[Topaz] crystal from near Streeter, Mason County, Texas.
[Topaz] probably originates when hot [fluids] move up out of molten [magma] into cracks and cavities in the surrounding rocks. There, the fluids react with [elements] in the rocks to form the topaz.
[Topaz] is a good gemstone because, in addition to its beauty, it is hard and is not easily marred by scratches. The Mason County topaz makes excellent gemstones. Most of it is beautiful and clear and is either colorless or of a pleasing blue color. These stones are cut, polished, and mounted in rings and other jewelry. A number of specimens of this Mason County topaz are displayed in museums.
Tourmaline
[Tourmaline] is a complex silicate of boron and aluminum. Other [elements], such as magnesium, sodium, lithium, calcium, iron, or fluorine, also may be present. This mineral has a glassy to resinous luster. Only the dark-colored varieties of tourmaline have been found in Texas. One is a black variety called [schorl], and another is a brown variety called [dravite]. Other kinds of tourmaline, although not found in Texas, are colorless or some shade of blue, yellow, red, pink, or green. Some crystals even show more than one color.
[Tourmaline] is too hard to scratch with a steel file, it has a [specific gravity] of 3 to 3.25, and it has a [conchoidal] to uneven [fracture]. Very little light passes through the dark varieties, and some fragments of [schorl] look like shiny, black coal.
[Tourmaline] occurs as masses without crystal shapes, but crystals are commonly found. The crystals are prism-shaped and have small vertical grooves, called striations, on the prism faces. When you look at some crystals from an end, you will see that the cross section is a triangle with the sides bowed outward.
Black [tourmaline] crystals with [milky quartz] from north of Llano, Llano County, Texas.
Both the black and the brown varieties of [tourmaline] have been found at several places in the [Llano uplift] of central Texas. One well-known locality is at Town Mountain north of Llano in Llano County. Here, the tourmaline occurs in [milky quartz] that is associated with [Precambrian] [granite] rocks. In west Texas, in Culberson and Hudspeth counties, black tourmaline occurs in [pegmatite] rocks in the Van Horn Mountains, the Carrizo Mountains, and the Wylie Mountains. In the Eagle Mountains of Hudspeth County, it is found in [metamorphic rocks] as well as in pegmatites.