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 chrysoberyl 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.
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