Editing Granite (section)

==Weathering==
{{further|Weathering}}
[[File:GrusSand.JPG|thumb|left|[[Grus (geology)|Grus]] sand and granitoid from which it derived]]
[[Physical weathering]] occurs on a large scale in the form of [[exfoliation joint]]s, which are the result of granite's expanding and fracturing as pressure is relieved when overlying material is removed by erosion or other processes.

[[Chemical weathering]] of granite occurs when dilute [[carbonic acid]], and other acids present in rain and soil waters, [[mineral alteration|alter]] feldspar in a process called [[weathering|hydrolysis]].<ref>{{cite web |url=http://www.ucl.ac.uk/earth-sciences/impact/geology/london/citycemetery/weathering/granite |title=Granite [Weathering] |work=[[University College London]] |access-date=10 July 2014 |archive-url=https://web.archive.org/web/20141015040859/http://www.ucl.ac.uk/earth-sciences/impact/geology/london/citycemetery/weathering/granite |archive-date=15 October 2014 |url-status=dead }}</ref><ref>{{cite web |url=http://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3566.html |title= Hydrolysis |work=[[Geological Society of London]] |access-date=10 July 2014 }}</ref> As demonstrated in the following reaction, this causes potassium feldspar to form [[kaolinite]], with potassium ions, bicarbonate, and silica in solution as byproducts. An end product of granite weathering is [[grus (geology)|grus]], which is often made up of coarse-grained fragments of disintegrated granite.

{{block indent|2 KAlSi<sub>3</sub>O<sub>8</sub> + 2 H<sub>2</sub>CO<sub>3</sub> + 9 H<sub>2</sub>O → Al<sub>2</sub>Si<sub>2</sub>O<sub>5</sub>(OH)<sub>4</sub> + 4 H<sub>4</sub>SiO<sub>4</sub> + 2 K<sup>+</sup> + 2 HCO<sub>3</sub><sup>−</sup>}}

Climatic variations also influence the weathering rate of granites. For about two thousand years, the relief engravings on [[Cleopatra's Needle (London)|Cleopatra's Needle]] obelisk had survived the arid conditions of its origin before its transfer to London. Within two hundred years, the red granite has drastically deteriorated in the damp and polluted air there.<ref>{{cite book|last1=Marsh |first1=William M.|first2=Martin M. |last2=Kaufman|title=Physical Geography: Great Systems and Global Environments|year=2012|publisher=Cambridge University Press|isbn=9781107376649|page=510}}</ref>

Soil development on granite reflects the rock's high quartz content and dearth of available bases, with the base-poor status predisposing the soil to [[soil acidification|acidification]] and [[podzol]]ization in cool humid climates as the weather-resistant quartz yields much sand.<ref>{{cite web |url=http://luitool.soilweb.ca/podzols/Land |title=Land Use Impacts |work=Land Use Impacts on Soil Quality |access-date=23 March 2022}}</ref> Feldspars also weather slowly in cool climes, allowing sand to dominate the fine-earth fraction. In warm humid regions, the weathering of feldspar as described above is accelerated so as to allow a much higher proportion of clay with the [[Cecil (soil)|Cecil]] soil series a prime example of the consequent [[Ultisol]] great soil group.<ref>{{cite web |url=https://www.soils4teachers.org/files/s4t/k12outreach/nc-state-soil-booklet.pdf |title=Cecil – North Carolina State Soil |publisher=Soil Science Society of America |access-date=23 March 2022}}</ref>

Fires can also contribute to the weathering of granite. The high temperatures reached during a fire—often exceeding 1000&nbsp;°C—can cause significant physical and chemical processes that alter the rock. Among the physical processes, the differential thermal expansion of individual mineral grains, the anisotropic expansion of certain minerals, and polymorphic transformations, such as the alpha-beta quartz transition, induce substantial volume changes and generate internal stresses that damage the granite.<ref name=":0">{{Cite journal |last=Heuze |first=F. E. |date=1983-02-01 |title=High-temperature mechanical, physical and Thermal properties of granitic rocks— A review |url=https://linkinghub.elsevier.com/retrieve/pii/0148906283916091 |journal=International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts |volume=20 |issue=1 |pages=3–10 |doi=10.1016/0148-9062(83)91609-1 |issn=0148-9062}}</ref><ref name=":1">{{Cite journal |last=Tomás |first=R. |last2=Cano |first2=M. |last3=Pulgarín |first3=L. F. |last4=Brotóns |first4=V. |last5=Benavente |first5=D. |last6=Miranda |first6=T. |last7=Vasconcelos |first7=G. |date=2021-11-01 |title=Thermal effect of high temperatures on the physical and mechanical properties of a granite used in UNESCO World Heritage sites in north Portugal |url=https://linkinghub.elsevier.com/retrieve/pii/S2352710221006811 |journal=Journal of Building Engineering |volume=43 |pages=102823 |doi=10.1016/j.jobe.2021.102823 |issn=2352-7102|hdl=10045/115630 |hdl-access=free }}</ref> Additionally, the decomposition of certain granite constituents, such as phyllosilicates, at specific temperatures further contributes to granite degradation. As a result, granite becomes micro-fractured, its total porosity increases, and its mechanical strength is significantly reduced.<ref name=":0" /><ref name=":1" /><ref>{{Cite journal |last=Sha |first=Song |last2=Rong |first2=Guan |last3=Peng |first3=Jun |last4=Li |first4=Bowen |last5=Wu |first5=Zhijun |date=2019-11-01 |title=Effect of Open-Fire-Induced Damage on Brazilian Tensile Strength and Microstructure of Granite |url=https://link.springer.com/article/10.1007/s00603-019-01871-z |journal=Rock Mechanics and Rock Engineering |language=en |volume=52 |issue=11 |pages=4189–4202 |doi=10.1007/s00603-019-01871-z |issn=1434-453X}}</ref>