brownish black gelatin, “jello”), which remains. Likewise, in
ages past, more and more plant material continued to live, fall, and
accumulate in the old coal swamps until very thick deposits of the woody
gel existed.

Eventually land-sea or climatic conditions changed, and plant life died
out as mud, sand, or other rock-forming material was swept in to cover,
as a lid, the stored-up plant remains. The weight of overlying beds
squeezed out excess water from the woody gel, and from the time of
covering through the present day, gases (like mine gases), and other
volatile constituents of the coal have been given off.

A bed of coal, which consists chiefly of black combustible carbon, with
volatile constituents and non-volatile ash substances, has resulted. Man
uses the coal by burning it directly, or it may be coked and the
volatile constituents recovered in coal tar and other compounds. The
mineral impurities like the calcite, gypsum, clay, sand, and brassy
pyrite or marcasite, are shaken through the grates as ash or melted as
clinkers.

In nature, the pyrite and marcasite minerals may oxidize in ground water
percolating over them to form dilute sulphuric acid, the acid mine
waters.

Cannel coal in Missouri has been found chiefly in old sinkhole deposits
through part of central Missouri. It is characterized by fracturing
conchoidally and having a more massive structure (instead of the layered
structure common to bituminous coal). Cannel coal burns to a very hot,
rather quick fire because of high volatile content, and is thought to
have developed from accumulations very rich in plant spores.

Coal mining is an important industry in Missouri, and a special bulletin
on coal has been published by the State Geological Survey at Rolla,
Missouri.


                          Pyrite and Marcasite

Pyrite and Marcasite (Fool’s gold, “sulphur”) are brassy yellow,
metallic, heavy minerals which will scratch glass but which cannot
themselves be scratched by a knife, and which will leave a dark-greenish
to black mark or streak when rubbed across unglazed porcelain or chert
rock. Both are composed of iron sulphide, FeS₂—iron 46.6 per cent, and
sulphur 53.4 per cent. Although they have the same chemical composition,
they differ in internal atomic and crystalline structure, which is of
interest to scientific mineralogists. Pyrite may crystallize in cubes,
or in forms called pyritohedrons, named from pyrite, whereas marcasite
crystallizes in characteristic arrow-shaped or cockscomb forms.
Marcasite weathers a little more readily than does pyrite, but otherwise
they are much the same to the casual observer.

Pyrite and marcasite have been called “fool’s gold” because so many
persons have been fooled, sometimes with serious financial consequences,
by their slight resemblance to true gold. True gold is soft, usually
slightly orange-yellow in color, malleable, and unaffected by ordinary
acids; and it leaves a gold-colored streak when rubbed on unglazed
porcelain or a hard white rock. Pyrite, in contrast, is quite hard
(harder than steel), is brassy yellow with perhaps a slight greenish
tinge except where tarnished, is brittle, is corroded by acids or
oxidizing ground waters, and leaves a greenish black to black streak on
a white rock. One readily notices the difference in color between pyrite
and gold (such as is in a piece of good quality jewelry), when the two
are viewed close together. Yellowish, partially weathered mica has also
been mistaken for gold.

    [Illustration: Brassy, granular pyrite in hand specimen.]

    [Illustration: Pyrite in crystal cubes, and replacement of fossils.]

Pyrite and marcasite occur abundantly in most of the metal-mining
districts of Missouri, as the “brass,” or “sulphur balls,” etc., in
coal, as small nodules or pellets in some limestone, shale and
sandstone, as replacements of fossils, and as minute crystals in
granite, porphyry, and the other igneous rocks. Several marcasite mines
have been developed in old sinkhole deposits in south central Missouri,
but these are not in production at the time of this writing. The
sinkhole iron mines of south central Missouri contained pyrite-marcasite
before oxidation to the iron oxide ore, and some of them still contain
the sulphides in their lower levels.

    [Illustration: Marcasite crystal cluster from Joplin region. The
    arrowhead or cockscomb crystal form is characteristic of marcasite.]

Marcasite weathers (oxidizes) very readily under most conditions, with
the formation of (1) yellowish brown iron oxide, the mineral limonite,
which may stain rocks, soil, stream bank, etc., and (2) weak sulphuric
acid water. The sulphuric acid solution may react with more marcasite or
pyrite and evolve a gas, hydrogen sulphide, H₂S, which has a rotten-egg
odor. This explains the foul odor often noticed around old coal mine
dumps. Heat is evolved in these reactions, and coal waste on the dump
may be ignited by the heat of the chemical reactions. The burning
pyrite, or elemental sulphur, gives off sulphur dioxide, “burning
sulphur fumes,” which add to the odor and heat around a coal mine dump.
The burning coal waste and the chemical reactions may raise the
temperature of the coal waste pile high enough to fire or “burn” the
shale rock to a red, partially vitrified, natural brick-like material,
which is sold or distributed as “coal dump shale” or “burned shale,” or
“red shale” for all-weather surfacing of drives or walks.

Pyrite and marcasite have been used in the commercial manufacture of
sulphuric acid, but elemental sulphur can now be utilized more
economically, so that now no market exists for pyrite or marcasite in
Missouri. In earlier times only large deposits containing thousands of
tons of the mineral had any value. In some foreign countries pyrite is
burned and the fumes utilized for the manufacture of sulphuric acid,
while the cinder, an iron oxide and iron ore, is smelted to recover
metallic iron.

The origin of pyrite and marcasite is as variable as its enclosing rock.
No general statement can be made which will include the igneous rock
pyrite, the Joplin marcasite, the “sulphur” of the coal, and occurrences
in sink holes and various sedimentary rocks. A discussion of all these
origins alone would fill a pamphlet as large as this one on Missouri
rocks.


                              Conglomerate

Conglomerate is a rock composed of gravel, pebbles, and boulders
cemented together, with more or less sand and clay between the larger
fragments. It is truly a conglomeration of rock fragments as one would
find loose today in a stream or ocean shore gravel bar, or in a hillside
gravel bank. Probably the conglomerate most abundantly exposed in
Missouri is that overlying the igneous rocks in the southeast part of
the state.


                                 Gneiss

Gneiss is a hard, granular rock which exhibits a coarsely banded
structure (resulting from metamorphism). The bands are evident because
of color differences due to different mineral content; those dark in
color are commonly rich in dark mica (biotite) or hornblende (a dark
green to black, hard mineral), whereas the light bands contain feldspar
and quartz. Many gneisses have about the same mineral composition as
granite; hence, for our nontechnical purposes, a banded rock, otherwise
granite-like, is a gneiss.

    [Illustration: Gneiss typically banded.]

Gneiss is a metamorphic rock, a _changed_ rock. The banded structure was
developed by a combination of very high pressure, high temperature, and
solutions acting on a previously existing rock in essentially a solid
condition. The original rock may have been an igneous or sedimentary
rock which has been crushed or made to flow into bands, or has been
re-crystallized. The tremendous pressure which operated during the
banding of most gneisses also crumpled square miles of rock thousands of
feet thick into folded and broken (faulted) mountains. True slates,
marbles, and some quartzites are formed from soft shales, limestones,
and sandstones, respectively, in the metamorphic process.

Almost no metamorphic rock of this regional type crops out in Missouri,
but the boulders of gneiss which are found in the glacial deposits were
picked up in Canada or the northern United States and carried to
Missouri by a continental glacier thousands of years ago.

Except for use as bulk stone or possible structural purposes the gneiss
in Missouri has no value. The glistening yellowish mica sometimes seen
in gneiss is not gold, of course, and is likewise valueless.


                                Hematite

Hematite (“keel”) is a heavy, red to purplish red, dull to glistening
mineral which leaves a red mark or streak when rubbed on a hard white
rock (like chert) or on unglazed porcelain. This red color of hematite
coating or stain is responsible for our red clays, red soils, red iron
rust, reddish creek-water, and almost every bit of natural, red mineral
matter in Missouri. Hematite is iron oxide, Fe₂O₃, and has a close
associate, limonite, which is yellow to brown in color, and has the
chemical composition Fe₂O₃·nH₂O. The two are mentioned together here
because they are commonly associated in nature, where they can be
recognized in mixture by the yellowish red or reddish brown colors on
rocks or soils. Individual discussion is given limonite under its
heading, but its relationship to hematite is repeated here for obvious
reasons.

    [Illustration: Hematite: glistening, fine-grained, and dark red.]

    [Illustration: Hematite makes a deep red mark or streak on a hard
    white rock or unglazed porcelain.]

Hematite varies in hardness enough that some specimens can be scratched
easily with iron, whereas others are almost as hard as that metal
itself. Where clay occurs mixed with hematite, as in paint ore, it may
be quite soft, but “blue kidney ore” is usually hard.

Hematite is the ore (iron ore) mineral at Iron Mountain and Pilot Knob
mining districts and in the various sink-hole mines or pits in south
central Missouri. Scattered boulders of hematite occur in non-commercial
quantities within a shaly layer (lower part of Pennsylvanian age rocks)
which crops out extensively in central Missouri, and the finding of
these boulders has at times, unfortunately, stimulated short-lived hopes
of locating a valuable deposit of iron ore. Flaming red soil or
mountains of red solid rock (as are present in western United States)
may be colored by less than five per cent iron oxide and are in no sense
iron ore because the iron is not concentrated. Iron is the fourth most
abundant element in the earth’s crust, but workable iron mines and
deposits are few and far between. To be commercially valuable an iron
ore deposit must contain tens of thousands of tons and be relatively
free from impurities, notably sulphur and phosphorus. Hence, not many
Missouri farms are locations of iron ore deposits.

The origin of Missouri hematite is about as diverse as its occurrences.
Hot iron-rich solutions coming from an igneous source below are believed
to have introduced the hematite in the Iron Mountain-Pilot Knob area,
but the sink-hole hematite resulted from the oxidation of iron sulphide.
Weathering of older iron-containing rocks and minerals gave rise to the
coloring hematite seen on our sub-soil and surface rock.

Hematite is used as a polishing agent, as a pigment in paint, and, of
course, as an ore of metallic iron. In the smelting of iron from
hematite the ore is mixed in a huge, chimney-shaped blast furnace with
coke (from coal) and limestone. Air is blown into the furnace as into a
blacksmith’s forge; and the coke and gasses, burning at an incandescent
heat, take the oxygen from the Fe₂O₃, leaving metallic iron which melts
and is run out of the furnace at periodic intervals. Thus the smelting
process is the opposite of the rusting process. The impurities and
cinder run out as molten slag.


                                Limonite

    [Illustration: Dark brown limonite.]

    [Illustration: Stalactitic limonite from southeastern Missouri.]

Limonite is a heavy, yellow to brown, or brownish black mineral which
always leaves a yellow to brown mark or streak when rubbed across a hard
white rock or unglazed porcelain. It usually has a dull luster on a
broken surface, and may vary from thumb-nail hardness to almost that of
steel. The distinguishing test is its yellow to brown streak.

In composition limonite is iron oxide which contains more or less water
chemically combined, Fe₂O₃·nH₂O. That is, it may be dried bone-dry at
the temperature of boiling water, but upon heating to redness the
additional, chemically held water will be driven off.

Limonite is ordinarily formed from the weathering of other
iron-containing minerals (pyrite, for example) and is therefore a
wide-spread mineral in surface rock, in films on pools of water, and in
soil, all of which it colors yellow to brown. In fact, almost all of the
yellow to brown inorganic mineral color and stain seen in nature is that
of limonite.

Commercial deposits of limonite occur in southeastern Missouri where
large boulders, discontinuous and irregular lenses or beds, pipes,
nodules, and gravel to clay-sized particles of the mineral are
associated with the cherty, gravelly residual clay. Usually the ore is
crushed, hand-sorted, and washed preparatory to concentration for
shipment to a furnace or for use in cement manufacture. As in the case
of hematite, unless one has a deposit amounting to thousands of tons of
ore it has little commercial value, and unless the mineral is relatively
pure it can not be used.


                         Paint Ore or Red Ochre

An intensely red-colored, clayey iron ore has been mined for paint
pigment in several deposits in south central Missouri. It occurs in sink
hole deposits like those containing fire clay. Brown ocher may be
available from southeast Missouri.


                           Iron Band Diaspore

Shells of red or reddish brown iron oxide occur about cores of diaspore
clay in some of those deposits south of the Missouri River. Previously
this material had no value, but in the last few years it has been
purchased for and shipped to a cement company, which used it in the
manufacture of cement. Diaspore clay is discussed elsewhere in this
pamphlet.


                             Manganese Ore

Several manganese minerals make up the manganese ore which occurs to a
limited extent in southeast Missouri, principally in Shannon, Reynolds,
Carter, Iron, and Madison counties. Although the Missouri manganese
minerals are usually heavy, black or nearly so, and have a black or
brownish-black mark or streak, the identification of the individual
minerals is difficult and should be left to a technically trained
mineralogist.

Manganese minerals are used in the chemical industry and in the
production of certain kinds of iron. A special report on the manganese
deposits of Missouri is available at the Missouri Geological Survey,
Rolla, Missouri.


                                 Galena

Galena (“lead”) is a heavy, soft, somewhat brittle ore of lead. It has a
brilliant metallic luster, and silvery gray color on a freshly broken
surface. Where weathered it appears dull gray. It can be scratched with
a knife, and breaks with surfaces at 90°, forming cubes. The unbroken,
original crystal form of galena which has grown unobstructed in a vein
opening is commonly cubical in habit or a modification thereof. It
leaves a dark, lead-gray to black mark or streak when rubbed across
unglazed porcelain or chert.

    [Illustration: A “cube” of galena.]

    [Illustration: Cluster of galena crystals from Joplin region.]

Galena is lead sulphide, PbS, and when pure contains 86.6 per cent lead
and 13.4 per cent sulphur. Small amounts of silver may also be present.

Galena commonly occurs in Missouri as a cavity filling in crushed
limestone or chert, or as a replacement in limestone or dolomite, or in
shale, so that a large quantity of practically worthless enclosing rock
(gangue) must be taken out in order to obtain the desired galena. If a
person desires to estimate the value of his galena (lead) prospect by
having an analysis or assay made of his ore, he must include in his
sample the gangue rock that would of necessity have to be taken out when
mining his ore. Too often persons carefully select for analysis a choice
galena specimen which may run over 80% lead, only to find that as a
practical mine product it would be reduced to less than 5% lead in all
the rock which also would have to be taken out.

After a galena ore is mined it is customarily crushed and the galena
removed from the gangue by a gravity-separation process which takes
advantage of the difference in “heaviness” (specific gravity) between
galena (7.5) and limestone (calcite) or chert (2.7-2.6), or by a froth
flotation process in which the galena is preferentially wetted and
carried off by an oily froth or foam. The galena concentrate is roasted
to burn out the sulphur, reduced by carbon, and smelted to metallic
lead. The origin of some Missouri lead deposits is debatable, but the
writer believes the most reasonable explanation to be that warm,
chemically active waters arose from an igneous body below and carried to
the place of deposition the lead which they held in solution.

Missouri is one of the leading producers of lead in the world from its
Flat River, Fredericktown, Joplin, and central Missouri districts, from
which in 1941 lead concentrates having a value of over $15,000,000 were
produced.


                               Sphalerite

Sphalerite (locally called Jack, Rosin Jack, Black Jack, Ruby Jack,
Zinc, Rosin Spar) is a tan-brown, resinous, brown or brownish black
mineral having a very high luster on its broken (cleavage) surfaces.
Much of it so strongly resembles lump rosin that the term “Rosin Jack”
is truly descriptive. Less commonly, a ruby red variety occurs as
crystals perched on other sphalerite or on waste rock. Sphalerite is
readily scratched with steel. Its chemical composition is zinc sulphide,
ZnS—zinc 67 per cent, sulphur 33 per cent—and it is an important ore of
zinc.

Sphalerite occurs abundantly in the mining district of southwest
Missouri, but small, non-commercial amounts of it have been found
through an area extending even north of the Missouri River. At the
mines, after the ore and rock are taken out, they are crushed and
separated, the ore going to the smelter and the rock to tailings piles.
Under the old milling process employed in south_western_ Missouri,
thousands of tons of coarse tailings, largely chert, were poured onto
huge “chat” piles, many of which remain as a low-priced by-product for
some one to put to use. This chat differs mineralogically from the
south_eastern_ Missouri chat, which is largely dolomite.

    [Illustration: Sphalerite from near Joplin.]


                            Barite (“Tiff”)

Barite (“Tiff” in south_east_ Missouri, Heavy Spar, Barytes) occurs in
Missouri predominantly as a white, quite heavy, soft, non-metallic
mineral which has a high luster on a freshly broken surface. Slightly
bluish “glass” barite or “glass tiff” has been found in smaller quantity
with the more abundant, opaque white material. The glassy barite may
superficially resemble calcite or selenite gypsum, but in distinction,
barite breaks or cleaves to surfaces joining at right angles and does
not effervesce with acid, whereas calcite does effervesce in acid and
cleaves at oblique angles (rhombohedral cleavage). Gypsum is so soft
that it can be scratched very easily with the thumb-nail, whereas barite
is scratched with difficulty, if at all, by the thumb-nail. Notably,
again, barite is “heavy,” with a specific gravity of about 4.5, whereas
calcite, gypsum, limestone, and chert are “lighter,” with a specific
gravity of about 2.6 to 2.7. Barite has the composition barium sulphate,
BaSO₄, of which barium oxide constitutes 65.7 per cent.

    [Illustration: Three pieces of barite, the crested and bladed form
    at the left, “glass” barite in the center, and a small crystal at
    the right.]

Barite occurs in abundance in the Jefferson-Washington counties
district, which furnishes about 80% of Missouri production. Other
production comes from near Houston, Texas county, and from the central
district—Miller, Moniteau, Morgan, Cole counties, and adjacent
territory. In the Jefferson-Washington counties district, it is dug from
residual clay over dolomite and is run through washing and concentrating
mills which remove the clay and lighter waste rock. Most of the central
district production comes from old sinkhole deposits, the ore being also
crushed, washed, and concentrated in preparation for shipment. Missouri
barite which was produced during 1941 had a value of over $1,300,000 and
constituted about 40% of the total United States productions.

Barite is used as a paint pigment and extender, as a flux, as a source
of barium in the chemical industry, as a filler in rubber, paper, oil
cloth, textiles, and leather, and as a heavy substance in oil well
drilling mud. The largest single use is in the manufacture of lithopone
paint.


                                 Gypsum

Gypsum is a soft mineral which can be scratched easily with the finger
or thumb-nail. It may be glassy or transparent, or may grade into an
opaque white body, possibly stained by iron oxide, but it is always very
soft. Of the three varieties of gypsum—selenite, alabaster, and
satinspar—only the first two have been found in Missouri by the writer.
The chemical composition of gypsum is CaSO₄·2H₂O.

    [Illustration: Transparent, flexible variety of gypsum (selenite).]

    [Illustration: Fine-grained, white, opaque gypsum (alabaster).]

The chief use of gypsum is in the manufacture of plaster of paris,
during which it is pulverized and heated to drive off part of the water
of crystallization so that its composition corresponds to CaSO₄·½H₂O.
This powder, when mixed with water and poured into a mold, heats and
sets; that is, it hardens by taking up enough of the water to restore
its original composition.

Although thick, wide-spread beds of gypsum occur in other localities,
probably most of the gypsum in Missouri has been secondarily formed, as
from the reaction of sulphuric acid from oxidizing pyrite on calcite;
and its quantity is limited to small crystals, veins, and crusts in or
on other rocks. Gypsum may be an impurity in coal, and some beautiful
crystals a few inches long have been found in weathering clay deposits.
It therefore cannot be considered as a commercially valuable mineral of
this state.


                               Meteorites

Meteorites, the rock-like specimens which have come to our earth as
sparkling meteors in the sky, are perhaps the most prized specimens
which the average collector hopes to find, and perhaps more specimens
are mistaken for meteorites than for any other geological substance.
Meteorites are rare and not easy to find; they are also not easy to
determine.

The iron variety is usually a heavy, roughly-pitted, brown, tough,
metallic, nickel alloy of iron. Therefore, a positive chemical test for
nickel is usually strongly suggestive of a meteoric origin, but
confirmation almost requires that a surface be polished and etched with
dilute acids to bring out typical and characteristic structures.

    [Illustration: The polished and acid-etched surface of an iron
    meteorite. Shows the Widmanstatten figures characteristic of iron
    meteorites. (Photo courtesy of American Museum of Natural History,
    New York).]

The stony variety of meteorites usually contains a rock-forming mineral
called olivine, beneath its pitted brown surface. In case of either
variety, since special equipment is required for final testing and
determination, it is recommended that this be done at a laboratory
appropriately equipped.


                                  Gold

Gold is not known to occur in Missouri, except for very small quantities
which have been carried into the state with the glacial deposits in the
north half. Miners have searched carefully, and geologists have studied
Missouri rocks intently, comparing them with the gold veins of the
western states, but they find no promise of a gold deposit in Missouri.
We have been favored with other geological products, but it is a waste
of time to search for gold in Missouri.


                                 Silver

Silver has been recovered from ore in the Silver Mines area in Madison
county and from the galena of southeastern Missouri. Except for
occurrences within the igneous rock area and the lead mining regions,
geologists do not expect to find additional silver ore deposits.


                                Diamonds

No diamond has ever been found in native Missouri rock. It is possible
for diamonds to have been carried into the state with the glacial
deposits in the northern part, but the probability of finding one, if it
did come in, is extremely remote.

Diamonds do occur in one part of Arkansas, but those rocks are
strikingly different from all Missouri rocks except in a few localities,
having small areas about the size of one’s house, in the southeastern
part of the state. The writer has received quartz and calcite crystals
for testing from persons who hoped they might be diamonds. It is almost
a foregone conclusion that diamonds do not occur in Missouri.

A diamond may be recognized by its extreme hardness. It is the hardest
substance known, natural or artificial, and will scratch any known
substance; but it, in turn, is scratched only by another diamond. Acids
do not affect diamonds in the least.


                            Uranium Minerals

Three uranium-containing minerals, tyuyamunite (pronounced
tyew-yuh-moon-ite), possibly carnotite, and metatorbernite, have been
found in Missouri but none has been mined commercially. Tyuyamunite and
carnotite are canary yellow powdery minerals so similar in appearance
they can be differentiated only by chemical and x-ray properties. Both
minerals contain uranium, vanadium, oxygen, water, and one other
element, which, if it is calcium, the mineral is tyuyamunite, but if it
is potassium the mineral is carnotite. The canary yellow color referred
to is distinctly different from the brownish or reddish yellow color of
iron oxide minerals. These yellow uranium minerals have been found near
Ste. Genevieve along cracks in limestone and in the black shale above
the limestone, and in dark, sandy shales near Shelbina, and elsewhere
north of the Missouri River.

Black shales (high in organic matter) of marine origin are the most
highly radioactive, whereas black shales deposited on land (as with
coal), and all shales of other colors are usually lower in
radioactivity.

Metatorbernite is a soft, pale apple-green scaly mineral that has been
found in paper-thin cracks in flint fire clay deposits. It contains
uranium, copper, phosphorus, oxygen, and water. All of these uranium
minerals activate a Geiger counter.




                     MISCELLANEOUS ROCK STRUCTURES


                              Concretions

A concretion is an aggregate of inorganic matter in the shape, roughly,
of a ball, disc, rod, or irregular nodular body. Usually the aggregation
or accumulation started around a small center grain or particle and
continued in the growth of layers about it like the shells of an onion,
or in the growth of needle-like fibers which radiate from the center
like pins stuck into a spherical pin cushion. Concretions vary in size
from buck-shot (buck-shot concretions in the soil) to oddities ten or
twenty feet in diameter, or even longer in elongate forms. The variety
about one-sixteenth or one-thirty-second of an inch in diameter is
called an oolite (pronounced oh-oh-lite). Some chert of southern
Missouri, most of the diaspore and burley clay, and a limestone cropping
out near Louisiana, Missouri, are made up partly to almost entirely of
oolites. See page 29.

Concretions may be composed of pyrite, calcite, limonite, chert,
cemented sandstone, or even cemented clay. They are usually recognized
by their structure after the previously enclosing rock has been eroded.
Thus pyrite, limonite, or calcite (limestone) concretions remain after
shale has softened and washed away, chert remains after limestone, and
strongly cemented “irony” (limonite or hematite) or siliceous sandstone
concretions may be found on the outcrop where the softer or less
resistant host rock has been carried off. The irregular-shaped,
intergrown, nodular limestone concretions (sometimes called
“loess-kinder”, or loess dolls) in the upper part of loess deposits
along the Missouri and Mississippi Rivers can be found remaining on
rain-washed slopes. Limy, mudstone concretions and brown iron carbonate
concretions are abundant in certain localities in northwestern and
southeastern Missouri, where they are used as oddities in rock gardens
or walls.

    [Illustration: Concretions. Dark, limy concretion at left and brassy
    pyrite at center and right. Note the inter-grown pair in center.]

Some concretions are formed at the same general time as the surrounding
rock accumulates, but others may be formed years after the surrounding
rock has been buried or removed from the environment of its formation.
In either case, deposition of the mineral matter follows the pattern of
addition or “growth” from inside out. This growth, of course, does not
involve a life process like that of a plant or animal. If two or more
centers of deposition occur close together, the several growing
concretions may touch, intergrow, and develop some weird forms,
suggesting organic growth. However odd these curiosities may become,
there is no question that they are not fossils, or evidence of life.
Probably concretions excite the interest of persons more than any other
rock structure.

Ground water, carrying calcium carbonate, silica, or iron compounds in
solution, is a great concretion builder. It percolates through sandstone
or other permeable rock and slowly leaves behind enveloping layers or
additions of mineral matter, until a concretion is formed, to remain
hidden from view until its host rock is softened and removed by the
action of the weather.


                                 Geodes

A geode is usually a hollow, more or less spherical or ball-shaped shell
of mineral and crystal growth which has formed within surrounding rock.
Missouri geodes commonly vary in size from hickory nuts to small
watermelons, although neither direction of variation is limited. They
weather out abundantly at several localities in northeast Missouri from
the so-called Warsaw formation, a limy shale. Here they are dark brown,
rough and irregular on the outside, but where broken open show many
brilliant, glistening faces of intergrown quartz crystals. Less
frequently calcite, chalcedony, kaolinite, and rarely millerite (nickel
sulphide) may occur in Missouri geodes.

    [Illustration: Typical small geode from northeastern Missouri.]

The minerals and crystals of a geode grow inward from the walls of a
cavity in the rocks. The mineral matter is carried there in solution by
ground water and crystallizes out very much more slowly but in the same
manner that sugar or salt crystals develop in a saturated solution of
those substances. If crystal growth continues until the geode is solid,
it may bear superficial resemblance to a concretion, but the latter
structure is one which has grown outward. The idea of “growth” in either
case is that of mineral crystallization and enlargement, but does not in
the least involve life like that of a plant or animal. Geodes have no
value or use other than for ornamental purposes.


                                Fossils

Fossils are also found and collected by persons who are interested in
rocks and minerals. The varied remains of plants and animals long since
petrified or replaced by mineral matter have stimulated the curiosity
and become a source of enjoyment to many persons, from those who merely
give a passing glance to the peculiar organic structures in the rocks to
those who make a serious hobby or business of collecting and classifying
the unreplaceable heritage from the ancient rocks. Fossils are
interesting in part because of their variety, for they include petrified
wood, shells like those of oysters, fish teeth, foot-prints, amber,
dinosaur eggs, coal, imprints of fern leaves, of insects, and of fishes,
and the bones of small and gigantic dinosaurs and elephants. In fact, a
fossil is any evidence of life in the geologic past preserved in the
rocks. Missouri rocks furnish fossils ranging in size from
microscopically small fish teeth to the big skeletal remains of the
mastodon, an ancestor of the elephant; but the most common ones are the
structures and shells of ancient clams, corals, brachiopods, crinoids,
and trilobites.

    [Illustration: A tooth of a mastodon, about one-half natural size.
    (Photo courtesy of Mr. J. R. Morrison, Louisiana, Missouri.)]

    [Illustration: Fossils. Upper row, coral on left, trilobite on
    right; center row, brachiopods; lower row, coiled cephalapod,
    crinoid head, and a bryozoan spiral.]

The accompanying photographs illustrate a few fossils that may be found
within our state, but a thorough, non-technical treatment of Missouri
fossils is available in a companion volume to this booklet, “The Common
Fossils of Missouri” by Prof. A. G. Unklesbay, Missouri Handbook No. 4.

The study of fossils, or paleontology, is a fascinating branch of
geology which extends far beyond the recognition and cataloging of the
specimens. It has been found that certain particular fossils occur in
rocks of the ages which produce petroleum, and the search for that
valuable substance has been directed in many instances by the fossil
content of the rocks. Rocks of different ages carry different fossil
assemblages, and a man skilled in paleontology utilizes the fossils in
dating geologic history like the page numbers in a book of human
history. Further, any student of present-day animals and plants is aided
in his understanding of them if he knows the fossil record of their
ancestors of the long geologic past.


                 Arrow Heads and Other Indian Artifacts

Arrow heads, scrapers, rock knives and saws which were left by the
Indians who formerly lived in Missouri may be found in moderate
abundance in many parts of the state. Usually these artifacts are chert
in its various colors, white, gray, mottled, reddish, or black (flint).
See the discussion of chert on page 34. Chert, because of its conchoidal
fracture, lack of cleavage, resistance to chemical weathering, and
superior hardness, is an exceptionally useful rock for making tools and
weapons.

Hammers and axes of basalt, and arrow heads of rhyolite are less
abundant than the chert artifacts.




                         THE ROCKS OF MISSOURI


Geologists classify rocks into these groups: igneous, sedimentary or
metamorphic. Representatives of all three have been described in the
preceding pages.

    [Illustration: Arrowheads made from white, gray, pink, and black
    chert. (Courtesy of Mr. A. A. Jeffrey, Columbia, Mo.)]

Sedimentary rocks are those whose particles settled down through the air
or water to form rocks in layers or beds; hence layered, bedded, or
so-called stratified rocks are sedimentary rocks. For instance, the sand
and mud settling out of the Gulf of Mexico (or ocean) after being
brought in by the Mississippi River is on its way toward becoming
sandstone and shale. Limestone is forming off the coast of Florida now.
All of these rocks are accumulating in layers. Where one sees
regularly-layered or stratified rocks in streams, road cuts, quarries,
bluffs or hillsides, he expects them to be sedimentary rocks. The
sedimentary rocks that have been described herein include:

  Limestone
  Dolomite
  Chert
  Shale
  Fire clay
  Flint fire clay
  Diaspore and Burley clay
  Sandstone
  Quartzite
  Travertine
  Coal

Igneous rocks are those which solidified from a hot liquid which was
either forced into older surrounding rocks (intrusive) or discharged on
the earth’s surface as a lava flow or products from a volcano
(extrusive).

The examples given below illustrate the two types. Everyone knows about
the extrusive forms from accounts of present-day volcanoes and
occasional lava flows, like those of Vesuvius, Paricutin, and Mauna Loa.
An intrusion was injected beneath the Yellowstone Park area years ago,
and its heat, with steam and gases, is contributing to the unusual
natural features which are found in the park and which make it famous.

Igneous rocks in Missouri are:

  Granite
  Porphyry, Rhyolite, Rhyolite porphyry
  Gabbro and Diabase
  Basalt

Metamorphic rocks are rocks which have been changed through the effects
of tremendous pressure (enough to raise mountains) and high temperature
while in the solid state. In most cases a banded rock results. The
metamorphic rocks mentioned in this booklet are:

  Gneiss
  Marble

No doubt it has become apparent to the reader that rocks ordinarily
occur in great quantities, that they are composed of multitudes of
grains (mineral grains), and that their properties and compositions vary
with the different minerals which are present in the grains of the rock.
A _rock_ can, therefore, be different from a _mineral_. In fact, a rock
may be defined as “an aggregate of mineral particles,” or more broadly
“a typical part of the earth.” To focus closer attention on minerals we
may discuss them for their own sake below.




                          MINERALS OF MISSOURI


A mineral is characterized by a constancy of composition and of
properties which sets it apart from rocks which vary widely. Minerals
may be metallic, like pyrite, or non-metallic, like barite; they may be
ore, like galena, or rock-forming, like quartz or feldspar; they may
show crystal faces, or they may be fragments with rounded or broken
surfaces. A favored definition teaches that “a mineral is a naturally
occurring, inorganic substance having a definite chemical composition
and definite physical properties, within limits.” The Missouri minerals
listed herein include:

  Quartz
  Mica
  Calcite
  Dolomite
  Sphalerite
  Galena
  Barite
  Marcasite
  Carnotite
  Tyuyamunite
  Pyrite
  Hematite
  Limonite
  Gypsum
  Pyroxene
  Orthoclase feldspar
  Microcline feldspar
  Plagioclase feldspar
  Metatorbernite




                            GEOLOGIC VALUES


Although the emphasis in this pamphlet has been on the recognition of
Missouri rocks and minerals, it is not out of order to consider the
broad values that they contribute to our civilization. Their use as
building materials has been noted, but it should be further recognized
that as our timber is being rapidly depleted more and more structures
will be built out of earth materials. Missouri possesses a wealth of
beautiful limestone that is serviceable and readily quarried. Where
limestone is not near, there is usually shale or glacial clay which can
be used in the manufacture of brick and tile. Permanency will be the
keynote of the rock and ceramic structures. Gravel and sand are abundant
in Missouri for concrete and other varied uses.

The soil is Missouri’s most valuable earth material. Hundreds to
thousands of years of normal weathering are required to develop the
rocks and minerals and texture of the inorganic fraction of the soil. We
should preserve it and prevent disastrous soil erosion.

Aside from these more tangible values, a fascinating and instructive
hobby can be made of collecting, arranging, and studying rocks and
minerals. One gains a fuller understanding and appreciation of nature
from their study. The orderliness, constancy, and interrelation within
the rock and mineral “world” is a restful contrast to the one which man
often keeps in turmoil. The beauty of a glistening crystal or a polished
mineral or stone is as inspiring as a lovely flower, yet it lasts and
lasts through centuries, a veritable “rock of ages.”


                 Suggested Collateral Reading Material


                      Books on Rocks and Minerals

How to Know the Minerals and Rocks, by Pearl; publisher, McGraw-Hill
      Book Co., New York.

A Field Guide to Rocks and Minerals, by Pough; publisher, Houghton,
      Mifflin Co., Boston.

Gemstones and Minerals: How and Where To Find Them, by Sinkankas;
      publisher, Van Nostrand, Princeton, New Jersey.

Look for paper back editions of these and other books which may be
      widely available.


                                Fossils

The Common Fossils of Missouri, by A. G. Unklesbay, Missouri Handbook
      No. 4.


               Magazines on Rocks, Minerals, and Fossils

Rocks and Minerals, Box, 29, Peekskill, N.Y.

Gems and Minerals, P.O. Box 687, Mentone, Calif.

The Mineralogist, P.O. Box 808, Mentone, Calif.

American Mineralogist, technical official publication of the American
      Mineralogical Society, Ann Arbor, Michigan, editorial office,
      Dept. of Mineralogy, University of Michigan.


               Books on Mineralogy and Rocks (Technical)

Dana’s Manual of Mineralogy, by Hurlbut; publisher, John Wiley & Sons,
      New York.

Dana’s Textbook of Mineralogy, by Ford; publisher, John Wiley & Sons,
      New York.

Mineralogy, by Berry and Mason; publisher, Freeman & Co., San Francisco.

Rocks and Rock Minerals, by Knopf; publisher John Wiley & Sons, New
      York.

Guide to the Study of Rocks, by Spock; publisher, Harper & Co., New
      York.


                        Books on General Geology

Introduction to Geology, by Branson, Tarr, and Keller; publisher,
      McGraw-Hill Book Co., New York City.

Introduction to College Geology, by Holmes; publisher, Macmillan, New
      York.


                       Books on Physical Geology

Geology, by Emmons, Thiel, Stauffer and Allison; publisher McGraw-Hill
      Book Co., New York.

Principles of Geology, by Gilluly, Woodford, and Waters; publisher,
      Freeman & Co., San Francisco.

Physical Geology, by Leet and Judson; publisher, Prentice-Hall & Co.,
      New York.


                      Books on Historical Geology

The Geological Evolution of North America, by Clark and Stearn;
      publisher, Ronald Press Co., New York.

Time, Life, and Man, by Stirton; publisher, John Wiley & Sons, New York.

These books may be borrowed from public libraries, or purchased from the
publishers and retail book stores. At Columbia, the University Book
Store, and the Missouri Store Co., sell most of them from shelf stock.


                     Missouri Geology Publications

Missouri has an excellent State Geological Survey which has published
numerous volumes on various geologic topics and areas within the State.
Inquiry about these bulletins, circulars, maps, and individually handled
correspondence, should be addressed to the:

  State Geologist
  Missouri Geological Survey
  Rolla, Mo.




                               FOOTNOTES


[1]This service is also offered by the Department of Geology, Missouri
    School of Mines and Metallurgy, Rolla, Missouri, and by the State
    Geologist, Rolla, Missouri.




                                 INDEX


                                   A
  Acid, testing, muriatic, hydrochloric, storage battery, sulphuric   10
  Agate                                                               37
  Alabaster gypsum                                                    63
  Aluminum                                                            23
  Amethyst                                                            42
  Aragonite                                                           17
  Arrow heads                                                 34, 71, 72
  Artifacts                                                       71, 72
  Asphaltic sandstone                                                 32
  Audrain County                                                      26


                                   B
  Barite                                                      19, 61, 74
  Barton County                                                       32
  Basalt                                      13, 44, 46, 47, 48, 71, 73
  Bauxite                                                         23, 29
  Biotite mica                                                    44, 54
  Black jack zinc ore                                                 60
  Bloodstone                                                          42
  Blossom rock                                                        42
  Boone County                                                        26
  Brick                                                           22, 74
  Burley clay                                                 29, 66, 73
  Burlington limestone                                                12
  Burned shale                                                    21, 54


                                   C
  Calcite                     12, 16, 37, 49, 61, 62, 63, 65, 66, 68, 74
  Calcium carbonate                                       12, 16, 37, 67
  Callaway County                                                 26, 27
  Cannel Coal                                                         51
  Carnelian                                                           42
  Carnotite                                                           65
  Carter County                                                       58
  Carthage marble                                                     15
  Cave deposits                                                       16
  Chalcedony                                                      37, 68
  Chats                                                       35, 43, 60
  Chert                               14, 34, 37, 42, 59, 62, 66, 71, 73
  Clinton                                                             33
  Coal                                                20, 49, 53, 63, 73
  Cole County                                                         62
  Conchoidal fracture                                         26, 34, 51
  Concretion                                                      66, 68
  Conglomerate                                                        54
  Copper                                                          40, 66
  Cotton rock                                                         15
  Crawford County                                                     27
  Crinoids                                                            12
  Cross-bedding                                                   30, 31
  Crystal City                                                    33, 41


                                   D
  Definition, rock and mineral                                 5, 73, 74
  Developing mineral deposit                                      24, 59
  Diabase                                                 44, 48, 49, 73
  Diamonds                                                        40, 65
  Diaspore clay                                           27, 58, 66, 73
  Dike                                                        46, 47, 48
  Dolomite                                    10, 11, 18, 59, 60, 73, 74
  Dolomite chemical composition                                   12, 20
  Double refraction                                                   18
  Drusy quartz                                                        42


                                   E
  Effervescence                                   10, 11, 16, 17, 18, 19
  Elephant Rocks                                                  39, 41


                                   F
  Feldspar                                    38, 39, 43, 45, 46, 54, 74
  Festus                                                              33
  Fire clay                                                   19, 24, 73
  Flat River                                                          60
  Flint                                                           14, 34
  Flint fire clay                                                 26, 73
  Fool’s gold                                                     14, 51
  Fossils                                     12, 22, 35, 36, 52, 53, 69
  Franklin County                                                     27
  Fredericktown                                                       60


                                   G
  Gabbro                                              13, 38, 44, 48, 73
  Galena                                                      59, 65, 74
  Gasconade County                                                26, 27
  Geiger Counter                                                      66
  Geode                                                           42, 67
  Geological Survey, Missouri                                          6
  Glacial boulders and deposits                       40, 48, 55, 65, 74
  Glass “tiff,” barite                                                61
  Gneiss                                                          54, 73
  Gold                                                        51, 53, 65
  Granite                         16, 31, 38, 43, 46, 47, 49, 53, 54, 73
  Graniteville                                                    39, 43
  Gypsum                                          19, 49, 61, 62, 63, 74


                                   H
  Hardness                                                     6, 19, 65
  Heavy spar                                                          61
  Hematite                                                    56, 66, 74
  Hermann                                                             33
  Houston                                                             62
  Hydrochloric acid                                                   10


                                   I
  Igneous rock                                                        73
  Iron band diaspore                                                  58
  Iron County                                                 39, 45, 58
  Iron Mountain                                                       56
  Iron ore                                                        56, 57
  Isinglass                                                           44


                                   J
  Jack zinc ore                                                       60
  Jasper                                                              38
  Jefferson County                                                    62
  Joplin                                                              60
  Joplin dolomite                                                     19


                                   K
  “Kaoleen”                                                           37
  “Keel”                                                              56
  Klondike                                                            33


                                   L
  Lafayette County                                                    32
  La Grange                                                           37
  Lava flow                                                       46, 73
  Lead ore                                                            59
  Lexington                                                           33
  Lime                                                                13
  Limestone                           10, 22, 53, 55, 59, 62, 66, 73, 74
  Limestone, chemical, composition                                12, 23
  Limonite                                            53, 56, 57, 66, 74
  Lincoln County                                                      27
  Loess dolls, -kinder                                                66


                                   M
  Madison County                                              39, 45, 58
  Magnesium carbonate                                                 12
  Manganese ore                                                       58
  Marble                                                      15, 55, 73
  Marcasite                                           49, 51, 53, 57, 74
  Maries County                                                       27
  Mark of mineral                                                  6, 56
  Metamorphic rock                                        15, 21, 55, 73
  Metatorbernite                                                      65
  Meteorites                                                          64
  Mica                                                38, 39, 44, 53, 74
  Microcline feldspar                                             44, 74
  Miller County                                                       62
  Millerite                                                           68
  Mineral, definition                                              5, 74
  Missouri Geological Survey                                       6, 59
  Missouri School of Mines and Metallurgy                              6
  Moberly                                                             33
  Moniteau County                                                     62
  Morgan County                                                       62
  Muriatic acid                                                       10
  Muscovite mica                                                      44


                                   N
  Nickel                                                              64
  “Niggerheads”                                                   32, 48


                                   O
  Ochre                                                               58
  Olivine                                                             65
  Onyx                                                            16, 42
  Oolites                                                     27, 29, 66
  Orthoclase feldspar                                             44, 74
  Osage County                                                    26, 27
  Ozora marble                                                        15


                                   P
  Pacific                                                         33, 41
  Paint ore                                                           58
  Paleontology                                                        71
  Paris                                                               33
  Petrified wood                                              35, 43, 69
  Petroleum                                                           71
  Phelps County                                                   26, 27
  Phenocrysts                                                         46
  Pilot Knob                                                          56
  Plagioclase feldspar                                        44, 49, 74
  Plaster of paris                                                    63
  Plastic fire clay                                                   26
  Polish on marble and granite                                        16
  Pop-corn flint fire clay                                            26
  Porphyry                                        31, 40, 44, 45, 53, 73
  Porphyry, chemical composition                                      40
  Potosi                                                              37
  Pyrite                          14, 49, 51, 52, 53, 57, 58, 63, 66, 74
  Pyroxene                                                        49, 74


                                   Q
  Quarry                                                              14
  Quartz                      30, 38, 39, 40, 41, 45, 49, 54, 65, 68, 74
  Quartzite                                                   32, 55, 73


                                   R
  Radioactivity                                                       66
  Reynolds County                                                     58
  Rhyolite, rhyolite porphyry                                 45, 71, 73
  Ripple marks                                                        33
  Rock crystal                                                        42
  Rock, definition                                                 5, 73
  Rock wool                                                           13
  Rose quartz                                                         42
  Rosin jack zinc ore                                                 60
  Rosin spar zinc ore                                                 60
  Ruby jack zinc ore                                                  60


                                   S
  Sampling rock or ore                                            15, 59
  Sand                                                            14, 30
  Sandstone                                   30, 41, 43, 53, 55, 66, 73
  Sandstone, chemical composition                                     23
  Satinspar gypsum                                                    63
  Sedimentary rock                                                72, 73
  Selenite gypsum                                                     63
  Shale                               19, 20, 24, 50, 53, 55, 66, 73, 74
  Shale, chemical composition                                         23
  Shannon County                                                      58
  Silica                                                      35, 43, 66
  Silver                                                          59, 65
  Silver Mines                                                        65
  Six-sided crystals                                              16, 41
  Slate                                                       21, 50, 55
  Soapstone                                                           21
  Soil sweetening                                             13, 14, 20
  Sphalerite                                                      60, 74
  “Sponge” limestone rock                                             13
  Stalactites                                                         16
  Stalagmites                                                         16
  State Geologist, Geological Survey                       6, 24, 51, 59
  St. Francois County                                             39, 45
  St. Louis County                                                    26
  St. Peter sandstone formation                                       41
  Ste. Genevieve                                                      65
  Streak of mineral                                                6, 56
  Sulphur                                                             51
  Sulphuric acid                                              10, 53, 63


                                   T
  Texas County                                                        62
  Tiff                                                            16, 61
  Travertine                                                      16, 73
  Tripoli                                                         37, 43
  Tyuyamunite                                                     65, 74


                                   U
  University of Missouri Geology Department                            6
  Uranium Minerals                                                65, 66


                                   V
  Vanadium                                                            66
  Vernon County                                                       32


                                   W
  Warren County                                                       27
  Warrensburg                                                         33
  Washington County                                                   62
  Weathered chert                                         19, 35, 36, 37
  Widmanstatten figure                                                64


                                   Z
  Zinc ore                                                            60


                              OF RELATED INTEREST

  THE COMMON FOSSILS OF MISSOURI
    A. G. Unklesbay
  OUR STOREHOUSE OF MISSOURI PLACE NAMES
    Robert L. Ramsay
  INDIANS AND ARCHAEOLOGY OF MISSOURI, REVISED EDITION
    Carl H. Chapman and Eleanor F. Chapman

                                                     ISBN-13: 978-0-8262




                      UNIVERSITY OF MISSOURI PRESS
                          Columbia and London




                          Transcriber’s Notes


—Silently corrected a few typos.

—Retained publication information from the printed edition: this eBook
  is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by
  _underscores_.