Symplectite
In geology, symplektite or symplektitic intergrowth describes the microstructure of a rock in which two or more mineral phases penetrate one another, one of which usually takes on a lamellar or worm-shaped appearance.
Emergence
Symplectic structures can arise, on the one hand, when the physical conditions (pressure, temperature) in a rock change to such an extent that the stability range of at least one of the mineral phases present therein is left. This often happens in the context of retrograde metamorphosis . The original mineral can be partially preserved in the form of relics within the symplectite. Alternatively, two adjacent mineral phases in the rock can also form a contact zone through a chemical reaction, in which the reaction products are symplectitically grown together.
Examples
Well-known examples of symplectic adhesions are:
- Worm-shaped quartz in plagioclase crystals from granites or gneiss: Myrmecite
- Corona-like adhesions of amphibole, pyroxene, plagioclase and spinel around crystals of garnet : Kelyphite
- Adhesion of augite, plagioclase, rhönite and magnetite in former hornblende or biotite crystals of basaltic magmas: opacite
- Retrograde metamorphosis of eclogite (pressure relief at high temperature) leads to the conversion of the mineral omphacite into a symplektitic intergrowth of pyroxene and plagioclase, whereby the pyroxenes can convert further into amphiboles as the process progresses .
Individual evidence
- ↑ D. Fettes, J. Desmonds, Metamorphic Rocks. A Classification and Glossary of Terms. Cambridge University Press, Cambridge, 2007, p. 199
- ↑ M. Okrusch, S Matthes: Mineralogie. 8th edition. Springer Verlag, Berlin, 2009, p. 409
- ^ W. Wimmenauer: Petrography of igneous and metamorphic rocks. Enke Verlag, Stuttgart, 1985, pp. 243-244