Editing Spinel (section)

===Geologic occurrence===
Spinel is found as a [[metamorphic rock|metamorphic mineral]] in metamorphosed [[limestone]]s and silica-poor [[mudstone]]s.<ref name="klein-hurlbut"/> It also occurs as a primary mineral in rare mafic [[igneous rock]]s; in these igneous rocks, the [[magma]]s are relatively deficient in [[alkali]]s relative to [[aluminium]], and aluminium oxide may form as the mineral corundum or may combine with magnesia to form spinel. This is why spinel and [[ruby]] are often found together. The spinel petrogenesis in mafic magmatic rocks is strongly debated, but certainly results from mafic magma interaction with more evolved magma <ref>{{cite journal|vauthors= Irvine TN |title= Origin of chromite layers in the Muskox intrusion and other stratiform intrusions: a new perspective|journal= Geology |volume=5|issue= 5|pages=273|year= 1977|doi=10.1130/0091-7613(1977)5<273:ooclit>2.0.co;2}}</ref> or rock (e.g. gabbro, troctolite).<ref>{{cite journal|vauthors= Leuthold J, Blundy JD, Brooker RA |title= Experimental petrology constraints on the recycling of mafic cumulate: A focus on Cr-spinel from the Rum Eastern Layered Intrusion, Scotland|journal= Contributions to Mineralogy and Petrology |volume=170|issue= 2|page=12|year= 2015|doi=10.1007/s00410-015-1165-0|url= https://research-information.bristol.ac.uk/en/publications/experimental-petrology-constraints-on-the-recycling-of-mafic-cumulate(43578f76-07c8-4676-84d1-d763d5228efb).html|bibcode= 2015CoMP..170...12L|hdl= 1983/43578f76-07c8-4676-84d1-d763d5228efb|s2cid= 129562202|hdl-access= free}}</ref><ref>{{cite journal|vauthors= O Driscoll B, Emeleus CH, Donaldson CH, Daly JS |title= The roles of melt infiltration and cumulate assimilation in the formation of anorthosite and a Cr-spinel seam in the Rum Eastern Layered Intrusion, NW Scotland|journal= Lithos|volume= 111|issue= 1–2|pages= 6–20|year= 2009|doi= 10.1016/j.lithos.2008.11.011|bibcode= 2009Litho.111....6O}}</ref>

Spinel, {{chem2|(Mg,Fe)(Al,Cr)2O4}}, is common in [[peridotite]] in the uppermost [[Earth's mantle]], between approximately 20&nbsp;km to approximately 120&nbsp;km, possibly to lower depths depending on the chromium content.<ref>{{cite journal|url=http://www.eeo.ed.ac.uk/homes/sklemme/publications/Klemme_Lithos_2004.pdf|doi=10.1016/j.lithos.2004.03.017|title=The influence of Cr on the garnet–spinel transition in the Earth's mantle: Experiments in the system MgO—Cr<sub>2</sub>O<sub>3</sub>—SiO<sub>2</sub> and thermodynamic modelling|journal=Lithos|volume=77|issue=1–4|pages=639–646|year=2004|last1=Klemme|first1=Stephan|bibcode=2004Litho..77..639K}}</ref>  At significantly shallower depths, above the [[Mohorovičić discontinuity|Moho]], calcic [[plagioclase]] is the more stable aluminous mineral in peridotite while [[garnet]] is the stable phase deeper in the mantle below the spinel stability region.<ref>{{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=17}}</ref>

Spinel, {{chem2|(Mg,Fe)Al2O4}}, is a common mineral in the [[Ca-Al-rich inclusion]]s (CAIs) in some [[chondrite|chondritic meteorite]]s.<ref>{{cite journal |last1=MacPherson |first1=G.J. |title=Calcium–Aluminum-Rich Inclusions in Chondritic Meteorites |journal=Treatise on Geochemistry |date=2007 |pages=1–47 |doi=10.1016/B0-08-043751-6/01065-3|isbn=9780080437514 }}</ref>