Emerald is a variety of the mineral beryl, colored green by trace amounts of chromium and sometimes iron. It is highly prized as a gemstone and by weight is the most valuable gemstone in the world, often made more so by inclusions. Beryl has a hardness of 8 on the 10 point Mohs scale of hardness.

Emerald is a rare and valuable gemstone and, as such, provided the incentive for developing synthetic emeralds. Both hydrothermal and flux-growth synthetics have been produced and a method has been developed for producing an emerald overgrowth on colorless beryl. Synthetic emeralds fluoresce a dull red with long wave UV whereas most natural specimens do not. Also both the specific gravities (natural: 2.70 - 2.78, synthetic: 2.66) and refractive indices (natural: 1.576 - 1.582, synthetic: 1.565) of synthetics are slightly lower. Wispy inclusions are common in flux-grown synthetic emeralds.

Emerald is regarded as the birthstone for May. In some cultures the emerald is the traditional gift for the 55th wedding anniversary.

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