gemstone

Polished blue-black cabochon, likely blue obsidian or dyed glass-like stone

Indeterminate from image; possible natural obsidian (volcanic glass), commonly SiO₂-rich rhyolitic glass

AI-generated identification · may be incorrect

Highly polished, domed cabochon with deep cobalt-blue color, black margins, and vitreous luster. Obsidian has Mohs hardness about 5–5.5, no cleavage, amorphous structure, and specific gravity around 2.35–2.65; the intense uniform blue may indicate dyeing or synthetic material.

Identified August 14, 2026More gemstone →

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At a glance

Common name: Polished blue-black cabochon, likely blue obsidian or dyed glass-like stone
Scientific name: Indeterminate from image; possible natural obsidian (volcanic glass), commonly SiO₂-rich rhyolitic glass
Category: gemstone
Identified: August 14, 2026
Method: Standard

AI Estimated Value

$5–$30 for a common polished cabochon; approximately $30–$100 if verified as unusual natural blue obsidian, with provenance and quality strongly affecting value.

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

Natural obsidian forms when silica-rich lava cools rapidly, generally during Quaternary to older volcanic activity. Blue varieties are uncommon; without testing, dyed chalcedony, synthetic glass, or another treated stone cannot be excluded.

Uses & applications

Used as a jewelry cabochon, ornamental stone, or collector piece; obsidian is also used for decorative objects and exceptionally sharp experimental tools.

Geological facts

Obsidian lacks true crystals because it cools too quickly for crystallization. A flashlight may reveal translucency at thin edges, while conchoidal fracture is characteristic of natural obsidian.

Field identification & locations

Inspect edges and inclusions with magnification; glassy bubbles, perfectly uniform color, or dye concentration suggest imitation or treatment. Common obsidian sources include Mexico, the western United States, Armenia, and Turkey.