Sodium montmorillonite, a mineral clay. A highly compressible colloidal clay which, when introduced into certain soils, reduces their permeability. 1. Introduced in pellet form and tamped into place to restrict water seepage. 2. Suspended in water to form a slurry, Bentonite Slurry, helps to prevent earth from falling into an augered hole or excavated trench. 3. Provides viscosity to suspend cuttings and helps seal walls of borings.