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cat's-eye,gemstone that displays a thin band of reflected light on its surface when cut as a cabochon. Its name is derived from its supposed resemblance to the eye of a cat. The optical effect, known as chatoyancy, is caused by the reflection of light from very thin, closely spaced filaments in parallel arrangement within the stone. True cat's-eye, a variety of chrysoberylchrysoberyl
[Gr.,=golden beryl], a beryllium aluminate used as a gem. It has a vitreous luster and is transparent to translucent. The more valuable cat's-eye is a variety of chrysoberyl. Another variety, alexandrite, was first discovered in the Ural Mts.
..... Click the link for more information. from Sri Lanka and Brazil, is the most valuable, but some quartz, tourmaline, and a few other minerals that display chatoyancy are also used as gems. A golden-yellow species called tiger's-eye is a form of quartz that contains crocidolite asbestos.