Sapphire Diamond Ring
A huge variety of minerals -- 200 or more -- have been used as gemstones at one time or another. But not all of these are suitable as jewelry gemstones, since many are too soft, too brittle or are too easily damaged by environmental factors. Some gemstones are best reserved for collectors rather than jewelry.
Jewelry gemstones have varying requirements depending on the type of jewelry. Gemstones set in rings get the hardest wear, since they often come in contact with hard surfaces. Gems set in earrings are less subject to daily wear and tear, and the same is true for pendants.
It is generally recommended that colored gemstones set in rings have a hardness on the Mohs scale of 7 or greater. Rings worn everyday, such as engagement rings, are usually made with stones such as ruby and sapphire, which have a hardness rating of 9. Rings worn only occasionally, or set in protective settings such as bezels, can be made with softer stones. Some very popular gems, such as tanzanite (hardness of 6.5 to 7) and opal (5.5 to 6.5), are often set in rings, though neither are particularly hard.
However, hardness is not the only measure of a gem's suitability for jewelry. Some gems which are quite hard, such as emerald (hardness of 8), have internal fractures which make them more fragile. Nephrite jade, by contrast, is extremely durable, despite having a hardness of 6 to 6.5; its strength is due to its internal structure, where fibrous crystals interlock in a matted texture.
Despite these practical constraints, the variety of gemstones used in jewelry is actually increasing, as jewelry designers seek out rarer gemstones for making distinctive jewelry. Gems such as prehnite and andalusite were once rarely found in jewelry; today one will also find apatite, mali garnet, charoite and seraphinite used as jewelry gemstones for their unique colors and textures.
At one time the choice in jewelry gemstones was restricted by what was available in mass-produced jewelry. Now it is possible to select from a vast range of gemstones carried by a dealer who specializes in colored gems, and have custom jewelry created by the jeweler of your choice.