FREIBERGITE

    Class : Sulfides and sulfosalts
    Subclass : Sulfides
    Crystal system : Cubic
    Chemistry : (Ag,Cu,Fe)12(Sb,As)4S13
    Rarity : Common


Freibergite is the least common mineral of the gray copper group. It forms a series (continuous solid solution) with tetrahedrite, the antimoniferous pole, and some authors still consider it as an argentiferous variety of this mineral. Freibergite remains much rarer than the latter, but is frequently associated with it in deposits rich in silver. It is known in polymetallic veins and gold-bearing epithermal veins, as well as in massive sulfide masses where its easy alteration into blue and green carbonates (azurite, malachite) makes it easily detectable. It was named after its location of discovery : Freiberg (Saxony, Germany). Freibergite has a metallic luster and an iron gray to black color, with a sub-conchoidal fracture and a generally tetrahedral appearance. It is an accessory ore of copper and silver. It is likely that it was confused with tetrahedrite in many deposits.


Main photo : Freibergite on rhodochrosite from Freiberg, Saxony, Germany © Jordi Fabre

Freibergite in the World


The most remarkable crystals of freibergite, centimeter-sized tetrahedra, were extracted from the mines of Freiberg (Germany), Mount Isa (Australia), Kutna Hora (Czech Republic) and numerous mines in Japan.

Right photo : Freibergite from Borgofranco Mines, Piedmont, Italy © Enrico Bonacina

Freibergite in France

In France, freibergite is reported in many occurrences including : Echassières (Allier), Langeac and Chavagniac-Lafayette (Haute-Loire), Pontgibaud (Puy-de-Dôme), Les Farges (Corrèze), Alzen (Ariège) , etc...

Twinning

Twins are known on {111}.

Fakes and treatments

No fakes recorded for this mineral species.



Hardness : 3 to 4
Density : 4.97
Fracture : Sub-conchoidal
Streak : Reddish to black


TP : Opaque
RI : -
Birefringence : 0
Optical character : None
Pleochroism : None
Fluorescence : None


Solubility : Nitric acid


Magnetism : Paramagnetic
Radioactivity : None