mineral

Tumbled black tourmaline (likely schorl)

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

AI-generated identification · may be incorrect

Black to brown-black, vitreous to resinous luster, commonly opaque with pale quartz or feldspar veining; Mohs hardness 7–7.5, trigonal crystal structure, poor cleavage, and specific gravity about 3.1–3.3. The rounded shape indicates tumbling or natural abrasion.

Identified September 18, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in boron-rich granitic pegmatites and hydrothermal veins as elongated prismatic crystals; associated rocks are commonly Paleozoic to younger, though tourmaline occurs across much of geologic time.

Uses & applications

Used as a collectible, lapidary stone, and occasional gemstone; industrial tourmaline has limited use, while polished pieces are sold for decorative and metaphysical purposes.

Geological facts

Schorl is the most common tourmaline species and can become strongly electrically polarized when heated or rubbed (pyroelectric and piezoelectric effects).

Field identification & locations

Look for deep black color, longitudinal striations, glassy luster, lack of cleavage, and attraction of light fibers or ash after rubbing; confirm with hardness and specific-gravity tests. Common sources include Brazil, Afghanistan, Pakistan, Madagascar, and the United States.