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Corundum
A valid IMA mineral species - grandfathered
This page kindly sponsored by Eric D. Fritzsch
About Corundum
Formula:
Al2O3
As a Commodity:
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 be similar to the gamma form of Al2O3.
Paglia (2004) reports the following calcination pathway: gibbsite → böhmite → γ-Al2O3 (Unnamed (gamma-alumina)) → δ-Al2O3 (synthetic equivalent of deltalumite) → θ-Al2O3 (synthetic equivalent of UM1990-23-O:Al) → α-Al2O3 (corundum).
Visit gemdat.org for gemological information about Corundum.
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 be similar to the gamma form of Al2O3.
Paglia (2004) reports the following calcination pathway: gibbsite → böhmite → γ-Al2O3 (Unnamed (gamma-alumina)) → δ-Al2O3 (synthetic equivalent of deltalumite) → θ-Al2O3 (synthetic equivalent of UM1990-23-O:Al) → α-Al2O3 (corundum).
Visit gemdat.org for gemological information about Corundum.Unique Identifiers
Mindat ID:
1136
Long-form identifier:
mindat:1:1:1136:1
IMA Classification of Corundum
Approved, 'Grandfathered' (first described prior to 1959)
Classification of Corundum
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
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
4 : SIMPLE OXIDES
3 : A2X3
7.6.1
7 : Oxides and Hydroxides
6 : Oxides of Al
7 : Oxides and Hydroxides
6 : Oxides of Al
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
Please only use the official IMA–CNMNC symbol. Older variants are listed for historical use only.
Please only use the official IMA–CNMNC symbol. Older variants are listed for historical use only.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Crn | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
| Crn | Kretz (1983) | Kretz, R. (1983) Symbols of rock-forming minerals. American Mineralogist, 68, 277–279. |
| Crn | Siivolam & Schmid (2007) | Siivolam, J. and Schmid, R. (2007) Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: List of mineral abbreviations. Web-version 01.02.07. IUGS Commission on the Systematics in Petrology. download |
| Crn | Whitney & Evans (2010) | Whitney, D.L. and Evans, B.W. (2010) Abbreviations for names of rock-forming minerals. American Mineralogist, 95, 185–187 doi:10.2138/am.2010.3371 |
| Crn | The Canadian Mineralogist (2019) | The Canadian Mineralogist (2019) The Canadian Mineralogist list of symbols for rock- and ore-forming minerals (December 30, 2019). download |
Pronunciation of Corundum
Pronunciation:
| Play | Recorded by | Country |
|---|---|---|
| Jolyon Ralph | United Kingdom |
Physical Properties of Corundum
Adamantine, Vitreous, Pearly
Transparency:
Transparent, Translucent, Opaque
Colour:
Colourless, blue, red, pink, yellow, grey, golden-brown
Streak:
White
Hardness:
9 on Mohs scale
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 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.
Max. Birefringence:
δ = 0.008 - 0.009
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
Very High (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized uniaxial interference figure - the conoscopic
(convergent-light, Bertrand-lens-in) view, for a grain cut with the optic axis
centred and vertical. The coloured rings are isochromatics, computed with the
same physics as the Michel-Lévy bar above; the dark cross is the isogyre.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
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.
Chemistry of Corundum
Mindat Formula:
Al2O3
Elements listed:
Common Impurities:
Cr,Fe,V,Ti
Crystallography of Corundum
Crystal System:
Trigonal
Class (H-M):
3m(32/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 [0110]. Lines in the direction [1120] divide the base into six sectors at times.
Forms include {0001}, {1000}, {1120}, {7180}, {1015}, {1013}, {1012}, {1011}, {7072}, {7071}, {0111}, {0221}, {0772}, {2245}, {2243}, {7·7·14·9}, {1121}, {7·7·14·6}, {4488}, {11·11·22·6}, {2241}, {7·7·14·3}, {8·8·16·3}, {4481}, {14·14·28·3}, {4265}, {3254}, {2·8·10·9}
Forms include {0001}, {1000}, {1120}, {7180}, {1015}, {1013}, {1012}, {1011}, {7072}, {7071}, {0111}, {0221}, {0772}, {2245}, {2243}, {7·7·14·9}, {1121}, {7·7·14·6}, {4488}, {11·11·22·6}, {2241}, {7·7·14·3}, {8·8·16·3}, {4481}, {14·14·28·3}, {4265}, {3254}, {2·8·10·9}
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 Corundum
Crystal Atlas:
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Corundum no.17 - {hhl} - Goldschmidt (1913-1926)
Corundum no.34 - {773} - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by
www.smorf.nl.
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0009327 | Corundum | Kirfel A, Eichhorn K (1990) Accurate structure analysis with synchrotron radiation. The electron density in Al2O3 and Cu2O Acta Crystallographica A46 271-284 |  | 1990 | synthetic | 0 | 293 |
| 0010593 | Corundum | Newnham R E, de Haan Y M (1962) Refinement of the alpha Al2O3, Ti2O3, V2O3 and Cr2O3 structures Zeitschrift fur Kristallographie 117 235-237 |  | 1962 | synthetic | 0 | 293 |
| 0014077 | Corundum | Pauling L, Hendricks S B (1925) Crystal structures of hematite and corundum Journal of the American Chemical Society 47 781-790 | 1925 | Ceylon | 0 | 293 | |
| 0014072 | Corundum | Wang X, Hubbard C, Alexander K, Becher P (1994) Neutron diffraction measurements of the residual stresses in Al2O3 - ZrO2 (CeO2) ceramic composites _cod_database_code 1000059 Journal of the American Ceramic Society 77 1569-1575 | 1994 | 0 | 293 | ||
| 0012859 | Corundum | Lutterotti L, Scardi P (1990) Simultaneous structure and size-strain refinement by the Rietveld method _cod_database_code 1000032 Journal of Applied Crystallography 23 246-252 | 1990 | 0 | 293 | ||
| 0015110 | Corundum | Tsirelson V, Antipin M, Gerr R, Ozerov R, Struchkov Y (1985) Ruby structure peculiarities derived from X-ray data. Localization of chromium atoms and electron deformation density _cod_database_code 1000017 Physica Status Solidi A87 425-433 | 1985 | 0 | 293 | ||
| 0009325 | Corundum | Lewis J, Schwarzenbach D, Flack H D (1982) Electric field gradients and charge density in corundum alpha-Al2O3 Acta Crystallographica A38 733-739 |
In den Dellen quarries, Mendig, Mendig, Mayen-Koblenz, Rhineland-Palatinate, Germany