The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al2(SiO3)6. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare. Beryl exhibits conchoidal fracture, has a hardness of 7.5–8, and a specific gravity of 2.63–2.80. It has a vitreous luster and can be transparent or translucent. Its cleavage is poor basal and its habit is dihexagonal bipyramidal. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red, and white. The name comes from the Greek beryllos which referred to a precious blue-green color of sea water stone. The term was later adopted for the mineral beryl more exclusively.
Colorless beryl is called goshenite, pink beryl is morganite, red beryl is bixbite or "red emerald" or "scarlet emerald," clear bright yellow beryl is "golden beryl," yellow-green beryl is heliodor, green beryl is emerald, blue beryl is aquamarine, and deep blue beryl is maxixe. Red beryl is extremely rare. Usually gems are under a carat, are only used in very special jewelry. It is mined primarily in Utah. Blue beryl (aquamarine) will not fade in color when exposed to sunlight. Maxixe is a deep blue stone that fades to white when exposed to sunlight or is subjected to heat treatment, though the color returns with irradiation. Other, unnamed shades such as honey yellow are also known.
The most famous source of emeralds in the world is at Muzo and Chivor, Boyacá, Colombia, where they make a unique appearance in limestone. Emerald are also found in the Transvaal, South Africa; Minas Gerais, Brazil; Zambia, and near Mursinka in the Urals in Russia. In the United States, emeralds are found in North Carolina.
New England's pegmatites have produced some of the largest beryls found, including one massive crystal with dimensions 5.5 m by 1.2 m (18 ft by 4 ft) with a mass of around 18 metric tons; it is New Hampshire's state mineral. As of 1999, the largest known crystal of any mineral in the world is a crystal of beryl from Madagascar, 18 metres long and 3.5 metres in diameter.