Clay is a complex material. Even the meaning of the word is confusing. It can be used to describe a rock or a small lump of rock saturated with water. On clay particles are less than 100m across.
Clay is made from aluminum silicate combined with water. Clay materials are plastic when wet, and stick together when dry. Most clays are the result of weathering. Clay is the most important earth material for people. It is used in a wide variety of industries. It provides the soil for plant growth.
One theory says that clay might have been important in the . See the website by Cairns-Smith for example.
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