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perthite thin section

Posté par le 1 décembre 2020

Catégorie : Graphisme

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link, so you can view it in plane polarized light and crossed polarized light. Thin section in crossed polarized light of microcline Thin section in crossed polarized light of perthite. Originally described from North Burgess, Drummond Township, Lanark Co., Ontario, Canada. Maria Rowley (00), Sharon Mason (05), Danielle Schmandt (07). Typically the host grain is orthoclase or microcline, and the lamellae are albite. The microcline has tartan twinning, while with albite intergrowth. Thin section shows lamellae bands with twinning. Perthite in thin section: --small a 525 by 700 pixel JPEG. Strictly speaking a perthite has blebs or irregular lamellae of sodic feldspar within potassic alkali feldspar, however, the term perthite is often used to … Appear in thin section as felsic thin parallel wispy layers on many cleavages embedded within a mafic host. Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8, in composition). Typically the host grain is orthoclase or microcline, and the lamellae are albite. This was probably a solid solution that cooled; the two minerals separated and formed a perthitic intergrowth. https://en.wikipedia.org/w/index.php?title=Perthite&oldid=981184645, Creative Commons Attribution-ShareAlike License, This page was last edited on 30 September 2020, at 19:59. Fick's Laws of diffusion) that provide multiple representations of the process of exsolution. Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8, in composition). The lamellae are K- and Na-fledspars. The intergrowth forms by exsolution due to cooling of a grain of alkali feldspar with a composition intermediate between K-feldspar and albite. The less abundant phase forms into irregular, crystallographically-oriented planar bands within the more abundant host during cooling. The largest documented single crystal of perthite was found in Hugo Mine in South Dakota and measured about 10.7 m (35 ft) x 4.6 m (15 ft) x 1.8 m (5 ft 11 in).[2]. The orthoclase(K-feldspar) will have the lower refractive index, and the Perthite in thin section Originally uploaded in Cutting Edge:Develop Program-Wide Abilities:Complex Systems:Workshop 2010:Participant Workspace. The intergrowths in perthite have a great variety of shapes. Perthite from a metaluminous biotite granite. Note the faint, irregular stripes that run from the upper right to lower left. If cooling is sufficiently slow, the alkali feldspar may exsolve to form separate grains with near-endmember albite and K-feldspar compositions. albite will have a higher refractive index. Mircoperthite is only seen microscopically, cryptoperthite is submicroscopic and needs x-ray diffraction to see extremely fine lamellae. If an alkali feldspar grain with an intermediate composition cools slowly enough, K-rich and more Na-rich feldspar domains separate from one another. The exsolution lamellae of Na- and Bands lose their appearance as strips and seem less uniform when the axis' are not well aligned to the plane. An intergrowth of albiteor oligoclase with a microclinehost, occasionally also with a orthoclasehost. Perthite in thin section. intergrowth. When megascopically developed, the texture may consist of distinct pink and white lamellae representing exsolved white albite (NaAlSi3O8) in pink microcline. This was probably a solid Perthite in sample K-21 showing coarse intergrowth. Image 23498 is a 525 by 700 pixel JPEG Uploaded: Apr30 10. If sodic feldspar is the dominant phase, the result is an antiperthite and where the feldspars are in roughly equal proportions the result is a mesoperthite.[1]. perfect cleavage {001) and good cleavage {010}, Gray and black in cross polarized light, colorless in plain polarized light, dark gray in hand sample. To recognize complex-system behavior in the relatively common feature of perthitic alkali feldspar. Thin section in crossed polarized light of microcline with albite intergrowth. Microcline and albite both exsolved (unmixed) from the homogeneous solid solution during cooling. The microcline has tartan twinning, while the albite is the globular gray areas. There is complete solid solution between albite and K-feldspar at temperatures near 700 °C and pressures like those within the crust of the Earth, but a miscibility gap is present at lower temperatures. A Na-rich host with K-rich lamellae is an antiperthite. the albite is the globular gray areas. If sodic feldspar is the dominant phase, the result is an antiperthite and where the feldspars are in roughly equal proportions the result is a mesoperthite. The gem varieties of potassium feldspar, amazonite and moonstone are variant colored perthites. Natural occurrences of perthite (observed in hand sample, thin section and TEM images) are related to physical, computer, and mathematical models (e.g. A perthite is an intimate intergrowth of sodic and potassic feldspar resulting from subsolidus exsolution (unmixing of two minerals). Common in granite pegmatites. Indices between those of microcline and albite. The intergrowths or exsolution lamellae of the albite are visible as white lines coursing through the K feldspar groundmass. Perthite is an unmixing texture of an originally homogeneous feldspar grain. The lamellae are K- and Na-fledspars. K-rich feldspar are created in the bulk composition of the K-feldspar. Perthite in plane polarized light, click to go to rollover solution that cooled; the two minerals separated and formed a perthitic Thin section in crossed polarized light of perthite. Perthite, any member of a class of alkali feldspars in which tiny crystals of sodium-rich feldspar (albite; NaAlSi 3 O 8) are intimately intergrown with, but distinct from, tiny crystals of potassium-rich feldspar (orthoclase or, less commonly, microcline; KAlSi 3 O 8). In the presence of water, the process occurs quickly. View Original Image at Full Size. Orthoclase perthite thin section under microscope - YouTube Exsolution lamellae visible in thin section and sometimes in handsection.

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