Weathering - The Chemical process
Granite contains four types of minerals - Alkali feldspar, Quartz, Plagioclase feldspar and Olivine. Natural chemical agents react with these minerals slowly and results in clay.
Water combines with Carbon Dioxide and the resulting acid reacts with the granite materials as follows:
K2O.Al2O3.6SiO2 + 2H2O+CO2 = Al2O3.SiO2.2H2O + 4SiO2 + K2CO3
Orthoclase <——> derived from percolating water <————> clay <———————> removed in solution
CaO.Al2O3.2SiO2 + 2CO2+3H2O = Ca(HCO3)2 + Al2O3.2SiO2.2H2O
Anorthite <———> derived from percolating water <———>removed in solution<———-> clay
2MgO.SiO2 + 4CO2+2H2O = 2Mg(HCO3)2 + 2SiO2
Olivine —–>derived from percolating water<—->removed in solution<—>partially removed in exceedingly fine solution
2FeO.SiO2+4CO2+2H2O=2Fe(HCO3)2+2SiO2
4Fe(HCO3)2+O2=Fe2O3.H2O+3H2O+8CO2
<———————————->Limonite
Clay thus formed contains granite grains, quartz grains, grains of feldspar and olivine. This clay available at source is called primary clay or residual clay. This clay is carried to different places by natural transporting agents like wind, river streams, etc causing natural complex sorting and remixing resulting in contamination with other minerals and organic material. This now becomes Secondary Clay.
