Investigations On Boggild Intergrowth Of Intermediate Plagioclase By High Resolution Transmission Electron Microscopy

Boggild intergrowth of an intermediate plagioclase from Ylamma, Finland was investigated by high resolution transmission electron microscopy. A quantitative chemical analysis was carried out on the exsolution lamellae by means of an energy dispersive analyzer. The chemical compositions of the two alternating phases were determined by point analysis to Ab(38.7)An(60.1)Or(1.2) and Ab(51.0)An(46.8)Or(2.2) for the thicker and the thinner lamellae, respectively. The bulk chemical composition Ab(42.0)An(56.5)Or(1.5) calculated from the thickness of lamellae was consistent with that determined by X-ray microprobe analysis except for Or contents. Continuous resolution of lattice fringes across exsolution lamellae shows matching of lattices, which is consistent with the compositional difference in the exsolution lamellae.