mineral
Tumbled brown tourmaline (likely dravite)
Tourmaline-group mineral; probably dravite, NaMg₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectSmall polished, dark brown, translucent-to-opaque crystal with a vitreous luster. Tourmaline is trigonal, typically Mohs 7–7.5, with no prominent cleavage; the photo alone cannot confirm the variety.
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Physical properties
Small polished, dark brown, translucent-to-opaque crystal with a vitreous luster. Tourmaline is trigonal, typically Mohs 7–7.5, with no prominent cleavage; the photo alone cannot confirm the variety.
Formation & geological history
Tourmaline crystallizes in boron-rich pegmatites and metamorphic rocks; its age depends on the source deposit and cannot be determined from the specimen.
Uses & applications
Used as a gemstone and collected as a mineral; tourmaline varieties also have limited industrial use in pressure and temperature sensors.
Geological facts
Tourmaline is strongly pleochroic and can acquire electrical charge when heated or rubbed (pyroelectric and piezoelectric effects).
Field identification & locations
Look for elongated, often striated prismatic crystals and test hardness only on an inconspicuous area; brown dravite occurs in several metamorphic and pegmatite localities worldwide.
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Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
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Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Granite
Granite (Phaneritic intrusive igneous rock)
igneous
Septarian Pebble
Septarian nodule / Concretion
sedimentary