Hellyerite

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Hellyerite
Hellyerite-Heazlewoodite-Zaratite-255032.jpg
Zaratite (emerald-green coating), hellyerite (powder-blue) and heazlewoodite (light bronze)
General
Category Carbonate mineral
Formula
(repeating unit)
NiCO3·6(H2O)
Strunz classification 05.CA.20
Crystal symmetry Monoclinic 2/m
Unit cell a = 10.77 Å, b = 7.29 Å, c = 18.68 Å; β = 94°: Z = 8
Identification
Color Pale blue
Crystal habit As crystal fragments and microcrystalline coatings,
Crystal system Monoclinic
Twinning Fine lamellar parallel to cleavage
Cleavage One perfect, two good at 112° to each other and perpendicular to the perfect cleavage
Mohs scale hardness 2.5
Luster Vitreous
Diaphaneity Semitransparent
Specific gravity 1.97
Optical properties Biaxial (-)
Refractive index nα = 1.455 nβ = 1.503 nγ = 1.549
Birefringence δ = 0.094
Pleochroism X = Y = very pale greenish blue; Z = pale greenish blue
2V angle Measured: 85°
Alters to Decomposes on air exposure
References [1][2][3]

Hellyerite, NiCO3·6(H2O), 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.

Occurrence[edit]

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.

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 ~4,000 ppm nickel within olivine.

It was first identified in 1958 in the Old Lord Brassy mine,[4] Tasmania, Australia and named after Henry Hellyer (1791–1832), Chief Surveyor of the Van Diemens Land Company.[2] It is also reported from the Pafuri nickel deposit in Limpopo Province, South Africa.[3]

References[edit]

  1. ^ Hellyerite at Webmineral.com
  2. ^ a b Handbook of Mineralogy
  3. ^ a b Mindat.org
  4. ^ Williams KL,Threadgold IM,Hounslow AW. Hellyerite: A new nickel carbonate from Heazlewoord, Tasmania. The American Mineralogist,1959;44:533-538. [1]