Bentonite clay also known as montmorillonite clay are of two types: sodium bentonite and calcium bentonite. Basically the determination of sodium or calcium bentonite is done by whether the dominant element is sodium or calcium.
Sodium bentonite has a higher pH level. This provides it with natural swelling abilities and makes it a natural 'hole plug'. While calcium bentonite has a lower pH and do not swell. The former has more industrial uses and the later is used mostly on body for healing purposes, both internally and externally. Both the bentonite clays contain various minerals and metals.