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Bytownite is a calcium rich member of the plagioclase solid solution series of feldspar minerals with composition between anorthite and labradorite.It is usually defined as having between 70 and 90%An (formula: (Ca 0.7−0.9 Na 0.3−0.1)[Al(Al,Si)Si 2 O 8]).
Plagioclase displaying cleavage. (unknown scale) In volcanic rocks, fine-grained plagioclase can display a "microlitic" texture of many small crystals. Plagioclase (/ ˈ p l æ dʒ (i) ə ˌ k l eɪ s, ˈ p l eɪ dʒ-,-ˌ k l eɪ z / PLAJ-(ee)-ə-klayss, PLAYJ-, -klayz) [4] is a series of tectosilicate (framework silicate) minerals within the feldspar group.
Feldspar is present as plagioclase (typically oligoclase or andesine) with alkali feldspar making up less than 10% of the total feldspar content. Quartz (SiO 2 ) is present as more than 20% of the total quartz-alkali feldspar-plagioclase-feldspathoid ( QAPF ) content of the rock.
QAPF diagram for volcanic rock with quartz latite field highlighted in yellow. Quartz latite is the fine-grained equivalent of a quartz monzonite, containing approximately equal amounts of plagioclase and alkali feldspar and between 5% and 20% quartz and with plagioclase making up 35% to 65% of its total feldspar content.
Feldspar is present as plagioclase (typically oligoclase or andesine) with 10% or less potassium feldspar. Quartz is present at between 5 and 20% of the rock. Biotite, amphiboles and pyroxenes are common dark accessory minerals. [1] Quartz diorite occurs in association with other granitic rock such as granodiorite, and with volcanic rock. In ...
The most common mineral assemblage of granulite facies consists of antiperthitic plagioclase, alkali feldspar containing up to 50% albite and Al 2 O 3-rich pyroxenes. Transition between amphibolite and granulite facies is defined by these reaction isograds: amphibole → pyroxene + H 2 O biotite → K-feldspar + garnet + orthopyroxene + H 2 O.
A poikilitic texture is most easily observed in petrographic thin sections. In some rocks there seems to be little tendency for the minerals to envelop one another. This is true of many gabbros, aplites and granites. The grains then lie side by side, with the faces of the latter moulded on or adapted to the more perfect crystalline outlines of ...
Potassium feldspar is also noticeably more prevalent as the pluton gets thicker, suggesting that the pluton is zoned compositionally. [8] Overall, the granite is a porphyritic rock that is composed of plagioclase feldspar, quartz, and biotite, and contains large pink microcline chunks throughout the matrix. The microcline megacrysts appear as ...