Reference work entry
Gem is a collective generic term for rare and precious natural stone objects. All minerals and rocks that are beautiful, durable, rare and can be made into jewellery or decorative crafts can be called gems. In a narrow sense, gems are mineral crystals that can be used to make valuable jewellery. In a broad sense, gems include jade, coloured stones, organic substances such as pearls, coral and amber as well as artificial gemstones. Approximately 200 known minerals can be made into gems. The most precious minerals are diamond, emerald, jadeite, ruby, sapphire and alexandrite. Others are aquamarine, olivine, tourmaline, topaz, amethyst, turquoise, opal, zircon, garnet, chalcedony, agate and jasper. In the contemporary jewellery market, gemstones can be divided into six types according to the degree of artificial alteration: (1) genuine natural gemstones; (2) artificially modified natural gemstones; (3) synthetic gemstones; (4) artificial gemstones; (5) imitation gemstones; and (6) bonded...
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