mineral
Schorl (Black Tourmaline)
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Hardness: 7-7.5 (Mohs), Color: brownish-black to jet black, Luster: vitreous to sub-metallic, Crystal structure: trigonal (often striated), Cleavage: poor/indistinct, Specific Gravity: 3.0-3.2
- Hardness
- 7-7
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Physical properties
Hardness: 7-7.5 (Mohs), Color: brownish-black to jet black, Luster: vitreous to sub-metallic, Crystal structure: trigonal (often striated), Cleavage: poor/indistinct, Specific Gravity: 3.0-3.2
Formation & geological history
Formed in igneous and metamorphic rocks, most commonly in granitic pegmatites. It forms during late-stage crystallization from hydrothermal or magmatic fluids rich in boron.
Uses & applications
Used primarily as a gemstone, as specimens for mineral collectors, and in grounding jewelry. In industry, its pyroelectric and piezoelectric properties are sometimes utilized.
Geological facts
Black tourmaline is unique because it becomes electrically charged when heated (pyroelectricity) or squeezed (piezoelectricity). It is the most common member of the tourmaline mineral group.
Field identification & locations
Identify in the field by its deep black color, lack of cleavage, brittle fracture, and distinctive vertical striations (lines) along the length of the crystals. Often found in quartz veins.
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Mineral
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Mineral/Rock
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igneous