Emerald (Be3Al2(SiO3)6) is a variety of the mineral beryl, colored green by trace amounts of chromium and sometimes iron. It is highly prized as a precious gemstone and by weight is the most valuable gemstone in the world, often made less so by inclusions, which all emeralds have. Beryl has a hardness of 7.5 on the 10 point Mohs scale of hardness. However, this Mohs rating is often adversely affected and can decrease, depending on the number and severity of inclusions in a particular stone. Many countries import emeralds, Colombia being the preeminent exporter of emeralds in the world.

Emeralds have a tendency to appear fuzzy, dull and more included on television or in pictures than they really are.

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 light due to an indicator added during the process of synthesizing the emerald, whereas 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 traditional birthstone for May. According to legend, the emerald has the power to protect the chastity of the wearer and to ward off evil spirits. Furthermore, it was used as a cure for epilepsy and dysentery as well as to aid weak eyesight.

According to Rebbenu Bachya, the word "Nofech" in the verse Exodus 28:18 means "Emerald" and was the stone on the Ephod representing the tribe of Judah.

In some cultures the emerald is the traditional gift for the 55th wedding anniversary. It is also used as the 20 and 35th wedding anniversary stone.
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