The earliest studies of minerals by reflected and emitted infrared radiation were those of Coblentz (1, 2). Since then mineralogical uses of reflected infrared radiation have been restricted primarily to studies of glass, and to minerals like quartz and cristobalite which play a prominent part in the understanding of glass structures. In a similar manner infrared emission studies have been restricted almost exclusively to ceramics and refractories. This paper deals with the reflected infrared analysis of several common minerals, rocks, and meteoritic materials. The optical principles involved, and the typical spectra to be obtained from quartz plates, fused silica, and glasses are briefly reviewed and recent spectral data from minerals and rocks are examined. Similarities and differences between absorption and reflection spectra for the same materials are discussed, and some of the problems encountered in the calculations of composition (modal analysis) are indicated.Applications to nondestructive testing of polished rock surfaces (or gems) and to the calculation of ambient-temperature emissivity curves for rocks are shown. Such spectral emissivity curves are an important prerequisite for the remote mapping of the lunar and other planetary surfaces.