mineral
Likely black tourmaline (schorl)
Schorl, NaFe2+3Al6Si6O18(BO3)3Si6O18(OH)4
AI-generated identification · may be incorrectBlack, vitreous-to-submetallic luster; typically prismatic with striated faces, though this fragment is poorly formed. Mohs hardness 7–7.5, trigonal crystal system, indistinct cleavage, and specific gravity about 3.1–3.3.
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Physical properties
Black, vitreous-to-submetallic luster; typically prismatic with striated faces, though this fragment is poorly formed. Mohs hardness 7–7.5, trigonal crystal system, indistinct cleavage, and specific gravity about 3.1–3.3.
Formation & geological history
Forms mainly in granite pegmatites and hydrothermal veins when boron-rich fluids crystallize; specimens range from Precambrian to recent geologic ages. The image appears to show a small broken crystal or fragment.
Uses & applications
Used as a collector mineral and occasionally as a gemstone when transparent; black schorl is primarily ornamental and educational rather than industrial.
Geological facts
Tourmaline is strongly piezoelectric and can become electrically charged when heated or compressed. Schorl is the most common tourmaline variety.
Field identification & locations
Common in pegmatites worldwide, notably Brazil, Afghanistan, Pakistan, Madagascar, and the United States. Look for black color, hardness, elongated striated crystals, and lack of a strong metallic streak; a definitive identification may require testing.
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