In mineralogy, a symplectite (or symplektite) is a very fine intergrowth of two or more distinct mineral phases. Symplectites are largely considered to result from the breakdown of unstable minerals.
If, during cooling or metamorphism, a rock undergoes a rapid temperature or pressure drop, some minerals may be rendered unstable and will consequently decay and crystallise as more stable constituents. Symplectites are usually considered to be the result of such a process.
Symplectites may be due to a reaction between adjacent phases or to exsolution of a rapidly cooling solid solution. Exsolution symplectite may be used as temperature proxies.[1] They may be lamellar or globular. Lamellar symplectites are common in eclogite formed during retrograde metamorphism. Kelyphitic structures are symplectites formed around olivine containing pyroxenes, amphiboles, spinel or garnet.[1] Myrmekite is a globular or bulbous symplectite of quartz in plagioclase resulting from the dissolution of potassium feldspar in high grade metamorphic or igneous rocks.[1]