Spectral reflectance systematics for mixtures of powdered hypersthene, labradorite, and ilmenite

Spectral reflectance measurements in the range 0.4–2.5 μm were made for synthetic powder mixtures of a single suite of plagioclase, pyroxene, and ilmenite, which are the principal mineral phase types making up virtually all lunar surface materials studied to date. Binary and ternary data plots of the parameters albedo, band depth, and red to blue ratios versus mixture composition show how variation in the concentration of each mineral phase in a mixture affects changes in the overall reflectance spectrum of the mixture. Principal mixing effects noted are (1) the disproportionate darkening effect of opaque ilmenites and (2) the persistence, the wavelength stability, and the depth versus concentration proportionality of the 1μm band of pyroxene. These results indicate that by comparing the albedo and band depth of an unknown spectrum with calibration data obtained with laboratory standards one can determine the ratio of crystalline phases in the material producing the spectra such as may be obtained telescopically from small areas on lunar and planetary surfaces.