Spectral properties of halite-rich mineral mixtures: Implications for middle infrared remote sensing of highly saline environments

Middle infrared reflectance of minerals is often used to qualitatively predict their spectral emittance characteristics. Reflectance spectra of particulate minerals dispersed in a nonabsorbing material such as halite (NaCl) can be very different from those of the isolated minerals, and often resemble transmittance spectra. To illustrate this behavior, diffuse reflectance spectra (4.3 μm – 14.3 μm) of particulate samples of calcite, gypsum, quartz and montmorillonite in various mixtures with NaCl are compared with reflectance and transmittance spectra of the pure minerals. Diffuse reflectance of a natural efflorescence associated with a sample of Mojave Desert playa material is also illustrated. Similarities in the spectra of the field sample and certain of the laboratory mixtures suggest that high concentrations of NaCl could produce ambiguities for remotely sensed observations in certain saline environments. However these preliminary laboratory measurements need supporting field studies to determine their significance in actual remote sensing situations.