mineral

Black polished stone, likely black tourmaline or obsidian

Possibly schorl tourmaline, NaFe3Al6(BO3)3Si6O18(OH)4, or volcanic glass (obsidian), SiO2-rich

AI-generated identification · may be incorrect

Dark opaque to translucent material with a glassy-to-subvitreous luster; identification is uncertain because the specimen is enclosed and the image is blurred. Tourmaline has Mohs hardness 7–7.5 and prismatic crystal structure; obsidian has hardness about 5–5.5 and no crystal structure.

Identified September 18, 2026More mineral →

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At a glance

Common name: Black polished stone, likely black tourmaline or obsidian
Scientific name: Possibly schorl tourmaline, NaFe3Al6(BO3)3Si6O18(OH)4, or volcanic glass (obsidian), SiO2-rich
Category: mineral
Identified: September 18, 2026
Method: Standard

AI Estimated Value

About $2–$20 for a small common specimen; $20–$100+ if crystalline, unusually transparent, or from a desirable locality.

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 tourmaline crystallizes in hydrothermal veins and granitic pegmatites, while obsidian forms when silica-rich lava cools rapidly; both are geologically young to ancient depending on locality.

Uses & applications

Tourmaline is collected, used as a gemstone, and sometimes in electrical applications; obsidian is used for carvings, jewelry, ornaments, and historically sharp tools.

Geological facts

Black tourmaline commonly shows longitudinal striations and may attract lightweight particles when heated; obsidian typically breaks with conchoidal, razor-sharp fractures.

Field identification & locations

Check for prismatic striations, crystal faces, and lack of conchoidal fracture for tourmaline; a uniform glassy body with curved fracture favors obsidian. Common sources include Brazil, Afghanistan, Madagascar, Mexico, and the western United States.