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. [Illustration: 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. [Illustration: 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.