Weathering refers to mechanical or chemical erosion of rocks due to weather. Fracturing and abrasion are the two broad types of mechanical erosion. Chemical methods include hydrolysis, hydration, ion exchange and oxidation.
Characteristics of chemical weathering include the following: increasing the volume of the rock, which creates stresses; decreasing particle size so more surface is available to weather; creating more mobile particles; and creating more stable minerals.
Dissolution, also known as carbonic acid action, degrades limestone with acidic water (either from pollution or naturally acidic). It can cause sinkholes.
Some types of minerals, when exposed to water, turn into clay minerals, which are more stable, though more malleable and conducive to erosion. The highly abundant mineral feldspar is an example.
Oxidation is the combination of oxygen with other elements in rock to form new rock types. The new rock is usually softer, and breaks apart more easily. Rust is an example.
Ion exchange involves the exchange of charged particles between water and rock. It is important in the change of clay from one type to another.
Chelation is the absorption of metal atoms by hydrocarbons. It is fundamental to soil formation.