mineral
Schorl (Black Tourmaline)
Sodium Iron Aluminum Borosilicate Hydroxide - 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
Usually forms in granitic pegmatites, hydrothermal veins, and metamorphic rocks such as schists and marbles. It occurs as a late-stage crystallization product of silica-rich magma.
Uses & applications
Used primarily for gemstone carving, bead jewelry, mineral collecting, and industrial applications involving high-pressure gauges due to its piezoelectric properties.
Geological facts
Black tourmaline is piezoelectric, meaning it generates an electrical charge when mechanically stressed. It is the most common variety of the tourmaline group.
Field identification & locations
Identify by its characteristic trigonal cross-sections, vertical striations on crystal faces, and lack of cleavage. Found globally, with significant deposits in Brazil, Africa, and the USA.
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