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**Chemical formula:** (Ca,K,Na)(Al,Fe,Li,Mg,Mn)₃(Al,Cr, Fe,V)₆(BO₃)₃(Si,Al,B)₆O₁₈(OH,F)₄ **Hardness:** 7‒7.5 **Density:** 2.9‒3.2 g/cm³ **Crystal symmetry:** Trigonal **Luster:** Glassy **Description:** Tourmaline is a semi-precious stone that occurs in a wide range of colors, including brownish black to black (schorl), dark yellow to brownish black (dravite), red or pinkish-red (rubellite), light blue to bluish-green (indicolite) and green (verdelite). Tourmalines are commonly found in igneous and metamorphic rocks, hydrothermal veins and pegmatites. They are a significant source of boron and lithium. ## Keywords mineral Tourmaline texture color ornamental stone semi-precious gemstone
