Retgersite

retgersite

gersdorffite

minasragrite

morenosite

Formula: Ni(SO4).6H2O
Hydrated normal sulphate, tetragonal paramorph of nickelhexahydrite, which is monoclinic
Specific gravity: 2.04
Hardness: 2½
Streak: Greenish white
Colour: Emerald green with blue tinge, pale green in transmitted light
Solubility: Soluble in water
Environments:

Hydrothermal environments

Retgersite is an uncommon secondary mineral in the oxidation zone of nickel-bearing hydrothermal mineral deposits, formed from an aqueous solution between 31.5oC and 53.5oC. Associated minerals include nickeline, gersdorffite, nickel-bearing pyrite, morenosite, chalcanthite and annabergite (HOM).

Localities

Lichtenstein, Bayreuth, Upper Franconia, Bavaria, Germany: Retgersite has been identified as crusts and veinlets associated with fine-grained annabergite on a specimen labeled morenosite from this locality (AM 34.188-194).

At Aït Ahmane, Zagora Province, Drâa-Tafilalet Region, Morocco, retgersite is found on specimens of gersdorffite as aggregates to 3 mm associated with annabergite. In a carbonate vein crusts of retgersite, a few enclosing tiny grains of native sulphur, have been found in the interiors of porous masses of gersdorffite. It seldom rains in the area, but even a bried shower can dissolve any retgersite present on the surface (Minrec 38.5.389).

At the type locality, the Ragra Mine, Huayllay District, Pasco Province, Pasco, Peru, retgersite is found as crystals encrusting a mass of patronite and associated with morenosite and minasragrite (AM 34.188-194).

At Cottonwood Canyon, Table Mountain Mining District, Churchill county, Nevada, USA, retgersite occurs as an alteration product of nickeline (Dana). A specimen has been found in nickeline-bearing vein material. It has been thoroughly oxidised and is crusted over and veined by granular masses of annabergite and fibrous aggregates of retgersite. The retgersite is an original deposit, in part earlier formed than annabergite, and is not a dehydration productof morenosite (AM 34.188-194).

Alteration

Retgersite may occur as a dehydration product of morenosite (Mindat). It can be synthesised by crystallisation from aqueous solution at temperatures between 31.5oC, below which orthorhombic NiSO4.7H2O is stable, and 53.3oC, above which monoclinic NiSO4.6H2O is stable. Retgersite also can crystallise at temperatures at least as low as 0oC from solutions which contain an appropriate excess of free H2SO4. This factor may determine its formation in nature in place of morenosite. Under certain circumstances both retgersite and morenosite have been observed to crystallise simultaneously, one or the other of the two compounds being in metastable equilibrium (AM 34.188-194).

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