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.
A small amount of turquoise has been mined from several localities a few miles northwest of Sierra Blanca in the Sierra Blanca Mountains of Hudspeth County.