Chlorargyrite - Encyclopedia

    Class : Halides
    Subclass : Chlorides
    Crystal system : Cubic
    Chemistry : AgCl
    Rarity : Unommon


Chlorargyrite (or cerargyrite) is a fairly common silver halide that sometimes forms abundantly in the oxidation zone of silver deposits in arid regions. It forms a complete solid solution with bromargyrite and usually occurs in "horny", waxy, sometimes columnar, rarely fibrous masses. It owes its name to its chemical composition : chlorine and silver (arguros in Greek). Chlorargyrite is translucent, resinous to adamantine in luster, pearl gray to grayish green in color, most often ; photosensitive, it becomes purple-brown then black in the light. The crystals are cubic or octahedral, often in sub-parallel groupings. Of low hardness (1.5 to 2.5), chlorargyrite is plastic and cuts into chips like wax. It is unalterable in air and remains stable in outcrops, often in the company of native silver, argentite and various metallic oxides. Chlorargyrite, unlike other silver halides, once existed in considerable quantities in outcrops and may thus have constituted an important silver ore. Large quantities of chlorargyrite have in fact been exploited in several deposits : Potosi (Bolivia), where Pone de Léon (1547) speaks of 6000 furnaces treating cerargyrite by fusion ; Johanngeorgenstadt and Schneeberg, in the Erzgebirge of Saxony ; Chañarcillo and Caracoles (Chile) ; finally, more anecdotally, at Treasure Hill (Nevada), where a 6-ton mass of chlorargyrite was extracted.

Main photo : Chlorargyrite from Broken Hill, Australia © Chris Stefano

Chlorargyrite from Reward Mine, Arizona, USA © Elmar Lackner
Chlorargyrite from Broken Hill, Australia © Mark Willoughby
Chlorargyrite on native silver from Poullaouen, Finistère, France © Serge Lavarde
Chlorargyrite from Clara Mine, Freiburg, Germany © Carsten Slotta

Chlorargyrite in the World

The most beautiful crystals known are perfect 15 mm cubo-octahedra from Broken Hill (Australia). But other beautiful crystals come from Chile (Chañarcillo, Huantajaya), Bolivia, Idaho (Silver City), and Saxon mines (Germany).

Chlorargyrite in France

In France, the silver veins of Huelgoat (Finistère) and Ste-Marie-aux-Mines (Haut-Rhin) produced millimeter cubes. It is also reported at Cap Garonne (Var).

Twinning

Twins are common on {111} but rarely visible.

Fakes and treatments

No fake identified for this mineral species.



Hardness : 1.5 to 2.5
Density : 5.55
Fracture : Irregular
Streak : White



TP : Translucent to transparent
RI : 2.07
Birefringence : 0
Optical character : None
Pleochroism : None
Fluorescence : None


Solubility : Ammonia and potassium cyanide


Magnetism : None
Radioactivity : None

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