TEST OF PRACTICAL KNOWLEDGE QUESTION (a) Define the term weathering (b) Describe four processes of chemical weathering

Answer Details

(a) Definition of weathering

Weathering is the breaking down, disintegration and decomposition of rocks in situ (in place) by the action of the weather and other agents, without the broken material being carried away. It differs from erosion because no transport of the debris is involved.

(b) Four processes of chemical weathering

1. Solution: some minerals dissolve directly in water. Rain water, being slightly acidic, dissolves soluble rocks such as rock salt and limestone, removing them in solution.
2. Carbonation: rain water combines with carbon dioxide to form weak carbonic acid, which attacks limestone. The insoluble calcium carbonate is changed to soluble calcium bicarbonate and washed away, forming features such as caves and clints and grikes.
3. Oxidation: oxygen dissolved in water reacts with iron-bearing minerals in the rock to form iron oxides (rust). The rock is stained reddish-brown, weakened and crumbles.
4. Hydrolysis (and hydration): water reacts chemically with minerals such as the feldspar in granite, changing them into soft clay minerals; in hydration minerals absorb water, swell and flake away, so the rock decays.