mineral
Polished black tourmaline (probable)
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectSmall rounded, polished black specimen with a vitreous-to-submetallic luster. Schorl has Mohs hardness 7–7.5, a trigonal crystal structure, and poor cleavage; the photo alone cannot confirm the identification or specific gravity.
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Physical properties
Small rounded, polished black specimen with a vitreous-to-submetallic luster. Schorl has Mohs hardness 7–7.5, a trigonal crystal structure, and poor cleavage; the photo alone cannot confirm the identification or specific gravity.
Formation & geological history
Tourmaline crystallizes in boron-rich granitic pegmatites and related rocks, commonly during late-stage magma cooling. Its age depends on the deposit and cannot be determined from the image.
Uses & applications
Tourmaline is used as a gemstone and mineral-collection specimen; black schorl is also sometimes sold as a polished bead or worry stone.
Geological facts
Schorl is the most common tourmaline species and often forms long, striated prismatic crystals before polishing.
Field identification & locations
A black color and polished surface fit schorl, but similar dark minerals can look alike; hardness testing or examination of crystal striations can help. Schorl occurs in pegmatites worldwide, including Brazil, the United States, and Europe.
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