Annabergite

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Annabergite
Mineraly.sk - annabergit 2.jpg
Annabergite, Dobšiná, Slovakia
General
Category Arsenate minerals
Formula
(repeating unit)
Ni3(AsO4)2·8H2O
Strunz classification 08.CE.40
Crystal symmetry Monoclinic prismatic H–M Symbol (2/m)
Unit cell a = 10.179(2) Å, b = 13.309(3) Å, c = 4.725(1) Å; β = 105(1)°; Z = 2
Identification
Color Apple-green, pale green, pale rose or pale pink, white, gray; may be zoned
Crystal habit Usually as fibrous veinlets, crystalline crusts, or earthy; rare as well formed crystals
Crystal system Monoclinic
Cleavage Perfect on {010}, indistinct on {100} and {102}
Tenacity Sectile
Mohs scale hardness 1.5 – 2.5
Luster Subadamantine, pearly on cleavages, may be dull or earthy
Streak Pale green to white
Diaphaneity Transparent to translucent
Specific gravity 3.07
Optical properties Biaxial (-)
Refractive index nα = 1.622 nβ = 1.658 nγ = 1.687
Birefringence δ = 0.065
2V angle Measured: 84°
References [1][2][3]

Annabergite is an arsenate mineral consisting of a hydrous nickel arsenate, Ni3(AsO4)2·8H2O, crystallizing in the monoclinic system and isomorphous with vivianite and erythrite. Crystals are minute and capillary and rarely met with, the mineral occurring usually as soft earthy masses and encrustations. A fine apple-green colour is its characteristic feature. It was long known (since 1758) under the name nickel ochre; the name annabergite was proposed by H. J. Brooke and W H. Miller in 1852, from Annaberg in Saxony, one of the localities of the mineral. It occurs with ores of nickel, of which it is a product of alteration. A variety, from Creetown in Kirkcudbrightshire, in which a portion of the nickel is replaced by calcium, has been called dudgeonite, after P. Dudgeon, who found it.

Annabergite from Lavrion (Laurium), Greece

Closely related is cabrerite wherein some of the nickel is replaced by magnesium. It is named for Sierra Cabrera in Spain where it was originally found.

References[edit]