Reflectance spectroscopy in the visible to near-infrared (VNIR, 350–2500 nm) of Martian meteorite slabs and powders: Mafic silicate compositions and abundances

This study investigated the spectral reflectance properties (350–2500 nm) of a suite of 14 different martian meteorites, as rough, saw-cut slabs and powders, derived from the spectrally-characterized slabs; saw-cut powders (<5 μm) were also available for three of the samples. Various spectral metrics, including wavelength positions of the major mafic silicate absorption bands in the 1000 and 2000 nm regions (Band I and Band II), intensity of the bands (band areas), and spectral slopes were determined for the spectra. We found that band centers and band area ratio could be used to determine the presence, and constrain the abundance, of dominant mafic silicates (low-calcium pyroxene, pigeonite, high-calcium pyroxene, and olivine). These identifications were supplemented by the presence of absorption bands in the visible spectral region attributable to these minerals, as well as an Fe 3+ -Fe 2+ absorption band that is present in nakhlite spectra and reflects their unique Fe oxidation state. The spectrally-determined mafic mineralogies were generally consistent with independently-determined mineralogy. Slab spectra are always more blue-sloped (reflectance decreasing toward longer wavelengths) than their powder spectra, but absolute reflectance and absorption band depths are not always different between slabs and powders. High-versus low-shock powdered sample spectra did not reveal any systematic spectral differences for shergottites. Spectroscopic studies of martian meteorites can be useful in the interpretation of Mars observational data, identifying possible source regions for martian meteorites, and informing the collection of samples for return to Earth that represent different lithologies.