Optical properties of a silicate grain with a total radius of 0.35 μm, consisting of an Mg₂SiO₄ core and an MgFeSiO₄ mantle corresponding to 2% of the grain radius. Top panel: absorption efficiency (red dashed line), scattering efficiency (blue dash-triple-dotted line), and the resulting efficiency factor for radiative pressure (black line). Middle panel: relative difference of the absorption efficiency for the composite grain plotted in the top panel compared to a grain consisting entirely of Mg₂SiO₄. Bottom panel: same as the middle panel, but for the scattering efficiency (blue dash-triple-dotted line) and the efficiency factor for radiative pressure (black line). We note the different scales. The absorption efficiency of the Fe-enriched grain is almost 30 times higher around 1 μm (near the stellar flux maximum) than that of the Fe-free grain, leading to significantly stronger radiative heating. The radiative pressure efficiency factor, dominated by the almost unchanged scattering efficiency (weighted with the scattering angle; see Paper I), on the other hand, is only slightly higher for the Fe-bearing composite grain in this spectral region, explaining the moderate effect on the wind velocity.