Relation of the spectroscopic reflectance of olivine to mineral chemistry and some remote sensing implications

Abstract

Using high-resolution visible and near-infrared diffuse spectral reflectance, we have systematically investigated apparent wavelength shifts as a function of mineral chemistry in the Fe/Mg olivine series from Foil to Fo91. The study also shows that trace amounts of nickel can be spectrally detected in the olivine structure. We show that significant compositional information can only be extracted at relatively high resolution, because the overall spectral characteristics of the olivines change only subtly as a function of the Fe/Mg ratio. Significant spectral variation as a function of grain size is also demonstrated, adding a further complication to the interpretation of remotely sensed data from olivine-rich surfaces. This laboratory study is expected to aid in the interpretation of remotely sensed data from both terrestrial and extraterrestrial bodies. Terrestrial applications may include the recognition of ultramafic, ultrabasic, and basaltic terrains which in themselves may have mineral potential. Among extraterrestrial applications, the asteroids are obvious candidates for further examination if instrumentation can provide the necessary wavelength coverage, resolution, and signal-to-noise ratio so that spectra can be compared to those laboratory data discussed here. Some permutations of Fe-Mg-Ni relations in olivines are discussed as they apply to the interpretation of asteroid surfaces and other extraterrestrial bodies. CRYSTALLOGRAPHIC CONSIDERATIONS The olivine group of minerals is a closely related group of silicates with orthorhombic symmetry [Deer et al., 1982]. The structure of all the minerals of the group consist of independent SiO44-tetrahedra linked by divalent atoms in sixfold coordination. Silicon is not replaced by aluminum, the octahedral positions are almost exclusively filled by divalent ions, Paper number 7B4004. 0148-0227/87/007 B-4004 $05.00 and the trivalent ions Fe +3 and A1 +3 are either absent or present in only trace amounts [Deer et al., 1982]. The olivines studied in this investigation are members of the forsteritc (Mg2SiO4) fayalite (Fe2SiO4) solid solution series' therefore the octahedral positions are filled dominantly by Fe +2 and Mg +2 The ideal structure of forsterite, determined by Bragg and Brown [1926], is characterized by individual silicon-oxygen tetrahedra linked by magnesium atoms each with six nearestneighbor oxygens. The silicon-oxygen tetrahedra point in alternate directions in the X-Y plane, with one half of the octahedral voids filled by either Fe or Mg atoms and one eighth of the tetrahedral voids filled by Si atoms [Bragg and Brown, i•20]. I ne oiivines depart from ideal hexagonal ciosest packing and exhibit two distinct types of polyhedra, designated the M1 and M2 sites [Birle et al., 1968]. According to Deer et al. [1982], the M1 polyhedron is flattened along a threefold axis, whereas the M2 polyhedron is less regular and does not approximate any particular distortion model. However, according to Lumpkin and Ribbe [1983] and Princivalle and Secco [1985-1, the ...

Spectral and mineralogical characterization of inner main-belt V-type asteroids

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

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More chips off of Asteroid (4) Vesta: Characterization of eight Vestoids and their HED meteorite analogs

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