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**Chemical composition:** (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
**Info:** Tourmaline is classified as a semi-precious stone and comes in a wide variety of colours, e.g. brownish black to black (schorl), dark yellow to brownish black (dravite), red or pinkish-red (rubellite), light blue to bluish green (indicolite) or green (verdelite). Tourmalines are found in igneous, metamorphic, hydrothermal veins and pegmatites. They are an important source of boron and lithiumin.
## Keywords
mineral Tourmaline texture color ornamental stone semi-precious gemstone