Ajay Kumar at 14:40, 28 August 2023

2023-08-28T14:40:22Z

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{{short description|Oxide mineral}}
{{distinguish|Carborundum}}
{{Infobox mineral
| name = Corundum
| category = [[Oxide mineral]] – Hematite group
| boxwidth =
| boxbgcolor =
| image = Several corundum crystals.jpg
| imagesize = 260px
| caption =
| formula = [[Aluminium oxide]], {{chem2|auto=1|Al2O3}}
| IMAsymbol = Crn<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| strunz = 4.CB.05
| dana = 4.3.1.1
| system = [[Trigonal]]
| class = Hexagonal scalenohedral ({{overline|3}}m) [[H-M symbol]]: ({{overline|3}} 2/m)
| symmetry = {{mvar|R}}{{overline|3}}{{mvar|c}} (No. 167)
| unit cell = {{nowrap|{{mvar|a}} {{=}} 4.75 Å}}, {{nowrap|{{mvar|c}} {{=}} 12.982 Å}}; {{nowrap|{{mvar|Z}} {{=}} 6}}
| color = Colorless, gray, golden-brown, brown; purple, pink to red, orange, yellow, green, blue, violet; may be color zoned, asteriated mainly grey and brown
| habit = Steep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular
| twinning = Polysynthetic twinning common
| cleavage = None – parting in 3 directions
| tenacity = Brittle
| fracture = Conchoidal to uneven
| mohs = 9 (defining mineral)<ref>{{cite web |title=Mohs' scale of hardness |url=http://www.minsocam.org/msa/collectors_corner/article/mohs.htm |work=Collector's corner |publisher=Mineralogical Society of America |access-date=10 January 2014}}</ref>
| luster = Adamantine to vitreous
| refractive = {{nowrap|{{mvar|n}}{{sub|{{math|ω}}}} {{=}} 1.767–1.772}} {{nowrap|{{mvar|n}}{{sub|{{math|ε}}}} {{=}} 1.759–1.763}}
| opticalprop = Uniaxial (−)
| pleochroism = None
| streak = Colorless
| diaphaneity = Transparent, [[translucent]] to [[opacity (optics)|opaque]]
| gravity = 3.95–4.10
| melt = {{cvt|2044|°C}}
| fusibility = Infusible
| diagnostic =
| solubility = Insoluble
| other = May fluoresce or phosphoresce under UV light
| alteration = May alter to mica on surfaces causing a decrease in hardness
| references = <ref name=Handbook>{{cite book |editor1=Anthony, John W. |editor2=Bideaux, Richard A. |editor3=Bladh, Kenneth W. |editor4=Nichols, Monte C. |title=Handbook of Mineralogy |year=1997 |publisher=Mineralogical Society of America |place=Chantilly, VA, US |url=http://rruff.geo.arizona.edu/doclib/hom/corundum.pdf |archive-url=https://web.archive.org/web/20060905204655/http://rruff.geo.arizona.edu/doclib/hom/corundum.pdf |archive-date=2006-09-05 |url-status=live |chapter=Corundum |isbn=0962209724 |volume=III Halides, Hydroxides, Oxides}}</ref><ref name=Mindat>{{cite web |url=http://www.mindat.org/min-1136.html |title=Corundum |website=Mindat.org}}</ref><ref name=Webmin>{{cite web |url=http://www.webmineral.com/data/Corundum.shtml |title=Corundum |website= Webmineral.com |archive-url=https://web.archive.org/web/20061125202622/http://webmineral.com/data/Corundum.shtml |archive-date=2006-11-25 |df=dmy-all}}</ref><ref name=Hurlbut>{{cite book |author1=Hurlbut, Cornelius S. |author2=Klein, Cornelis |year=1985 |title=Manual of Mineralogy |url=https://archive.org/details/manualofmineralo00klei |url-access=registration |edition=20th |publisher=Wiley |pages=[https://archive.org/details/manualofmineralo00klei/page/300 300]–302 |isbn=0-471-80580-7}}</ref>
| var1 = [[Sapphire]]|var1text = Any color except red
| var2 = [[Ruby]] |var2text = Red
| var3 = [[Emery (mineral)|Emery]] |var3text = Black granular corundum intimately mixed with [[magnetite]], [[hematite]], or [[hercynite]]
}}
'''Corundum''' is a [[crystal]]line form of [[aluminium oxide]] ({{chem2|Al2O3}}) typically containing traces of [[iron]], [[titanium]], [[vanadium]] and [[chromium]].<ref name=Handbook/><ref name=Mindat/> It is a [[rock (geology)|rock]]-forming [[mineral]]. It is a naturally [[transparency and translucency|transparent]] material, but can have different colors depending on the presence of [[transition metal]] impurities in its crystalline structure.<ref name=":0">{{cite book |title=Gem Corundum |last1=Giuliani |first1=Gaston |last2=Ohnenstetter |first2=Daniel |last3=Fallick |first3=Anthony E. |last4=Groat |first4=Lee |last5=Fagan |last6=Andrew J. |publisher=Mineralogical Association of Canada |year=2014 |isbn=978-0-921294-54-2 |location=Research Gate |pages=37–38 |chapter=The Geology and Genesis of Gem Corundum Deposits}}</ref> Corundum has two primary gem varieties: [[ruby]] and [[sapphire]]. Rubies are red due to the presence of [[chromium]], and sapphires exhibit a range of colors depending on what transition metal is present.<ref name=":0"/> A rare type of sapphire, [[Sapphire#Padparadscha|padparadscha]] sapphire, is pink-orange.

The name "corundum" is derived from the [[Tamil language|Tamil]]-[[Dravidian languages|Dravidian]] word ''kurundam'' (ruby-sapphire) (appearing in [[Sanskrit language|Sanskrit]] as ''kuruvinda'').<ref>{{OEtymD|corundum}}</ref><ref>{{Cite journal |last1=Jeršek |first1=Miha |last2=Jovanovski |first2=Gligor |last3=Boev |first3=Blažo |last4=Makreski |first4=Petre |date=2021 |title=Intriguing minerals: corundum in the world of rubies and sapphires with special attention to Macedonian rubies |url=https://link.springer.com/10.1007/s40828-021-00143-0 |journal=ChemTexts |language=en |volume=7 |issue=3 |pages=19 |doi=10.1007/s40828-021-00143-0 |s2cid=233435945 |issn=2199-3793}}</ref>

Because of corundum's hardness (pure corundum is defined to have 9.0 on the [[Mohs scale of mineral hardness|Mohs]] scale), it can scratch almost all other minerals. It is commonly used as an [[abrasive]] on [[sandpaper]] and on large tools used in machining metals, plastics, and wood. [[Emery (rock)|Emery]], a variety of corundum with no value as a gemstone, is commonly used as an abrasive. It is a black granular form of corundum, in which the mineral is intimately mixed with [[magnetite]], [[hematite]], or [[hercynite]].<ref name=Hurlbut/>

In addition to its hardness, corundum has a density of {{cvt|4.02|g/cm3|lb/cuft}}, which is unusually high for a transparent mineral composed of the low-[[atomic mass]] elements [[aluminium]] and [[oxygen]].<ref>{{cite web |url=http://www.galleries.com/Corundum |title=The Mineral Corundum |website=galleries.com}}</ref>

==Geology and occurrence==
[[File:Corindon azulEZ.jpg|thumb|left|180px|Corundum from [[Brazil]], size about {{convert|2|×|3|cm|in|sigfig=1|abbr=on}}]]
Corundum occurs as a mineral in mica [[schist]], [[gneiss]], and some [[marble]]s in [[metamorphic]] [[terrane]]s. It also occurs in low-silica [[igneous]] [[syenite]] and [[nepheline syenite]] [[intrusive rock|intrusive]]s. Other occurrences are as masses adjacent to [[ultramafic]] intrusives, associated with [[lamprophyre]] [[dike (geology)|dikes]] and as large crystals in [[pegmatite]]s.<ref name=Hurlbut/> It commonly occurs as a [[detrital]] mineral in stream and beach sands because of its hardness and resistance to weathering.<ref name=Hurlbut/> The largest documented single crystal of corundum measured about {{convert|65|×|40|×|40|cm|in|abbr=on}}, and weighed {{convert|152|kg|lb|abbr=on}}.<ref>{{cite journal |author=Rickwood, P. C. |year=1981 |title=The largest crystals |journal=American Mineralogist |volume=66 |pages=885–907 |url=http://www.minsocam.org/ammin/AM66/AM66_885.pdf |archive-url=https://web.archive.org/web/20090620081033/http://www.minsocam.org/ammin/AM66/AM66_885.pdf |archive-date=2009-06-20 |url-status=live}}</ref> The record has since been surpassed by certain synthetic [[boule (crystal)|boules]].<ref>{{cite web |url=http://www.ledinside.com/news/2009/4/Rubicon_Technology_Grows_Super_boule_of_200kg_Weight_20090421 |title=Rubicon Technology grows 200 kg "super boule" |website=LED Inside |date=April 21, 2009 |df=dmy-all}}</ref>

Corundum for [[abrasive]]s is mined in Zimbabwe, Pakistan, Afghanistan, Russia, Sri Lanka, and India. Historically it was mined from deposits associated with [[dunite]]s in [[North Carolina]], US, and from a [[nepheline syenite]] in [[Craigmont, Ontario]].<ref name=Hurlbut/> [[Emery (mineral)|Emery]]-grade corundum is found on the [[list of islands of Greece|Greek island]] of [[Naxos]] and near [[Peekskill, New York]], US. Abrasive corundum is synthetically manufactured from [[bauxite]].<ref name=Hurlbut/>

Four corundum axes dating to 2500 BC from the [[Liangzhou culture]] have been discovered in China.<ref>{{cite web |url=http://news.bbc.co.uk/2/hi/science/nature/4555235.stm |title=Chinese made first use of diamond |publisher=BBC |date=May 2005 |work=BBC News}}</ref>

==Synthetic corundum==
* In 1837, [[Marc Antoine Auguste Gaudin|Marc Antoine Gaudin]] made the first synthetic rubies by reacting [[alumina]] at a high temperature with a small amount of [[chromium]] as a [[colourant]].<ref>{{cite journal |url=http://www.gem-a.com/media/94808/duroc%20danner%20website.pdf |journal=Journal of Gemmology |volume=32 |pages=175–178 |year=2011 |title=Untreated yellowish orange sapphire exhibiting its natural colour |author=Duroc-Danner, J. M. |issue=5 |doi=10.15506/jog.2011.32.5.174 |url-status=dead |archive-url=https://web.archive.org/web/20130516231326/http://www.gem-a.com/media/94808/duroc%20danner%20website.pdf |archive-date=2013-05-16 |df=dmy-all}}</ref>
* In 1847, [[Jacques-Joseph Ebelmen|J. J. Ebelmen]] made white [[sapphire#Synthetic sapphire|synthetic sapphires]] by reacting [[Aluminium oxide|alumina]] in [[boric acid]].
* In 1877, Frenic and Freil made crystal corundum from which small stones could be cut. Frimy and [[Auguste Victor Louis Verneuil|Auguste Verneuil]] manufactured artificial ruby by fusing {{chem2|link=barium fluoride|BaF2}} and {{chem2|link=aluminium oxide|Al2O3}} with a little chromium at temperatures above {{convert|2000|C|abbr=on}}.
* In 1903, [[Auguste Victor Louis Verneuil|Verneuil]] announced that he could produce synthetic rubies on a commercial scale using this [[flame fusion]] process.<ref>{{cite web |url=http://farlang.com/books/bahadur-a-handbook-of-precious-stones |author=Bahadur |title=A Handbook of Precious Stones |year=1943 |access-date=2007-08-19 |df=dmy-all}}</ref>

The [[Verneuil process]] allows the production of flawless single-crystal [[sapphire]] and [[ruby]] gems of much larger size than normally found in nature. It is also possible to grow gem-quality synthetic corundum by flux-growth and [[hydrothermal synthesis]]. Because of the simplicity of the methods involved in corundum synthesis, large quantities of these crystals have become available on the market at a fraction of the cost of natural stones.<ref>{{cite journal |last1=Walsh |first1=Andrew |title=The commodification of fetishes: Telling the difference between natural and synthetic sapphires |journal=American Ethnologist |date=February 2010 |volume=37 |issue=1 |pages=98–114 |doi=10.1111/j.1548-1425.2010.01244.x}}</ref>

Apart from ornamental uses, synthetic corundum is also used to produce mechanical parts (tubes, rods, bearings, and other machined parts), scratch-resistant optics, scratch-resistant [[watch#Overview|watch]] crystals, instrument windows for satellites and spacecraft (because of its transparency in the ultraviolet to infrared range), and [[laser]] components. For example, the [[KAGRA]] gravitational wave detector's main mirrors are {{cvt|50|lb|adj=on|order=flip}} sapphires,<ref>{{cite journal |first1=Eiichi |last1=Hirose |display-authors=etal |year=2014 |title=Sapphire mirror for the KAGRA gravitational wave detector |journal=Physical Review D |volume=89 |issue=6 |page=062003 |doi=10.1103/PhysRevD.89.062003 |bibcode=2014PhRvD..89f2003H |url=https://authors.library.caltech.edu/45938/1/PhysRevD.89.062003.pdf |archive-url=https://web.archive.org/web/20180724161640/https://authors.library.caltech.edu/45938/1/PhysRevD.89.062003.pdf |archive-date=2018-07-24 |url-status=live}}</ref> and [[Advanced LIGO]] considered {{cvt|40|kg}} sapphire mirrors.<ref>{{cite web |first=GariLynn |last=Billingsley |title=Advanced Ligo Core Optics Components – Downselect |url=https://labcit.ligo.caltech.edu/~gari/LIGOII/Downselect/ |publisher=LIGO Laboratory |year=2004 |access-date=2020-02-06 |df=dmy-all}}</ref> Corundum has also found use in the development of ceramic armour thanks to its high hardiness.<ref>Defense World.Net, [https://www.defenseworld.net/news/27805/Russia___s_Armored_Steel_Comparable_Ceramic_Plate_Clears_Tests Russia’s Armored Steel-Comparable Ceramic Plate Clears Tests], 5th September 2020, Retrieved 29th December 2020</ref>

==Structure and physical properties==
[[File:Corundum.png|thumb|250 px|left|Crystal structure of corundum]]
[[File:Corundum-pV.svg|thumb|250 px|right|Molar volume vs. pressure at room temperature]]
Corundum crystallizes with trigonal symmetry in the space group [[hexagonal crystal family#Crystal classes|{{mvar|R}}{{overline|3}}{{mvar|c}}]] and has the lattice parameters {{nowrap|{{mvar|a}} {{=}} 4.75 Å}} and {{nowrap|{{mvar|c}} {{=}} 12.982 Å}} at standard conditions. The unit cell contains six formula units.<ref>{{cite journal |last1=Newnham |first1=R. E. |last2=de Haan |first2=Y. M. |title=Refinement of the α Al2O3, Ti2O3, V2O3 and Cr2O3 structures* |journal=Zeitschrift für Kristallographie |date=August 1962 |volume=117 |issue=2–3 |pages=235–237 |doi=10.1524/zkri.1962.117.2-3.235|bibcode=1962ZK....117..235N }}</ref><ref name=Mindat/>

The toughness of corundum is sensitive to surface roughness<ref>{{cite journal |url=https://rd.springer.com/article/10.1007/BF00638054?no-access=true |title=Effect of machining on fracture toughness of corundum |first1=Farrokh |last1=Farzin-Nia |first2=Terry |last2=Sterrett |first3=Ron |last3=Sirney |journal=Journal of Materials Science |year=1990 |volume=25 |issue=5 |pages=2527–2531 |doi=10.1007/bf00638054|bibcode=1990JMatS..25.2527F |s2cid=137548763 }}</ref><ref>{{cite journal |doi=10.1111/j.1151-2916.1976.tb09390.x |volume=59 |title=Fracture-Strength Anisotropy of Sapphire |journal=Journal of the American Ceramic Society |year=1976 |pages=59–61|last1=Becker |first1=Paul F. |issue=1–2 }}</ref> and crystallographic orientation.<ref name="Fracture of Sapphire">{{cite journal |doi=10.1111/j.1151-2916.1969.tb09199.x |volume=52 |title=Fracture of Sapphire |journal=Journal of the American Ceramic Society |year=1969 |pages=485–491|last1=Wiederhorn |first1=S. M. |issue=9 }}</ref> It may be 6–7 MPa·m{{sup|1/2}} for synthetic crystals,<ref name="Fracture of Sapphire"/> and around 4 MPa·m{{sup|1/2}} for natural.<ref>{{cite web |title=Corundum, Aluminum Oxide, Alumina, 99.9%, Al2O3 |website=www.matweb.com |url=http://www.matweb.com/search/datasheet_print.aspx?matguid=c8c56ad547ae4cfabad15977bfb537f1}}</ref>

In the lattice of corundum, the oxygen atoms form a slightly distorted [[hexagonal close packing]], in which two-thirds of the octahedral sites between the oxygen ions are occupied by aluminium ions.<ref name="nesse">{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |pages=363–364}}</ref> The absence of aluminium ions from one of the three sites breaks the symmetry of the hexagonal close packing, reducing the space group symmetry to {{mvar|R}}{{overline|3}}{{mvar|c}} and the crystal class to trigonal.<ref>{{cite book |last1=Borchardt-Ott |first1=Walter |last2=Kaiser |first2=E. T. |title=Crystallography |date=1995 |publisher=Springer |location=Berlin |isbn=3540594787 |page=230 |edition=2nd}}</ref> The structure of corundum is sometimes described as a pseudohexagonal structure.<ref>{{cite journal |last1=Gea |first1=Laurence A. |last2=Boatner |first2=L. A. |last3=Rankin |first3=Janet |last4=Budai |first4=J. D. |title=The Formation Al 2 O 3 /V 2 O 3 Multilayer Structures by High-Dose Ion Implantation |journal=MRS Proceedings |date=1995 |volume=382 |pages=107 |doi=10.1557/PROC-382-107}}</ref>

==Generalization==
{{Main|Corundum (structure)}}
Because of its prevalence, corundum has also become the name of a major structure type (''corundum type'') found in various [[Binary compound|binary]] and [[Ternary compound|ternary compounds]].<ref>{{Cite book |last1=Muller |first1=Olaf |last2=Roy |first2=Rustum |url=https://www.worldcat.org/oclc/1056558 |title=The major ternary structural families |date=1974 |publisher=Springer-Verlag |isbn=0-387-06430-3 |location=New York |oclc=1056558}}</ref>

==See also==
{{Commons category|Corundum}}
* [[Aluminium oxynitride]]
* [[Gemstone]]
* [[Spinel]] – natural and synthetic mineral often mistaken for corundum

{{clear left}}

==References==
{{reflist|25em}}

{{Mohs}}
{{Authority control}}

[[Category:Abrasives]]
[[Category:Aluminium minerals]]
[[Category:Corundum varieties]]
[[Category:Hematite group]]
[[Category:Industrial minerals]]
[[Category:Luminescent minerals]]
[[Category:Oxide minerals]]
[[Category:Polymorphism (materials science)]]
[[Category:Superhard materials]]
[[Category:Trigonal minerals]]
[[Category:Minerals in space group 167]]

Corundum - Revision history

Ajay Kumar at 14:40, 28 August 2023