Mineralogy and geochemistry of four lunar soils by laser-Raman study

Laser Raman spectroscopy is used to investigate four lunar soils, focusing on mineralogy of grains of <45 μm size. Apollo samples 14163, 15271, 67511, and 71501 were selected as endmembers to study, based on their soil chemistry, maturity, and sample locations. Typical Raman spectral features for major and minor lunar minerals are discussed on the basis of major vibrational modes. We used the Raman peak shift to calculate Mg/(Mg + Fe + Ca) and Ca/(Mg + Fe + Ca) for pyroxene and Mg/(Mg + Fe) for olivine, and thus obtained the compositional distributions of these two minerals in each of the four lunar soils. Classification of feldspar grains was made based on recognition of their Raman patterns. A Raman point-counting procedure was applied to derive mineral modes of the soils, and these are found to be consistent with published modal analysis of these soils. The compositional distributions of pyroxene and olivine grains in each soil sample, as well as the mineral modes, reflect characteristics of the main source materials for these soils. Raman patterns and peak positions also reflect shock effects on plagioclase and quartz, found in 14163.