mineral

Black Tourmaline

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

Hardness: 7-7.5 on 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
Color: Inky black
Luster: Vitreous to sub-metallic

Identified June 28, 2026More mineral →

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Physical properties

Hardness: 7-7.5 on 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 granitic pegmatites and metamorphic rocks through hydrothermal processes involving boron-rich fluids. Can be found in rocks from the Precambrian to recent ages.

Uses & applications

Used in pressure gauges (piezoelectric properties), as a minor ore of boron, and widely in jewelry or as metaphysical pocket stones. Also used in industrial acoustic equipment.

Geological facts

Black tourmaline is both pyroelectric (develops electric charge when heated) and piezoelectric (develops charge under pressure). In the 1700s, Dutch traders used heated tourmaline to pull ash out of their meerschaum pipes.

Field identification & locations

Identified by its long, vertical striations on crystal faces and its characteristic rounded-triangular cross-section. Commonly found in Brazil, Namibia, and the USA (Maine/California). Collectors should look for luster and lack of fractures.