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Kingstonite, (Rh,Ir,Pt)3S4, a new mineral species from Yubdo, Ethiopia

Published online by Cambridge University Press:  05 July 2018

C. J. Stanley ,
A. J. Criddle ,
J. Spratt ,
A. C. Roberts ,
J. T. Szymański  and
M. D. Welch
C. J. Stanley*
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
A. J. Criddle
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
J. Spratt
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
A. C. Roberts
Affiliation:
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8
J. T. Szymański
Affiliation:
Canmet, 555 Booth Street, Ottawa, Ontario, Canada K1A 0G1
M. D. Welch
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
*
*E-mail: [email protected]
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Abstract

Kingstonite, ideally Rh3S4, is a new mineral from the Bir Bir river, Yubdo District, Wallaga Province, Ethiopia. It occurs as subhedral, tabular elongate to anhedral inclusions in a Pt-Fe nugget with the associated minerals isoferroplatinum, tetraferroplatinum, a Cu-bearing Pt-Fe alloy, osmium, enriched oxide remnants of osmium, laurite, bowieite, ferrorhodsite and cuprorhodsite. It is opaque with a metallic lustre, has a black streak, is brittle and has a subconchoidal fracture and a good cleavage parallel to [001]. VHN25 is 871–920 kg/mm2. In plane-polarized reflected light, kingstonite is a pale slightly brownish grey colour. It is weakly pleochroic and displays a weak bireflectance. It does not possess internal reflections. The anisotropy is weak to moderate in dull greys and browns. Reflectance data and colour values are tabulated. Average results of twenty electron microprobe analyses on four grains give Rh 46.5, Ir 16.4, Pt 11.2, S 25.6, total 99.7 wt.%. The empirical formula is (Rh2.27Ir0.43Pt0.29)Σ2.99S4.01, based on 7 atoms per formula unit (a.p.f.u.). Kingstonite is monoclinic (C2/m) with a = 10.4616(5), b = 10.7527(5), c = 6.2648(3) Å, β = 109.000(5)°, V = 666.34(1) Å3 (Z = 6). The calculated density is 7.52 g/cm3 (on the basis of the empirical formula and unit-cell parameters refined from powder data). The seven strongest X-ray powder-diffraction lines [d in Å(I) (hkl)] are: 3.156 (100) (310), 3.081 (100) (31), 2.957 (90) (002), 2.234 (60) (202), 1.941 (50) (23), 1.871 (80) (41) and 1.791 (90) (060, 33). The structure of kingstonite was solved and refined to Rp = 3.8%. There are four distinct metal sites with Rh occupancies of 0.64–0.89. Two metal sites are regular RhS6 octahedra that share edges to form a ribbon running parallel to c. The other two metal sites are coordinated by 4 S + 2 Rh and 5 S + 2 Rh and define a puckered Rh6 ring. The ribbons of regular RhS6 octahedra alternate with the columns of Rh6 rings linked by S atoms. S–S bridges also connect the ribbons and columns. As such, the kingstonite structure is essentially that of synthetic Rh3S4. Minor differences in the unit-cell parameters, atom coordinates and displacement parameters of kingstonite and synthetic Rh3S4 arise from the considerable substitution of Ir for Rh. The mineral name honours Gordon Kingston (formerly of Cardiff University) in recognition of his contributions to platinum group element mineralogy and the geology of their mineral deposits.

Keywords

kingstonitenew mineralplatinum-group mineralRh-Ir-Pt sulphideYubdoEthiopiaelectron microprobe datareflectance dataX-ray diffraction datacrystal-structure analysis
Type
Research Article
Information
Mineralogical Magazine , Volume 69 , Issue 4 , August 2005 , pp. 447 - 453
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2005

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Footnotes

†

deceased

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