Schorl (Black Tourmaline)
Image: Photographer: Henk Caspers/Naturalis (CC BY-SA 3.0)
Mineral NameSchorl (Black Tourmaline)
Chemical FormulaNa(Fe²⁺)₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH)
Mohs Hardness7
Crystal Systemtrigonal
Lustervitreous
Streak Colorwhite
Cleavageindistinct to none
Fractureconchoidal
Specific Gravity3.1
Colorsblack, dark brown
Transparencyopaque
Type LocalityBrazil, Pakistan, Afghanistan, USA, Namibia, Madagascar
Mineral GroupSilicates
Usescollector's specimens, gemstone (cabochons), industrial
Associated Mineralsquartz, feldspar, mica, beryl, garnet
Raritycommon
Description
A large, dark, typically black, prismatic mineral specimen, often showing vertical striations on crystal faces, commonly found in museum displays.
Geological Context
Schorl is a common accessory mineral in granitic pegmatites, high-temperature hydrothermal veins, and some metamorphic rocks like schists and gneisses, forming from boron-rich fluids.
