mineral

Black Tourmaline

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

Hardness: 7-7.5 (Mohs scale), Color: Inky black, Luster: Vitreous to sub-metallic, Crystal Structure: Trigonal (striated prisms), Cleavage: Indistinct, Specific Gravity: 3.0-3.2

Hardness: 7-7

Identified May 10, 2026More mineral →

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Physical properties

Hardness: 7-7.5 (Mohs scale), Color: Inky black, Luster: Vitreous to sub-metallic, Crystal Structure: Trigonal (striated prisms), Cleavage: Indistinct, Specific Gravity: 3.0-3.2

Formation & geological history

Formed in igneous and metamorphic rocks, most commonly in pegmatites through hydrothermal activity. Found in formations ranging from Precambrian to more recent geological eras.

Uses & applications

Used primarily in jewelry as a gemstone, as an industrial source of boron, and in pressure-sensitive gauges due to its piezoelectric properties.

Geological facts

Black tourmaline is both piezoelectric (generates electricity when stressed) and pyroelectric (generates electricity when heated), which allows it to attract dust particles.

Field identification & locations

Identify by its characteristic vertical striations along the length of the crystal and its triangular cross-section. Commonly found in Brazil, Africa, and the United States (Maine, California).