Transmission electron microscope study of the domain structures associated with the b-, c-, d-, e- and f-reflections in plagioclase feldspars |
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Authors: | A. C. McLaren D. B. Marshall |
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Affiliation: | 1. Department of Physics, Monash University, 3168, Clayton, Victoria, Australia
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Abstract: | Ten specimens of plagioclase feldspars (An100 to An25) have been examined by transmission electron microscopy using dark field and direct lattice imaging. The specimens are classified into two groups: (i) those that have been quenched from the melt (synthetic An100, An95, An66 and An50) and (ii) those that have been cooled relatively slowly (An94, An77, An75, An52, An32 and An26). The observed contrast is interpreted in detail using the two-beam dynamical theory of electron diffraction contrast. The fault vectors of the antiphase boundaries (APBs) observed in An100 and An77 are determined. Direct resolution of the sublattice and superlattice in specimens of intermediate composition (An75 to An25) indicates that the superlattice is not a regular array of out-of-step faults and is probably due to a simple sinusoidal distortion of the structure. Only three specimens (An100, An77 and An50) exhibited a single structural type. All the remaining specimens consisted of intergrowths of two structural types. The structural type present in any particular specimen depends upon its An-content and thermal history. The rate of transformation from any structural type to a lower-temperature structural type appears to decrease with decreasing An-content. |
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