Variations in the Near-Infrared Spectral Properties of Ferrous Mineral Mixtures With Different Relative Abundances

Abstract

In near-infrared spectral studies, the relationship between the 1-μm absorption (Band I) center and the band area ratio (BAR, the area ratio of 2–1-μm absorption features) is useful in compositional and mineralogical analyses of ferrous mineral-bearing mixtures. Zhang and Cloutis (2020), https://doi.org/10.1029/2020ea001153, investigated various lunar ferrous iron-bearing rocks and minerals and found that pyroxene-bearing materials rich in ilmenite (Ilm), plagioclase (Pl), or glass are offset from the lunar olivine-clinopyroxene-orthopyroxene (Ol-Cpx-Opx) mixing line in the plot of the BAR versus the Band I center. To analyze the variation trends of the spectral properties of these mixtures with different components, this study presents a systematic evaluation of laboratory spectra of terrestrial and synthetic ferrous iron-bearing mineral mixtures based on published databases. In general, the mixing trends of the Pl-pyroxene mixtures, the glass-pyroxene mixtures, and the Ilm-basalt mixtures are consistent with the findings of Zhang and Cloutis (2020), https://doi.org/10.1029/2020ea001153. Moreover, this study also finds that the BAR of the Pl-pyroxene mixtures varies nonlinearly with different relative abundances and that the BAR is generally not sensitive to Pl abundances below 60%. For glass-pyroxene mixtures, the corresponding data points are usually appreciably offset from the Ol-Cpx-Opx mixing line at glass abundances above 20%. The BAR of the Ilm-basalt mixtures increases with increasing Ilm content, mainly due to the weakening of 1-μm absorption generally being greater than that of 2-μm absorption.