Chemical composition -- Aluminum silicate with fluorine
and hydroxyl.
Color -- Colorless, yellow, brown, red, blue, pink.
Optics -- R.I. 1.60-1.62.
Durability -- Hardness 8.
Crystal structure -- Orthorhombic. One direction of perfect cleavage which is often troublesome in polishing, but not in cutting.
Specific Gravity -- 3.50-3.57.
Sources -- U.S., Pakistan, Brazil, Russia, Mexico, etc.
Topaz is often found in huge crystals. Natural pink and red material is rare. Fine orange-yellow material (Imperial topaz) is relatively scarce. Abundant colorless or pale colored material is irradiated and heat-treated to produce blue material resembling aquamarine.