mineral
Black tourmaline (schorl) in matrix
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectOpaque black, vitreous to resinous luster; Mohs hardness 7–7.5, trigonal crystal structure, and poor cleavage with uneven fracture. The rusty-brown areas appear to be iron-oxide staining; the pale grains may be quartz or feldspar.
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Physical properties
Opaque black, vitreous to resinous luster; Mohs hardness 7–7.5, trigonal crystal structure, and poor cleavage with uneven fracture. The rusty-brown areas appear to be iron-oxide staining; the pale grains may be quartz or feldspar.
Formation & geological history
Schorl typically crystallizes in boron-rich granitic pegmatites and hydrothermal veins as magma cools; such deposits range widely in age. The specimen’s exact age and matrix cannot be established from the photo.
Uses & applications
Used as a collectible mineral and occasionally in jewelry; tourmaline also has specialized piezoelectric and pyroelectric applications.
Geological facts
Schorl is the most common tourmaline species and is strongly pleochroic in suitable crystals.
Field identification & locations
Look for black, elongated, striated crystals with a triangular cross-section, commonly in pegmatites with quartz and feldspar. Common localities include Brazil, Afghanistan, Pakistan, and the United States.
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