Crysoberyl is a beryllium aluminum oxide, which produces the gemstones alexandrite and cat's - eye. It's tabular crystals (orthorhombic system) are transparent to translucent, yellowish green to green or brown, and have a vitreous luster. Common chrysoberyl occurs as crystals or loose, rounded grains in granitic pegmatites, and in metamorphic rocks such as schist and gneiss.