Rock Identifier
Black Tourmaline (Schorl (Sodium Iron Aluminum Borosilicate Hydroxide); NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)) — mineral
mineral

Black Tourmaline

Schorl (Sodium Iron Aluminum Borosilicate Hydroxide); NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)

Hardness: 7-7.5 on the Mohs scale. Color: Opaque black. Luster: Vitreous to resinous. Crystal Structure: Trigonal/Hexagonal, often showing long, needle-like or columnar crystals with vertical striations. Cleavage: Indistinct. Specific Gravity: 3.0-3.25.

Hardness
7-7
Color
Opaque black
Luster
Vitreous to resinous
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Physical properties

Hardness: 7-7.5 on the Mohs scale. Color: Opaque black. Luster: Vitreous to resinous. Crystal Structure: Trigonal/Hexagonal, often showing long, needle-like or columnar crystals with vertical striations. Cleavage: Indistinct. Specific Gravity: 3.0-3.25.

Formation & geological history

Formed primarily in pegmatites through hydrothermal processes involving boron-rich fluids. It can also be found in high-grade metamorphic rocks like granitic gneisses. It has no specific geological age as it forms across various eras depending on tectonic activity.

Uses & applications

Commonly used as a pocket stone or in jewelry (beads, pendants) for its aesthetic appeal. Industrially, it has been used in pressure gauges due to its piezoelectric properties. Highly valued in metaphysical circles as a protective 'grounding' stone.

Geological facts

Black tourmaline is both pyroelectric (generates an electrical charge when heated) and piezoelectric (generates a charge when under pressure). It was once used by Dutch sailors to pull ash out of their meerschaum pipes, earning it the nickname 'Aschentrekker' (ash puller).

Field identification & locations

Identify in the field by its intense black color, high hardness (cannot be scratched by steel), and the presence of deep vertical striations along the crystal faces. Often found in Brazil, Namibia, Madagascar, and the United States (Maine/California).

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