The origin of tektites is of great scientific interest and is currently the subject of much debate. Some scientists believe that tektites are of meteoritic origin, while others believe that tektites were formed by various terrestrial processes. Since no one has actually observed a tektite to fall or form, and many of the theories of origin are difficult to prove without direct observation, the origin of tektites is likely to remain in controversy for some time. Topaz _Composition_: Al₂(F, OH)₂SiO₄. _Crystal system_: orthorhombic. _Hardness_: 8. _Specific gravity_: 3.4 to 3.6. _Luster_: vitreous. _Color_: pale blue, sky blue, greenish, white, wine yellow, straw yellow, grayish, pink, reddish, and orange. _Streak_: uncolored. _Cleavage_: one direction, basal, highly perfect. _Fracture_: conchoidal to uneven. _Tenacity_: brittle. _Diaphaneity_: transparent to subtranslucent. _Refractive index_: about 1.60 to 1.63. _Dispersion_: moderate. Various yellow and smoky colored quartz gems are offered for sale as “Spanish Topaz,” “Smoky Topaz,” “Madeira Topaz,” and “Topaz Quartz.” These names are entirely misleading and should be dropped from usage. Fine gem-quality white, pale-blue, and sky-blue topaz has been found near Streeter, Grit, and Katemcy, Mason County. This Texas gem material compares favorably in color, size, and clarity with topaz found anywhere in the United States. Fine crystals of topaz (Pl. V, B, and fig. 18) occasionally are found in pegmatite dikes associated with quartz, black tourmaline, cassiterite, and pink microcline. Many of the gem-bearing pegmatites have been eroded away, leaving the topaz concentrated in the stream beds. The stones mostly occur as frosted, stream-worn pebbles (Pl. VI, A) in the numerous small creeks in the area. The topaz is heavier than the quartz and microcline that compose the stream gravel and is commonly found immediately on top of the granite bed-rock in the bottom of the stream bed. The stones tend to lodge behind boulders or small dikes cutting across the stream. [Illustration: Fig. 18. Crystal faces on topaz crystal shown in Plate V, B. This crystal habit is typical of the topaz from Mason County.] The white or colorless stones are by far the most common, outnumbering the bluish stones about ten to one. The color of the blue stones tends to be irregularly distributed in zones parallel to the crystal faces. Topaz that is colored in this manner should be cut with the best blue color near the bottom or culet of the gem (fig. 19). If done correctly, this will give the entire gemstone the desirable blue color. [Illustration: Fig. 19. Cross section showing the proper orientation of dark-color zone in a gem cut from an irregularly colored stone.] COLORLESS BLUE