mineral

Raw black tourmaline (probable schorl)

Schorl, NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Black to brown-black, commonly vitreous to resinous luster with prismatic or striated crystal surfaces; Mohs hardness 7–7.5, no distinct cleavage, trigonal crystal structure, specific gravity about 3.1–3.3. The specimen appears massive or poorly crystallized and may include attached matrix.

Identified August 10, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in boron-rich granitic pegmatites and hydrothermal veins during late-stage igneous crystallization, commonly in Precambrian to Phanerozoic terrains. Exact age and locality cannot be determined from the image.

Uses & applications

Used as a collector mineral and occasionally as a black gemstone when clean and well-crystallized; tourmaline is also valued for its piezoelectric and pyroelectric properties. This rough piece has limited industrial or jewelry value.

Geological facts

Schorl is the most common tourmaline species and is often strongly striated along its length. Tourmaline crystals can develop electrical charge when heated or compressed.

Field identification & locations

Look for elongated, triangular-to-rounded prismatic crystals, longitudinal striations, glassy luster, and resistance to scratching by steel; a streak test is usually white or colorless. Common sources include Brazil, Afghanistan, Namibia, Madagascar, Pakistan, and the United States.