Clay soil is common in many parts of the world; different types of clay contain different minerals and so have different characteristics. All consist of very small particles and are generally smooth-textured when dry but very sticky when wet.

Cracked pattern on extremely dry soil
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Some clay soils crack when they dry.

Kaolinite

Kaolinite clay soil is white and appears powdery. It occurs as the result of the weathering of feldspars, silicate minerals found in igneous rocks. Named for the Kaolin area of China, where this type of clay is found, it is used for making ceramics and forms the basis for the type of dishes known as porcelain, also known as china. It was also the main ingredient used to create the original version of Kaopectate.

Vermiculite

Vermiculite clay soil is able to absorb water, which means to attract it to the outer part of individual particles, but it is not able to do so time after time. Gardeners may be familiar with vermiculite because it is sold as a soil enhancement to aid in moisture retention for potted plants. It also is used as a cushion in shipping packages.

Smectite

Smectite clay soil is sometimes referred to as "swelling clay." It is also known as bentonite, and deposits of this type of clay are found in Wyoming and Minnesota, as well as other places. When wet, Wyoming smectite, a form of sodium smectite, can increase its original volume by up to 18 times. Pioneers used it to seal their cabin roofs and to quiet squeaky wagon wheels. Today it is used to line ponds and as an ingredient in cat litter and pelleted feed.

Calcium Smectite

Calcium smectite clay does not swell as much as sodium smectite clay, the other common form of smectite. That is because calcium smectite adsorbs much less water. It is suitable for use as drilling mud because it has the ability to hold large particles in suspension during the drilling process. A lot of the U.S. calcium smectite is mined in Georgia.

Attapulgite

Attapulgite clay soil, also called palygorskit, is used in some drilling operations because it is able to hold together even when used in saltwater during offshore drilling projects. Smectite disintegrates under those conditions. Attapulgite replaced kaolinite in Kaopectate until it was taken off the market in 2003. It is commonly found in arid locations where the soil contains plenty of magnesium.

Chlorite

Chlorite clay soil is commonly found in the Midwestern areas of the United States, often with another clay soil known as illite. Chlorite clay is created by the weathering process of mafic silicates – which are somewhat high in the heavy elements – and sometimes is found in chlorite schist and other metamorphic rocks. It is stable in dry, temperate or cool climates.