Complex Investigation Data on Tourmaline from Granitic Pegmatites

The mineral samples analysed in this paper belong to the tourmaline group and were separated from granitic pegmatite specimens collected from the Contu-Negovanu area, in the Southern Carpathians (Romania). Tourmaline is a complex borosilicate of variable composition, including at least 12 recognized and hypothetical end-members of solid-solution series and a great number of varieties: schorl, dravite, elbaite etc. Our investigations on tourmaline samples concern X-ray powder diffraction and optical measurements, as well as chemical analysis, by means of EMPA and X-ray fluorescence techniques. The X-ray powder diffraction data (lambda = 0.1518 nm) enabled the identification of the precise tourmaline end-members as dravite-schorl, and to a lesser extent foitite and uvite. Unit-cell parameters were also calculated using a computer program for lattice parameter refinement. The main refractive indices have been interferometrically determined using the monochromatic yellow radiation of a Na lamp (lambda = 589.3 nm). The obtained data were plotted on a determinative chart, confirming the chemical composition of the investigated samples. The bulk chemical analyses display normal figures for the main oxydes, showing that the determined tourmaline compositions fall indeed within the dravite-schorl range, with lower amounts of foitite and uvite end-members.