Reflectivity of natural and powdered minerals at CO_2 laser wavelengths

The diffuse reflectance and depolarization properties of natural and powdered minerals were examined at 128 CO2 laser wavelengths. Powder reflectivity was classified into three regimes: (1) surface (reststrahlen); (2) low intermediate; and (3) bulk (Kubelka-Munk) remission from subsurface grains. Data are presented on NaCl, Al2O3, MgO, BaCO3, CaCO3, BaSO4, feldspar (NaAlSi3O8), and apatite [Ca5F(PO4)3]. Reduction of feldspar rocks to 210-μm grain size had little effect on their reflectance spectra. Kubelka-Munk-type behavior seems unlikely to dominate the reflectance spectra of natural surfaces. Albedos were measured for NaCl, sulfur, gold-plated sandpaper, graphite, and sandblasted aluminum.