mineral

Black tourmaline (schorl)

Schorl, NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Typically black, vitreous to resinous, with strong lengthwise striations and irregular fracture; Mohs hardness 7–7.5, trigonal crystal system, no distinct cleavage, specific gravity about 3.1–3.3. The specimen appears massive or fractured rather than a complete crystal.

Identified August 28, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in boron-rich granitic pegmatites, hydrothermal veins, and metamorphic rocks during late-stage crystallization; most examples are Paleozoic to younger, depending on locality. Common sources include Brazil, Afghanistan, Madagascar, Namibia, and the United States.

Uses & applications

Used as a collector mineral, ornamental stone, and occasionally in cabochons; gem-quality transparent tourmaline is valuable, while opaque black schorl is inexpensive.

Geological facts

Tourmaline is strongly piezoelectric and becomes electrically charged when heated or compressed. Its characteristic striated prismatic crystals help distinguish it from many black minerals.

Field identification & locations

Look for a black, elongated crystal with parallel grooves, glassy luster, and uneven fracture; test cautiously because hardness can scratch glass. A definitive identification may require streak, density, or analytical testing.