Chemical weathering

This is the process of rotting of rocks. Minerals within the rocks are decomposed by agents such as water, carbon dioxide and various organic acids. Since minerals vary in their resistance to chemical agents, this type of weathering attacks rocks selectively and may penetrate them deeply in places. The products of chemical weathering are generally ‘finer’ than those of physical weathering.

There are few processes of chemical weathering:

	hydration
	oxidation
	hydrolysis
	solution
	carbonation

　

Hydration

Certain minerals take up water and expand. This causes additional stresses within the rock e.g. Anhydrite takes up water to become gypsum.

	Oxidation This is the process of taking up oxygen from the air. For example, below the water table gault clay is blue or grey but above the water table where the water and the clay are replaced by air it is oxidized into red or brown ferric compounds.
	Hydrolysis Felspars are important constituents of igneous rocks. Hydrolysis is a process which leads to the breakdown of felspars. It is caused by a chemical reaction with the water which involves H and OH ions.
	Solution This is not a very common process because few minerals re soluble. Solution may help weathering by removing the products resulting from other types of chemical weathering.
	Carbonation This occurs when carbonate ions combine with minerals. Carbon dioxide solution in the atmosphere converts calcium carbonate into the much more soluble calcium bicarbonate. This process is important in limestones and chalk.

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