Items Unit Index Chemical composition Al2O3 % 70.00-77.00 SiO2 % 22.00-29.00 Fe2O3 % 0.1max Na2O % 0.40max Refractoriness 1850min Bulk density g/ cm3 3.00min Glass phase content % 5-6 3Al2O3.2SiO2 Phase % 95min