exsolution

This term is a specialized geological and mineralogical descriptor. It describes a specific phase separation where a solid solution becomes unstable, causing one component to migrate and form separate layers or inclusions. It is distinct from general precipitation or crystallization from a melt, as it occurs entirely within a solid state.

In technical literature, the term is almost exclusively used to describe the internal textures of minerals, such as the perthitic textures found in alkali feldspars. Because it refers to a specific chemical process of separation, it is treated as an uncountable mass noun representing a phenomenon rather than a discrete event.