gemstone
Onyx (Agate) or Black Spinel/Glass
SiO2 (Silicon dioxide) if onyx/agate
AI-generated identification · may be incorrectHardness 6.5-7 (Onyx) or 8 (Spinel), opaque black color, vitreous luster.
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Physical properties
Hardness 6.5-7 (Onyx) or 8 (Spinel), opaque black color, vitreous luster.
Formation & geological history
Formed in cavities of igneous rocks (onyx/agate) or metamorphic rocks (spinel). Commonly dyed chalcedony is used in commercial jewelry.
Uses & applications
Used primarily in jewelry making, often fashioned into beads or cabochons.
Geological facts
Most commercially available "black onyx" is actually dyed chalcedony, treated to achieve a uniform black color.
Field identification & locations
Identified by uniform color, lack of banding, and hardness. True black onyx is rare compared to treated stones.
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