Gem is a mineral or other material used in jewelry and other ornaments. Gems include diamonds, emeralds, opals, and rubies, as well as laboratory-grown gems and other artificially created imitations. When mined, most natural gemstones have a rough surface and irregular shape. Skilled gem cutters then cut and polish the stones to increase their beauty.
Most gems are minerals. However, some gems have organic origins. For example, pearls are formed in the shells of living oysters. Amber is a fossil resin from ancient pine trees. Coral consists of the skeletons of tiny sea animals. Jet is a fossil wood related to coal.
Many gems are beautiful, durable, rare, and valuable. But there are numerous exceptions. For example, some rare and beautiful minerals are too soft to be used in jewelry, and many artificial gems are beautiful and durable, but neither rare nor valuable.
