CLINOCLASE

    Class : Phosphates, arsenates, vanadates
    Subclass : Anhydrous arsenates
    Crystal system : Monoclinic
    Chemistry : Cu3(AsO4)(OH)3
    Rarity : Uncommon

Clinoclase (sometimes also called clinoclasite) is a secondary arsenate from the oxidation zone of arsenic-rich copper deposits. Its name comes from the Greek klino (to lean) and klasis (to break), due to its oblique basal cleavage in relation to the main faces. In its deposits, clinoclase is usually part of a large procession of secondary copper minerals (chrysocolla, malachite, cornubite, etc...) mixed with goethite. The crystals are essentially flattened needles up to 5 mm, gathered in rosettes or fibroradiated spherolites measuring up to 5 cm ; pseudorhombohedral prismatic crystals are rarer, as are encrustations. The color is dark greenish blue to greenish black.


Main photo : Clinoclase from Majuba Hill Mine, Nevada, USA © Vincent Bourgoin

3 cm clinoclase from Mammoth Mine, Utah, USA © Rock Currier
Clinoclase from Majuba Hill Mine, Nevada, USA © Louis Verschuren
Clinoclase from the Clara Mine, Freiburg, Germany © Christian Rewitzer
Clinoclase of Faymont, Vosges, France © Thierry Brunsperger

Clinoclase in the World

The finest samples of clinoclase have been described in the mines of English Cornwall, at St-Day and Gwennap, and in the veins of Majuba Hill (Nevada). Good specimens come from the nearby Gold Hill and Mammoth (Utah) mines. Isolated 5 mm crystals and millimeter radiated aggregates come from the Hillside mine, near Stavoren (South Africa). In addition, clinoclase is known from polymetallic veins in the Black Forest (Germany).

Clinoclase in France

In France, clinoclase is found in Ste-Marie-aux-Mines (Haut-Rhin), as well as in Cap Garonne (Var), but also in Faymont (Vosges), at the Tistoulet mine (Aude) and in Rabejac (Herault).

Twinning

No twins known for this mineral species.

Fakes and treatments

No fake identified for this mineral species.


Hardness : 2.5 to 3
Density : 4.38
Fracture : Irregular
Streak : Blue-green

TP : Translucent to transparent
RI : 1.730 to 1.910
Birefringence : 0.180
Optical character : Biaxial -
Pleochroism : Low
Fluorescence : None

Solubility : Acids


Magnetism : None
Radioactivity : None

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