mineral
Black Tourmaline (Schorl)
Schorl (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness: 7 to 7.5 Mohs; Color: Jet black to brownish-black; Luster: Vitreous to sub-metallic; Crystal Structure: Trigonal/Hexagonal; Cleavage: Indistinct; Specific Gravity: 3.06 to 3.20.
- Hardness
- 7 to 7
- Color
- Jet black to brownish-black
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 7 to 7.5 Mohs; Color: Jet black to brownish-black; Luster: Vitreous to sub-metallic; Crystal Structure: Trigonal/Hexagonal; Cleavage: Indistinct; Specific Gravity: 3.06 to 3.20.
Formation & geological history
Formed in igneous and metamorphic rocks, most commonly in pegmatites and hydrothermal veins. It crystallizes from boron-rich fluids during the final stages of magma cooling.
Uses & applications
Used in jewelry, as mineral specimens for collectors, and in some specialized industrial equipment for its piezoelectric and pyroelectric properties.
Geological facts
Black tourmaline is pyroelectric, meaning it can generate an electrical charge when heated. It was historically used by Dutch traders to pull ash out of long-stemmed pipes, earning it the nickname 'Aschentrekker' (ash puller).
Field identification & locations
Identified by its deep black color, brittle nature, and characteristic three-sided or triangular cross-sections in well-formed crystals. Common in granitic pegmatites in Brazil, Africa, and the USA.
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