gemstone
Black Onyx
Chalcedony (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, solid black color, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture with no true cleavage, and a specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, solid black color, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture with no true cleavage, and a specific gravity of 2.60 to 2.65.
Formation & geological history
Formed through the deposition of silica in gas cavities of volcanic lavas or groundwater solutions, typically found worldwide in association with volcanic rocks.
Uses & applications
Extensively used in jewelry, cameos, beads, intaglios, and ornamental carvings.
Geological facts
Black onyx has been used for thousands of years in ancient civilizations such as Greece and Rome for signet rings and protective amulets.
Field identification & locations
Identified by its deep opaque black color, smooth polish, and vitreous luster. Commonly sourced from Brazil, India, Madagascar, and the USA.
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