Laboratory spectral reflectance of mafic silicates has been measured over a temperature range characteristic of solar system objects to study the variation of diagnostic mineral absorption bands. This information has become increasingly important with recent improvements in the quality of remotely sensed planetary data and the concurrent increase in sophistication of quantitative and qualitative spectrum analysis techniques.

In this study, visible and near-IR reflectance spectra (0.4--2.5 μm) of pyroxenes and olivine were obtained over a sample temperature range of 80--448 K. These are the first published reflectance data for these mineral at temperatures significantly below ambient (≈300 K). Additionally, thermal radiation emitted from the samples at elevated temperatures was effectively removed, disclosing for the first time the high-temperature reflectance behavior of pyroxenes in the diagnostic 2-μm spectral region. As expected from basic physical considerations, Fe2+ crystal field absorptions in all samples become narrower with decreasing temperature.

The three components of the composite olivine band centered near 1 μm become better resolved with decreased temperature and show changes in relative absorption strength. There is not, however, any significant wavelength shift of the olivine reflectance minimum. Both orthopyroxene and clinopyroxene spectra show dramatic changes in band symmetry with temperature, with the greatest change in the longer-wavelength edge. Despite these significant changes in shape, little if any change is observed in the wavelength position of reflectance minima of pyroxene absorptions near 1 μm. The ''2-μm'' pyroxene absorptions, in contrast, demonstrate major shifts of reflectance minima but in different directions. In orthopyroxene spectra the band shifts to longer wavelengths with increased temperature, while for the clinopyroxene spectra the band shifts to shorter wavelengths. This behavior results in greatly improved spectral differentiation of orthopyroxene and clinopyroxene components in a mixture (such as a basalt) at reduced temperatures. Application of the results presented here to remote-sensing mineral characterization techniques currently in use for determination of pyroxene composition can provide a moderate improvement to quantitative interpretations: from 5 to 20 wt % FeO for orthopyroxene and ¿5 wt % CaO for clinopyroxenes depending on planetary surface temperature.