EMERALD CHARACTERIZATION BY RAMAN SPECTROSCOPY AND ITS APPLICATION FOR PROVENANCE
Preliminary results of Raman spectra obtained parallel and perpendicular to the c axis for 46 natural emerald and other beryl varieties from 19 localities are presented. The Raman shift between 150 and 2500 cm-1 of each crystal was characterized, and vibrations for Si-O, Be-O, Al-O, and the CO2 Fermi doublet were identified based on previous studies. At higher frequencies (3300-3900 cm-1) two major peaks exist at 3593 cm-1 ± 3 cm-1 and 3605 cm-1 ± 3cm-1. The first peak at 3593 cm-1 is attributed to type-II water, whereas that at 3605 cm-1 corresponds to type-I water. The water region in the spectra of Colombian emeralds and those from Nigeria, Australia, Brazil, China, South Africa, and Russia is similar in that they are bimodal, showing the presence of the two peaks at 3593 cm-1 and 3605 cm-1. In emeralds from these localities the intensity of the 3605 cm-1 Raman shift is the highest of the two, showing the dominance of type-I water. Non-emerald beryl varieties have a bimodal peak, but this feature is more prevalent when the crystal is oriented parallel to the c axis. Preliminary data show that Raman spectroscopy is powerful to characterize beryl varieties and to determine provenance for major gem-quality emerald deposits.