Normally the formula for Clay is:
Al2O3.2SiO2.2H2O
One molecule of Al2O3 is associated with two molecules of SiO2 and two molecules of H2O. Kaolinite is the mineralogical name which has been given to this pure clay substance.
The clay which is the end product of a long process of erosion and change is an extremely inert material chemically. […]