The formation of clays is an important part of the soil forming processes. Expandable clays Illite Kaolinite forms when the climate is warm to tropical and when there is sufficient time for the reactions to go to completion. All of the major cations except Al and Si must be leached from the parent material to form kaolinite. If the area is geologically stable the probability that there is sufficient time is increased. Kaolinite is an excellent starting material for making ceramics and is also used in making Kaopectate.
Expandable clays can form from a variety of different parent materials including volcanic glass.
They pose a real challenge to engineers and home owners. Illite often forms by the alteration of feldspars in temperate climates when there is not sufficient time to completely remove the potassium. It should be noted that clay minerals are not necessarily clay sized. However, it is true that clay minerals usually are in the fine silt to clay sized range. Soils Loose rock material at the surface of the Earth is referred to as regolith .