{{Short description|Variety of high-magnesium basalt that is very rich in the mineral olivine}} {{Distinguish|Pykrete}} {{redirect|Picrite|the component of triple-base NQ propellants|Nitroguanidine}} {{Use dmy dates|date=February 2020}} [[Image:Oceanite grand brule dsc03601.jpg|thumb|Picrite basalt or oceanite from the Piton de la Fournaise]]
'''Picrite basalt''' or '''picrobasalt''' is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite.
The olivine-rich picrite basalts that occur with the more common tholeiitic basalts of Kīlauea and other volcanoes of the Hawaiian Islands are the result of accumulation of olivine crystals either in a portion of the magma chamber or in a caldera lava lake.{{ref|Carmichael}} The compositions of these rocks are well represented by mixes of olivine and more typical tholeiitic basalt.
The name "picrite" can also be applied to an olivine-rich alkali basalt: such picrite consists largely of phenocrysts of olivine and titanium-rich augite pyroxene with minor plagioclase set in a groundmass of augite and more sodic plagioclase and perhaps analcite and biotite.
More generally the classification of fine grained rocks recognizes a group known as 'picritic rocks' that are characterised by high magnesium content and low SiO<sub>2</sub> content. They fit in the TAS classification system only at the lowest level of SiO<sub>2</sub> (41 to 43% by weight) and Na<sub>2</sub>O + K<sub>2</sub>O (up to 3% by weight). They include picrite, komatiite and meimechite.
Picrites and komatiites are somewhat similar chemically (defined as >18% MgO), but differ in having 1 to 3% total alkalis and less than 1% total alkalis respectively. Komatiite lavas are products of more magnesium-rich melts, and good examples exhibit the spinifex texture.{{ref|Kerr}} They are largely restricted to the Archean. In contrast, picrites are magnesium-rich because crystals of olivine have accumulated in more normal melts by magmatic processes.<ref>{{Cite journal |last1=Vozniak |first1=Alexey A. |last2=Kopylova |first2=M.G. |last3=Peresetskaya |first3=Ekaterina |last4=Nosova |first4=Anna |last5=Sazonova |first5=L.V. |last6=Anosova |first6=M.O. |date=2022 |title=Olivine in Lamprophyres of the Kola Alkaline Province: Insights into the Magmatic Evolution of Olivine in Carbonate Melts |url=https://doi.org/10.2139/ssrn.4169719 |journal=SSRN Electronic Journal |doi=10.2139/ssrn.4169719 |issn=1556-5068|url-access=subscription }}</ref>
Picrite basalt is found in the lavas of Mauna Kea and Mauna Loa in Hawai{{okina}}i{{ref|Rhodes}}, Curaçao, in the Piton de la Fournaise{{ref|Metrich}} volcano on Réunion Island and various other oceanic island volcanoes.
*Picrite basalt has erupted in historical times from Mauna Loa during the eruptions of 1852 and 1868 (from different flanks of Mauna Loa).{{ref|Wilkenson}} *Picrite basalt with 30% olivine commonly erupts from the Piton de la Fournaise.{{ref|Metrich}}
In addition to extrusive occurrences, it also occurs in minor intrusions.
==Oceanite== '''Oceanite''' is a variety of picritic basalt characterized by its large amounts of olivine phenocrysts and lesser amounts of augite and by having a groundmass of olivine, plagioclase and augite. The term was coined by Antoine Lacroix in 1923 for rare basalts with more than 50% olivine.{{ref|LeMaitre}}
==Common uses== Olivine basalt is commonly used by foundries, boilermakers and boiler users to protect the area around a burner tip or to protect a floor from molten metal and other slag. Its use in this fashion is appropriate since olivine is a highly refractory, high-melting-temperature mineral.<ref>{{Cite web |last=moshiri |first=hossien |date=2023-10-30 |title=Olivine Sand Metal foundry- |url=https://chemkraft.ir/en/olivine-sand-metal-foundry-quality/ |access-date=2024-12-12 |website=Iran Chemkraft Representative Office |language=en-US}}</ref><ref>{{Cite journal |last1=Huo |first1=Yonglin |last2=Qin |first2=Guilu |last3=Huo |first3=Jichuan |last4=Zhang |first4=Xingquan |last5=Zhu |first5=Yongchang |date= 2022|title=Crystallization Kinetics of Basalt Glass-Ceramics Produced from Olivine Basalt Rock |journal=Crystals |language=en |volume=12 |issue=7 |pages=899 |doi=10.3390/cryst12070899 |doi-access=free |bibcode=2022Cryst..12..899H |issn=2073-4352}}</ref>
==References== {{Reflist}} * {{note|Carmichael}}{{cite book|author-link1=Ian S. E. Carmichael|last1=Carmichael|first1=Ian S. E.|last2=Turner|first2=Francis J.|last3=Verhoogen|first3=John|date=1974|title=Igneous Petrology|publisher=McGraw-Hill|pages=406–426}} * {{note|Metrich}} {{cite journal|last1=Metrich|first1=Nicole|first2=Françoise|last2=Pineau|first3=Marc|last3=Javoy|date=1988|archive-url=https://web.archive.org/web/20051108173330/http://www.the-conference.com/JConfAbs/1/88.html|url=http://www.the-conference.com/JConfAbs/1/88.html|archive-date=8 November 2005 |title=Volatiles: Mantle Source Characterization and Degassing Process for Hot Spot Volcanism - The Piton de la Fournaise (Reunion Island) Example|url-status=dead}} * {{note|Kerr}}{{cite web|last=Kerr|first=A. C.|date=1997|archive-url=https://web.archive.org/web/20040622175836/http://www.le.ac.uk/geology/ack2/komatiite/difference.html|url=http://www.le.ac.uk/geology/ack2/komatiite/difference.html |archive-date=22 June 2004 |title=What is the difference between a komatiite and a picrite?|url-status=dead}}. * {{note|LeMaitre}}{{cite book|editor-last=Le Maitre|editor-first=L. E.|date=2002|title=Igneous Rocks: A Classification and Glossary of Terms|edition=2nd|publisher=Cambridge|page=118}} * {{note|rhodes}}{{cite journal|last=Rhodes|first=J. M.|date=1995|title=The 1852 and 1868 Mauna Loa Picrite Eruptions|journal=Geophysical Monograph Series|volume=92|publisher=American Geophysical Union|url=http://www.geo.umass.edu/xrf/picrite.html|access-date=18 February 2006}} * {{cite journal|last1=Wilkinson|first1=J. F. G.|last2=Hensel|first2=H. D.|title=The petrology of some picrites from Mauna Loa and Kilauea volcanoes, Hawaii|journal=Contributions to Mineralogy and Petrology|date=1988|volume=98|issue=3|pages=326–345|doi=10.1007/bf00375183|bibcode=1988CoMP...98..326W|s2cid=115132181}} * {{note|Williams}}{{cite book|last1=Williams|first1=Howel|first2=Francis J.|last2=Turner|first3=Charles M.|last3=Gilbert|date=1954|title=Petrography|publisher=W. H. Freeman|pages=40–41}}
{{basalt}} {{Rock type}}
{{DEFAULTSORT:Picrite Basalt}} Category:Aphanitic rocks Category:Mafic rocks Category:Ultramafic rocks Category:Volcanology Category:Basalt