Grain temperature as a function of distance from the star for a model with stellar parameters M = 1 M_⊙, L = 5000 L_⊙ and T_∗ = 2800 K during luminosity minimum. Top panel: the original temperature structure of the Mg₂SiO₄ grains (black) and the temperature structure when setting a minimum temperature of 800 K (red) and 500 K (blue). Lower panels: the original temperature structure of the Mg₂SiO₄ grains (black) and the temperature structure of dust particles with a core of Mg₂SiO₄ and a mantle of MgFeSiO₄ when it is thermally stable (T< 1000 K), as indicated by the vertical grey line. The green, red and blue lines show the temperature structure for a mantle size that is 1%, 5% and 10% of the grain radius, respectively.