An aluminum oxide, it occurs as shapeless grains and masses (emery), rhombohedral crystals. Ruby contains traces of chromium oxide, when red and Fe2O3, which modified the color. The color of sapphire results from a combination of titanium and iron oxides,
A hard, important gem mineral, of which alexandrite and cymophane are two varieties. Occasionally a greenish chatoyancy can be seen which was formerly known as cymophane, but is now called chrysoberyl cat's eye, or oriental cat's eye, when cut en cabochon