mineral
Black tourmaline (schorl) in host rock
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectTypically opaque black with vitreous luster and elongated, striated crystals; Mohs hardness 7–7.5. The image shows loose black fragments alongside pale, coarse host-rock pieces, consistent with tourmaline-bearing pegmatite, though the identification is visual.
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Physical properties
Typically opaque black with vitreous luster and elongated, striated crystals; Mohs hardness 7–7.5. The image shows loose black fragments alongside pale, coarse host-rock pieces, consistent with tourmaline-bearing pegmatite, though the identification is visual.
Formation & geological history
Schorl commonly crystallizes in boron-rich granitic pegmatites as magma cools; specimens may be hundreds of millions to billions of years old, depending on the deposit.
Uses & applications
Used as a mineral specimen and occasionally in jewelry; black, fractured pieces are more often collected than cut as gems.
Geological facts
Tourmaline crystals can become electrically charged by heating or pressure (pyroelectric and piezoelectric effects).
Field identification & locations
Look for hard, glassy black fragments and prismatic crystals with lengthwise grooves, commonly in light-colored quartz- and feldspar-rich pegmatite. Tourmaline-bearing pegmatites occur worldwide, including Brazil, Africa, and the United States.
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Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
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