chemical weathering

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Form of weathering brought about by chemical attack on rocks, usually in the presence of water. Chemical weathering involves the breakdown of the original minerals within a rock to produce new minerals (such as clay minerals, bauxite, and calcite). The breakdown of rocks occurs because of chemical reactions between the minerals in the rocks and substances in the environment, such as water, oxygen, and weakly acidic rainwater. Some chemicals are dissolved and carried away from the weathering source, while others are brought in.

Material worn away from rocks by weathering, either as fragments of rock or dissolved material, may be transported and deposited as sediments, which eventually become compacted to form sedimentary rocks. Thus chemical weathering plays a part in the rock cycle.

Chemical processes involved in weathering include carbonation (breakdown by weakly acidic rainwater), hydrolysis (breakdown by water), hydration (breakdown by the absorption of water), and oxidation (breakdown by the oxygen in air and water).

The reaction of carbon dioxide gas in the atmosphere with silicate minerals in rocks to produce carbonate minerals is called the ‘Urey reaction’ after the chemist who proposed it, Harold Urey. The Urey reaction is an important link between Earth's climate and the geology of the planet. It has been proposed that chemical weathering of large mountain ranges like the Himalayas can remove carbon dioxide from the atmosphere by the Urey reaction (or other more complicated reactions like it), leading to a cooler climate as the greenhouse effects of the lost carbon dioxide are diminished.

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