# Mafic

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{{short description|Silicate mineral or igneous rock that is rich in magnesium and iron}}
{{Use American English|date=January 2021}}thumbnail|Basalt
'''Mafic''' is a term used in geology to describe [silicate minerals](/source/silicate_mineral), [magmas](/source/Magma), and [igneous rocks](/source/igneous_rock) that are rich in [magnesium](/source/magnesium) and [iron](/source/iron), while being relatively low in silica content. Most mafic minerals are dark in color, and common rock-forming mafic minerals include [olivine](/source/olivine), [pyroxene](/source/pyroxene), [amphibole](/source/amphibole), and [biotite](/source/biotite). Common mafic rocks include [basalt](/source/basalt), [diabase](/source/diabase) and [gabbro](/source/gabbro). Mafic rocks often also contain [calcium](/source/calcium)-rich varieties of [plagioclase](/source/plagioclase) feldspar. Mafic materials can also be described as '''ferromagnesian'''.

==History==
The term ''mafic'' is a [portmanteau](/source/portmanteau) of "magnesium" and "ferric" and was coined by [Charles Whitman Cross](/source/Charles_Whitman_Cross), [Joseph P. Iddings](/source/Joseph_P._Iddings), [Louis V. Pirsson](/source/Louis_V._Pirsson), and [Henry Stephens Washington](/source/Henry_Stephens_Washington) in 1912. Cross's group had previously divided the major rock-forming minerals found in igneous rocks into ''salic'' minerals, such as [quartz](/source/quartz), [feldspar](/source/feldspar)s, or [feldspathoid](/source/feldspathoid)s, and ''femic'' minerals, such as [olivine](/source/olivine) and [pyroxene](/source/pyroxene). However, [mica](/source/mica)s and aluminium-rich [amphibole](/source/amphibole)s were excluded, while some calcium minerals containing little iron or magnesium, such as [wollastonite](/source/wollastonite) or [apatite](/source/apatite), were included in the femic minerals.<ref>{{cite journal |last1=Cross |first1=Whitman |last2=Iddings |first2=Joseph P. |last3=Pirsson |first3=Louis V. |last4=Washington |first4=Henry S. |title=A Quantitative Chemico-Mineralogical Classification and Nomenclature of Igneous Rocks |journal=The Journal of Geology |date=September 1902 |volume=10 |issue=6 |pages=555–690 |doi=10.1086/621030|bibcode=1902JG.....10..555C |s2cid=140683261 }}</ref> Cross and his coinvestigators later clarified that micas and aluminium amphiboles belonged to a separate category of ''alferric'' minerals. They then introduced the term ''mafic'' for ferromagnesian minerals of all types, in preference to the term ''femag'' coined by A. Johannsen in 1911, whose sound they disliked.<ref>{{cite journal |last1=Cross |first1=Whitman |last2=Iddings |first2=J. P. |last3=Pirsson |first3=L. V. |last4=Washington |first4=H. S. |title=Modifications of the "Quantitative System of Classification of Igneous Rocks" |journal=The Journal of Geology |date=September 1912 |volume=20 |issue=6 |pages=550–561 |doi=10.1086/621996|bibcode=1912JG.....20..550C |s2cid=129515388 }}</ref><ref name="Jackson1997">{{cite book |url=https://archive.org/details/glossaryofgeolog0000unse_k9a5 |title=Glossary of geology. |date=1997 |publisher=American Geological Institute |isbn=0922152349 |editor1-last=Jackson |editor1-first=Julia A. |edition=Fourth |location=Alexandria, Virginia |chapter=mafic |url-access=registration}}</ref>

==Mineralogy ==
thumb|192x192px|Apatite
The term ''mafic'' is still widely used for dark-colored ferromagnesian minerals.<ref name="Jackson1997" /> Modern classification schemes, such as the [International Union of Geological Sciences](/source/International_Union_of_Geological_Sciences) (IUGS) classification of igneous rocks, include some light-colored ferromagnesian minerals, such as [melilite](/source/melilite), in the mafic mineral fraction.<ref name="lebas-streckeisen-1991">{{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> [Accessory mineral](/source/Accessory_mineral)s, such as [zircon](/source/zircon) or apatite, may also be included in the mafic mineral fraction for purposes of precise classification.<ref name="PhilpottsAgue2009">{{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 |page=137}}</ref> 

In Earth's interior, this ferromagnesian dominance is reflected in the mantle's composition. [Bridgmanite](/source/Bridgmanite), a magnesium and iron-rich silicate, constitutes the majority of Earth's [lower mantle](/source/lower_mantle) and is consistent with its ultramafic [geochemical](/source/geochemical) character. <ref>{{Cite journal |last=Katsura |first=Tomoo |date=2025-02-01 |title=Phase relations of bridgmanite, the most abundant mineral in the Earth's lower mantle |url=https://pmc.ncbi.nlm.nih.gov/articles/PMC11787361/ |journal=Communications Chemistry |volume=8 |issue=1 |pages=28 |doi=10.1038/s42004-024-01389-8 |issn=2399-3669 |pmc=11787361 |pmid=39893284}}</ref>

==Rocks==
thumb|225x225px|Total alkali-silica (TAS) diagram for classification of volcanic rocks (after Le Maitre et al., 2002)<ref>{{Cite book |url=https://doi.org/10.1017/cbo9780511535581 |title=Igneous Rocks |date=2002 |publisher=Cambridge University Press |isbn=978-0-511-53558-1 |editor-last=Le Maitre |editor-first=R. W. |location=Cambridge |editor-last2=Streckeisen |editor-first2=A. |editor-last3=Zanettin |editor-first3=B. |editor-last4=Le Bas |editor-first4=M. J. |editor-last5=Bonin |editor-first5=B. |editor-last6=Bateman |editor-first6=P.}}</ref>
When applied to rocks, the term ''mafic'' is used primarily as a [field term](/source/Field_work) to describe dark-colored igneous rocks.<ref name=PhilpottsAgue2009/> The term is not used as a rock classification in the IUGS classification scheme.<ref name="lebas-streckeisen-1991"/> Mafic rocks are sometimes more precisely defined as igneous rocks with a high proportion of pyroxene and olivine, so that their [color index](/source/Color_index_(geology)) (the volume fraction of dark mafic minerals) is between 50 and 90.<ref name="Allaby2013">{{cite book |last1=Allaby |first1=Michael |url=https://books.google.com/books?id=2r7xyJSp4R0C |title=A dictionary of geology and earth sciences |date=2013 |publisher=Oxford University Press |isbn=9780199653065 |edition=Fourth |location=Oxford |chapter=mafic}}</ref> Most mafic volcanic rocks are more precisely classified as [basalt](/source/basalt)s.<ref>{{cite book |last1=Schmincke |first1=Hans-Ulrich |url=https://books.google.com/books?id=XHlJrFAhth4C&pg=PA23 |title=Volcanism |date=2003 |publisher=Springer |isbn=978-3-540-43650-8 |location=Berlin |page=23}}</ref>

Chemically, mafic rocks are sometimes defined as rocks with a silica content between 45 and 55 [wt%](/source/wt%25), corresponding to the silica content of basalt in the [TAS classification](/source/TAS_classification).<ref>{{cite book |last1=Nesse |first1=William D. |url=https://archive.org/details/introductiontomi0000ness_m9a6 |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |isbn=9780195106916 |location=New York |url-access=registration}}</ref> Such rocks are enriched in iron, magnesium, and [calcium](/source/calcium) and typically dark in color. In contrast, the [felsic](/source/felsic) rocks are typically light in color and enriched in [aluminium](/source/aluminium) and [silicon](/source/silicon) along with [potassium](/source/potassium) and [sodium](/source/sodium). Mafic rocks also typically have a higher [density](/source/density) than felsic rocks. The term roughly corresponds to the older ''basic rock'' class.<ref>{{cite book |last1=Islam |first1=M. R. |last2=Hossain |first2=M. E. |last3=Islam |first3=A. O. |title=Hydrocarbons in Basement Formations |date=2018 |publisher=John Wiley & Sons |isbn=978-1-119-29453-5 |page=80 |url=https://books.google.com/books?id=xK5JDwAAQBAJ&pg=PA80 |language=en}}</ref>

== Geological significance ==
thumb|An ʻaʻā flow from Mauna Loa (a volcano in Hawaii), composed of mafic magma.
Mafic rocks are a major component of Earth's crust and are closely linked to processes happening within the [mantle](/source/Earth's_mantle). They form primarily through the [partial melting](/source/partial_melting) of mantle [peridotite](/source/peridotite) and provide insight into mantle composition and melt generation<ref>{{Citation |title=Introduction to Igneous and Metamorphic Petrology |date=2022-01-06 |work=Principles of Igneous and Metamorphic Petrology |pages=1–19 |url=https://doi.org/10.1017/9781108631419.002 |access-date=2026-03-11 |publisher=Cambridge University Press |isbn=978-1-108-63141-9}}</ref>. [Basalt](/source/Basalt), the most common mafic [igneous rock](/source/igneous_rock), is produced at [mid-ocean ridges](/source/Mid-ocean_ridge) by [decompression melting](/source/decompression_melting) of upwelling mantle material and constitutes a majority of [oceanic crust](/source/oceanic_crust)<ref>{{Cite journal |last=McKENZIE |first=D. |last2=Bickle |first2=M. J. |date=1988-06-01 |title=The Volume and Composition of Melt Generated by Extension of the Lithosphere |url=https://academic.oup.com/petrology/article-lookup/doi/10.1093/petrology/29.3.625 |journal=Journal of Petrology |language=en |volume=29 |issue=3 |pages=625–679 |doi=10.1093/petrology/29.3.625 |issn=0022-3530|url-access=subscription }}</ref>.  

Upon eruption, mafic [lava](/source/lava) has less [viscosity](/source/viscosity) than felsic lava, due to the lower [silica](/source/silica) content in mafic [magma](/source/magma). Water and other volatiles can more easily and gradually escape from mafic lava. As a result, eruptions of volcanoes made of mafic lavas are less explosive than felsic-lava eruptions.<ref>{{Cite web|url=http://www.columbia.edu/~vjd1/volcs.htm|title=Volcanoes|website=Columbia University|access-date=18 June 2019}}</ref>

== See also ==

*[QAPF diagram](/source/QAPF_diagram)
*[List of minerals](/source/List_of_minerals)
*[List of rock types](/source/List_of_rock_types)
*[Bowen's reaction series](/source/Bowen's_reaction_series)

==References==
{{Reflist}}

{{igneous rocks}}

Category:Igneous petrology
Category:Mineralogy concepts
Category:Petrology

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Adapted from the Wikipedia article [Mafic](https://en.wikipedia.org/wiki/Mafic) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Mafic?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.