CLAY

Clay is formed from the disintegration of felspathic rocks, by the combined action of air and water. Its plasticity, when moist, and its capability of being made hard by heat, are properties which render it available for many useful purposes. The purest kind of clay is kaolin, or China clay, which consists almost entirely of silicate of aluminum. It is found in China; but a precisely similar substance is obtained from deposits in Cornwall and some parts of France. Pipe-clay, a white clay nearly free from iron, is found in large quantity in the island of Purbeck. Potter’s clay is found in many parts of Britain; that of Devons hire and Dor sets hire is much valued. Brick clay contains varying proportions of iron; hence the different colours of the bricks used in different countries. See Aluminum, Fuller’s earth, Ochre, .