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Burangaite and brazilianite association from Divino das Laranjeiras, Minas Gerais, Brazil

Grains of closely associated burangaite and brazilianite were found in the granite pegmatite situated in the Córrego Pomarolli Area, Divino das Laranjeiras, Minas Gerais, Brazil. This finding of burangaite and brazilianite is interesting for two reasons. First, both phosphate minerals do not occur frequently. Moreover, the association of these minerals has not been described yet. The grains of intimately associated minerals are bluish colored with a vitreous luster and it is difficult to distinguish the two mineral phases macroscopically. However, the X-ray diffraction pattern shows clearly the presence of both burangaite and brazilianite. Both minerals are monoclinic, although not of the same crystal structure. The calculated unit cell parameters for brazilianite (P21/n) are a=11.136(5)&Aring ; , b=10.025(5)&Aring ; , c=7.034(4)&Aring ; , ß=97.39(6)°, V=778.7(6)&Aring ; ; 3 and for burangaite (C2/c) a=25.056(5)&Aring ; , b=5.035(1)&Aring ; , c=13.422(3)&Aring ; , ß=110.90(1)°, V=1581.8(4)&Aring ; 3. The chemical analysis performed by EMPA yielded the following composition: Al2O3 45.81, FeO 0.14, CaO 0.15, MgO 0.09, MnO 0.02, Na2O 3.37, K2O 0.02 and P2O5 41.67% for brazilianite, and Al2O3 39.82, FeO 2.20, CaO 0.05, MgO 4.68, MnO 0.06, Na2O 1.28, P2O5 42.70 and F 0.03 % for burangaite. SEM images were produced in order to distinguish the minerals more thoroughly and recognize their morphology. Burangaite occurs in a form of long prismatic crystals, with parallel growth in packages of different orientation. Brazilianite shows its frequent habit with a narrow prism zone as described by Pough and Henderson (1945). Brazilianite was found to precipitate from low temperature hydrothermal solutions percolating through the granitic pegmatite and dissolving other phosphate minerals such as triphylite (Frondel et al., 1948). The original burangaite found in the Buranga pegmatite in Rwanda replaces scorzalite (Knorring et al., 1977). Here, the grains containing both burangaite and brazilianite show no indication that one mineral replaces another and they seem to have grown simultaneously.

burangaite; brazilianite; Divino das Laranjeiras; Brazil

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