Clay is a general term that includes many combination of one or more minerals with metal oxide and organic matter. Geology of the clay deposits largely made up of phyllosilicate minerals contain variable amounts of water trapped in the mineral structure.
Minerals usually form over long periods of time by chemical weathering of rock, usually stepwise silicate-bearing, by low concentrations of carbonic acid and other diluted solvents. This solvent, usually acidic, migrate through the weathering Rock after leaching through upper rock layers. In addition to the process of weathering, some minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits on the ground, but thick deposits usually formed as a result of a secondary sedimentary deposition process after they have been eroded and transported from the original location of the establishment. Soil deposits are typically associated with very low energy depositional environments such as large lakes and marine deposits.
Primary clays, also known as kaolins, located in the place of establishment. Secondary Clay deposits have been removed by erosion and water from their primary location.