Calcium bentonite by SEM. Bentonite is an absorbent aluminium phyllosilicate generally impure clay consisting mostly of montmorillonite. Two types exist: swelling sodium bentonite and non-swelling calcium bentonite. It forms from the weathering of volcanic ash, most often in the presence of water. In health applications, the microscopic structure of calcium bentonite (Pascalite) is believed to draw impurities from the digestive system, which are then excreted along with the bentonite. On the alternative health market, bentonite is part of a detox diet. In the drilling and geotechnical engineering industry, bentonite is used for its unique rheological properties. Relatively small quantities of bentonite suspended in water form a viscous, shear thinning material. Most often, bentonite suspensions are also thixotropic, although rare cases of rheopectic behavior have also been reported. Bentonite has other uses in many industries. Enhanced SEM. Image width: 800 micrometers. Magnification: 125x if the image is printed 10 cm wide.