Phase diagram (upper panel) and entropy excess (lower panel) for the exsolution process in a binary ONe mixture taken from Baiko (2023). Upper panel: the purple line is the solvus and the region below it is the miscibility gap. A solid solution with an initial Ne numerical abundance X_initial will begin exsolution at a temperature T_Exol determined by the solvus. By the time the temperature drops to the value T₁, the solid will be decomposed into two mixtures, one depleted in Ne, with a Ne abundance X_Ne = a₁, and the other enriched in Ne, with a Ne abundance X_Ne = b₁. By the time the temperature drops to the value T₂, the two solids will have respective abundances of a₂ and b₂. The exsolution process is completed at temperature T = 0, where the solid is separated into two components, pure O and pure Ne. Lower panel: excess entropy of exsolution as a function of Ne numerical abundance in a solid undergoing decomposition.