Out of the thousands of minerals in the world, only a few hundred minerals are considered gems. To be considered a gemstone, a rock or mineral must be hard/durable, rare and beautiful.
Gemstones can be carved, faceted, tumbled, or cut in cabochon. The Museum displays many examples of cut gemstones.
Transparent gemstones are generally faceted. The symmetrical series of planes cut at slightly different angles refracts light and makes the stones sparkle. Opaque gemstones are usually cut as cabochons, polished domes with flat or rounded backs. Phenomenal stones that present special visual effects, such as a star (asterism) in sapphires, or a cat's eye (chatoyancy) in moonstones, are also cut as cabochons.