Editing Soil formation (section)

==== Weathering ====
The weathering of parent material takes the form of physical weathering (disintegration), chemical weathering (decomposition) and chemical transformation. Weathering is usually confined to the top few meters of geologic material, because physical, chemical, and biological stresses and fluctuations generally decrease with depth.<ref>{{cite web |url=http://uregina.ca/~sauchyn/geog323/weather.html |title=Weathering |website=University of Regina |access-date=7 November 2021 }}</ref> Physical disintegration begins as rocks that have solidified deep in the Earth are exposed to lower pressure near the surface and swell and become mechanically unstable. Chemical decomposition is a function of mineral solubility, the rate of which doubles with each 10&nbsp;°C rise in temperature but is strongly dependent on water to effect chemical changes. Rocks that will decompose in a few years in tropical climates will remain unaltered for millennia in deserts.<ref name="Gilluly1975">{{cite book |author-link1=James Gilluly |last1=Gilluly |first1=James |last2=Waters |first2=Aaron Clement |last3=Woodford |first3=Alfred Oswald |title=Principles of geology |date=1975 |edition=4th |publisher=W.H. Freeman |location=San Francisco, California |isbn=978-0-7167-0269-6 }}</ref> Structural changes are the result of [[Hydration reaction|hydration]], [[Redox|oxidation]], and [[Redox|reduction]]. Chemical weathering mainly results from the excretion of [[organic acids]] and [[chelating]] compounds by bacteria<ref>{{cite journal |last1=Uroz |first1=Stéphane |last2=Calvaruso |first2=Christophe |last3=Turpault |first3=Marie-Pierre |last4=Frey-Klett |first4=Pascale |year=2009 |title=Mineral weathering by bacteria: ecology, actors and mechanisms |journal=[[Trends in Microbiology]] |volume=17 |issue=8 |pages=378–87 |doi=10.1016/j.tim.2009.05.004 |pmid=19660952 |url=https://art1lib.org/book/17303331/fda878 |access-date=7 November 2021 |archive-date=7 November 2021 |archive-url=https://web.archive.org/web/20211107091125/https://art1lib.org/book/17303331/fda878 |url-status=dead }}</ref> and fungi,<ref name="Landeweert2001">{{cite journal |last1=Landeweert |first1=Renske |last2=Hoffland |first2=Ellis |last3=Finlay |first3=Roger D. |last4=Kuyper |first4=Thom W. |last5=Van Breemen |first5=Nico |year=2001 |title=Linking plants to rocks: ectomycorrhizal fungi mobilize nutrients from minerals |journal=[[Trends in Ecology and Evolution]] |volume=16 |issue=5 |pages=248–54 |doi=10.1016/S0169-5347(01)02122-X |pmid=11301154 |url=https://www.academia.edu/13679137 |access-date=7 November 2021 }}</ref> thought to increase under [[greenhouse effect]].<ref>{{cite journal |last1=Andrews |first1=Jeffrey A. |last2=Schlesinger |first2=William H. |year=2001 |title=Soil CO2 dynamics, acidification, and chemical weathering in a temperate forest with experimental CO2 enrichment |journal=Global Biogeochemical Cycles |volume=15 |issue=1 |pages=149–62 |doi=10.1029/2000GB001278 |bibcode=2001GBioC..15..149A |s2cid=128612522 |url=https://www.researchgate.net/publication/248816941 |access-date=7 November 2021 |doi-access=free }}</ref>
* ''Physical disintegration'' is the first stage in the transformation of parent material into soil. Temperature fluctuations cause expansion and contraction of the rock, splitting it along lines of weakness.<ref>{{cite journal |last1=Halsey |first1=Dave P. |last2=Mitchell |first2=David J. |last3=Dews |first3=S. J. |year=1998 |title=Influence of climatically induced cycles in physical weathering |journal=[[Quarterly Journal of Engineering Geology & Hydrogeology|Quarterly Journal of Engineering Geology and Hydrogeology]] |volume=31 |issue=4 |pages=359–67 |url=https://art1lib.org/book/35607238/7259bb |doi=10.1144/GSL.QJEG.1998.031.P4.09 |bibcode=1998QJEGH..31..359H |s2cid=128917530 |access-date=7 November 2021 }}</ref> Water may then enter the cracks and freeze and cause the physical splitting of material along a path toward the center of the rock, while temperature gradients within the rock can cause exfoliation of "shells". Cycles of wetting and drying cause soil particles to be abraded to a finer size, as does the physical rubbing of material as it is moved by wind, water, and gravity. Organisms may reduce parent material size and create crevices and pores through the mechanical action of plant roots and the digging activity of animals.{{sfn|Donahue|Miller|Shickluna|1977|pp=28–31}} 
* ''Chemical decomposition'' and ''structural changes'' result when minerals are made soluble by water or are changed in structure. The first three of the following list are solubility changes, and the last three are structural changes.{{sfn|Donahue|Miller|Shickluna|1977|pp=31–33}}

# The ''[[Solution (chemistry)|solution]]'' of salts in water results from the action of bipolar [[water molecules]] on [[ionic salt]] compounds producing a solution of ions and water, removing those minerals and reducing the rock's integrity, at a rate depending on [[water flow]] and pore channels.<ref>{{cite journal |last1=Li |first1=Li |last2=Steefel |first2=Carl I. |last3=Yang |first3=Li |year=2008 |title=Scale dependence of mineral dissolution rates within single pores and fractures |journal=[[Geochimica et Cosmochimica Acta]] |volume=72 |issue=2 |pages=360–77 |url=https://www.researchgate.net/publication/223835697 |doi=10.1016/j.gca.2007.10.027 |access-date=14 November 2021 |bibcode=2008GeCoA..72..360L |archive-date=1 November 2015 |archive-url=https://web.archive.org/web/20151101231923/http://lili.ems.psu.edu/publication/liligca08.pdf |url-status=live }}</ref>
# ''[[Hydrolysis]]'' is the transformation of minerals into [[Chemical polarity|polar]] molecules by the splitting of intervening water. This results in soluble [[acid-base]] pairs. For example, the hydrolysis of [[orthoclase]]-[[feldspar]] transforms it to acid [[silicate]] clay and basic [[potassium hydroxide]], both of which are more soluble.<ref>{{cite journal |last1=Oelkers |first1=Eric H. |last2=Schott |first2=Jacques |year=1995 |title=Experimental study of anorthite dissolution and the relative mechanism of feldspar hydrolysis |journal=[[Geochimica et Cosmochimica Acta]] |volume=59 |issue=24 |pages=5039–53 |url=https://art1lib.org/book/19648369/edea24 |doi=10.1016/0016-7037(95)00326-6 |bibcode=1995GeCoA..59.5039O |access-date=14 November 2021 }}</ref>
# In ''[[carbonation]]'', the solution of [[carbon dioxide]] in water forms [[carbonic acid]]. Carbonic acid will transform [[calcite]] into more soluble [[calcium bicarbonate]].<ref>{{cite journal |last1=Al-Hosney |first1=Hashim |last2=Grassian |first2=Vicki H. |year=2004 |title=Carbonic acid: an important intermediate in the surface chemistry of calcium carbonate |journal=[[Journal of the American Chemical Society]] |volume=126 |issue=26 |pages=8068–69 |doi=10.1021/ja0490774 |pmid=15225019 |bibcode=2004JAChS.126.8068A |url=https://art1lib.org/book/18790192/b47eec |access-date=14 November 2021 }}</ref>
# ''[[Hydration reaction|Hydration]]'' is the inclusion of water in a mineral structure, causing it to swell and leaving it stressed and easily [[Chemical decomposition|decomposed]].<ref>{{cite journal |last1=Jiménez-González |first1=Inmaculada |last2=Rodríguez-Navarro |first2=Carlos |last3=Scherer |first3=George W. |year=2008 |title=Role of clay minerals in the physicomechanical deterioration of sandstone |journal=[[Journal of Geophysical Research]] |volume=113 |issue=F02021 |pages=1–17 |doi=10.1029/2007JF000845 |bibcode=2008JGRF..113.2021J |doi-access=free }}</ref>
# ''[[Oxidation]]'' of a mineral compound is the inclusion of [[oxygen]] in a mineral, causing it to increase its [[oxidation number]] and swell due to the relatively large size of oxygen, leaving it stressed and more easily attacked by water (hydrolysis) or carbonic acid (carbonation).<ref>{{cite journal |last1=Mylvaganam |first1=Kausala |last2=Zhang |first2=Liangchi |year=2002 |title=Effect of oxygen penetration in silicon due to nano-indentation |journal=[[Nanotechnology (journal)|Nanotechnology]] |volume=13 |issue=5 |pages=623–26 |url=https://www.researchgate.net/publication/230680185 |doi=10.1088/0957-4484/13/5/316 |access-date=14 November 2021 |bibcode=2002Nanot..13..623M |s2cid=250738729 }}</ref>
# ''[[Redox|Reduction]]'', the opposite of oxidation, means the removal of oxygen, hence the oxidation number of some part of the mineral is reduced, which occurs when oxygen is scarce. The reduction of minerals leaves them electrically unstable, more soluble and internally stressed and easily decomposed. It mainly occurs in [[Waterlogging (agriculture)|waterlogged]] conditions.<ref>{{cite journal |last1=Favre |first1=Fabienne |last2=Tessier |first2=Daniel |last3=Abdelmoula |first3=Mustapha |last4=Génin |first4=Jean-Marie |last5=Gates |first5=Will P. |last6=Boivin |first6=Pascal |year=2002 |title=Iron reduction and changes in cation exchange capacity in intermittently waterlogged soil |journal=European Journal of Soil Science |volume=53 |issue=2 |pages=175–83 |doi=10.1046/j.1365-2389.2002.00423.x |bibcode=2002EuJSS..53..175F |s2cid=98436639 |url=https://art1lib.org/book/5115541/2bfa4e |access-date=14 November 2021 }}</ref>

Of the above, hydrolysis and carbonation are the most effective, in particular in regions of high rainfall, temperature and physical [[erosion]].<ref>{{cite journal |last1=Riebe |first1=Clifford S. |last2=Kirchner |first2=James W. |last3=Finkel |first3=Robert C. |year=2004 |title=Erosional and climatic effects on long-term chemical weathering rates in granitic landscapes spanning diverse climate regimes |journal=[[Earth and Planetary Science Letters]] |volume=224 |issue=3/4 |pages=547–62 |url=http://www.geog.ucsb.edu/~bodo/Geog295-Fall2012/riebe2004_mineral_weathering.pdf |doi=10.1016/j.epsl.2004.05.019 |access-date=21 November 2021 |bibcode=2004E&PSL.224..547R }}</ref> Chemical weathering becomes more effective as the surface area of the rock increases, thus is favoured by physical disintegration.<ref>{{cite web |url=http://midwaymsscience.weebly.com/uploads/8/2/9/8/8298729/section_2_-_rates_of_weathering.pdf |title=Rates of weathering |access-date=21 November 2021 |archive-date=13 June 2013 |archive-url=https://web.archive.org/web/20130613022251/http://midwaymsscience.weebly.com/uploads/8/2/9/8/8298729/section_2_-_rates_of_weathering.pdf |url-status=dead }}</ref> This stems in latitudinal and altitudinal climate gradients in [[regolith]] formation.<ref>{{cite journal |last1=Dere |first1=Ashlee L. |last2=White |first2=Timothy S. |last3=April |first3=Richard H. |last4=Reynolds |first4=Bryan |last5=Miller |first5=Thomas E. |last6=Knapp |first6=Elizabeth P. |last7=McKay |first7=Larry D. |last8=Brantley |first8=Susan L. |year=2013 |title=Climate dependence of feldspar weathering in shale soils along a latitudinal gradient |journal=[[Geochimica et Cosmochimica Acta]] |volume=122 |pages=101–26 |doi=10.1016/j.gca.2013.08.001 |url=https://booksc.eu/book/23749430/d62f8e |bibcode=2013GeCoA.122..101D |access-date=21 November 2021 }}</ref><ref>{{cite journal |last1=Kitayama |first1=Kanehiro |last2=Majalap-Lee |first2=Noreen |last3=Aiba |first3=Shin-ichiro |year=2000 |title=Soil phosphorus fractionation and phosphorus-use efficiencies of tropical rainforests along altitudinal gradients of Mount Kinabalu, Borneo |journal=[[Oecologia]] |volume=123 |issue=3 |pages=342–49 |doi=10.1007/s004420051020 |pmid=28308588 |bibcode=2000Oecol.123..342K |s2cid=20660989 |url=https://booksc.eu/book/7650890/88e945 |access-date=21 November 2021 }}</ref>

[[Saprolite]] is a particular example of a residual soil formed from the transformation of granite, metamorphic and other types of bedrock into clay minerals. Often called weathered granite, saprolite is the result of weathering processes that include: hydrolysis, chelation from organic compounds, hydration and physical processes that include freezing and thawing. The mineralogical and chemical composition of the primary bedrock material, its physical features (including [[grain size]] and degree of consolidation), and the rate and type of weathering transforms the parent material into a different mineral. The texture, pH and mineral constituents of saprolite are inherited from its parent material. This process is also called ''arenization'', resulting in the formation of sandy soils, thanks to the much higher resistance of quartz compared to other mineral components of granite (e.g., [[mica]], [[amphibole]], feldspar).<ref>{{cite journal |last1=Sequeira Braga |first1=Maria Amália |last2=Paquet |first2=Hélène |last3=Begonha |first3=Arlindo |year=2002 |title=Weathering of granites in a temperate climate (NW Portugal): granitic saprolites and arenization |journal=Catena |volume=49 |issue=1/2 |pages=41–56 |url=http://home.uevora.pt/~lopes/Artigos/23.PDF |doi=10.1016/S0341-8162(02)00017-6 |bibcode=2002Caten..49...41S |access-date=21 November 2021 }}</ref>