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. [Illustration: Talc schist from the Allamoore area of Hudspeth County, Texas.] 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.