Euclase is a mineral with a hardness of 8 out of 10 on the Mohs scale of mineral hardness [?]. These Monoclinicly structured gems are made of beryllium aluminum hydrosilicate, their full chemical compound being Be(Al,OH)SiO4.
Euclase is a silicate with a monoclinic crystal system. It is considered a very rare gem of light blue color.
It appears as long or short prismatic crystals, flattened and transparent.
It is colorless, white, green, or blue, commonly a pale aquamarine or green, but crystals of a very fine dark blue (from iron) have been found at the Miami mine in Zimbabwe. Crystals are often striated.
It is very hard, light, with one direction of perfect cleavage and conchoidal fracture. It is transparent to translucent with bright, vitreous luster. It is insoluble and fuses with difficulty.
Euclase occurs principally in granite pegmatites associated with topaz. It can also occur in alluvial placer sediments and geodes.
The finest crystals of colorless, blue and green gem-quality euclase have been mined near Ouro Prieto, Minas Gerais (Brazil). Crystals up to 5cm or larger have been found. Other sources in Kenya, Tanzania, Sanarka River (Soviet Republics), Ireland, Australia, and Park County, Colorado (USA)
It can be confused with topaz, aquamarine, beryl, and hiddenite, and is sometimes erroneously called "prismatic emerald."
Its name derives from its quality of having perfect cleavage, leading Rene Hauy to call it after the Greek words for "fracture" and "easily." It is formed from the decomposition of beryl.
Euclase is occasionally faceted into gems with high brilliance. Because of its perfect cleavage, it is difficult to cut, but a number of faceted specimens exist, and are prized by collectors.