Infrared spectroscopy of hydrous glasses of arc magma compositions

Molar absorption coefficients of water in glasses of arc magma compositions have been determined for -2.8 μm, -2.2 μm, and -1.9 μm bands. Excellent agreement was found between the water contents calculated from the absorption peak heights and those determined by H₂ manometry when the following molar absorption coefficients (m³/mol m) are used for different glass compositions: ε_2.8μm = 6.4 ± 0.1, ε_2.2μm = 0.085 ± 0.007, and ε_1.9μm = 0.084 ± 0.006 for tholeiite and high-Al basalt glasses; ε_2.8μm = 6.8 ± 0.1. ε_2.2μm = 0.094 ± 0.006, and ε_1.9μm = 0.16 ± 0.03 for dacite glass. With IR spectroscopy using these coefficients, water concentrations up to -3 wt.% in the arc basalt and dacite glasses can be determined accurately.