n.
Soil particles with diameters less than 0.
005 mm; also a material composed essentially of clay particles (see clay mineral ). In soils, clays provide the environment for almost all plant growth. The use of clay in pottery making predates recorded human history. As building materials, clay brick s (baked and as adobe ) have been used in construction since earliest times. Kaolin, or china clay, is required for the finer grades of ceramic materials; used for paper coating and filler, it gives the paper a gloss, permitting high-quality reproduction, and increases paper opacity. Clay materials have many uses in engineering; earth dams are made impermeable to water by a core of clay, and water loss in canals may be reduced by lining the bottom with clay (called puddling). The essential raw materials of portland cement include clays.