diamond, a mineral composed of pure carbon. It is the hardest naturally occurring substance known; it is also the most popular gemstone. Because of their extreme hardness, diamonds have a number of important industrial applications.

Is diamond a crystal or stone?

Diamond is also a natural crystal. It is formed in deep earth layers by compression of the mineral carbon under very high pressure. Gemstones can be cut and polished into beautiful shapes due to their composition and hardness.

Are all diamonds gemstones?

Diamonds are technically gemstones.

All other gemstones, besides diamonds, rubies, emeralds, and sapphires, are considered semi-precious because they are more abundant than their precious counterparts.