Cat's Eye is a form of Chrysoberyl and is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words ???s?? chrysos and ß??????? beryllos, meaning "a gold-white spar". Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones. Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the hardness scale, between corundum (9) and topaz (8).