gemstone
Black Onyx
Chalcedony (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, color is opaque black, vitreous to waxy luster, microcrystalline (cryptocrystalline) crystal structure, conchoidal fracture with no cleavage, specific gravity of 2.58 to 2.64.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, color is opaque black, vitreous to waxy luster, microcrystalline (cryptocrystalline) crystal structure, conchoidal fracture with no cleavage, specific gravity of 2.58 to 2.64.
Formation & geological history
Forms in gas cavities in lava or as deposits in silica-rich solutions in groundwater. Found worldwide.
Uses & applications
Widely used in jewelry such as rings, necklaces, and cameos, as well as for carving beads and decorative items.
Geological facts
In ancient times, black onyx was used by Romans and Greeks for seal rings and intaglios because wax would not stick to it.
Field identification & locations
Identified by its deep opaque black color, waxy luster, and high scratch resistance. Often found in regions with volcanic activity.
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