Exsolution, precipitation, and spinodal decomposition

In addition to epitaxial relations, characteristic textures appear due to the intergrowth of crystals of two different species in a certain crystallographic relation. Various terms have been used in the mineralogical field to describe textures, as summarized in Table 7.2 [15], [16]. Observations of descriptive and taxonomy type have been accumulated, since they show the origin of rocks and ores, but understanding the mechanism of their formation still remains a future subject of research. 

These intergrowth relations are formed through the processes of crystal growth, phase transformation or decomposition associated with a decrease in temperature and pressure, or metasomatism due to the supply of new components from outside. 

Coaxial intergrowth is a paragenetic relation that describes crystals of two different species growing with a common axis the misfit ratios between the two crystals in the direction of the common axis are small, without exception. The formation of coaxial intergrowth can be understood to be one crystal conjunct to the other in an epitaxial relation, where both continue to grow. If a liquid of eutectic A-B component is solidified from one side (unidirectional solidification), crystals of the two phases A and B precipitate in dotted, columnar or lamellar (with common axis) form, and show unique textures for unidirectional solidification. This is a well known phenomenon in metallurgy. 

The solubility of a solid-solution component varies depending on temperature and pressure. 

The widths of these lamellae depend on the thermal history. Many examples have been observed in minerals, and these lamellae widths are used to analyze the thermal histories. 

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