Visible to Mid-Infrared Optical Constants of Orthopyroxenes

Abstract

Radiative transfer models of remotely acquired infrared spectra result in quantitative identification of minerals on planetary surfaces. Optical constants, or the real (n) and imaginary (k) indices of refraction are necessary inputs in such models. Pyroxenes are ubiquitous on the surfaces of terrestrial bodies within our solar system and can be readily used as thermo-barometers to interpret magmatic histories. However, optical constants for intermediate pyroxene compositions are undetermined. Here, we have determined the optical constants of two natural orthopyroxenes both in the visible/near-infrared (VNIR) and mid-infrared (MIR) regions. VNIR reflectance spectra were measured using powdered samples and modeled using a combination of Hapke theory and Kramers-Kronig analysis. MIR reflectance spectra were measured on oriented single crystal samples with non-normal incidence and modeled using Lorentz-Lorenz dispersion theory. The optical constants derived here are available to the scientific community at https://doi.org/10.5281/zenodo.4758045 to be used in the interpretation of remote sensing data.