from the AGI Dictionary of Geological Terms, with comments; Bentonite ... It is composed essentially of montmorillonite and related minerals of the smectite group. The properties of bentonite depend largely on its ion-exchange characteristics. ...
The mineral montmorillonite and minerals of the smectite group are usually highly expansive & can take on large amounts of water. Unfortunately, the term bentonite is commonly applied to any light-colored medium to high plastic clay. X-ray defraction or other elaborate testing is required for positive identification. The montmorillonite and smectite minerals, from a foundation engineering viewpoint, have a 'damned nasty' attitude. Kaolinite ... Kaolinite is a high-alumina clay mineral that does not appreciably expand under varying water content and does not exchange iron or magnesium. ...
Kaolinite is a large group of minerals, very useful for higher quality clay products. Include the refractory clays, used for fine china and quality pottery.
From an engineering point of view. Bentonite swells a super lot when wetted and shrinks a super lot when dried. Kaolinite has low to moderate swelling/shrinkage potential.
