A photomicrograph of a plagioclase crystal (gray) under cross polarized light. The plagioclase crystal shows a distinct banding effect called polysynthetic twinning.
Albite insoluble in HCl, anorthite decomposed by HCl[2]
References
[3]
Plagioclase displaying cleavage. (unknown scale)In volcanic rocks, fine-grained plagioclase can display a "microlitic" texture of many small crystals.
Plagioclase (/ˈplædʒ(i)əˌkleɪs,ˈpleɪdʒ-,-ˌkleɪz/PLAJ-(ee)-ə-klayss, PLAYJ-, -klayz)[4] 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. 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 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 Moon. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars.[5]
Its name comes from Ancient Greek πλάγιος (plágios) 'oblique', and κλάσις (klásis) 'fracture', in reference to its two cleavage angles.
^Milam, K. A.; et al. (2010). "Distribution and variation of plagioclase compositions on Mars". Journal of Geophysical Research: Planets. 115 (E9). Bibcode:2010JGRE..115.9004M. doi:10.1029/2009JE003495.
Plagioclase (/ˈplædʒ(i)əˌkleɪs, ˈpleɪdʒ-, -ˌkleɪz/ PLAJ-(ee)-ə-klayss, PLAYJ-, -klayz) is a series of tectosilicate (framework silicate) minerals within...
potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars...
and plagioclase makes up more than 65% of the total feldspar content. Gabbroids are distinguished from dioritoids by an anorthite (calcium plagioclase) fraction...
sodic plagioclase (An70–85), norites (plagioclase-orthopyroxene), and gabbronorites (plagioclase-clinopyroxene-orthopyroxene) with similar plagioclase compositions...
phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene...
effect (schiller). Labradorite is an intermediate to calcic member of the plagioclase series. It has an anorthite percentage (%An) of between 50 and 70. The...
intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides...
quartz in plagioclase. The intergrowths are microscopic in scale, typically with maximum dimensions less than 1 millimeter. The plagioclase is sodium-rich...
plagioclase phenocrysts, but 4% olivine microphenocrysts, might be termed an aphyric to sparsely plagioclase-olivine phyric basalt, where plagioclase...
contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored...
percentages of quartz (crystalline silica (SiO2)), alkali feldspar, plagioclase, and feldspathoid (QAPF) being particularly important. An aphanitic (fine-grained)...
porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende. Andesite is the extrusive equivalent of...
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than...
Anorthite (an = not, ortho = straight) is the calcium endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is CaAl2Si2O8...
distinguished from gabbro on the basis of the composition of the plagioclase species; the plagioclase in diorite is richer in sodium and poorer in calcium. Geologists...
is enriched in alkali metal oxides. Monzonite is composed mostly of plagioclase and alkali feldspar. Syenodiorite is an obsolescent term for monzonite...
Anorthosite – Mafic intrusive igneous rock composed predominantly of plagioclase Aplite – Fine-grained intrusive igneous rock type similar to granite...
are similar in size and carry the same charge as Ca2+, an ion found in plagioclase and other minerals. While Eu is an incompatible element in its trivalent...
magma chamber, although they are possible on the roofs if anorthite plagioclase is able to float free of a denser mafic melt. Cumulates are typically...
orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse-grained) to porphyritic granitic rock. The plagioclase is typically...
syenite is predominantly alkaline in character (usually orthoclase). Plagioclase feldspars may be present in small proportions, between 10% and 35% of...
(phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used...
their mineralogy. The acronym QAPF stands for "Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)", which are the four mineral groups used for classification...
silicate minerals in the Bowen's Series. Rocks dominated by quartz, plagioclase, alkali feldspar and muscovite are felsic. Mafic rocks are primarily...
Other incorporated silicate minerals may include, very minor amounts of plagioclase feldspar, mica in the form of muscovite and/or biotite, and amphibole...
composition between andesite and rhyolite. It is composed predominantly of plagioclase feldspar and quartz. Dacite is relatively common, occurring in many tectonic...
groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite. Its high silica content makes...
Global Information
