I’m impressed at your work. Anorthite weathers quite readily, so it’s not terribly abundant on Earth. To link to this object paste this link in email im or document to embed this object paste this html in website. Alkali feldspars are grouped into two types: those containing potassium in combination with sodium, aluminum, or silicon; and those where potassium is replaced by barium. Leucite is also present in a minimal quantity. K feldspar in thin section rarely has well developed cleavage but two cleavage planes may be visible in some crystals. Thedeflection angle is an optical characteristic and varies according to thealbite fraction (Ab). The plagioclase has polysynthetic twinning.The muscovite is pleochroic under PPL and has clinopyroxene embayed in the core. Unlike plagioclase feldspars, alkali feldspars are divided into separate minerals not only based on their chemistry, but more importantly, based on optical properties determined by a petrographic microscope. In thin section, plagioclase feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). var sc_project=12387068; Thin-section Bands of interlocking quartz grains and some feldspar (plagioclase and alkali, lamellar twinning and alteration ), alternate with bands composed … Re: you latest post: How is that low grade process preserved in a gniess? Plagioclase feldspar thin section view description. 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Mike // Undergrad Geology major at SUNY Oswego // Focus in Petrology/Mineralogy. Unless it’s heavily altered, you’ll still be able to identify the underlying feldspar by rotating the stage and looking for its wispy lamellae. The rock formed due to an eruption of gaseous, low viscous magma which resulted in vesicles throughout much of the rock. This thin section shows an amygdule in a sample of amygdaloid basalt. Section 2 Complex Patterns Of Inheritance, Section 13050 Of The California Probate Code. Anorthite is the calcic end member of the plagioclase feldspar series. D1 had a direct effect on the foliation (S1) of minerals that already crystallized. Alkali Feldspar (Click PPL image to show labels) Orthoclase in a granite from Fionnphort, Isle of Mull. In thin section microcline orthoclase and sanidine are distinguished by their twinning optical sign and 2vo. Around 20 meters from where I collected this sample is a massive iron ore deposit which mineralized from hydrothermal alteration of surrounding country rock. Another metamorphic event occured after this gneiss formed. The silica content was too great and the leucite reacted with the melt to form alkali feldspar. //. It is sodic in composition, optically triclinic and characterized by a twinning similar to microcline but on a smaller scale. The quartzy matrix in some areas is intergrown at the edge of the alkali feldspar crystal faces. An iridescent play of light can result from optical interference inside some feldspars. Required fields are marked *. The muscovite crystallized in the interstitial space and have anhedral crystal faces. Syenites are usually either peralkaline with high proportions of alkali elements relative to aluminum, or peraluminous with a higher concentration of aluminum relative to alkali elements (K, Na, Ca). DATA . White, grayish, reddish; colorless in thin section: 2V: ... Moonstone is a name given to a gem material that consists of very thin, alternating layers of orthoclase (an alkali feldspar) and albite (a plagioclase feldspar). K feldspar in thin section rarely has well developed cleavage but two cleavage planes may be visible in some crystals. The feldspar component of syenite is predominantly alkaline in character (usually orthoclase). Thin Section of a Trachyte, XPL view Trachyte is an igneous volcanic rock with aphanitic to porphyritic texture. Add tags comment rate. Save my name, email, and website in this browser for the next time I comment. Your email address will not be published. There are several plagioclase feldspars in the seriesbetween albite and anorthite. Due to the composition the rock would just be classified as a granite. Opaques (oxides) also present. The alkali feldspar grains are large and take up a decent amount of the slide.

alkali feldspar vs plagioclase thin section

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