Silicate mass fraction (color) distribution in radius (y-axis) and time (x-axis). The evolution is shown for 5 M_⊕ (left), 10 M_⊕ (middle), and 20 M_⊕ (right). The x-axis has different ranges (1 Gyr, 5 Gyr, and 10 Gyr). The dotted black curves indicate Z = 0.98 and Z = 0.02 silicate mass fraction levels. The dashed red curve signifies the boundary between saturated and undersaturated regions, according to Eq. (9). A core-envelope boundary is approximately indicated by the Z = 0.98 curve. Because of the high temperatures at the core-envelope boundary, the (saturated) envelope is characterized by a silicate mass fraction of a few percent.