Calcium bentonite is a useful adsorbent of ions in solution. as well as fats and oils, being a main active ingredient of fuller's earth, probably one of the earliest industrial cleaning agents.
Also known as potash bentonite or K-bentonite, potassium bentonite is a potassium rich illitic clay formed from alteration of volcanic ash.
Sodium bentonite expands when wet, possibly absorbing several times its dry mass in water. Because of its excellent colloidal properties (see odom ref below) it is often used in drilling mud for oil and gas wells and for geotechnical and environmental investigations.