mineral

Polished black stone, likely black tourmaline or black obsidian

Most consistent with schorl tourmaline (NaFe3Al6(BO3)3Si6O18(OH)4), though black obsidian (volcanic glass) is also possible

AI-generated identification · may be incorrect

Opaque black, vitreous to glossy luster, smoothly polished; tourmaline has Mohs hardness 7–7.5 and no cleavage, while obsidian is glassy, about 5–5.5, and conchoidally fractures. The visible pale vein-like lines may indicate tourmaline matrix or a composite/polished rough stone.

Identified September 3, 2026More mineral →

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At a glance

Common name: Polished black stone, likely black tourmaline or black obsidian
Scientific name: Most consistent with schorl tourmaline (NaFe3Al6(BO3)3Si6O18(OH)4), though black obsidian (volcanic glass) is also possible
Category: mineral
Identified: September 3, 2026
Method: Standard

AI Estimated Value

Approximately $10–$40 for a common polished palm stone; $50–$150 or more if confirmed as attractive natural tourmaline.

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 boron-rich granitic pegmatites; obsidian forms when silica-rich lava cools rapidly, generally in the Quaternary to recent geologic record. A photograph alone cannot distinguish them reliably.

Uses & applications

Used as a decorative palm stone, ornamental material, and collectible; tourmaline is also used in jewelry and mineral specimens. Obsidian is used for carvings, jewelry, and historically sharp tools.

Geological facts

Schorl is the most common tourmaline variety and is strongly piezoelectric. Obsidian lacks a true crystalline structure and is technically volcanic glass.

Field identification & locations

Check edges and fractures: obsidian shows sharp conchoidal breaks, whereas tourmaline commonly reveals elongated striations or prismatic texture; hardness and streak tests can help, but avoid damaging the polished piece. Common sources include Brazil, Africa, the United States, and Mexico.