View source for Chemistry:Spinel

{{Short description|Mineral or gemstone}}
{{Infobox mineral
|boxtextcolor = White
|boxbgcolor   = #cb236b
| name        = Spinel
| category    = {{plainlist|
* [[Chemistry:Oxide minerals|Oxide minerals]]
* [[Chemistry:Spinel group|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 crystal system|Cubic]]
| class       = Hextetrahedral ({{overline|4}}3m)<br/>H–M symbol: ({{overline|4}}3m)<ref>{{cite web |last1=Robert John Lancashire |title=Normal Spinels |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 |website=CHEM2101 (C 21J) Inorganic Chemistry – Chemistry of Transition Metal Complexes |publisher=University of the West Indies}}</ref><ref>{{cite journal |display-authors=0|last1=N. W. Grimes |title=New Symmetry and Structure for Spinel |journal=Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences |volume=386 |issue=1791 |pages=333–345 |date=Apr 8, 1983 |doi=10.1098/rspa.1983.0039 |jstor=2397417 |bibcode=1983RSPSA.386..333G |s2cid=96560029 }}</ref><ref>{{cite journal |display-authors=0|last1=L. Hwang |title=On the space group of {{chem|MgAl|2|O|4}} spinel |journal=[[Physics:Philosophical Magazine|Philosophical Magazine]] |date=Jul 1973 |doi=10.1080/14786437308217448 |url=https://www.researchgate.net/publication/233373497}}</ref>
| symmetry    = {{nowrap|1=''F'' {{overline|4}} 3 m}} (No. 216)
| unit cell   = a = 8.0898(9)&nbsp;Å; Z&nbsp;=&nbsp;8
| color       = Various; red, pink, blue, lavender/violet, dark green, brown, black, colourless
| 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       = Weak to medium magnetic, sometimes fluorescent (red synthetic yes, natural red sometimes)
| references  = <ref name=Mindat>{{Mindat|id=3729|name=Spinel}}</ref><ref>{{WebMineral|url=http://webmineral.com/data/Spinel.shtml|title=Spinel Mineral Data}}</ref>
}}
[[File:MgAl2O4.png|thumb|Polyhedral representation of spinel MgAl<sub>2</sub>O<sub>4</sub>]]
'''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 [[Chemistry:Magnesium|magnesium]]/[[Chemistry:Aluminium|aluminium]] member of the larger [[Chemistry:Spinel group|spinel group]] of minerals. It has the formula {{chem|Mg|Al|2|O|4}} in the [[Cubic crystal system|cubic crystal system]]. Its name comes from the Latin word {{lang|la|spinella}}, a diminutive form of ''spine,'' in reference to its pointed crystals.<ref name=Mindat/>

==Properties==
[[File:Spinelgem.JPG|thumb|left|Cut spinel]]
Spinel crystallizes in the isometric system; common crystal forms are [[Octahedron|octahedra]], usually [[Physics:Crystal twinning|twinned]]. It has no true [[Physics:Cleavage (crystal)|cleavage]], but shows an octahedral parting and a [[Earth:Conchoidal fracture|conchoidal fracture]].<ref>{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |pages=362–363}}</ref> Its [[Physics:Mohs scale of mineral hardness|hardness]] is 8, its [[Physics:Specific gravity|specific gravity]] is 3.5–4.1, and it is transparent to opaque with a vitreous to dull [[Earth:Lustre (mineralogy)|luster]]. It may be colorless, but is usually various shades of red, [[Lavender (color)|lavender]], blue, green, brown, black, or yellow.<ref name="klein-hurlbut">{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st}}</ref> Chromium(III) causes the red color in spinel from Burma.<ref>{{Cite web |title=Minerals Colored by Metal Ions |url=http://minerals.gps.caltech.edu/color_causes/Metal_Ion/index.html |access-date=2023-03-01 |website=minerals.gps.caltech.edu}}</ref> Some spinels are among the most famous gemstones; among them are 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 is the largest known spinel in the world, weighing {{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>

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> In the past, before the arrival of modern science, spinels and rubies were equally known as rubies. After the 18th century, the word ruby was only used for the red gem variety of the mineral [[Chemistry:Corundum|corundum]], and the word spinel came to be used.{{sfn|Pardieu|Farkhodova|2019}} "Balas" is derived from Balascia, the ancient name for [[Place:Badakhshan|Badakhshan]], a region in central [[Earth:Asia|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 [[Social:Sanskrit|Sanskrit]] ''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 Tajikistan constituted for centuries the main source for red and pink spinels.{{sfn|Pardieu|Farkhodova|2019}}

==Occurrence==

===Geologic occurrence===
Spinel is found as a [[Earth:Metamorphic rock|metamorphic mineral]] in metamorphosed [[Earth:Limestone|limestone]]s and silica-poor mudstones.<ref name="klein-hurlbut"/> It also occurs as a primary mineral in rare mafic [[Earth:Igneous rock|igneous rock]]s; in these igneous rocks, the [[Biology:Magma|magma]]s are relatively deficient in [[Chemistry:Alkali|alkali]]s relative to [[Chemistry:Aluminium|aluminium]], and aluminium oxide may form as the mineral corundum or may combine with magnesia to form spinel. This is why spinel and [[Chemistry:Ruby|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:Earth's mantle|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 [[Earth:Mohorovičić discontinuity|Moho]], calcic [[Chemistry:Plagioclase|plagioclase]] is the more stable aluminous mineral in peridotite while [[Chemistry:Garnet|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 [[Astronomy: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>

===Geographical occurrence===
Spinel has long been found in the [[Earth:Gemstone|gemstone]]-bearing gravel of Sri Lanka and in [[Earth:Limestone|limestone]]s 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 ({{wipe|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 [[Chemistry:Cobalt|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 Vientam|journal=Gems & Gemology|date=Spring 2015}}</ref>

==Synthetic spinel==
Synthetic spinel can be produced by similar means to synthetic corundum, including the [[Physics:Verneuil method|Verneuil method]] and the [[Chemistry:Ceramic flux|flux method]] pioneered by Edmond Frémy. It is widely used as an inexpensive cut gem in [[Chemistry:Birthstone|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 [[Earth:Sintering|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>

{{clear}}

==See also==
* [[Chemistry:Aluminium oxynitride|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). ''[[Earth:An Introduction to the Rock-Forming Minerals|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==
* [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:Aluminium minerals]]
[[Category:Cubic minerals]]
[[Category:Minerals in space group 227]]
[[Category:Magnesium minerals]]
[[Category:Luminescent minerals]]
[[Category:Transparent materials]]

{{Sourceattribution|Spinel}}