Abstract

Correianevesite, ideally Fe2+Mn22+(PO4)2·3H2O, is a new reddingite-group mineral approved by the CNMNC (IMA 2013-007). It occurs in a phosphate-rich granite pegmatite that outcrops near the Cigana mine, Conselheiro Pena, Rio Doce valley, Minas Gerais, Brazil. Associated minerals are: triphylite, lithiophilite, frondelite, rockbridgeite, eosphorite, vivianite, fairfieldite, leucophosphite, cyrilovite, phosphosiderite, etc. Correianevesite occurs as grayish-brown to reddish-brown transparent bipyramidal crystals up to 4 mm in size. The streak is white, and the luster is vitreous. Mohs hardness is 3½. Cleavage is poor on (010). Fracture is laminated, uneven across cleavage. The measured density is 3.25(2) g/cm3; the calculated density is 3.275 g/cm3. The mineral is biaxial (+), α = 1.661(5), β = 1.673(5), γ = 1.703(5), 2Vmeas = 70(10)°, 2Vcalc = 65.6°. The IR spectrum confirms the presence of H2O. The Mössbauer spectrum shows the presence of two sites for Fe2+ and one site for Fe3+ occupied in the ratio Fe12+:Fe22+:Fe3+ = 39:55:6. The chemical composition is as follows (electron microprobe, H2O determined by gas chromatography of ignition products, Fe apportioned between FeO and Fe2O3 based on Mössbauer data, wt%): MnO 29.21, FeO 21.74, Fe2O3 1.54, P2O5 34.59, H2O 12.6, total 99.68. The empirical formula, based on 11 O apfu, is H5.78Mn1.70Fe2+1.25Fe3+0.08P2.015O11. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 5.08 (43) (020), 4.314 (28) (002, 210), 3.220 (100) (221, 202), 3.125 (25) (122), 2.756 (35) (103, 230), 2.686 (25) (222, 113), 2.436 (22) (123), and 2.233 (23) (411, 331). The crystal structure is solved (R1 = 0.0176). Correianevesite is orthorhombic, space group Pbna, a = 9.4887(2), b = 10.1149(2), c = 8.7062(2) Å, V = 835.60(3) Å3, Z = 4. The refined crystal-chemical formula is: (Fe2+0.72Mn2+0.20Fe3+0.08)(Mn1.48Fe2+0.52)(PO4)2 (H2O,OH)3.

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