mineral

Polished black tourmaline (schorl), probable

Schorl tourmaline — NaFe3Al6(BO3)3Si6O18(OH)4

AI-generated identification · may be incorrect

Black, opaque, vitreous to resinous luster with subtle lengthwise striations; Mohs hardness 7–7.5, trigonal crystal structure, no prominent cleavage, and specific gravity about 3.0–3.3. The rounded form appears tumbled or naturally water-worn, with pale inclusions or surface fractures.

Identified August 17, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in boron-rich granitic pegmatites and hydrothermal veins when magma cools, commonly during the Precambrian to Phanerozoic. Weathering releases durable crystals into stream gravels.

Uses & applications

Used as a gemstone, ornamental stone, metaphysical specimen, and collector mineral; rarely used industrially because gem-quality black tourmaline is abundant.

Geological facts

Schorl is the most common tourmaline species and is strongly piezoelectric and often weakly pyroelectric. Long crystals typically show triangular cross-sections and parallel striations.

Field identification & locations

Confirm with a hardness test against glass, visible striations, and a potential electrical charge when warmed or rubbed; magnetism may be slight from iron. Common localities include Brazil, Afghanistan, Pakistan, Madagascar, Namibia, and the United States.