What is exsolution in mineralogy ?
Exsolution : definition
Exsolution is the result of the transformation by solid state cooling of a single phase stable at high temperature into a polymineral assembly at low temperature.
The classic example is that of perthites in feldspars. A solid solution of formula (K, Na) AlSi3O8 crystallizing at high temperature splits into two mineral phases on cooling : albite (NaAlSi3O8) and orthoclase (KAlSi3O8). Minority albite appears as fine oriented inclusions, exsolutions are called perthites in this specific case.
On the right, a green amazonite (microcline) with white albite exsolution.
The classic example is that of perthites in feldspars. A solid solution of formula (K, Na) AlSi3O8 crystallizing at high temperature splits into two mineral phases on cooling : albite (NaAlSi3O8) and orthoclase (KAlSi3O8). Minority albite appears as fine oriented inclusions, exsolutions are called perthites in this specific case.
On the right, a green amazonite (microcline) with white albite exsolution.