Editing Basanite (section)

==Description==
[[File:Qapf basanite.jpg|thumb|QAPF diagram showing the basanite/tephrite field in yellow]]
[[File:TAS-Diagramm-basanite.png|thumb|TAS diagram with basanite/tephrite field highlighted]]
Basanite is an aphanitic (fine-grained) igneous rock that is low in silica and enriched in alkali metals. Of its total content of quartz, feldspar, and feldspathoid ([[QAPF classification|QAPF]]), between 10% and 60% by volume is feldspathoid and over 90% of the feldspar is plagioclase. Quartz is never present. This places basanite in the basanite/[[tephrite]] field of the QAPF diagram. Basanite is further distinguished from tephrite by having a [[normative mineralogy|normative]] olivine content greater than 10%. While the [[IUGS]] recommends classification by mineral content whenever possible, volcanic rock can be glassy or so fine-grained that this is impractical, and then the rock is classified chemically using the [[TAS classification]]. Basanite then falls into the U1 (basanite-tephrite) field of the TAS diagram. Basanite is again distinguished from tephrite by its normative olivine content and from [[nephelinite]] by a normative [[albite]] content of over 5% and a normative [[nepheline]] content under 20%.<ref>{{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>{{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>

The [[mineral]] assembly in basanite is usually abundant [[feldspathoid]]s ([[nepheline]] or [[leucite]]), [[plagioclase]], and [[augite]], together with [[olivine]] and lesser iron-titanium oxides such as [[ilmenite]] and [[magnetite]]-[[ulvospinel]]; minor alkali [[feldspar]] may be present. [[Clinopyroxene]] ([[augite]]) and [[olivine]] are common as [[phenocryst]]s and in the [[matrix (geology)|matrix]].<ref name="Carracedo 2016">{{Cite book|last=Carracedo|first=J. C.|url=https://www.worldcat.org/oclc/951031503|title=The Geology of the Canary Islands|date=2016|author2=V. R. Troll|isbn=978-0-12-809663-5|location=Amsterdam, Netherlands|publisher=Elsevier|oclc=951031503|doi=10.1016/C2015-0-04268-X}}</ref> The augite contains significantly greater [[titanium]], [[aluminium]] and [[sodium]] than that in typical [[Tholeiite|tholeiitic basalt]].<ref>{{Cite journal|last1=Weis|first1=Franz A.|last2=Skogby|first2=Henrik|last3=Troll|first3=Valentin R.|last4=Deegan|first4=Frances M.|last5=Dahren|first5=Börje|date=2015|title=Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=16|issue=7|pages=2127–2146|doi=10.1002/2015GC005800|bibcode=2015GGG....16.2127W |issn=1525-2027|doi-access=free|hdl=10553/72171|hdl-access=free}}</ref> [[Quartz]] is absent, as are [[orthopyroxene]] and [[pigeonite]].<ref>{{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=0716724383 |pages=164–165 |edition=2nd}}</ref>

Chemically, basanites are [[mafic]]. They are low in [[silica]] (42 to 45% SiO<sub>2</sub>) and high in [[alkali]]s (3 to 5.5% Na<sub>2</sub>O and K<sub>2</sub>O) compared to basalt, which typically contains more SiO<sub>2</sub>, as evident on the diagram used for TAS classification. Nephelinite is yet richer in Na<sub>2</sub>O plus K<sub>2</sub>O compared to SiO<sub>2</sub>.