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The composition of plagioclase feldspar is typicallyindicated by the general anorthite (% An) or albite (% Ab) fraction and iseasily determined by measuring the refractive index or peel angle within thecrushed particles by measuring the refraction angle under a thin section. The silica content was too great and the leucite reacted with the melt to form alkali feldspar. var sc_security="b06e0aa2"; You can find the explanation on the plagioclase feldspar page. In thin section, plagioclase feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). The plagioclase has polysynthetic twinning.The muscovite is pleochroic under PPL and has clinopyroxene embayed in the core. Plagioclase Feldspar (thin section) View Description. The rock then underwent hydrothermal alteration and low temperature alteration minerals formed in the once vesicles, forming amygdules. Alkali Feldspar crystals are large in this thin section. The feldspar component of syenite is predominantly alkaline in character (usually orthoclase). Both are pleochroic under PPL. ... Alkali Feldspar group . This happened when the alkali feldspar started to crystalize. The formula actually is a blend ranging from all sodium (albite) to all potassium (microcline), but albite is also one endpoint in the plagioclase series so we classify it there. Composition includes: biotite, muscovite, chlorite, feldspars, oxides, and quartz. (leucite in 2nd pic), Olivine groundmass with an orthopyroxene phenocryst. 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). 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. The leucite is embayed in the alkali feldspar. Plagioclase feldspars may be present in small quantities, less than 10%. To link to this object paste this link in email im or document to embed this object paste this html in website. What would really help the viewers would be a photo of the rock illustrated in the thin sections. In general keys to identifying k feldspar are its lack of color its low birefringence and its twinning. Alkali Feldspar (Click PPL image to show labels) Orthoclase in a granite from Fionnphort, Isle of Mull. It is volcanic equivalent of Syenite. To differentiate between the muscovite and the biotite pleochroism comes into effect. The plagioclase in this thin section has polysynthetic twinning. Re: you latest post: How is that low grade process preserved in a gniess? An iridescent play of light can result from optical interference inside some feldspars. var sc_invisible=1; Feldspar Augen Ppl In A Gneiss How To Dry Basil Fabric Textures Gneiss, Bookshelf Feldspar In Quartzofeldspathic Mylonite The Shear Zones Between The Books Contain Recrystallized Feldspar Grains 15 Microns In Diameter, Perthite Fabric Textures Feldspar Utility Rooms, Tartan Twinning In Alkali Feldspar In A Granite Rocks And Minerals Microscopic Photography Geology, Basalt In Thin Section In Xpl With Phenocrysts Of Plagioclase Feldspar And Pyroxene Mostlikely Opx Mineralogy Rocks And Minerals Geology Rocks, Related Image Fabric Textures Feldspar Texture, Alkali Feldspar Var Microcline With Tartan Twinning And Perthitic Texture The Light Colored Fuzzy Patches Xpl Light Colors Optical Microscope Feldspar, Potassium Feldspar Orthoclase In A Dacite Hypobyssal Intrusive Notice The Two Carlsbad Twin Domains Separated By The Carlsbad C Geology Mineralogy Fractals, Coarse Feldspathic Sandstone Torridon Group Torridonian Xpl There Is Quartz E G Large Grain At Left Potassium Feldspar With Tartan Geology Rock Gneiss, Thinsectionthursday Thin Section Microphotograph And Sem Image Of The Notikewan Formation Showing Secondary Dissolution Porosity O Porosity Oil And Gas Image, Hummingbird Geology On Twitter Geology Rocks Nature Inspiration Geology, Video Tartan Twinning In Alklai Feldspar Microcline In 2020 Feldspar Optical Microscope Tartan, Alkali Feldspar Var Microcline In Xpl Showing Distinctive Tartan Twinning Metamorphic Rocks And Minerals Minerals, The Mineralogist Mineralogy Minerals Patterns In Nature, Flow Banding In A Rhyolite Ppl The Groundmass Flows Around Large Feldspar Phenocrysts, How2readarock On Instagram Tartan Twinning In The Microcline Form Of Alkali Feldspar Seen In Cross Polarizing L Rocks And Minerals Feldspar Amazing Stories, Your email address will not be published.

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