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.