A gemstone or gem is a piece of mineral crystal, which, in cut and polished form, is used to make jewellery or other adornments. Most gemstones are hard, but some softminerals are used in jewellery because of their lustre or other physical properties thathave aesthetic value. Rarity is another characteristic that lends value to a gemstone.Apart from jewellery, from earliest antiquity engraved gems and hardstone carvings,such as cups, were major luxury art forms.

In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The main characteristic a gemologist uses to identify a gemstone is its chemical composition. A few gemstones are used as gems in the crystal or other form in which they are found. Most however, are cut and polished for usage as jewellery.