Dioptase - Encyclopedia

    Class : Silicates
    Subclass : Cyclosilicates
    Crystal system : Trigonal
    Chemistry : CuSiO3 . H2O
 
    Rarity : Rare

Formerly confused with emerald because of its intense bluish green color, it has been defined and discovered by René Just Haüy. Dioptase comes from ancient Greek dia (through) and optadzo (vision) because its cleavages can be seen simply by transparency within crystals. It is a mineral species highly prized by collectors from around the World. It occurs in the oxidation zones of copper deposits under hot climates. Crystals are often elongated rhombohedra vertically striated and more rarely scalenohedra. Because of its low hardness and its easy cleavage, it is not very present in the jewelery sector, although faceted specimens were cut, they are often destined for collection.

Dioptase from Kimbedi, Mindouli, Dem. Rep. of Congo
Dioptase from Kimbedi, Mindouli, Dem. Rep. of Congo
Dioptase on calcite from Tsumeb, Namibia
Dioptase on calcite from Tsumeb, Namibia

Dioptase in the World

The best deposits are located in Central Africa, especially in Congo and in Democratic Republic of Congo where crystals up to 8 by 2 cm lining geodes in chrysocolla. Namibia also provides superb crystals up to 5 cm in Tsumeb Mine on white calcite, or quartz in Kaokoland. The largest known crystals exceed 15 cm and come from Angola, these are not a pleasing look. Beautiful crystals are also found in Kazakhstan and in several copper mines of Arizona as Mammoth-Saint Anthony Mine, where it can sometimes be associated with wulfenite (see picture in margin).

Dioptase in France

In France dioptase is anecdotal, it occurs in microcrystals in uraninite veins in red Permian clay schists, the deposit is located about 7 km south / southeast from Lodève in Hérault.

Twinning

There is a twinning plane for dioptase, however the samples are extremely rare.

Fakes and treatments

Among the fakes listed for this mineral, there are some assemblages, see our article about this on the subject: "assemblages".



Hardness : 5
Density : 3,38 to 3,35
Fracture : Conchoidale
Trace : Green




TP : Transparent to translucent
RI : 1,644 à 1,709
Birefringence :  0,051 to 0,053
Optical character : Uniaxial +
Pleochroism : Weak
Fluorescence : None


Solubility : Hydrochloric acid

Magnetism : None
Radioactivity : None