Which gemstone exhibits a property known as "chatoyancy"?

Chatoyancy, often referred to as the "cat's eye" effect, is a phenomenon that occurs when a gemstone exhibits a narrow band of reflected light that resembles the slit eye of a cat. This optical effect is typically caused by the presence of parallel inclusions or fibrous structures within the stone.

Cat’s-eye quartz is a prime example of chatoyancy, as it displays this striking visual characteristic when cut and polished in a cabochon shape. When the stone is moved in light, the band of light appears to shift across the surface, providing a beautiful and dynamic appearance. This effect is specifically associated with certain minerals that possess a fibrous structure, enabling the distinct cat’s eye appearance.

While opals, diamonds, and peridots are valued for their unique optical properties, they do not exhibit chatoyancy in the same way as cat’s-eye quartz. Opals are known for their play-of-color, diamonds for their brilliance and fire, and peridots for their vibrant green hues, but none showcase the unmistakable cat's eye effect characteristic of chatoyancy. Thus, cat’s-eye quartz stands out as the gemstone that truly embodies this optical phenomenon.