basalt#Columnar basalt

File:Basalt qapf.jpg with basalt/andesite field highlighted in yellow. Basalt is distinguished from andesite by SiO₂ < 52%.]]

File:TAS-Diagramm-basalt.png.]]

File:VesicularBasalt1.jpg, Arizona. US quarter (24mm) for scale.]]

Columnar basalt flows in [[Yellowstone National Park, US|thumb]]

Basalt is composed mostly of oxides of silicon, iron, magnesium, potassium, aluminum, titanium, and calcium. Geologists classify igneous rock by its mineral content whenever possible; the relative volume percentages of quartz (crystalline silica (SiO₂)), alkali feldspar, plagioclase, and feldspathoid (QAPF) are particularly important. An aphanitic (fine-grained) igneous rock is classified as basalt when its QAPF fraction is composed of less than 10% feldspathoid and less than 20% quartz, and plagioclase makes up at least 65% of its feldspar content. This places basalt in the basalt/andesite field of the QAPF diagram. Basalt is further distinguished from andesite by its silica content of under 52%.{{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}}{{Cite journal|date=1999|title=Rock Classification Scheme - Vol 1 - Igneous|url=http://nora.nerc.ac.uk/id/eprint/3223/1/RR99006.pdf |archive-url=https://web.archive.org/web/20180329022649/http://nora.nerc.ac.uk/id/eprint/3223/1/RR99006.pdf |archive-date=2018-03-29 |url-status=live|journal=British Geological Survey: Rock Classification Scheme|volume=1|pages=1–52}}{{Cite web|url=http://geology.csupomona.edu/alert/igneous/igclass.htm|title=CLASSIFICATION OF IGNEOUS ROCKS|archive-url=https://web.archive.org/web/20110930102012/http://geology.csupomona.edu/alert/igneous/igclass.htm|archive-date=30 September 2011|url-status=dead}}{{sfn|Philpotts|Ague|2009|pp=139–143}}

It is often not practical to determine the mineral composition of volcanic rocks, due to their very small grain size, in which case geologists instead classify the rocks chemically, with particular emphasis on the total content of alkali metal oxides and silica (TAS); in that context, basalt is defined as volcanic rock with a content of between 45% and 52% silica and no more than 5% alkali metal oxides. This places basalt in the B field of the TAS diagram.{{sfn|Philpotts|Ague|2009|pp=139–143}} Such a composition is described as mafic.{{cite web |url=http://www.glossary.oilfield.slb.com/en/Terms/m/mafic.aspx |publisher=Schlumberger Ltd. |title=Oilfield Glossary |year=2021}}

Basalt is usually dark grey to black in colour, due to a high content of augite or other dark-coloured pyroxene minerals,{{sfn|Hyndman|1985|p={{pn|date=June 2021}}}}{{sfn|Blatt|Tracy|1996|p=57}}{{sfn|Levin|2010|p=63}} but can exhibit a wide range of shading. Some basalts are quite light-coloured due to a high content of plagioclase; these are sometimes described as leucobasalts.{{cite journal |last1=Wilson |first1=F. H. |title=The Meshik Arc – an eocene to earliest miocene magmatic arc on the Alaska Peninsula |date=1985 |pages=PR 88 |doi=10.14509/2269|doi-access=free |journal=Alaska Division of Geological & Geophysical Surveys Professional Report |volume=88|bibcode=1985usgs.rept....1W }}{{cite journal |last1=Nozhkin |first1=A.D. |last2=Turkina |first2=O.M. |last3=Likhanov |first3=I.I. |last4=Dmitrieva |first4=N.V. |title=Late Paleoproterozoic volcanic associations in the southwestern Siberian craton (Angara-Kan block) |journal=Russian Geology and Geophysics |date=February 2016 |volume=57 |issue=2 |pages=247–264 |doi=10.1016/j.rgg.2016.02.003|bibcode=2016RuGG...57..247N }} It can be difficult to distinguish between lighter-colored basalt and andesite, so field researchers commonly use a rule of thumb for this purpose, classifying it as basalt if it has a color index of 35 or greater.{{sfn|Philpotts|Ague|2009|p=139}}

The physical properties of basalt result from its relatively low silica content and typically high iron and magnesium content.{{cite web | url=https://volcanoes.usgs.gov/vsc/glossary/basalt.html | title=Basalt | publisher=USGS | website=USGS Volcano Hazards program – Glossary | date=8 April 2015 | access-date=27 July 2018}} The average density of basalt is 2.9 g/cm³, compared, for example, to granite’s typical density of 2.7 g/cm³.{{sfn|Philpotts|Ague|2009|p=22}} The viscosity of basaltic magma is relatively low—around 10⁴ to 10⁵ cP—similar to the viscosity of ketchup, but that is still several orders of magnitude higher than the viscosity of water, which is about 1 cP).{{sfn|Philpotts|Ague|2009|pp=23–25}}

Basalt is often porphyritic, containing larger crystals (phenocrysts) that formed before the extrusion event that brought the magma to the surface, embedded in a finer-grained matrix. These phenocrysts are usually made of augite, olivine, or a calcium-rich plagioclase,{{sfn|Blatt|Tracy|1996|p=57}} which have the highest melting temperatures of any of the minerals that can typically crystallize from the melt, and which are therefore the first to form solid crystals.{{sfn|Klein|Hurlbut|1993|pp=558–560}}{{cite web |last1=Nave |first1=R. |title=Bowen's Reaction Series |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Geophys/Bowen.html |website=Hyperphysics |publisher=Georgia State University |access-date=24 March 2021}}

Basalt often contains vesicles; they are formed when dissolved gases bubble out of the magma as it decompresses during its approach to the surface; the erupted lava then solidifies before the gases can escape. When vesicles make up a substantial fraction of the volume of the rock, the rock is described as scoria.{{sfn|Blatt|Tracy|1996|pp=27, 42–44}}{{cite web |last1=Jones |first1=C.E. |title=Scoria and Pumice |url=https://www.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousTextures/8PumiceScoria.html |website=Department of Geology & Planetary Science |publisher=University of Pittsburgh |access-date=24 March 2021}}

The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarser) groundmass are more properly referred to either as diabase (also called dolerite) or—when they are more coarse-grained (having crystals over 2 mm across)—as gabbro. Diabase and gabbro are thus the hypabyssal and plutonic equivalents of basalt.{{sfn|Levin|2010|pp=58–60}}

File:Szentgyörgyhegy03.jpg

During the Hadean, Archean, and early Proterozoic eons of Earth's history, the chemistry of erupted magmas was significantly different from what it is today, due to immature crustal and asthenosphere differentiation. The resulting ultramafic volcanic rocks, with silica (SiO₂) contents below 45% and high magnesium oxide (MgO) content, are usually classified as komatiites.{{sfn|Philpotts|Ague|2009|pp=399–400}}{{cite web |title=Komatiite |url=http://www.atlas-hornin.sk/en/record/54/komatiite |website=Atlas of Magmatic Rocks |publisher=Comenius University in Bratislava |access-date=24 March 2021}}

The word "basalt" is ultimately derived from Late Latin {{Lang|la|basaltes}}, a misspelling of Latin {{Lang|la|basanites}} "very hard stone", which was imported from Ancient Greek {{Lang|grc|βασανίτης}} ({{Transliteration|grc|basanites}}), from {{Lang|grc|βάσανος}} ({{Transliteration|grc|basanos}}, "touchstone").{{cite journal |last1=Tietz |first1=O. |last2=Büchner |first2=J. |title=The origin of the term 'basalt' |journal=Journal of Geosciences |date=29 December 2018 |pages=295–298 |doi=10.3190/jgeosci.273|doi-access=free }} The modern petrological term basalt, describing a particular composition of lava-derived rock, became standard because of its use by Georgius Agricola in 1546, in his work De Natura Fossilium. Agricola applied the term "basalt" to the volcanic black rock beneath the Bishop of Meissen's Stolpen castle, believing it to be the same as the "basaniten" described by Pliny the Elder in AD 77 in {{Lang|la|Naturalis Historiae}}.{{cite journal |last1=Tietz |first1=Olaf |last2=Büchner |first2=Joerg |title=The origin of the term 'basalt' |journal=Journal of Geosciences |date=2018 |volume=63 |issue=4 |pages=295–298 |doi=10.3190/jgeosci.273 |url=http://www.jgeosci.org/content/jgeosci.273_tietz.pdf |archive-url=https://web.archive.org/web/20190428204828/http://www.jgeosci.org/content/jgeosci.273_tietz.pdf |archive-date=2019-04-28 |url-status=live |access-date=19 August 2020|doi-access=free }}

File:Causeway23.jpg in Northern Ireland]]

File:Базальтове.jpg, Ukraine]]

On Earth, most basalt is formed by decompression melting of the mantle.{{sfn|Philpotts|Ague|2009|pp=16–17}} The high pressure in the upper mantle (due to the weight of the overlying rock) raises the melting point of mantle rock, so that almost all of the upper mantle is solid. However, mantle rock is ductile (the solid rock slowly deforms under high stress). When tectonic forces cause hot mantle rock to creep upwards, pressure on the ascending rock decreases, and this can lower its melting point enough for the rock to partially melt, producing basaltic magma.{{cite book |doi=10.1029/GM013p0489 |chapter=The Origin of Basalt Magmas |title=The Earth's Crust and Upper Mantle |series=Geophysical Monograph Series |year=2013 |last1=Green |first1=D. H. |last2=Ringwood |first2=A. E. |volume=13 |pages=489–495 |isbn=978-1-118-66897-9 |bibcode=1969GMS....13..489G }}

Decompression melting can occur in a variety of tectonic settings, including in continental rift zones, at mid-ocean ridges, above geological hotspots,{{sfn|Blatt|Tracy|1996|pp=151–156, 191–195, 162–163, 200}}{{sfn|Philpotts|Ague|2009|pp=236, 593–595}} and in back-arc basins.{{cite journal |last1=Stern |first1=Robert J. |title=Subduction zones |journal=Reviews of Geophysics |date=2002 |volume=40 |issue=4 |pages=1012 |doi=10.1029/2001RG000108 |bibcode=2002RvGeo..40.1012S |s2cid=15347100 |doi-access=free }} Basalt also forms in subduction zones, where mantle rock rises into a mantle wedge above the descending slab. The slab releases water vapor and other volatiles as it descends, which further lowers the melting point, further increasing the amount of decompression melting.{{sfn|Stern|2002|p=22–24}} Each tectonic setting produces basalt with its own distinctive characteristics.{{sfn|Philpotts|Ague|2009|pp=356–361}}

• Tholeiitic basalt, which is relatively rich in iron and poor in alkali metals and aluminium,{{sfn|Philpotts|Ague|2009|pp=143–146}} include most basalts of the ocean floor, most large oceanic islands,{{sfn|Philpotts|Ague|2009|pp=365–370}} and continental flood basalts such as the Columbia River Plateau.{{sfn|Philpotts|Ague|2009|pp=52–59}}
• High- and low-titanium basalt rocks, which are sometimes classified based on their titanium (Ti) content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalt have been distinguished from each other in the Paraná and Etendeka traps{{cite journal |last1=Gibson |first1=S. A. |last2=Thompson |first2=R. N. |last3=Dickin |first3=A. P. |last4=Leonardos |first4=O. H. |title=High-Ti and low-Ti mafic potassic magmas: Key to plume-lithosphere interactions and continental flood-basalt genesis |journal=Earth and Planetary Science Letters |date=December 1995 |volume=136 |issue=3–4 |pages=149–165 |doi=10.1016/0012-821X(95)00179-G |bibcode=1995E&PSL.136..149G }} and the Emeishan Traps.{{cite journal |last1=Hou |first1=Tong |last2=Zhang |first2=Zhaochong |last3=Kusky |first3=Timothy |last4=Du |first4=Yangsong |last5=Liu |first5=Junlai |last6=Zhao |first6=Zhidan |title=A reappraisal of the high-Ti and low-Ti classification of basalts and petrogenetic linkage between basalts and mafic–ultramafic intrusions in the Emeishan Large Igneous Province, SW China |journal=Ore Geology Reviews |date=October 2011 |volume=41 |issue=1 |pages=133–143 |doi=10.1016/j.oregeorev.2011.07.005 |bibcode=2011OGRv...41..133H }}
• Mid-ocean ridge basalt (MORB) is a tholeiitic basalt that has almost exclusively erupted at ocean ridges; it is characteristically low in incompatible elements.{{sfn|Blatt|Tracy|1996|pp=156–158}}{{sfn|Hyndman|1985|p={{pn|date=June 2021}}}} Although all MORBs are chemically similar, geologists recognize that they vary significantly in how depleted they are in incompatible elements. When they are present in close proximity along mid-ocean ridges, that is seen as evidence for mantle inhomogeneity.{{cite journal |last1=Waters |first1=Christopher L. |last2=Sims |first2=Kenneth W. W. |last3=Perfit |first3=Michael R. |last4=Blichert-Toft |first4=Janne |author4-link=Janne Blichert-Toft |last5=Blusztajn |first5=Jurek |title=Perspective on the Genesis of E-MORB from Chemical and Isotopic Heterogeneity at 9–10°N East Pacific Rise |journal=Journal of Petrology |date=March 2011 |volume=52 |issue=3 |pages=565–602 |doi=10.1093/petrology/egq091 |doi-access=free }}
• Enriched MORB (E-MORB) is defined as MORB that is relatively undepleted in incompatible elements. It was once thought to be mostly located in hot spots along mid-ocean ridges, such as Iceland, but it is now known to be located in many other places along those ridges.{{cite journal |last1=Donnelly |first1=Kathleen E. |last2=Goldstein |first2=Steven L. |last3=Langmuir |first3=Charles H. |last4=Spiegelman |first4=Marc |title=Origin of enriched ocean ridge basalts and implications for mantle dynamics |journal=Earth and Planetary Science Letters |date=October 2004 |volume=226 |issue=3–4 |pages=347–366 |doi=10.1016/j.epsl.2004.07.019|bibcode=2004E&PSL.226..347D }}
• Normal MORB (N-MORB) is defined as MORB that has an average amount of incompatible elements.
• D-MORB, depleted MORB, is defined as MORB that is highly depleted in incompatible elements.
• Alkali basalt is relatively rich in alkali metals. It is silica-undersaturated and may contain feldspathoids,{{sfn|Philpotts|Ague|2009|pp=143–146}} alkali feldspar, phlogopite, and kaersutite. Augite in alkali basalts is titanium-enriched augite; low-calcium pyroxenes are never present.{{sfn|Blatt|Tracy|1996|p=75}} They are characteristic of continental rifting and hotspot volcanism.{{sfn|Philpotts|Ague|2009|pp=368–370, 390–394}}
• High-alumina basalt has greater than 17% alumina (Al₂O₃) and is intermediate in composition between tholeiitic basalt and alkali basalt. Its relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. These represent the low-silica end of the calc-alkaline magma series and are characteristic of volcanic arcs above subduction zones.{{sfn|Philpotts|Ague|2009|pp=375–376}}
• Boninite is a high-magnesium form of basalt that is erupted generally in back-arc basins; it is distinguished by its low titanium content and trace-element composition.{{sfn|Crawford|1989|p={{pn|date=June 2021}}}}
• Ocean island basalts include both tholeiites and alkali basalts; the tholeiites predominate early in the eruptive history of the island. These basalts are characterized by elevated concentrations of incompatible elements, which suggests that their source mantle rock has produced little magma in the past (it is undepleted).{{sfn|Philpotts|Ague|2009|pp=368–370}}

File:Мікрофотографія шліфа базальту із заповідника Базальтові стовпи в поляризованому світлі.jpg of a thin section of basalt from Bazaltove, Ukraine]]

The mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene. Olivine can also be a significant constituent.{{sfn|Levin|2010|p=62}} Accessory minerals present in relatively minor amounts include iron oxides and iron-titanium oxides, such as magnetite, ulvöspinel, and ilmenite.{{sfn|Blatt|Tracy|1996|p=75}} Because of the presence of such oxide minerals, basalt can acquire strong magnetic signatures as it cools, and paleomagnetic studies have made extensive use of basalt.{{sfn|Levin|2010|p=185}}

In tholeiitic basalt, pyroxene (augite and orthopyroxene or pigeonite) and calcium-rich plagioclase are common phenocryst minerals. Olivine may also be a phenocryst, and when present, may have rims of pigeonite. The groundmass contains interstitial quartz or tridymite or cristobalite. Olivine tholeiitic basalt has augite and orthopyroxene or pigeonite with abundant olivine, but olivine may have rims of pyroxene and is unlikely to be present in the groundmass.{{sfn|Blatt|Tracy|1996|p=75}}

Alkali basalts typically have mineral assemblages that lack orthopyroxene but contain olivine. Feldspar phenocrysts typically are labradorite to andesine in composition. Augite is rich in titanium compared to augite in tholeiitic basalt. Minerals such as alkali feldspar, leucite, nepheline, sodalite, phlogopite mica, and apatite may be present in the groundmass.{{sfn|Blatt|Tracy|1996|p=75}}

Basalt has high liquidus and solidus temperatures—values at the Earth's surface are near or above 1200 °C (liquidus){{sfn|McBirney|1984|pp=366–367}} and near or below 1000 °C (solidus); these values are higher than those of other common igneous rocks.{{sfn|Philpotts|Ague|2009|p=252}}

The majority of tholeiitic basalts are formed at approximately 50–100 km depth within the mantle. Many alkali basalts may be formed at greater depths, perhaps as deep as 150–200 km.{{cite book |doi=10.1016/B978-075063386-4/50003-3 |chapter=Tectonic settings |title=Plate Tectonics and Crustal Evolution |year=1997 |last1=Condie |first1=Kent C. |pages=69–109 |isbn=978-0-7506-3386-4 }}{{cite journal |last1=Kushiro |first1=Ikuo |title=Origin of magmas in subduction zones: a review of experimental studies |journal=Proceedings of the Japan Academy, Series B |date=2007 |volume=83 |issue=1 |pages=1–15 |doi=10.2183/pjab.83.1 |pmid=24019580 |pmc=3756732 |bibcode=2007PJAB...83....1K }} The origin of high-alumina basalt continues to be controversial, with disagreement over whether it is a primary melt or derived from other basalt types by fractionation.{{cite journal|last1=Ozerov|first1=Alexei Y|title=The evolution of high-alumina basalts of the Klyuchevskoy volcano, Kamchatka, Russia, based on microprobe analyses of mineral inclusions|journal=Journal of Volcanology and Geothermal Research|date=January 2000|volume=95|issue=1–4|pages=65–79|doi=10.1016/S0377-0273(99)00118-3|bibcode=2000JVGR...95...65O|url=http://repo.kscnet.ru/2569/1/my_2000_f_en_JVGR.pdf |archive-url=https://web.archive.org/web/20200306105257/http://repo.kscnet.ru/2569/1/my_2000_f_en_JVGR.pdf |archive-date=2020-03-06 |url-status=live}}{{rp|65}}

Relative to most common igneous rocks, basalt compositions are rich in MgO and CaO and low in SiO₂ and the alkali oxides, i.e., Na₂O + K₂O, consistent with their TAS classification. Basalt contains more silica than picrobasalt and most basanites and tephrites but less than basaltic andesite. Basalt has a lower total content of alkali oxides than trachybasalt and most basanites and tephrites.{{sfn|Philpotts|Ague|2009|pp=139–143}}

Basalt generally has a composition of 45–52 wt% SiO₂, 2–5 wt% total alkalis,{{sfn|Philpotts|Ague|2009|pp=139–143}} 0.5–2.0 wt% TiO₂, 5–14 wt% FeO and 14 wt% or more Al₂O₃. Contents of CaO are commonly near 10 wt%, those of MgO commonly in the range 5 to 12 wt%.{{cite journal |last1=Irvine |first1=T. N. |last2=Baragar |first2=W. R. A. |title=A Guide to the Chemical Classification of the Common Volcanic Rocks |journal=Canadian Journal of Earth Sciences |date=1 May 1971 |volume=8 |issue=5 |pages=523–548 |doi=10.1139/e71-055|bibcode=1971CaJES...8..523I }}

High-alumina basalts have aluminium contents of 17–19 wt% Al₂O₃; boninites have magnesium (MgO) contents of up to 15 percent. Rare feldspathoid-rich mafic rocks, akin to alkali basalts, may have Na₂O + K₂O contents of 12% or more.{{sfn|Irvine|Baragar|1971}}

The abundances of the lanthanide or rare-earth elements (REE) can be a useful diagnostic tool to help explain the history of mineral crystallisation as the melt cooled. In particular, the relative abundance of europium compared to the other REE is often markedly higher or lower, and called the europium anomaly. It arises because Eu²⁺ can substitute for Ca²⁺ in plagioclase feldspar, unlike any of the other lanthanides, which tend to only form ³⁺ cations.{{sfn|Philpotts|Ague|2009|p=359}}

Mid-ocean ridge basalts (MORB) and their intrusive equivalents, gabbros, are the characteristic igneous rocks formed at mid-ocean ridges. They are tholeiitic basalts particularly low in total alkalis and in incompatible trace elements, and they have relatively flat REE patterns normalized to mantle or chondrite values. In contrast, alkali basalts have normalized patterns highly enriched in the light REE, and with greater abundances of the REE and of other incompatible elements. Because MORB basalt is considered a key to understanding plate tectonics, its compositions have been much studied. Although MORB compositions are distinctive relative to average compositions of basalts erupted in other environments, they are not uniform. For instance, compositions change with position along the Mid-Atlantic Ridge, and the compositions also define different ranges in different ocean basins.{{cite book |doi=10.1016/B978-0-08-095975-7.00203-5 |chapter=Sampling Mantle Heterogeneity through Oceanic Basalts: Isotopes and Trace Elements |title=Treatise on Geochemistry |year=2014 |last1=Hofmann |first1=A.W. |pages=67–101 |isbn=978-0-08-098300-4 }} Mid-ocean ridge basalts have been subdivided into varieties such as normal (NMORB) and those slightly more enriched in incompatible elements (EMORB).{{sfn|Philpotts|Ague|2009|p=312}}

Isotope ratios of elements such as strontium, neodymium, lead, hafnium, and osmium in basalts have been much studied to learn about the evolution of the Earth's mantle.{{sfn|Philpotts|Ague|2009|loc=Chapter 13}} Isotopic ratios of noble gases, such as ³He/⁴He, are also of great value: for instance, ratios for basalts range from 6 to 10 for mid-ocean ridge tholeiitic basalt (normalized to atmospheric values), but to 15–24 and more for ocean-island basalts thought to be derived from mantle plumes.{{cite journal |last1=Class |first1=Cornelia |last2=Goldstein |first2=Steven L. |title=Evolution of helium isotopes in the Earth's mantle |journal=Nature |date=August 2005 |volume=436 |issue=7054 |pages=1107–1112 |doi=10.1038/nature03930|pmid=16121171 |bibcode=2005Natur.436.1107C |s2cid=4396462 }}

Source rocks for the partial melts that produce basaltic magma probably include both peridotite and pyroxenite.{{cite journal|author=Alexander V. Sobolev|author2=Albrecht W. Hofmann|author3=Dmitry V. Kuzmin|author4=Gregory M. Yaxley|author5=Nicholas T. Arndt|author6-link=Sun-Lin Chung|author6=Sun-Lin Chung|author7=Leonid V. Danyushevsky|author8=Tim Elliott|author9=Frederick A. Frey|author10=Michael O. Garcia|author11=Andrey A. Gurenko|author12=Vadim S. Kamenetsky|author13=Andrew C. Kerr|author14=Nadezhda A. Krivolutskaya|author15=Vladimir V. Matvienkov|author16=Igor K. Nikogosian|author17=Alexander Rocholl|author18=Ingvar A. Sigurdsson|author19=Nadezhda M. Sushchevskaya|author20=Mengist Teklay|name-list-style=amp |title=The Amount of Recycled Crust in Sources of Mantle-Derived Melts|journal=Science|date=20 April 2007|volume=316|issue=5823|pages=412–417|bibcode=2007Sci...316..412S|doi=10.1126/science.x|pmid=17395795|url=http://eprints.utas.edu.au/2614/1/Science2007.pdf}}

File:20011005-0039 DAS large.jpg

The shape, structure and texture of a basalt is diagnostic of how and where it erupted—for example, whether into the sea, in an explosive cinder eruption or as creeping pāhoehoe lava flows, the classic image of Hawaiian basalt eruptions.{{sfn|Schmincke|2003|p={{pn|date=June 2021}}}}

{{Main|Subaerial eruption}}

Basalt that erupts under open air (that is, subaerially) forms three distinct types of lava or volcanic deposits: scoria; ash or cinder (breccia);{{sfn|Blatt|Tracy|1996|pp=27–28}} and lava flows.{{sfn|Blatt|Tracy|1996|pp=22–23}}

Basalt in the tops of subaerial lava flows and cinder cones will often be highly vesiculated, imparting a lightweight "frothy" texture to the rock.{{sfn|Blatt|Tracy|1996|pp=43–44}} Basaltic cinders are often red, coloured by oxidized iron from weathered iron-rich minerals such as pyroxene.{{sfn|Lillie|2005|p=41}}

{{okina}}A{{okina}}ā types of blocky cinder and breccia flows of thick, viscous basaltic lava are common in Hawai{{okina}}i. Pāhoehoe is a highly fluid, hot form of basalt which tends to form thin aprons of molten lava which fill up hollows and sometimes forms lava lakes. Lava tubes are common features of pāhoehoe eruptions.{{sfn|Blatt|Tracy|1996|pp=22–23}}

Basaltic tuff or pyroclastic rocks are less common than basaltic lava flows. Usually basalt is too hot and fluid to build up sufficient pressure to form explosive lava eruptions but occasionally this will happen by trapping of the lava within the volcanic throat and buildup of volcanic gases. Hawai{{okina}}i's Mauna Loa volcano erupted in this way in the 19th century, as did Mount Tarawera, New Zealand in its violent 1886 eruption. Maar volcanoes are typical of small basalt tuffs, formed by explosive eruption of basalt through the crust, forming an apron of mixed basalt and wall rock breccia and a fan of basalt tuff further out from the volcano.{{sfn|Schmincke|2003|loc=Chapter 12}}

Amygdaloidal structure is common in relict vesicles and beautifully crystallized species of zeolites, quartz or calcite are frequently found.{{sfn|Philpotts|Ague|2009|p=64}}

{{Main|Columnar jointing}}

{{See also|List of places with columnar basalt}}

File:Causeway-code poet-4.jpg in Northern Ireland]]

File:Boyabat.jpg basalt in Turkey]]

File:Мыс Столбчатый. После заката.jpg, Russia]]

During the cooling of a thick lava flow, contractional joints or fractures form.{{cite journal |last1=Smalley |first1=I. J. |title=Contraction Crack Networks in Basalt Flows |journal=Geological Magazine |date=April 1966 |volume=103 |issue=2 |pages=110–114 |doi=10.1017/S0016756800050482 |bibcode=1966GeoM..103..110S |s2cid=131237003 }} If a flow cools relatively rapidly, significant contraction forces build up. While a flow can shrink in the vertical dimension without fracturing, it cannot easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. These structures, or basalt prisms, are predominantly hexagonal in cross-section, but polygons with three to twelve or more sides can be observed.{{cite journal |last1=Weaire |first1=D. |last2=Rivier |first2=N. |title=Soap, cells and statistics—random patterns in two dimensions |journal=Contemporary Physics |date=January 1984 |volume=25 |issue=1 |pages=59–99 |doi=10.1080/00107518408210979 |bibcode=1984ConPh..25...59W }} The size of the columns depends loosely on the rate of cooling; very rapid cooling may result in very small (<1 cm diameter) columns, while slow cooling is more likely to produce large columns.{{cite journal |last1=Spry |first1=Alan |title=The origin of columnar jointing, particularly in basalt flows |journal=Journal of the Geological Society of Australia |date=January 1962 |volume=8 |issue=2 |pages=191–216 |doi=10.1080/14400956208527873 |bibcode=1962AuJES...8..191S }}

{{Main|Submarine eruption}}

File:Pillow basalt crop l.jpg

The character of submarine basalt eruptions is largely determined by depth of water, since increased pressure restricts the release of volatile gases and results in effusive eruptions.Francis, P. (1993) Volcanoes: A Planetary Perspective, Oxford University Press. It has been estimated that at depths greater than {{convert|500|m||}}, explosive activity associated with basaltic magma is suppressed.{{sfn|Parfitt|Parfitt|Wilson|2008|p={{pn|date=June 2021}}}} Above this depth, submarine eruptions are often explosive, tending to produce pyroclastic rock rather than basalt flows.{{cite journal |last1=Head |first1=James W. |last2=Wilson |first2=Lionel |title=Deep submarine pyroclastic eruptions: theory and predicted landforms and deposits |journal=Journal of Volcanology and Geothermal Research |date=2003 |volume=121 |issue=3–4 |pages=155–193 |doi=10.1016/S0377-0273(02)00425-0 |bibcode=2003JVGR..121..155H }} These eruptions, described as Surtseyan, are characterised by large quantities of steam and gas and the creation of large amounts of pumice.[http://www.volcano.si.edu/galleries.cfm?p=11], Smithsonian Institution National Museum of Natural History Global Volcanism Program (2013).

{{Main|Pillow lava}}

When basalt erupts underwater or flows into the sea, contact with the water quenches the surface and the lava forms a distinctive pillow shape, through which the hot lava breaks to form another pillow. This "pillow" texture is very common in underwater basaltic flows and is diagnostic of an underwater eruption environment when found in ancient rocks. Pillows typically consist of a fine-grained core with a glassy crust and have radial jointing. The size of individual pillows varies from 10 cm up to several metres.{{sfn|Schmincke|2003|p=64}}

When pāhoehoe lava enters the sea it usually forms pillow basalts. However, when {{okina}}a{{okina}}ā enters the ocean it forms a littoral cone, a small cone-shaped accumulation of tuffaceous debris formed when the blocky {{okina}}a{{okina}}ā lava enters the water and explodes from built-up steam.{{sfn|Macdonald|Abbott|Peterson|1983|p={{pn|date=June 2021}}}}

The island of Surtsey in the Atlantic Ocean is a basalt volcano which breached the ocean surface in 1963. The initial phase of Surtsey's eruption was highly explosive, as the magma was quite fluid, causing the rock to be blown apart by the boiling steam to form a tuff and cinder cone. This has subsequently moved to a typical pāhoehoe-type behaviour.{{cite journal |last1=Kokelaar |first1=B.Peter |last2=Durant |first2=Graham P. |title=The submarine eruption and erosion of Surtla (Surtsey), Iceland |journal=Journal of Volcanology and Geothermal Research |date=December 1983 |volume=19 |issue=3–4 |pages=239–246 |doi=10.1016/0377-0273(83)90112-9|bibcode=1983JVGR...19..239K }}{{cite journal |last1=Moore |first1=James G. |title=Structure and eruptive mechanisms at Surtsey Volcano, Iceland |journal=Geological Magazine |date=November 1985 |volume=122 |issue=6 |pages=649–661 |doi=10.1017/S0016756800032052 |bibcode=1985GeoM..122..649M |s2cid=129242411 }}

Volcanic glass may be present, particularly as rinds on rapidly chilled surfaces of lava flows, and is commonly (but not exclusively) associated with underwater eruptions.{{sfn|Blatt|Tracy|1996|pp=24–25}}

Pillow basalt is also produced by some subglacial volcanic eruptions.{{sfn|Blatt|Tracy|1996|pp=24–25}}

Basalt is the most common volcanic rock type on Earth, making up over 90% of all volcanic rock on the planet.{{cite web | url=https://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/basalt.html | title=Basalt | publisher=The University of Auckland | website=Geology: rocks and minerals | date=2005 | access-date=27 July 2018}} The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below the ocean ridges.{{sfn|Philpotts|Ague|2009|pp=366–368}} Basalt is also the principal volcanic rock in many oceanic islands, including the islands of Hawai{{okina}}i,{{sfn|Philpotts|Ague|2009|pp=365–370}} the Faroe Islands,{{sfn|Schmincke|2003|p=91}} and Réunion.{{cite journal |last1=Upton |first1=B. G. J. |last2=Wadsworth |first2=W. J. |title=Geology of Réunion Island, Indian Ocean |journal=Nature |date=July 1965 |volume=207 |issue=4993 |pages=151–154 |doi=10.1038/207151a0 |bibcode=1965Natur.207..151U |s2cid=4144134 }} The eruption of basalt lava is observed by geologists at about 20 volcanoes per year.{{Cite book |last1=Walker |first1=G.P.L. |chapter=Basaltic-volcano systems |editor1-last=Prichard |editor1-first=H.M. |editor2-last=Alabaster |editor2-first=T. |editor3-last=Harris |editor3-first=N.B.W. |editor4-last=Neary |editor4-first=C.R. |title=Magmatic Processes and Plate Tectonics |pages=3–38 |publisher=The Geological Society |series=Geological Society Special Publication 76 |date=1993 |isbn=978-0-903317-94-8 }}

File:Parana traps.JPG, Brazil]]

Basalt is the rock most typical of large igneous provinces. These include continental flood basalts, the most voluminous basalts found on land.{{sfn|Philpotts|Ague|2009|pp=52–59}} Examples of continental flood basalts included the Deccan Traps in India,{{cite book |doi=10.1007/978-94-015-7805-9_5 |chapter=Deccan Traps |title=Continental Flood Basalts |series=Petrology and Structural Geology |year=1988 |last1=Mahoney |first1=John J. |volume=3 |pages=151–194 |isbn=978-90-481-8458-3 }} the Chilcotin Group in British Columbia,{{cite journal |last1=Bevier |first1=Mary Lou |title=Regional stratigraphy and age of Chilcotin Group basalts, south-central British Columbia |journal=Canadian Journal of Earth Sciences |date=1 April 1983 |volume=20 |issue=4 |pages=515–524 |doi=10.1139/e83-049|bibcode=1983CaJES..20..515B }} Canada, the Paraná Traps in Brazil,{{cite journal |last1=Renne |first1=P. R. |last2=Ernesto |first2=M. |last3=Pacca |first3=I. G. |last4=Coe |first4=R. S. |last5=Glen |first5=J. M. |last6=Prevot |first6=M. |last7=Perrin |first7=M. |title=The Age of Parana Flood Volcanism, Rifting of Gondwanaland, and the Jurassic-Cretaceous Boundary |journal=Science |date=6 November 1992 |volume=258 |issue=5084 |pages=975–979 |doi=10.1126/science.258.5084.975|pmid=17794593 |bibcode=1992Sci...258..975R |s2cid=43246541 }} the Siberian Traps in Russia,{{cite journal |last1=Renne |first1=P. R. |last2=Basu |first2=A. R. |title=Rapid Eruption of the Siberian Traps Flood Basalts at the Permo-Triassic Boundary |journal=Science |date=12 July 1991 |volume=253 |issue=5016 |pages=176–179 |doi=10.1126/science.253.5016.176 |pmid=17779134 |bibcode=1991Sci...253..176R |s2cid=6374682 }} the Karoo flood basalt province in South Africa,{{cite journal |last1=Jourdan |first1=F. |last2=Féraud |first2=G. |last3=Bertrand |first3=H. |last4=Watkeys |first4=M. K. |title=From flood basalts to the inception of oceanization: Example from the 40 Ar/ 39 Ar high-resolution picture of the Karoo large igneous province |journal=Geochemistry, Geophysics, Geosystems |date=February 2007 |volume=8 |issue=2 |pages=n/a |doi=10.1029/2006GC001392 |bibcode=2007GGG.....8.2002J |doi-access=free }} and the Columbia River Plateau of Washington and Oregon.{{cite journal |last1=Hooper |first1=P. R. |title=The Columbia River Basalts |journal=Science |date=19 March 1982 |volume=215 |issue=4539 |pages=1463–1468 |doi=10.1126/science.215.4539.1463 |pmid=17788655 |bibcode=1982Sci...215.1463H |s2cid=6182619 }} Basalt is also prevalent across extensive regions of the Eastern Galilee, Golan, and Bashan in Israel and Syria.{{Cite book |last1=Reich |first1=Ronny |title=The Architecture of Ancient Israel |last2=Katzenstein |first2=Hannah |date=1992 |publisher=Israel Exploration Society |isbn=978-965-221-013-5 |editor-last=Kempinski |editor-first=Aharon |location=Jerusalem |pages=312 |chapter=Glossary of Archaeological Terms |editor-last2=Reich |editor-first2=Ronny }}

Basalt also is common around volcanic arcs, specially those on thin crust.{{sfn|Philpotts|Ague|2009|pp=374-380}}

Ancient Precambrian basalts are usually only found in fold and thrust belts, and are often heavily metamorphosed. These are known as greenstone belts,{{sfn|Philpotts|Ague|2009|pp=398–399}}{{cite journal |last1=Smithies |first1=R. Hugh |last2=Ivanic |first2=Tim J. |last3=Lowrey |first3=Jack R. |last4=Morris |first4=Paul A. |last5=Barnes |first5=Stephen J. |last6=Wyche |first6=Stephen |last7=Lu |first7=Yong-Jun |title=Two distinct origins for Archean greenstone belts |journal=Earth and Planetary Science Letters |date=April 2018 |volume=487 |pages=106–116 |doi=10.1016/j.epsl.2018.01.034 |bibcode=2018E&PSL.487..106S }} because low-grade metamorphism of basalt produces chlorite, actinolite, epidote and other green minerals.{{sfn|Blatt|Tracy|1996|pp=366-367}}

As well as forming large parts of the Earth's crust, basalt also occurs in other parts of the Solar System. Basalt commonly erupts on Io (the third largest moon of Jupiter),{{cite book | title=Volcanic Worlds: Exploring The Solar System's Volcanoes | publisher=Springer-Praxis | last1=Lopes | first1=Rosaly M. C. | author1-link=Rosaly Lopes | last2=Gregg | first2=Tracy K. P. | year=2004 | page=135 | isbn=978-3-540-00431-8}} and has also formed on the Moon, Mars, Venus, and the asteroid Vesta.

File:Lunar Olivine Basalt 15555 from Apollo 15 in National Museum of Natural History.jpg basalt collected by Apollo 15 astronauts]]

The dark areas visible on Earth's moon, the lunar maria, are plains of flood basaltic lava flows. These rocks were sampled both by the crewed American Apollo program and the robotic Russian Luna program, and are represented among the lunar meteorites.{{cite journal |last1=Lucey |first1=P. |title=Understanding the Lunar Surface and Space-Moon Interactions |journal=Reviews in Mineralogy and Geochemistry |date=1 January 2006 |volume=60 |issue=1 |pages=83–219 |doi=10.2138/rmg.2006.60.2|bibcode=2006RvMG...60...83L }}

Lunar basalts differ from their Earth counterparts principally in their high iron contents, which typically range from about 17 to 22 wt% FeO. They also possess a wide range of titanium concentrations (present in the mineral ilmenite),{{cite news |last=Bhanoo |first=Sindya N. |title=New Type of Rock Is Discovered on Moon |url=https://www.nytimes.com/2015/12/29/science/new-type-of-rock-is-discovered-on-moon.html |date=28 December 2015 |work=The New York Times |access-date=29 December 2015 }}{{cite journal |last1=Ling |first1=Zongcheng |last2=Jolliff |first2=Bradley L. |last3=Wang |first3=Alian |last4=Li |first4=Chunlai |last5=Liu |first5=Jianzhong |last6=Zhang |first6=Jiang |last7=Li |first7=Bo |last8=Sun |first8=Lingzhi |last9=Chen |first9=Jian |last10=Xiao |first10=Long |last11=Liu |first11=Jianjun |last12=Ren |first12=Xin |last13=Peng |first13=Wenxi |last14=Wang |first14=Huanyu |last15=Cui |first15=Xingzhu |last16=He |first16=Zhiping |last17=Wang |first17=Jianyu |title=Correlated compositional and mineralogical investigations at the Chang'e-3 landing site |journal=Nature Communications |date=December 2015 |volume=6 |issue=1 |pages=8880 |doi=10.1038/ncomms9880 |pmid=26694712 |pmc=4703877 |bibcode=2015NatCo...6.8880L |doi-access=free }} ranging from less than 1 wt% TiO₂, to about 13 wt.%. Traditionally, lunar basalts have been classified according to their titanium content, with classes being named high-Ti, low-Ti, and very-low-Ti. Nevertheless, global geochemical maps of titanium obtained from the Clementine mission demonstrate that the lunar maria possess a continuum of titanium concentrations, and that the highest concentrations are the least abundant.{{cite journal |last1=Giguere |first1=Thomas A. |last2=Taylor |first2=G. Jeffrey |last3=Hawke |first3=B. Ray |last4=Lucey |first4=Paul G. |title=The titanium contents of lunar mare basalts |journal=Meteoritics & Planetary Science |date=January 2000 |volume=35 |issue=1 |pages=193–200 |doi=10.1111/j.1945-5100.2000.tb01985.x |bibcode=2000M&PS...35..193G |doi-access=free }}

Lunar basalts show exotic textures and mineralogy, particularly shock metamorphism, lack of the oxidation typical of terrestrial basalts, and a complete lack of hydration.{{sfn|Lucey|2006}} Most of the Moon's basalts erupted between about 3 and 3.5 billion years ago, but the oldest samples are 4.2 billion years old, and the youngest flows, based on the age dating method of crater counting, are estimated to have erupted only 1.2 billion years ago.{{cite journal |last1=Hiesinger |first1=Harald |last2=Jaumann |first2=Ralf |last3=Neukum |first3=Gerhard |last4=Head |first4=James W. |title=Ages of mare basalts on the lunar nearside |journal=Journal of Geophysical Research: Planets |date=25 December 2000 |volume=105 |issue=E12 |pages=29239–29275 |doi=10.1029/2000JE001244 |bibcode=2000JGR...10529239H |doi-access=free }}

From 1972 to 1985, five Venera and two VEGA landers successfully reached the surface of Venus and carried out geochemical measurements using X-ray fluorescence and gamma-ray analysis. These returned results consistent with the rock at the landing sites being basalts, including both tholeiitic and highly alkaline basalts. The landers are thought to have landed on plains whose radar signature is that of basaltic lava flows. These constitute about 80% of the surface of Venus. Some locations show high reflectivity consistent with unweathered basalt, indicating basaltic volcanism within the last 2.5 million years.{{cite journal |last1=Gilmore |first1=Martha |last2=Treiman |first2=Allan |last3=Helbert |first3=Jörn |last4=Smrekar |first4=Suzanne |title=Venus Surface Composition Constrained by Observation and Experiment |journal=Space Science Reviews |date=November 2017 |volume=212 |issue=3–4 |pages=1511–1540 |doi=10.1007/s11214-017-0370-8|bibcode=2017SSRv..212.1511G |s2cid=126225959 }}

Basalt is also a common rock on the surface of Mars, as determined by data sent back from the planet's surface,{{cite journal|last1=Grotzinger|first1=J. P.|title=Analysis of Surface Materials by the Curiosity Mars Rover|journal=Science|date=26 September 2013|volume=341|issue=6153|pages=1475|doi=10.1126/science.1244258|pmid=24072916|bibcode=2013Sci...341.1475G|doi-access=free}} and by Martian meteorites.{{Cite web |last1=Choi |first1=Charles Q. |date=11 October 2012| url=http://www.space.com/18014-mars-meteorites-black-glass.html | title=Meteorite's Black Glass May Reveal Secrets of Mars |website=Space.com | publisher=Future US, Inc. |access-date=24 March 2021}}{{cite journal |last1=Gattacceca |first1=Jérôme |last2=Hewins |first2=Roger H. |last3=Lorand |first3=Jean-Pierre |last4=Rochette |first4=Pierre |last5=Lagroix |first5=France |last6=Cournède |first6=Cécile |last7=Uehara |first7=Minoru |last8=Pont |first8=Sylvain |last9=Sautter |first9=Violaine |author9-link=Violaine Sautter|last10=Scorzelli |first10=Rosa. B. |last11=Hombourger |first11=Chrystel |last12=Munayco |first12=Pablo |last13=Zanda |first13=Brigitte |last14=Chennaoui |first14=Hasnaa |last15=Ferrière |first15=Ludovic |title=Opaque minerals, magnetic properties, and paleomagnetism of the Tissint Martian meteorite |journal=Meteoritics & Planetary Science |date=October 2013 |volume=48 |issue=10 |pages=1919–1936 |doi=10.1111/maps.12172|bibcode=2013M&PS...48.1919G |doi-access=free }}

Analysis of Hubble Space Telescope images of Vesta suggests this asteroid has a basaltic crust covered with a brecciated regolith derived from the crust.{{cite journal |last1=Binzel |first1=Richard P |last2=Gaffey |first2=Michael J |last3=Thomas |first3=Peter C |last4=Zellner |first4=Benjamin H |last5=Storrs |first5=Alex D |last6=Wells |first6=Eddie N |title=Geologic Mapping of Vesta from 1994 Hubble Space Telescope Images |journal=Icarus |date=July 1997 |volume=128 |issue=1 |pages=95–103 |doi=10.1006/icar.1997.5734|bibcode=1997Icar..128...95B |doi-access=free }} Evidence from Earth-based telescopes and the Dawn mission suggest that Vesta is the source of the HED meteorites, which have basaltic characteristics.{{cite journal |last1=Mittlefehldt |first1=David W. |title=Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites |journal=Geochemistry |date=June 2015 |volume=75 |issue=2 |pages=155–183 |doi=10.1016/j.chemer.2014.08.002 |bibcode=2015ChEG...75..155M }} Vesta is the main contributor to the inventory of basaltic asteroids of the main Asteroid Belt.{{cite journal |last1=Moskovitz |first1=Nicholas A. |last2=Jedicke |first2=Robert |last3=Gaidos |first3=Eric |last4=Willman |first4=Mark |last5=Nesvorný |first5=David |last6=Fevig |first6=Ronald |last7=Ivezić |first7=Željko |title=The distribution of basaltic asteroids in the Main Belt |journal=Icarus |date=November 2008 |volume=198 |issue=1 |pages=77–90 |doi=10.1016/j.icarus.2008.07.006 |arxiv=0807.3951 |bibcode=2008Icar..198...77M |s2cid=38925782 }}

Lava flows represent a major volcanic terrain on Io.{{cite journal |last1=Keszthelyi |first1=L. |last2=McEwen |first2=A. S. |last3=Phillips |first3=C. B.|author3-link=Cynthia B. Phillips |last4=Milazzo |first4=M. |last5=Geissler |first5=P. |last6=Turtle |first6=E. P. |last7=Radebaugh |first7=J. |last8=Williams |first8=D. A. |last9=Simonelli |first9=D. P. |last10=Breneman |first10=H. H. |last11=Klaasen |first11=K. P. |last12=Levanas |first12=G. |last13=Denk |first13=T. |title=Imaging of volcanic activity on Jupiter's moon Io by Galileo during the Galileo Europa Mission and the Galileo Millennium Mission |journal=Journal of Geophysical Research: Planets |date=2001-12-25 |volume=106 |issue=E12 |pages=33025–33052 |doi=10.1029/2000JE001383 |bibcode=2001JGR...10633025K |doi-access=free }} Analysis of the Voyager images led scientists to believe that these flows were composed mostly of various compounds of molten sulfur. However, subsequent Earth-based infrared studies and measurements from the Galileo spacecraft indicate that these flows are composed of basaltic lava with mafic to ultramafic compositions.{{Cite conference |title= A Jökulhlaup-like Model for Secondary Sulfur Flows on Io |conference=50th Lunar and Planetary Science Conference. 18–22 March 2019. The Woodlands, Texas. |first=Steven M. |last=Battaglia |date=March 2019 |id=LPI Contribution No. 1189 |url=https://www.hou.usra.edu/meetings/lpsc2019/pdf/1189.pdf | bibcode=2019LPI....50.1189B}} This conclusion is based on temperature measurements of Io's "hotspots", or thermal-emission locations, which suggest temperatures of at least 1,300 K and some as high as 1,600 K.{{cite journal |last1=Keszthelyi |first1=Laszlo |last2=Jaeger |first2=Windy |last3=Milazzo |first3=Moses |last4=Radebaugh |first4=Jani |last5=Davies |first5=Ashley Gerard |last6=Mitchell |first6=Karl L. |title=New estimates for Io eruption temperatures: Implications for the interior |journal=Icarus |date=December 2007 |volume=192 |issue=2 |pages=491–502 |doi=10.1016/j.icarus.2007.07.008 |bibcode=2007Icar..192..491K |url=https://zenodo.org/record/1259031 }} Initial estimates suggesting eruption temperatures approaching 2,000 K{{cite journal |title=High-temperature silicate volcanism on Jupiter's moon Io |journal=Science |last=McEwen |first=A. S. |display-authors=etal |pages=87–90 |volume=281 |issue=5373 |date=1998 |doi=10.1126/science.281.5373.87 |pmid=9651251 |bibcode=1998Sci...281...87M |s2cid=28222050 }} have since proven to be overestimates because the wrong thermal models were used to model the temperatures.{{sfn|Battaglia|2019}}

{{See also|Weathering}}

File:Absolute iron accumulation in kaolinized basalt. C 015.jpg

Compared to granitic rocks exposed at the Earth's surface, basalt outcrops weather relatively rapidly. This reflects their content of minerals that crystallized at higher temperatures and in an environment poorer in water vapor than granite. These minerals are less stable in the colder, wetter environment at the Earth's surface. The finer grain size of basalt and the volcanic glass sometimes found between the grains also hasten weathering. The high iron content of basalt causes weathered surfaces in humid climates to accumulate a thick crust of hematite or other iron oxides and hydroxides, staining the rock a brown to rust-red colour.{{sfn|Blatt|Middleton|Murray|1980|pp=254–257}}{{cite journal |last1=Mackin |first1=J.H. |year=1961 |title=A stratigraphic section in the Yakima Basalt and the Ellensburg Formation in south-central Washington |journal=Washington Division of Mines and Geology Report of Investigations |volume=19 |url=https://www.dnr.wa.gov/Publications/ger_ri19_strat_yakima_basalt_ellensburg_form.pdf |archive-url=https://web.archive.org/web/20100124083749/http://www.dnr.wa.gov/Publications/ger_ri19_strat_yakima_basalt_ellensburg_form.pdf |archive-date=2010-01-24 |url-status=live }}{{cite web |title=Holyoke Basalt |url=https://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=CTJho%3B0 |website=USGS Mineral Resources Program |publisher=United States Geological Survey |access-date=13 August 2020}}{{cite journal |last1=Anderson |first1=J. L. |title=Geologic map of the Goldendale 15' quadrangle, Washington |journal=Washington Division of Geology and Earth Resources Open File Report |date=1987 |volume=87-15 |url=https://www.dnr.wa.gov/Publications/ger_ofr87-15_goldendale_39k.pdf |archive-url=https://web.archive.org/web/20091220013300/http://www.dnr.wa.gov/Publications/ger_ofr87-15_goldendale_39k.pdf |archive-date=2009-12-20 |url-status=live |access-date=13 August 2020}} Because of the low potassium content of most basalts, weathering converts the basalt to calcium-rich clay (montmorillonite) rather than potassium-rich clay (illite). Further weathering, particularly in tropical climates, converts the montmorillonite to kaolinite or gibbsite. This produces the distinctive tropical soil known as laterite.{{sfn|Blatt|Middleton|Murray|1980|pp=254–257}} The ultimate weathering product is bauxite, the principal ore of aluminium.{{sfn|Blatt|Middleton|Murray|1980|pp=263–264}}

Chemical weathering also releases readily water-soluble cations such as calcium, sodium and magnesium, which give basaltic areas a strong buffer capacity against acidification.{{cite journal |last1=Gillman |first1=G. P. |last2=Burkett |first2=D. C. |last3=Coventry |first3=R. J. |title=Amending highly weathered soils with finely ground basalt rock |journal=Applied Geochemistry |date=August 2002 |volume=17 |issue=8 |pages=987–1001 |doi=10.1016/S0883-2927(02)00078-1|bibcode=2002ApGC...17..987G }} Calcium released by basalts binds CO₂ from the atmosphere forming CaCO₃ acting thus as a CO₂ trap.{{cite journal |last1=McGrail |first1=B. Peter |last2=Schaef |first2=H. Todd |last3=Ho |first3=Anita M. |last4=Chien |first4=Yi-Ju |last5=Dooley |first5=James J. |last6=Davidson |first6=Casie L. |title=Potential for carbon dioxide sequestration in flood basalts: Sequestration in flood basalts |journal=Journal of Geophysical Research: Solid Earth |date=December 2006 |volume=111 |issue=B12 |pages=n/a |doi=10.1029/2005JB004169|doi-access=free }}

File:Archean Greenstone Pillow Lava in Michigan USA 3.jpg greenstone belt in Michigan, US. The minerals that gave the original basalt its black colour have been metamorphosed into green minerals.]]

Intense heat or great pressure transforms basalt into its metamorphic rock equivalents. Depending on the temperature and pressure of metamorphism, these may include greenschist, amphibolite, or eclogite. Basalts are important rocks within metamorphic regions because they can provide vital information on the conditions of metamorphism that have affected the region.{{sfn|Blatt|Tracy|1996|loc=chapter 22}}

Metamorphosed basalts are important hosts for a variety of hydrothermal ores, including deposits of gold, copper and volcanogenic massive sulfides.{{Cite journal|last1=Yardley|first1=Bruce W. D.|last2=Cleverley|first2=James S.|date=2015|title=The role of metamorphic fluids in the formation of ore deposits|journal=Geological Society, London, Special Publications|language=en|volume=393|issue=1|pages=117–134|doi=10.1144/SP393.5|bibcode=2015GSLSP.393..117Y|s2cid=130626915|issn=0305-8719|doi-access=free}}

The common corrosion features of underwater volcanic basalt suggest that microbial activity may play a significant role in the chemical exchange between basaltic rocks and seawater. The significant amounts of reduced iron, Fe(II), and manganese, Mn(II), present in basaltic rocks provide potential energy sources for bacteria. Some Fe(II)-oxidizing bacteria cultured from iron-sulfide surfaces are also able to grow with basaltic rock as a source of Fe(II).{{cite journal|first1=Katrina J. |last1=Edwards |first2=Wolfgang |last2=Bach |first3=Daniel R. |last3=Rogers |title=Geomicrobiology of the Ocean Crust: A Role for Chemoautotrophic Fe-Bacteria |journal=Biological Bulletin |volume=204 |issue=2 |pages=180–185 |date=April 2003 |doi=10.2307/1543555 |pmid=12700150 |jstor=1543555 |s2cid=1717188 |url=https://www.biodiversitylibrary.org/part/9233 }} Fe- and Mn- oxidizing bacteria have been cultured from weathered submarine basalts of Kamaʻehuakanaloa Seamount (formerly Loihi).{{cite journal|last1=Templeton|first1=Alexis S.|last2=Staudigel|first2=Hubert|last3=Tebo|first3=Bradley M.|title=Diverse Mn(II)-Oxidizing Bacteria Isolated from Submarine Basalts at Loihi Seamount|journal=Geomicrobiology Journal|date=April 2005|volume=22|issue=3–4|pages=127–139|doi=10.1080/01490450590945951|bibcode=2005GmbJ...22..127T |s2cid=17410610}} The impact of bacteria on altering the chemical composition of basaltic glass (and thus, the oceanic crust) and seawater suggest that these interactions may lead to an application of hydrothermal vents to the origin of life.{{cite journal |last1=Martin |first1=William |last2=Baross |first2=John |last3=Kelley |first3=Deborah |last4=Russell |first4=Michael J. |title=Hydrothermal vents and the origin of life |journal=Nature Reviews Microbiology |date=November 2008 |volume=6 |issue=11 |pages=805–814 |doi=10.1038/nrmicro1991|pmid=18820700 |bibcode=2008NRvM....6..805M |s2cid=1709272 }}

File:P1050763 Louvre code Hammurabi face rwk.JPG was engraved on a {{height|m=2.25}} tall basalt stele in around 1750 BC.]]

Basalt is used in construction (e.g. as building blocks or in the groundwork),{{cite journal |last1=Raj |first1=Smriti |last2=Kumar |first2=V Ramesh |last3=Kumar |first3=B H Bharath |last4=Iyer |first4=Nagesh R |title=Basalt: structural insight as a construction material |journal=Sādhanā |date=January 2017 |volume=42 |issue=1 |pages=75–84 |doi=10.1007/s12046-016-0573-9|doi-access=free }} making cobblestones (from columnar basalt){{cite journal |last1=Yıldırım |first1=Mücahit |title=Shading in the outdoor environments of climate-friendly hot and dry historical streets: The passageways of Sanliurfa, Turkey |journal=Environmental Impact Assessment Review |date=January 2020 |volume=80 |pages=106318 |doi=10.1016/j.eiar.2019.106318|doi-access=free |bibcode=2020EIARv..8006318Y }} and in making statues.{{cite journal |last1=Aldred |first1=Cyril |title=A Statue of King Neferkarē c Ramesses IX |journal=The Journal of Egyptian Archaeology |date=December 1955 |volume=41 |issue=1 |pages=3–8 |doi=10.1177/030751335504100102|s2cid=192232554 }}{{cite journal |last1=Roobaert |first1=Arlette |title=A Neo-Assyrian Statue from Til Barsib |journal=Iraq |date=1996 |volume=58 |pages=79–87 |doi=10.2307/4200420|jstor=4200420 }} Heating and extruding basalt yields stone wool, which has potential to be an excellent thermal insulator.{{cite web |url=http://basalt.pro/activities/materials/|title=Research surveys for basalt rock quarries |website=Basalt Projects }}{{cite web |last1=De Fazio |first1=Piero |title=Basalt fiber: from earth an ancient material for innovative and modern application |url=http://www.enea.it/it/seguici/pubblicazioni/EAI/anno-2011/indice-world-view-3-2011/basalt-fiber-from-earth-an-ancient-material-for-innovative-and-modern-application |website=Italian national agency for new technologies, energy and sustainable economic development |access-date=17 December 2018 |language=en, it |archive-date=17 May 2019 |archive-url=https://web.archive.org/web/20190517081412/http://www.enea.it/it/seguici/pubblicazioni/EAI/anno-2011/indice-world-view-3-2011/basalt-fiber-from-earth-an-ancient-material-for-innovative-and-modern-application/ |url-status=dead }}{{Cite web|url=http://www.ptonline.com/articles/composites-higher-properties-lower-cost|title=Composites: Higher Properties, Lower Cost|last=Schut|first=Jan H.|website=www.ptonline.com|date=August 2008 |access-date=2017-12-10}}{{Cite web|url=http://www.compositesworld.com/articles/basalt-fibers-alternative-to-glass|title=Basalt Fibers: Alternative To Glass?|last=Ross|first=Anne|website=www.compositesworld.com|date=August 2006 |access-date=2017-12-10}}

Carbon sequestration in basalt has been studied as a means of removing carbon dioxide, produced by human industrialization, from the atmosphere. Underwater basalt deposits, scattered in seas around the globe, have the added benefit of the water serving as a barrier to the re-release of CO₂ into the atmosphere.{{cite news|last1=Hance|first1=Jeremy|title=Underwater rocks could be used for massive carbon storage on America's East Coast|url=http://news.mongabay.com/2010/0104-hance_ccs.html|access-date=4 November 2015|publisher=Mongabay|date=5 January 2010}}{{cite journal |last1=Goldberg |first1=D. S. |last2=Takahashi |first2=T. |last3=Slagle |first3=A. L. |title=Carbon dioxide sequestration in deep-sea basalt |journal=Proceedings of the National Academy of Sciences |date=22 July 2008 |volume=105 |issue=29 |pages=9920–9925 |doi=10.1073/pnas.0804397105|pmid=18626013 |pmc=2464617 |bibcode=2008PNAS..105.9920G |doi-access=free }}

• {{annotated link|Basalt fan structure}}
• {{annotated link|Basalt fiber}}
• {{annotated link|Bimodal volcanism}}
• {{annotated link|Plutonism}}
• {{annotated link|Polybaric melting}}
• {{annotated link|Shield volcano}}
• {{annotated link|Spilite}}
• {{annotated link|Sideromelane}}
• {{annotated link|Volcano}}
• {{portal-inline|Geology}}

{{reflist}}

• {{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=978-0-7167-2438-4 |edition=2nd }}
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{{Refbegin}}

• {{cite book |last1=Francis |first1=Peter |last2=Oppenheimer |first2=Clive |title=Volcanoes |date=2003 |publisher=Oxford University Press |location=Oxford |isbn=978-0-19-925469-9 |edition=2nd |ref=none}}
• {{cite book |last1=Gill |first1=Robin |title=Igneous rocks and processes: a practical guide |url=https://archive.org/details/Igneous_Rocks_and_Processes_A_Practical_Guide_by_R_Gill |date=2010 |publisher=Wiley-Blackwell |location=Chichester, West Sussex, UK |isbn=978-1-4443-3065-6 |ref=none}}
• {{cite book |last1=Hall |first1=Anthony |title=Igneous petrology |date=1996 |publisher=Longman Scientific & Technical |location=Harlow |isbn=978-0-582-23080-4 |ref=none}}
• {{cite book |editor-last1=Siegesmund |editor-first1=Siegfried |editor-last2=Snethlage |editor-first2=Rolf |title=Stone in architecture properties, durability |date=2013 |publisher=Springer Science & Business Media |isbn=978-3-662-10070-7 |edition=3rd |ref=none}}
• {{cite book |last1=Young |first1=Davis A. |title=Mind over magma : the story of igneous petrology |date=2003 |publisher=Princeton University Press |location=Princeton, N.J. |isbn=978-0-691-10279-5 |ref=none}}

{{Refend}}

{{Commons category|Basalt}}

{{Wikisource1911Enc|Basalt}}

• [https://web.archive.org/web/20071107063242/http://giantcrystals.strahlen.org/europe/basalt.htm Basalt Columns]
• [http://geographyinaction.co.uk//Geology%20files/Basalt.html Basalt in Northern Ireland] {{Webarchive|url=https://web.archive.org/web/20210224191248/http://geographyinaction.co.uk//Geology%20files/Basalt.html |date=24 February 2021 }}
• [https://web.archive.org/web/20070913025149/http://www.geology.sdsu.edu/how_volcanoes_work/lava_water.html Lava–water interface]
• [https://web.archive.org/web/20080820010048/http://www.petdb.org/ PetDB, the Petrological Database]
• [https://web.archive.org/web/20080607121825/http://www.union.edu/PUBLIC/GEODEPT/COURSES/petrology/moon_rocks/ Petrology of Lunar Rocks and Mare Basalts]
• [https://web.archive.org/web/20080916123604/http://volcanoes.usgs.gov/images/pglossary/PillowLava.php Pillow lava USGS]

{{Igneous rocks}}

{{basalt}}

{{Rock type}}

{{Volcanoes}}

{{Authority control}}