Editing Basanite

{{Short description|Type of volcanic rock}}
{{hatnote|This article is about the igneous rock. Basanite is also a variety of [[Jasper#basanite|Jasper]]}}
{{Distinguish|Bassanite}}
{{Infobox rock
|name=Basanite
|alternative_name=
|type=Igneous
|image=Basanite&Dunite bomb.JPG
|image_size=300
|alt=
|caption=[[Volcanic bomb]] of black basanite enclosing a [[xenolith]] of green [[dunite]] from [[Réunion]]
|coordinates=
|composition=
|composition_secondary=
}}
'''Basanite''' ({{IPAc-en|ˈ|b|æ|s|.|ə|ˌ|n|aɪ|t}}) is an [[igneous rock|igneous]], volcanic ([[extrusive]]) [[rock (geology)|rock]] with [[aphanitic]] to [[porphyritic]] texture. It is composed mostly of [[feldspathoid]]s, [[pyroxene]]s, [[olivine]], and calcic [[plagioclase]] and forms from magma low in [[silica]] and enriched in [[alkali metal oxide]]s that solidifies rapidly close to the [[Earth's surface]].

==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>.

==Occurrences==
[[File:Livia Drusilla Louvre Ma1233.jpg|thumb|Basanite sculpture of [[Livia Drusilla]]<ref name="LiviaBasanite">{{cite web | url=https://library.nga.gov/discovery/fulldisplay/alma991077873804896/01NGA_INST:IMAGE | title=Livia | publisher=National Gallery of Art Library | work=Image Collections Digital (NGA Exhibitions, 2008–2009) | accessdate=26 March 2021}}</ref>]]
Basanite appears early in the [[alkaline magma series]] and basanites are found wherever alkaline magma is erupted.<ref>{{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=139–148}}</ref> This includes both continental and ocean island settings. Together with basalts, they are produced by [[Hotspot (geology)|hotspot]] volcanism, for example in the [[Hawaiian Islands]], the [[Comoros Islands]]<ref>{{cite web|url=http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65599.htm|title=Geochemistry and Petrology of a Miocene Trachyte-Basanite Suite from Mt. Tsaratanana, Northern Madagascar|website=gsa.confex.com|access-date=2006-04-05|archive-url=https://web.archive.org/web/20070513192113/http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65599.htm|archive-date=2007-05-13|url-status=dead}}</ref> and the [[Canary Islands]].<ref name="Carracedo 2016"/> They are particularly common in areas of [[rift]]ing.<ref>{{cite book |last1=Fisher |first1=Richard V. |last2=Schmincke |first2=H.-U. |title=Pyroclastic rocks |date=1984 |publisher=Springer-Verlag |location=Berlin |isbn=3540127569 |pages=19–20}}</ref>

During eruption of the [[Laacher See]] [[caldera]] some 12,900 years ago, the final phase of the eruption, which tapped the deepest part of the [[magma chamber]], produced basanite [[lapilli]] mixed with [[phonolite]] lapilli.<ref>{{cite book |last1=Schmincke |first1=Hans-Ulrich |title=Volcanism |date=2003 |publisher=Springer |location=Berlin |isbn=9783540436508 |page=33}}</ref> This has been interpreted as fresh magma injected into the magma chamber that may have helped trigger the eruption.{{sfn|Schmincke|2003|p=205}}

Eruption of basanite and other [[alkaline magma series|alkaline magmas]] characterizes the late alkaline phase (rejuvenation phase)<ref>{{cite book |last1=Macdonald |first1=Gordon A. |last2=Abbott |first2=Agatin T. |last3=Peterson |first3=Frank L. |title=Volcanoes in the sea : the geology of Hawaii |date=1983 |publisher=University of Hawaii Press |location=Honolulu |isbn=0824808320 |pages=152–154 |edition=2nd}}</ref> of volcanic islands, which often comes 3 to 5 million years after the main [[volcanic shield|shield]]-building phase.{{sfn|Schmincke|2003|pp=80-81}}

==See also==
*{{annotated link|Limburgite}}

== References ==
{{Reflist}}
{{Rock type}}

==External links==
{{Commons category|Basanite|position=left}}

{{Authority control}}

[[Category:Aphanitic rocks]]
[[Category:Porphyritic rocks]]
[[Category:Mafic rocks]]
[[Category:Volcanic rocks]]

[[fr:Basalte#La basanite]]