The translucent honey-yellow to greenish or brownish yellow chatoyant chrysoberyl which, when cut with a domed surface (cabochon) show a mobile streak of light are called as cymophane or cat’s eye chrysoberyl. cat’s eye is a band of light that runs length wise from one end of the stone to the other. This effect is called chatoyancy.
In gemology, chatoyancy (or chatoyance) is an optical reflectance effect seen in certain natural gemstones. Coined from the French “oeil de chat”, meaning ‘cat’s eye’, chatoyancy arises either from the fibrous structure of a material, as seen in tiger eye quartz, or from fibrous inclusions or cavities within the stone, as seen in chrysoberyl cat’s eye .