Fe3+-rich montmorillonite-beidellite series in Ayvacik bentonite deposit, Biga Peninsula, northwest Turkey

The Ayvaclk bentonites, products of Miocene calc-alkaline volcanic rocks, a re composed of smectite of the montmorillonite-beidellite series. Fault-rel ated hydrothermal solutions have altered andesitic rocks to dioctahedral sm ectites. Differences in the micro-morphology of the two end-members are dis tinguished by scanning electron microscopy (SEM) studies. The beidellite pa rticles are of delicate ribbons and rosette habits, whereas montmorillonite particles are very thin, curled sheets and flakes. Clay size (<2 mu m) fra ctions contain (in wt. %) 54.90-56.80 SiO2, 19.65-28.54 Al2O3, 0.45-6.28 Fe 2O3, 0.10-1.72 CaO, 0.80-4.15 MEG, 0.55-1.88 K2O, and 0.08-1.15 Na2O, which confirm that the beidellites are Fe-rich (5.06-6.28 wt. %), except for one sample (0.45 wt. % Fe2O3). The Greene-Kelly test (Li-saturation and heatin g) gave very good results for the measurement of the d(001) of the two end- members. Nickel, Ti, and Cr enrichment in smectite is related to the chemic al composition of hydrothermal solutions that passed through the ophiolite complex.