Characterization of water in synthetic rhyolitic glasses and natural melt inclusions by Raman spectroscopy

Raman spectroscopy was used to analyze quantitatively water in silicate glasses and melt inclusions and to monitor H2O–OH speciation. Calibration is based on synthetic glasses with various water contents (0.02–7.67% H2O); water determination and OH–H2O differentiation on the area of the Si–O broad band at 468 cm–1 and the asymmetric O–H band at 3,550 cm–1. Each Raman spectrum has been decomposed into four Gaussian + Lorentzian components centered at 3,330, 3,458, 3,560, and 3,626 cm–1 using the Levenberg–Marquardt algorithm. These components are interpreted to be two different types of H2O molecule sites. The influence of the temperature on the loss of water is more important for molecular water than for the hydroxyl groups. The H2O–OH partition confirms the typical evolution of water speciation in rhyolitic glasses as a function of the bulk water content. Method limitations have been studied for the application to natural melt inclusions.