Occurrence of a new brazilian bentonite in the weathered basalts of the Mosquito formation, Parna?ba basin, southern Maranh?o, Brazil.

No munic?pio de Formosa da Serra Negra, sul do Maranh?o, ?s margens da rodovia MA006, encontram-se afloramentos de basaltos intemperizados da Forma??o Mosquito, apresentando textura bastante argilosa e potencial de ser um material benton?tico. Neste trabalho, esse material que vem sendo considerado uma nova ocorr?ncia de bentonita no Brasil e, batizado de Formosa, foi caracterizado por difra??o de raios X, fluoresc?ncia de raios X, microscopia eletr?nica de varredura, espectroscopia M?ssbauer e capacidade de troca cati?nica, em amostra total e ap?s separa??o granulom?trica, e ainda, comparada com duas das principais bentonitas brasileiras, Chocolate e Bofe. Apesar das varia??es qu?micas e mineral?gicas encontradas, muito comuns nesse tipo de argila, as semelhan?as observadas convencem o promissor uso da argila Formosa como bentonita, uma vez que o ponto principal da caracteriza??o est? na presen?a dominante de montmorillonita e baixa concentra??o de outras fases minerais, mostrando que esse material apresenta mineralogia importante do ponto de vista tecnol?gico.Extensive weathered basalt outcrops can be found in the vicinities of the Formosa da Serra Negra town, southern of Maranh?o state, northern Brazil. They exhibit typical clay texture and an enormous potential to be used and explored as bentonite. This work deals with the chemical and mineralogical characterization of this material that has been named as Formosa Bentonite. The main following methods and analytical techniques were used: XRD, XRF, SEM, M?ssbauer spectroscopy and CEC in total sample and after grain size separation. Two samples from the main Brazilian ?Para?ba bentonites? (Chocolate and Bofe types) were used for comparison purposes. The results show that the Formosa bentonite exhibit some chemical and mineralogical differences in comparison with the two reference samples, although the main and most important feature is the presence of montmorillonite as the major mineral phase