Part 12

In the Frasch method of sulfur mining, a well is drilled into the salt-dome cap-rock, and three pipes, one inside the other, are put into the well. Superheated water under pressure (hotter than 212° Fahrenheit, the temperature at which water ordinarily turns into steam) is sent down one of the pipes to melt the sulfur in the cap-rock around the bottom of the well. Then, compressed air is sent down another of the pipes. This air presses against the liquid sulfur and forces it up to the surface through the third pipe. At the surface, the sulfur is poured into bins, where it cools and becomes a solid again, or it is transported molten, in pipelines and tankers.

Sulfur has been obtained from a number of the Texas Gulf Coast salt domes including Bryan Mound, Clemens dome, Damon Mound, and Hoskins Mound in Brazoria County; Palangana dome in Duval County; Long Point dome, Nash dome, and Orchard dome in Fort Bend County; High Island dome in Galveston County; Fannett dome and Spindletop dome in Jefferson County; Moss Bluff dome in Liberty County; Gulf dome in Matagorda County; and Boling dome in Wharton County.

In west Texas, sulfur occurs in Permian rocks both at the surface and underground. A small amount of sulfur has been mined in the Rustler Springs area of northeastern Culberson County and northwestern Reeves County, about 50 miles northwest of Pecos. There, scattered grains, crystals, and irregular masses of sulfur occur in cracks and in dissolved-out openings in the Castile Gypsum and in the surface gravel, gypsum, sand, and clay that cover most of this formation.

Sulfur has many uses. It is used as an insect-killer, thus helping our food crops to grow. It is used in pulp and paper manufacturing and in the vulcanizing of rubber. Some other uses are in the making of paints, dyes, and explosives. A large amount of sulfur goes to make sulfuric acid, which itself has numerous uses in the chemical, steel, oil refining, and other industries.

Sulfur Uncemented Sediments Limestone Sulfur-Bearing Limestone Hot Water Melted Sulfur Anhydrite

Talc and Soapstone

Talc, a hydrous magnesium silicate, is an extremely soft mineral—your fingernail scratches it easily. It has a greasy or a pearly luster, and its color is white, light green, or gray. When rubbed across a streak plate, it leaves a white streak.

Talc cleaves perfectly in one direction, and the cleavage fragments are thin, flat, and sheet-like. Its fracture is uneven. This mineral has a soaplike or greasy feel, and it is sectile—a knife will cut through it. Talc is not particularly heavy—it has a specific gravity of 2.7 to 2.8. This mineral seldom occurs with a crystal shape. More commonly it is massive and is granular or layered.

Talc is not always found as a single, pure mineral. In nature, it commonly occurs mixed with one or more other minerals, such as tremolite, anthophyllite, chlorite, and magnetite. This combination of talc with other minerals forms a soft, greasy or soapy-feeling metamorphic rock called soapstone. The talc in this rock may be difficult to identify without special laboratory tests.

In Texas, talc and soapstone are found in Precambrian metamorphic rocks. In west Texas, talc occurs in an area about 20 miles long (just north of U. S. Highway 80 in the vicinity of Allamoore, Eagle Flat siding, and Talc Rock siding) in Hudspeth County. Some of this talc is mined from open pits and used by the ceramic industry to make wall tile. Some of it is finely ground, mixed with insect poison, and used as insect powders and dusts.

Deposits of soapstone, containing talc, occur in the Llano uplift area of central Texas with schist, gneiss, and serpentine rocks in northeastern Gillespie, northwestern Blanco, and southern Llano counties. Smaller deposits occur in northeastern Mason County and in northwestern and southeastern Llano County.

The Llano uplift area soapstones are light green to light buff. It is thought that some of them were once igneous rocks that contained magnesium minerals. Fluids, along with great heat and pressures below the earth’s surface, changed these igneous rocks into soapstone.

Some of this Llano uplift area soapstone is mined from open pits near Willow City in Gillespie County. It is used mostly in making insect powders and roofing granules. In addition, some of the central Texas soapstones have been used for hearths and for fireplace linings.

Topaz

Topaz, an aluminum fluorosilicate, is a mineral especially prized by collectors because many specimens are gemstones. Topaz is transparent, has a glassy luster, and is quite hard (neither quartz nor a steel file will scratch it). The topaz that has been found in Texas is either colorless, pale blue, or sky blue. This mineral is fairly heavy—its specific gravity is 3.4 to 3.6. It cleaves perfectly in one direction (called basal cleavage), and some of the cleavage fragments have a flat, slabby appearance.

Topaz is commonly found as prism-shaped crystals, as cleavage fragments, and as irregular grains. Some fragments of topaz look like quartz. Topaz, however, is harder and heavier than quartz, and it has perfect basal cleavage, which quartz does not have.

In Texas, crystals, grains, and cleavage fragments of topaz occur in the Llano uplift area of central Texas. They are found near Streeter and Grit in west-central Mason County and near Katemcy in northern Mason County. Here, some of the topaz occurs in Precambrian pegmatite veins that cut through granite rocks. Most of the topaz, however, is found as pebbles in the gravels of nearby creeks, where it has washed after weathering out of the rocks.

Topaz probably originates when hot fluids move up out of molten magma into cracks and cavities in the surrounding rocks. There, the fluids react with elements in the rocks to form the topaz.

Topaz is a good gemstone because, in addition to its beauty, it is hard and is not easily marred by scratches. The Mason County topaz makes excellent gemstones. Most of it is beautiful and clear and is either colorless or of a pleasing blue color. These stones are cut, polished, and mounted in rings and other jewelry. A number of specimens of this Mason County topaz are displayed in museums.

Tourmaline

Tourmaline is a complex silicate of boron and aluminum. Other elements, such as magnesium, sodium, lithium, calcium, iron, or fluorine, also may be present. This mineral has a glassy to resinous luster. Only the dark-colored varieties of tourmaline have been found in Texas. One is a black variety called _schorl_, and another is a brown variety called _dravite_. Other kinds of tourmaline, although not found in Texas, are colorless or some shade of blue, yellow, red, pink, or green. Some crystals even show more than one color.

Tourmaline is too hard to scratch with a steel file, it has a specific gravity of 3 to 3.25, and it has a conchoidal to uneven fracture. Very little light passes through the dark varieties, and some fragments of schorl look like shiny, black coal.

Tourmaline occurs as masses without crystal shapes, but crystals are commonly found. The crystals are prism-shaped and have small vertical grooves, called _striations_, on the prism faces. When you look at some crystals from an end, you will see that the cross section is a triangle with the sides bowed outward.

Both the black and the brown varieties of tourmaline have been found at several places in the Llano uplift of central Texas. One well-known locality is at Town Mountain north of Llano in Llano County. Here, the tourmaline occurs in milky quartz that is associated with Precambrian granite rocks. In west Texas, in Culberson and Hudspeth counties, black tourmaline occurs in pegmatite rocks in the Van Horn Mountains, the Carrizo Mountains, and the Wylie Mountains. In the Eagle Mountains of Hudspeth County, it is found in metamorphic rocks as well as in pegmatites.

Some tourmaline formed from hot fluids containing boron that were given off by magmas far below the earth’s surface. These fluids traveled up through cracks and other openings in overlying rocks. As the fluids reacted with other elements and compounds, the tourmaline formed.

The clear, light-colored varieties of tourmaline are much admired, and they are more widely used as gemstones than are the dark-colored varieties. Some collectors, however, find that the dark-colored Texas tourmalines, when cut and polished, make shiny, attractive gemstones.

Some tourmaline is used as grinding material, but no Texas tourmaline is produced for this purpose.

Travertine. _See_ Calcite.

Uranium Minerals (Carnotite, Uranophane, Pitchblende)

In 1945, the world suddenly became aware of the awesome power of atomic energy when the element _uranium_ was used to produce some of the first atomic bombs. Uranium does not occur alone in nature but is found combined with other elements in a number of minerals.

All of the uranium minerals are radioactive. The uranium they contain is gradually breaking down and changing into a series of 13 other elements, called _daughter_ elements. Each daughter element breaks down and changes into the next daughter element of the series. While breaking down, these elements give off particles and rays of energy.

This energy or _radioactivity_ is made up of what are called alpha particles, beta particles, and gamma rays. You cannot see, hear, taste, smell, or feel them. The alpha and beta particles are weak and do not travel far. The gamma rays, however, can travel farther and can pass through seemingly solid material. Scientists have found that these rays can move through about 1 foot of rock, 2½ feet of water, and several hundred feet of air.

Prospectors searching for uranium minerals carry instruments that are able to detect this radioactivity. The uranium itself gives off only alpha particles, but some of its daughter elements give off gamma rays. These daughter elements are normally found with the uranium, and it is their strong gamma rays that the instruments are most apt to detect.

One of the instruments used is the _Geiger counter_. It indicates radioactivity by means of a meter, a flashing light, or a clicking sound, which can be heard through earphones. Another instrument for detecting radioactivity is the _scintillation counter_. It is more sensitive than the Geiger counter and it can detect radioactivity from a greater distance. The scintillation counter can be used from an automobile or an airplane, but the Geiger counter must be quite close to the source of radioactivity to be of use.

Various uranium minerals have been found, mostly in small amounts, in a number of places in Texas. Some of these minerals, such as uraninite or pitchblende, are heavy and dark colored. Others, including carnotite, tyuyamunite, autunite, and uranophane, are a shade of yellow or green. They are quite soft. Deposits of the light-colored uranium minerals have been mined from two areas of Texas. One of these areas is in Garza County on the Texas High Plains, and the other is in Karnes and Live Oak counties in the Gulf Coastal Plain.

One of the light-colored uranium minerals, _carnotite_, is a potassium-uranium vanadate, which has a bright canary-yellow or lemon-yellow color. This mineral is transparent to translucent and has an earthy or a pearly luster. Carnotite usually is found as crusts and as powdery masses. It is quite soft and can be scratched with a fingernail.

Carnotite, along with tyuyamunite, autunite, and several other soft, yellowish or greenish uranium minerals, is found in the Texas Gulf Coastal Plain. These minerals occur in the Jackson, Catahoula, and Oakville strata (which are Tertiary in age) in an area extending from Gonzales County to the Rio Grande (in parts of the area indicated by no. 2 and no. 3 on the geologic map, pp. 4-5). The largest deposits in this district have been found in the Karnes County area.

The Gulf Coastal Plain uranium minerals occur mostly with sandstones and clays in a sequence of strata that contains volcanic ash. It is believed that small scattered amounts of uranium compounds that were present in the volcanic ash sediments were dissolved by seeping underground water. These waters then moved into the sandstones and clays where they deposited the uranium as carnotite and as other uranium minerals.

Another uranium mineral, _uranophane_ (calcium-uranium silicate), also occurs in Texas. Uranophane has a yellow to yellow-orange color and a pearly to greasy luster. When rubbed across a streak plate, it leaves a light yellow to a light yellow-orange streak. It is soft enough to be scratched by a copper penny. Uranophane has been found in extrusive igneous rocks in northwestern Presidio County in west Texas.

A dark-colored uranium mineral, _pitchblende_, is a variety of the mineral _uraninite_, uranium dioxide. Pitchblende does not occur with a crystal shape but rather as rounded and irregular-shaped masses. It is brownish black, greenish black, or black. If you rub it across a streak plate, pitchblende leaves a brownish-black streak. This mineral is heavy (it has a specific gravity of 6.5 to 8.5) and hard (a pocket knife will not scratch it, although a steel file will). Pitchblende has a submetallic luster and looks dull, greasy, or like pitch or tar.

Small amounts of pitchblende have been found at several places in Texas. One of these localities is a few miles west of Burnet in Burnet County in central Texas. Here, the pitchblende occurs in Precambrian igneous rocks that are associated with gneiss. In south Texas, some fine, scattered particles of pitchblende have been found about 325 feet below the surface in Tertiary (Pliocene) sediments that cover the Palangana salt dome in Duval County. No pitchblende is mined in Texas.

Uranophane. _See_ Uranium Minerals.

Vitrophyre. _See_ Obsidian and Vitrophyre.

Volcanic Ash (Pumicite)

Volcanic ash deposits, which also are known as _pumicite_, are loose and powdery. They are made up mostly of material that is thrown into the air when volcanoes erupt. If a volcano erupts with a violent explosion, the nearby rocks are blown into powder. Molten lava also is hurled into the air, where some of it immediately cools to become tiny bubbles and particles of glass. The winds may carry some of this fine material far away before depositing it.

Deposits of volcanic ash are white, bluish, greenish, yellowish, or grayish, and some of them glisten like snow in the sunlight. They feel rough and gritty. When examined under a microscope, this material shows the tiny curved and sharp-cornered particles of the broken volcanic glass. Deposits of volcanic ash may also contain clay, silt, sand, or other impurities.

Volcanoes, which may have been located in the Davis Mountains and in other areas of west Texas and in northern Mexico, erupted during Tertiary time. The volcanic ash that we find at the surface today in some of the Tertiary formations in Texas could have come from these volcanoes. Tertiary volcanic ash deposits occur in the Texas Gulf Coastal Plain (such as in Brazos, Fayette, Karnes, Polk, Starr, Trinity, and other counties) and in the Trans-Pecos country of west Texas.

Volcanic ash deposits of Quaternary (Pleistocene) age, which are less than a million years old, are found in a number of counties on the Texas High Plains. Farther to the east, ash deposits occur in Baylor, Dickens, Kent, and Wilbarger counties. This volcanic ash may have come from a volcano that erupted in northern New Mexico during Quaternary time.

Volcanic ash or pumicite has several commercial uses. Some is used to make pozzolan cement, and some is used in sweeping compounds, cleansing and scouring powders, and abrasive soaps. Pumicite has been mined in Dickens, Scurry, Starr, and several other counties of Texas.

Wad. _See_ Manganese Minerals.

Wood Opal. _See_ Opal.

COMPOSITION, HARDNESS, AND SPECIFIC GRAVITY OF SOME TEXAS MINERALS

For convenient reference, the Texas minerals described in this book are listed below, together with their chemical compositions, specific gravities, and hardness. You will be able to find similar information about additional minerals in mineralogy textbooks such as those noted on page 24.

_Mineral_ _Composition_ _Specific Gravity_ _Hardness_ Albite NaAlSi₃O₈ 2.62 6 Almandite Fe₃Al₂ (SiO₄)₂ 4.2 7 Amphibole Ca₂Mg₅Si₈O₂₂(OH)₂ 3.0-3.3 1-2½ asbestos Anhydrite CaSO₄ 2.9 3-3½ Argentite Ag₂S 7.3 2-2½ Azurite Cu₃(CO₃)₂(OH)₂ 3.77 3½-4 Barite BaSO₄ 4.5 3-3½ Biotite K(Mg, 2.8-3.2 2½-3 Fe)₃AlSi₃O₁₀(OH)₂ Braunite 3MnMnO₃MnSiO₃ 4.75-4.82 6-6½ Calcite CaCO₃ 2.72 3 Carnotite K₂O·2UO₃·V₂O₅·nH₂O 5.03 2 Cassiterite SnO₂ 6.8-7.1 6-7 Celestite SrSO₄ 3.95-3.97 3-3½ Cerargyrite AgCl 5.5 1-1½ Chalcocite Cu₂S 5.5-5.8 2½-3 Chalcopyrite CuFeS₂ 4.1-4.3 3½-4 Cinnabar HgS 8.10 2½ Dolomite CaMg(CO₃)₂ 2.85 3½-4 Feldspar (_see_ Albite, Microcline, Orthoclase) Fluorite CaF₂ 3.18 4 Galena PbS 7.4-7.6 2½ Garnet (_see_ Almandite, Grossularite) Gold Au 15.0-19.3 2½-3 Graphite C 2.2 1-2 Grossularite Ca₃Al₂(SiO₄)₃ 3.53 6½ Gypsum CaSO₄·2H₂O 2.32 2 Halite NaCl 2.16 2½ Hematite Fe₂O₃ 5.26 1-6½ Hollandite MnBaMn₁₆O₁₄ 4.7-5 4-6 Limonite FeO(OH)·nH₂O 3.6-4.0 1-5½ Magnetite Fe₃O₄ 5.18 6 Malachite Cu₂CO₃(OH)₂ 3.9-4.03 3½-4 Mica (_see_ Muscovite, Biotite) Microcline KAlSi₃O₈ 2.54-2.57 6 Muscovite KAl₃Si₃O₁₀(OH)₂ 2.76-3.1 2-2½ Opal SiO₂·nH₂O 1.9-2.2 5-6 Orthoclase KAlSi₃O₈ 2.57 6 Pitchblende UO₂ 6.5-8.5 5½ Pyrite FeS₂ 5.02 6-6½ Pyrolusite MnO₂ 4.75 1-2 Quartz SiO₂ 2.65 7 Serpentine Mg₃Si₂O₅(OH)₄ 2.48 3-4 Silver Ag 10.5 2½-3 Sulfur S 2.05-2.09 1½-2½ Talc Mg₃Si₄O₁₀(OH)₂ 2.7-2.8 1 Topaz Al₂SiO₄(F,OH)₂ 3.4-3.6 8 Tourmaline Complex silicate of 3.0-3.25 7-7½ boron and aluminum Uranophane CaO·2UO₃·2SiO₂·7H₂O 3.8-3.9 2-3

BOOKS ABOUT ROCKS AND MINERALS

Many books have been written about rocks and minerals. Some are listed below, and it is likely that your librarian will be able to suggest others.

Nontechnical Books for Beginners

Getting Acquainted With Minerals, by George L. English and David E. Jensen. McGraw-Hill Book Company, Inc., New York, N. Y. (second edition, 1958).

The Rock Book, by Carroll L. Fenton and Mildred A. Fenton. Doubleday & Company, Inc., Garden City, N. Y. (1940).

Mineral Collector’s Guide, by David E. Jensen. Ward’s Natural Science Establishment, Inc., Rochester, N. Y. (1953).

My Hobby is Collecting Rocks and Minerals, by David E. Jensen. Hart Book Company, New York, N. Y. (1955).

Rocks and Minerals, by Richard M. Pearl. Barnes & Noble, New York, N. Y. (1956).

1001 Questions Answered About the Mineral Kingdom, by Richard M. Pearl. Dodd, Mead & Company, New York, N. Y. (1959).

Rocks and Minerals, by Herbert S. Zim and Paul R. Schaffer. Simon and Schuster, Inc., New York, N.Y. (1957).

Textbooks and Other Reference Books

Economic Mineral Deposits, by Alan M. Bateman. John Wiley & Sons, Inc., New York, N. Y. (second edition, 1950).

A Textbook of Mineralogy, by Edward S. Dana, revised by William E. Ford. John Wiley & Sons, Inc., New York, N. Y. (fourth edition, 1932).

Industrial Minerals and Rocks (Nonmetallics Other Than Fuels), Joseph L. Gillson, Editor-in-Chief. The American Institute of Mining, Metallurgical, and Petroleum Engineers, New York, N. Y. (third edition, 1960).

Dana’s Manual of Mineralogy, revised by Cornelius S. Hurlbut, Jr. John Wiley & Sons, Inc., New York, N. Y. (seventeenth edition, 1959).

Mineralogy, by Edward H. Kraus, Walter F. Hunt, and Lewis S. Ramsdell. McGraw-Hill Book Company, Inc., New York, N. Y. (fifth edition, 1959).

Nonmetallic Minerals, by Raymond B. Ladoo and W. M. Meyers. McGraw-Hill Book Company, Inc., New York, N. Y. (second edition, 1951).

Rocks and Rock Minerals, by Louis V. Pirsson, revised by Adolph Knopf. John Wiley and Sons, Inc., New York, N. Y. (third edition, 1947).

A Field Guide to Rocks and Minerals, by Frederick H. Pough. Houghton Mifflin Company, Boston, Mass. (third edition, 1960).

Mineral Facts and Problems, by the Staff of the Bureau of Mines. U. S. Bureau of Mines Bulletin 585. U. S. Government Printing Office, Washington, D. C. (1960).

Selected References on Texas Rocks and Minerals

Entries marked with an asterisk are published by the Bureau of Economic Geology, The University of Texas, Austin. Those not out of print are distributed at nominal sale price, and a list of publications will be sent on request. These publications can be consulted at many public libraries and Chamber of Commerce offices.

*Report on the Pavitte Silver-Copper Prospect in Burnet County, Texas, by V. E. Barnes. Univ. Texas, Bureau Econ. Geol. Mineral Resource Survey Circ. 5 (1936).

*Report on the Sheridan Copper Prospect in Burnet County, Texas, by V. E. Barnes. Univ. Texas, Bur. Econ. Geol. Mineral Resource Survey Circ. 9 (1936).

*Building Stones of Central Texas, by V. E. Barnes, R. F. Dawson, and G. A. Parkinson. Univ. Texas Pub. 4246 (1947).

*Iron Ore in the Llano Region, Central Texas, by V. E. Barnes. Univ. Texas, Bur. Econ. Geol. Rept. Inves. No. 5 (1949).

*Utilization of Texas Serpentine, by V. E. Barnes, D. A. Shock, and W. A. Cunningham. Univ. Texas Pub. 5020 (1950).

*Lead Deposits in the Upper Cambrian of Central Texas, by V. E. Barnes. Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 26 (1956).

*Mineral Resources of the Colorado River Industrial Development Association Area, by J. W. Dietrich and J. T. Lonsdale. Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 37 (1958).

*Some Uranium Occurrences in West Texas, by D. H. Eargle. Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 27 (1956).

*A Preliminary Report on the Stratigraphy of the Uranium-Bearing Rocks of the Karnes County Area, South-Central Texas, by D. H. Eargle and J. L. Snider. Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 30 (1957).