{{Short description|Mineral or gemstone}} {{About||the larger class of minerals|Spinel group|the Russian painter|Joseph Spinel|the Steven Universe character|List of Steven Universe characters#Spinel}} {{Infobox mineral |boxtextcolor = White |boxbgcolor = #cb236b | name = Spinel | category = {{plainlist| * Oxide minerals * Spinel group * Spinel structural group}} | image = Calcite-Spinel-dtn37a.jpg | imagesize = 260px | caption = Small spinel crystal on top of a white calcite from Mogok, Myanmar, measuring 1.5 × 1.1 × 1 cm in size | formula = {{chem|Mg|Al|2|O|4}} | IMAsymbol = Spl<ref>{{cite journal |last=Warr |first=L.N. |title=IMA–CNMNC approved mineral symbols |journal=Mineralogical Magazine |volume=85 |pages=291–320 |date=2021|issue=3 |doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616 |doi-access=free }}</ref> | strunz = 4.BB.05 | system = Cubic | class = Hextetrahedral ({{overline|4}}3m)<br/>H–M symbol: ({{overline|4}}3m)<ref>{{cite web |first=Robert John |last=Lancashire |title=Normal spinels |website=CHEM2101 (C 21J) Inorganic Chemistry |series=Chemistry of transition metal complexes |publisher=University of the West Indies |place=Kingston, Jamaica |url=http://wwwchem.uwimona.edu.jm/courses/spinel.html |archive-url=https://web.archive.org/web/20180808174808/http://wwwchem.uwimona.edu.jm/courses/spinel.html |url-status=dead |archive-date=2018-08-08 }}</ref><ref>{{cite journal |last1=Grimes |first1=N.W. |display-authors=etal |date=8 April 1983 |title=New symmetry and structure for spinel |journal=Proceedings of the Royal Society of London |series=Series A, Mathematical and Physical Sciences |volume=386 |issue=1791 |pages=333–345 |doi=10.1098/rspa.1983.0039 |jstor=2397417 |bibcode=1983RSPSA.386..333G |s2cid=96560029 }}</ref><ref>{{cite journal |last1=Hwang |first1=L. |display-authors=etal |date=July 1973 |title=On the space group of {{chem|MgAl|2|O|4}} spinel |journal=Philosophical Magazine |doi=10.1080/14786437308217448 |url=https://www.researchgate.net/publication/233373497 }}</ref> | symmetry = {{nobr|''F'' {{overline|4}} 3 m}} (No.&nbsp;216) | unit cell = a = 8.0898(9)&nbsp;Å; {{nobr|Z {{=}} 8}} | color = Various: red, pink, blue, lavender / violet, dark green, brown, black, clear | habit = Octahedral or flat triangular plates caused by twinning | twinning = common | cleavage = None | fracture = Conchoidal | mohs = 7.5–8.0 | luster = Vitreous | refractive = 1.719 | opticalprop = Isotropic | birefringence = | pleochroism = Absent | streak = White | gravity = (Depending on the composition) The rare Zn-rich spinel can be as high as 4.40, otherwise it averages from 3.58 to 3.61. | melt = | fusibility = | diagnostic = | solubility = None | diaphaneity = Transparent to opaque | other = Weakly to medium magnetic; sometimes fluorescent (natural: sometimes red; synthetic: red) | references = <ref name=Mindat>{{Mindat|id=3729|name=Spinel}}</ref><ref>{{WebMineral|url=http://webmineral.com/data/Spinel.shtml|title=Spinel Mineral Data}}</ref> }}

'''Spinel''' ({{IPAc-en|s|p|ɪ|ˈ|n|ɛ|l|,_|ˈ|s|p|ɪ|n|əl}}<ref>{{cite book|title=The Chambers Dictionary|publisher=Chambers|year=2003|isbn=0-550-10105-5|edition=9th|chapter=spinel}}</ref>) is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula {{chem|Mg|Al|2|O|4}} in the cubic crystal system. The name comes from the Latin word {{lang|la|spinella}}, a diminutive form of ''spine,'' in reference to its pointed crystals.<ref name=Mindat/>

==Properties== Spinel crystallizes in the isometric system; common crystal forms are octahedra, usually twinned. It has no true cleavage, but shows an octahedral parting and a conchoidal fracture.<ref>{{cite book |last1=Nesse |first1=William D. |year=2000 |title=Introduction to mineralogy |publisher =Oxford University Press |place=New York, NY |isbn =9780195106916 |pages =362–363}}</ref> Its hardness is 8, its specific gravity is 3.5–4.1, and it is transparent to opaque with a vitreous to dull luster. It may be colorless, but usually comes in shades of red, lavender, blue, green, brown, black, or yellow.<ref name="klein-hurlbut">{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S., Jr. |year=1993 |title=Manual of Mineralogy (after James D. Dana) |edition=21st |publisher=Wiley |location=New York, NY |isbn=047157452X }}</ref> Chromium(III) causes the red color in spinel from Burma.<ref>{{cite web |title=Minerals colored by metal ions |publisher=CalTech |url=http://minerals.gps.caltech.edu/color_causes/Metal_Ion/index.html |access-date=2023-03-01 |website=minerals.gps.caltech.edu }}</ref> thumb|left|Polyhedral representation of spinel MgAl<sub>2</sub>O<sub>4</sub> ==History== Some spinels are among the most famous gemstones; these include the Black Prince's Ruby and the Timur Ruby in the British Crown Jewels,<ref name="Butler1989">{{cite book |author=Sir Thomas Butler |title=The Crown Jewels and Coronation Ceremony |url=https://books.google.com/books?id=brbvmKAQ5PEC |year=1989 |publisher=Pitkin |isbn=978-0-85372-467-4 |page=6}}</ref> and the "Côte de Bretagne", formerly from the French Crown jewels.<ref>{{cite journal |last1 =Pardieu |first1 =V. |last2 =Farkhodova |first2 =T. |title=Spinel from Tajikistan |journal =InColor |date =Summer 2019 |pages =30–33 |url =https://www.researchgate.net/publication/339439345 |accessdate =28 April 2021}}</ref> The Samarian Spinel, the largest known spinel in the world, weighs {{convert|500|carat|g}}.<ref>{{cite journal |title =Samarian spinel |journal =Dictionary of Gems and Gemology |date =2005 |pages =657–737 |doi =10.1007/3-540-27269-0_19}}</ref>

== Nomenclature == The transparent red spinels were called spinel-rubies<ref>{{cite journal |last1 =Lytvynov |first1 =L.A. |year=2011 |title =On the words used as names for ruby and sapphire |journal =Functional Materials |volume =18 |number =2 |page =275 |url=http://dspace.nbuv.gov.ua/bitstream/handle/123456789/135445/21-Lytvynov.pdf?sequence=1 |accessdate=29 April 2021}}</ref> or balas rubies.<ref>{{cite journal |last1 =Hughes |first1 =R.W. |year =1994 |title =The rubies and spinels of Afghanistan: A brief history |journal=Journal of Gemmology |volume=24 |number=4 |pages=256–267 |doi =10.15506/JoG.1994.24.4.256 |url =https://gem-a.com/images/Documents/JoG/Archive/1956-97/JoG1994_24_4.pdf#page=26 |accessdate =29 April 2021}}</ref> Before the development of modern science and the establishment of a formal definition of "ruby", the name was also applied to spinels. {{sfn|Pardieu|Farkhodova|2019}} "Balas" derives from Balascia, the ancient name for Badakhshan, a region in central Asia situated in the upper valley of the Panj River, one of the principal tributaries of the Oxus River. However, "Balascia" itself may be derived from Sanskrit {{translit | sa | bālasūryaka}}, which translates as "crimson-coloured morning sun".<ref>{{cite book |last1=Biswas |first1=A.K. |editor1-last =Ramachandra Rao |editor1-first =P. |editor2-last =Goswami |editor2-first =N.G. |title =Metallurgy in India : a retrospective |date =2001 |publisher =India International Publisher |location =New Delhi |asin =B002A9M6QU |pages=1–22 |chapter=Minerals and their Exploitation in Ancient and Pre-modern India}}</ref> Mines in the Gorno Badakhshan region of present-day Tajikistan constituted for centuries the main source for red and pink spinels.{{sfn|Pardieu|Farkhodova|2019}}

==Occurrence==

===Geologic occurrence=== Spinel is found as a metamorphic mineral in metamorphosed limestones and silica-poor mudstones.<ref name="klein-hurlbut"/> It also occurs as a primary mineral in rare mafic igneous rocks; in these igneous rocks, the magmas are relatively deficient in alkalis 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 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 inclusions (CAIs) in some chondritic meteorites.<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>

===Geographical occurrence=== Spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestones of the Badakshan Province in modern-day Afghanistan and Tajikistan; and of Mogok in Myanmar. Over the last decades gem quality spinels are found in the marbles of Lục Yên District (Vietnam), Mahenge and Matombo (Tanzania), Tsavo (Kenya) and in the gravels of Tunduru (Tanzania) and Ilakaka (Madagascar).{{sfn|Pardieu|Farkhodova|2019}}<ref>{{cite journal |last1=Pardieu |first1=Vincent |first2=R. W. |last2=Hughes |first3=E. |last3=Boehm |journal=InColor Magazine |title=Spinel: Resurrection of a classic |year=2008 |pages=10–18 |url=https://www.researchgate.net/publication/264973257 |accessdate=29 April 2021}}</ref>

Since 2000, in several locations around the world, spinels have been discovered with unusual vivid pink or blue colors. Such "glowing" spinels are known from Mogok (Myanmar),<ref>{{cite journal|url=https://www.gia.edu/gems-gemology/spring-2014-pardieu-jedi-spinels-in-mogok/|first=Vincent|last=Pardieu|title=Hunting for "Jedi" Spinels in Mogok|journal=Gems & Gemology|volume=50|number= 1|date=2014|pages=46–57|doi=10.5741/GEMS.50.1.46|doi-access=free}}</ref> Mahenge plateau (Tanzania), Lục Yên District (Vietnam)<ref>{{cite web|url=https://www.wondermondo.com/blue-spinel-in-luc-yen/|author=Wondermondo|title=Finds of cobalt blue spinel in Lục Yên, Vietnam|date=16 June 2019}}</ref> and some more localities. In 2018 bright blue spinels have been reported also in the southern part of Baffin Island (Canada).<ref>{{cite web|url=https://www.mining.com/scientists-figure-origin-cobalt-blue-spinel-canadas-arctic/|author=Mining.Com|title=Scientists figure out origin of cobalt-blue spinel in Canada's Arctic|date=5 April 2019}}</ref> The pure blue coloration of spinel is caused by small additions of cobalt.<ref>{{cite journal|url=https://www.researchgate.net/publication/276519619|author=Boris Chauviré, Benjamin Rondeau, Emmanuel Fritsch, Phillipe Ressigeac, and Jean-Luc Devidal|title=Blue Spinel From the Luc Yen District of Vietnam|journal=Gems & Gemology|date=Spring 2015}}</ref>

==Synthetic spinel== Synthetic spinel can be produced by similar means to synthetic corundum, including the Verneuil method and the flux method pioneered by Edmond Frémy. It is widely used as an inexpensive cut gem in birthstone jewelry for the month of August. Light blue synthetic spinel is a good imitation of aquamarine beryl, and green synthetic spinel is used as an emerald or tourmaline simulant.<ref>Simon & Schuster's Guide to Gems and Precious Stones, K. Lyman, 1996</ref> By 2015, transparent spinel was being made in sheets and other shapes through sintering.<ref>{{cite web|url=http://phys.org/news/2015-04-applications-tough-spinel-ceramic.html|title=Researchers finding applications for tough spinel ceramic|work=Phys.org|date=24 April 2015}}</ref> Synthetic spinel, which looks like glass but has notably higher strength against pressure, can also have applications in military and commercial use.<ref>{{cite web|url=https://www.nrl.navy.mil/Media/News/Article/2534832/transparent-armor-from-nrl-spinel-could-also-ruggedize-your-smart-phone/|title=Transparent Armor from NRL; Spinel Could Also Ruggedize Your Smart Phone|publisher=Naval Research Laboratory|date=23 April 2015 |access-date=4 August 2023 |url-status=live |archive-url=https://web.archive.org/web/20230804234329/https://www.nrl.navy.mil/Media/News/Article/2534832/transparent-armor-from-nrl-spinel-could-also-ruggedize-your-smart-phone/ |archive-date=4 August 2023}}</ref>

Spinel-type chalcogenides are also investigated as optoelectronic semiconductors. In 2025, Hanzawa et al. reported {{mvar|d}}{{sup|0}}-cation spinel sulfides based on {{chem2|ZnSc2S4}} and (Zn,Mg)Sc<sub>2</sub>S<sub>4</sub> with color-tunable direct band gaps and ambipolar dopability.<ref>{{cite journal |last1=Hanzawa |first1=Kota |last2=Nagai |first2=Takayuki |last3=Nagasawa |first3=Ryoga |last4=Katase |first4=Takayoshi |last5=Hosono |first5=Hideo |last6=Hiramatsu |first6=Hidenori |date=1 October 2025 |title=d0 Cation-Based Spinel-Type Sulfide Semiconductors with Color-Tunable Direct-Gap and Ambipolar Dopability |journal=Journal of the American Chemical Society |volume=147 |issue=39 |pages=35935-35941 |doi=10.1021/jacs.5c12816}}</ref>

==See also== * {{Portal-inline|Minerals}} * Aluminium oxynitride * Ceylonite * The Three Brothers, a lost 14th-century crown jewel with three red spinels in a triangular arrangement

==References== {{reflist|22em}}

==Bibliography== * Deer, Howie and Zussman (1966). ''An Introduction to the Rock-Forming Minerals'', Longman, pp.&nbsp;424–433, {{ISBN|0-582-44210-9}}. * Shumann, Walter (2006). ''Gemstones of the World'' 3rd edition, Sterling, pp.&nbsp;116–117.

==External links== {{commons category|Spinel}} * [http://www.uwgb.edu/dutchs/PETROLOGY/Spinel%20Structure.HTM Spinel structure] at the University of Wisconsin - Green Bay * [http://www.tf.uni-kiel.de/matwis/amat/def_en/kap_2/basics/b2_1_6.html Spinel structure] at the Institut for materials science of the University of Kiel * [http://www.gemsociety.org/article/spinel-jewelry-and-gemstone-information/ Value of Spinel]

{{Minerals}} {{Gemstone}} {{Jewelry}}

Category:Spinel gemstones Category:Aluminium minerals Category:Cubic minerals Category:Minerals in space group 227 Category:Magnesium minerals Category:Luminescent minerals Category:Transparent materials