mineral

Black tourmaline (schorl)

Schorl, NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Typically black, opaque, and vitreous to resinous, with a trigonal prismatic crystal structure, strong longitudinal striations, and uneven fracture; Mohs hardness 7–7.5, specific gravity about 3.0–3.3. The specimen appears to be a rough, fractured fragment rather than a complete crystal.

Identified September 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in boron-rich hydrothermal veins, pegmatites, and metamorphic rocks during late-stage crystallization; specimens range from Precambrian to modern geological settings. Common localities include Brazil, Afghanistan, Madagascar, the United States, and Pakistan.

Uses & applications

Used as a collector mineral, ornamental stone, and occasionally in jewelry; industrial tourmaline is studied for piezoelectric and pyroelectric properties, though schorl is not a major construction material.

Geological facts

Tourmaline can develop electric charge when heated or compressed. Black schorl is the most abundant tourmaline variety and commonly occurs with quartz, feldspar, and mica.

Field identification & locations

Identify it by black color, elongated striated surfaces, high hardness, and prismatic crystal habit; unlike obsidian, it is not glassy and commonly shows striations. A definitive identification may require hardness, streak, or analytical testing.