Chatoyancy

  In gemology, chatoyancy (or chatoyance) is an optical reflectance effect seen in certain gemstones. Coined from the French "chat oeil," meaning "cat's eye," chatoyancy arises either from the fibrous structure of a material, as in tiger eye quartz, 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.

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Some gem species known for this phenomenon include the aforementioned quartz, chrysoberyl, beryl (especially var. aquamarine), tourmaline, apatite, moonstone and scapolite.

Chatoyancy can also be used to refer to a similar effect in woodworking, where certain finishes will cause the wood grain to achieve a striking three-dimensional appearance.[1]

See also

• asterism
• optical phenomenon

References

• Webster, R., Jobbins, E. A. (Ed.). (1998). Gemmologist's compendium. St Edmundsbury Press Ltd, Bury St Edwards.