The only wellknown natural gemstones harder than chrysoberyl are corundum and diamond.
British Dictionary definitions for chrysoberyl
a rare very hard greenish-yellow mineral consisting of beryllium aluminate in orthorhombic crystalline form and occurring in coarse granite: used as a gemstone in the form of cat's eye and alexandrite. Formula: BeAl2O4
gemstone, beryllium and aluminum oxide (BeAl2O4). A variety that is often cloudy, opalescent, and chatoyant is known as cymophane. Some cymophane, when cut en cabochon (in convex form), comprises the most highly prized cat's-eye.
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