Sapphire

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 All colors
  • White Sapphire
  • Blue Sapphire
  • Pink Sapphire
  • Green Sapphire
  • Yellow Sapphire
  • Pink-Orange Sapphire (Padparadscha)
  • Phenomenal
    • Color Changing Sapphire
    • 6-Ray Star Sapphire
    • Parti-colored Sapphire
    • Trapiche Sapphire
4. Crystal System Trigonal System
5. Hardness 9
6. Specific Gravity 3.98 - 4.00
7. Cleavage / Fracture None may show parting / Conchoidal fracture. (Parting or false cleavage occurs along directions of weakness which are parallel to the basal plane or the rhombohedral faces of the crystal and are observed externally as grooves or striations on the surface.
8. Optic Character Anisotropic, D.R., Uniaxial negative
9. Lustre Vitreous
10. Refractive Index / Birefringence 1.762 - 1.770 / 0.008; Range: 1.754 - 1.778
11. Pleochroism Strong in deep colored varieties
12. Dispersion 0.018
13. Magnification
  • Crystals of calcite, dolomite, apatite, etc.
  • Silk - three directional needles of rutile intersecting at 60° / 120°; Needles of boehmite intersecting at almost 90°; Needles of ilmenite etc.
  • Parallel polysynthetic twin lamellae.
  • Color zoning and angular growth zoning.
  • Fingerprints and fluid inclusions.
  • Zircon halo inclusions etc.
14. U.V. Fluorescence Varies according to the color.
15. Cause of Color
  • Blue Sapphire: Traces of Iron and Titanium.
  • Green / Yellow Sapphire: Traces of Iron (Fe2+ / Fe3+).
  • Color Changing Sapphire: Traces of Chromium and Vanadium.
16. Spectrum Blue, green, brown and yellow sapphires: shows a three band absorption in the blue at 450nm, 460nm and 470nm. Generally at least one of these bands is present.
17. Treatment (Enhancement)
18. Specific Tests & Remarks -
19. Synthesis
20. Simulants (with key separation tests)
  • Blue Sapphire: Tanzanite (optic figure, pleochroism, R.I., S.G.), Natural / Synthetic Spinel (optic character, pleochroism, R.I., spectrum, S.G.), Benitoite (dispersion, doubling), Iolite (optic figure, pleochroism, R.I., S.G.), Kyanite (optic figure, R.I., S.G., inclusions), Synthetic Quartz (optic figure, R.I., S.G.), Glass (optic character, inclusions), Doublets (inclusions, U.V. fluorescence).
  • Yellow Sapphire: Chrysoberyl (optic figure, spectrum, inclusions), Citrine (optic figure, R.I., S.G., inclusions), Topaz (optic figure, R.I., S.G.), Yellow Beryl (R.I., S.G., inclusions), Hessonite Garnet (optic character, inclusions), Sillimanite (optic figure, inclusions, R.I., S.G.), Synthetic Cubic Zirconia (dispersion, S.G., U.V. fluorescence), etc.
21. Geological Occurrence In igneous and metamorphic rocks (marble, dolomite, etc.)
22. Sources India (from Kashmir as Kashmiri Sapphire, Karnataka, Orissa), Myanmar (known as Burmese Sapphire), Thailand, Sri Lanka, Australia, Africa (Tanzania, Nigeria, Kenya, Madagascar), U.S.A. (Montana), Cambodia (Pailin).
23. Cuts & Uses Facetted cuts (usually mixed cuts), cabochons, beads, carvings, etc.