690210 Refractory bricks, blocks, tiles , Containing by weight, singly or together, more than 50 percent of the elements magnesium, calcium, or chromium, epressed as MgO, CaO or Cr2O3
690220 Refractory bricks, blocks, tiles Containing by weight more than 50 percent of alumina (Al2O3), of silica (SiO2) or of a miture or compound of these products:
690290 Other Refractory bricks, blocks, tiles