| Annabergite | |
|---|---|
Annabergite, Dobšiná, Slovakia |
|
| General | |
| Category | Arsenate minerals |
| Chemical formula | 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.
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.