Types of weathering

(carbon dioxide + water → carbonic acid)

CO2 + H2O → H2CO3

(calcite + carbonic acid → calcium + bicarbonate)

CaCO3 + H2CO3 → Ca2+ + 2HCO3-

Carbonation

Carbonation is the process of rock minerals reacting with carbonic acid. Carbonic acid is formed when water combines with carbon dioxide. Carbonic acid dissolves or breaks down minerals in the rock.

Hydrolysis of feldspar

2KAISi3O8 + 2H+ + 9H20 → H4Al2Si2O9 + 4H4SiO4 + 2K+ (orthoclase + water → kaolinite + silicic acid + potassium)

Chemical weathering

*Chemical weathering* is the weakening and subsequent disintegration of rock by chemical reactions. These reactions include oxidation, hydrolysis, and carbonation. These processes either form or destroy minerals, thus altering the nature of the rock's mineral composition. Temperature and, especially, moisture are critical for chemical weathering; chemical weathering of rock minerals generally occurs more quickly in hot, humid climatic regions.

Hydrolysis

*Hydrolysis* is a chemical reaction caused by water. Water changes the chemical composition and size of minerals in rock, making them less resistant to weathering. Click on the video clip below to see hydrolysis of a relatively weathering resistant mineral, feldspar. When this mineral is completely hydrolyzed, clay minerals and quartz are produced and such elements as K, Ca, or Na are released. A hydrolysis reaction of orthoclase (alkali feldspar), a common mineral found in igneous rock, yields kaolinite, silicic acid, and potassium.

Oxidation

is the reaction of rock minerals with oxygen, thus changing the mineral composition of the rock. When minerals in rock oxidize, they become less resistant to weathering. Iron, a commonly known mineral, becomes red or rust colored when oxidized.