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. The chemical composition of the clay can be determined by a routine analysis. The size and shape of the particles can be studied through microscopic studies.
The extremely small size of the grains of clay account for most of its physical characteristics. Many clays have a substantial amount of particles below one micron and these clay particles are plate shaped. The extremely fine particle size of clay can be accounted for by the process of weathering, chemical changes, disintegration, water transportation and sorting in to different particle size during sedimentation.
