Acta Musei Moraviae

Andradite-meionite-pyroxene rock in amphibolite from the contact of corundum pegmatite at Pokojovice, Moldanubian Zone, Western Moravia

Andradite-meionite-clinopyroxene rock represents one of the host rocks of known corundum pegmatite at Pokojovice (near Třebíč, Western Moravia). It forms layers in the amphibolite body, which together with quartzites, ultrapotassic leucocratic gneisses, marbles and calc- silicate rocks occur in biotite paragneisses of Varied Unit (Moldanubian Zone). The main components of rocks are diopside/hedenbergite, andradite garnet (63–69 % Adr) with increased proportion of TiO₂ (0.071 to 0.079 apfu Ti) at a relatively low proportion of Mn (0.054 to 0.056 apfu). Besides feldspars (plagioclase An_<35 > Kfs) abundant skapolite (X_Mei ~ 72–73) with relatively high sulphate component (1.91 to 2.29 wt. % SO₃; 0.225–0.272 apfu S), potassian hastingsite and minor calcite are characteristic. Accessory minerals are titanite, chromiumbearing magnetite, chalcopyrite, zircon, apatite, and scheelite. The rock probably originated by regional metamorphism of chemically suitable protolith (basic tuffs and tuffites) at relatively oxidic conditions. Andradite-meionite-pyroxene rock occurs in lithologically specific sequences which can be characterized mainly by the presence of biotite-magnetite leucocratic gneisses and calcite-andradite microclinites including locally unusual andradite pegmatites.