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Abstract:
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⊥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 tourma-lines. 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.
