mineral

Black tourmaline (schorl), probable

Schorl tourmaline — NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Usually black, opaque, with vitreous to resinous luster and commonly prismatic, striated crystals; Mohs hardness 7–7.5, specific gravity about 3.1–3.3, and poor/inconspicuous cleavage. The specimen appears massive or fractured rather than well-crystallized.

Identified September 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in boron-rich granitic pegmatites and hydrothermal veins during late-stage igneous activity, commonly in Paleozoic to younger rocks. It may also occur as resistant grains in metamorphic and alluvial deposits.

Uses & applications

Used as a collector mineral and occasionally as ornamental stone; gem-quality tourmaline is cut for jewelry, but opaque schorl generally has modest commercial value.

Geological facts

Tourmaline is strongly piezoelectric and becomes electrically charged when heated or pressed. Black schorl is the most common tourmaline variety.

Field identification & locations

Identify by its deep black color, elongated striated crystals, hardness, and possible electric charge when rubbed or warmed; distinguish from coal, slag, or hornblende with a hardness and streak test. Common localities include Brazil, Afghanistan, Pakistan, Namibia, Madagascar, and U.S. pegmatites.