Elongated prism of ditrigonal section, terminated by a rhombohedron; the prismatic faces are vertically striated.

Transparent to translucent in all colours: pink, red, green, blue, black, sometimes bicoloured. Intense pleochroism.

Tourmaline is found in veins of granitic rocks, in gneisses and pegmatites.

The chemical composition of tourmaline is variable. The atoms of Fe, Mg, Li and Al are interchangeable. This explains the great diversity of colours that tourmaline can take. The name « Paraïba » is reserved for a turquoise-blue tourmaline from the Province of the same name in Brazil.