mineral
Black Tourmaline (Schorl)
Schorl (NaFe2+3Al6(Si6O18)(BO3)3(OH)3OH)
Hardness: 7-7.5. Color: Black. Luster: Vitreous to sub-metallic. Crystal structure: Trigonal/Hexagonal. Cleavage: Indistinct. Specific gravity: 3.0-3.2.
- Hardness
- 7-7
- Color
- Black
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 7-7.5. Color: Black. Luster: Vitreous to sub-metallic. Crystal structure: Trigonal/Hexagonal. Cleavage: Indistinct. Specific gravity: 3.0-3.2.
Formation & geological history
Part of the tourmaline group, it typically forms in granitic pegmatites, hydrothermal veins, and metamorphic rocks like schists. It is a boron-rich silicate mineral commonly associated with quartz and feldspar.
Uses & applications
Used as an industrial abrasive, in pressure gauges due to its piezoelectric properties, but most commonly used as a protective stone in jewelry and metaphysical collections.
Geological facts
Schorl accounts for approximately 95% of all tourmaline found in nature. It is strongly pleochroic and exhibits both pyroelectric and piezoelectric properties, meaning it can generate an electrical charge when heated or compressed.
Field identification & locations
Identify in the field by its characteristic elongated, striated black crystals that often have a triangular or hexagonal cross-section. It is common in pegmatite-rich areas like those in Brazil, Pakistan, and the USA (California and Maine).
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sedimentary
Schist
Schist
Metamorphic
Epidote
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metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock
Granite
Granite (Phaneritic intrusive igneous rock)
igneous