An experimental alteration of montmorillonite to a di plus trioctahedral smectite assemblage at 100 and 200 degrees C

Hydrothermal experiments were performed at 100 and 200 degreesC and at diff erent clay:water ratios in order to investigate the transformation of smect itic layers during the alteration of a montmorillonitic starting material. This study focused on three phenomena: (1) the amount and localization of c harge within the layer of the newly-formed dioctahedral smectite; (2) the s tacking of low- and high-charge layers in the dioctahedral smectitic materi al; and (3) the neoformation of trioctahedral smectites. In all of the runs, the formation of beidellite from montmorillonite induce d morphological changes in clay particles which suggests a reaction proceed ing by a dissolution-crystallization mechanism. Illite layers were detected in K-saturated montmorillonite runs after the transformation of similar to 50% of the starting montmorillonite into beidellite (i.e. after 5 months o f reaction with distilled water at 200 degreesC). These illite layers were interstratified with both high-charge and low-charge dioctahedral smectites in a hypothetical three-component mixed-layer mineral.