A Raman spectroscopic tool to estimate chemical composition of natural volcanic glasses

A correlation between Raman spectra of silicate glasses and their chemical composition is investigatedusing a collection of 31 natural multicomponent silicate glasses. The sample suite comprises the largestdatabase of Raman spectra collected on natural volcanic materials and spans subalkaline to Na-rich and Krich alkaline compositions. Raman spectra were acquired using a Nd solid state green laser having anexcitation wavelength of 532 nm. The model was verified against an independent database of 8 additionalsamples (i.e. not used for calibration). Ratios of Raman peaks (R, Rn) retrieved from spectra are shown tohave a strong covariance with concentrations of six oxides (SiO2, TiO2, Al2O3, FeOT, MgO and CaO) acrossthe compositional range of the sample suite. The Raman ratios are also strongly correlated to pseudostructural parameters (e.g., NBO/T, SM) calculated from oxide concentrations of SiO2, TiO2, Al2O3, FeOT,MgO, CaO, Na2O and K2O. The Raman ratios are relatively insensitive to variations in Na2O andK2O contents and, as a consequence, their concentrations can only be estimated if additional independentconstraints on chemical content are available. This work constitutes the first generalized model forretrieving chemical compositions of natural glasses from corresponding Raman spectra. The modelprovides a rapid, robust and inexpensive way to retrieve compositions of volcanic glasses in bothlaboratory and field environments and thus represents a powerful new tool for earth and planetary,archaeological and glass sciences. A similar strategy can be applied to silicate melts and glasses usedin industrial activities.