Mehrabad bentonite deposit appears to be derived from the volcano- sedimentary materials of Oligo-Miocene age by transformation in a lagoon environment. Based on analysis, bentonite samples contain minerals such as montmorillonite, albite, clinoptilolite, quartz, cristobalite, calcite, gypsum, halite, muscovite and nantronite. Conversion of shard glasses to bentonite and zeolite has occurred under diagenetic conditions with acidic to intermediate composition. The bentonite deposit is halmyrolytic clays in type. According to geochemical studies, bentonite’s magmatic series is subalkaline (calc- alkaline) and their tectonic setting is volcanic arc and syn- collision.