mineral
Black Tourmaline (Schorl)
Schorl (NaFe2+3Al6(BO3)3Si6O18(OH)4)
Hardness: 7 to 7.5; Color: Deep black; Luster: Vitreous to sub-metallic; Crystal Structure: Trigonal (striated prisms); Cleavage: Indistinct; Specific Gravity: 3.06 to 3.26.
- Hardness
- 7 to 7
- Color
- Deep black
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 7 to 7.5; Color: Deep black; Luster: Vitreous to sub-metallic; Crystal Structure: Trigonal (striated prisms); Cleavage: Indistinct; Specific Gravity: 3.06 to 3.26.
Formation & geological history
Typically forms in granitic pegmatites, hydrothermal veins, and metamorphic rocks such as schist. Formed under high pressure and temperature during late-stage crystallization of magma.
Uses & applications
Used primarily in metaphysical industries, as decorative ornaments, and occasionally in electrical components due to its pyroelectric and piezoelectric properties.
Geological facts
Black tourmaline is known for its ability to generate an electrical charge when heated (pyroelectricity) or squeezed (piezoelectricity). It is the most common variety of tourmaline.
Field identification & locations
Identified by its distinctive triangular-rounded cross-section, vertical striations (lines) along the long faces of the crystal, and its opaque black color. Commonly found in Brazil, Namibia, and the USA.
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