mineral
Likely tumbled black tourmaline (schorl)
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectDark gray to black, with a vitreous-to-dull luster; tourmaline has Mohs hardness 7–7.5 and a trigonal crystal structure. The rounded shape appears polished, and the image does not show enough detail to confirm identification.
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Physical properties
Dark gray to black, with a vitreous-to-dull luster; tourmaline has Mohs hardness 7–7.5 and a trigonal crystal structure. The rounded shape appears polished, and the image does not show enough detail to confirm identification.
Formation & geological history
Tourmaline commonly crystallizes in granitic pegmatites and metamorphic rocks as magma cools or fluids alter surrounding rock. Such deposits formed across many geological periods.
Uses & applications
Used as a jewelry and collector’s mineral; black tourmaline is also sold as decorative stone.
Geological facts
Schorl is the most common tourmaline species and is typically iron-rich.
Field identification & locations
A dark, elongated crystal with lengthwise striations is characteristic of schorl, but tumbling obscures these clues. Common sources include Brazil, Afghanistan, Pakistan, and parts of 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
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