chemicalweathering

Chemical weathering is the breakdown and alteration of rocks and minerals by chemical reactions with water and atmospheric gases, rather than by mechanical fragmentation alone. It transforms primary minerals into new, more stable secondary minerals and dissolved ions, contributing to soil formation and the long-term evolution of landscapes.

The main processes are dissolution, hydrolysis, and oxidation-reduction. Dissolution occurs when minerals dissolve in water, especially when enhanced by weak acids such as carbonic acid formed from carbon dioxide in rain; this process commonly releases ions like calcium, magnesium, bicarbonate, and silica. Hydrolysis involves the reaction of minerals with water to form new minerals and ions, notably turning feldspars into clay minerals such as kaolinite or illite and releasing silica and base cations. Oxidation-reduction reactions alter iron-bearing minerals, producing oxides and hydroxides such as goethite or hematite. Carbonate minerals, like calcite, readily dissolve under acidic rain, contributing to karst features in landscapes.

Rates of chemical weathering depend on climate, rock composition, surface area, fracture density, moisture, temperature, and biological activity. Warm, wet climates typically accelerate weathering, while resistant rocks weather slowly. Weathering products include dissolved ions carried to rivers and oceans, and secondary minerals such as clays and iron oxides that accumulate in soils and regolith.

Chemical weathering plays a crucial role in soil fertility, geochemical cycling, and long-term climate regulation, through processes such as silicate weathering and CO2 sequestration over geological timescales.