Corundum

Properties

Chemical Composition: 

Aluminium Oxide - Al₂O₃ (trace elements Chromium, Iron, Titanium, etc. are responsible for the different colored varieties.

Classification / Type: 

-

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

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.

Hardness: 

9

Specific Gravity: 

3.98 - 4.00

Optic Character: 

Anisotropic, D.R., Uniaxial negative

Lustre: 

Vitreous

Refractive Index / Birefringence: 

1.762 - 1.770 / 0.008; Range: 1.754 - 1.778

Pleochroism: 

Strong in deep colored varieties

Dispersion: 

0.018

Treatment (Enhancement): 

• Coating
• Colorless Impregnation
• Colored Impregnation
• Heat Treatment
• Irradiation
• Diffusion Treatment

Specific Tests & Remarks: 

-

Synthesis: 

• Verneuil Method
• Czochralski
• Flux Fusion Method
• Hydrothermal Method

Geological Occurrence: 

In igneous and metamorphic rocks (marble, dolomite, etc.)

Cuts & Uses: 

Facetted cuts (usually mixed cuts), cabochons, beads, carvings, etc.