mineral
Black Tourmaline (Schorl)
Schorl (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness: 7-7.5 (Mohs scale), Color: Jet black, Luster: Vitreous to sub-metallic, Crystal Structure: Trigonal, Cleavage: Indistinct, Specific Gravity: 3.1-3.2.
- Hardness
- 7-7
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Physical properties
Hardness: 7-7.5 (Mohs scale), Color: Jet black, Luster: Vitreous to sub-metallic, Crystal Structure: Trigonal, Cleavage: Indistinct, Specific Gravity: 3.1-3.2.
Formation & geological history
Formed in igneous and metamorphic rocks, most commonly in pegmatites and granites through hydrothermal activity. Frequently found in Precambrian and Paleozoic formations.
Uses & applications
Used in jewelry, metaphysical collecting, and as a source of boron. Historically used for polarizing filters in scientific instruments.
Geological facts
Black tourmaline is pyroelectric and piezoelectric, meaning it can generate an electrical charge when heated or mechanically stressed. It was often called 'Aschentrekker' by the Dutch because it attracted ash.
Field identification & locations
Identify in the field by its black color, columnar crystal habit with triangular cross-sections, and deep vertical striations on the long faces. Common in Brazil, Africa, and Maine.
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Mineral
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