Editing Granite (section)

==Description==
{{multiple image
|align=right
|perrow=2
|total_width=400

|image1=Granite Rosa Porriño - es (rotated).jpg
|caption1=Granite with a moderate amount of plagioclase, alkali feldspar, and quartz

|image2=Granite BALMORAL.jpg
|caption2=Granite with a composition of alkali feldspar and quartz

}}
The word "granite" comes from the [[Latin]] ''granum'', a grain, in reference to the coarse-grained structure of such a [[holocrystalline|completely crystalline]] rock.<ref name="read-1943">{{cite journal |last1=Read |first1=H.H. |title=Meditations on granite: Part one |journal=Proceedings of the Geologists' Association |date=January 1943 |volume=54 |issue=2 |pages=64–85 |doi=10.1016/S0016-7878(43)80008-0|bibcode=1943PrGA...54...64R }}</ref> Granites can be predominantly white, pink, or gray in color, depending on their [[mineralogy]]. Granitic rocks mainly consist of [[feldspar]], [[quartz]], [[mica]], and [[amphibole]] [[mineral]]s, which form an interlocking, somewhat [[equigranular]] [[Matrix (geology)|matrix]] of feldspar and quartz with scattered darker [[biotite]] mica and amphibole (often [[hornblende]]) peppering the lighter color minerals. Occasionally some individual crystals ([[phenocryst]]s) are larger than the [[groundmass]], in which case the texture is known as [[porphyritic]]. A granitic rock with a porphyritic texture is known as a granite [[Porphyry (geology)|porphyry]]. [[Granitoid]] is a general, descriptive [[Field research|field]] term for lighter-colored, coarse-grained igneous rocks. [[Petrography|Petrographic]] examination is required for identification of specific types of granitoids.<ref>{{cite web |url=http://geology.about.com/od/more_igrocks/a/granitoids.htm |title=Granitoids – Granite and the Related Rocks Granodiorite, Diorite and Tonalite |publisher=Geology.about.com |date=2010-02-06 |access-date=2010-05-09 |archive-date=2009-08-10 |archive-url=https://web.archive.org/web/20090810214900/http://geology.about.com/od/more_igrocks/a/granitoids.htm |url-status=dead }}</ref> The [[alkali feldspar]] in granites is typically [[orthoclase]] or [[microcline]] and is often [[perthitic]]. The plagioclase is typically sodium-rich [[oligoclase]]. Phenocrysts are usually alkali feldspar.<ref name="blatt-tracy-1996-45">{{cite book |last1=Blatt |first1=Harvey |last2=Tracy |first2=Robert J. |title=Petrology : igneous, sedimentary, and metamorphic. |date=1996 |publisher=W.H. Freeman |location=New York |isbn=0-7167-2438-3 |page=45 |edition=2nd}}</ref>

Granitic rocks are classified according to the [[QAPF diagram]] for coarse grained [[pluton|plutonic rocks]] and are named according to the percentage of [[quartz]], alkali feldspar ([[orthoclase]], [[sanidine]], or [[microcline]]) and [[plagioclase]] feldspar on the A-Q-P half of the diagram. True granite (according to modern [[petrology|petrologic]] convention) contains between 20% and 60% quartz by volume, with 35% to 90% of the total feldspar consisting of [[alkali feldspar]]. Granitic rocks poorer in quartz are classified as [[syenite]]s or [[monzonite]]s, while granitic rocks dominated by plagioclase are classified as [[granodiorite]]s or [[tonalite]]s. Granitic rocks with over 90% alkali feldspar are classified as [[alkali feldspar granite]]s. Granitic rock with more than 60% quartz, which is uncommon, is classified simply as quartz-rich granitoid or, if composed almost entirely of quartz, as [[quartzolite]].<ref name="iugs-1991">{{Cite journal|last1=Le Bas|first1=M. J.|last2=Streckeisen|first2=A. L.|title=The IUGS systematics of igneous rocks|journal=Journal of the Geological Society|volume=148|issue=5|pages=825–833|doi=10.1144/gsjgs.148.5.0825|bibcode=1991JGSoc.148..825L|year=1991|citeseerx=10.1.1.692.4446|s2cid=28548230}}</ref><ref name="BGS-1999">{{Cite journal|date=1999|title=Rock Classification Scheme - Vol 1 - Igneous|url=http://nora.nerc.ac.uk/id/eprint/3223/1/RR99006.pdf|journal=British Geological Survey: Rock Classification Scheme|volume=1|pages=1–52}}</ref><ref name="philpotts-ague-2009-139-143">{{cite book |last1=Philpotts |first1=Anthony R. |last2=Ague |first2=Jay J. |title=Principles of igneous and metamorphic petrology |date=2009 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=9780521880060 |edition=2nd |pages=139–143}}</ref>
[[File:Гранит под микроскопом 2.jpg|thumb|left|Granite in [[thin section]], under cross-polarized light]]
True granites are further classified by the percentage of their total feldspar that is alkali feldspar. Granites whose feldspar is 65% to 90% alkali feldspar are [[syenogranite]]s, while the feldspar in [[monzogranite]] is 35% to 65% alkali feldspar.<ref name="BGS-1999"/><ref name="philpotts-ague-2009-139-143"/> A granite containing both muscovite and biotite [[mica]]s is called a binary or ''two-mica'' granite. Two-mica granites are typically high in [[potassium]] and low in plagioclase, and are usually S-type granites or A-type granites, as described [[#Alphabet classification system|below]].<ref name="barbarin-1996">{{cite journal |last1=Barbarin |first1=Bernard |title=Genesis of the two main types of peraluminous granitoids |journal=Geology |date=1 April 1996 |volume=24 |issue=4 |pages=295–298 |doi=10.1130/0091-7613(1996)024<0295:GOTTMT>2.3.CO;2|bibcode=1996Geo....24..295B }}</ref><ref>{{cite journal |last1=Washington |first1=Henry S. |title=The Granites of Washington, D. C. |journal=Journal of the Washington Academy of Sciences |volume=11 |number=19 |year=1921 |pages=v459–470 |jstor=24532555}}</ref>

Another aspect of granite classification is the ratios of metals that potentially form feldspars. Most granites have a composition such that almost all their aluminum and alkali metals (sodium and potassium) are combined as feldspar. This is the case when [[Potassium oxide|K<sub>2</sub>O]] + [[Sodium oxide|Na<sub>2</sub>O]] + [[Calcium oxide|CaO]] > [[Alumina|Al<sub>2</sub>O<sub>3</sub>]] > K<sub>2</sub>O + Na<sub>2</sub>O. Such granites are described as ''normal'' or ''metaluminous''. Granites in which there is not enough aluminum to combine with all the alkali oxides as feldspar (Al<sub>2</sub>O<sub>3</sub> < K<sub>2</sub>O + Na<sub>2</sub>O) are described as ''peralkaline'', and they contain unusual sodium amphiboles such as [[riebeckite]]. Granites in which there is an excess of aluminum beyond what can be taken up in feldspars (Al<sub>2</sub>O<sub>3</sub> > CaO + K<sub>2</sub>O + Na<sub>2</sub>O) are described as ''peraluminous'', and they contain aluminum-rich minerals such as [[muscovite]].<ref>Harvey Blatt; Robert J. Tracy (1997). Petrology (2nd ed). New York: Freeman. p. 66. ISBN 0-7167-2438-3.</ref>

===Physical properties===
The average [[density]] of granite is between {{convert|2.65|and|2.75|g/cm3|lb/ft3|abbr=on}},<ref>{{cite web |url=http://www.edumine.com/xtoolkit/tables/sgtables.htm |title=Rock Types and Specific Gravities |website=EduMine |access-date=2017-08-27 |archive-url=https://web.archive.org/web/20170831000357/http://www.edumine.com/xtoolkit/tables/sgtables.htm |archive-date=2017-08-31 |url-status=dead }}</ref> its [[compressive strength]] usually lies above 200 MPa (29,000 psi), and its [[viscosity]] near [[Standard temperature and pressure|STP]] is 3–6·10<sup>20</sup> Pa·s.<ref>{{cite journal
  | last = Kumagai
  | first = Naoichi
  | author2 = Sadao Sasajima
  | author3 = Hidebumi Ito
  | title = Long-term Creep of Rocks: Results with Large Specimens Obtained in about 20 Years and Those with Small Specimens in about 3 Years
  | journal = Journal of the Society of Materials Science (Japan)
  | volume = 27
  | issue = 293
  | pages = 157–161
  |doi=10.2472/jsms.27.155
  | date = 1978| doi-access = free
  }}</ref>

The melting temperature of dry granite at ambient pressure is {{convert|1215–1260|°C|comma=off}};<ref>{{cite journal |url=http://www.minsocam.org/msa/collectors_corner/arc/tempmagmas.htm |journal=American Mineralogist |volume=14 |pages=81–94 |year=1929 |title=The temperatures of magmas |author=Larsen, Esper S.}}</ref> it is strongly reduced in the presence of water, down to 650&nbsp;°C at a few hundred megapascals of pressure.<ref>{{cite journal |author=Holland, Tim |author2=Powell, Roger |title=Calculation of phase relations involving haplogranitic melts using an internally consistent thermodynamic dataset |journal= Journal of Petrology |volume=42 |issue=4 |pages=673–683 |year=2001 |doi=10.1093/petrology/42.4.673 |bibcode=2001JPet...42..673H|doi-access=free }}</ref>

Granite has poor primary [[permeability (earth sciences)|permeability]] overall, but strong secondary permeability through cracks and fractures if they are present.

===Chemical composition===
[[File:Intrusive big.png|thumb|[[QAPF diagram]] with the granite field in pink]]
A worldwide average of the chemical composition of granite, by mass percent, based on 2485 analyses:<ref name="blatt-tracy-66">Blatt and Tracy 1996, p.66</ref>
{|
| [[Silicon dioxide|SiO<sub>2</sub>]]                 || {{bartable|72.04|% (silica)|5}}
|-
| [[Aluminium oxide|Al<sub>2</sub>O<sub>3</sub>]]     || {{bartable|14.42|% (alumina)|5}}
|-
| [[Potassium oxide|K<sub>2</sub>O]]                  || {{bartable|4.12|%|5}}
|-
| [[Sodium oxide|Na<sub>2</sub>O]]                    || {{bartable|3.69|%|5}}
|-
| [[Calcium oxide|CaO]]                               || {{bartable|1.82|%|5}}
|-
| [[Iron(II) oxide|FeO]]                              || {{bartable|1.68|%|5}}
|-
| [[Iron(III) oxide|Fe<sub>2</sub>O<sub>3</sub>]]     || {{bartable|1.22|%|5}}
|-
| [[Magnesium oxide|MgO]]                             || {{bartable|0.71|%|5}}
|-
| [[Titanium dioxide|TiO<sub>2</sub>]]                || {{bartable|0.30|%|5}}
|-
| [[Phosphorus pentoxide|P<sub>2</sub>O<sub>5</sub>]] || {{bartable|0.12|%|5}}
|-
| [[Manganese(II) oxide|MnO]]                         || {{bartable|0.05|%|5}}
|}

The medium-grained equivalent of granite is '''microgranite'''.<ref name="Microgran">{{cite web | url=https://www.open.edu/openlearn/science-maths-technology/science/geology/microgranite | title=Microgranite | publisher=[[The Open University]] | work=OpenLearn | accessdate=28 December 2021}}</ref> The [[extrusive]] igneous rock equivalent of granite is [[rhyolite]].<ref name="Haldar2014">{{cite book | title=Introduction to Mineralogy and Petrology | publisher=Elsevier |author1=Haldar, S.K.  |author2=Tišljar, J. | year=2014 | page=116 | isbn=978-0-12-408133-8}}</ref>