Blue dravite (“indicolite”) from the Elahera gem field, Sri Lanka

A strongly dichroic (vivid blue to near-colourless) tourmaline specimen from the Elahera gem field, central Sri Lanka, was identified as dravite. The sample shows strong Fe2+-related optical absorption (E perpendicular to c) in the red range and comparably weak red emission due to Cr3+. The discovery of virtually Cu-free blue dravite (with a Li content of only about 3 ppm) shows that blue colour in gem tourmaline is not restricted to Cu- and/or Fe-bearing elbaite and other lithium tourmalines. Also, this study reconfirms the usefulness of Raman spectroscopy for non-destructive mineral identification. The sensitivity of Raman shifts of O-H stretching bands to their nearest-neighbour cations allowed us to exclude the presence of significant amounts of Li ions, even before obtaining results of light-element analysis. (C) 2021 Gem-A (The Gemmological Association of Great Britain)