Quantitative Analysis Of Bulk Composition Of Small-Size Lunar Samples Using Energy Dispersive X-Ray Spectroscopy

Abstract

: The major element composition analysis of lunar mare basalt bulk rock is crucial for understanding the thermochemical evolution of the lunar interior. However, lunar regolith and soils returned by the Apollo and Chang’E-5 missions have small particle sizes (mostly < 3 mm), making quantitative analyses of the bulk rock composition difficult. Herein, we developed a non-destructive technique to determine the bulk composition (comprising SiO 2 , TiO 2 , Al 2 O 3 , FeO, MnO, MgO, CaO, Na 2 O, and K 2 O) of rare lunar samples with a small size using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS) mapping techniques. In this study, a set of certified reference materials were used to calibrate the spectrometer; the precision and accuracy of the EDS analyses were verified using silicate glass and mineral reference materials. Measurements performed on a lunar meteorite sample with a known composition, NWA 4734, confirmed the reliability of the mapping method. The EDS data for the standard glasses and minerals were consistent with the reference values, within the error limits. A small fragment of NWA 4734 was measured using EDS mapping, and the bulk composition obtained was comparable to that measured using inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectrometry. Our method is standardized and minimizes the acquisition time compared to other quantitative mapping methods. The non-destructive and quantitative analysis method used in this study can support research on the bulk compositions of Chang’E-5 lunar samples and can be applied to research on both terrestrial and extraterrestrial samples at the micron- to centimeter-scale.