mineral/gemstone
Black Tourmaline (Schorl)
Sodium Iron Aluminum Borate Silicate (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness: 7-7.5. Color: Inky black. Luster: Vitreous to sub-metallic. Crystal Structure: Trigonal. Cleavage: Indistinct. Specific Gravity: 3.0-3.2.
- Hardness
- 7-7
- Color
- Inky black
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 7-7.5. Color: Inky black. Luster: Vitreous to sub-metallic. Crystal Structure: Trigonal. Cleavage: Indistinct. Specific Gravity: 3.0-3.2.
Formation & geological history
Typically forms in granitic pegmatites, hydrothermal veins, and metamorphic rocks like schists during the cooling of molten rock or high-pressure geological events.
Uses & applications
Used in jewelry (beads and pendants), as an industrial source of boron, and in scientific instruments due to its piezoelectric and pyroelectric properties.
Geological facts
Black tourmaline is known as Schorl. It is unique for being both pyroelectric and piezoelectric, meaning it can generate an electrical charge when heated or mechanically stressed.
Field identification & locations
Identify by its deep black color, high hardness (can scratch glass), and frequent columnar crystal habits with vertical striations. Found in Brazil, Africa, and the USA (California/Maine).
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