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.
[Illustration: 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.
Azurite. _See_ Copper Minerals.