OCORRÊNCIA, CONTEXTO MINERALÓGICO E QUÍMICA MINERAL DA BRAZILIANITA E SEUS DEPÓSITOS EM MINAS GERAIS.

OCORRÊNCIA, CONTEXTO MINERALÓGICO E QUÍMICA MINERAL DA BRAZILIANITA E SEUS DEPÓSITOS EM MINAS GERAIS.
Brazilianite is a relatively rare gem phosphate mineral, yellow to greenish yellow, that was described in 1945 from samples of the Córrego Frio pegmatite (Divino das Laranjeiras county, Minas Gerais state), where several similar deposits were subsequently reported. Also in this State, another mineralized pegmatite occurs (Itinga county). Such pegmatites, studied in the present paper, were originated from some granitogenesis related to the Araçuaí Orogen, generally constituting small tabular bodies, with low differentiation degree. Chemical analysis by electronic microprobe in the mineral showed very homogeneous values for the different studied pegmatites, similar to the original description. Analyses on associated feldspars showed that the host pegmatites are B, Cs, Rb and Zr-poor, however, F-rich. One of them, Telírio Pegmatite, presents an anomaly in Li compared to the others. EPR and optical absorption studies indicated that the yellow component of the color is due to an absorption band in the near UV and its intensity is directly correlated with a localized O^1- hole center. Different types of electron centers are responsible for the broad thermal annealing range of the mineral color; the greenish component is caused by a very broad absorption band in the red spectral range. In the studied deposits, brazilianite seems to be a secondary product of montebrasite alteration in a hydrothermal early stage (350-250ºC).