Editing Mafic

{{short description|Silicate mineral or igneous rock that is rich in magnesium and iron}}
{{Use American English|date=January 2021}}[[File:BasaltUSGOV.jpg|thumbnail|Basalt]]
A '''mafic''' mineral or rock is a [[silicate mineral]] or [[igneous rock]] rich in [[magnesium]] and [[iron]]. Most mafic minerals are dark in color, and common rock-forming mafic minerals include [[olivine]], [[pyroxene]], [[amphibole]], and [[biotite]]. Common mafic rocks include [[basalt]], [[diabase]] and [[gabbro]]. Mafic rocks often also contain [[calcium]]-rich varieties of [[plagioclase]] feldspar. Mafic materials can also be described as '''ferromagnesian'''.

==History==
The term ''mafic'' is a [[portmanteau]] of "magnesium" and "ferric" and was coined by [[Charles Whitman Cross]], [[Joseph P. Iddings]], [[Louis V. Pirsson]], and [[Henry Stephens Washington]] in 1912. Cross' group had previously divided the major rock-forming minerals found in igneous rocks into ''salic'' minerals, such as [[quartz]], [[feldspar]]s, or [[feldspathoid]]s, and ''femic'' minerals, such as [[olivine]] and [[pyroxene]]. However, [[mica]]s and aluminium-rich [[amphibole]]s were excluded, while some calcium minerals containing little iron or magnesium, such as [[wollastonite]] or [[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>

==Minerals==
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]] (IUGS) classification of igneous rocks, include some light-colored ferromagnesian minerals, such as [[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]]s, such as [[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>

==Rocks==
When applied to rocks, the term ''mafic'' is used primarily as a [[Field work|field term]] 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 (geology)|color index]] (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]]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%]], corresponding to the silica content of basalt in the [[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]] and typically dark in color. In contrast, the [[felsic]] rocks are typically light in color and enriched in [[aluminium]] and [[silicon]] along with [[potassium]] and [[sodium]]. The mafic rocks also typically have a higher [[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>

Mafic [[lava]], before cooling, has a low [[viscosity]], in comparison with felsic lava, due to the lower [[silica]] content in mafic [[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 explosively violent 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]]
*[[List of minerals]]
*[[List of rock types]]
*[[Bowen's reaction series]]

==References==
{{Reflist}}

{{igneous rocks}}

[[Category:Igneous petrology]]
[[Category:Mineralogy concepts]]
[[Category:Petrology]]