gemstone

Black polished stone, likely black onyx or obsidian

Probable chalcedony (microcrystalline SiO₂) or volcanic glass (obsidian, SiO₂)

AI-generated identification · may be incorrect

Small oval cabochon with black color, vitreous-to-waxy luster, and polished surface; hardness is about Mohs 6.5–7 for onyx or 5–5.5 for obsidian. No visible cleavage; density is approximately 2.3–2.7 g/cm³.

Identified August 29, 2026More gemstone →

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At a glance

Common name: Black polished stone, likely black onyx or obsidian
Scientific name: Probable chalcedony (microcrystalline SiO₂) or volcanic glass (obsidian, SiO₂)
Category: gemstone
Identified: August 29, 2026
Method: Standard

AI Estimated Value

Approximately $5–$25 for a common polished cabochon; $25–$100+ for unusually fine material, larger size, or verified provenance.

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 onyx forms when silica-rich groundwater deposits layered chalcedony in cavities; obsidian forms when felsic lava cools rapidly, commonly during the Quaternary and older volcanic episodes.

Uses & applications

Used for cabochon jewelry, beads, carvings, ornaments, and decorative objects; black onyx is generally more durable for jewelry than obsidian.

Geological facts

The image cannot distinguish the two reliably: obsidian commonly shows conchoidal fracture and glassy translucence at thin edges, while onyx may show subtle bands or a waxier appearance.

Field identification & locations

Common sources include Mexico, the United States, Turkey, Brazil, and India. Test cautiously: quartz-rich onyx scratches glass, whereas obsidian is somewhat softer; avoid destructive testing on a polished piece.