 Clays typically are phyllosilicate minerals with a sheet-like structure. The very small clay particles interact with each other physically and chemically. Even a small proportion of clay affects the physical properties of the soil much more than might be expected. Clays such as kaolinite do not expand or contract when wetted or dried, and are useful for brick-making. Others, such as smectites, expand or contract considerably when wet or dry, and are not suitable for building.
