Chatoyancy

Chatoyancy, also known as the “cat’s eye” effect, refers to the thin band of brilliant light observed in stones cut with a curved surface (cabochon). Embedded beneath the surface of these stones are thin, needle-like crystals aligned parallel to one another. When light hits these parallel crystals, often rutile or hematite, it is nearly always reflected back to the onlooker, creating an intense line of light. This effect can be found in cabochon-cut species of Tiger Eye, , Heliodor, Blue Apatite, Iolite, and Seraphinite.