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Corundum

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United Jack Mine, Zoutpansberg District, Murchison Range, Limpopo Province, South Africa
© Rob Lavinsky

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Formula:
Al
 
2
O
 
3
System:TrigonalColour:Colourless, blue, red, ...
Hardness:9
Name:Derived from the Sanskrit, kuruvinda ("Ruby")


Hematite Group.
The aluminum analogue of Eskolaite, Hematite, and Karelianite.
The red (Cr-bearing) gem variety is called Ruby.

Classification of Corundum

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:4/C.04-10
Nickel-Strunz 10th (pending) edition ID: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 edition ID:4.3.1.1
Dana 8th edition ID:4.3.1.1

4 : SIMPLE OXIDES
3 : A2X3
Hey's CIM Ref.:7.6.1

7 : Oxides and Hydroxides
6 : Oxides of Al
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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

Lustre: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 (measured):3.98 - 4.1 g/cm3
Density (calculated):3.997 g/cm3

Crystallography of Corundum

Crystal System:Trigonal
Class (H-M):3m (3 2/m) - Hexagonal Scalenohedral
Space Group:R3c (R3 2/c)
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}.
Crystal Atlas:
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Corundum no.17 - Goldschmidt (1913-1926)
Corundum no.34 - Goldschmidt (1913-1926)

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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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X-Ray Powder Diffraction:
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Radiation - Copper Kα
Data Set:
Horizontal Axis: ° to ° Vertical Axis: % Source Data: Filtered Data: Peaks:
Data courtesy of RRUFF project at University of Arizona, used with permission.

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.
Maximum Birefringence:δ = 0.008 - 0.009

Chart 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:
Al
 
2
O
 
3
Essential elements:Al, O
All elements listed in formula:Al, O
Analyical Data:
Al(52.93)
O(47.07)
Empirical Formula:
Al
 
2
O
 
3
Common Impurities:Cr,Fe,V,Ti

Relationship of Corundum to other Species

Related to:
  • Hematite Group
    • Related Minerals - Nickel-Strunz Grouping):
    4.CB.05Brizziite
    NaSb
    5+
     
    		O
     
    3
    4.CB.05Ecandrewsite
    (Zn,Fe
    2+
     
    		,Mn
    2+
     
    		)TiO
     
    3
    4.CB.05Eskolaite
    Cr
     
    2
    		O
     
    3
    4.CB.05Geikielite
    MgTiO
     
    3
    4.CB.05Hematite
    Fe
     
    2
    		O
     
    3
    4.CB.05Ilmenite
    Fe
    2+
     
    		TiO
     
    3
    4.CB.05Karelianite
    V
     
    2
    		O
     
    3
    4.CB.05Melanostibite
    Mn
    2+
     
    		(Sb
    5+
     
    		,Fe
    3+
     
    		)O
     
    3
    4.CB.05Pyrophanite
    Mn
    2+
     
    		TiO
     
    3
    4.CB.05Auroantimonate
    AuSbO
     
    3
    4.CB.05Romanite
    ([],Pb,Ca)UFe
    2+
    2
    		(Ti,Fe
    3+
     
    		)
     
    6
    		Ti
     
    12
    		O
     
    38
    4.CB.10Avicennite
    Tl
     
    2
    		O
     
    3
    4.CB.10Bixbyite
    (Mn
    3+
     
    		,Fe
    3+
     
    		)
     
    2
    		O
     
    3
    4.CB.15Armalcolite
    (Mg,Fe
    2+
     
    		)Ti
     
    2
    		O
     
    5
    4.CB.15Pseudobrookite
    Fe
     
    2
    		TiO
     
    5
    4.CB.15Mongshanite
    (Mg,Cr,Fe
    2+
     
    		)
     
    2
    		(Ti,Zr)
     
    5
    		O
     
    12
    4.CB.20Zincohögbomite-2N2S
    Ti(Zn,Mg,Fe)
     
    2
    		Al
     
    8
    		O
     
    15
    		(OH)
    4.CB.20Zincohögbomite-2N6S
    Ti(Zn,Mg,Fe)
     
    6
    		Al
     
    16
    		O
     
    31
    		(OH)
    4.CB.20Magnesiohögbomite-6N6S
    Ti(Mg,Fe)
     
    2
    		Al
     
    8
    		O
     
    15
    		(OH)
    4.CB.20Magnesiohögbomite-2N3S
    Ti(Mg,Fe)
     
    3
    		Al
     
    10
    		O
     
    19
    		(OH)
    4.CB.20Magnesiohögbomite-2N2S
    Ti(Mg,Fe)
     
    2
    		Al
     
    8
    		O
     
    15
    		(OH)
    4.CB.20Ferrohögbomite-6N12S
    Ti(Fe,Mg)
     
    4
    		Al
     
    12
    		O
     
    23
    		(OH)
    4.CB.25Pseudorutile
    Fe
     
    2
    		Ti
     
    3
    		O
     
    9
    4.CB.25Tietaiyangite
    Fe
    3+
    4
    		Fe
    2+
     
    		TiO
     
    9
    4.CB.30Berdesinskiite
    V
    3+
    2
    		TiO
     
    5
    4.CB.35Kyzylkumite
    V
     
    2
    		Ti
     
    3
    		O
     
    9
    4.CB.35Olkhonskite
    (Cr,V)
     
    2
    		Ti
     
    3
    		O
     
    9
    4.CB.35Schreyerite
    V
     
    2
    		Ti
     
    3
    		O
     
    9
    4.CB.40Kamiokite
    Fe
     
    2
    		Mo
     
    3
    		O
     
    8
    4.CB.40Nolanite
    (V,Fe,Fe,Ti)
     
    10
    		O
     
    14
    		(OH)
     
    2
    4.CB.40Rinmanite
    Zn
     
    2
    		Sb
     
    2
    		Mg
     
    2
    		Fe
     
    4
    		O
     
    14
    		(OH)
     
    2
    4.CB.45Claudetite
    As
     
    2
    		O
     
    3
    4.CB.45Stibioclaudetite
    AsSbO
     
    3
    4.CB.50Arsenolite
    As
     
    2
    		O
     
    3
    4.CB.50Sénarmontite
    Sb
     
    2
    		O
     
    3
    4.CB.55Valentinite
    Sb
     
    2
    		O
     
    3
    4.CB.60Bismite
    Bi
     
    2
    		O
     
    3
    4.CB.65Sphaerobismoite
    Bi
     
    2
    		O
     
    3
    4.CB.70Sillénite
    Bi
     
    12
    		SiO
     
    20
    Related Minerals - Hey's Index Grouping:
    7.6.2Böhmite
    AlO(OH)
    7.6.2Diaspore
    AlO(OH)
    7.6.4Gibbsite
    Al(OH)
     
    3
    7.6.5Bayerite
    Al(OH)
     
    3
    7.6.6Nordstrandite
    Al(OH)
     
    3
    7.6.7Doyleite
    Al(OH)
     
    3
    7.6.8Akdalaite
    4Al
     
    2
    		O
     
    3
    		 · H
     
    2
    		O
    Related Minerals - Dana Grouping):
    4.3.1.2Hematite
    Fe
     
    2
    		O
     
    3

    Other Names for Corundum

    Synonyms:
    α-Aluminaa-Corundumα-CorundumAluminaAyatite
    CorinendumCorinindumCorivendumCorivindumCorrindon
    CorunditeCorundum-αCorundum-alphaCorundumiteHarmophane
    KarundKorunduviteSoimontiteSpath AdamantinWhite Sapphire
    Zircolite
    French names:
    CorindonCorindon adamantinCorindon harmophane
    German names:
    AjatitAyatitCorunditCorundumitDemantspath
    KorundKorunduvitSoimontitZircolith
    Italian names:
    Corindone
    Latin names:
    Adamas siderites
    Russian names:
    Корунд
    Spanish names:
    AyatitaCorunditaCorundumitaKorunduvitaSoimontita
    Zircolita
    Varieties:
    Adamantine SparAlundumAsteriated SapphireBarklyiteBlue Alexandrite
    ChlorosapphirLedo frozen fireOriental AmethystOriental EmeraldOriental Topaz
    PadmaragayaRubySapphireStar CorundumStar Ruby
    Star Sapphire

    Other Information

    Health Warning:None.
    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

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Search for Corundum in the Natural History Museum (London) online catalogue
  • Corundum details from Handbook of Mineralogy (PDF)
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    Localities for Corundum

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