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Colourless, blue, red, pink, yellow, grey, golden-brown
Adamantine, Vitreous, Pearly
Specific Gravity:
3.98 - 4.1
Crystal System:
Member of:
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.

Compare 'silicon spinel', that might possibly be similar to the gamma form of Al2O3.

Visit for gemological information about Corundum.

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Classification of CorundumHide

Approved, 'Grandfathered' (first described prior to 1959)

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.:

3 : A2X3

7 : Oxides and Hydroxides
6 : Oxides of Al

Physical Properties of CorundumHide

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

Optical Data of CorundumHide

Uniaxial (-)
RI values:
nω = 1.767 - 1.772 nε = 1.759 - 1.763
Measured: 58°
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:
Colour in reflected light:
Not Visible
Weak in sapphire (e = blue-green to yellow-green, o = pale to deep blue), otherwise none visible.
Asterism often present due to oriented needle-like inclusions or to colloidal or other material deposited in oriented tubules.

Chemical Properties of CorundumHide

Common Impurities:

Crystallography of CorundumHide

Crystal System:
Class (H-M):
3m (3 2/m) - Hexagonal Scalenohedral
Space Group:
Cell Parameters:
a = 4.75 Å, c = 12.982 Å
a:c = 1 : 2.733
Unit Cell V:
253.54 ų
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.
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 CorundumHide

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

Edge Lines | Miller Indicies | Axes

Opaque | Translucent | Transparent

Along a-axis | Along b-axis | Along c-axis | Start rotation | Stop rotation

X-Ray Powder DiffractionHide

Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.
Powder Diffraction Data:
3.48 (70)
2.551 (97)
2.379 (42)
2.085 (100)
1.7398 (42)
1.6014 (82)
1.3738 (45)

Synonyms of CorundumHide

Other Language Names for CorundumHide

Varieties of CorundumHide

Adamantine SparA silky brown variety of corundum.
AlundumAn artificial Corundum used as an abrasive.
Asteriated SapphireA variety of Sapphire exhibiting the property of asterism.
BarklyiteA magenta-coloured variety of ruby (Corundum).
Originally reported from Victoria, Australia.
Blue AlexandriteA trade name for blue/violet sapphire
Cat SapphireOriental sapphires of some value but not of the characteristic colour.
ChlorosaphirA deep green variety of Corundum from Drachenfels, Königswinter, Siebengebirge, North Rhine-Westphalia, Germany.
Chromian CorundumAn unnecessary name for a Cr-bearing Corundum. Note that much Corundum contains traces of Cr.
Ledo frozen fireA Fe Ti rich blue gem variety of Corundum
Oriental AmethystA purple gem variety of Corundum.
Oriental EmeraldA green gem variety of Corundum.
Oriental TopazA yellow gem variety of Corundum.
PadmaragayaA trade name for a yellow gem variety of Corundum.
PadparadschaA salmon-pink coloured gem sapphire.
RubyA red, gem variety of corundum. The red colour is caused by minor amounts of trivalent Cr replacing Al in the crystal structure.
SapphireMost commonly refers to a blue gem variety of Corundum, but other coloured varieties of Corundum are also described as Sapphire, except red Corundum, which is better known as Ruby.
Star CorundumA variety of corundum exhibiting a star pattern when viewed down the C axis. The chatoyance is due to oriented microscopic inclusions.
Star RubyA variety of ruby exhibiting a star pattern when viewed down the c axis. The chatoyance is due to oriented microscopic inclusions (nanorods) of diaspore (Nadin, 2007).
Star SapphireA variety of sapphire that exhibits a star pattern when viewed down the c axis. The chatoyance is due to oriented microscopic inclusions (nanorods) of diaspore (Nadin, 2007).
Titanian Corundum
Trapiche rubyVariety showing six-spoked growth features.
Compare trapiche emerald.

Relationship of Corundum to other SpeciesHide

Member of:
Other Members of this group:
HematiteFe2O3Trig. 3m (3 2/m) : R3c
TistariteTi3+2O3Trig. 3m (3 2/m) : R3c

Common AssociatesHide

Associated Minerals Based on Photo Data:
Biotite53 photos of Corundum associated with Biotite on
Rutile26 photos of Corundum associated with Rutile on
Kyanite24 photos of Corundum associated with Kyanite on
Phlogopite18 photos of Corundum associated with Phlogopite on
Muscovite18 photos of Corundum associated with Muscovite on
Sapphire14 photos of Corundum associated with Sapphire on
Feldspar Group14 photos of Corundum associated with Feldspar Group on
Hematite13 photos of Corundum associated with Hematite on
Calcite12 photos of Corundum associated with Calcite on
Spinel11 photos of Corundum associated with Spinel on

Related Minerals - Nickel-Strunz GroupingHide

4.CB.05BrizziiteNaSb5+O3Trig. 3 : R3
4.CB.05Ecandrewsite(Zn,Fe2+,Mn2+)TiO3Trig. 3 : R3
4.CB.05GeikieliteMgTiO3Trig. 3 : R3
4.CB.05HematiteFe2O3Trig. 3m (3 2/m) : R3c
4.CB.05IlmeniteFe2+TiO3Trig. 3 : R3
4.CB.05PyrophaniteMn2+TiO3Trig. 3 : R3
4.CB.05TistariteTi3+2O3Trig. 3m (3 2/m) : R3c
4.CB.10AvicenniteTl2O3Iso. m3 (2/m 3) : Ia3
4.CB.10BixbyiteMn3+2O3Iso. m3 (2/m 3) : Ia3
4.CB.15Armalcolite(Mg,Fe2+)Ti2O5Orth. mmm (2/m 2/m 2/m)
4.CB.15PseudobrookiteFe2TiO5Orth. mmm (2/m 2/m 2/m)
4.CB.20Zincohögbomite-2N2S[(Zn,Al,Fe2+)3(Al,Fe3+,Ti)8O15(OH)]2Hex. 6mm : P63mc
4.CB.20Zincohögbomite-2N6S[(Zn,Mg)7(Al,Fe3+,Ti)16O31(OH)]2Hex. 6mm : P63mc
4.CB.20Magnesiohögbomite-6N6S[(Mg,Fe2+)3(Al,Ti,Fe3+)8O15(OH)]6Trig. 3m (3 2/m) : R3m
4.CB.20Magnesiohögbomite-2N3S[(Mg,Fe2+,Zn)4(Al,Ti,Fe3+)10O19(OH)]2Trig. 3m (3 2/m) : P3 1m
4.CB.20Magnesiohögbomite-2N2S[(Mg,Fe2+)3[Al7(Ti,Fe3+)]O15(OH)]2Hex. 6mm : P63mc
4.CB.20Ferrohögbomite-6N12S[(Fe2+,Mg,Zn)5(Al,Ti,Fe3+)12O23(OH)]6Trig. 3m (3 2/m) : R3m
4.CB.25KleberiteFeTi6O11(OH)5Mon. 2/m : P21/b
4.CB.30OxyvaniteV3+2V4+O5Mon. 2/m : B2/b
4.CB.40RinmaniteZn2Sb2Mg2Fe4O14(OH)2Hex. 6 : P63
4.CB.40IseiteMn2Mo3O8Hex. 6mm : P63mc
4.CB.40MajindeiteMg2Mo3O8Hex. 6mm : P63mc
4.CB.45ClaudetiteAs2O3Mon. 2/m
4.CB.45StibioclaudetiteAsSbO3Mon. 2/m : P21/m
4.CB.50ArsenoliteAs2O3Iso. m3m (4/m 3 2/m) : Fd3m
4.CB.50SenarmontiteSb2O3Iso. m3m (4/m 3 2/m) : Fd3m
4.CB.55ValentiniteSb2O3Orth. mmm (2/m 2/m 2/m) : Pccn
4.CB.60BismiteBi2O3Mon. 2/m : P21/b
4.CB.70SilléniteBi12SiO20Iso. 2 3 : I2 3
4.CB.75KyzylkumiteV3+Ti2O5(OH)Mon. 2/m : P21/b

Related Minerals - Dana Grouping (8th Ed.)Hide 3m (3 2/m) : R3c

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

7.6.2BöhmiteAlO(OH)Orth. mmm (2/m 2/m 2/m)
7.6.2DiasporeAlO(OH)Orth. mmm (2/m 2/m 2/m)
7.6.4GibbsiteAl(OH)3Mon. 2/m
7.6.5BayeriteAl(OH)3Mon. 2/m : P21/m
7.6.6NordstranditeAl(OH)3Tric. 1 : P1
7.6.8Akdalaite5Al2O3 · H2OHex.

Other InformationHide

Health Risks:
Industrial Uses:
Corundum is used as an abrasive ("Emery"), and the gem varieties of corundum are better-known as Ruby and Sapphire.

Corundum in petrologyHide

An essential component of (items highlighted in red)
Common component of (items highlighted in red)

References for CorundumHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Haüy (1805): Ann. Phys.: 20: 187.
Lucas (1806): 1: 257.
Edmond Frémy (1891): Synthèse du rubis. Vve. Ch. Dunod, France. []
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 temperatures 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 CorundumHide

Localities for CorundumHide

This 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.

Locality ListShow