Spectral reflectance 0.4 to 2.0 microns of silicate rock powders

Abstract

Silicate rocks in powdered form can be classified as belonging to the broad categories of rock glasses, crystalline acidic rocks, or crystalline basic-ultrabasic rocks, on the basis of spectral reflectance properties in the 0.4- to 2.0-μ wavelength region. Distinguishing characteristics are the ratio of reflected light at 0.7 μ to that at 0.4 μ, here termed R/B, the change in R/B with albedo, the maximum albedo of a rock powder, and the occurrence of broad absorption bands in the reflectance spectrums between 0.8 and 2.0 μ. Spectral reflectance properties depend strongly on particle opacity which, in turn, is controlled by chemical composition, mineralogy, and particle size; but reflectance also is affected in a regular way by particle packing, particle shape, and illumination geometry. The experimental results have potential application in determining gross compositional trends on planetary surfaces, but they also emphasize that many variables must be considered in any geologic interpretation of spectral reflectance data.