Corundum
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 ruby. Other impurities can make sapphire.
| Corundum | |
|---|---|
 | |
| General | |
| Category | Oxide mineral – Hematite group |
| Formula (repeating unit) | Aluminium oxide, Al2O3 |
| 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 Media
Corundum from Brazil, size about Lua error in Module:Convert at line 1850: attempt to index local 'en_value' (a nil value).
Crystal structure of corundum
Molar volume vs. pressure at room temperature
Related pages
References
- ↑ "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
