Coordinated visible/near-infrared reflectance/mid-infrared
reflectance and emissivity spectra of four groups of phyllosilicates were undertaken to provide insights
into the differences within and among groups of smectites, kaolinite-serpentines, chlorites and micas.
Identification and characterization of phyllosilicates via remote sensing on Earth and Mars can be
acheived using the OH combination bands in the 2.2-2.5 mm region and the tetrahedral SiO4
vibrations from ~8.8-12 mm (~1140-830 cm-1) and ~20-25
mm (500-400 cm-1). The sharp
and well-resolved OH combination bands in the 2.2-2.5 mm region provide unique fingerprints for specific
minerals. Al-rich phyllosilicates exhibit OH combination bands near 2.2 mm, while these bands are
observed near 2.29-2.31, 2.33-2.34 mm and near 2.35-2.37 mm for Fe3+-rich, Mg-rich, and Fe
2+ phyllosilicates, respectively. When a tetrahedral substitution of Al or Fe3+ for Si
occurs, the position of the Si(Al,Fe)O4 bending mode near 500 cm-1 is split into
multiple bands that may be distinguished via octahedral cations, such that Al-rich, Fe-rich, and Mg-rich
phyllosilicates can be discriminated in reflectance and emissivity spectra based on diagnostic positions of
the stretching and bending bands. Differences among formation conditions for these four groups of phyllosilicates
are also discussed. Hyperspectral remote sensing can be used to identify specific phyllosilicates using
electronic and vibrational features and thus provide constraints on the chemistry and formation conditions
of soils.