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

Abstract Kingstonite, ideally Rh 3 S 4 , 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]. VHN 25 is 871–920 kg/mm 2 . 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 2.27 Ir 0.43 Pt 0.29 ) Σ2.99 S 4.01 , based on 7 atoms per formula unit (a.p.f.u.). Kingstonite is monoclinic ( C 2/ m ) with a = 10.4616(5), b = 10.7527(5), c = 6.2648(3) Å, β = 109.000(5) ° , V = 666.34(1) Å 3 (Z = 6). The calculated density is 7.52 g/cm 3 (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 R p = 3.8%. There are four distinct metal sites with Rh occupancies of 0.64–0.89. Two metal sites are regular RhS 6 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 Rh 6 ring. The ribbons of regular RhS 6 octahedra alternate with the columns of Rh 6 rings linked by S atoms. S–S bridges also connect the ribbons and columns. As such, the kingstonite structure is essentially that of synthetic Rh 3 S 4 . Minor differences in the unit-cell parameters, atom coordinates and displacement parameters of kingstonite and synthetic Rh 3 S 4 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.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.