mineral

Black tourmaline (schorl) fragments

Schorl, NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Opaque black to brown-black fragments with vitreous to resinous luster and commonly prismatic, striated crystal faces. Mohs hardness 7–7.5; trigonal crystal structure, poor cleavage, and specific gravity about 3.0–3.3.

Identified September 13, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granitic pegmatites and hydrothermal veins as boron-rich magma cools, commonly during the Precambrian to Phanerozoic. The pictured pieces appear broken or rough rather than naturally terminated crystals.

Uses & applications

Used as mineral specimens, beads, carvings, and occasionally in jewelry; industrial-quality material has limited value. Its durability makes it suitable for polished cabochons and ornamental objects.

Geological facts

Schorl is the most common tourmaline species and is strongly pleochroic. Heating or rubbing can produce electrical polarization (pyroelectric and piezoelectric effects).

Field identification & locations

Identify by black color, elongated triangular-prismatic form, lengthwise striations, high hardness, and absence of obvious cleavage; a glass scratch test can help, but avoid damaging specimens. Common sources include Brazil, Afghanistan, Madagascar, Namibia, and the United States.