The four major classifications of clay are illite, cholrite, kaolinite and montmorillonite-smectite, but sub-types of clay exist in each group. Sub-types are a combination of these main groups and sometimes include other minerals. Clay is soil with fine grains composed of metal, silicate and organic particles, combined with water.
Clay has been used throughout history and serves a variety of purposes. Clay is commonly used by potters for making urns, dishware and decorative items. In its normal state, clay has a plasticity that is enhanced with water. Dry clay takes on a firm texture. When it is heated, such as in a kiln, its properties change, and it forms a ceramic material.