Bentonite is a natural clay of the smectite family. The montmorillonite platelet structure within bentonite makes it a versatile mineral, no two natural forms are the same and the chemistry is complex. Bentonite sometimes acts more like a chemical than a mineral. Bentonite has some interesting properties. The individual platelets of bentonite can be thought of as a "club sandwich". The platelet consisting of a tetrahedral Silicon Oxide layer with some Silicon replaced with trivalent cations, sandwiched between two octahedral Aluminium Oxide layer with some Aluminium replaced with divalent cations. The edge of each platelet has a hydroxide group which allows it to form thixotropic gels in water.
Charge imbalances are generated on the surface due to the metal replacements in the structure which are countered by the cations bound to the surface. The individual platelets are surrounded by lattice moisture and stack together to form agglomerates. As a result, the overall properties of a bentonite are determined by the platelet size, number & size of charges.