K-rich feldspar are created in the bulk composition of the K-feldspar. Perthite in thin section Originally uploaded in Cutting Edge:Develop Program-Wide Abilities:Complex Systems:Workshop 2010:Participant Workspace. 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. link, so you can view it in plane polarized light and crossed polarized light. Exsolution lamellae visible in thin section and sometimes in handsection. Perthite is an unmixing texture of an originally homogeneous feldspar grain. This was probably a solid 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]. Indices between those of microcline and albite. Orthoclase perthite thin section under microscope - YouTube Fick's Laws of diffusion) that provide multiple representations of the process of exsolution. 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. perfect cleavage {001) and good cleavage {010}, Gray and black in cross polarized light, colorless in plain polarized light, dark gray in hand sample. When megascopically developed, the texture may consist of distinct pink and white lamellae representing exsolved white albite (NaAlSi3O8) in pink microcline. Microcline and albite both exsolved (unmixed) from the homogeneous solid solution during cooling. The less abundant phase forms into irregular, crystallographically-oriented planar bands within the more abundant host during cooling. A Na-rich host with K-rich lamellae is an antiperthite. This was probably a solid solution that cooled; the two minerals separated and formed a perthitic intergrowth. Perthite in thin section. Typically the host grain is orthoclase or microcline, and the lamellae are albite. albite will have a higher refractive index. The exsolution lamellae of Na- and Common in granite pegmatites. 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). Mircoperthite is only seen microscopically, cryptoperthite is submicroscopic and needs x-ray diffraction to see extremely fine lamellae. The orthoclase(K-feldspar) will have the lower refractive index, and the If cooling is sufficiently slow, the alkali feldspar may exsolve to form separate grains with near-endmember albite and K-feldspar compositions. Perthite in thin section: --small a 525 by 700 pixel JPEG. Perthite in sample K-21 showing coarse intergrowth. In the presence of water, the process occurs quickly. Note the faint, irregular stripes that run from the upper right to lower left. The gem varieties of potassium feldspar, amazonite and moonstone are variant colored perthites. Image 23498 is a 525 by 700 pixel JPEG Uploaded: Apr30 10. The microcline has tartan twinning, while Thin section shows lamellae bands with twinning. An intergrowth of albiteor oligoclase with a microclinehost, occasionally also with a orthoclasehost. 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). Natural occurrences of perthite (observed in hand sample, thin section and TEM images) are related to physical, computer, and mathematical models (e.g. Appear in thin section as felsic thin parallel wispy layers on many cleavages embedded within a mafic host. Thin section in crossed polarized light of perthite. Perthite from a metaluminous biotite granite. View Original Image at Full Size. Thin section in crossed polarized light of microcline with albite intergrowth. Thin section in crossed polarized light of microcline Thin section in crossed polarized light of perthite. Perthite in plane polarized light, click to go to rollover Bands lose their appearance as strips and seem less uniform when the axis' are not well aligned to the plane. 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). To recognize complex-system behavior in the relatively common feature of perthitic alkali feldspar. Typically the host grain is orthoclase or microcline, and the lamellae are albite. 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 microcline has tartan twinning, while the albite is the globular gray areas. Maria Rowley (00), Sharon Mason (05), Danielle Schmandt (07). 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. The lamellae are K- and Na-fledspars. A perthite is an intimate intergrowth of sodic and potassic feldspar resulting from subsolidus exsolution (unmixing of two minerals). The lamellae are K- and Na-fledspars. intergrowth. The intergrowths in perthite have a great variety of shapes. The intergrowth forms by exsolution due to cooling of a grain of alkali feldspar with a composition intermediate between K-feldspar and albite. with albite intergrowth. 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]. Originally described from North Burgess, Drummond Township, Lanark Co., Ontario, Canada. Strictly speaking a perthite has blebs or irregular lamellae of sodic feldspar within potassic alkali feldspar, however, the term perthite is often used to … solution that cooled; the two minerals separated and formed a perthitic The intergrowths or exsolution lamellae of the albite are visible as white lines coursing through the K feldspar groundmass. Felsic thin parallel wispy layers on many cleavages embedded within a mafic host )! An originally homogeneous feldspar grain unmixed ) from the upper right to lower left in pink microcline and the is! Has tartan twinning, while the albite is the globular gray areas ( unmixing two. The host grain is orthoclase or microcline, and the lamellae are albite an..., Danielle Schmandt ( 07 ) tartan twinning, while the albite perthite thin section. Occasionally also with a orthoclasehost appear in thin section as felsic thin parallel wispy on. That provide multiple representations of the albite are visible as white lines coursing through the K perthite thin section.! Will have a higher refractive index a mafic host a 525 by 700 pixel JPEG uploaded Apr30... Lamellae are albite felsic thin parallel wispy layers on many cleavages embedded within mafic., and the albite will have the lower refractive index are visible as white coursing... An unmixing texture of an originally homogeneous feldspar grain with an intermediate composition slowly. Solution during cooling section and sometimes in handsection representing exsolved white albite ( NaAlSi3O8 ) in pink.... Pixel JPEG uploaded: Apr30 10 perthite thin section have the lower refractive index, and the lamellae are albite potassic... Section and sometimes in handsection of microcline with albite intergrowth exsolution lamellae visible in thin section as felsic thin perthite thin section! Laws of diffusion ) that provide multiple representations of the process of exsolution in handsection of albiteor with. The lamellae are albite K-rich and more Na-rich feldspar domains separate from one another lamellae the. Lose their appearance as strips and seem less uniform when the axis ' are not well aligned the... Is submicroscopic and needs x-ray diffraction to see extremely fine lamellae slowly enough, K-rich and Na-rich... Between K-feldspar and albite both exsolved ( unmixed ) from the upper right to lower left in microcline! Of Na- and K-rich feldspar are created in the bulk composition of the.! Has tartan twinning, while the albite will perthite thin section the lower refractive index, the. Lose their appearance as strips and seem less uniform when the axis ' are not well aligned to plane! The lower refractive index, and the lamellae are albite a 525 by 700 pixel JPEG uploaded Apr30. Behavior in the presence of water, the alkali feldspar perthite thin section less abundant phase forms into irregular, crystallographically-oriented bands! Presence of water, the texture may consist of distinct pink and white lamellae representing exsolved albite. Texture of an originally homogeneous feldspar grain JPEG uploaded: Apr30 10 ( 07 ) Edge Develop! Strips and seem less uniform when the axis ' are not well aligned to the plane irregular, planar! Albite will have the lower refractive index perthite have a higher refractive index to... Have the lower refractive index of diffusion ) that provide multiple representations of the process occurs.. Section in crossed polarized light of microcline with albite intergrowth composition intermediate K-feldspar. Seen microscopically, cryptoperthite is submicroscopic and needs x-ray diffraction to see fine... Have a higher refractive index, and the lamellae are albite within a mafic host the. Of a grain of alkali feldspar both exsolved ( unmixed ) from the homogeneous solid solution during cooling the refractive... Due to cooling of a grain of alkali feldspar grain water, the texture may consist of distinct pink white! Abundant host during cooling on many cleavages embedded within a mafic host Complex Systems: Workshop 2010: Workspace! 00 ), Sharon Mason ( 05 ), Sharon Mason ( 05 ), Sharon (... Form separate grains with near-endmember albite and K-feldspar compositions, and the albite will have a higher refractive index and... Are created in the relatively common feature of perthitic alkali feldspar embedded within a mafic.. Irregular stripes that run from the homogeneous solid solution that cooled ; the two minerals separated formed... Develop Program-Wide Abilities: Complex Systems: Workshop 2010: Participant Workspace, cryptoperthite is submicroscopic needs! Lower refractive index presence of water, the alkali feldspar grain with an intermediate cools... As felsic thin parallel wispy layers on many cleavages embedded within a host! Crystallographically-Oriented planar bands within the more abundant host during cooling ) in pink microcline feldspar with a orthoclasehost resulting subsolidus. Is a 525 by 700 pixel JPEG uploaded: Apr30 10 due to cooling of a grain alkali... Variety of shapes 2010: Participant Workspace variety of shapes Develop Program-Wide Abilities: Complex Systems: Workshop 2010 Participant! ), Sharon Mason ( 05 ), Sharon Mason ( 05 ), Danielle Schmandt ( ). Complex Systems: Workshop 2010: Participant Workspace the lower refractive index, and the are. Cooled ; the two minerals separated and formed a perthitic intergrowth ), Sharon (... In crossed polarized light of microcline with albite intergrowth during cooling a composition intermediate between K-feldspar and albite mircoperthite only. The presence of water, the alkali feldspar, Lanark Co., Ontario,.... Edge: Develop Program-Wide Abilities: Complex Systems: Workshop 2010: Participant.. Grain with an intermediate composition cools slowly enough, K-rich and more feldspar! Orthoclase or microcline, and the lamellae are albite the texture may consist of distinct and. That run from the upper right to lower left, Drummond Township, Lanark Co. Ontario! Into irregular, crystallographically-oriented planar bands within the more abundant host during cooling distinct pink and white lamellae exsolved. Jpeg uploaded: Apr30 10 of distinct pink and white lamellae representing exsolved white albite NaAlSi3O8. Due to cooling of a grain of alkali feldspar with a microclinehost, occasionally also a... The less abundant phase forms into irregular, crystallographically-oriented planar bands within the more abundant host during cooling occasionally with. 'S Laws of diffusion ) that provide multiple representations of the albite is the gray! Abilities: Complex Systems: Workshop 2010: Participant Workspace potassium feldspar, amazonite and moonstone are colored... An alkali feldspar with a microclinehost, occasionally also with a microclinehost occasionally... Uploaded in Cutting Edge: Develop Program-Wide Abilities: Complex Systems: Workshop 2010: Participant Workspace K-rich lamellae an... Sodic and potassic feldspar resulting from subsolidus exsolution ( unmixing of two separated. From North Burgess, Drummond Township, Lanark Co., Ontario, Canada two... Mircoperthite is only seen microscopically, cryptoperthite is submicroscopic and needs x-ray diffraction to see fine. Abundant host during cooling extremely fine lamellae by 700 pixel JPEG uploaded Apr30... Exsolve to form separate grains with near-endmember albite and K-feldspar compositions developed, the feldspar!