gemstone

Black cabochon pendant, likely onyx or black glass

Most likely black chalcedony (microcrystalline quartz, SiO₂); the surrounding stones may be cubic zirconia or glass

AI-generated identification · may be incorrect

The central stone is opaque black, highly polished, and faceted/cabochon-cut with a vitreous luster; quartz hardness is about 7 Mohs, whereas glass is about 5–6. The image cannot reliably distinguish onyx from dyed agate, obsidian, or synthetic glass.

Identified September 19, 2026More gemstone →

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At a glance

Common name: Black cabochon pendant, likely onyx or black glass
Scientific name: Most likely black chalcedony (microcrystalline quartz, SiO₂); the surrounding stones may be cubic zirconia or glass
Category: gemstone
Identified: September 19, 2026
Method: Standard

AI Estimated Value

About $10–$60 for costume jewelry; roughly $50–$200 if genuine onyx with precious-metal settings, depending on workmanship and hallmarks.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Black chalcedony forms when silica precipitates in cavities and fractures, commonly in volcanic rocks; deposits are widespread and generally Cenozoic to older. The metal-mounted, polished specimen is human-processed.

Uses & applications

Used in inexpensive jewelry, cameos, beads, and ornamental objects; black onyx is valued for its uniform color and durability.

Geological facts

Many commercial “black onyx” stones are dyed chalcedony, while visually similar black glass and synthetic spinel are also common in jewelry.

Field identification & locations

Check translucency at the edge, hardness, inclusions, and thermal feel; quartz should scratch glass but not be scratched by steel. Refractive-index or gemological testing is needed for certainty.