FTIR 2-16 micron spectroscopy of micron-sized olivines from primitive meteorites

Infrared spectra of mineral grains from primitive meteorites could be useful for comparison with astronomical infrared spectra since some of their grains might be similar to those formed in the planet-forming disks around young stars or in the envelopes surrounding late-type stars. To assess the usefulness of meteorite spectra, olivine grains separated from primitive meteorites have been analyzed using FTIR microscope techniques in the 2-16 mu m wavelength range. The sub-micron sizes of the grains made a complex preparation process necessary. Five characteristic bands were measured near 11.9, 11.2, 10.4, 10.1, and 10.0 mu m. The results of 59 analyses allow the calculation of band positions for meteoritic olivines as a function of their iron and magnesium contents. Comparison of the meteoritic results with astronomical data for comets and dust around young and old stars, which exhibit bands similar to the strongest infrared bands observed in the grains (at 11.2 mu m), show that the spectral resolution of the astronomical observations is too low to ascertain the exact iron and magnesium (Mg:Fe) ratio of the dust in the 8-13 mu m wavelength range.