mineral

Black tourmaline (schorl)

Schorl, NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Black, opaque, vitreous-to-resinous luster with a commonly striated prismatic crystal habit; Mohs hardness 7–7.5, specific gravity about 3.1–3.3, and poor-to-indistinct cleavage. The specimen appears as a rough, elongated tourmaline crystal or fragment.

Identified September 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms in boron-rich hydrothermal fluids, especially granite pegmatites, and sometimes metamorphic rocks; individual crystals may be Paleozoic to Cenozoic depending on the deposit. Common localities include Brazil, Afghanistan, Pakistan, Madagascar, Namibia, and the United States.

Uses & applications

Used as a collector mineral, ornamental stone, and occasionally in black gemstone jewelry; large undamaged crystals are more valuable than industrial material.

Geological facts

Schorl is the most common tourmaline species and is strongly piezoelectric and pyroelectric, developing electrical charges when compressed or heated.

Field identification & locations

Identify it by its deep black color, elongated striated prisms, triangular or rounded cross-section, and hardness sufficient to scratch glass; distinguish it from hornblende by tourmaline’s stronger longitudinal striations and typical crystal shape.