mineral
Black tourmaline (schorl)
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectBlack, opaque to translucent at thin edges, with a vitreous luster and typically striated, prismatic crystals; Mohs hardness 7–7.5, trigonal crystal system, poor cleavage, specific gravity about 3.0–3.3. The image is consistent with schorl, though identification from appearance alone is not definitive.
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Physical properties
Black, opaque to translucent at thin edges, with a vitreous luster and typically striated, prismatic crystals; Mohs hardness 7–7.5, trigonal crystal system, poor cleavage, specific gravity about 3.0–3.3. The image is consistent with schorl, though identification from appearance alone is not definitive.
Formation & geological history
Forms in boron-rich granitic pegmatites and some metamorphic rocks as magma or fluids cool; deposits span many geological ages.
Uses & applications
Used as a mineral specimen and occasionally in jewelry; tourmaline varieties are also valued as gemstones. Schorl is generally too opaque for faceted gems.
Geological facts
Tourmaline crystals can develop electric charge when heated or pressed (pyroelectricity and piezoelectricity).
Field identification & locations
Look for a dark, hard crystal with lengthwise grooves; common sources include Brazil, Afghanistan, Pakistan, and the United States. Confirm with crystal form and hardness rather than color alone.
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Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
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Tumbled granite
Granite, a coarse-grained felsic intrusive igneous rock
igneous
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Granite
Granite (Phaneritic intrusive igneous rock)
igneous