mineral
Black Tourmaline (Schorl)
Schorl (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness: 7 to 7.5 Mohs. Color: Inky black. Luster: Vitreous to sub-metallic. Crystal structure: Trigonal/Hexagonal with vertical striations. Cleavage: Indistinct. Specific gravity: 3.0 to 3.2.
- Hardness
- 7 to 7
- Color
- Inky black
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 7 to 7.5 Mohs. Color: Inky black. Luster: Vitreous to sub-metallic. Crystal structure: Trigonal/Hexagonal with vertical striations. Cleavage: Indistinct. Specific gravity: 3.0 to 3.2.
Formation & geological history
Typically formed in granitic pegmatites or metamorphic rocks like schists during the cooling of molten rock or hydrothermal activity. Often found in deposits dating back to the Paleozoic or Mesozoic eras.
Uses & applications
Primarily used in jewelry as a gemstone, as decorative specimens for collectors, and in some industrial applications requiring its pyroelectric and piezoelectric properties.
Geological facts
Black tourmaline is known for its ability to become electrically charged through heat (pyroelectricity) or pressure (piezoelectricity). It is a boron silicate mineral and constitutes about 95% of all tourmaline found in nature.
Field identification & locations
Identify by its deep black color, vertical striations (lines) along the length of the crystal, and its prismatic shape. Commonly found in Brazil, Namibia, the United States (California/Maine), and Pakistan. Collectors look for sharp, hexagonal edges.
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