× Sell your old school/college notes here at www.studyalways.com and make money for free
Emerald is a gemstone, and a variety of the mineral beryl [Be3Al2(SiO3)6] coloured 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. Emeralds occur in hues ranging from yellow-green to blue-green, with the primary hue necessarily being green. Yellow and blue are the normal secondary hues found in emeralds. Only gems that are medium to dark in tone are considered emerald; light-toned gems are known instead by the species name green beryl. The finest emeralds are approximately 75% tone on a scale where 0% tone would be colourless and 100% would be opaque black. In addition, a fine stone should be well saturated; the hue of an emerald should be bright (vivid).