Editing Feldspar (section)

{{Short description|Group of rock-forming minerals}}
{{Other uses}}
{{Use British English|date=March 2021}}
{{Stack|
{{Infobox mineral
| name        = Feldspar
| category    = [[Tectosilicate]]
| boxwidth    = 
| boxbgcolor  = #eae6de
| image       = Feldspar diversity.png
| imagesize   = 350px
| caption     = Feldspar minerals. Clockwise from top left: [[Orthoclase]], [[Albite]], [[Microcline]], and an indeterminate [[plagioclase]]
| formula     = {{chem|[[Potassium|K]][[Aluminium|Al]][[silicon|Si]]|3|[[Oxygen|O]]|8|&nbsp;– [[Sodium|Na]]AlSi|3|O|8|&nbsp;– [[Calcium|Ca]]Al|2|Si|2|O|8|}}
|IMAsymbol=Fsp<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   = 
| color       = pink, white, gray, brown, blue
| habit       = 
| system      = [[Triclinic]] or [[monoclinic]]
| twinning    = 
| cleavage    = two or three
| fracture    = along cleavage planes
| mohs        = 6.0–6.5
| luster      = Vitreous
| tenacity    = 
| polish      = 
| refractive  = 1.518–1.526
| opticalprop = 
| birefringence = first order
| dispersion  = 
| pleochroism = none
| fluorescence= 
| absorption  = 
| streak      = white
| gravity     = 2.55–2.76
| density     = 2.56
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| diaphaneity = opaque
| other       = exsolution lamellae common
| references  = <ref>{{cite web|title=Feldspar|url=http://www.gemologyonline.com/feldspar.html|work=Gemology Online|access-date=8 November 2012}}</ref> 
}}
}}

'''Feldspar''' ({{IPAc-en|ˈ|f|ɛ|l|(|d|)|ˌ|s|p|ɑːr}} {{respell|FEL(D)|spar}}; sometimes spelled '''felspar''') is a group of rock-forming [[Aluminosilicate|aluminium tectosilicate minerals]], also containing other [[cation]]s such as sodium, calcium, potassium, or barium.<ref name="Glossary2005">{{cite book | title=Glossary of Geology | publisher=American Geological Institute | editor-last1=Neuendorf | editor-first1=K.K.E. | editor-last2=Mehl | editor-first2=J.P. Jr. | editor-last3=Jackson | editor-first3=J.A. | year=2005 | location=Alexandria, Virginia | page=232 | isbn=978-0922152896| edition=5th }}</ref> The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldspars and the ''alkali'' (potassium-sodium) feldspars.<ref name="DeerHowieZussman2001">{{cite book | title=Rock-forming Minerals (2nd edition) Volume 4A | publisher=Geological Society of London | last1=Deer | first1=W.A | last2=Howie | first2=R.A. | last3=Zussman | first3=J. | year=2001 | location=London | pages=2 | isbn=1-86239-081-9}}</ref> Feldspars make up about 60% of the [[Earth's crust]]<ref name="Glossary2005"/> and 41% of the Earth's [[continental crust]] by weight.<ref>{{cite book |first1=Robert S. |last1=Anderson |first2=Suzanne P. |last2=Anderson |title=Geomorphology: The Mechanics and Chemistry of Landscapes |publisher=Cambridge University Press |year=2010 |page=187|url=https://books.google.com/books?id=hDt5A2-km_wC&q=Geomorphology%3A+The+Mechanics+and+Chemistry+of+Landscapes|isbn=9781139788700 }}</ref><ref name="Rudnick2003">{{cite book |chapter=Composition of the Continental Crust |publisher=Elsevier Science |location=New York |first1=R. L. |last1=Rudnick |first2=S. |last2=Gao |title=Treatise on Geochemistry |editor1-first=H. D. |editor1-last=Holland |editor2-first=K. K. |editor2-last=Turekian |volume=3 |pages=1–64 |year=2003 |doi=10.1016/B0-08-043751-6/03016-4 |isbn=978-0-08-043751-4|bibcode=2003TrGeo...3....1R }}</ref>

Feldspars [[crystal]]lize from [[magma]] as both [[Intrusive rock|intrusive]] and [[extrusive]] [[igneous]] rocks<ref>{{Cite journal|last=Troll|first=V. R.|date=2002-02-01|title=Magma Mixing and Crustal Recycling Recorded in Ternary Feldspar from Compositionally Zoned Peralkaline Ignimbrite A', Gran Canaria, Canary Islands|journal=Journal of Petrology|volume=43|issue=2|pages=243–270|doi=10.1093/petrology/43.2.243|bibcode=2002JPet...43..243T|issn=1460-2415|doi-access=free}}</ref> and are also present in many types of [[metamorphic rock]].<ref>"Metamorphic Rocks." <span class="plainlinks">[http://seis.natsci.csulb.edu/bperry/ROCKS.htm Metamorphic Rocks Information] {{webarchive|url=https://web.archive.org/web/20070701111134/http://seis.natsci.csulb.edu/bperry/ROCKS.htm |date=2007-07-01 }}</span>. Retrieved on July 18, 2007</ref> Rock formed almost entirely of calcic [[plagioclase]] feldspar is known as [[anorthosite]].<ref>Blatt, Harvey and Tracy, Robert J. (1996) ''Petrology,'' Freeman, 2nd ed., pp. 206–210 {{ISBN|0-7167-2438-3}}</ref> Feldspars are also found in many types of [[sedimentary rock]]s.<ref>"Weathering and Sedimentary Rocks." <span class="plainlinks">[http://geology.csupomona.edu/drjessey/class/Gsc101/Weathering.html Geology.] {{webarchive |url=https://web.archive.org/web/20070703170212/http://geology.csupomona.edu/drjessey/class/Gsc101/Weathering.html |date=2007-07-03 }}</span> Retrieved on July 18, 2007.</ref>