Visible and near-InfraRed (VNIR) reflectance of silicate glasses: Characterization of a featureless spectrum and implications for planetary geology

Silicate glasses represent a major component in volcanic products, both in pyroclastic deposits and lavas. To date, their spectral characteristics are not thoroughly investigated in the context of their characterization as possible analogues of planetary surfaces, mainly due to their lack of spectral features. Nevertheless, featureless VIS-NIR spectra for which it is only possible to retrieve relative parameters (slope, albedo) are commonly observed on the surface of planetary bodies, and volcanic structures are supposed to be widely present in all terrestrial planets within the Solar System. Therefore, the correct interpretation of their geochemical signature is important in the attempt to shed new light on the evolution of these planets, and detailed knowledge about the spectral response of silicate glasses is fundamental for such a purpose. In this study, experimental petrology techniques have been used to produce 15 silicate glasses having complex chemical composition corresponding to three of the most common magmatic series on planet Earth. These glasses have been investigated in the Visible and Near/Infrared range to observe and interpret the variation of slope, albedo, and spectral ratio R1.55/R0.8 as a function of chemical composition. We found that, despite the complexity of factors influencing the spectral response, a good correlation can be derived linking spectral parameters with both iron content and composite Silicium-Calcium-Iron-Magnesium content (SCFM parameter). Results presented in this work might represent the baseline for new research lines focused on deciphering the significance of silicate glasses in the context of planetary exploration, opening new windows to access information on planetary differentiation that cannot be obtained using only existing materials and methods.