mineral
Black Tourmaline (Schorl)
Schorl (NaFe3Al6(BO3)3Si6O18(OH)4)
Hardness: 7 to 7.5 on Mohs scale; Color: Jet black; Luster: Vitreous to sub-metallic; Crystal structure: Trigonal; Cleavage: Indistinct; Specific gravity: 3.0 to 3.25.
- Hardness
- 7 to 7
- Color
- Jet black
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 7 to 7.5 on Mohs scale; Color: Jet black; Luster: Vitreous to sub-metallic; Crystal structure: Trigonal; Cleavage: Indistinct; Specific gravity: 3.0 to 3.25.
Formation & geological history
Formed in granitic pegmatites, hydrothermal veins, and metamorphic rocks such as mica schists. These specimens can date back hundreds of millions of years and occur during the final stages of magma crystallization.
Uses & applications
Widely used in jewelry when polished, but most commonly used as a metaphysical grounding stone. Industrially used in pressure gauges due to its piezoelectric and pyroelectric properties.
Geological facts
Schorl accounts for approximately 95% of all tourmaline found in nature. It was used by early Dutch traders to pull ash out of clay pipes because of its ability to hold an electric charge when heated.
Field identification & locations
Identified by its deep black color, vertical striations (furrows) along the crystal length, and its triangular cross-section. Commonly found in Brazil, Namibia, and the USA (notably California and Maine).
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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
Granite
Granite (Phaneritic intrusive igneous rock)
igneous