chatoyance

Chatoyance is an optical phenomenon in gemstones in which a narrow band of reflected light, resembling a cat’s eye, sweeps across the surface as the stone is moved or rotated. The term derives from chatoyant, meaning “cat’s eye,” and is used to describe the characteristic luminous band produced by certain fibrous inclusions or internal channels within the mineral.

The effect occurs when light enters the gem and reflects off aligned, parallel inclusions or cavities—often rutile needles or other fibrous structures. These closely spaced features act like a row of tiny mirrors, concentrating and directing light to form a bright, focused band. A well-cut cabochon surface helps reveal a sharp, consistent band that remains visible as light changes.

Chrysoberyl with rutile silk is the classical and most prized source of cat’s eye, producing a very sharp, narrow band. Other stones can show chatoyance as well, including tiger’s eye and hawk’s eye varieties of quartz, cat’s eye quartz, and some tourmalines or other minerals that contain parallel fibrous inclusions. Synthetic or treated stones may also display chatoyance.

Quality is judged by several factors: brightness or intensity of the band, sharpness and width of the line, and its evenness across the stone. The surrounding body color and overall polish can influence perceived effect. Chatoyance is distinct from related phenomena such as asterism, which forms a star-like pattern rather than a single moving band.