| General Information |
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| Varieties/Types: | Ruby - A red gem variety of corundum Flux-Grown Ruby - A synthetic ruby grown from alumina dissolved in a molten flux. Geneva Ruby - Earliest synthetic rubies (circa 1885) created in Geneva. Star Ruby - A chatoyant ruby showing asterism. Verneuil Ruby - A synthetic ruby created using the flame fusion process. |
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| Chemical Formula | Arthur Thomas, Gemstones (2009) |
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| Significant stones |
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| Click here to view all significant Corundum gemstones |
| Corundum Treatments |
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| A significant percentage of the corundum gemstones are enhanced. Artificial healing of cracks and cavities and high-temperature thermal processing are used to increase the transparency and to improve the colour (Nassau, 1981). Near surface cracks are healed with wax or with silicate glass, during which the processable stone is immersed into a silicate melt or heated in conjuction with a powder-like filling material such as, borax or glass. At high-temperatures the filling material melts and enters into cracks and cavities (Themelis, 1986). |
| Physical Properties of Corundum |
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| Mohs Hardness | 9Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)More from other references |
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| Specific Gravity | 3.90 to 4.05Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)More from other references |
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| Cleavage Quality | NoneE.Ya.Kievlenko, Geology of gems (2003)More from other references |
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| Fracture | Uneven,ConchoidalE.Ya.Kievlenko, Geology of gems (2003)More from other references |
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| Optical Properties of Corundum |
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| Refractive Index | 1.758 to 1.780Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)More from other references |
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| Optical Character | Uniaxial/-Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)More from other references |
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| Birefringence | 0.007 to 0.010Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)More from other references |
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| Pleochroism | Dichroism: blue - violet-blue and greenish-blue; green - yellowish-green; yellow - pale yellow; purple - violet; orange, yellowish-red - deep crimson.E.Ya.Kievlenko, Geology of gems (2003)More from other references |
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| Dispersion | 0.018Arthur Thomas, Gemstones (2009) |
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| Colour |
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| Colour (General) | All coloursUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)More from other references |
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| Causes of Colour | Purple, Fe2+-O-Ti4+ charge transfer coexisting with Cr3+ in octahedral coordination. Blue, Fe2+-O-Ti4+ charge transfer with influence of Fe2+→Fe3+ charge transfer. Green, Fe3+ in octahedral coordination coexisting with Fe2+→Ti4+ charge transfer, Ti3+ and Cr3+ in octahedral coordination. Yellow, O2-→Fe3+ charge transfer; Fe3+ and Ti3+, a variety of unstable color centers of unknown structure; Fe3+ pairs. Orange to orange-brown Cr3+ in octahedral coordination and color centers; with a contribution of Fe3+. Orangy pink ("padparadscha"), Cr3+ in octahedral coordination and color centers, Cr4+ in octahedral coordination due to Cr4+ and Mg2+ substituting for Al3+ in the crystal structure. Red (ruby), Cr3+ in octahedral coordination with minor contributions of V3+ and Fe3+ in octahedral coordination. Pink, Cr3+ in octahedral coordination. Color-change, Cr3+ and/or V3+ in octahedral coordination in a particular range of concentrationW. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011) |
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| Transparency | Transparent,Translucent,OpaqueUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)More from other references |
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| Lustre | Adamantine,VitreousArthur Thomas, Gemstones (2009) |
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| Crystallography of Corundum |
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| Crystal System | TrigonalUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)More from other references |
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| Habit | Tabular, barrel-shapedArthur Thomas, Gemstones (2009) |
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| Geological Environment |
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| Where found: | Found in granular limestone, gneiss, mica or chlorite schists.Arthur Thomas, Gemstones (2009) |
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| Spectrographic Data |
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Calculated Spectra:
Click spectra for more information |  Ruby - Locality: Hunza, Pakistan  Ruby - Locality: Winza, Tanzania  Ruby - Locality: Winza, Tanzania  Sapphire - Locality: Unknown  Sapphire - Locality: Afghanistan  Sapphire - Locality: Kenya  Sapphire - Locality: Mozambique  Sapphire - Locality: Tunduru, Tanzania  Sapphire - Locality: Unknown (possibly Australia)  Sapphire - Locality: Unknown  Verneuil Ruby - Locality: Synthetic  Verneuil Ruby - Locality: Synthetic |
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| Inclusions: rutile, zircon, apatite, calcite, spinel, etc., healing cracks, liquid and two-phase inclusions, negative crystals, hollow tubes (boehmite tubes), twinning lamellaes - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 26 |
 | Rutile inclusions |
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| Inclusions: |
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