|Category||Crystals and geodes|
|Group||Crystals on ganges|
|Country||Congo - kinshasa|
|Formula CuSiO3Â·H2O] DIOPTASE|
|O||Oxygen||Other no metal||40.59%|
|H||Hydrogen||Other no metal||1.27%|
Dioptase is a mineral from the group of silicates. The dioptase forms transparent to translucent prismatic crystals of which the largest, found in Angola, exceed 15 centimeters. It is a stone of emerald green to dark green color, see blue. It is a fairly rare stone, which is found in soils comprising zones of oxidation of copper deposits. It is often found associated with chrysocolla, quartz or wulfenite. Dioptase was still considered until the end of the 18th century as an emerald. This mineral is sought after by collectors for its color.