The bentonites of Aftar region, with average of 15 meters thickness and about 10 km long, are volcanoclastic sequence of Semnan Formation that formed in a shallow sea water environment. Based on the field, XRD data, microscopic and scanning electron microscopic (SEM) studies, as well as chemistry, the bentonite beds contain zeolites (clinoptilolite and mordenite), gypsum, calcite, celestine, op...