What is this SMECTITE you speak of?

Bentonites belong to the Smectite Family of clays. Smectites are characterized by their expandable properties and a Cation Exchange Capacity of 80-100 meq 100 g^-1 , meaning they absorb and adsorb. They also have the largest specific surface area of 700-800 m²/g. 

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