Analytical Electron Microscopy of Exsolution Lamellae in Plagioclase Feldspars

  • G. Cliff
  • P. E. Champness
  • H.-U. Nissen
  • G. W. Lorimer


Lamellar structures occur in plagioclase feldspars representing low-temperature conditions for three composition ranges; An2–26 (theperisterites), An42–58 (labradoritas) and An65–95 (bytownites). Diffraction evidence and qualitative scans in the ion-or electron-microprobe have shown that, for the peristerites and bytownites, two phases with different anorthite contents arepresent (Weber, 1972; Nissen, 1974). Estimates of the compositions of the two phases in peristerites from measured cell dimensions give approximately An0 and An25 (Laves, 1954; Gay and Smith, 1955; Brown, 1960; Ribbe, 1960). In bytownites measurements of the proportions of the two phases as a function of bulk composition lead to estimates of about An67 and An95 for the compositions of the two phases (Nissen, 1971, 1974).


Minor Phase Major Phase Count Ratio Plagioclase Feldspar Exsolution Lamella 
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© Springer-Verlag Berlin · Heidelberg 1976

Authors and Affiliations

  • G. Cliff
  • P. E. Champness
  • H.-U. Nissen
  • G. W. Lorimer

There are no affiliations available

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