Translucent yellowish chatoyant chrysoberyl is called cymophane or cat’s eye. It is a yellow or green opalescent variety of chrysoberyl. Cymophane has its derivation also from the Greek words meaning ‘wave’ and ‘appearance’, in reference to the chatoyancy sometimes exhibited. In reference to the haziness that visually distorts what would normally be viewed as a well-defined surface of a cabochon.
Cymophane is an opalescent variety of Chrysoberyl. It exhibits a bluish (or yellowish according to other sources) chatoyancy which is caused by microscopic tube-like cavities or needle-like inclusions of rutile in an orientation parallel to the c-axis. This effect is best seen in gemstones cut in cabochon form perpendicular to the c-axis. The color in yellow chrysoberyl is due to Fe3+ impurities.
- Color: Black, Green, Grey, Yellow, Red, Pink, Brown, Orange
- Luster: Vitreous
- Crystal system: Orthorhombic crystal system
- Chemical formula: BeAl₂O₄
- Hardness (Mohs hardness scale): 8.5
- Mineral class: Chrysoberyl
Gems lacking the silky inclusions required to produce the cat’s eye effect are usually faceted. An alexandrite cat’s eye is a chrysoberyl cat’s eye that changes color. “Milk and honey” is a term commonly used to describe the color of the best cat’s eyes. The honey color is considered to be top-grade by many gemologists but the lemon yellow colors are also popular and attractive. Cat’s eye material is found as a small percentage of the overall chrysoberyl production wherever chrysoberyl is found.
Cat’s eye really became popular by the end of the 19th century when the Duke of Connaught gave a ring with a cat’s eye as an engagement token; this was sufficient to make the stone more popular and increase its value greatly. Until that time, cat’s eye had predominantly been present in gem and mineral collections. The increased demand, in turn, created an intensified search for it in Sri Lanka.