Corundum
Appearance
Corundum | |
---|---|
General | |
Category | Oxide mineral – Hematite group |
Formula (repeating unit) | Aluminium oxide, Al 2O 3 |
Strunz classification | 04.CB.05 |
Dana classification | 4.3.1.1 |
Crystal symmetry | Trigonal (32/m) |
Unit cell | a = 4.75 Å, c = 12.982 Å; Z=6 |
Identification | |
Color | Colorless, gray, brown; pink to red, orange, yellow, green, blue, violet; may be color zoned, asteriated mainly grey and brown |
Crystal habit | Steep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular |
Crystal system | Trigonal (Hexagonal Scalenohedral) Symbol (32/m) Space group: R3c |
Twinning | Polysynthetic twinning common |
Cleavage | None – parting in 3 directions |
Fracture | Conchoidal to uneven |
Tenacity | Brittle |
Mohs scale hardness | 9 (defining mineral)[1] |
Luster | Adamantine to vitreous |
Streak | White |
Diaphaneity | Transparent, translucent to opaque |
Specific gravity | 3.95–4.10 |
Optical properties | Uniaxial (–) |
Refractive index | nω = 1.767–1.772 nε = 1.759–1.763 |
Pleochroism | None |
Melting point | 2044 °C |
Fusibility | Infusible |
Solubility | Insoluble |
Alters to | May alter to mica on surfaces causing a decrease in hardness |
Other characteristics | May fluoresce or phosphoresce under UV light |
References | [2][3][4][5] |
Major varieties | |
Sapphire | Any color except red |
Ruby | Red |
Emery | Black granular corundum intimately mixed with magnetite, hematite, or hercynite |
Corundum is a mineral. It is very hard, with a Mohs hardness of 9 (diamond is 10). It is usually clear. Its chemical formula is aluminium oxide, Al2O3. Sometimes some of the aluminium atoms get replaced with chromium atoms. It then becomes a ruby. Other impurities can make a sapphire.
Related pages
[change | change source]References
[change | change source]- ↑ "Mohs' scale of hardness". Collector's corner. Mineralogical Society of America. Retrieved 10 January 2014.
- ↑ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. and Nichols, Monte C., ed. (1997). "Corundum". Handbook of Mineralogy (PDF). Vol. III(Halides, Hydroxides, Oxides). Chantilly, VA, US: Mineralogical Society of America. ISBN 0962209724.
{{cite book}}
: CS1 maint: multiple names: editors list (link) - ↑ Corundum. Mindat.org
- ↑ Corundum. Webmineral
- ↑ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, pp. 300–302 ISBN 0-471-80580-7