Evaluation of IR Spectra of Mixtures of Natural Ca-Plagioclases and Olivines for Remote Determination of Composition

The features of the IR spectra (mid-IR range) for mixtures of the main minerals of lunar rocks—olivines and Ca-plagioclases (anorthites)—were studied, which complicate the possibility of remote determination of the composition. A comparison was made between numerical models constructed using the CUSTEP software module (Biovia Materials Studio software) and measurements of natural samples using IR spectra. For these purposes, a Fourier spectrometer FT-801 and the double-pass method (Simex, Novosibirsk) were used. Numerical calculations revealed characteristic absorption lines of pure minerals (end members of solid melts), which made it possible, in comparison with the spectra of natural samples, to determine the influence of chemical composition and impurities. IR transmission spectra of experimental mixtures of anorthite and olivine with different proportions made it possible to identify the most characteristic signs of the presence of olivines in Ca-plagioclase powder. Estimates have been made of the corresponding changes in the diffuse reflectance spectra, which are important for the interpretation of measurements by instruments being prepared for operation on planned lunar orbital stations.