Hellyerite

Carbonate mineral
(repeating unit)NiCO3·5.5(H2O)IMA symbolHy[1]Strunz classification5.CA.20Crystal systemMonoclinicCrystal classPrismatic (2/m)
(same H-M symbol)Space groupC2/cUnit cella = 10.77, b = 7.29
c = 18.68 [Å]; β = 94°: Z = 8IdentificationColorPale blueCrystal habitAs crystal fragments and microcrystalline coatingsTwinningFine lamellar parallel to cleavageCleavageOne perfect, two good at 112° to each other and perpendicular to the perfect cleavageMohs scale hardness2.5LusterVitreousDiaphaneitySemitransparentSpecific gravity1.97Optical propertiesBiaxial (−)Refractive indexnα = 1.455 nβ = 1.503 nγ = 1.549Birefringenceδ = 0.094PleochroismX = Y = very pale greenish blue; Z = pale greenish blue2V angleMeasured: 85°Alters toDecomposes on air exposureReferences[2][3][4]

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. It is a pentahydrate according to X-ray crystallography. The solid consists of [Ni2(CO3)2(H2O)8] subunits with an extra pair of water of hydration.[5]

Occurrence

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,[6] Tasmania, Australia and named after Henry Hellyer (1791–1832), Chief Surveyor of the Van Diemens Land Company.[3] It is also reported from the Pafuri nickel deposit in Limpopo Province, South Africa.[4]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Hellyerite at Webmineral.com
  3. ^ a b Handbook of Mineralogy
  4. ^ a b Mindat.org
  5. ^ Bette, Sebastian; Rincke, Christine; Dinnebier, Robert E.; Voigt, Wolfgang (2016). "Crystal Structure and Hydrate Water Content of Synthetic Hellyerite, NiCO3·5.5H2O". Zeitschrift für Anorganische und Allgemeine Chemie. 642 (9–10): 652–659. doi:10.1002/zaac.201600044.
  6. ^ Williams KL,Threadgold IM,Hounslow AW. Hellyerite: A new nickel carbonate from Heazlewoord, Tasmania. The American Mineralogist,1959;44:533–538. [1]