mineral

Tourmaline (Schorl or Dravite) on Matrix

Complex Borosilicate - Na(Mg,Fe,Li,Al,Mn)3Al6(BO3)3Si6O18(OH,F)4

Hardness: 7-7.5 (Mohs scale); Color: Dark brown to black; Luster: Vitreous to resinous; Crystal Structure: Trigonal (often columnar with striated faces); Cleavage: Indistinct; Specific Gravity: 3.0-3.2

Hardness: 7-7
Color: Dark brown to black
Luster: Vitreous to resinous

Identified March 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in granitic pegmatites and metamorphic rocks like schist through hydrothermal and pneumatolytic processes where boron-rich fluids are present. These can range from hundreds of millions to several billion years old depending on the host formation.

Uses & applications

Used in gemstone production (though dark varieties are less common for jewelry), industrial pressure gauges due to piezoelectric properties, and highly sought after by mineral collectors for its aesthetic crystal forms.

Geological facts

Tourmaline is pyroelectric, meaning it develops an electrical charge when heated. It was historically known as 'Aschentrekker' (ash puller) by the Dutch because it could attract light ashes when warmed by a fireplace.

Field identification & locations

Identify in the field by its distinct vertical striations on elongated prismatic crystals and its triangular or rounded-triangular cross-section. Commonly located in pegmatitic outcrops in regions like Minas Gerais, Brazil, or the Northeastern United States.

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