page_title: Plagioclase
hierarchical_section_title: Plagioclase
caption_attribution_description: Čeština: Ve výbrusu je dobře rozpoznatelné zrno plagioklasu s rovnoběžnou lamelací, podle albitového zákona, které je ve svrchní části omezeno velikým zrnem biotitu. Ve spodní části se nacházejí zrna amfibolitu. Pozorováno přes 2 nikoly. (Zvětšeno 100x, 1 mm odpovídá 100 dílům na stupnici) English: On area is grain of Plagioclase. On the top is big grain of biotite and in the button are some Amphibole. Observed by 2 nikols. (Zoom in 100times, 1 millimetre corresponding to 100 units on the scale)
context_page_description: Plagioclase is a series of tectosilicate minerals within the feldspar group. 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. This was first shown by the German mineralogist Johann Friedrich Christian Hessel in 1826. The series ranges from albite to anorthite endmembers, 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 crystal 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. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars.
context_section_description: Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. 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 (from the Ancient Greek for "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 crystal 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. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars.
caption: A photomicrograph of a plagioclase crystal under cross polarized light. The plagioclase crystal shows a distinct banding effect called polysynthetic twinning.
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