Alteration of biotite by suspended montmorillonite

Summary Alteration of biotite flakes which were placed in suspensions of Na⁺ — and Mg⁺⁺-montmorillonite for different contact periods at two different temperatures, were followed using X-ray and petrographic microscope.The biotite seemed to alter to a mineral of the vermiculite type. Na⁺-montmorillonite changed the biotite more than Mg⁺⁺-montmorillonite at 21°C. At 50°C, however, no changes of the biotite flakes could be observed using Na⁺-montmorillonite in contrast to the case when Mg⁺⁺-montmorillonite was used. A good correlation between X-ray measurements and optical observations was found.With 3 figures and 3 tables