spinel

File:Spinelgem.JPG

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.{{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}} 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 is usually various shades of red, lavender, blue, green, brown, black, or yellow.{{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}} Chromium(III) causes the red color in spinel from Burma.{{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}} 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,{{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}} and the "Côte de Bretagne", formerly from the French Crown jewels.{{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}} The Samarian Spinel is the largest known spinel in the world, weighing {{convert|500|carat|g}}.{{cite journal |title=Samarian spinel |journal=Dictionary of Gems and Gemology |date=2005 |pages=657–737 |doi=10.1007/3-540-27269-0_19}}

The transparent red spinels were called spinel-rubies{{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}} or balas rubies.{{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}} 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 corundum, and the word spinel came to be used.{{sfn|Pardieu|Farkhodova|2019}} "Balas" is derived 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 bālasūryaka, which translates as "crimson-coloured morning sun".{{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}} Mines in the Gorno Badakhshan region of Tajikistan constituted for centuries the main source for red and pink spinels.{{sfn|Pardieu|Farkhodova|2019}}

Spinel is found as a metamorphic mineral in metamorphosed limestones and silica-poor mudstones. 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 {{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}} or rock (e.g. gabbro, troctolite).{{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}}{{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}}

Spinel, {{chem2|(Mg,Fe)(Al,Cr)2O4}}, is common in peridotite in the uppermost Earth's mantle, between approximately 20 km to approximately 120 km, possibly to lower depths depending on the chromium content.{{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—Cr₂O₃—SiO₂ and thermodynamic modelling|journal=Lithos|volume=77|issue=1–4|pages=639–646|year=2004|last1=Klemme|first1=Stephan|bibcode=2004Litho..77..639K}} 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.{{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}}

Spinel, {{chem2|(Mg,Fe)Al2O4}}, is a common mineral in the Ca-Al-rich inclusions (CAIs) in some chondritic meteorites.{{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 }}

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}}{{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}}

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),{{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}} Mahenge plateau (Tanzania), Lục Yên District (Vietnam){{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}} and some more localities. In 2018 bright blue spinels have been reported also in the southern part of Baffin Island (Canada).{{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}} The pure blue coloration of spinel is caused by small additions of cobalt.{{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}}

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.Simon & Schuster's Guide to Gems and Precious Stones, K. Lyman, 1996 By 2015, transparent spinel was being made in sheets and other shapes through sintering.{{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}} Synthetic spinel, which looks like glass but has notably higher strength against pressure, can also have applications in military and commercial use.{{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}}

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

{{reflist|22em}}

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

{{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]

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Category:Aluminium minerals

Category:Cubic minerals

Category:Minerals in space group 227

Category:Magnesium minerals

Category:Luminescent minerals

Category:Transparent materials