Mineralogy
Onyx is a precious gemstones found in various regions of the world, particularly Brazil. It can also be found in Uruguay, Pakistan, Sri Lanka, India and Madagascar. Onyx is formed in the gas cavities of lava.
| Chemical composition and name | SiO2 – Silicon dioxide |
| Hardness (Mohs scale) | 7 |
| Specific gravity | 2.65–2.667 |
| Refractive index (R.I.) | 1.543–1.552 to 1.545–1.554 |
| Birefringence | 0.009 |
| Optic sign | Positive |
| Optical character | Uniaxial |
Read more about this topic: Black Onyx