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Formula: Ni(SO4).6H2O
Hydrated normal sulphate, tetragonal paramorph of monoclinic
nickelhexahydrite
Crystal System: Tetragonal
Specific gravity: 2.04 measured, 2.07 calculated
Hardness: 2½
Streak: Greenish white
Colour: Emerald green with blue tinge, pale green in transmitted light
Solubility: Soluble in water
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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