mineral

Black tourmaline (schorl)

Schorl, sodium iron aluminum borosilicate hydroxide: NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Typically black, opaque, and vitreous to resinous, with Mohs hardness 7–7.5, poor cleavage, and a trigonal crystal structure. The specimen appears to be a naturally terminated or cut prismatic crystal, though the image alone cannot exclude another dark mineral.

Identified September 4, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granite pegmatites, hydrothermal veins, and metamorphic rocks during late-stage boron-rich crystallization. Tourmaline ranges from Precambrian to modern geological settings and commonly occurs with quartz and feldspar.

Uses & applications

Used as a durable collector mineral and occasionally as a gemstone; gem-quality tourmaline is faceted, while common schorl has limited industrial use. Tourmaline’s piezoelectric and pyroelectric properties support scientific and specialty applications.

Geological facts

Elongated crystals commonly show strong lengthwise striations and can become electrically charged when heated or rubbed. Black tourmaline is the most abundant tourmaline variety.

Field identification & locations

Look for a black, strongly striated prismatic crystal, hardness near quartz, and lack of obvious cleavage; a streak test is usually pale gray to black. Common sources include Brazil, Afghanistan, Madagascar, the United States, and Namibia.