ШИРОЦУЛИТ ИЗ МАРГАНЦЕВЫХ МЕСТОРОЖДЕНИЙ ЮЖНОГО УРАЛА, ЕГО ХИМИЧЕСКИЙ СОСТАВ И ФОРМУЛЫ МАРГАНЦЕВЫХ СЛЮД

Abstract

The rare manganese mica - shirozulite, K[(Si3Al)Oio](OH)2, has been found, for the first time in Russia, within the low-metamorphosed rocks (T ~ 250 °C, P ~ 2.5 kbar) of three volcano-sedimentary manganese ore deposits: Bikkulovskoye, Kazgan-Tash and Kusimovskoye (the South Urals). Shirozulite occurs there as an accessory mineral (in contents lesser than 1 %) associating with rhodonite, johannsenitc, pumpellyite-Mn, epidotc, andradite, parscttensite, hematite, quartz and some other minerals. It forms fine-grained (up to 0.2 mm) lamellar individuals constantly in close intergrowths with parsettcnsitc - another manganese phyllosilicate. Together these minerals form radiaxial, sheaf-like entangled and parallel-fibrous aggregates, up to 2 mm in cross size. In samples the shirozulitc-parsettensite aggregates are brown, in thin section they have distinct pleochroism: Ng - dark-brown, Np - light-yellow; clear cleavage in one direction; direct extinction, п„~\.5%-1.60, "g-«/, ~ 0.030-0.035. Chemical composition of shirozulite was determined by microprobe analysis (wt%): SiO2 43.54, A12O3 4.43, FeO10' 1.70, MnO'01 33.94, MgO 1.61, CaO 0.41, Na2O 0.57, K2O 8.25, total 94.46. The crystal chemical formula of shirozulit is (K^^Nao.osCao.o^i.ootMnzjeMgo^oFeo.nAlo.oib^KSij.jgAliwzkooOio] (OH)2oo. Comparison of data on chemical composition of manganese micas from Japan and the South Urals shows that their ideal formulas may be represented in two ways: 1) К.Мп3[(51зА1)Ою](ОН)2 (Ishida e. a., 2004), and 2) KMn2.5[Si4O10](OH)2 (authors' data).