Widgiemoolthalite

Widgiemoolthalite is a rare hydrated nickel(II) carbonate mineral with the chemical formula (Ni,Mg)5(CO3)4(OH)2·5H2O. Usually bluish-green in color, it is a brittle mineral formed during the weathering of nickel sulfide. Present on gaspéite surfaces, widgiemoolthalite has a Mohs scale hardness of 3.5 and an unknown though likely disordered crystal structure. Widgiemoolthalite was first discovered in 1992 in Widgiemooltha, Western Australia, which is to date its only known source. It was named the following year by the three researchers who first reported its existence, Ernest H. Nickel, Bruce W. Robinson, and William G. Mumme.

Widgiemoolthalite
Widgiemoolthalite (bright green) intermingled with gaspéite (yellow-green). Field of view is three millimeters (0.12 in).
General
CategoryCarbonate minerals
Formula
(repeating unit)		(Ni,Mg)5(CO3)4(OH)2·5H2O
Strunz classification5.DA.05
Dana classification16b.7.1.2
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Unit cella = 10.06, b = 8.75
c = 8.32 [Å]; β = 114.3°, Z = 2
Identification
ColorBluish-green, grass-green
Crystal habitFibrous, rarely massive, pseudo-orthorhombic
TenacityBrittle
Mohs scale hardness3.5
LusterSilky
StreakPale bluish-green
DiaphaneityTransparent
Specific gravity
  • 3.13 (observed)
  • 3.24 (calculated)
Optical propertiesBiaxial (+)
Refractive indexnω = 1.630
nε = 1.640
Birefringence0.010
PleochroismNone
2V angleHigh
Length fast/slowFast
References[1][2][3]

Origins

One consequence of the 1966 discovery of nickel deposits in Western Australia and subsequent nickel mining boom was the discovery of novel secondary mineral species in mined regions beginning in the mid-1970s.[4][5] Widgiemoolthalite was first found at 132 North, a nickel deposit near Widgiemooltha, Western Australia, controlled by the Western Mining Corporation. Blair J. Gartrell collected the holotype widgiemoolthalite specimen from a stockpile of secondary minerals at the site. The mineral was discovered in 1992 and was first reported in American Mineralogist in 1993 by Ernest H. Nickel, Bruce W. Robinson, and William G. Mumme, when it received its name for its type locality.[2][6] Widgiemoolthalite's existence was confirmed and name was approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association the same year. The holotype specimen was stored in Perth's Western Australian Museum.[2]

Occurrence

Widgiemoolthalite occurs as a secondary mineral. It is found overlaying nickel sulfide that has undergone weathering, often in hollow spaces on gaspéite surfaces, and often exhibiting fibrous and rarely massive crystal habits.[2] Other minerals associated with widgiemoolthalite include annabergite, carrboydite, dolomite, glaukosphaerite, hydrohonessite, kambaldaite, magnesite, nepouite, nullaginite, olivenite, otwayite, paratacamite, pecoraite, reevesite, retgersite, and takovite.[2][7] Two additional unnamed minerals were also reported as associated secondary minerals from the 132 North site, the only locality at which widgiemoolthalite has been found.[3][7] The 132 North waste pile from which widgiemoolthalite was first recovered is no longer in existence, making it a rare mineral.[8] In support of the designation of an Anthropocene epoch, the existence and provenance of widgiemoolthalite, along with 207 other mineral species, have been cited as evidence of uniquely human action upon global stratigraphy.[9]

Structure
A ball-and-stick model of a possible widgiemoolthalite crystal structure, adapted from the atomic parameters of its structural analog hydromagnesite as reported by Akao and Iwai[10] modified with measurements by Nickel et al.[2] The model is viewed down the b axis. Gray atoms are nickel, black are carbon, red are oxygen, and blue are hydrogen.

Widgiemoolthalite is a nickel(II) carbonate that has undergone mineral hydration. Tests by Nickel, Robinson, and Mumme yielded the chemical formula (Ni,Mg)5.00(CO3)4.15-(OH)1.70·5.12H2O. The researchers observed that widgiemoolthalite is the nickel structural analog to the hydrated magnesium carbonate hydromagnesite and considering this relationship, determined that widgiemoolthalite's ideal makeup is Ni5(CO3)4(OH)2·4-5H2O though because it may contain either nickel or magnesium, widgiemoolthalite's makeup may also be written (Ni,Mg)5(CO3)4(OH)2·5H2O.[2][11] By weight, the mineral is 49.58% oxygen, 34.41% nickel, 8.05% carbon, 6.11% magnesium, and 1.86% hydrogen.[12] As of 2016, the exact crystal structure of widgiemoolthalite was not known though based on the patterns produced when the mineral was analyzed with X-ray crystallography, a high degree of structural disorder was suspected.[13][14] Under an optical microscope, Nickel, Robinson, and Mumme reported difficulty discerning individual crystals as their lateral dimensions were too small.[2]

Crystals of widgiemoolthalite conform to a monoclinic system of symmetry, occupying space group P21/c. A unit cell of the mineral, the smallest divisible unit that possesses the same symmetry and properties, is packed with twice the atoms of its formula unit and has the dimensions a = 10.06(17), b = 8.75(5), and c = 8.32(4) Å. Each unit cell of widgiemoolthalite has a β value of 114.3(8)° and an approximate volume of 667.48 Å3.[2][6]

Characteristics

Hand specimens of widgiemoolthalite tend to be bluish-green though may also be grass-green in rare cases. Widgiemoolthalite is transparent in hand sample with a silky luster and a pale bluish-green streak. The mineral is brittle and breaks along its fiber contacts. Its observed specific gravity is 3.13(1) while its calculated specific gravity is 3.24, with a hardness of 3.5 on the Mohs scale.[2][3]

When viewed with polarized light under a petrographic microscope, widgiemoolthalite appears bluish-green and does not exhibit pleochroism. It is biaxial positive and has a high optic angle (or 2V). When measured perpendicular and parallel to its axis of anisotropy, its refractive indices are 1.630 and 1.640 respectively. This gives it a birefringence of 0.010.[2][3]

References

This article was submitted to WikiJournal of Science for external academic peer review in 2019 (reviewer reports). The updated content was reintegrated into the Wikipedia page under a CC-BY-SA-3.0 license (2019). The version of record as reviewed is: Collin Knopp-Schwyn; et al. (25 August 2019). "Widgiemoolthalite" (PDF). WikiJournal of Science. 2 (1): 7. doi:10.15347/WJS/2019.007. ISSN 2470-6345. Wikidata Q81440318.

  1. Schorn, S.; et al. (2017). "Widgiemoolthalite". Mineral Atlas. Retrieved January 5, 2017.
  2. Nickel, E. H.; Robinson, B. W.; Mumme, W. G. (August 1993). "Widgiemoolthalite: The new Ni analogue of hydromagnesite from Western Australia" (PDF). American Mineralogist. 78 (7–8): 819–821.
  3. "Widgiemoolthalite". Mindat.org. Hudson Institute of Mineralogy. May 1, 2016. Retrieved May 3, 2016.
  4. Prider, R. T. (May 1970). "Nickel in Western Australia". Nature. 226 (5247): 691–693. Bibcode:1970Natur.226..691P. doi:10.1038/226691a0. PMID 16057474. S2CID 4202704.
  5. Birch, B. (December 1997). "New minerals in Australia". Geology Today. 13 (6): 230–234. doi:10.1046/j.1365-2451.1997.t01-1-00017.x.
  6. Gamsjäger, H.; Bugajski, J.; Gajda, T.; Lemire, R. J.; Preis, W. (2005). Chemical Thermodynamics of Nickel. Amsterdam: Elsevier. p. 216. ISBN 978-0-444-51802-6.
  7. Nickel, E. H.; Clout, J. F. M.; Gartrell, B. J. (July 1994). "Secondary nickel minerals from Widgiemooltha". Mineralogical Record. 25 (4): 283–291. ProQuest 211708719.
  8. Whitfield, P. S. (December 2014). "Diffraction studies from minerals to organics: lessons learned from materials analyses". Powder Diffraction. 29 (S1): S2–S7. Bibcode:2014PDiff..29S...2W. doi:10.1017/S0885715614001146. OSTI 1185457.
  9. Hazen, R. M.; Grew, E. S.; Origlieri, M. J.; Downs, R. T. (March 2017). "On the mineralogy of the 'Anthropocene Epoch'". American Mineralogist. 102 (3): 595–611. Bibcode:2017AmMin.102..595H. doi:10.2138/am-2017-5875. S2CID 111388809.
  10. Akao, M.; Iwai, S. (April 1977). "The hydrogen bonding of hydromagnesite". Acta Crystallographica Section B. 33 (4): 1273–1275. doi:10.1107/S0567740877005834.
  11. Tao, Q.; Reddy, B. J.; He, H.; Frost, R. L.; Yuan, P.; Zhu, J. (December 2008). "Synthesis and infrared spectroscopic characterization of selected layered double hydroxides containing divalent Ni and Co" (PDF). Materials Chemistry and Physics. 112 (3): 869–875. doi:10.1016/j.matchemphys.2008.06.060.
  12. "Widgiemoolthalite". WebMineral. Retrieved January 7, 2016.
  13. Bette, S.; Rincke, C.; Dinnebier, R. E.; Voigt, W. (May 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.
  14. Reddy, B. J.; Keeffe, E. C.; Frost, R. L. (January 2010). "Characterisation of Ni carbonate-bearing minerals by UV–Vis–NIR spectroscopy" (PDF). Transition Metal Chemistry. 35 (3): 279–287. doi:10.1007/s11243-009-9324-7. S2CID 93689608.
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