Part 25

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).