Chatoyancy is a single band of light that glides across a gem, like the slit eye of a cat. Light reflects from many aligned, needle-like inclusions.
In more detail
The stone must be cut as a cabochon to show it. Asterism is two or more chatoyant bands that cross.
On a grading report
Labs name the phenomenon, for example cat's-eye chrysoberyl.
Related terms
- Asterism: Asterism is a star of light that glides across the dome of a gem. Light reflects from fine needles, often rutile, that lie in two or three directions.
- Needle: A needle is a thin, elongated crystal inclusion that looks like a tiny rod at 10x.
- Silk: Silk is a mass of fine, crossing needle inclusions, usually rutile, in ruby and sapphire.