igneous

Black obsidian

Volcanic glass; predominantly rhyolitic, silica-rich glass (approximately 70–80% SiO₂)

AI-generated identification · may be incorrect

Typically jet-black with vitreous luster, conchoidal fracture, no visible crystals, and hardness about 5–5.5 Mohs. The specimen appears rough and naturally fractured, though lighting obscures surface detail.

Identified September 16, 2026More igneous →

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At a glance

Common name: Black obsidian
Scientific name: Volcanic glass; predominantly rhyolitic, silica-rich glass (approximately 70–80% SiO₂)
Category: igneous
Identified: September 16, 2026
Method: Standard

AI Estimated Value

Approximately $5–$25 for a common rough specimen of this size; $20–$100 or more if unusually attractive, patterned, provenance-rich, or expertly polished.

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

Forms when silica-rich lava cools so rapidly that crystals cannot grow, commonly around volcanic domes and lava flows, generally during the Quaternary or younger volcanic history. It is not technically crystalline rock, but natural volcanic glass.

Uses & applications

Used for decorative objects, cabochons, beads, knife blades, and historically extremely sharp cutting tools; also collected as a lapidary material. Common pieces usually have modest commercial value.

Geological facts

Obsidian can produce exceptionally sharp edges because of its conchoidal fracture. Black color commonly results from microscopic iron-bearing minerals, while sheen, snowflake, mahogany, or rainbow varieties reflect inclusions or structural effects.

Field identification & locations

Identify by its glassy appearance, sharp curved fractures, lack of cleavage, and inability to scratch ordinary glass reliably in every case. Common localities include Mexico, the western United States, Iceland, Armenia, Japan, and New Zealand.