Natural Black Tourmaline — Rough

Black Tourmaline, known mineralogically as Schorlite, is a complex boron silicate with the chemical formula NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄. It is the most abundant variety of the tourmaline group and forms predominantly in granitic pegmatites, hydrothermal veins and boron-rich metamorphic rocks. Its black to brownish-black color results from the high concentration of iron (Fe²⁺ and Fe³⁺) in its crystalline structure. The characteristic opacity is a direct consequence of this high concentration of iron ions, which absorb practically all visible light. Hardness: 7 to 7.5 on the Mohs scale. Density: 3.1 to 3.2 g/cm³. Crystalline system: trigonal. Available variations, approximate data: 1 to 3 cm — up to 0.010 kg — 40 pieces per kg 3 to 6 cm — 0.030 to 0.150 kg — 30 pieces per kg 6 to 15 cm — 0.150 to 0.800 kg — 2 to 3 pieces per kg