mineral
Likely black tourmaline (schorl) in host rock
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectDark brown-black, rough, with a vitreous-to-submetallic sheen and apparent lengthwise striations; tourmaline is trigonal and has Mohs hardness 7–7.5, but the specimen’s identity and properties cannot be confirmed from the photo alone.
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Physical properties
Dark brown-black, rough, with a vitreous-to-submetallic sheen and apparent lengthwise striations; tourmaline is trigonal and has Mohs hardness 7–7.5, but the specimen’s identity and properties cannot be confirmed from the photo alone.
Formation & geological history
Schorl commonly crystallizes in boron-rich granitic pegmatites and hydrothermal veins; such deposits formed at varied geological ages. The lighter surrounding material may be host rock or another mineral.
Uses & applications
Tourmaline crystals are collected and sometimes cut as gemstones; common dark, fractured pieces have limited jewelry or industrial use.
Geological facts
Tourmaline crystals often show strong longitudinal striations, a useful clue when distinguishing them from other dark minerals.
Field identification & locations
Look for a prismatic crystal habit, parallel lengthwise grooves, and hardness sufficient to scratch glass; commonly found in pegmatites worldwide, including Brazil, Afghanistan, and the United States.
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Epidote
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Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
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Granite
Granite (Phaneritic intrusive igneous rock)
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