The Cat's Eye Effect
"Chatoyancy" comes from the French phrase "œil de chat," meaning cat's eye. It is an optical illusion where a band of light seems to hover directly below the surface of a polished stone, moving as the stone is turned.
The Fibrous Secret
In Tiger's Eye, this effect is created by thousands of microscopic, parallel fibers of crocidolite (blue asbestos) that were entirely replaced by silica (quartz) over millions of years through a process called pseudomorphism. The "silicified" fibers reflect light perpendicular to their orientation.
Lapidary Implications
To highlight chatoyancy, a lapidary must cut the stone as a cabochon, orienting the dome perfectly parallel to the fiber structure. If cut at an angle, the 'eye' will be weak or disappear entirely.
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