Buergerite in pegmatites from the Plana Cretaceous pluton, Western Bulgaria (original) (raw)

Buergerite, a rare tourmaline, first described from Mexquitic, San Louis Potosi, Mexico, was found in thin (3-10 cm) aplite-pegmatite veins, cutting quartz-monzodiorites of the Plana polyphase pluton. It forms dark-brown, almost black grains, tiny prismatic crystals (2-3 mm) and aggregates, in association with quartz, pale-pink K-feldspar, oligoclase, albite, biotite, magnetite, hematite, ilmenite, garnet, beryl, cyrtolite, allanite, titanite, epidote, adularia, muscovite and stilbite. Buergerite is a relatively late mineral, crystallized after feldspars, magnetite, biotite and garnet, and before the hydrothermal quartz, adularia, muscovite and stilbite. EPMA analyses of a zonal buergerite grain (core-rim) and of a single prismatic crystal gave (wt. %): SiO 2 33.10-32.98; 34.16, TiO 2 1.39-1.09; 1.19, Al 2 O 3 24.49-25.15; 26.90, Cr 2 O 3 0.00-0.11; 0.00, V 2 O 3 0.00-0.15; 0.15, Fe 2 O 3 (total) 23.39-22.48; 20.57, MnO 1.23-1.10; 1.19, MgO 0.64-1.07; 1.07, CaO 0.38-0.39; 0.34, Na 2...