Explanatory notes
… (bricks, building tiles, porcelain, china, earthenware, refractory bricks and other refractory goods, etc.); common … also fall in the heading : (1) Bentonite , a clay derived from volcanic ash; largely used as an ingredient of moulding … sillimanite , natural anhydrous aluminium silicates used as refractories. (4) Mullite , obtained by heat treatment of …