Overview
In gemology, chatoyancy, also called chatoyance or the cat's-eye effect, is an optical phenomenon in which a narrow, luminous band of reflected light appears across the surface of certain gemstones. The band resembles the slit pupil of a cat's eye and appears to glide across the surface as the stone, the light source, or the observer moves. The same terminology is used also in wood science to describe the phenomenon happening in some valuable wood species, like genuine mahoganies, khaya, sapele, sipo etc.