Onyx
What is Onyx?
Onyx is a variety of chalcedony, which is itself a form of quartz. It’s characterized by its parallel banded layers, which can be black, white, or a combination of both. Onyx is primarily found in various regions including Brazil, India, and Madagascar. It has been used for centuries for both decorative and functional purposes, including in jewelry and carving.
Onyx is a banded variety of chalcedony characterized by parallel layers of black and white. Its striking appearance makes it a popular choice for jewelry and decorative items. The stone has a long history of use, dating back to ancient civilizations.
| Chemical Classification | Inorganic - Silicate (Chalcedony) |
| Color | Typically black, but can also be white or banded black and white. |
| Streak | Green |
| Luster | Waxy to vitreous. |
| Transparency | Opaque. |
| Occurrence | Brazil, India, Madagascar. |
| Formation | Onyx is formed in the gas cavities of lava. |
| Diaphaneity | Translucent to opaque |
| Cleavage | None |
| Mohs Hardness | 6.5 to 7. |
| Specific Gravity | Approximately 2.55 to 2.70. |
| Diagnostic Properties | Banded chalcedony, often black and white. |
| Chemical Composition | SiO2 |
| Pleochroism | Not exhibited in onyx. |
| Crystal System | Hexagonal (variety of Quartz) |
| Optical Properties | Uniaxial (+) |
| Refractive Index | 1.530 - 1.539 |
| Birefringence | 0.009 |
| 2V angle | Not applicable (isometric) |
| Dispersion | Not typically relevant for onyx. |