Bentonite is a term that is usually restricted to aggregates of clay
formed in situ alteration of volcanic ash.
The clay type that results is Smectite. The composition of the Smectite
varies greatly among bentonites.

Diatomaceous earth is the result of accumulations of siliceous sediment,
made up more or less entirely  of the skeletal remains of microscopic
plants called Diatoms. It is exceedingly fine grained, incoherent and
highly absorbent.

Peter