mineral

Polished black tourmaline

Schorl tourmaline — NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Hardness 7–7.5 Mohs; black to dark brown, commonly with longitudinal striations and a vitreous-to-resinous luster. Trigonal crystal structure; typically lacks obvious cleavage and has moderate specific gravity around 3.1–3.3.

Identified September 3, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in boron-rich hydrothermal veins and granitic pegmatites during late-stage magma crystallization, generally in ancient to relatively young continental crust. The pictured piece appears tumbled or polished rather than naturally crystal-terminated.

Uses & applications

Used as a collectible mineral, lapidary cabochon, and ornamental stone; attractive specimens may be set in jewelry. Industrial tourmaline has limited use, though its piezoelectric and pyroelectric properties are notable.

Geological facts

Schorl is the most common tourmaline species and can become electrically charged when heated or rubbed. Longitudinal grooves are a strong diagnostic feature.

Field identification & locations

Identify by its opaque black color, elongated striations, glassy luster, and lack of cleavage; it is commonly found in pegmatites in Brazil, Afghanistan, Madagascar, Pakistan, and the United States. A streak test is usually brownish-black, and it is harder than glass.