Onyx
Onyx is a banded variety of chalcedony, a cryptocrystalline form of quartz. The colours of its bands are white and black. It is usually cut as a cabochon, or into beads, and is also used for intaglios and cameos. Some onyx is natural but much is produced by the staining of agate.
Technical Details
| Chemical Composition and Name | SiO2 - Silicon dioxide | |
| Hardness (Mohs Scale) | 7 | |
| Specific Gravity* | 2.65 - 2.66 | |
| Refractive index (R.I.) | 1.543 - 1.552 to 1.545 - 1.554 | |
| Birefringence | 0.009 | |
| Optic Sign | Positive | |
| Optical Character | Uniaxial |
- For information about Specific Gravity, see Density
