[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.
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.
