The relation between composition and swelling in clays

The phenomenon of swelling is associated with the hydration of clays; however, all clays do not swell when hydrated. those of the kaolin group, for example, exhibit little or no swelling on hydration. Sodiwm montmoillonite, on the other hand, characteristically swells in water to many times its dry volume. Calcium and magnesium montmorillonite and the hydrous micas, or so called illites, fall between these two extremes in swelling properties, but are, in general, much closer to kaolinite than to sodium montmorillonite in their increase in volume on hydration. These differences in the swelling characteristics of different clays may be related to their chemical composition, to the kind and degree of isomorphous replacements in their structure, and to the amount and nature of their associated exchangeable cations.