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By | September 2013
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Chemical weathering
is a process of alteration of rocks of the Earth’s crust.
is a chemical decomposition process.
is brought out by atmospheric gases and moisture.
End product has a different chemical composition and poorer physical constitution.

The process:
Chemical change in the nature of rock takes place in the presence of moisture containing many active gases such as CO2, N2, H2, and O2.

Rocks are made up of minerals.
All the minerals in a rock are not in chemical equilibrium with the atmosphere around them. Chemical weathering is essentially a process of chemical reactions between the surfaces of rocks and the atmospheric gases. This process takes place so as to establish chemical equilibrium.

Chemical weathering eats up the rocks in a number of ways.
The process depends upon
the rocks’ mineralogical composition, and
the nature of chemical environment surrounding them.

Some of the main processes of chemical weathering are:
1. solution,
2. hydration and hydrolysis,
3. oxidation and reduction,
4. carbonation,
5. base exchange, and
6. formation of colloids.

Some rocks contain one or more minerals that are soluble in water to some extent. Rock salt (NaCl), gypsum (CaSO4. 2H2O) and calcite (CaCO3)
As it is, pure water is not a good solvent of minerals in most cases. But when pure water is carbonated, its power of dissolving (solvent action) is enhanced. Limestone is not soluble in pure water.

But carbonated water dissolves limestone effectively.
Limestone gets pitted and porous due to chemical weathering. H2O + CO2 → H2CO3 → H+ + HCO3-
CaCO3 + H2CO3 → Ca+2 + 2HCO3

In these two processes of chemical weathering, atmospheric moisture directly attacks on the individual minerals of a rock. It ultimately affects the mineral’s structural make-up.

The interior of many minerals is in electric equilibrium.
But the surfaces of many crystals are not.
These may have...