VOLTAITE

    Class : Sulfates, chromates, molybdates
    Subclass : Hydrated sulfates
    Crystal system : Cubic
    Chemistry : K2Fe9(SO4)12 18H2O
    Rarity : Common

Voltaite is a double sulfate of potassium and ferrous (Fe2+) and ferric (Fe3+) iron. It is a rare secondary mineral formed by the alteration of iron sulfides, mainly in arid climates, which is part of a classic mineralogical procession to which other iron sulfates belong (copiapite, jarosite, coquimbite, botryogen, etc...). These sulfates result, like it, from precipitation from "natural" sulfuric acid, formed by the reaction of surface water with iron sulfides ; by changing the environmental conditions (temperature, pH, oxidation-reduction potential) they are easily hydrolyzed into ferric hydroxides (goethite and limonite). Voltaite is also known from volcanic fumaroles. It was named in honor of Alessandro Giusepe Antonio Anastasio Volta, an Italian physicist who discovered the electric battery in 1800. Voltaite occurs in the form of cubes, octahedra, rarely dodecahedra, of a black to greenish-black color.

Main photo : Voltaïte from Monte Arsiccio Mine, Tuscany, Italy © Uwe Haubenreisser

Voltaite from Meggen Mine, Germany © Elmar Lackner
Voltaite from Rio Tinto, Huelva, Spain © Christian Rewitzer
Voltaite and römerite from Vieux Travaux, Gard, France © Yannick Vessely
Voltaite and römerite from Vieux Travaux, Gard, France © Yannick Vessely

Voltaite in the World

Magnificent centimeter octahedra come from the old pyrite mines of Rio Tinto Tinto (Huelva, Spain) where they are observed lying on a fragile layer of acicular gypsum and other iron sulfates. It is also found in beautiful crystals on Italian pyrite deposits such as Monte Arsiccio Mine. Voltaïte is also known in the oxidation zone of the large copper deposits of northern Chile (Alcaparrosa, Chuquicamata), those of Arizona (Bisbee, Jerome), as well as in the oxidized part of the Rammelsberg sulfidic mass (Germany).

Voltaite in France

In France, voltaite is known at Vieux Travaux near St-Laurent-le-Minier (Gard) as well as at Jas Roux (Hautes-Alpes).

Twinning

No twinning known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 3 to 3.5
Density : 2.65
Fracture : Conchoidal
Streak : Gray-green

TP : Opaque
RI : 1.593 to 1.608
Birefringence : 0
Optical character : None
Pleochroism : None
Fluorescence : None

Solubility : Water, acids

Magnetism : NoneRadioactivity : None

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