mineral

Black tourmaline (schorl)

Schorl, NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Typically black, opaque, and vitreous to submetallic, with strong longitudinal striations and an elongated trigonal crystal habit; Mohs hardness 7–7.5, specific gravity about 3.1–3.3, and poor-to-indistinct cleavage. The rounded shape appears tumbled or naturally water-worn.

Identified September 5, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granitic pegmatites and hydrothermal veins through boron-rich fluids, commonly during late stages of granite crystallization; specimens range from Precambrian to recent geological settings. It is commonly found in Brazil, Afghanistan, Pakistan, Madagascar, the United States, and Namibia.

Uses & applications

Used as a collector mineral, ornamental stone, and occasionally in jewelry; industrial tourmaline has limited applications involving piezoelectric and pyroelectric behavior.

Geological facts

Tourmaline becomes electrically polarized when heated or compressed, attracting dust and tiny particles. Black schorl is the most abundant tourmaline species.

Field identification & locations

Identify it by its black color, elongated striated surfaces, glassy luster, hardness, and resistance to scratching by steel; confirm with composition or testing because obsidian and industrial slag can look similar. Common value is about $5–$30 for a small tumbled piece, or $20–$150+ for attractive crystal specimens.