What is Cat' Eye

Cat's Eye is the name given to a gem which, when cut cabochon, shows a single light streak across its face. It is caused by innumerable parallel inclusions, of minute needle-like crystals or tubular cavities, the sides of which reflect light.
Cat's eyes are known in many stones, but the unmodified word refers to chrysoberyl.
Tourmaline cat's eyes, beryl, diopside, and scapolite cat's eyes are not uncommon.

16.23ct yellow-green cat’s-eye chrysoberyl from GIA