mineral
Black tourmaline (schorl)
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectTypically black to dark brown with a vitreous to slightly dull luster and prominent lengthwise striations; Mohs hardness 7–7.5. Trigonal crystals commonly form stout prisms; cleavage is poor or indistinct, and specific gravity is about 3.2.
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Physical properties
Typically black to dark brown with a vitreous to slightly dull luster and prominent lengthwise striations; Mohs hardness 7–7.5. Trigonal crystals commonly form stout prisms; cleavage is poor or indistinct, and specific gravity is about 3.2.
Formation & geological history
Forms in boron-rich granitic pegmatites and some metamorphic rocks as magma cools and fluids crystallize; specimens may range from ancient to geologically recent depending on the deposit.
Uses & applications
Used as a collector mineral and occasionally as a black gemstone; tourmaline is also studied for its electrical properties, but schorl has limited industrial use.
Geological facts
Schorl is the most common tourmaline species and is distinguished by strong, parallel striations along its crystal faces.
Field identification & locations
Look for opaque black, striated prismatic crystals, often associated with quartz and feldspar in pegmatites. Common sources include Brazil, Afghanistan, Pakistan, and the United States; the image’s rough specimen cannot be precisely localized.
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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
Unidentified pink-and-gray mineral or rock specimen
Undetermined; the image is too blurry for reliable identification
mineral