The diverse kinds of bentonite are each named after the corresponding to the dominant element, such as potassium, sodium, calcium, and aluminum. Authorities discuss several kinds of nomenclatorial obstacles with the combination of bentonite clays. Nevertheless, the verb bentonite, as well as a similar clay called tonstein, has been utilized to characterize clay beds of undetermined source. For technical purposes, two main types of bentonite exist i.e. sodium and calcium bentonite. In stratigraphy and tephrochronology, simply devitrified ash-fall beds are usually assigned to as K-bentonites when the principal clay kind is illite. In addition to montmorillonite and illite, another natural clay variety that is seldom aggressive is kaolinite. Kaolinite-dominated clays are usually pointed to as tonsteins and are typically compared with coal.
