Chemical Weathering
The rocks while getting disintegrated may also undergo chemical change. Water is an important agent in bringing about chemical changes due to dissolution or reaction of one or more components of rock materials. Presence of dissolved materials and warm temperature favour chemical weathering. Some components of the rock may get dissolved and reprecipitated. Some minerals like feldspar and mica readily combine with water through the process of hydration and become soft and easily weatherable. Another very important process of chemical weathering is through hydrolysis in which water dissociates (particularly in the presence of carbon dioxide and organic acids) into H+ and OH-ions which act on silicates like orthoclase to produce silicate clays. Oxidation and reduction reactions and carbonation are other important means of chemical weathering. It is important to realise that weathering of rocks is a continuous phenomenon, that helps in soil formation. It is, however, a very slow process, and may take hundreds or thousands of years to make a few centimetres of soil, depending on-the nature of the parent rock material