chrysoberyl

An orthorhombic mineral, BeAl2 O4 ; vitreous; green, brown,
yellow, or red (alexandrite variety appears emerald green in sunlight, but
red by incandescent light); occurs in granites, granite pegmatites,
schists, and alluvial deposits; a gemstone. Gem varieties: alexandrite,
chrysopal, cymophane, and golden beryl. Known as cat's-eye when it has
chatoyancy. Syn:cymophane
chrysopal.