What are the final solid products of composition X? 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. Definition of solvus.The effect of water pressure on albite-Exercise 3: Granite, granodiorite, syenite, diorite rocks. 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. 1 displays an alloy of two metals which forms a solid solution at all relative concentrations of the two species. Values which show more than a 5% divergence in the extinction angles for adjacent twin lamellae should be discarded, but lesser variations may be averaged; it is essential to take measurements from several (6–12) suitable grains, and the highest extinction angle must then be used. The color is usually white and sometimes changes from pale pink to reddish due to admixtures of iron (especially microcline). Results of modal analyses are commonly plotted in triangular diagrams ostensibly for uniform communication with the three poles marked as Q, F, and L or R or RF. In the field, the Creighton Granite is broken out into porphyritic and hybrid-felsic variants (Fig. The Perthite Monzonite Suite (PMS) is represented by large peraluminous to metaluminous intrusions in the northwestern part of Norrbotten, but such rocks are rare in the eastern part (Geijer, 1931; Witschard, 1984; Bergman et al., 2001). (D) Quartz (Qtz) lamellae in omphacite from a UHP eclogite (East Kunlun, China). 2. It is found only in young volcanic discharges or volcanic rocks (rhyolite, trachyte, and dacite). Fig. But see Bangs-Rooney and Basu (1994) for a possible alternative. It is notable that both zoning schemes recognized assemblages of quartz plus lithium aluminosilicates or equivalent phosphates (zones (7) or [6]) as primary, despite their distinctly non-granitic compositions (cf. The Creighton Granite forms the immediate footwall to parts of the Creighton Deposit, and it develops a black color in close proximity to the base of the SIC and the associated mineral zones; this rock is termed the “Black Porphyry” and appears only to be developed in the footwall of the Creighton Embayment. Modal analyses by these three methods of the same thin section of a sandstone plot differently (Fig. Microcline typically displays albite and pericline twining show fine parallel twin laminae typically found in the alkali feldspars microcline. This zoning sequence was later revised by Norton (1983) on the basis of exposures in the large lithium-rich pegmatites of Tanco, Manitoba (Crouse and Černý, 1972), Bikita, Zimbabwe (Cooper, 1964), and similar pegmatites in the Black Hills, South Dakota: Plagioclase–quartz–spodumene (or petalite or montebrasite or both), Quartz–spodumene (or petalite or montebrasite or both). It is a typical mineral of the sillimanite zone of metamorphism and, in rocks of argillaceous composition, does not appear at lower grades. Label the fields and any peritectics or eutectics on the diagram. The most familiar evidence for their existence is the play of iridescent colors they produce by the diffraction of light. (E) Plagioclase phenocrystal in basalt fragment, showing complex pattern of alteration (volcanic ash soil, Isla Santa Cruz, Galápagos) (PPL). Homogeneous pegmatites of … Fig. Figure 6. Plagioclase is not stable in the P–T environment of the eclogite facies; under these conditions the albite and anorthite components enter the compositions of omphacite and garnet, respectively. In either scheme of zoning, the outer zones (1)–(3), corresponding mostly to the border and wall zones, are dominated by plagioclase. In sedimentary rocks, plagioclase feldspars may occur via a variety of sources, including detrital minerals, authigenic minerals, and the products of volcaniclastic activity. + MELT Ab-rich feld. 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). Fig. Refractive indices of the plagioclases. Mattinson, in Gondwana Research, 2017. (a) Dry conditions; in these conditions there is the presence of a large stability field of leucite. Depending on the original composition we can end up with K- … 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. Variation of refractive indices with composition for the alkali feldspars; α and γ for the sanidine–anorthoclase–high albite series are shown as dashed lines, and those for the orthoclase (microcline)–low albite series as full lines. 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).

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