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Corundum

This page kindly sponsored by Norman King
Formula:
Al2O3
View Commodity Page:
Colour:
Colourless, blue, red, pink, yellow, grey, golden-brown
Lustre:
Adamantine, Vitreous, Pearly
Hardness:
9
Specific Gravity:
3.98 - 4.1
Crystal System:
Trigonal
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.

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

Visit gemdat.org for gemological information about Corundum.


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Classification of CorundumHide

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

Pronounciation of CorundumHide

Pronounciation:
PlayRecorded byCountry
Jolyon & Katya RalphUnited Kingdom

Physical Properties of CorundumHide

Adamantine, Vitreous, Pearly
Transparency:
Transparent, Translucent, Opaque
Colour:
Colourless, blue, red, pink, yellow, grey, golden-brown
Streak:
White
Hardness:
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)

Optical Data of CorundumHide

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 CorundumHide

Formula:
Al2O3
Common Impurities:
Cr,Fe,V,Ti

Crystallography of CorundumHide

Crystal System:
Trigonal
Class (H-M):
3m (3 2/m) - Hexagonal Scalenohedral
Space Group:
R3c
Cell Parameters:
a = 4.75 Å, c = 12.982 Å
Ratio:
a:c = 1 : 2.733
Unit Cell 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 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 www.smorf.nl.

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Edge Lines | Miller Indicies | Axes

Transparency
Opaque | Translucent | Transparent

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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:
d-spacingIntensity
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. Red, Cr-bearing corundum is ruby.
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.

In traditional gemmological terms, ruby has to be blood-red and of clear, facetable quality to justify the name, however in...
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).

The Star of India is the largest star sapphire in the world (563 carats or 11...
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:
EskolaiteCr2O3Trig.
HematiteFe2O3Trig. 3m (3 2/m) : R3c
KarelianiteV3+2O3Trig.
TistariteTi3+2O3Trig. 3m (3 2/m) : R3c

Common AssociatesHide

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

Related Minerals - Nickel-Strunz GroupingHide

4.CB.05BrizziiteNaSb5+O3Trig. 3 : R3
4.CB.05Ecandrewsite(Zn,Fe2+,Mn2+)TiO3Trig. 3 : R3
4.CB.05EskolaiteCr2O3Trig.
4.CB.05GeikieliteMgTiO3Trig. 3 : R3
4.CB.05HematiteFe2O3Trig. 3m (3 2/m) : R3c
4.CB.05IlmeniteFe2+TiO3Trig. 3 : R3
4.CB.05KarelianiteV3+2O3Trig.
4.CB.05MelanostibiteMn2+(Sb5+,Fe3+)O3Trig.
4.CB.05PyrophaniteMn2+TiO3Trig. 3 : R3
4.CB.05Akimotoite(Mg,Fe2+)SiO3Trig.
4.CB.05AuroantimonateAuSbO3
4.CB.05UM1998-11-O-AuHSbAu+2Sb3+O2(OH)
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.25PseudorutileFe2Ti3O9Hex.
4.CB.25KleberiteFeTi6O11(OH)5Mon. 2/m : P21/b
4.CB.30BerdesinskiiteV3+2TiO5Mon.
4.CB.30OxyvaniteV3+2V4+O5Mon. 2/m : B2/b
4.CB.35Olkhonskite(Cr,V)2Ti3O9Mon.
4.CB.35SchreyeriteV3+2Ti3O9Mon.
4.CB.40KamiokiteFe2Mo3O8Hex.
4.CB.40Nolanite(V3+,Fe3+,Fe2+,Ti)10O14(OH)2Hex.
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.65SphaerobismoiteBi2O3Tet.
4.CB.70SilléniteBi12SiO20Iso. 2 3 : I2 3
4.CB.75KyzylkumiteV3+Ti2O5(OH)Mon. 2/m : P21/b
4.CB.80TietaiyangiteFe3+4Fe2+TiO9Hex.

Related Minerals - Dana Grouping (8th Ed.)Hide

4.3.1.2HematiteFe2O3Trig. 3m (3 2/m) : R3c
4.3.1.3EskolaiteCr2O3Trig.
4.3.1.4KarelianiteV3+2O3Trig.

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
7.6.7DoyleiteAl(OH)3Tric.
7.6.8Akdalaite5Al2O3 · H2OHex.

Other InformationHide

Health Risks:
None.
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 rock names highlighted in red, an accessory component in rock names highlighted in green.

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. [https://archive.org/details/SyntheseDuRubis]
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