Bentonite Bentonite is an extremely fine clay formed by the disintegration of volcanic ashes, used mainly to increase the plasticity of ceramic clay. It was named by Wilbur Knight in 1898 after the Cretaceous Benton Shale near Rock River in Wyoming, USA. The type of clay is an absorbent aluminium phyllosilicate clay and consists mostly of montmorillonite. Many sculptors have modelled particularly figurative work using the clay. Bentonite is used and abused in many other contexts than art.TO name but a few examples it is used in cosmetic face masks, as a corrosive in soaps.In addition, it is claimed by some to have healing powers or dermatological health benefits.