David H. Shaw, in Pharmacology and Therapeutics for Dentistry (Seventh Edition), 2017. Kaolin. Kaolin is a hydrated aluminum silicate with a crystalline structure that allows for a large surface area that adsorbs many times its weight in water. Its use in the treatment of diarrhea is based on its purported ability to absorb fluid, bacteria, toxins, and various noxious materials in the ...