Bentonites (Smectites) are the favored health clays

Smectites (Bentonites) comprise 99% of all clays used for health purposes today. It is the favored clay for health and dietary use as well as for many industrial applications. This is because Smectites are more complicated clays having a higher Cation Exchange Capacity (CEC), a larger surface area and are considered expanding clays.

(from Perry A~ Arledge's Living Clay, Nature's Own Miracle Cure)