exsolve

Exsolve is a term used in geology and materials science to describe the process by which a homogeneous solid solution becomes unstable and separates into two or more distinct phases. This separation typically occurs upon cooling or changes in composition that move the system across a solvus boundary, causing components to exsolve from a single phase into discrete, intimately mixed phases.

Mechanisms and textures associated with exsolution include nucleation and growth or spinodal decomposition. The resulting microstructures often take the form of lamellae or intergrowths, where the exsolved phases occupy alternating domains within a crystal. These textures can be aligned along crystallographic directions and are commonly revealed by microscopy, often requiring polarized light, scanning or transmission electron microscopy, or diffraction techniques for confirmation.

Exsolution is particularly significant in minerals and metallic systems. In sulfide minerals, exsolution can produce alternating lamellae of different sulfide compositions, while in feldspars and other silicates, exsolution textures can reflect the cooling history and diffusion rates of end-member components. The development of exsolution textures can affect physical properties such as hardness, magnetic behavior, and electrical conductivity, thereby providing insights into a rock’s thermal history and diffusion processes.

Detection and analysis of exsolution involve petrographic microscopy, electron microscopy, and diffraction methods, sometimes combined with diffusion modeling to estimate temperatures and timescales. Interpretation relies on identifying characteristic lamellar or intergrowth textures and correlating them with known solvus relationships for the relevant mineral system. Exsolution thus serves as a record of crystallization and cooling histories in minerals and alloys.