The chemical composition of refractory clay is one of the important factors affecting its quality. Al2O3 is a beneficial component of refractory clay, mainly occurring in aluminum hydroxide minerals (diaspore, boehmite, gibbsite), followed by aluminosilicate minerals (kaolinite, illite) , montmorillonite, etc.). Generally speaking, soft and semi-soft clays contain 30% to 45% Al2O3, 35% to 50% for hard clays, and 55% to 70% for high alumina clays.

SiO2 mainly occurs in clay minerals, and there are also traces of primary quartz debris. The content of SiO2 varies greatly, generally 3% to 35% in high alumina clay, and 43% to 66% in hard clay.

Fe2O3 mainly occurs in hematite, magnetite, goethite and siderite, and is the main harmful component of refractory clay. The content of Fe2O3 has no obvious regularity. The content of high alumina clay is 0.5% to 2.2%, that of hard clay is 0.5% to 2.5%, and that of soft clay is generally 1.0% to 2.5%.

K2O and Na2O are also harmful impurities in refractory clay, which mainly occur in minerals such as illite and mica, and their contents vary greatly.