Magnesium and aluminum borosilicate. The colour of the crystals varies from black (chlorite) to pink (rubellite), through brown, green (dravite) and light blue (elbaïte). This stone is found in magmatic and metamorphic rock: granite, quartz veins, mica shists, gneiss, etc.
Presently the richest deposits are located in Maine and California. The Elba tourmalines offer the greatest diversity of colours. In the Urals tourmaline is generally bright red, and, as such, it is called “the Siberian ruby”. In Brazil, tourmalines are green (“Brazil emeralds”) and in Madagascar they exhibit a yellow gold colour.