Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Stanley, C. J. Articles by Welch, M. D. Search for Related Content GeoRef GeoRef Citation

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

C. J. Stanley^1,*, A. J. Criddle^1,, J. Spratt¹, A. C. Roberts², J. T. Szymaski³ and M. D. Welch¹

¹ Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
² Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8
³ CANMET, 555 Booth Street, Ottawa, Ontario, Canada K1A 0G1

^* E-mail: c.stanley{at}nhm.ac.uk

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 (Rh_2.27Ir_0.43Pt_0.29)_2.99S_4.01, 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, ß = 109.000(5)°, V = 666.34(1) ų (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: kingstonite, new mineral, platinum-group mineral, Rh-Ir-Pt sulphide, Yubdo, Ethiopia, electron microprobe data, reflectance data, X-ray diffraction data, crystal-structure analysis