mineral

Raw black tourmaline (likely schorl)

Schorl, a sodium–iron tourmaline; approximate formula NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Typically black, strongly vitreous to submetallic, with prismatic or irregular crystals and distinctive lengthwise striations; Mohs hardness 7–7.5, no cleavage, specific gravity about 3.1–3.3. The specimen appears very small, rough, and partly matrix-coated.

Identified August 15, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in boron-rich granitic pegmatites and hydrothermal veins during late-stage crystallization of granite, generally in Phanerozoic to Precambrian terrains. Exact age and locality cannot be determined from the photograph.

Uses & applications

Used as a minor industrial mineral and widely sold as a collector specimen or jewelry stone; polished black tourmaline is common in beads and cabochons. It is not generally used as a construction rock.

Geological facts

Schorl is the most abundant tourmaline species and is strongly pleochroic; tourmalines can become electrically polarized when heated or compressed (pyroelectric and piezoelectric effects).

Field identification & locations

Identify it by its black color, hard glassy surface, striated prismatic form, and lack of cleavage; distinguish it from obsidian by the crystal striations and from metallic sulfides by its nonmetallic fracture. Common sources include Brazil, Afghanistan, Pakistan, Namibia, Madagascar, and the United States.