PLANCHEITE

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Orthorhombic
    Chemistry : Cu8Si8O22(OH)4 H2O
    Rarity : Rare

Plancheite is a relatively rare secondary copper silicate, which has adopted the double-chain crystal structure of amphiboles (inosilicates). It is frequently associated with chrysocolla, malachite and dioptase in the oxidation zone of copper deposits in an arid climate. It was named in honor of the French explorer Planché who discovered this mineral in Africa at Mindouli (Congo). Plancheite occurs in small acicular crystals most often united in fibroradiated aggregates forming concretionary masses. Translucent, its luster is pearly and its color pale blue to dark blue. It is exceptionally cut but is more of a collector's stone than jewelry.

Main photo : Plancheite from M'sesa Mine, Kambove, Democratic Republic of Congo © Paul de Bondt

Plancheite from Shangulowé Mine, Kambove, DR Congo © Stephan Wolfsried
Plancheite pseudomorph after dioptase from Tantara Mine, DR Congo © Peter Slootweg
Plancheite pseudomorph after calcite from Tantara Mine, DR Congo © Valere Berlage
Plancheite pseudomorph after cuprite from M'sesa Mine, DR Congo © Jasun D. McAvoy

Plancheite in the World

The best specimens of plancheite come from the copper deposits of Katanga (Kambove, Pimbi, Tantara) and Congo (Renéville, Mindouli), where plancheite occurs in encrustations of fibroradiated spherules 2 cm in diameter associated with malachite and sometimes with dioptase. Mindouli is famous for its centimeter-sized asbestiform crystals of plancheite alongside cuprite and native silver. In Tsumeb (Namibia), plancheite forms bluish masses. The American deposits of Arizona (Ajo, Bisbee, Tiger) also yielded bluish masses and microcrystals.

Plancheite in France

In France, plancheite is reported in Chessy (Rhône).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 6
Density : 3.65 to 3.80
Fracture : Fibrous
Streak : Light blue

TP : Translucent
RI : 1.697 to 1.741
Birefringence : 0.044
Optical character : Biaxe +
Pleochroism : Visible
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : None