ФЕРРИВИНЧИТ NACAMG4FE3+ [SI8O22](OH,F)2 - НОВЫЙ МИНЕРАЛ ГРУППЫ АМФИБОЛОВ (ИЛЬМЕНОГОРСКИЙ ЩЕЛОЧНОЙ КОМПЛЕКС, ЮЖНЫЙ УРАЛ)

Abstract

Ferriwinchite, the new amphibole group mineral, was found occurring in veins cross-cutting pyroxene feni-tes of Ilmensky alkaline complex, in association with calcite, quartz and pyrite. It has thin needle-shaped habit, black color, greenish-gray streak. The Mohs' hardness 5.5, brittle, with clear {110} cleavage. Density (meas.) = = 3.14 g/cm3. Biaxial (-), np 1.670(2), nm 1.680(5), ng 1.685(6). Plane of optical axes ┴(010). Ng = b. Pleochro-ism in immersion specimen: с - deep blue, b - violet, ┴bc - light brownish-yellow; absorption: c = b>┴bc. Monoclinic, space group C2/m, a= 9.811(6), b= 18.014(6), c= 5.295(4)Å, β = 104.10(6)° Main bounds of X-ray powder pattern [d, Å(I, Ш)]: 8.42(100, 110), 4.507(5, 040), 4.203(4, 220), 3.391(10, 131), 3.268(13, 240), 3.116(60, 310), 2.957(7, 221), 2.800(10, 330), 2.711(20, 151), 2.167(7, 261), 2.024(5, 251), 1.656(7, 461). Chemical composition, by microprobe analysis (wt %): SiO2 54.90, T1O2 0.11, A12O3 1.12, FeO 15.91, MnO 0.76, MgO 14.17, CaO 5.10, Na2O 5.18, K2O 0.51; sum 97.76 %. Empirical formula, calculated for 13 cations: (Na0.21K0.09)0.30(Ca0.78Na1.22)2.00(Mg3.01Mn0.09Fe2+0.85Ti0.01Fe3+1.04)5.00 [(Si7.81Al0.19)8.00O22](OH,F)2. Ferri-winchite Na CaMg4Fe3+[Si8O22](OH,F)2 is the ferri-analog of winchite with 0.50 < Fc3+ < 1.50. Its type specimen is deposited in the Natural history museum of Ilmensky reservation, the Urals division of the Russian Academy of Sciences, Miass.