Composition of silicate grains in the DARWIN models. Upper panel: Total value for a grain, with Fe/Mg taken from Table 1. Lower panel: Estimated value at the grain surface x_surf as given by Eq. (A.3), using condensation degrees f_Mg and f_Mg from Table 1 in Eq. (A.2) for (to account for the depletion of Fe and Mg in the gas phase in the growth rates). In both panels, red symbols mark models of series A and blue symbols models of series B (triangles and diamonds indicate pulsation amplitudes of 3 and 4 km/s, respectively); models of series M2 are shown as green circles.