Black tourmaline is a complex borosilicate mineral with a high iron content, giving it its deep black color. It belongs to the tourmaline group, which forms in long, striated crystals and is commonly found in igneous and metamorphic rocks. This mineral is well known for its durability and distinctive crystal structure.
Features:
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Composition: Black tourmaline is a sodium iron aluminum boro-silicate with the general formula NaFe³⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄.
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Crystal Habit: Typically forms elongated, vertically striated prismatic crystals, often with a triangular or rounded cross-section. It exhibits no cleavage and breaks with an uneven to subconchoidal fracture.
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Formation: Occurs in granite pegmatites, high-temperature hydrothermal veins, and in metamorphic rocks such as schist and gneiss.
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Physical Properties: Strongly piezoelectric and pyroelectric, meaning it can generate an electrical charge when subjected to pressure or temperature changes—useful in scientific and industrial applications.
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Educational Value: Ideal for studying silicate mineral groups, crystal systems (hexagonal/trigonal), and mineral growth in igneous and metamorphic environments.
This specimen offers a durable and visually striking example of a common but scientifically significant rock-forming mineral.
