Tourmaline
Image: Robert M. Lavinsky (CC BY-SA 3.0)
Mineral NameTourmaline
Chemical Formula(Na,Ca)(Li,Mg,Fe,Mn,Al)3Al6(BO3)3Si6O18(OH)4
Mohs Hardness7
Crystal Systemtrigonal
Lustervitreous
Streak Colorwhite
Cleavageindistinct/poor basal
Fractureuneven to conchoidal
Specific Gravity3.06
Colorsblack, dark green, dark blue
Transparencytranslucent
Type LocalityMomeik, Mogok, Sagaing District, Mandalay Division, Burma (Myanmar)
Mineral GroupSilicates
Usesjewelry, collector specimens, industrial (minor)
Associated Mineralsquartz, feldspar, mica, beryl, spodumene
Raritycommon
Description
The image shows a dark, likely black or very dark green, prismatic tourmaline crystal with characteristic vertical striations along its length. The crystal appears opaque to translucent and has a natural, somewhat rough termination.
Geological Context
Tourmaline is commonly found in granite pegmatites, metamorphic rocks like schists and gneisses, and hydrothermal veins. It forms from boron-rich fluids during the late stages of igneous crystallization or during regional metamorphism.
