Emeralds are a variety of the mineral beryl (Be3Al26) colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7.5–8 on the 10 point Mohs scale of mineral hardness. Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor.
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emerald A type of precious stone, green in colour.
emerald Having a clear, deep-green color.
emerald A transparent piece of emerald that has been cut and polished and is valued as a precious gem.