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Manganilvaite, CaFe2+Fe3+(Mn,Fe2+)(Si2O7)O(OH), a new mineral of the ilvaite group from Pb-Zn skarn deposits in the Rhodope Mountains, Bulgaria

Bonev, I. K.
Vassileva, R. D.
Zotov, N.
Published in Canadian Mineralogist. 2005, vol. 43, no. 3, p. 1027-1042
Abstract Manganilvaite, CaFe2+Fe3+(Mn,Fe2+)(Si2O7)O(OH), is a new mineral species, the Mn end-member of the ilvaite group of minerals. It was found in the Pb–Zn–(Mn) skarn deposits of the central Rhodope Mountains, Bulgaria, and especially in the Ossikovo and Mogilata deposits (Madan ore district) and the Govedarnika deposit (Laki district). In the marble-hosted distal skarn-type orebodies, it is closely associated with Mn-rich clinopyroxene (hedenbergite–johannsenite) ± rhodonite, and with the products of their retrograde alteration (manganoan amphiboles and chlorites, bustamite, manganoan carbonates, quartz). The mineral is black, with a vitreous luster, brittle, with a distinct cleavage. It has Mohs hardness of 5½–6 and a micro-indentation hardness (VHN100) of 868 kg/mm2. The measured density Dx is 3.92 g/cm3. In reflected light, it is opaque with moderate pleochroism, from bluish gray to grayish brown, strongly anisotropic in grayish blue to pale reddish brown colors and with red internal reflections. It is homogeneous in BSE images and in thin sections under the IR microscope, where it is transparent. The reflectance is low, in the range 8.3–5.7% for Rmin (// c) and 10.0–9.3% for Rmax (// a). In some cases, well-shaped dipyramidal crystals occur, with a prismatic habit along c and forms r{011}, m{110}, s{210} and o{111}. The average results of 62 and 17 electron-microprobe analyses of manganilvaite from Ossikovo and Govedarnika, respectively, are (in wt.%): MgO 0.48, 0.45; Al2O3 0.20, 0.34; SiO2 29.65, 29.48; CaO 12.62, 13.06; TiO2 0.02, 0.04; MnO 11.99, 13.54; FeO 40.93, 39.31, (H2O 2.21), total 98.10, 98.43. The MnO content varies in the ranges 9.02–14.96 and 12.57–14.86%, respectively, the amount of Mn attaining 0.85 apfu. The mineral is of ilvaite-type structure, monoclinic, P21/a, with cell-edge parameters a 13.0250(7), b 8.8514(5), c 5.8486(3) Å, β90.167(1)°, V 674.28 Å3, Z = 4, as determined by composite X-ray and neutron powder-diffraction studies (see the companion paper). Manganese occupies the M2 octahedral position together with some Fe2+. Ilvaite and manganilvaite form a continuous solid-solution series, and gradations between them can be observed even in a single crystal. The strongest eight lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 2.875(85)(130), 2.848(90)(401), 2.718(100)(112), 2.687(70)(230), 2.442(33)(231), 2.180(48)(140,402), 2.111(47)(322,412), and 1.475(48)(060,252). As a product of retrograde alteration of the early-skarn pyroxenes, manganilvaite indicates evolution of the hydrothermal process from reduction to more oxidized and hydrated environment. The mineral name recalls its composition and relation to ilvaite.
Keywords ManganilvaiteNew mineral speciesIlvaite–manganilvaite solid-solution seriesElectron-microprobe dataRefl ectanceX-ray dataOssikovo mineGovedarnika mineCentral Rhodope MountainsBulgaria
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Research group Mineral Resources and Geofluids
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BONEV, I. K. et al. Manganilvaite, CaFe2+Fe3+(Mn,Fe2+)(Si2O7)O(OH), a new mineral of the ilvaite group from Pb-Zn skarn deposits in the Rhodope Mountains, Bulgaria. In: Canadian Mineralogist, 2005, vol. 43, n° 3, p. 1027-1042.

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Deposited on : 2013-05-15

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