High resolution transmission electron microscope study of exsolution in synthetic pigeonite
Feuer, Helmut; Schröpfer, Lothar; Fuess, Hartmut; Jefferson, David A.
European Journal of Mineralogy Volume 1 Number 4 (1989), p. 507 - 516
published: Aug 31, 1989
manuscript accepted: Feb 1, 1989
manuscript received: Feb 1, 1989
ArtNo. ESP147050104003, Price: 29.00 €
Abstract The exsolution products in synthetic pigeonites of composition Wo6-9En75-79Fs15-16 have been characterized by high resolution transmission electron microscopy. The pyroxene crystals were prepared from the melt and cooled to room temperature at a rate of 8°/h. Antiphase domain boundaries, "tweed"-patterns due to spinodal decomposition, coarse augite exsolution lamellae approximately parallel to (001) and (100), and augite like platelets with a distinct S-shaped morphology have been observed in pigeonites which are in contact with orthopyroxene (Wo4En83Fs13). Diffraction patterns of those platelets display streaks and satellite reflections convoluted about the reciprocal lattice of the pigeonite host. The satellites reflect shape, orientation and periodic arrangement of the precipitates which are approximately parallel to (101). Lattice images suggest a C-centred pyroxene structure (augite related) for the platelets although the diffraction patterns do not give direct evidence for a distinct augite lattice. A full calculation of the platelet structure in order to simulate the high resolution images was not possible.