Plagioclase

Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series (from the Greek "oblique fracture", in reference to its two cleavage angles). This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic twinning or 'record-groove' effect.

Plagioclase is a major constituent mineral in the Earth's crust, and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks. Plagioclase is also a major constituent of rock in the highlands of the Earth's moon.

Read more about PlagioclasePlagioclase Series Members

Other articles related to "plagioclase":

Myrmekite Formed During Na-Ca-metasomatism
... During this process a reequilibration with the Na-poorer feldspars (plagioclase) in the enclaves takes place ... As a consequence Ca gets released in plagioclase which in turn can now react upon K-feldspar to form myrmekite ... replacement of primary K-feldspar (perthitic and non-perthitic microcline) to the formation of plagioclase (albite or oligoclase) and in certain places also ...
Phenocryst
... Plagioclase phenocrysts often exhibit zoning with a more calcic core surrounded by progressively more sodic rinds ... of orthoclase are enveloped within rinds of sodic plagioclase such as oligoclase ... Thus, olivine-plagioclase phyric basalt contains >10% phenocrysts, the dominant phenocryst being olivine, with lesser amounts of plagioclase ...
Shoshonite
... rock, properly a potassic trachyandesite, composed of olivine, augite and plagioclase phenocrysts in a groundmass with calcic plagioclase and sanidine and ... and grades into absarokite with the loss of plagioclase phenocrysts and into bannakite with an increase in sanidine ...
Myrmekite - Formation
... Accordingly the texture was created as plagioclase formed by exsolution from alkali feldspar during cooling, under conditions in which silicon was mobile in the rock ... replacement of deformed primary plagioclase by secondary K-feldspar different varieties of Ca- and Na-Ca-metasomatism acting mainly upon deformed primary alkali feldspar, an exception being ...
Plagioclase Series Members - Intermediate Members
... The intermediate members of the plagioclase group are very similar to each other and normally cannot be distinguished except by their optical properties ... of the intrusive igneous rock anorthosite which is composed almost entirely of plagioclase ...