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Mineralogical ClassificationIMA 2009-056 = ferhodsite

2nd May 2018 17:14 UTCMarco E. Ciriotti Manager

Reference:

▪ Begizov, V.D. & Zavjalov, E.N. (2016): Ferhodsite (Fe,Rh,Ir,Ni,Cu,Co,Pt)9–xS8 — new mineral from Nizhny Tagil ultramafic complex. Novye Dannye o Mineralakh (New Data on Minerals), 51, 8–11 (in Russian with English abstract).

Abstract:

The new mineral ferhodsite (IMA 2009-056), ideally (Fe,Rh,Ni,Ir,Cu,Co,Pt)9–xS8 (abstract) or (Fe,Rh,Ir,Ni,Cu,Co,Pt)9–xS8 (title and text) was discovered in mineral separates from dunite of the Solov’yova Gora (central part of the Nizhniy Tagil ultramafic massif), Urals, Russia, and in a heavy mineral concentrate from the Konder placer deposit, Ayano-Mayaskiy region, Khabarovskiy kray, Russia.

The mineral is usually observed as isometric or platy, triangular, and corroded grains located along periphery of isoferroplatinum grains. Commonly, the new mineral is mantled and corroded by chengdeite and a solid solution that is intermediate in composition between isoferroplatinum and tetraferroplatinum. Other minerals observed in intergrowths with ferhodsite are cooperite, cuproiridsite, bowieite, and kashinite (laurite and erlichmanite are also mentioned, but only in the English version of the abstract). Opal commonly penetrates along well-developed {111} cleavage fractures in ferhodsite grains varying in size from a few to 100 μm with a mean of 30–40 μm (text); size of grains 10–50 μm and size of aggregates 40–70 or 100 μm (abstract). Ferhodsite has a black streak, metallic luster, in reflected light opaque, and light brownish-gray (English abstract) but also “grayish-creamy with a brownish tint” in Russian text. The micro-indentation hardness VHN20 = 516(15) kg/mm2. The density was not measured; Dcalc = 7.186 g/cm3 (without specifying a composition). Under reflected light the mineral appears brownish gray with very weak bireflectance and weak to moderate anisotropism (gray colors with a cream tint). Internal reflections and pleochroism were not observed. The reflectance values with a 20 nm interval vary from 36.8% (700 nm) to 37.5% (400 nm) for ferhodsite and from 32.8% (700 nm) to 33.8% (400 nm) for the Ir-rich variety described as “Ir ferhodsite.” The values for the COM wavelengths [Rmax/Rmin (nm)] are: 35.6/33.0 (470), 36.0/33.8 (546), 36.2/34.0 (589), 37.1/34.8 (650) for ferhodsite, and 30.0/27.0 (470), 31.3/27.5 (546), 31.3/28.3 (589), 32.0/29.3 (650) for “Ir ferhodsite.” The empirical formulas based on 17 apfu are given in the paper separately for each of 19 analyses. The Fe content varies from 2.82 to 3.99 apfu; Rh 0.18–2.68, Ir 0–2.12, Ni 0.50–1.96, Cu 0–1.64, and S 7.98–8.05 apfu. The powder X‑ray diffraction data of ferhodsite are generally similar to those of pentlandite, however differs by an observed displacement or presence in ferhodsite of some lines and by several doublets. The selected lines of the ferhodsite X‑ray powder diffraction pattern [d Å (I%; hkl)] are (lines absent or significantly differ in position or/and intensity compare to pentlandite are in bold): 5.72 50; 111), 3.01 (70; 311), 2.97 (20; 113), 2.81 (30; 302), 2.74 (203; <10), 2.60 (213; <10), 2.50 (20; 400), 2.23(100; 402), 2.21 (30; 204), 1.933 (60, 105), 1.772 (40; 440), 1.367 (30; 614), 1.167 (40; 803). The data was refined in a tetragonal unit-cell with а = 10.009(5) and с = 9.840(8) Å, V = 985.78 Å3, Z = 4, space group P42/n (or, possibly, P4/nmm). The mineral is named after its two main elements but the I-rich compositions are referred to as “Ir ferhodsite.” The type specimen is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia.

10th Aug 2018 12:20 UTCRonnie Van Dommelen 🌟 Manager

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