mineral

Tumbled brown tourmaline

Dravite–schorl tourmaline, complex borosilicate; approximate formula Na(Mg,Fe)₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Hardness 7–7.5 Mohs; brown to nearly black, vitreous luster, commonly elongated prismatic crystals with strong striations and poor cleavage. The polished surface and rounded shape indicate a tumbled or otherwise finished specimen.

Identified September 4, 2026More mineral →

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Physical properties

Formation & geological history

Tourmaline crystallizes in boron-rich hydrothermal veins, pegmatites, and metamorphic rocks during late magmatic or metamorphic activity; individual crystals may be millions to billions of years old. Brown varieties are commonly magnesium-rich dravite or iron-bearing schorl.

Uses & applications

Used as a collector mineral and occasional gemstone; tourmaline’s durability and attractive color support cabochons and beads, while its piezoelectric and pyroelectric properties have technical applications.

Geological facts

Tourmaline can become electrically charged when heated or compressed, attracting dust or small particles. Brown tourmaline is generally more common and less valuable than vivid green, blue, or watermelon varieties.

Field identification & locations

Identify it by its elongated shape, longitudinal striations, glassy luster, and hardness; it should scratch ordinary glass but not quartz. Common sources include Brazil, Namibia, Afghanistan, Sri Lanka, and the United States.