mineral
Black Tourmaline (Schorl)
Schorl (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness: 7-7.5 on Mohs scale; Color: Opaque black; Luster: Vitreous to resinous; Crystal Structure: Trigonal; 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 Mohs scale; Color: Opaque black; Luster: Vitreous to resinous; Crystal Structure: Trigonal; Cleavage: Indistinct; Specific Gravity: 3.0-3.25
Formation & geological history
Typically forms in felsic igneous rocks, specifically pegmatites, and in metamorphic rocks like schist and marble. It develops through hydrothermal activity involving boron-rich fluids.
Uses & applications
Used extensively in jewelry (as beads or pendants), as a protective stone in metaphysical practices, and historically in scientific instruments due to its piezoelectric properties.
Geological facts
Black tourmaline is both pyroelectric (develops charge when heated) and piezoelectric (develops charge under pressure). It is the most common variety of the tourmaline group, accounting for 95% of all tourmaline in nature.
Field identification & locations
Identified by its jet-black color, lack of transparency, and vertical striations when in raw crystal form. Tumbled specimens are smooth, heavy for their size, and highly reflective. Common in Brazil, Namibia, and the USA.
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Other mineral specimens
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Sandstone with Mineral Veining or Crust
Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)
sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock