Bentonite is an absorbent aluminum polysilicate, a generally impure clay consisting mostly of smectite minerals such as montmorillonite with traces of other metals, (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2·(H2O)n. There are two types of bentonites. There is a non-swelling bentonite or calcium bentonite and a swelling bentonite which is also called sodium bentonite. Bentonite forms from the weathering of volcanic ash, mostly in the presence of water. As a mineral, it was first found around 1890 in deposits in the western part of the United States, in Montana, Wyoming and elsewhere. However, the actual name is derived from where it was originally found in Montmorillon in Southern France. The main characteristic of this mineral is its layering properties and its ability to absorb water in the presence of ions in these layers. Under the right conditions, certain grades of this mineral have the ability to swell.
The non-swelling calcium bentonite is sold within the alternative health market for its purported cleansing properties, yet no scientific studies exist to support these claims.