annabergite

(mineralogy) (Ni,Co)₃(AsO₄)₂·8H₂O A monoclinic mineral usually found as apple-green incrustations as an alteration product of nickel arsenides; it is isomorphous with erythrite. Also known as nickel bloom; nickel ocher.

Environment

Secondary (weathered) portion of nickel ore deposits.

Usually in light green earthy crusts and films; crystals slender capillary needles, always small.

Light apple green to pale pink. Luster silky or glassy; hardness 2Ɖ-3; specific gravity 3.0; never solid enough to show a fracture; cleavage side pinacoid, usually not visible. Earthy; translucent.

Hydrous nickel arsenate (35.5% NiO, 38.4% As ₂ O ₅ , and 24.1% H ₂ O, usually with cobalt replacing part of the Ni). See erythrite (preceding). From its ability to impart color, Co appears to dominate the Ni, and examples that are actually higher in Ni than in Co can still be pink in hue.

Fuses, and with strong heating in reducing flame can be fused into a magnetic metallic bead. If doubt remains, the chemical test for nickel can be made: the mineral dissolved in nitric acid neutralized with ammonia (NH ₄ OH), and a little dimethylglyoxime solution added. Boiling makes a bright pink solution.

The green nickel color might be confused with a copper color, but the magnetic bead would prove nickel. Green minerals owing their color to chromium do not reduce to a magnetic bead under the blowpipe.

A rare mineral, forming near the surfaces of cobalt nickel-silver arsenide sulfide veins, usually just a greenish film, as in Cobalt, Ontario, and Saxony, Germany. Good small crystals are almost restricted to a Lavrion, Greece, occurrence, where it is known as cabrerite (from a Spanish occurrence in the Sierra Cabrera). Unlike erythrite, has never been found in really outstanding specimens. The best U.S. occurrence is in Humboldt Co., Nevada. Like erythrite, the green annabergite coating also has a prospector's name, "nickel bloom," and has served as a good guide to ore.

Annabergite

Annabergite is a 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.

References

This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

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