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Compositional variations in smectites: Part I. Alteration of intermediate volcanic rocks. A case study from Milos island, Greece

Christidis Georgios, Dunham A. C.

Πλήρης Εγγραφή

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Περίληψη

The chemistry of smectites from some bentonite deposits derived from intermediate rocks has been examined by electron microprobe methods. A large variation in chemical composition within very short distances, principally controlled by a well-defined negative relationship between Si and A1, and between A1 vI and Fe 3§ and A1 vl and Mg has been observed. On the other hand, Mg does not vary systematically with either Si or Fe 3+. In several bentonites beidellite coexists with montmorillonite and there is a compositional transition between the two smectite minerals, implying the existence of a possible solid-solution series. This transition occurs only when Cheto-type montmorillonites are present, being absent for Wyoming-type montmorillonites. No compositional transition between Wyoming- and Cheto-type montmorillonite was observed. It is believed that the compositional variations reflect initial chemical gradients originated during the devitrification of the volcanic glass, due to the migration of chemical components.

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