mineral
Black Tourmaline
Schorl (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness 7.0-7.5, black opaque color, vitreous to sub-metallic luster, trigonal crystal system with vertical striations, no true cleavage, specific gravity 3.0-3.3
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Physical properties
Hardness 7.0-7.5, black opaque color, vitreous to sub-metallic luster, trigonal crystal system with vertical striations, no true cleavage, specific gravity 3.0-3.3
Formation & geological history
Found in granitic pegmatites, metamorphic rocks, and hydrothermal veins. Formed from boron-rich fluids during final stages of magma crystallization.
Uses & applications
Used in gemstone and jewelry trade, industrial pressure gauges (due to piezoelectricity), filtering, and as a popular protection stone for collectors.
Geological facts
It is pyroelectric, meaning it generates an electric charge when heated. It also features a unique triangular cross-section in its raw crystal form.
Field identification & locations
Identify by its intense black color, deep vertical striations on sides, and lack of cleavage. Common in Brazil, Namibia, and USA (California/Maine).
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Other mineral specimens
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Nephrite Jade
Nephrite
Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
Metamorphic Rock
![Biotite Schist (Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]) — metamorphic](https://media.rock.id/9ca564b5-bc87-402b-965a-69b21f9aa6bf-thumbnail.jpg)
Biotite Schist
Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]
metamorphic