Sapphire
In Old Testament times, this name referred to lapis lazuli, but since the Middle Ages, it has referred to all varieties of corundum (Al2O3) except red. It was discovered in 1783 to be the same material as ruby. Its wide range of colors is due to impurities such as Fe, Ti, and Cr, and its unique luster is a key identifying feature.
The depth from cornflower to royal blue
Basic Information
| English Name | Sapphire |
|---|---|
| Japanese Name | Seigyoku (Corundum in a broad sense) |
| Chemical Composition | Al2O3 |
| Crystal System | Hexagonal (Trigonal) |
| Hardness | 9 |
| Specific Gravity | Approx. 4.02 |
Colors, Varieties, and Treatments
- Famous Colors: Cornflower (Kashmir), Royal (Myanmar), Padparadscha (orange-pink).
- Varieties: Star Sapphire (6 to 12-ray stars due to rutile inclusions), parti-colored, and trapiche structure types.
- Treatments: Heating (color improvement to turning colorless stones blue), Be-diffusion. Commercial labels like "pink/purple ruby" are inappropriate; these are classified as sapphire.
Similar Stones: Spinel, colored kyanite, zoisite, and brownish spessartite, etc.