Good crystals of black and dark brown tourmaline occur at Town Mountain near Llano, Llano County. The tourmaline crystals average about 1 inch in length, do not commonly exceed 2 inches, and are associated with white vein quartz. The quartz completely encloses the tourmaline, but the crystals can be broken free or the quartz can be trimmed away with the use of a diamond saw. The latter procedure is recommended whenever possible, for it is very easy to shatter the tourmaline crystals while trying to remove them from the quartz by other means. Many of the crystals are completely unsuitable for cutting, being too brittle or too badly cracked and flawed. However, some small crystals have been found that are of sufficient quality and size to yield flawless stones of a few carats. Few of these stones have been cut since the tourmaline is so dark that it appears opaque, and few persons find a gem of this nature attractive. Good black and dark brown crystals of tourmaline associated with andalusite and graphite occur in the Packsaddle schist (Precambrian) near Sunrise Beach, Llano County (Pl. VI, B, and fig. 20). Although generally smaller in diameter than the crystals found at Town Mountain, they commonly exceed 3 inches in length, although the average size is a little over 1 inch. Many of these crystals are suitable for cutting into opaque or nearly opaque stones of about 5 or 6 carats. Black tourmaline has also been found in Hudspeth and Culberson counties but not of sufficient quality to be used as a gemstone. [Illustration: Fig. 20. Common crystal form of Llano County tourmaline.] Turquoise _Composition_: hydrous phosphate of aluminum and copper. _Crystal system_: triclinic. _Hardness_: 5 to 6. _Specific gravity_: variable, 2.6 to about 2.8. _Luster_: dull, sometimes waxy. _Color_: sky blue to greenish blue. _Streak_: white to greenish. _Cleavage_: none in massive material, two directions in crystals. _Fracture_: conchoidal to subconchoidal. _Tenacity_: brittle. _Diaphaneity_: subtranslucent to opaque. _Refractive index_: 1.61 to 1.65. Turquoise of good sky-blue to greenish-blue color has been found a few miles southwest of Van Horn, Culberson County. Several shallow pits were dug at this locality about 1910; however, the amount of turquoise produced was small. The main occurrence of the turquoise was in seams about 1 millimeter thick along joints in the fine-grained rocks of this area. Persons who have visited Culberson County more recently report that even minute traces of the turquoise are now difficult to find at the old prospect pits. However, further prospecting in the area might yield some additional localities. Small amounts of turquoise have been reported near El Paso, El Paso County, and also in volcanic rocks near the Jeff Davis-Brewster County line, north of Alpine.