Spectral analysis of synthetic quartzofeldspathic glasses using laboratory thermal infrared spectroscopy

Si-O-Si bond vibrations within silicate materials produce a prominent absorption feature in the 8-12 mu m region of thermal infrared (TIR) spectra. The wavelength position of this absorption varies with SiO2 content and may be used to determine rock composition. However, the presence of glass greatly affects the measurement of emitted and reflected TIR energy from the surface, a phenomenon which is not currently well understood. This study examines the TIR spectral characteristics of a suite of synthetic high-SiO2 quartzofeldspathic glasses that vary systematically in composition. Glasses were synthesized in the albite-quartz, oligoclase-quartz, and andesine-quartz systems. Microreflectance (similar to 1000 mu m(2)) and TIR emission spectra (bulk sample) were collected, and the spectral band maxima and minima were determined for each. Reflectance band maximum positions show a strong correlation with emissivity band minimum positions, indicating that the two types of spectra are comparable for this study. Excellent correlations are obtained between weight percent SiO2 and reflectance maxima position, emission minima position, and spectral shoulder position. Molar Al/[Al+Si] and [Na+Ca]/ Si are all well-correlated with reflectance maxima and shoulder positions but slightly less correlated with emission minima. Results of this study will contribute to a better understanding of spectral properties of quartzofeldspathic glasses and will provide a means to more accurately detect and map glassy surfaces (e. g., volcanoes and impact craters) remotely from the ground and from orbit.