mineral

Black tourmaline (likely schorl)

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

AI-generated identification · may be incorrect

Typically black, opaque, and vitreous to resinous, with a trigonal crystal structure and prominent lengthwise striations; Mohs hardness 7–7.5, no distinct cleavage, and specific gravity about 3.1–3.3. The pictured prismatic, fractured piece is consistent with schorl, though the image alone cannot exclude obsidian or an…

Identified August 17, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granitic pegmatites, hydrothermal veins, and metamorphic rocks during boron-rich fluid activity, commonly in the Precambrian to younger igneous systems. Tourmaline is widespread and chemically durable.

Uses & applications

Used as a gemstone when transparent or attractively terminated, in mineral collecting, and occasionally as an industrial electrical/thermal material; opaque fragments have limited commercial value.

Geological facts

Tourmaline is strongly pleochroic and can become electrically polarized when heated or compressed (the tourmaline effect). Schorl is the most abundant tourmaline species.

Field identification & locations

Look for a black, elongated trigonal prism with parallel grooves, curved/uneven fracture, and lack of cleavage; it commonly occurs with quartz and feldspar in pegmatites. Common localities include Brazil, Afghanistan, Pakistan, Madagascar, Namibia, and the United States.