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Corundum

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Formula:
Al
 
2
O
 
3
System:TrigonalColour:Colourless, blue, red, ...
Hardness:9
Member of:Hematite Group
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.


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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
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)

About Crystal Atlas

The mindat.org Crystal Atlas allows you to view a selection of crystal drawings of real and idealised crystal forms for this mineral and, in certain cases, 3d rotating crystal objects. The 3d models and HTML5 code are kindly provided by www.smorf.nl.

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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
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:
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
Simplified for copy/paste:Al2O3
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.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
Ti
 
2
V
3+
 
O
 
5
(OH)
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

Internet Links for Corundum

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    Localities for Corundum

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