Chemical Weathering

                     CHEMICAL WEATHERING 

     It is also known as mineral alteration, consists of a number of chemical reactions, all these reactions change the original silicate minerals of igneous rock, the primary minerals, into new compounds, the secondary minerals, that are stable in the surface environment. Besides, sedimentary and metamorphic rocks are also substantially affected by the chemical process of weathering. Chemical is more important than mechanical weathering in almost all the climatic regions. 

Three processes are notably responsible for chemical weathering : 

         a) Oxidation 

         b) Hydration

         c) Carbonation 

Oxidation : 

                  The presence of dissolved oxygen in water in contact with mineral surface leads to oxidation. Which is the chemical union of oxigen atoms with atoms of other metallic elements. Oxygen has a particular affinity for iron compounds and these are among the most commonly oxidized materials.

Hydration : 

                   The chemical union of water with a mineral is called hydration. It is sometimes confused with hydrolysis. The reaction between water and a compound. The process of hydration is particularly effective of some aluminum bearing minerals, such as feldspar. 

Carbonation : 

                     Carbon dioxide is a gas and is a common constituents of the earth's atmosphere. Rain water in course of its passage through the atmosphere, dissolves some of the carbon dioxide present in the air. It thus turns into a week acid called Carbonic acid, and is the most common solvent acting on the crust. The effect of this process is well noticed in the limestone or chalk areas in the humid regions of the world. 

                    Besides the above, another process known as Solution is quite significant in bringing about the chemical weathering of rocks. In this case, some of the minerals got dissolved by water and thus removed in solution, for example gypsum halite etc..