The Earth Contents

3. Weathering

The breakdown and alteration of minerals weathers rock through mineral oxidation

Acid mine drainage can cause severe environmental problems

Rocks formed below the Earth's surface, in the absence of air, may often contain reduced iron and sulfur. Elements in their reduced states are unstable in contact with air, and are easily oxidised. The breakdown and alteration of minerals containing reduced elements is an effective weathering mechanism.

One of the most striking occurrences of mineral oxidation is in the production of acid drainage from abandoned coal mines. Coal-bearing rocks frequently contain the mineral pyrite which is comprised of both reduced iron and sulphur. On contact with water the oxidation process occurs rapidly producing a solution of sulphuric acid and colloidal iron hydroxides. The latter form red precipitates which deposit on stream beds and are harmful to aquatic life. The effects of acid mine drainage may be noticeable in the small streams draining from abandoned mines.

Explain mineral oxidation.