Translucent yellowish chrysoberyl exhibiting chatoyance is called cymophane or cat’s eye. Cymophane is derived from the Greek words meaning ‘wave’ and ‘appearance’, with reference to the chatoyancy sometimes exhibited.

In this variety, microscopic linear cavities or needle thin inclusions of rutile occur. When their orientation is parallel to the base they produce a chatoyant effect exhibited as a single ray of light passing across the crystal. This effect is best seen in gemstones cut in cabochon form. The color in yellow chrysoberyl is due to Fe3+ impurities.

Many other minerals like tourmaline, scapolite, corundum, spinel and quarts can form “cat’s eye” stones similar in appearance to cymophane. These stones as known as “quartz cat’s eyes”, or “ruby cat’s eyes” etc. Only chatoyant chrysoberyl can be referred to as “cat’s eye” with no other designation.

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.

Cat’s eye became very popular by the end of the 19th century. Until that time, cat’s eye had been present only in gem and mineral collections. The popularity and the value of the stone increased so much that in the early 20th century the prices could go up as high as $8000 for a cut stone.