Midinfrared spectroscopy of synthetic olivines: Thermal emission, specular and diffuse reflectance, and attenuated total reflectance studies of forsterite to fayalite

Abstract

[1] Synthetic olivine samples ranging in composition from forsterite to fayalite are analyzed in the midinfrared using thermal emission, specular and diffuse reflectance, and attenuated total reflectance spectroscopies to study the spectral effects of Mg-Fe solid solution. For each method, fundamental bands gradually change in position and strength from Mg 2 SiO 4 at larger wave numbers to Fe 2 SiO 4 at smaller wave numbers. Each spectrum is diagnostic of chemistry within the continuum, as previously noted. In this study, 10 identified fundamental bands are traceable across the solid solution series for each technique. In pelletized sample spectra, the 10 bands shift approximately linearly in position by as little as 11 to as much as 64 cm −1 . In powdered sample spectra, the bands shift by as little as 12 to as much as 74 cm −1 (disregarding one outlier point). Moreover, for every spectral technique, an even larger linear shift is identified of a specific emissivity maximum/reflectivity minimum (the flection position). From forsterite to fayalite, this flection position shifts by at least 88 cm, which is, on average, 48% more than the largest fundamental band shift within the same data set for the pelletized spectra and 44% more for the powdered spectra. Also the R 2 and 2s values of the best fit line for the flection position shift (versus Fo # ) generally were as good as or routinely better than those of the fundamental bands. Thus, the flection position should be considered as a means of determining Mg-Fe olivine composition when using thermal emission, specular reflectance, diffuse reflectance, or attenuated total reflectance spectroscopic data.

Case study of chondrule alteration with IR spectroscopy in NWA 2086 CV3 meteorite

“…In the strongly altered zone (and also in the matrix) a new peak emerges around 958 cm À 1 (Fig. 5), in agreement with Lane et al (2011). 1000-1020 cm À 1 region has a broad height, which is present only in the case of low Fe and high Mg content; thus this is a good indicator of intact olivine in the analysed chondrule.…”

“…We aimed to analyze how far this alteration penetrated into the chondrule with infrared method. Lane et al (2011) and Hamilton (2010) investigated olivine according to Fo% (Fo¼ forsterite-Mg endmember of olivine) by FTIR spectroscopy. They observed that increasing Fe content decreases the wavenumber of IR-bands.…”

Visible to near-infrared optical properties of pure synthetic olivine across the olivine solid solution

“…Dyar et al (2009) incorporated various analytical spectroscopic techniques to characterize the properties and systematics of olivine with the high degree of fidelity afforded by the use of synthetic samples. Lane et al (2011) conducted a systematic survey of the group 1 subset of these samples (subset groups 1 and 2 are defined below) using various spectroscopic techniques at mid-infrared wavelengths. However, the full sample suite is not perfect, and minor levels of contamination and the presence of minor amounts of Fe 3+ (stoichiometric olivine would contain only Fe 2+ and Mg 2+ cations) affect the VNIR spectral properties of some samples significantly.…”

Microscopic emission and reflectance thermal infrared spectroscopy: instrumentation for quantitative in situ mineralogy of complex planetary surfaces

“…Furthermore the spectral range covered by the MCT detectors is often limited to ∼600 cm −1 , though they can measure to lower wavenumbers using special coatings but with reduced signal-to-single noise (SNR). These longer wavelengths (>20 μm) often provide valuable and diagnostic absorption features for primary mafic and secondary alteration mineralogy [45,46,51] and are important for mineralogical studies of planetary surfaces.…”

“…Furthermore, not every possible mineral has an easily accessible pure component that can be measured in the laboratory to make up a diverse and comprehensive endmember library (e.g., pigeonite). Further complicating matters, spectral features vary as solid solution series minerals vary in composition, so oftentimes a range of compositions is needed for individual minerals like olivine, where the major spectral absorptions move to either higher or lower wavelength as a function of forsterite number [e.g., 45,46].…”