igneous
Schorl (Black Tourmaline) in Granite
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Hardness: 7 Mohs; Color: Jet black crystals in white/grey matrix; Luster: Vitreous to sub-metallic; Crystal structure: Trigonal (often long prismatic/needle-like); Cleavage: Indistinct; Specific gravity: 3.0-3.2
- Hardness
- 7 Mohs
- Color
- Jet black crystals in white/grey matrix
- Luster
- Vitreous to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 7 Mohs; Color: Jet black crystals in white/grey matrix; Luster: Vitreous to sub-metallic; Crystal structure: Trigonal (often long prismatic/needle-like); Cleavage: Indistinct; Specific gravity: 3.0-3.2
Formation & geological history
Formed in granitic pegmatites during the late stages of magma cooling where boron is concentrated. These specimens can range from hundreds of millions to billions of years old depending on the specific mountain range formation.
Uses & applications
Used popularily for ornamental 'chakra' use and metaphysical collecting; in industry, tourmaline is used in pressure gauges due to its piezoelectric properties. Granite matrix is used in construction and sculpture.
Geological facts
Tourmaline is both pyroelectric and piezoelectric, meaning it can generate an electrical signal when heated or subjected to mechanical stress. It was once used by Dutch traders to pull ash out of long-stemmed pipes.
Field identification & locations
Identify by the distinct, elongated black crystals with vertical striations embedded within course-grained igneous rock. Often found in mountain ranges with exposed granite cores like the Appalachians or the Rockies.
