mineral

Black tourmaline (schorl)

Schorl, NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Typically black, vitreous to resinous, with irregular fracture and weak-to-distinct prismatic cleavage; Mohs hardness 7–7.5 and specific gravity about 3.0–3.3. The glossy, uneven black surface and apparent prismatic form are consistent with tourmaline, though a photo cannot confirm it.

Identified September 7, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granitic pegmatites, hydrothermal veins, and metamorphic rocks during late-stage crystallization of boron-rich fluids; specimens range from Precambrian to recent geological settings.

Uses & applications

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

Geological facts

Tourmaline is strongly piezoelectric and can develop electrical charges when heated or pressed. Schorl is the most common tourmaline species and is commonly associated with quartz and feldspar.

Field identification & locations

Look for elongated striated prisms, black color, vitreous luster, and hardness sufficient to scratch glass; test streak, crystal form, and associations rather than relying on color alone. Common localities include Brazil, Afghanistan, Namibia, Pakistan, and the United States.