ABSTRACT

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.