Solution

Carbonation

Carbon dioxide in the air dissolves in rainwater and becomes weakly acidic.

This weak “carbonic acid” is able to dissolve limestone as it seeps into cracks and cavities. Over many years, solution of the rock can form spectacular cave systems (see photo).

Note: Stalagmites and stalactites form in caves as water drips from the roof, depositing some of its dissolved calcium carbonate, as carbon dioxide is released into the air.

Acid rain

Polluting gases, like sulphur dioxide and nitrogen oxide dissolve in rainwater to make stronger acids. When this rainwater falls, we get acid rain. This acid attacks many rock types, both by solution and hydrolysis, seriously damaging buildings and monuments.