Ratios of intensities of near-infrared spectral bands, measured in reflectance, quantitively predict the iron content of granitic rocks. Such data from the 1.60- and 1.05-μm bands of the shuttle multispectral infrared radiometer have been used to study granite rocks along orbits crossing Baja California, Mexico, and the Eastern Desert of Egypt. Both regions are arid and relatively to essentially free of vegetation, and there is no indication in the spectra that surface chemical alteration masks the true composition of the unweathered rock. Predicted values of iron are consistent with known compositional types of most of the rocks along the orbital paths. Results demonstrate that the near-infrared method used is a powerful technique to average the variability of these rocks on the scales of meters of kilometers.