Bentonites are classified according to several types (e.g. calcium, sodium, potassium) but in the ceramic industry sodium Bentonite is the material of commerce (this is the same material used by the drilling industry). Sodium bentonites have incredibly small particle sizes (and thus surface areas). Combine this with the active particle surface chemistry (which makes them hold onto water) and it the most plastic and impermeable common clay material used in ceramics. Its contribution to working properties in glazes and clay bodies is balanced by the undesirable properties that are also imparted.
There is wide variation in the chemistry of bentonites, it is impossible to specify an average (Bentonite is not employed in ceramics for its chemistry). Any generic chemical analysis is thus only an attempt to represent the amount you might find in a common variety. Because of the high iron content, Bentonite is considered a dirty material and thus the tug-of-war between the valuable working properties it imparts and the need for whiteness or pure color that it impedes.

1. Microngel 90C

Premium Bentonite Powder – Greater plasticity with firing L value 90*

2. Microngel 90CR

Premium Bentonite Powder – Greater plasticity for ceramic glazes