In gemology, chatoyancy is an optical reflectance effect seen in certain gemstones. Coined from the French, meaning "cat's eye," chatoyancy arises either from the fibrous structure of a material, as in tiger eyequartz, or from fibrous inclusions or cavities within the stone, as in cat's eye chrysoberyl. The effect can be likened to the sheen off a spool of silk; the mobile, wavering reflection always being perpendicular to the direction of the fibres. For a gemstone to show this effect it must be cut en cabochon, with the fibers or fibrous structures parallel to the base of the finished stone.
Chatoyancy is a band or star of reflected light or color that moves through a gem depending on its orientation.
Originally, tiger's eye's chatoyancy was attributed to chalcedony a fibrous form of quartz replacing fibrous crocidolite.
Because crocidolite, and not quartz, is the cause of the shimmer in the tiger's eye, the variable chatoyancy that is tiger's eye's signature actually is a record of the structural path of the parent rock during tectonic events, says Heaney.
Chatoyancy - Phenomenon of certain cat's eye minerals which causes it to exhibit a concentrated narrow band of reflected light across the center of the mineral.
Chatoyancy is the lustrous, cat's eye effect seen in some cabochon stones, like cat's eye, tiger's eye (pictured above), and sometimes in other stones, like aquamarine.
CHATOYANCY: Or the Cat's Eye Effect is a reflection effect that appears as a single bright band of light across the surface of a gemstone.
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