Gersdorffite - Encyclopedia

Class : Sulfides and sulfosalts
Subclass : Sulfides
Crystal system : Cubic
Chemistry : NiAsS
Rarity : Uncommon

Gersdorffite is a sulfo-arsenide of nickel-arsenic hydrothermal veins, in particular polymetallic veins of the "Ni-Co-Bi-Ag-U" type, sometimes also present in deposits of basic magmatic rocks (Sudbury type). It has a pyrite type structure. It was named in honor of Hofrath Johann von Gersdorffs, owner of the Schladming nickel mine near Salzburg (Austria), where the definition samples came from. The crystals are rare (octahedra, cubo-octahedra or pyritohedra) although they can reach 4 cm. Gersdorffite is usually in shapeless masses, the frequent zoning of which testifies to variations in the composition of this mineral which admits cobalt (more than 8%) and iron (more than 10%) in substitution for nickel. With a metallic luster, gersdorffite is steel gray to silver white in color, tarnished to dark gray. It is commonly associated with pyrite, arsenopyrite and many nickel sulfides and arsenides. It is an accessory nickel ore.

Main photo : Gersdorffite from Aït Ahmane, Bou Azzer, Morocco © Marc Dolivet

Gersdorffite from Friedrichssegen Mine, Germany © Volker Betz

Gersdorffite and annabergite from Aït Ahmane, Bou Azzer, Morocco © John Sobolewski

Gersdorffite from the Clara Mine, Germany © Michael Förch

Gersdorffite from Bou Azzer, Morocco © R. Nakanishi

Gersdorffite in the World

Splendid centimeter-sized crystals, the most beautiful known, come from the Aït Amane structure, in Bou-Azzer (Morocco), this district being the most important known stock of gersdorffite. The veins of the Rhineland (Germany), mainly those of Freidrichssegen, near Bad Ems, also yielded quality crystals. The Canadian mines of Sudbury and Cobalt (Ontario) also contain good specimens of gersdorffite, which is a fairly common mineral but generally in very small quantities.

Gersdorffite in France

In France, gersdorffite is reported in numerous occurrences, but never in collection samples. We can cite the mines in the Brioude sector (Haute-Loire) such as Les Sausses, Marsanges, Le Barlet, Ricoules, etc... It is also reported in Sewen (Haute-Rhin), in Farges (Corrèze), in Kaymar ( Aveyron), in Cap Garonne (Var), etc...

Twinning

No twins known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.

Hardness : 5,5
Density : 5.9
Fracture : Irregular
Streak : Gray

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

Solubility : Nitric acid

Magnetism : None
Radioactivity : None

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