Annabergite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated Arsenates
    Crystal system : Monoclinic
    Chemistry : Ni3(AsO4)2 8H2O

    Rarity : Rare

Annabergite is a rare secondary mineral from the oxidation zone of nickel-cobalt deposits where it results in particular from the oxidation of skutterudite and cobaltite. Since cobalt can completely replace nickel, annabergite forms a continuous series with erythrite, which has the same crystal structure. Its name comes from its place of discovery : the locality of Annaberg in Germany. It is a mineral that never forms large crystals (maximum 1 cm): they are prismatic to acicular and striated according to [001]; it appears mainly in powdery coatings composed of fine needles flattened on {010}, in earthy aggregates, or in masses that can exceed one kilogram. With an adamantine luster, it has a pale green to apple green color which is its main criterion of distinction. However, the pink color due to the cobalt quickly obliterates the green tint of the nickel and many pink cobaltiferous annabergites are wrongly considered as erythrites.

Annabergite from Laurium, Greece - © Michael Pfeil
Annabergite from Laurium, Greece - © Edgar Müller
Bicolor annabergite from Aghbar Mine, Morocco - © Jean-Vincent Coureau
Annabergite from Mine de la Rabasse, Hérault, France - © Fabrice Moreau

Annabergite in the World

The finest known samples come from the Laurion mines (Greece) which produced almost centimetric crystals of the cabrerite variety. It is also very present in the German ore mountains ("Erzgebirge"), in pale green coatings and in rare millimetric crystals. The Canadian cobalt district of Cobalt-Gowganda (Ontario) is also one of the few sites in the world to produce distinct crystals. It is abundant in the Lovelock and Nickel mines (Nevada) and constitutes masses exceeding one kilogram in the Iranian mine of Anarak. Morocco's Bou-Azzer mine is also rich in annabergite.

Main photo : Annabergite from Laurion, Greece - © Stephan Wolfsried

Annabergite in France

In France, annabergite was abundant in earthy coatings mixed with erythrite, asbolane and native silver at Chalanches (Isère), and in certain veins of Ste-Marie-aux-Mines (Haut-Rhin). It is also found in microcrystals at the Orpierre mines near Gap (Hautes-Alpes), at the Rabasse mine (Hérault) and at Laguépie (Tarn-et-Garonne).

Twinning ans special crystallizations

No known twins for this mineral species

Fakes and treatments

No fake identified for this mineral species but very difficult to differentiate from erythrite without chemical analysis if the color is pink.

Hardness : 1.5 to 2.5
Density : 3.07
Fracture : Irregular
Trace : Pae green to white

TP : Transparent to translucent
RI : 1.622 to 1.687
Birefringence :  0.065
Optical character : Biaxial (+/-)
Pleochroism : None
Fluorescence : None

Solubility : Acids

Magnetism : None
Radioactivity : None


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