Wikipedia

Spinel

For the larger class of minerals, seeSpinel group.For the Russian painter, seeJoseph Spinel.For the Steven Universe character, seeList of Steven Universe characters § Spinel.

Spinel(/spɪˈnɛl,ˈspɪnəl/[7]) is themagnesium/aluminiummember of the largerspinel groupof minerals. It has the formulaMgAl
2O
4in thecubic crystal system.Its name comes from the Latin wordspinella,a diminutive form ofspine,in reference to its pointed crystals.[5]

Spinel
Small spinel crystal on top of a white calcite from Mogok, Myanmar, measuring 1.5 × 1.1 × 1 cm in size
General
Category
Formula
(repeating unit)		MgAl
2O
4
IMA symbolSpl[1]
Strunz classification4.BB.05
Crystal systemCubic
Crystal classHextetrahedral (43m)
H–M symbol:(43m)[2][3][4]
Space groupF43 m(No. 216)
Unit cella = 8.0898(9) Å; Z = 8
Identification
ColorVarious; red, pink, blue, lavender/violet, dark green, brown, black, colourless
Crystal habitOctahedral or flat triangular plates caused by twinning
Twinningcommon
CleavageNone
FractureConchoidal
Mohs scalehardness7.5–8.0
LusterVitreous
StreakWhite
DiaphaneityTransparent to opaque
Specific 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.
Optical propertiesIsotropic
Refractive index1.719
PleochroismAbsent
SolubilityNone
Other characteristicsWeak to medium magnetic, sometimes fluorescent (red synthetic yes, natural red sometimes)
References[5][6]
Polyhedral representation of spinel MgAl2O4

Properties

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Cut spinel

Spinel crystallizes in the isometric system; common crystal forms areoctahedra,usuallytwinned.It has no truecleavage,but shows an octahedralpartingand aconchoidal fracture.[8]Itshardnessis 8, itsspecific gravityis 3.5–4.1, and it is transparent to opaque with a vitreous to dullluster.It may be colorless, but is usually various shades of red,lavender,blue, green, brown, black, or yellow.[9]Chromium(III) causes the red color in spinel from Burma.[10]Some spinels are among the most famous gemstones; among them are theBlack Prince's Rubyand the "Timur ruby"in the BritishCrown Jewels,[11]and the "Côte de Bretagne", formerly from the French Crown jewels.[12]TheSamarian Spinelis the largest known spinel in the world, weighing 500 carats (100 g).[13]

The transparent red spinels were called spinel-rubies[14]or balas rubies.[15]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 mineralcorundum,and the word spinel came to be used.[16]"Balas" is derived from Balascia, the ancient name forBadakhshan,a region in centralAsiasituated in the upper valley of thePanj River,one of the principal tributaries of theOxus River.However, "Balascia" itself may be derived fromSanskritbālasūryaka,which translates as "crimson-coloured morning sun".[17]Mines in theGorno Badakhshanregion ofTajikistanconstituted for centuries the main source for red and pink spinels.[16]

Occurrence

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Geologic occurrence

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Spinel is found as ametamorphic mineralin metamorphosedlimestonesand silica-poormudstones.[9]It also occurs as a primary mineral in rare maficigneous rocks;in these igneous rocks, themagmasare relatively deficient inalkalisrelative toaluminium,and aluminium oxide may form as the mineral corundum or may combine with magnesia to form spinel. This is why spinel andrubyare often found together. The spinel petrogenesis in mafic magmatic rocks is strongly debated, but certainly results from mafic magma interaction with more evolved magma[18]or rock (e.g. gabbro, troctolite).[19][20]

Spinel,(Mg,Fe)(Al,Cr)2O4,is common inperidotitein the uppermostEarth's mantle,between approximately 20 km to approximately 120 km, possibly to lower depths depending on the chromium content.[21]At significantly shallower depths, above theMoho,calcicplagioclaseis the more stable aluminous mineral in peridotite whilegarnetis the stable phase deeper in the mantle below the spinel stability region.[22]

Spinel,(Mg,Fe)Al2O4,is a common mineral in theCa-Al-rich inclusions(CAIs) in somechondritic meteorites.[23]

Geographical occurrence

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Spinel has long been found in thegemstone-bearing gravel ofSri Lankaand inlimestonesof the Badakshan Province in modern-dayAfghanistanandTajikistan;and ofMogokinMyanmar.Over the last decades gem quality spinels are found in the marbles ofLục Yên District(Vietnam),Mahengeand Matombo (Tanzania), Tsavo (Kenya) and in the gravels of Tunduru (Tanzania) and Ilakaka (Madagascar).[16][24]

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),[25]Mahenge plateau (Tanzania), Lục Yên District (Vietnam)[26]and some more localities. In 2018 bright blue spinels have been reported also in the southern part ofBaffin Island(Canada).[27]The pure blue coloration of spinel is caused by small additions ofcobalt.[28]

Synthetic spinel

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Synthetic spinel can be produced by similar means to synthetic corundum, including theVerneuil methodand theflux methodpioneered byEdmond Frémy.It is widely used as an inexpensive cut gem inbirthstonejewelryfor the month ofAugust.Light blue synthetic spinel is a good imitation of aquamarine beryl, and green synthetic spinel is used as an emerald or tourmaline simulant.[29]By 2015, transparent spinel was being made in sheets and other shapes throughsintering.[30]Synthetic spinel, which looks like glass but has notably higher strength against pressure, can also have applications in military and commercial use.[31]

See also

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References

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  1. ^Warr, L.N. (2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3):291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
  2. ^Robert John Lancashire."Normal Spinels".CHEM2101 (C 21J) Inorganic Chemistry – Chemistry of Transition Metal Complexes.University of the West Indies. Archived fromthe originalon 2018-08-08.
  3. ^N. W. Grimes; et al. (Apr 8, 1983). "New Symmetry and Structure for Spinel".Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences.386(1791):333–345.Bibcode:1983RSPSA.386..333G.doi:10.1098/rspa.1983.0039.JSTOR2397417.S2CID96560029.
  4. ^L. Hwang; et al. (Jul 1973)."On the space group ofMgAl
    2    O
    4    spinel "    .Philosophical Magazine.doi:10.1080/14786437308217448.
  5. ^ab"Spinel".Mindat.org.
  6. ^Spinel Mineral Data,WebMineral
  7. ^"spinel".The Chambers Dictionary(9th ed.). Chambers. 2003.ISBN0-550-10105-5.
  8. ^Nesse, William D. (2000).Introduction to mineralogy.New York: Oxford University Press. pp.362–363.ISBN9780195106916.
  9. ^abKlein, Cornelis; Hurlbut, Cornelius S. Jr. (1993).Manual of mineralogy: (after James D. Dana)(21st ed.). New York: Wiley.ISBN047157452X.
  10. ^"Minerals Colored by Metal Ions".minerals.gps.caltech.edu.Retrieved2023-03-01.
  11. ^Sir Thomas Butler (1989).The Crown Jewels and Coronation Ceremony.Pitkin. p. 6.ISBN978-0-85372-467-4.
  12. ^Pardieu, V.; Farkhodova, T. (Summer 2019)."Spinel from Tajikistan".InColor:30–33.Retrieved28 April2021.
  13. ^"Samarian spinel".Dictionary of Gems and Gemology:657–737. 2005.doi:10.1007/3-540-27269-0_19.
  14. ^Lytvynov, L.A. (2011)."On the words used as names for ruby and sapphire"(PDF).Functional Materials.18(2): 275.Retrieved29 April2021.
  15. ^Hughes, R.W. (1994)."The rubies and spinels of Afghanistan: A brief history"(PDF).Journal of Gemmology.24(4):256–267.doi:10.15506/JoG.1994.24.4.256.Retrieved29 April2021.
  16. ^abcPardieu & Farkhodova 2019.
  17. ^Biswas, A.K. (2001). "Minerals and their Exploitation in Ancient and Pre-modern India". In Ramachandra Rao, P.; Goswami, N.G. (eds.).Metallurgy in India: a retrospective.New Delhi: India International Publisher. pp.1–22.ASINB002A9M6QU.
  18. ^Irvine TN (1977). "Origin of chromite layers in the Muskox intrusion and other stratiform intrusions: a new perspective".Geology.5(5): 273.doi:10.1130/0091-7613(1977)5<273:ooclit>2.0.co;2.
  19. ^Leuthold J, Blundy JD, Brooker RA (2015)."Experimental petrology constraints on the recycling of mafic cumulate: A focus on Cr-spinel from the Rum Eastern Layered Intrusion, Scotland".Contributions to Mineralogy and Petrology.170(2): 12.Bibcode:2015CoMP..170...12L.doi:10.1007/s00410-015-1165-0.hdl:1983/43578f76-07c8-4676-84d1-d763d5228efb.S2CID129562202.
  20. ^O Driscoll B, Emeleus CH, Donaldson CH, Daly JS (2009). "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".Lithos.111(1–2):6–20.Bibcode:2009Litho.111....6O.doi:10.1016/j.lithos.2008.11.011.
  21. ^Klemme, Stephan (2004)."The influence of Cr on the garnet–spinel transition in the Earth's mantle: Experiments in the system MgO—Cr2O3—SiO2and thermodynamic modelling "(PDF).Lithos.77(1–4):639–646.Bibcode:2004Litho..77..639K.doi:10.1016/j.lithos.2004.03.017.
  22. ^Philpotts, Anthony R.; Ague, Jay J. (2009).Principles of igneous and metamorphic petrology(2nd ed.). Cambridge, UK: Cambridge University Press. p. 17.ISBN9780521880060.
  23. ^MacPherson, G.J. (2007). "Calcium–Aluminum-Rich Inclusions in Chondritic Meteorites".Treatise on Geochemistry:1–47.doi:10.1016/B0-08-043751-6/01065-3.ISBN9780080437514.
  24. ^Pardieu, Vincent; Hughes, R. W.; Boehm, E. (2008)."Spinel: Resurrection of a classic".InColor Magazine:10–18.Retrieved29 April2021.
  25. ^Pardieu, Vincent (2014)."Hunting for" Jedi "Spinels in Mogok".Gems & Gemology.50(1):46–57.doi:10.5741/GEMS.50.1.46.
  26. ^Wondermondo (16 June 2019)."Finds of cobalt blue spinel in Lục Yên, Vietnam".
  27. ^Mining.Com (5 April 2019)."Scientists figure out origin of cobalt-blue spinel in Canada's Arctic".
  28. ^Boris Chauviré, Benjamin Rondeau, Emmanuel Fritsch, Phillipe Ressigeac, and Jean-Luc Devidal (Spring 2015)."Blue Spinel From the Luc Yen District of Vietnam".Gems & Gemology.{{cite journal}}:CS1 maint: multiple names: authors list (link)
  29. ^Simon & Schuster's Guide to Gems and Precious Stones, K. Lyman, 1996
  30. ^"Researchers finding applications for tough spinel ceramic".Phys.org.24 April 2015.
  31. ^"Transparent Armor from NRL; Spinel Could Also Ruggedize Your Smart Phone".Naval Research Laboratory. 23 April 2015.Archivedfrom the original on 4 August 2023.Retrieved4 August2023.

Bibliography

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