Determining the composition of olivine from reflectance spectroscopy

Abstract

Abstract. Reflectance spectra of olivines spanning the forsterite-fayalite solid-solution series have been analyzed with the modified Gaussian model (MGM). The compositional variability of the three primary absorption bands that constitute the diagnostic 1.0-gm olivine feature has been quantified by examining the centers, widths, and relative strengths in 18 spectra ranging in composition from Mg-rich forsterite to Fe-rich fayalite. These analyses have also revealed several interrelationships among the three absorption bands that prpvide new insights into their crystallographic origins. The primary olivine absorptions near 1.0-gin are well behaved and provide a means to remotely identify and estimate the composition of olivine from reflectance spectra. However, the spectral resolution and signal-to-noise of current remotely acquired data, combined with the significant overlap in the 1.0-gm region, provide enough uncertainty to allow models based on simple least squares minimization to reach solutions that are mathematically satisfying yet physically unrealistic. More sophisticated models using inverse theory that incorporate constraints among the absorption bands as determined from these laboratory MGM analysis are shown to yield meaningful results which can be confidently used to estimate composition in remote data. The MGM and inverse theory are used to analyze the spectrum of the olivine-rich asteroid 246 Asporina and to quantitatively show that the olivine component on Asporina is magnesium-rich (i.e., forsteritic). In contrast to the systematic behavior of the three primary olivine absorptions, absorption features short of 0.7 gm are found to exhibit no obvious relationship to composition and as such are not recommended for use in remote applications.

The stratigraphy and history of Mars' northern lowlands through mineralogy of impact craters: A comprehensive survey

“…Olivines ((Mg, Fe) 2 SiO 4 ) have a broad absorption centered at 1 μm that varies according to Fe content ( Figure 4a) [Burns, 1970]; Sunshine and Pieters, 1998]. Pyroxenes ((Ca, Fe, Mg) 2 Si 2 O 6 ) are identified by two broad absorptions around 1 and 2 μm, where the band centers shift to longer wavelengths with increasing calcium and iron content ( Figure 8) [Hazen et al, 1978;Klima et al, 2007;Klima et al, 2011].…”

A coordinated spectral, mineralogical, and compositional study of ordinary chondrites

“…The composite 1 lm band, which is attributed to electronic transitions of Fe 2+ occupying both the M1 and M2 crystallographic sites (Burns, 1970), moves to longer wavelengths as FeO content increases (King and Ridle, 1987;Sunshine and Pieters, 1998).…”

Science Applications of a Multispectral Microscopic Imager for the Astrobiological Exploration of Mars

“…exhibit an absorption between 1.03 and 1.05 lm, while Ferich endmembers (i.e., fayalite) exhibit an absorption between 1.05 and 1.08 lm (Sunshine and Pieters, 1998;Isaacson and Pieters, 2010).…”

“…The difference between the two endmember spectra may be attributed to grain size effects (e.g., Hapke, 1993;Clark, 1999), which affect the overall reflectance and depth of absorptions. Since the exact position and width of the 1.05 lm absorption in olivine depends on the Mg/Fe ratio (Burns, 1970;King and Ridley, 1987;Sunshine and Pieters, 1998;Isaacson and Pieters, 2010), the shift and width can be used to further distinguish between Fe-rich and Mg-rich olivine. Within the MMI channels, Fe-rich olivine (fayalite) exhibits a broader-shaped absorption at 1.05 lm compared to Mg-rich olivine (forsterite) (see Figs.…”