КАЛИЙПАРГАСИТ ИЗ ИЛЬМЕНОГОРСКОГО КОМПЛЕКСА (ЮЖНЫЙ УРАЛ)

Abstract

Potassicpargasite, ideally (K,Na)Ca2[(Mg,Fe2+)4(Al,Fe3+)]5(Si6A12)8O22(OH)2 is a potassic analogue of pargasite, from the amphibole group. This mineral was determined in garnet amphibolite of Ilmenogorsky complex (the South Urals). It occurs as black prismatic crystals, are large as 0.2—0.01 mm, associated with garnet, plagioclase, calcite. The mineral is brittle with an uneven conchoidal fracture, perfect {110} cleavage, and no parting observed. Its hardness is 403 N/mm2, Dcalc 3.26 g/sm3. Opticaly, potassicpargasite is biaxial negative, with  1.668,  1.673,  1.682, 2V ~ 100, Хл 40—42; absorption Z < Y < X, pleochroism Z olive green, Y pale olive green, X pale gray-green. The mineral is monoclinic, space group C2/m, with refined unit-cell parameters a = 9.893(1), b = 18.112(9). с = 5.291(2) Å;  105.09(3), V = 915.1 Å 3. The seven strong lines in the X-ray powder-diffraction pattern [d in Å (hdl)] are 8.44(100)(010), 3.28(40)(240), 3.13(90)(310), 2.71(40)(151), 2.35(30)(351), 2.16(25)032), 1.65(30)(461). Combined electron-microprobe, wet chemical, crystal structure. Mossbauer and combustion — IR analyses gave SiO2 37.19, ТiO2 1.57. Аl2Оз 17.90, FeO 18.15, MnO undetected, MgO 7.85. CaO 12.54, Na2O 0.87. K2O 2.06, total 98.13 (wt.%), corresponding to the formula (K0.40Na0.25)0.65Ca2.02(Mg1.76Fe2.28,Alo.78Ti0.18)5(Si5.60Al2.40)8О22(ОН)2 (average on 3) on the base of 13 cations. The mineral is named according rules of the current IMA nomenclature for amphiboles.