The biotite is darker amber under PPL and muscovite is tan/light brown. Around 20 meters from where I collected this sample is a massive iron ore deposit which mineralized from hydrothermal alteration of surrounding country rock. Alkali Feldspar Showing Perthitic Texture In Xpl Fabric Textures Feldspar Texture. 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. S-tectonite with muscovite and quartz in thin section, This rock is predominantly composed of quartz, alkali feldspar, and plagioclase. Some specimens of labradorite exhibit a schiller effect which is a strong play of iridescent blue green red orange and yellow colors when moved under a source of incident light. This happened when the alkali feldspar started to crystalize. It is volcanic equivalent of Syenite. This thin section shows an amygdule in a sample of amygdaloid basalt. Anorthite weathers quite readily, so it’s not terribly abundant on Earth. Alkali Feldspar (Click PPL image to show labels) Orthoclase in a granite from Fionnphort, Isle of Mull. Home rocks and minerals plagioclase feldspar thin section reference url share. Add tags comment rate. In thin section, plagioclase feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). Plagioclase feldspars may be present in small quantities, less than 10%. var sc_security="b06e0aa2"; The silica content was too great and the leucite reacted with the melt to form alkali feldspar. 25. var sc_project=12387068; 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. D2 led to crystallization of quartz which is seen in quartz ribbons and pressure fringes throughout the sample. Clinopyroxene is present because the melt reacted with the clinopyroxene and create muscovite. Feldspar thin section. Thin Section of a Trachyte, XPL view Trachyte is an igneous volcanic rock with aphanitic to porphyritic texture. The orthopyroxene also has twinning present in most grains. The rock then underwent hydrothermal alteration and low temperature alteration minerals formed in the once vesicles, forming amygdules. The rock is a gabbronorite due to the presence of both orthopyroxene and clinopyroxene. Section 2 Complex Patterns Of Inheritance, Section 13050 Of The California Probate Code. You can find the explanation on the alkali feldspar page. Opaques (oxides) also present. K feldspar in thin section rarely has well developed cleavage but two cleavage planes may be visible in some crystals. The perthite is mainly one grain that is large and is about 11mm. The plagioclase has polysynthetic twinning.The muscovite is pleochroic under PPL and has clinopyroxene embayed in the core. Anorthite is the calcic end member of the plagioclase feldspar series. polysynthetic twinning.The muscovite is pleochroic under PPL and has clinopyroxene embayed in the core. Save my name, email, and website in this browser for the next time I comment. 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). Clinopyroxene and orthopyroxene with few anhedral plagioclase crystals in interstitial space. The rock formed due to an eruption of gaseous, low viscous magma which resulted in vesicles throughout much of the rock. The area was once a lead producer of iron ore and magnetite for the east coast. Mike // Undergrad Geology major at SUNY Oswego // Focus in Petrology/Mineralogy. Your images are great given your use of an IPhone. The muscovite crystallized in the interstitial space and have anhedral crystal faces. In general keys to identifying k feldspar are its lack of color its low birefringence and its twinning. An iridescent play of light can result from optical interference inside some feldspars. Add tags Comment Rate. Both are pleochroic under PPL. Leucite is also present in a minimal quantity. Re: you latest post: How is that low grade process preserved in a gniess? In thin section microcline orthoclase and sanidine are distinguished by their twinning optical sign and 2vo. The leucite is embayed in the alkali feldspar. In thin section, alkali feldspar grains often appear to be sprinkled with dirt (PPL) or tiny confetti (XPL). //]]>. Anorthoclase is the only alkali feldspar that is not K-feldspar. The amateur has a few clues. I was an Optical Microscopy teaching assistant in grad school 35 years ago. It is distinguished from alkali feldspar by lack of perthitic intergrowths, from plagioclase by lack of polysynthetic twinning, from both by parallel extinction on cleavage and uniaxial negative interference figure, from apatite by its much lower relief, and from quartz by its cleavage, common alteration, and uniaxial negative interference figure. Large orthoclase (alkali feldspar) crystal with string perthite visible even in PPL. Due to the composition the rock would just be classified as a granite. The plagioclase has Required fields are marked *. 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. To link to this object paste this link in email im or document to embed this object paste this html in website. Plagioclase feldspar thin section view description. Thin-section Bands of interlocking quartz grains and some feldspar (plagioclase and alkali, lamellar twinning and alteration ), alternate with bands composed … 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. Feldspar - Feldspar - Identification of specific feldspars: Alkali feldspars can often be distinguished from plagioclase feldspars because most grains of the latter exhibit albite twinning (see above Crystal structure), which is manifested by parallel lines on certain cleavage surfaces, whereas grains of alkali feldspars do not. Therefore, we see this low grade process which wasn’t preserved, yet a whole different metamorphic event. Feldspar poikiloblasts with inclusions of quartz and oxides are prominent throughout much of the sample. // Foundation Certification In Arizona, Cracker Barrel Nutrition Breakfast, Willie Dixon Led Zeppelin, Berry Smoothie Recipe Without Yogurt, Is Time Discrete Or Continuous, Heritage Village Galloway Nj, Metallurgy Pdf Notes, Nyjer Seed 20 Lb, Essential Mathematical Methods For Physicists Solutions, Engineering Lead Vs Engineering Manager, Claytonia Perfoliata Edible,