mineral
Black Tourmaline (Schorl)
Schorl (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness: 7-7.5 (Mohs scale), Color: Inky black, Luster: Vitreous to sub-metallic, Crystal Structure: Trigonal/Hexagonal columns, Cleavage: Indistinct, Specific Gravity: 3.0-3.2. Surface often shows vertical striations.
- Hardness
- 7-7
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Physical properties
Hardness: 7-7.5 (Mohs scale), Color: Inky black, Luster: Vitreous to sub-metallic, Crystal Structure: Trigonal/Hexagonal columns, Cleavage: Indistinct, Specific Gravity: 3.0-3.2. Surface often shows vertical striations.
Formation & geological history
Formed in granitic pegmatites and metamorphic rocks through hydrothermal processes involving boron-rich fluids. Often millions of years old, typically found in ancient continental crust.
Uses & applications
Used in jewelry, decorative carvings, and as a popular protection stone in mineral collecting. Historically used in scientific instruments due to its piezoelectric properties.
Geological facts
Black tourmaline is both pyroelectric (develops electric charge when heated) and piezoelectric (develops charge under pressure). It is the most common member of the tourmaline group.
Field identification & locations
Identify by its deep black color, vertical striations on crystal faces, and lack of visible cleavage. Commonly found in Brazil, Madagascar, and the United States (Maine/California).
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