Minerals that are highly prized for their beauty are called gemstones. The main use of gemstones is in jewellery or other decorative work, although some are also used in industry. Around 90 minerals are classed as gems, but only about 20 of these are important gems. These include diamonds, the most valuable of all gemstones. Some minerals provide more than one type of gem. For example, different types of the mineral beryl form emerald, aquamarine, heliodor and morganite.

Gems such as ruby and emerald are distinctive because of their colour.