Thermal infrared emission spectroscopy of the pyroxene mineral series

The thermal infrared emissivity spectra of coarse particulate samples of co mpositions in the pyroxene series display reststrahlen features (absorption s) that distinguish not only orthorhombic from monoclinic structures, but a lso major end-members within the two structural groups, as well as minerals within solid solution series. The exact number of reststrahlen features ob served and their positions are dependent on mineral structure and cation oc cupancy of the M1 and M2 sites. End-member quadrilateral pyroxenes (Mg2Si2O 6-Fe2Si2O6-Ca[Mg,Fe]Si2O6) are easily distinguished from each other and fro m minerals in the nonquadrilateral series (NaFeSi2O6-Na[Al,Fe]Si2O6-LiAlSi2 O6). Furthermore, among quadrilateral pyroxenes, variations in Mg/(Mg + Fe) are linearly correlated with several band locations, as are variations in Ca content in high-Ca clinopyroxenes. In both quadrilateral and nonquadrila teral compositions, Christiansen feature positions are also diagnostic. No correlations with minor constituents (of the order of 0.05 atoms per formul a unit) were observed. The detailed spectral characteristics of pyroxenes a nd their variability as a function of structure and cation occupancy are pr esented here with determinative curves for the identification of pyroxene c omposition. These data have important implications for the interpretation o f spectral data from both laboratory and remote sensing instruments because they should permit a more detailed determination of pyroxene composition i n measured unknown pure mineral and bulk compositions dominated by surface scattering, i.e., all particulates greater than similar to 65 mu m, and sol id samples.