Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium. Beryl has a hardness ...
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of 7.5–8 on the Mohs scale. Most emeralds have lots of material trapped inside during the gem´s formation, so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.