mineral
Raw black tourmaline (probable schorl)
Schorl, NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectTypically black, vitreous to resinous, with striated prismatic crystals and uneven fracture; Mohs hardness 7–7.5, specific gravity about 3.1–3.3. The specimen appears opaque and irregular, consistent with a small rough fragment.
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Physical properties
Typically black, vitreous to resinous, with striated prismatic crystals and uneven fracture; Mohs hardness 7–7.5, specific gravity about 3.1–3.3. The specimen appears opaque and irregular, consistent with a small rough fragment.
Formation & geological history
Forms mainly in granite pegmatites and hydrothermal veins during late-stage crystallization of granitic magmas, commonly in Mesozoic to Precambrian terrains. Exact age and locality cannot be determined from the image.
Uses & applications
Used as a collector mineral, gemstone, and occasionally in ornamental objects; gem-quality tourmaline is faceted, while black schorl is usually sold as rough specimens.
Geological facts
Tourmaline is strongly pleochroic in colored varieties and can develop electric charge when heated or rubbed (pyroelectricity and triboelectricity). Schorl is the most common tourmaline species.
Field identification & locations
Look for lengthwise striations, a near-black color, and a hard crystal that resists scratching by steel. Common sources include Brazil, Afghanistan, Pakistan, Madagascar, Namibia, and the United States.
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