Editing Basalt (section)

{{short description|Magnesium- and iron-rich extrusive igneous rock}}
{{Other uses}}
{{good article}}
{{pp-semi-indef}}
{{Use British English|date=December 2020}} <!--based on existing usage ("colour")-->
{{Use dmy dates|date=December 2020}} <!--No existing usage; for consistency with British English-->
{{Infobox rock
|name=Basalt
|type=Igneous
|image=Basalt 12 (48674276333).jpg
|image_caption=
|composition=[[Mafic]]: [[plagioclase]], [[amphibole]], and [[pyroxene]]
|composition_secondary=Sometimes [[feldspathoid]]s or [[olivine]]
}}

'''Basalt''' ({{IPAc-en|UK|ˈ|b|æ|s|ɒ|l|t|,_|-|ɔː|l|t|,_|-|əl|t}};<ref name=cambridge>{{Cite dictionary |url=https://dictionary.cambridge.org/dictionary/english/basalt |access-date=4 December 2024 |title=basalt |dictionary=Cambridge Dictionary |publisher=[[Cambridge University Press]]}}</ref><ref name=lexico>{{Cite dictionary |url=http://www.lexico.com/definition/basalt |archive-url=https://web.archive.org/web/20200203123653/https://www.lexico.com/definition/basalt |url-status=dead |archive-date=3 February 2020 |title=basalt |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}</ref> {{IPAc-en|US|b|ə|ˈ|s|ɔː|l|t|,_|ˈ|b|eɪ|s|ɔː|l|t}})<ref name=MW>{{cite Merriam-Webster|basalt}}</ref> is an [[aphanite|aphanitic]] (fine-grained) [[extrusive]] [[igneous rock]] formed from the rapid cooling of low-[[viscosity]] [[lava]] rich in [[magnesium]] and [[iron]] ([[mafic]] lava) exposed at or very near the [[planetary surface|surface]] of a [[terrestrial planet|rocky planet]] or [[natural satellite|moon]]. More than 90% of all [[volcanic rock]] on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained [[gabbro]]. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the [[Solar System]]. For example, the bulk of the plains of [[volcanism on Venus|Venus]], which cover ~80% of the surface, are basaltic; the [[lunar mare|lunar maria]] are plains of flood-basaltic [[lava flow]]s; and basalt is a common rock on the surface of [[Mars]].

Molten basalt lava has a low viscosity due to its relatively low [[silica]] content (between 45% and 52%), resulting in rapidly moving lava flows that can spread over great areas before cooling and solidifying. [[Flood basalt]]s are thick sequences of many such flows that can cover hundreds of thousands of square kilometres and constitute the most voluminous of all volcanic formations.

Basaltic [[magma]]s within Earth are thought to originate from the [[upper mantle (Earth)|upper mantle]]. The chemistry of basalts thus provides clues to processes deep in [[structure of Earth|Earth's interior]].
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