![]() Plagioclase is the most common and abundant mineral group in the Earth's crust. Its name comes from Ancient Greek πλάγιος ( plágios) 'oblique', and κλάσις ( klásis) 'fracture', in reference to its two cleavage angles. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars. Plagioclase is also a major constituent of rock in the highlands of the Moon. Plagioclase is a major constituent mineral in Earth's crust and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or " record-groove" effect. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi 3O 8 to CaAl 2Si 2O 8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. ![]() Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. ![]() Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. In volcanic rocks, fine-grained plagioclase can display a "microlitic" texture of many small crystals. ![]()
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