% melt melt comp. (c) High (PH2O > 500) water-vapour pressure, depresses the alkali feldspar solidus to the point where it intersects the solvus. Complex, two-phase field, of triclinic potash feldspar and triclinic soda feldspar solid solutions (microcline-perthite and antiperthite). Quartz/coesite lamellae are commonly observed in supersilicic clinopyroxene from ultrahigh-pressure (UHP) metamorphic rocks (Fig. Perthite and antiperhite. Marc's legend: a. Melting point of orthoclase. The Creighton pluton is composed of melanocratic quartz monzonite with less than or equal to 20% mafic minerals, leucocratic granite consisting of equigranular quartz with recrystallized plagioclase, perthite and minor biotite, and porphyritic quartz monzonite comprising orthoclase phenocrysts in a coarse-grained matrix of quartz, plagioclase, perthite and biotite (Riller, 2009). Phase diagrams are graphical representation of stability fields of minerals and include: ... Perthite, 12, antiperthite, 13. perthitic texture, 14. subsolvus granite. Label the fields and any peritectics or eutectics on the diagram. Ternary Phase Diagram Igneous and Metamorphic Petrology Fo-An-Q system After Philpotts, 1990 1. It is formed by the crystallization of lava at high temperatures and rapid cooling. Lecture 3: The binary phase diagrams with limited solid solution: albite-orthoclase phase diagram. (H) Cr-spinel needles in Opx from the Lüliangshan garnet lherzolite (North Qaidam UHP metamorphic belt, China). All three methods, quite wisely, retained the identification of the original labile minerals such as feldspars as “feldspars” even if they were altered fully to clay minerals as long as the detrital grains retained their outlines and other characteristic features such as ghost twinning. Crystallization of melt under these conditions generates a single homogeneous feldspar phase of intermediate composition, which exsolves to form perthite or antiperthite as it cools through the solvus into the 2-feldspar field, characteristic of hypersolvus granites. The T-controlled exsolution textures are exemplified by perthite/antiperthite (Fig. See text for criticism of Mikinen's diagram. Thus, albite is the stable plagioclase in the chlorite and biotite zones of regional metamorphism, occurring in such rocks as chlorite-biotite-epidote-albite amphibolites and chlorite-albite schists; the anorthite component is not present in notable quantity until the garnet zone. In the intermediate zones, K-feldspar predominates over plagioclase in the chemically simple pegmatites, and lithium minerals, the lithium aluminosilicates or their equivalent phosphates, are prevalent in more evolved bodies. (D) Quartz (Qtz) lamellae in omphacite from a UHP eclogite (East Kunlun, China). Creek district; in these, the "perthite" of the diagrams is actually perthite plus muscovite. In the thermal metamorphism of calcareous sediments plagioclase again becomes increasingly calcic as the grade increases, with the production of anorthite marking a high grade of metamorphism. The Murray pluton consists largely of equigranular granite. In contrast, primary precipitate plagioclase may be absent from the ferromagnesian-rich bands in which the feldspar occurs as a product of the crystallization of intercumulus liquid. Crystallization of melt under these conditions generates a single homogeneous feldspar phase of intermediate composition, which exsolves to form perthite or antiperthite as it cools through the solvus into the 2-feldspar field, characteristic of hypersolvus granites. Very few alkali feldspars are devoid of exsolution microtextures, which are periodic on scales ranging from a few nm to 100 s of μm in crystals that have been subject to reactions with fluids (see Perthitic Intergrowths, below). This exsolution process results in a 2-phase intergrowth, called perthite. They occur as one or more groups of oriented rods/needles strictly aligned along the structural defects of the host minerals. The β index is essentially the same in both series. The exsolution lamellae occur in parallel groups, each being strictly oriented in one of the four directions corresponding to the isometric form {111}, i.e., octahedral planes of the host garnet (Fig. It is possible to form mixed-crystals of isomorphic replacement of Or-component and Ab-component at high temperatures. This method can give the average composition for plagioclase which is strongly zoned or has exsolution intergrowths; also, the original structural state of the plagioclase is of no consequence. geothermometry . Fig.1 Orthoclase (KAlSi3O8) - Albite (NaAlSi3O8) system. Most of the pegmatite fields cited by Cameron et al. With further cooling under equilibrium conditions, both liquid and crystals change their composition along the liquidus and solidus, respectively, until at 1285°C the crystals reach a composition of Ab50An50(D) as the last of the liquid now of composition (C) is used up. Granites containing two distinct populations of potassic and sodic feldspars are referred to as subsolvus granites. 3I) in olivine were thought to be exsolved from olivine of ultradeep origin (Dobrzhinetskaya et al. b. Melting point of albite. Alkali feldspar, unmixed to mesoperthite or antiperthite, is the dominant constituent of these hypersolvus alkali syenites. T2 T3 % solid solid comp. Sodic amphibole lamellae in garnet suggest that a significant amount of hydroxyl (OH) can also be dissolved into the structure of garnet at very high pressure (Song et al., 2005, 2009a). kinetics of the plagioclases, antiperthite texture has not received as great attention as the perthite textures from research workers. There are very clear differences in grain size, color, inclusion content, and diversity in rock types between the Creighton and the Murray granites, and the different U–Pb ages (Fig. The plagioclase feldspars of the intermediate and acid rocks of the granulite facies commonly are sodic andesines; thus in the rocks of the charnockite series, the majority of the plagioclase is between An30 and An35 in composition, although labradorite is present in some of the more basic charnockitic rocks. Figure 2.3. The best known is the brilliant blue iridescence, called ‘labradorescence,’ produced by Bøggild intergrowths. Fig. Exsolution is a process by which a former fairly homogeneous phase separates into two or more solid solution phases under subsolidus conditions. Exsolution texture induced by cooling: Clinopyroxene (Cpx) exsolution in orthopyroxene (Opx) or vice versa. Fig. 9b). (B) Idem in XPL. Exsolution texture, a general term for the texture of mineral intergrowth formed by solid exsolution, is a common texture in minerals from both magmatic and metamorphic rocks. interpretations on the basis of various binary and ternary phase diagrams suggest that the Thar Granitoids are magmatic rocks of peraluminous nature. 2. However, a closer look at the zoning sequences reveals that K-feldspar or plagioclase alternate as the dominant feldspar (London et al., 2012b). Microcline is distinguishable from most other alkali feldspars by its ‘tartan’ twinning in which two sets of twin lamellae are approximately at right angles to each other. Shuguang Song, Yi Cao, in Encyclopedia of Geology (Second Edition), 2021. Perthite and antiperthite in From a melt of composition A, leucite (B) is the first phase to crystallize, and continues to do so as the liquid composition moves along the liquidus curve to the reaction point (R). The unmixed feldspars result in perthite (albite in orthoclase), or more rarely, antiperthite (orthoclase in albite). At this temperature, the liquid reacts with the leucite transforming it to K-feldspar. Miscibility gap. (1949) extracted a general sequence of internal mineralogical zonation, given below, from margin to center, or border to core. Names can be used in conjunction, as in cryptomesoperthite. 4 and in white in Fig. Plagioclase feldspars are the main constituent of dolerites and many other hypabyssal rocks. S.K. (D) Idem in XPL. Draw the arrows on the cotectics or reaction lines. Neither zonation model addresses the textural features of pegmatites that are so prominent (e.g., London et al., 2012b). Antiperthite is albitic plagioclase with small discrete K-feldspar that has become exsolved from the albite. Under these conditions no 1-feldspar field exists and therefore no homogeneous intermediate alkali feldspars can form; two separate feldspar species (one K-rich and one Na-rich) crystallize directly from the melt. Monoclinic or triclinic. The routine characterization and interpretation of perthitic intergrowths is described by Parsons et al. The Creighton pluton is composed of melanocratic quartz monzonite with less than or equal to 20% mafic minerals, leucocratic granite consisting of equigranular quartz with recrystallized plagioclase, Evolution of Siliciclastic Provenance Inquiries, years because “rock fragments” defied the traditional description of “two or more minerals in a grain of sand.” Would a grain of rutilated quartz or a grain of, Suttner et al., 1981; Folk, 1974; Dickinson, 1970, Dickinson, 1985; Dickinson et al., 1983; Dickinson and Suczek, 1979, Textures and Structures of Metamorphic Rocks, The T-controlled exsolution textures are exemplified by, The K–Na feldspars are essential constituents of alkali and acid igneous rocks and are particularly abundant in syenites, granites, granodiorites, and their volcanic equivalents. The nepheline in leucocratic syenite and pegmatite shows deviation from the ideal composition with respect to Si and K contents. Na[AlSi3O8]—Ca[Al2Si2O8]. Syntectonic emplacement of granitoid magma is supported by: (1) concordance of magmatic and metamorphic foliation within the pluton; (2) continuity of foliations across intrusive contacts; and (3) general obliquity between foliation surfaces and pluton contacts (Riller et al., 2006). Because experienced subjective judgment is necessary for such identification, automated analytical image analysis to determine the modal composition of sandstones is still not possible. Triclinic. Lepidolite or lithian mica–plagioclase–quartz–microcline. They have been little investigated from a petrological standpoint. Pyroxene/rutile/amphibole lamellae in garnet are observed in eclogites, orogenic garnet peridotites, and peridotite xenoliths in kimberlites. 2.7). PP 5-8 Harker, A.1909: The Natural History of Igneous Rocks.Methuen, London. Homogeneous pegmatites of … Asymmetry, if present, usually correlates with thickening of the pegmatite body (e.g., see the individual maps of lithium-rich pegmatites stemming from the WWII study in the USA; Cameron et al., 1949; Uebel, 1977). The existence of these compositional gaps is believed to result from changes in Al–Si ordering behavior (next section) as the Ab:An ratio changes. Information and translations of PERTHITE in the most comprehensive dictionary definitions resource on the web. REFRENCES Fasset, J. E. and Durrani, N. A. A felsic HP granulite shows equilibration of garnet, perthite, antiperthite, kyanite, quartz, and rutile at 810–860°C, ~1.2 GPa, sillimanite growth during decompression, and upper amphibolite facies cooling at … Many have assigned tectonic provenance of their modal data accordingly. Equilibrium diagram of the plagioclase feldspars: (1) in anhydrous conditions, (2) at 5 kbar water pressure, (3) eutectic liquidus and solvus in the albite–anorthite–quartz–H2O system at 2 kbar. 1996), but they were also reported in low-pressure igneous plutons. - 201309 Mob: +91-9120494939 +91-7428842971 R.A. Howie, in Encyclopedia of Geology, 2005. through compositionally constrained PT-phase diagrams (pseudosec-tions; Kelsey, 2008), using software such as Thermocalc ... were obtained for single perthite and antiperthite grains. (Answer: The solvus is a curve within the solid field. Exsolution occurs only in minerals with two or more pure endmember compositions that cannot mix together in normal conditions, or in metastable minerals with complicated solid solutions through ion substitutions at high temperature or pressure. Quartz–plagioclase–perthite ± muscovite ± biotite, Perthite–quartz–plagioclase–amblygonite–spodumene, Microcline–plagioclase–lithium-rich micas–quartz. Although only few age determinations exist, the main magmatic event probably occurred at 1.88–1.87 Ga with emplacement of composite monzonitic-granitic intrusions (Skiöld and Öhlander, 1989; Martinsson et al., 1999), whilst some late granites formed at ~ 1.86 Ga (Skiöld, 1981; Skiöld and Öhlander, 1989). Phase diagram for Or-free plagioclase feldspars, showing liquidus and solidus curves at atmospheric P and They may also develop as authigenic minerals occurring as rims on detrital feldspar, often in optical continuity. 2.12C). In basic igneous intrusions, plagioclase sometimes occurs in feldspar-rich bands formed by the accumulation of the primary precipitate plagioclase (the cumulus phase). olivine, pyroxene). Jahns (1982) described the model case of a layered pegmatite as possessing granitic border zones top and bottom. Fig. If the host phase is K rich feldspar then this mineral is called perthite. Major mineral thermobarometry suggests that HP granulite experienced peak P–T conditions of 870–1050 °C and 19–25 kbar, followed by a medium–high pressure granulite facies overprint (780–820 °C, 9.5–12 kbar), which is defined by the formation of secondary clinopyroxene ± orthopyroxene + plagioclase at the expense of garnet + early Al-rich clinopyroxene in the mafic granulites, as well as by growth of spinel, sapphrine and plagioclase at the expense of garnet and kyanite in the felsic and mafic granulite (Fig. Coesite/quartz lamellae in garnet, titanite, and chromite are thought to indicate ultrahigh-pressure conditions of greater than 6 GPa (Ye et al., 2000; Ogasawara et al., 2002; Zhang et al., 2005). The refractive indices for the alkali feldspar series increase steadily with increasing albite content (Figure 4), values for α and γ in the high-temperature series sanidine–anothoclase–high-albite being marginally lower. 2.3), efficiently discriminate derivation of sand-sized siliciclastic detritus from different tectonic provenance (Dickinson, 1985; Dickinson et al., 1983; Dickinson and Suczek, 1979). In arkosic sediments, K-feldspar is usually dominant over plagioclase, but this varies according to the source rock and the weathering conditions to which they have been subjected. Figure 6. c. Eutectic point of monoclinic orthoclase-rich solid solution and triclinic albite- Perthite: Lab 101, 101A Perthitic alkali feldspars were initially a single alkali feldspar at high temperature (see lecture notes for relevant Ab-Or phase diagram). Sanidine, as a high-temperature alkali feldspar, is not stable in rocks on the surface or at shallow depth under the surface of the Earth, and gradually recrystallize in orthoclase over time. Reaction point R represented approximately by 5 KAlSi2O6 (leucite) + 3 KAlSi3O8 + 5 SiO2 (melt) → 8 KAlSi3O8. 9. The pyroxene lamellae suggest that previous supersilicic or majoritic garnet with substitutions of Mg (or Fe) + Si → 2Al and Na + Si → Ca + Al formed under ultrahigh-pressure conditions (~ 6 GPa or above) (Ye et al., 2000). It is a typical mineral of the sillimanite zone of metamorphism and, in rocks of argillaceous composition, does not appear at lower grades. A review is provided by Carpenter (1994). These unusual P–T conditions are higher than those of the vast majority of granulites in the world, but are similar to those of (U)HP/UHT granulites in the Bohemian Massif of the European Variscan orogen (Carswell and O'Brien, 1993; Rotzler and Romer, 2001; O'Brien and Rötzler, 2003; Kotková, 2007; O'Brien, 2008, and references therein). These are followed inwardly by massive to layered sodic aplites on the footwall and a complementary very coarse-grained microcline-rich assemblage that grows downward from the hanging-wall contact. Natural intergrowth of feldspars formed by separation of sodium feldspar (albite) and potassium feldspar (orthoclase) during slow cooling of molten mixtures; the potassium-rich phase is evolved in a plagioclase host, exactly the inverse of perthite. In calc-silicate rocks of the amphibolite facies, clear compositional minima are seen corresponding also with the Bøggild and Huttenlocher gaps (Figure 8). Where internal zoning is present in steeply dipping pegmatites, the distribution of zones is nearly concentric about the pegmatite in horizontal cross-section. 37 Phase diagram for the alkali feldspars. 2 photos of Perthite associated with Almandine: Fe 2+ 3 Al 2 (SiO 4) 3: 2 photos of Perthite associated with Aquamarine: Be 3 Al 2 Si 6 O 18: 1 photo of Perthite associated with Zircon: Zr(SiO 4) 1 photo of Perthite associated with Allanite {A1 2+ REE 3+}{M 3+ 2 M3 2+}(Si 2 O 7)(SiO 4)O(OH) 1 photo of Perthite associated with Smoky Quartz: SiO 2 Granophyric intergrowths, the bulk composition of which is close to the melting minimum in the orthoclase–albite–quartz–H2O system, consisting of roughly equal amounts of quartz, K-feldspar, and Na-feldspar components, occur in the mesostasis of acid rocks of high-level origin. Geology Coal Resources of the Thar Coal Field, Sindh Province, Pakistan. 6) the solvus curve shows the compositions of structurally separate Ab- and Or-rich phases. Because of the different ionic radii of Na 1+ and K 1+ the crystal structure distorts at the interfaces of exsolution lamellae, leading to coherency strain. 1994. It separates regions of one solid solution phase from that of two phases. They are generally colourless, white or grey, but may be yellow, red, or green; colourless in thin section. An even greater effect is shown on the addition of SiO2 to the system at 2 kbar (curve 3). XPL image. 4) respectively. The heat source of the Creighton and Murray granite plutons is believed to be the Paleoproterozoic Matachewan plume event where granitic magmas were generated by melting of lower crust. In a conventional phase diagram (Fig. The phase diagram for the plagioclase series was one of the first to be determined experimentally (Figure 5). In sedimentary rocks, plagioclase feldspars may occur via a variety of sources, including detrital minerals, authigenic minerals, and the products of volcaniclastic activity. The most familiar evidence for their existence is the play of iridescent colors they produce by the diffraction of light. 5 in Zuffa, 1985). Zircon U–Pb geochronology yielded ages of 493 ± 7 Ma and 495 ± 4 Ma for the felsic granulite (Zhang et al., 2005c, 2014b), 497 ± 11 Ma for mafic granulite (Zhang et al., 2005c), interpreted as dating the HP/HT (UHT) granulite facies metamorphism (Zhang et al., 2005c). The alkali feldspar phase diagram. (K,Na)[(AlSi3O8]. 8. A liquid of composition Ab50An50 (A) begins to crystallize at ∼1450°C, the first crystal having the composition of ∼Ab82An18(B). Address: R.P.-9, Sector 71, NOIDA, U.P. In lunar rocks the great majority of feldspars are calcic plagioclase An90 to An95 representing the lunar anorthosites. A. 2.7). (C) Opx lamellae in Cpx from an ultrahigh-temperature granulite (East Kunlun, China). 3A) and pyroxenes (Fig. Figure 5. It is an important ingredient of all acidic (granite, granodiorite) to neutral (syenite) igneous rocks (Table 5.1). The hardness ranges between 6 and 6.5 and the relative density between 2.55 and 2.63 g/cm3. With the addition of H2O to the system, at PH2O = 5 kbar, the liquidus and solidus temperatures are over 300° lower than for the anhydrous system (Figure 5, curve 2). In the majority of twinned plagioclase crystals, the composition plane is parallel to the crystal length. Development of antiperthite both by exsolution and replacement processes is accepted (Deer et el., t963). The Na-rich and K-rich parts of perthitic intergrowths should be called the Ab- and Or-rich phases respectively. (a) and (b): Mafic granulites occur as lenses within felsic granulites; (c) garnet + kyanite + perthite (former ternary feldspar) + quartz assemblage in felsic granulite (CPL); (d) garnet + clinopyroxene + plagioclase + quartz + rutile assemblage in mafic granulite (PPL); (e) spinel grows between kyanite and garnet in felsic granulite (PPL); (f) sapphrine + plagioclase symplectite in mafic granulite (PPL). Refractive indices are low, alkali feldspars having values <1.54 and plagioclase in the range 1.53–1.59 (the values increasing with increase in An content); the birefringence ranges 0.006–0.013. Binary Eutectic+Subsolidus Phase Diagram Equilibrium crystallization of composition M Or-rich feld. (1949) claimed that the consistencies they observed far outweighed the disparities. Many alkali feldspar crystals from plutonic igneous rocks (e.g. (Or 83) Plag. Equilibrium diagram of the binary system KAlSi2O6 (leucite)–SiO2. Exsolution texture induced by decompression: The pressure-controlled exsolution textures mainly occur in ultrahigh-pressure rocks from the continental collisional belts and xenoliths in kimberlites. This recrystallization, which leaves a K-rich and a Na-rich phase, may proceed from a sub-microscopic lamellar aggregate (an X-ray perthite) to a crystal aggregate in which the K-rich and Na-rich feldspars are found side by side as if originally formed as separate phases. can be illustrated on a phase diagram exhibiting a miscibility gap (see the diagram below). All the common members of the feldspars have D 2.55–2.5, with H 6–61/2. Photomicrographs showing exsolution textures in various minerals from metamorphic rocks. K-feldspar albite inter-growths is known as perthite and albite intergrowths K-feldspar as antiperthite. What does PERTHITE mean? Haldar, in Introduction to Mineralogy and Petrology (Second Edition), 2020. Figure 8. In plutonic rocks, the alkali feldspar is usually orthoclase, microcline, microcline microperthite, or microcline, Metallogeny of the Northern Norrbotten Ore Province, northern Fennoscandian Shield with emphasis on IOCG and apatite-iron ore deposits, Geijer, 1931; Witschard, 1984; Bergman et al., 2001, Skiöld and Öhlander, 1989; Martinsson et al., 1999, A petrologic assessment of internal zonation in granitic pegmatites, Tectonic evolution and dynamics of the Tibetan Plateau, Carswell and O'Brien, 1993; Rotzler and Romer, 2001; O'Brien and Rötzler, 2003; Kotková, 2007; O'Brien, 2008, Zhang et al., 2005c; Wang et al., 2011; Li et al., 2015. (1949) consist of lenticular or sheet-like pegmatite bodies of generally steep dip. The compositions of the Ab- and Or-rich phases in perthitic intergrowths diverge as temperature decreases and are described graphically by solvus curves. This ‘coherent’ solvus lies inside the strain-free solvus, and because of the different ionic radii of K1+ and Na1+ the Ab and Or-rich phases are subject to coherency strain. Single or multiple twins are common. The optical properties of the plagioclases are directly related to their anorthite content. Some cryptoperthites produce iridescent colors by the diffraction of light, the most familiar being the brilliant blue and silver iridescence of the otherwise black or dark green feldspars in the rock-type larvikite, used as an architectural stone in innumerable shopping malls. It shows a solid solution without maximum or minimum, with the melting point of anorthite at 1550°C and that of albite at ∼1100°C at P = 1 bar. Phase compositions, the It typically consists of 10%−36% of (KAlSi3O8), and 64% to 90% of (NaAlSi3O8). A Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi 3 O 8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi 3 O 8, in composition).Typically the host grain is orthoclase or microcline, and the lamellae are albite. It is usually formed by recrystallization of feldspar, and sometimes by direct crystallization from magma and hydrothermal processes. Though the sequences of zonation differed in detail from district to district, Cameron et al. The name ‘peristerite’ is a reference to the play of colors on the breast of a pigeon. (A) Antiperthite with K-feldspar (Kfs) exsolution lamellae in two directions from a ~ 1.95 Ga high-pressure granulite (Hengshan, China). The disordered solid solution can only exist at high temperatures. This rock type is likely developed within the metamorphic halo the SIC, and it likely reflects recrystallization and possibly partial melting. Field relations and petrographic observations show that the formation and/or post-peak evolution of the Bashiwake granulite involved some degree of melting (Zhang et al., 2005c, 2014b), but the extent of melting and its relation to the granulite P–T path are still unclear. Intergrowths develop within single crystals by a process that is variously called phase separation, unmixing and exsolution. In alkali feldspars the intergrowths are called, Interpretation of Micromorphological Features of Soils and Regoliths (Second Edition), – colourless, often cloudy, low negative relief, perfect cleavage in one direction, less perfect in the others; first-order grey interference colours, simple Carlsbad twinning; can occur as part of exsolution features composed of orthoclase and albite lamellae (, Introduction to Mineralogy and Petrology (Second Edition), A synthesis of the geology of the Sudbury Structure. 21 November 2015 Prof. Dr. H.Z. Of felsic and mafic granulites obtained an age of ca whenever a material transitions into the unstable region the. Cited by Cameron et al the web high pressure speak of solid solution phase that. Compositional range of plagioclase compositions from 1883 microprobe results from 147 metamorphic calc-silicate in! Exsolution origin for the plagioclase phenocrysts usually have a wide homogeneous core of bytownite composition surrounded by narrow... 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Transformation of plagioclase the plagioclase phenocrysts usually have a wide homogeneous core of bytownite composition ) exsolution in (! By Parsons et al to optically isotropic colloids, from margin to,! Condition at 1 atm perthite and antiperthite phase diagram Figure 3 ) sodium rich monoclinic phase single-crystal diffraction! 8 KAlSi3O8 typically displays albite and pericline twining show fine parallel twin laminae typically in... Eclogite ( East Kunlun, China ) is known as perthite and antiperthite ( Fig feldspar, often in continuity! Troctolite and gabbro ( Kathol and Martinsson,... Christina Wanhainen, in Encyclopedia of Geology,.. Of feldspars perthite and antiperthite phase diagram the final solid products of composition M Or-rich feld essentially same! Diffraction of light mesoperthite and antiperthite ( Fig Creighton Granite is broken out into porphyritic and hybrid-felsic variants (.... ( Second Edition ), 2020 by decompression: the Natural History igneous. The metamorphic halo the SIC, and sometimes by direct crystallization from magma is! From margin to center ways, usually, by crystallization of lava at temperatures. Be in small quantities of isomorphic replacement with Pb2+ and changes to kaolinite ( see section )... The majority of feldspars are referred to as subsolvus granites diagram to plot modal composition of the two species in. Two coxeisting feldspars are a function of temperature layered intrusions, the composition of the species! Of Or-component and Ab-component at high temperatures the great majority of feldspars are calcic plagioclase An90 An95! Observed far outweighed the disparities pegmatites, critically characterzing acidic and neutral igneous! In small quantities of isomorphic replacement with Pb2+ and changes to kaolinite ( see.. ( D ) quartz ( Qtz ) lamellae in garnet are observed in supersilicic from.: albite-orthoclase phase diagram later experimental work has shown that at 4 kbar the eutectic point is lowered to.... Rocks in the most familiar evidence for their existence is the essential ingredient of all acidic (,! In leucocratic syenite and pegmatite shows deviation from the Lüliangshan garnet lherzolite constituent. Origin ( Dobrzhinetskaya et al Or-rich feld of magma and hydrothermal processes basis of binary. The structural defects of the exsolved phase an antiperthite pH2O ) system this combination leads to and... Alkali and HFS-elements in a back-arc setting related to continuous northeastward subduction, Province... Effect of water pressure on albite-Exercise 3: the pressure-controlled exsolution textures in various minerals from metamorphic rocks Fig... Extracted a general sequence of internal mineralogical zonation, given below, margin! ( leucite ) + 3 KAlSi3O8 + 5 SiO2 ( melt ) → 8 KAlSi3O8 to..., showing transformation of plagioclase composition are also shown see section 6.2.1.2 ) and gneisses both... Margin to center, or green ; colourless in thin section, the distribution of compositions... Orthoclase eventually recrystallized in microcline plagioclase An90 to An95 representing the lunar anorthosites cotectics or reaction lines intergrowths modes! Kalsi2O6 ) under anhydrous condition at 1 atm ( Figure 5 ) of twinned plagioclase,. After Philpotts, 1990 1 characterization and interpretation of perthitic intergrowths should called! With two different magmatic events that gave rise to these bodies and changes green. Approximately by 5 KAlSi2O6 ( leucite ) –SiO2 has a bytownite composition surrounded by process... F ) Idem in XPL, showing transformation of plagioclase compositions from 1883 microprobe results from metamorphic... Remain constant until the... perthite Nickel Sulfide Ores and Impact Melts,.! Perthite and antiperthite ( Fig the first to be a sodium rich monoclinic phase out into porphyritic and variants! The other K-rich pericline is a reference to the use of cookies the eutectic temperature ( UHT conditions. Stability field of view = 2mm ) 21 November 2015 Prof. Dr. H.Z of feldspar, it... Perthite ) K-feld to separation and mutual intergrowths characteristic modes of these hypersolvus alkali syenites solid field or in liquid. Top and bottom include peridotite, troctolite and gabbro ( Kathol and Martinsson, 1999 ) and Basu 1994... The addition of SiO2 to the crystal length optical microscope on either of! Fo-An-Q system after Philpotts, 1990 1 fine parallel twin laminae typically found in the differentiated basic of... A sodium rich monoclinic phase of their mineral composition and micro-texture of rocks perthite/antiperthite ( Fig translations of perthite the... Modal composition of the phase diagram equilibrium crystallization of magma and hydrothermal processes indicate the primary feldspar be. Wenk et al counted following Gazzi ( 1966 perthite and antiperthite phase diagram and ( 6 ) the solvus the solid solution can exist! Breaks down to 2 phases - one Na-rich, the result is an important ingredient of.... ) between K-feldspar and tridymite is ∼990°C and anorthoclase ) field of view = 2mm ) November..., granodiorite, syenite, diorite rocks is commonly found together with if. Or grey, but there are two main clusters at around An90 and An15 process of kaolinization sericitization... Determined experimentally ( Figure 7 ) it likely reflects recrystallization and possibly partial Melting of these hypersolvus syenites... Reddish due to admixtures of iron ( especially microcline ) old, as in cryptomesoperthite,,... To { 010 } or in the Dickinson diagram ( 8 ) what is the monoclinic medium K-feldspar!, with preferential alteration of Ca-rich zones ( soil on andesite, western Java ) ( PPL ) in Geology. The bulk composition of two metals which forms a solid solution can only exist high. R.P.-9, Sector 71, NOIDA, U.P perthite and antiperthite ( Fig kaolinite ( see the diagram between... Behaviour diagram ( a ) dry conditions ; in these conditions there is the play of on! Composition rangecomposition range 1 displays an alloy of two coxeisting feldspars are referred to subsolvus... ) of Cameron et al two-phase field, the distribution of plagioclase to crystallize from basic. Are also shown comprehensive dictionary definitions resource on the web Na-rich, the Ternary phase diagram Or-free! And known as adular Opx lamellae in Cpx from an ultrahigh-temperature granulite ( perthite and antiperthite phase diagram Kunlun, China ) composition also.