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Corundum

This page kindly sponsored by Norman King
Formula:
Al2O3
System:
Trigonal
Colour:
Colourless, blue, red, ...
Hardness:
9
Member of:
Name:
Named "corinvindum" in 1725 by John Woodward and derived from the Sanskrit, kuruvinda ("Ruby"). Richard Kirwan used the current spelling "corundum" in 1794. Known by many names in ancient times: adamant, sapphire, ruby, hyacinthos, asteria, etc.
The aluminum analogue of Eskolaite, Hematite, and Karelianite.
The red (Cr-bearing) gem variety is called Ruby.
The blue (Fe- and Ti-bearing) gem variety is called Sapphire.


Visit gemdat.org for gemological information about Corundum.

Classification of Corundum

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
4.CB.05

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
C : Metal: Oxygen = 2: 3,3: 5, and similar
B : With medium-sized cations
Dana 7th ed.:
4.3.1.1
4.3.1.1

4 : SIMPLE OXIDES
3 : A2X3
7.6.1

7 : Oxides and Hydroxides
6 : Oxides of Al
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http://www.mindat.org/min-1136.html
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Occurrences of Corundum

Geological Setting:
Silica-poor rocks, such as Nepheline-Syenites, alkali igneous undersaturated rocks, contact aureoles in altered aluminous shales, aluminous xenoliths in high temperature plutonic and hypabyssal rocks, metamorphosed bauxite deposits, and as a detrital material in sediments.

Physical Properties of Corundum

Adamantine, Vitreous, Pearly
Diaphaneity (Transparency):
Transparent, Translucent, Opaque
Colour:
Colourless, blue, red, pink, yellow, grey, golden-brown
Streak:
White
Hardness (Mohs):
9
Hardness Data:
Mohs hardness reference species
Tenacity:
Brittle
Cleavage:
None Observed
Parting:
Rhombohedral and basal parting {0001}, sometimes perfect but interrupted; also on {1011} due to exsolution (Boehmite), observed on large blocks (Georgia, USA).
Fracture:
Irregular/Uneven, Conchoidal
Density:
3.98 - 4.1 g/cm3 (Measured)    3.997 g/cm3 (Calculated)

Crystallography of Corundum

Crystal System:
Trigonal
Class (H-M):
3m (3 2/m) - Hexagonal Scalenohedral
Space Group:
R3c
Cell Parameters:
a = 4.75Å, c = 12.982Å
Ratio:
a:c = 1 : 2.733
Unit Cell Volume:
V 253.54 ų
Z:
6
Morphology:
Often steep pyramidal on w, z, E, or ω. Barrel-shaped crystals that are often rough and rounded, of considerable size at times, varying from short prismatic [0001] with a large base to steep pyramidal. Less commonly, flat tabular {0001} or rhombohedral. Striae on {0001} parallel [011¯0]. Lines in the direction [112¯0] divide the base into six sectors at times.
Twinning:
1. Common {1011}; usually lamellar, producing a lamellar structure and striae on c and r. Less commonly penetration twins or arrowhead twins with crystals tabular {1120}. 2. On {0001}, less common. Pressure twinning produced on {1011}, and on {0001}.

Crystallographic forms of Corundum

Crystal Atlas:
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Corundum no.17 - Goldschmidt (1913-1926)
Corundum no.34 - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by www.smorf.nl.

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Crystal Structure

Structure
Reference
Pauling L Hendricks S B (1925) Crystal structures of hematite and corundum Locality: Ceylon. Journal of the American Chemical Society 47:781-790.

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More Crystal Structures
Click here to view more crystal structures at the American Mineralogist Crystal Structure Database
X-Ray Powder Diffraction:
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Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.
X-Ray Powder Diffraction Data:
d-spacingIntensity
3.48 (70)
2.551 (97)
2.379 (42)
2.085 (100)
1.7398 (42)
1.6014 (82)
1.3738 (45)

Optical Data of Corundum

Type:
Uniaxial (-)
RI values:
nω = 1.767 - 1.772 nε = 1.759 - 1.763
2V:
Measured: 58°
Birefringence:
Low, first-order greys and whites.
Max Birefringence:
δ = 0.008 - 0.009
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
High
Colour in reflected light:
Colourless
Pleochroism:
Not Visible
Comments:
Weak in sapphire (e = blue-green to yellow-green, o = pale to deep blue), otherwise none visible.
Comments:
Asterism often present due to oriented needle-like inclusions or to colloidal or other material deposited in oriented tubules.

Chemical Properties of Corundum

Formula:
Al2O3
Essential elements:
All elements listed in formula:
Analytical Data:
Al (52.93)
O (47.07)
Empirical Formula:
Al2O3
Common Impurities:
Cr,Fe,V,Ti

Relationship of Corundum to other Species

Member of:
Other Members of Group:
4.CB.05BrizziiteNaSb5+O3
4.CB.05Ecandrewsite(Zn,Fe2+,Mn2+)TiO3
4.CB.05EskolaiteCr2O3
4.CB.05GeikieliteMgTiO3
4.CB.05HematiteFe2O3
4.CB.05IlmeniteFe2+TiO3
4.CB.05KarelianiteV23+O3
4.CB.05MelanostibiteMn2+(Sb5+,Fe3+)O3
4.CB.05PyrophaniteMn2+TiO3
4.CB.05Akimotoite(Mg,Fe2+)SiO3
4.CB.05AuroantimonateAuSbO3
4.CB.05Romanite(◻,Pb,Ca)UFe22+(Ti,Fe3+)6Ti12O38
4.CB.05UM1998-11-O-AuHSbAu2+Sb3+O2(OH)
4.CB.05TistariteTi23+O3
4.CB.10AvicenniteTl2O3
4.CB.10BixbyiteMn23+O3
4.CB.15Armalcolite(Mg,Fe2+)Ti2O5
4.CB.15PseudobrookiteFe2TiO5
4.CB.20Zincohögbomite-2N2S[(Zn,Al,Fe2+)3(Al,Fe3+,Ti)8O15(OH)]2
4.CB.20Zincohögbomite-2N6S[(Zn,Mg)7(Al,Fe3+,Ti)16O31(OH)]2
4.CB.20Magnesiohögbomite-6N6S[(Mg,Fe2+)3(Al,Ti,Fe3+)8O15(OH)]6
4.CB.20Magnesiohögbomite-2N3S[(Mg,Fe2+,Zn)4(Al,Ti,Fe3+)10O19(OH)]2
4.CB.20Magnesiohögbomite-2N2S[(Mg,Fe2+)3[Al7(Ti,Fe3+)]O15(OH)]2
4.CB.20Ferrohögbomite-6N12S[(Fe2+,Mg,Zn)5(Al,Ti,Fe3+)12O23(OH)]6
4.CB.25PseudorutileFe2Ti3O9
4.CB.25KleberiteFeTi6O11(OH)5
4.CB.30BerdesinskiiteV23+TiO5
4.CB.30OxyvaniteV23+V4+O5
4.CB.35Olkhonskite(Cr,V)2Ti3O9
4.CB.35SchreyeriteV23+Ti3O9
4.CB.40KamiokiteFe2Mo3O8
4.CB.40Nolanite(V3+,Fe3+,Fe2+,Ti)10O14(OH)2
4.CB.40RinmaniteZn2Sb2Mg2Fe4O14(OH)2
4.CB.40IseiteMn2Mo3O8
4.CB.40MajindeiteMg2Mo3O8
4.CB.45ClaudetiteAs2O3
4.CB.45StibioclaudetiteAsSbO3
4.CB.50ArsenoliteAs2O3
4.CB.50SénarmontiteSb2O3
4.CB.55ValentiniteSb2O3
4.CB.60BismiteBi2O3
4.CB.65SphaerobismoiteBi2O3
4.CB.70SilléniteBi12SiO20
4.CB.75KyzylkumiteTi2V3+O5(OH)
4.CB.80TietaiyangiteFe43+Fe2+TiO9
7.6.2BöhmiteAlO(OH)
7.6.2DiasporeAlO(OH)
7.6.4GibbsiteAl(OH)3
7.6.5BayeriteAl(OH)3
7.6.6NordstranditeAl(OH)3
7.6.7DoyleiteAl(OH)3
7.6.8Akdalaite4Al2O3 · H2O

Other Names for Corundum

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Industrial Uses:
Corundum is used as an abrasive ("Emery"), and the gem varieties of corundum are better-known as Ruby and Sapphire.

References for Corundum

Reference List:
Haüy (1805), Ann. Phys.: 20: 187.

Lucas (1806): 1: 257.

Judd (1895), Mineralogical Magazine: 11: 49.

Goldschmidt and Schroeder (1910), Min. Mitt.: 29: 461.

Spencer (1927) Mineralogical Magazine: 21: 329.

Palache, Charles, Harry Berman & Clifford Frondel (1944), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume I: Elements, Sulfides, Sulfosalts, Oxides. John Wiley and Sons, Inc., New York. 7th edition, revised and enlarged: 520-527.

Anastasiou, P. and Seifert, F. (1972) Solid solubility of Al2O3 in enstatite at high teperatures and 1-5 kb water pressure. Contributions to Mineralogy and Petrology: 34: 272-287.

Arima, M. and Onuma, K. (1977) The solubility of alumina in enstatite and the phase equilibria in the join MgSiO3-MgAl2SiO6 at 10-25 kbar. Contributions to Mineralogy and Petrology: 61: 251-265.

Franzini M., Troysi M., Cecchini A.(1986): La microdurezza del corindone. Atti Soc. Sc. Nat. Mem. Serie A, 93, 87-100.

Zeitschrift für Kristallographie: 117: 233-237.

Sutherland, F.L., Hoskin, P.W.O., Fanning, C.M., and Coenraads, R.R. (1998) Models of corundum origin from alkali basaltic terrains: a reappraisal. Contributions to Mineralogy and Petrology: 133: 356-372.

Internet Links for Corundum

Specimens:
The following Corundum specimens are currently listed for sale on minfind.com.

Localities for Corundum

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
Mineral and/or Locality  
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