THE COMMON ROCKS AND MINERALS OF MISSOURI

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.

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.

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.

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.

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.

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.

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.

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