- Notes:
- Color designations for pleichroism and fluorescence generally follow our color description system. A '+' can represent either 'strong' or 'dark'.
- 'C' = colorless
- Transparency designations are those most commonly accepted for gem / jewelry quality material
The Tool - for Diamonds and Precious
Your Gem Material Selection
| Gem Material | Sapphire |
| Group | Corundum |
| Mohs Hardness | 9 to 9 |
| Colors |
|
| Refractive Index | 1.776 to 1.774 |
| Dispersion | 0.018 |
| Pleiochroism | Varies |
| Specific Gravity | 3.97 to 4 |
| Double Refraction | -0.008 to |
| Transparency | Transparent |
| Fluorescence | Varies |
| Chemical Composition | Al2O3 |
| Crystal System |  |
| Trigonal System (rhombohedral or three-sided) - Axes and angles are similar to the hexagonal system, so the two systems are often combined as hexagonal. Symmetry is the primary difference. In the hexagonal system, the cross-section of the prism base is six-sided, while in the trigonal system it is three-sided. Six-sided hexagonal shapes are formed by cutting-off the corners of the triangles. Typically, crystal forms in the trigonal system are trigonal prisms and pyramids, rhombohedra and scalenohedra. |