Chemical change in the rocks through formation of new compounds or formation of new substances is called chemical weathering. Chemical processes include oxidation, hydrolysis, and acid solution. Chemical weathering involves four major processes:
This is the process in which atmospheric oxygen reacts with the rock to produce oxides.
The process is called oxidation.
The greatest impact of this process is observed on ferrous minerals.
Oxygen present in humid air reacts with iron grains in the rocks to form a yellow or red oxide of iron.
This is called rusting of the iron.
Rust decomposes rocks completely with the passage of time.
This is the process by which various types of carbonates are formed.
Some of these carbonates are soluble in water.
For example, when rainwater containing carbon dioxide passes through limestone rocks, the rock joints enlarge due to the action of carbonic acid.
The joints enlarge in size and lime is removed in solution.
This type of breakdown of rocks is called carbonation.
This is the process by which water is absorbed by the minerals of the rock.
Due to the absorption of water by the rock, its volume increases and the grains lose their shape.
Feldspar, for example, is changed into kaolin through hydration.
Kaolin on Vindhyan Hills near Jabalpur has been formed in this manner.
This is the process in which some of the minerals get dissolved in water.
They are therefore removed in solution.
Rock salt and gypsum are removed by this process.