Gemstones Renown and valued for their beauty, gemstones are natural forms of matter that can be cut and polished for use as jewelry or other ornamental purposes. Durability The twofold test of durability for a mineral is of hardness and toughness. One misconception is that these are the same thing. Hardness, however, refers to a mineral's resistance to scratching while toughness refers to its resistance to breaking. A diamond, for example, is the hardest of all minerals, but can be crushed with enough force. Jade, on the other hand, is quite susceptible to scratching, but is considered one of the toughest gemstones. The hardness of a gemstone is determined by the Mohs scale, which ranges from 1 to 10. Talc, which is 1 on the scale, is softest, while diamonds are the hardest at 10 . Other classifications of gemstones include crystal structure, optical characteristics, and specific gravity. Mineral gemstones Mineral gemstones are naturally growing rocks found in the earth's surface. There are 16 groups of mineral gemstones, including: Beryl, Chrysoberyl, Corundum, Diamond, Feldspar, Garnet, Jade, Lapis Lazuli, Opal, Peridot, Quartz, Spinel, Topaz, Tourmaline, Turquoise, and Zircon. Organic gemstones Organic gemstones are not as durable as gemstones from minerals, and consist of four groups. Amber, a fossil resin found in the sap of ancient tree pines, usually lacks a crystalline structure. It is most often brown or semitransparent and mined. Coral is crafted when a small marine animal known as a coral polyp extracts calcium carbonate from the sea to build a protective home for itself. The result of gem coral ranges from semi translucent to opaque and can be white, pink, orange, red, blue, violet, gold, or black. Jet is a black coal that can be used as beads or for bracelets. Pearl is formed inside an oyster, or any other mollusk that deposits substances inside of its housing. Mollusks creating pearls can be found in either fresh or salt water, but salt water pearls are often more sought after for use in earrings, bracelets, and necklaces. Most pearls are white, but they also come in a variety of other colors, including black. Precious stones Five particular stones were once referred to as precious stones primarily because of historical and ceremonial use while other stones were referred to as semiprecious stones. These precious stones (diamond, ruby, sapphire, emerald, and amethyst), however, are now included by gemologists among the precious stones.