When quartz contains similarly oriented fibrous inclusions. appropriately cut. curved stones display what is known as chatoyancy. The result is a series of minor gemstones differing only in their ground color and that of the mobile reflection. The variety crocidolite is quartz pseudomorohous after riebeckite.

Appearance When the ground color is greenish gray or green, the gem is known as cat’s-eye quartz; 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 a tiger‘s-eye; and a stone with a mahogany-colored ground is called bull's-eye or ox-eye. It is normally cut en cabochon, to bring out the chatoyancy. which is. after all, its main characteristic; but it can be out into more or less round, polished pieces, for necklaces and pendants. The tiger‘s eye variety, in particular, is also used for carvings,boxes, ashtrays, and other ornamental items. although in these, the fibers are seen as stripes of color, not chatoyancy as such.

Distinctive features The colors and clearly fibrous appearance are normally distinctive. although other stones. as, for instance, some nephrites or chatoyant feldspars, may look quite similar. Cyrnophane chrysoberyl, on the other hand, is usually much more translucent and greenish yellow. with much greater hardness and density.

Occurrence Cat's-eye quartz comes mainly from SriLanka and West Germany (Bavaria), but also from Burma. Hawk's-eye. bull’s-eye, and the much more plentiful tiger's—eye, in particular, come principally from South Africa.

Value Despite its attractiveness, this material is not very valuable. The less common hawk's—eye variety is worth somewhat more.

Stimulants and synthetics Chatoyant quartz has sometimes been imitated by glass. but is not produced synthetically.