a siliceous clay rich in hydrous aluminum silicates, capable of withstanding high temperatures without deforming (either disintegrating or becoming soft and pasty) and useful for the manufacture of refractory ceramic products (such as crucibles, or firebrick for lining furnaces). It is deficient in iron, calcium and alkalies, and approaches kaolin in composition, the better grades containing at least 35% alumina when fired, põletamiseks sobiv savi