There are three main groups of clays: Kaolinite-Serpentine[?], Illite[?], and Smectite[?]. Altogether, there are about thirty different types of "pure" clays in these categories, but most natural clays are mixtures of these different types, as well as other weathered minerals.
Clays hardened by fire were the first ceramic, and remain one of the cheapest and most widely used materials to produce even in the present day. Bricks, cooking pots, art objects, spark plug tips, and even musical instruments such as the ocarina are all made with clay. Clay is also used in many industrial processes, such as paper making, concrete production, and chemical filtering.
Clay is also the name of
See also: List of minerals