Chalcophyllite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated arsenates
    Crystal system : Trigonal
    Chemistry : Cu18Al2(AsO4)4(SO4)3(OH)24. 36H2O
    Rarity : Uncommon to rare

Chalcophyllite is a secondary arseniosulphate of the oxidation zone of copper deposits. Its name is derived from the Greek khalkos (copper) and phullon (leaf) which emphasizes both its chemical composition and its structure. The crystals are very flattened rhombohedra with a perfect cleavage on {0001}, as for the micas, with faces sometimes striated in the 3 directions ; their habit is frequently hexagonal in appearance. Chalcophyllite also occurs in flaky aggregates, leaf masses and rosettes. Its emerald green to bluish green color, associated with a subadamantine luster is characteristic. It is a mineral that has no particular use, its crystals are only intended for the mineral collection.

Chalcophyllite in the World

The finest specimens, centimetric emerald green crystals, come from the copper mines in the districts of Gwennap and Gunnislake, in English Cornwall. Comparable crystals come from the El Teniente mine in Chile, while the copper mines in Arizona (Bisbee) and Nevada (Majuba Hill) provided crystals of lower quality.

Chalcophyllite in France

In France, superb millimeter-scale crystals associated with cyanotrichite were extracted from the Cap Garonne mine (Var). It is also still found in micro-crystals at Echassières (Allier), at the Mine de la Treille and Sankt Johann (Haut-Rhin) and at Faymont (Vosges). In Salsigne (Aude), crystals can reach half a centimeter.

Twinning and special characteristics

Chalcophyllite can be twinned on {10-10}, but this is hardly visible.

Fakes and treatments

No falke recorded for this mineral species.

Hardness : 2
Density : 2.67 to 2.69
Fracture : Uneven
Trace : Green

TP : Transparent to translucent
RI : 1.552 to 1.632
Birefringence :  0.066
Optical character : Uniaxial -
Pleochroism : Weak
Fluorescence : None

Solubility : Acids

Magnetism : None
Radioactivity : None