Chemical weathering breaks down the chemical structure and composition of minerals through various processes. These include hydrolysis where minerals react with water to form new minerals and acids, hydration where solids combine with water to form hydrates, carbonation where minerals react with carbon dioxide and acids to form soluble compounds, oxidation where electrons are removed from ions, and dissolution where simple salts dissolve. Factors that influence soil formation include climate, organisms, relief of the landscape, the parent material, and time, as described in models developed by Russian pedologist Dokuchaev and American soil scientist Jenny.

1. Weathering Processes
• Chemical weathering
– Change in chemical structure/ composition of
minerals
– Examples
– Hydrolysis
KAlSi3O8 + HOH HAlSi3O8 + KOH
(Orthoclase feldspar) Acid-silicate K hydroxide
2 HAlSi3O8 + HOH Al2Si2O5(OH)4 + 4SiO2
Kaolinite
HalSi3O8 + HOH Al(OH)3 + SiO2
Gibbssite

2. Weathering Processes
• Chemical weathering examples
– Hydration. The combination of solids with water to form hydrates.
2Fe2O3 + 3H2O 2Fe2O3.3H2O
Hematite (reddish) Limonite (yellowish)
– Carbonation and Other Acid Process/Acidification.
CaCO3 + H2CO3 Ca(HCO3)2
Limestone Carbonic acid Soluble bicarbonate
– Oxidation. Removal of one or more electrons from an ion
4FeO + 3O2 2Fe2O3
Ferrous Oxide Hematite (Ferric oxide)
– Solution. Dissolving of simple salts as carbonates or chlorides.
CaCO3 + 2 H H2CO3 + Ca++
– Complexation. Formation of organic matter complexes

3. Factors Influencing Soil Formation
• Dokuchaev (1846-1903), a Russian Pedologist, first to
publish a soil-forming factor equation :
S= f (cl, o, p) t°
– S = soil; cl= climate; o= the organisms (plants and
animals) p=the geologic substratum; t°= the relative age
of the soil
• Jenny (1961), formulated a soil-forming factor
equation: S= f (cl, o, r, p, t, …)
– Climate. Precipitation and temperature,
– Organisms. Vegetation, microbes and soil animals
– Relief. Slope aspect and landscape position
– Parent Material. Geological or organic
– Time