Reflectance spectra of mafic silicate-opaque assemblages with applications to meteorite spectra

Abstract

The reflectance spectra of wüstite and mixtures of mafic silicates plus carbon or magnetite can be used to interpret meteorite and asteroid spectra. Mafic silicate + magnetite spectra show many features characteristics of magnetite-bearing meteorites— an overall decline or constant reflectance and lown overall reflectance. Mafic silicate + amorphous carbon spectra show low overall reflectance and a red slope unlike that seen in CV and CO carbonaceous chondrite spectra, probably because the meteoritic carbon is in a more ordered form. The reflectance spectra of ureilites are largely consistent with an assemblage of mafic silicates and abundant carbon. Ordinary chondrite reflectance spectra cannot be reproduced by any of the laboratory mixture spectra. The reflectance spectrum of wüstite is a reasonable match to the spectrum of ordinary chondrite metal, suggesting that most ordinary chondrite metal grains are probably coated with an optically thick layer of an oxide. Ordinary chondrite and mafic silicate reflectance spectra are consistently less red-sloped than S-class asteroid spectra. The various spectral criteria use to deco0nvolve mafic silicate spectra are also applicable to CV and CO carbonaceous chondrites, ureilites, and ordinary chondrites, because the opaque phases present in these meteorites are spectrally neutral.