Large-angle convergent-beam electron diffraction (LACBED) characterization of (021) twinning in natural coesite

摘要

Large-angle convergent-beam electron diffraction (LACBED) is used to characterize a (021) twinning in metamorphic coesite from Parigi, Dora-Maira Massif, Western Alps. The orientation relationships between the adjacent parts of the twin are characterized in detail and the twin is described as a mirror along (021). This microscopic description is fully consistent with original descriptions of twinning in synthetic coesite. Due to the quasi-hexagonal dimensions of coesite (belonging to the monoclinic space group C12/c1 with a similar to c and beta similar to 120 degrees) such a result could not have been obtained using conventional electron diffraction experiments.