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Chem Phys Solids Interfaces, Chem Soc London, 7:1–30 McLaren AC (1978) Defects and microstructures in feldspars. Kroll H, Bambauer H-U, Schirmer U (1980) The high albite-monalbite and analbite-monalbite transitions. Kroll H, Bambauer H-U (1981) Diffusive and displacive transformations in plagioclase and ternary feldspar series. Gray NH, Anderson JB (1982) Polysynthetic twin width distributions in anorthoclase. Contrib Mineral Petrol 82:13–25įleet ME (1982) orientation of phase and domain boundaries in crystalline solids. The feldspars, Manchester Univ Press, pp 440–459īrown WL, Becker SM, Parsons I (1983) Cryptoperthites and cooling rate in a layered syenite pluton: a chemical and TEM study. Am Mineral 70:356–361īrown WL, Willaime C (1974) An explanation of exsolution orientations and residual strain in cryptoperthites. Contrib Mineral Petrol 86:335–341īrown WL, Parsons I (1985) Calorimetric and phase diagram approaches to two-feldspar geothermometry: a critique. Contrib Mineral Petrol 86:3–18īrown WL, Parsons I (1984b) The nature of potassium feldspar, exsolution microtextures and development of dislocations as a function of composition in perthitic alkali feldspars. Phys Chem Mineral 10:55–61īrown WL, Parsons I (1984a) Exsolution and coarsening mechanisms and kinetics in an ordered cryptoperthite series. A diagram is given showing the relationship between ternary bulk composition and the microtexture developed in coherent perthitic alkali feldspars and plagioclases from slowly-cooled rocks.īrown WL, Parsons I (1983) Nucleation on perthite-perthite boundaries and exsolution mechanisms in alkali feldspars.

Because of the zoning, microtextures that were initiated in areas of given composition, can propagate laterally into zones of different composition. Near the intermediate zone they coarsened to give larger plates which induced Albite-twins in the plagioclase. The platelets in the outer cores arose by heterogeneous nucleation on twin composition planes and by homogeneous nucleation elsewhere. The cryptomesoperthites are very regular where Or-rich and probably arose by spinodal decomposition. The intermediate zone between the core and rim is more complex and microtextures vary over distances of a few micrometres. The overall diffraction symmetry of the mesoperthites is monoclinic, showing that exsolution started in a monoclinic feldspar, whereas that of the antiperthites is triclinic. Albite and Pericline twins in plagioclase in an M-twin relationship, together with lenticular low sanidine, were found in only one small area. The microtextures in the rims are regular cryptomesoperthitic, with (¯601) lenses or lamellae, depending on the bulk Or-content, of low sanidine in Albite-twinned low oligoclase-andesine. Thicker, through-going plates in platelet-free areas are found, which induce Albite twins in the surrounding plagioclase. With further increase in bulk Or they are homogeneously distributed in the plagioclase. At first small platelets of low sanidine a few nanometres thick and up to ∼10 nm long occur sporadically only on Albite-twin composition planes. The inner plagioclase cores are homogeneous oligoclase-andesine with Albite growth twins only, but are crypto-antiperthitic towards the outer core. The following microtextural sequence was observed. The feldspars normally have a plagioclase core and an alkali feldspar rim cores become smaller and rims larger and the An content of both decrease with distance from the contact of the intrusion. The microtextures developed during relatively slow cooling as a function of bulk composition in zoned ternary feldspars from syenodiorites and syenites in the Klokken intrusion, described in the preceding paper, were determined by TEM and their origin and evolution deduced.