gemstone
Black Onyx
Chalcedony (SiO2)
Hardness of 6.5-7 on the Mohs scale, opaque black color, waxy to vitreous luster, microcrystalline quartz structure (cryptocrystalline), conchoidal fracture with no true cleavage, specific gravity of 2.58-2.64.
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Physical properties
Hardness of 6.5-7 on the Mohs scale, opaque black color, waxy to vitreous luster, microcrystalline quartz structure (cryptocrystalline), conchoidal fracture with no true cleavage, specific gravity of 2.58-2.64.
Formation & geological history
Forms by the deposition of silica from underground water, typically in gas cavities of volcanic rocks or in limestone replacement environments.
Uses & applications
Widely used in jewelry such as rings, necklaces, and brooches, as well as for carving cameos and beads.
Geological facts
Black onyx has been used for thousands of years in ancient civilizations like Egypt, Greece, and Rome for seals, signet rings, and protective amulets.
Field identification & locations
Identified by its uniform jet-black color and waxy luster when polished. Often found in Brazil, India, Madagascar, and the USA.
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