mineral
Black Tourmaline (Schorl)
Schorl (NaFe2+3Al6(Si6O18)(BO3)3(OH)3OH)
Hardness: 7-7.5. Color: Jet black. Luster: Vitreous to sub-metallic. Crystal system: Trigonal. Cleavage: Indistinct. Specific gravity: 3.1 - 3.2. Striated elongated crystals are common.
- Hardness
- 7-7
- Color
- Jet black
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 7-7.5. Color: Jet black. Luster: Vitreous to sub-metallic. Crystal system: Trigonal. Cleavage: Indistinct. Specific gravity: 3.1 - 3.2. Striated elongated crystals are common.
Formation & geological history
Formed in granitic pegmatites, hydrothermal veins, and metamorphic rocks such as schists. Usually formed through late-stage magmatic processes involving boron-rich fluids.
Uses & applications
Used primarily in jewelry as a gemstone, in crystal healing collections, and in scientific instruments due to its pyroelectric and piezoelectric properties.
Geological facts
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 from their smoking pipes.
Field identification & locations
Identified by its triangular-hexagonal cross-section and prominent vertical striations. It is non-magnetic and much harder than coal or shungite. Common in Brazil, Namibia, and California.
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