cat's-eye

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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cat's-eye

Chrysoberyl cat's-eye with yellow banding on a brown stone

(credit: John H. Gerard)

Any of several gemstones that display a luminous band reminiscent of the eye of a cat. Grayish green or greenish quartz cat's-eye is the most common type; although it comes from the Orient, it is often called occidental cat's-eye to differentiate it from the rarer, and more valuable, precious or oriental cat's-eye, which is a greenish variety of chrysoberyl. Crocidolite cat's-eye (African cat's-eye) is more commonly known as tigereye. Corundum cat's-eye is an imperfect star sapphire or ruby in which the star is reduced to a luminous zone.