Another [anhydrite] locality is in the subsurface [Permian] basin of west Texas. Oil wells drilled in this basin penetrate great, thick deposits of [massive] anhydrite. The anhydrite was deposited during the Permian [Period] from a sea that covered this area. As the sea gradually evaporated, the mineral matter that was dissolved in it came out of solution to form anhydrite, [halite], and several other minerals.
Antigorite. See [Serpentine].
Argentite. See [Silver Minerals].
Asbestos
[Asbestos] is not really any one particular mineral. It is the name given to several minerals that occur in masses of slender, delicate fibers. In the more typical kinds of asbestos, these fibers—when pulled apart—resemble soft, fluffy, silk strings.
Several small deposits of [amphibole asbestos] have been found in the [Llano uplift] area of central Texas. This [asbestos] is a variety of the mineral tremolite, a calcium-magnesium silicate. It has fibers that break rather easily, and it has a silky luster. It is a shade of green or gray and gives a white [streak] when rubbed across a streak plate. When you pull its fibers apart, you actually are breaking the mineral along its two directions of perfect [cleavage]. This amphibole asbestos is softer than other varieties of the mineral tremolite—a copper penny scratches it easily.
Greenish, silky [amphibole asbestos] from northeastern Gillespie County, Texas.
The [asbestos] occurs in veins in [Precambrian] [metamorphic rocks] in southern Llano County, northwestern Blanco County, and northeastern Gillespie County. These deposits are small.
A variety of the mineral [serpentine] called [chrysotile] [asbestos] is the kind most used by industry. Its fibers are commonly flexible enough and strong enough to be woven into cloth. This cloth is made into articles, such as fireproof suits, gloves, and theater curtains. Some chrysotile has been found in [Precambrian] [metamorphic] rocks in northwestern Blanco County, but it does not break into fibers fine enough or flexible enough to be called asbestos.