China Clay, or silicate of alumina forms part of the composition of several minerals, notably feldspar, granite, porphyry and similar rocks. By the action of the carbonic acid in the air, aided by water, these formations disintegrate and become soft pliable masses of earthy matter.

In Devonshire and Cornwall, England, occur large deposits of disintegrated white granite, furnishing large supplies of fine white china clay. The crude material is properly disintegrated and washed to separate the mica and quartz present and the milk-like liquid is stored in tanks. The clay settles out and is first dried in the air, and then in ovens. It is used to some extent in paints, and particularly in wood fillers. Being very bulky, it holds up well in solution, and has a smooth unctuous working quality. Its principal use is in the manufacture of porcelain.