mineral
Black tourmaline (schorl)
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectTypically black with a vitreous to slightly resinous luster and prominent lengthwise striations; trigonal crystals, Mohs hardness 7–7.5, no true cleavage, specific gravity about 3.0–3.3. The pictured specimen’s elongated, ridged form is consistent with schorl.
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Physical properties
Typically black with a vitreous to slightly resinous luster and prominent lengthwise striations; trigonal crystals, Mohs hardness 7–7.5, no true cleavage, specific gravity about 3.0–3.3. The pictured specimen’s elongated, ridged form is consistent with schorl.
Formation & geological history
Forms in boron-rich granitic pegmatites and some metamorphic rocks as magma cools; crystals may form during late stages of pegmatite growth, commonly in the Precambrian to younger crust.
Uses & applications
Used as a collectible mineral and, when attractive, as a gemstone; tourmaline’s electrical properties also support scientific and specialty applications.
Geological facts
Schorl is the most common tourmaline species; its strong longitudinal grooves are a useful identifying feature.
Field identification & locations
Look for opaque black, elongated prismatic crystals with parallel grooves, often associated with quartz and feldspar in pegmatites. Common localities include Brazil, Afghanistan, Pakistan, and the United States.
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Other mineral specimens
Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Tumbled granite
Granite, a coarse-grained felsic intrusive igneous rock
igneous
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