mineral
Black tourmaline bead bracelet, possibly mixed with smoky quartz or brown tourmaline
Schorl tourmaline, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄; exact beads cannot be confirmed visually
AI-generated identification · may be incorrectOpaque black to brown, vitreous to resinous luster, typically Mohs 7–7.5, trigonal crystal structure, and poor-to-indistinct cleavage. The polished spherical beads show reflective internal surfaces and occasional brown zoning.
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Physical properties
Opaque black to brown, vitreous to resinous luster, typically Mohs 7–7.5, trigonal crystal structure, and poor-to-indistinct cleavage. The polished spherical beads show reflective internal surfaces and occasional brown zoning.
Formation & geological history
Tourmaline forms mainly in granitic pegmatites and metamorphic rocks, crystallizing from boron-rich fluids during late-stage igneous activity; specimens range from Precambrian to recent geological settings. Brown beads could instead be smoky quartz (SiO₂), Mohs 7.
Uses & applications
Used as ornamental beads, jewelry, and collector material; tourmaline is also valued for its piezoelectric and pyroelectric properties. Common polished bracelets generally have modest commercial value.
Geological facts
Schorl is the most common tourmaline species and often appears nearly opaque black. Rubbing or heating tourmaline can produce electrical charge, attracting light fibers or dust.
Field identification & locations
Common sources include Brazil, Afghanistan, Pakistan, Madagascar, Namibia, and the United States. Identify tourmaline by its strong polish, hardness, and—on rough material—striated prismatic crystals; a gemological test is needed to distinguish it from black onyx, obsidian, or glass.
