A group of hydrated aluminium silicate clays. Kaolins are primary clays formed by the weathering of aluminium silicates such as feldspars and nephelite. When pure, kaolin is a soft, white, absorbent powder. Impurities may give it a yellow, red, blue, grey or brownish colour. It occurs at many locations around the world (France, England, Germany, China, United States, etc.). Kaolin is used as a base for lake colours and as a filler in paints, cements and epoxies. Kaolin (brick dust) has been used as an abrasive. Synonyms: kaolinite; China clay; bolus alba; porcelain clay; white bole; argilla; paper clay; brick dust; fuller's earth; white bolus; pipe clay; pipeclay. Museum of Fine Arts, Boston (2000). [J. Cassar, R. de Angelis]