Near-infrared spectral reflectance of mineral mixtures: Systematic combinations of pyroxenes, olivine, and iron oxides

Near-infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals. Mixtures were chosen for application to the study of the dark materials on Mars, but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system. Olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents. Clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 μm. The addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics. Using only spectral data in the 1-μm region, it is difficult to differentiate orthopyroxene and limonite (goethite) in a mixture. Additional spectral coverage or other evidence may be required for a unique interpretation. All composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end-member absorptions and have bandwidths greater than or equal to those for the end-members. In general, spectral properties in an intimate mixture combine in a complex, nonadditive manner, with features demonstrating a regular but usually nonlinear variation as a function of end-member phase proportions.