mineral
Black Onyx
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Jet black, Luster: Vitreous/Waxy, Crystal Structure: Hexagonal (Cryptocrystalline), Cleavage: None, Specific Gravity: 2.65-2.67
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Jet black, Luster: Vitreous/Waxy, Crystal Structure: Hexagonal (Cryptocrystalline), Cleavage: None, Specific Gravity: 2.65-2.67
Formation & geological history
Formed as a result of the deposition of silica in gas cavities (vesicles) in lava. It belongs to the chalcedony family of quartz.
Uses & applications
Used primarily in jewelry (rings, beads, cameos), ornamental carvings, and historical talismans.
Geological facts
Most solid black onyx sold today is actually gray chalcedony that has been dyed or treated with heat and sugar to achieve its deep black color, a practice that dates back to the Roman Empire.
Field identification & locations
Identify by its waxy luster, conchoidal fracture (curved glass-like breaks), and high hardness. Commonly found in volcanic regions of Brazil, India, and Uruguay.
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Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
Metamorphic Rock
![Biotite Schist (Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]) — metamorphic](https://media.rock.id/9ca564b5-bc87-402b-965a-69b21f9aa6bf-thumbnail.jpg)
Biotite Schist
Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]
metamorphic