Corundum

1. Chemical Composition Aluminium Oxide - Al2O3 (trace elements Chromium, Iron, Titanium, etc. are responsible for the different colored varieties.
2. Classification / Type -
3. Colors / Varieties
  • Ruby: Red / Pink
  • Sapphire (all colors)
    • White Sapphire
    • Blue Sapphire
    • Pink Sapphire
    • Green Sapphire
    • Yellow Sapphire
    • Pink-Orange Sapphire (Padparadscha)
  • Phenomenal
    • Color Changing Sapphire
    • 6-Ray Star Ruby / 6-Ray Star Sapphire
    • Parti-colored Sapphire
    • Trapiche Ruby / Sapphire
4. Crystal System / Forms Trigonal System / Variable: Generally pseudo-hexagonal prisms with either pyramidal and / or pinacoidal terminations. In some cases rhombohedral faces are also observed. Barrel shaped habits, tabular and rhombohedral habits are common.
5. Hardness 9
6. Specific Gravity 3.98 - 4.00
7. Optic Character Anisotropic, D.R., Uniaxial negative
8. Lustre Vitreous
9. Refractive Index / Birefringence 1.762 - 1.770 / 0.008; Range: 1.754 - 1.778
10. Pleochroism Strong in deep colored varieties
11. Dispersion 0.018
12. Treatment (Enhancement)
13. Specific Tests & Remarks -
14. Synthesis
15. Geological Occurrence In igneous and metamorphic rocks (marble, dolomite, etc.)
16. Cuts & Uses Facetted cuts (usually mixed cuts), cabochons, beads, carvings, etc.