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Corundum

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Big Photo

Sapphire
Gem gravels, Ratnapura, Ratnapura District, Sabaragamuwa Province, Sri Lanka
© Joseph A. Freilich

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


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.


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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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More Crystal Structures
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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:
Data courtesy of RRUFF project at University of Arizona, used with permission.
X-Ray Powder Diffraction:
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.
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
Analytical 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

Member of:Hematite Group
Other Members of Group:

- +
Eskolaite
Cr
 
2
O
 
3
Hematite
Fe
 
2
O
 
3
Karelianite
V
3+
2
O
 
3
Tistarite
Ti
3+
2
O
 
3
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
3+
2
O
 
3
4.CB.05Melanostibite
Mn
2+
 
(Sb
5+
 
,Fe
3+
 
)O
 
3
4.CB.05Pyrophanite
Mn
2+
 
TiO
 
3
4.CB.05Akimotoite
(Mg,Fe
2+
 
)SiO
 
3
4.CB.05Auroantimonate
AuSbO
 
3
4.CB.05Romanite
(◻,Pb,Ca)UFe
2+
2
(Ti,Fe
3+
 
)
 
6
Ti
 
12
O
 
38
4.CB.05UM1998-11-O-AuHSb
Au
+
2
Sb
3+
 
O
 
2
(OH)
4.CB.05Tistarite
Ti
3+
2
O
 
3
4.CB.10Avicennite
Tl
 
2
O
 
3
4.CB.10Bixbyite
Mn
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
[(Zn,Al,Fe
2+
 
)
 
3
(Al,Fe
3+
 
,Ti)
 
8
O
 
15
(OH)]
 
2
4.CB.20Zincohögbomite-2N6S
[(Zn,Mg)
 
7
(Al,Fe
3+
 
,Ti)
 
16
O
 
31
(OH)]
 
2
4.CB.20Magnesiohögbomite-6N6S
[(Mg,Fe
2+
 
)
 
3
(Al,Ti,Fe
3+
 
)
 
8
O
 
15
(OH)]
 
6
4.CB.20Magnesiohögbomite-2N3S
[(Mg,Fe
2+
 
,Zn)
 
4
(Al,Ti,Fe
3+
 
)
 
10
O
 
19
(OH)]
 
2
4.CB.20Magnesiohögbomite-2N2S
[(Mg,Fe
2+
 
)
 
3
[Al
 
7
(Ti,Fe
3+
 
)]O
 
15
(OH)]
 
2
4.CB.20Ferrohögbomite-6N12S
[(Fe
2+
 
,Mg,Zn)
 
5
(Al,Ti,Fe
3+
 
)
 
12
O
 
23
(OH)]
 
6
4.CB.25Pseudorutile
Fe
 
2
Ti
 
3
O
 
9
4.CB.25Kleberite
FeTi
 
6
O
 
11
(OH)
 
5
4.CB.30Berdesinskiite
V
3+
2
TiO
 
5
4.CB.30Oxyvanite
V
3+
2
V
4+
 
O
 
5
4.CB.35Olkhonskite
(Cr,V)
 
2
Ti
 
3
O
 
9
4.CB.35Schreyerite
V
3+
2
Ti
 
3
O
 
9
4.CB.40Kamiokite
Fe
 
2
Mo
 
3
O
 
8
4.CB.40Nolanite
(V
3+
 
,Fe
3+
 
,Fe
2+
 
,Ti)
 
10
O
 
14
(OH)
 
2
4.CB.40Rinmanite
Zn
 
2
Sb
 
2
Mg
 
2
Fe
 
4
O
 
14
(OH)
 
2
4.CB.40Iseite
Mn
 
2
Mo
 
3
O
 
8
4.CB.40Majindeite
Mg
 
2
Mo
 
3
O
 
8
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
4.CB.75Kyzylkumite
V
3+
2
TiO
 
6
4.CB.80Tietaiyangite
Fe
3+
4
Fe
2+
 
TiO
 
9
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:
a-Corundumα-Aluminaα-CorundumAluminaAyatite
CorinendumCorinindumCorivendumCorivindumCorrindon
CorunditeCorundum-αCorundum-alphaCorundumiteHarmophane
KarundKorunduviteSoimontiteSpath AdamantinWhite Sapphire
Zircolite
Other Languages:
French:Corindon
Corindon adamantin
Corindon harmophane
German:Ajatit
Ayatit
Corundit
Corundumit
Demantspath
Korund
Korunduvit
Soimontit
Zircolith
Italian:Corindone
Latin:Adamas siderites
Russian:Корунд
Simplified Chinese:刚玉
Spanish:Ayatita
Corundita
Corundumita
Korunduvita
Soimontita
Zircolita
Varieties:
Adamantine SparAlundumAsteriated SapphireBarklyiteBlue Alexandrite
Cat SapphireChlorosaphirChromian CorundumLedo frozen fireOriental Amethyst
Oriental EmeraldOriental TopazPadmaragayaPadparadschaRuby
SapphireStar CorundumStar RubyStar SapphireTrapiche ruby

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.

Mindat.org articles about Corundum

Article entries:
Corundum Crystals from the San Jacinto Mountains by K. L. Gochenour 2000Scott L. Ritchie

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    Locality Updated: Black Hawk Mine (Big Patch; Spink), Upper Mississippi Valley District, Grant Co., Wisconsin, USAFrom Bill Cordua, 20th Jun 2013 02:26:23