igneous
Schorl (Black Tourmaline) in Pegmatite
Sodium Iron Aluminum Borosilicate (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness: 7-7.5 (Mohs scale); Color: Jet black (Schorl) in tan/creamy matrix; Luster: Vitreous to sub-metallic; Crystal structure: Trigonal/Hexagonal elongated prisms; Cleavage: Poor/indistinct.
- Hardness
- 7-7
- Color
- Jet black (Schorl) in tan/creamy matrix
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 7-7.5 (Mohs scale); Color: Jet black (Schorl) in tan/creamy matrix; Luster: Vitreous to sub-metallic; Crystal structure: Trigonal/Hexagonal elongated prisms; Cleavage: Poor/indistinct.
Formation & geological history
Formed through the slow cooling of magmatic fluids rich in boron and rare elements. This typically occurs in granitic pegmatites during the final stages of magma crystallization, often dating from the Precambrian to Cenozoic eras.
Uses & applications
Used primarily for mineral collecting and as a healing stone in metaphysical communities. While Schorl is not usually used in jewelry due to its opacity, it is an industrial source of boron and is studied for its pyroelectric properties.
Geological facts
Black tourmaline is pyroelectric, meaning it generates an electrical charge when heated. It is also piezoelectric, generating a charge under mechanical stress. Large crystals can grow several meters long in rare pegmatite pockets.
Field identification & locations
Identify in the field by looking for black, columnar crystals with vertical striations (grooves) along the faces. They are typically found in granite-rich mountainous regions like Brazil, Namibia, or the Appalachian Mountains in the US. Collectors should look for 'pockets' in hard rock.
