Bentonite is an absorbent aluminium phyllosilicate,
essentially impure clay consisting mostly of montmorillonite. There
are different types of bentonite, each named after the respective
dominant element, such as potassium (K), sodium (Na), calcium (Ca),
and aluminium (Al). Experts debate a number of nomenclatorial
problems with the classification of bentonite clays. Bentonite
usually forms from weathering of volcanic ash, most often in the
presence of water. However, the term bentonite, as well as a
similar clay called tonstein, has been used for clay beds of
uncertain origin. For industrial purposes,
