mineral

Polished black tourmaline (schorl)

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

AI-generated identification · may be incorrect

Hardness 7–7.5 Mohs; black to brown-black with a vitreous-to-resinous luster and elongated, commonly striated prismatic structure. Tourmaline has poor cleavage and distinctive strong pleochroism; this specimen appears polished or naturally smoothed.

Identified September 3, 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, commonly in Precambrian to Phanerozoic rocks. Weathering can concentrate resistant crystals in placer deposits.

Uses & applications

Used as a collector mineral, lapidary material, ornamental stone, and occasionally in jewelry; tourmaline’s piezoelectric and pyroelectric properties have technical applications.

Geological facts

Schorl is the most abundant tourmaline species and is typically iron-rich and opaque. Heating or pressure can produce electrical charges at its ends.

Field identification & locations

Identify by its jet-black color, elongated form, longitudinal striations, low cleavage, and hardness; it may leave no streak on unglazed porcelain. Common sources include Brazil, Afghanistan, Madagascar, Namibia, and the United States.