China Clay, which falls under the Kaolinite group of clays is formed by weathering or hydrothermal alteration of felspathic rocks. It has the general formula A12, (Si205) (OH)4. It is a hydrated alumino-silicate having sheet structure. Free Silica (grit) is the most undesirable impurity and is removed during processing by levigation, sedimentation or air-separation.
Some of the basic features of this mineral are low cost, high brightness, fine particle size, platelet shape and hydrophilic surface chemistry
It is one of the essential raw materials in the ceramic industry. A small quantity is used in white cement, cosmetics, pharmaceuticals, abrasives, insecticides and ultramarine blue. It is also used in the manufacture of fine porcelain. The modern production method is a three-part process. First, the earth overlying the clay is removed, and a high-pressure water jet is fired at the quarry face, liberating the clay. The clay must then be sifted and refined to remove impurities before finally being dried to reduce its moisture content.

Key to Identification
SiO2 48 %
Alumina Al203 35 % to 40 %
Ferric Oxide Fe2O3 0.5%
Titanium Dioxide TiO2 0.75%
Magnaous Oxide MnO Traces
Calcium Oxide CaO Nil
Magnesium Oxide MgO 0.70%
Sodium Oxide Na2O 0.39%
Pottasium Oxide K2O 0.30%
Loss on Ignition L.O.I 13 %
Bulk Density (after 50 tabs ) 0.75 gm/cc
pH of 10 % Solution 8
Whiteness by reflection compared with MgO taken as 100 % 75 % to 90 %