Chatoyant Quartz is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of silicon dioxide, their full chemical compound being SiO2.
When quartz contains similarly-oriented fibrous inclusions, and is then appropriately-cut, in cabochon, curved stones display what is known as chatoyancy, meaning 'like a cat's eye.' The result is a series of minor gemstones differing only in their ground color and the mobile reflection.
Comes in colors white, gray, green, yellow, brown. When the ground color is greenish-gray or green, the gem is known as cat's-eye quartz (Sri Lanka, Bavaria, Burma). If the ground is blue-gray or bluish, the variety is called hawk's-eye; a golden yellow reflection on a brown ground is called tiger's-eye; and a stone with a mahogany-colored ground is called bull's-eye or ox-eye (all principally from South Africa).
Chatoyant quartz can also be cut into more or less round, polished pieces, for necklaces and pendants. It is sensitive to some acids.
It can be confused with chrysoberyl cat's-eye. The name "cat's-eye' without the word "quartz" is taken to mean only chrysoberyl cat's-eye. The tiger's-eye appearance was believed to improve eyesight and prevent eye diseases.
Chatoyant quartz has sometimes been imitated by glass, but is not produced synthetically. Dark stones have had their colors improved and been artificially lightened using nitric acid treatments.
The tiger's eye variety, in particular, is also used for carvings, boxes, ashtrays, wherein the fibers are seen as stripes of color instead of chatoyancy.