mineral
Black tourmaline (schorl)
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectTypically black with a vitreous to resinous luster; Mohs hardness 7–7.5; trigonal crystal structure and indistinct cleavage. The specimen appears to be a rough, dark tourmaline crystal, though the photo alone cannot confirm the identification.
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Physical properties
Typically black with a vitreous to resinous luster; Mohs hardness 7–7.5; trigonal crystal structure and indistinct cleavage. The specimen appears to be a rough, dark tourmaline crystal, though the photo alone cannot confirm the identification.
Formation & geological history
Tourmaline commonly crystallizes in boron-rich granitic pegmatites and metamorphic rocks as magma cools; such deposits range from ancient to geologically recent.
Uses & applications
Used as a collector mineral and, when transparent and well formed, as a gemstone; schorl is generally not an important construction material.
Geological facts
Tourmaline crystals can become electrically polarized when heated or cooled (pyroelectricity) or compressed (piezoelectricity).
Field identification & locations
Look for black, striated prismatic crystals with a triangular cross-section and hardness sufficient to scratch glass; common sources include Brazil, Afghanistan, and the United States. The image lacks diagnostic crystal faces, so identification is uncertain.
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Granite
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Septarian Pebble
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