Mavlyanovite, Mn₅Si₃: a new mineral species from a lamproite diatreme, Chatkal Ridge, Uzbekistan

Author： Yusupov R. G. Stanley C. J. Welch M. D. Spratt J. Cressey G. Rumsey M. S. Seltmann R. Igamberdiev E.

ISSN： 0026-461X

Source： Mineralogical Magazine, Vol.73, Iss.1, 2009-02, pp. : 43-50

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Abstract

Mavlyanovite, ideally Mn₅Si₃, is a new mineral from a lamproite diatreme close to the upper reaches of the Koshmansay river, Chatkal ridge, Uzbekistan. It occurs together with unnamed manganese siliciphosphide and manganese silicicarbide minerals in round to ovoid segregations, up to 10 cm in diameter, in volcanic glass. Segregations of hexagonal prismatic mavlyanovite up to 1–2 mm occur in interstices in the matrix and tiny inclusions (1–2 μm) of alabandite and khamrabaevite occur within mavlyanovite. It is opaque with a metallic lustre, has a dark-grey streak, is brittle with a conchoidal fracture and a near-perfect basal cleavage. VHN₁₀₀ is 1029–1098 kg/mm² (Mohs hardness ∼7). In plane-polarized reflected light, mavlyanovite is a pale-brownish-grey against the accompanying unnamed manganese silicicarbide (white). Reflectance values and colour data are tabulated. Average results of 19 electron microprobe analyses give Mn 70.84, Fe 6.12, Si 22.57, Ti 0.15, P 0.18, total 99.86 wt.% leading to an empirical formula of (Mn_4.66Fe_0.40)_5.06(Si_2.91Ti_0.01P_0.02)_2.94 based on 8 a.p.f.u. The calculated density is 6.06 g/cm³, (on the basis of the empirical formula and unit-cell parameters from the structure determination). Mavlyanovite is hexagonal (P6₃/mcm) with a 6.8971(7), c 4.8075(4) Å, V 198.05(3) Å³ and Z = 2. The structure has been determined and refined to R₁ = 0.017, wR₂ = 0.044, GoF = 1.16. Mavlyanovite is the naturally-occurring analogue of synthetic Mn₅Si₃ which is the parent aristotype structure of the Nowotny intermetallic phases studied extensively by the material-science community. It is also the Mn-dominant analogue of xifengite Fe₅Si₃. The mineral name honours Academician Gani Arifkhanovich Mavlyanov (1910–1988), for his contributions to the understanding of the geology of Uzbekistan.