We explore several issues relevant to assessments of solar and infrared radiative effects due to mineral aerosols. One issue is the importance of the vertical distribution of dust for calculations of dust radiative heating rates. Another issue is the role that clouds may play in augmenting the radiative forcing by dust. We also explore the importance of the composition of mineral aerosols by employing spectral optical properties for dust that comes from two different regions of the globe, the Saharan and Afghan deserts. A combined longwave and shortwave radiative transfer model was used to determine the instantaneous radiative forcing in the atmosphere, radiative fluxes at the surface, and radiative heating rates by airborne mineral aerosols for clear-sky and cloudy atmospheric conditions. Extensive calculations with our model show that increasing dust loading results in increasing both solar heating rates and infrared cooling rates. However, the net instantaneous rates during the day are always positive, yielding net radiative heating of the dust layer. With similar atmospheric conditions and dust loading, Saharan dust causes larger heating rates than Afghan dust. The magnitudes of the Saharan dust heating rates can easily be 25% larger than Afghan dust heating rates at high Sun angles and over bright surfaces. Also, Saharan dust yields more positive values of TOA (top of the atmosphere) radiative forcing than Afghan dust; and for a diurnal average, this can lead to a change of sign of the TOA radiative forcing from negative to positive just due to mineralogical composition. Clouds significantly influence the direct radiative impact of dust depending on cloud altitude and optical depth. Moreover, this influence is strongly dependent on Sun position and surface albedo. ¿ 2000 American Geophysical Union