Chemical weathering occurs when water, air or acids cause chemical changes in minerals within rocks, dissolving or transforming them. Solution, oxidation, hydration, carbonation, and hydrolysis are examples. Chemical weathering is more prevalent in tropical environments and affects rocks with larger surface areas.
Chemical weathering is a process that occurs when water, air or acids cause chemical changes in the minerals within rocks. These changes cause rocks to dissolve or transform into new elements. Unlike mechanical weathering, chemical weathering can change the composition of weathered rocks. Solution, oxidation, hydration, carbonation, and hydrolysis are all examples of this type of weathering.
Solution occurs when a solvent such as water breaks down and dissolves the rock. Water can have multiple chemical weathering effects on rocks. When minerals within the rock absorb water and expand, the rock structure becomes unstable. This effect is known as hydration.
While most minerals are not soluble in pure water, many will quickly age when even small amounts of acid are present. Water is made naturally acidic by combining it with carbon dioxide. Carbon dioxide is found in small amounts in the earth’s atmosphere, which can cause acidity in rain. Animal respiration and decaying organic matter can add carbon dioxide to the soil, causing groundwater to become slightly acidic. Carbonation occurs when carbon dioxide reacts with minerals in rocks to dissolve or weaken them.
Oxidation occurs when oxygen in the air combines with minerals within a rock to form new chemical compounds. Rust is an example of oxidation. Oxygen is abundant in the atmosphere, but oxidation occurs slowly unless water is present. Oxygen dissolved in water causes most of the oxidative weathering.
Hydrolysis occurs when minerals within a rock have a chemical reaction to the hydrogen present in rainwater. This causes new compounds to form, weakening the rock structure. When granite undergoes hydrolysis, for example, the feldspar contained in the rock turns into a clay-like material, weakening the rock.
When hydrolysis occurs, the rock is affected from the outside in. Many factors affect the rate of chemical weathering on a rock’s surface. If the rock contains cracks or fractures, erosion will make these faults worse. The chemical composition of the parent material also influences the aging rate. Some minerals are more vulnerable to these forms of weathering; for example, the rock known as basalt deteriorates rapidly due to the chemically unstable minerals it contains.
Chemical weathering is more prevalent in tropical environments than in arctic or arid environments. High amounts of precipitation, warmer temperatures, and low evaporation rates create an atmosphere that encourages chemical weathering. Particles with a larger surface area are more at risk from chemical weathering than particles with a smaller surface area. Since chemical erosion affects the surface of a stone, the larger the surface area of the stone, the greater the effect that erosion can have. Organisms such as fungi or algae that can grow on rocks can promote rapid weathering over rocks unaffected by these organisms.
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