Tourmaline

**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