Hellyerite
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Hellyerite, NiCO3·6H2O, is an hydrated nickel carbonate mineral.
It is light blue to bright green in colour, has a hardness of 2.5, a vitreous luster, a white streak and crystallises in the monoclinic system. The crystal habit is as platy and mammillary encrustations on its matrix.
The environment of formation, associated only with metamorphosed ultramafic rocks, is diagnostic compared with gaspeite, another nickel carbonate which is associated with supergene weathering of nickel sulfides.
[edit] Paragenesis
Hellyerite is observed forming in shear planes in serpentinite, produced by carbonation of the serpentinite. Hellyerite forms in this environment in nickel rich serpentinites, which are metamorphosed equivalents of ultramafic cumulate rocks such as peridotite and dunite. Peridotite and dunite, when fresh, can contain up to ~4,000ppm Ni within olivine.
First identified in 1958 in the Old Lord Brassy mine, Tasmania, Australia and named after Lord Hellyer, first Surveyor General of Van Diemens Land (later Tasmania).
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