Refractory bricks, blocks, tiles and similar refractory ceramic constructional goods (excl. containing, by weight, singly or together, > 50 % of the elements mg, Ca or Cr, expressed as Mgo, Cao or Cr2O3, containing, by weight, > 50 % alumina, silica or a miixture or compound of these products and those of siliceous fossil meals or similar siliceous earths) 10 4 3 2 1 0