Beryl
Composition: Be₃Al₂(SiO)₆. Crystal system: hexagonal. Hardness: 7.5 to 8.0. Specific gravity: 2.63 to 2.80. Luster: vitreous. Color: pale blue, blue, green, yellow, brownish, pink, and colorless. Streak: white. Cleavage: one direction, very imperfect. Fracture: conchoidal to uneven. Tenacity: brittle. Diaphaneity: transparent to subtranslucent. Refractive index: 1.56 to 1.60. Dispersion: low.
Gem-quality beryl has not been reported in Texas. A discussion of beryl is included herein because the writer believes it likely that beryl of gem quality will be found in Texas as a result of future investigations and exploration.
Beryl crystals have been found in pegmatite dikes in Llano, Blanco, and Gillespie counties. These crystals are commonly several inches long and exceed 1 inch in diameter but are very badly fractured. Most of the beryl crystals do not approach gem quality and are entirely unsuitable for any lapidary use. The color of the crystals found thus far is bluish, greenish, pinkish brown, yellowish, and colorless. Some very tiny colorless beryl crystals have been found that are transparent, but thus far such crystals have been too small to be cut into gems.
Fine blue beryl crystals have been found in the Franklin Mountains near El Paso, Texas. Unfortunately, these crystals are so badly flawed and fractured that they are not suitable for lapidary use.
It seems likely that careful prospecting of Texas pegmatites will reveal at least some gem-quality beryl.