A study has been made of the diffraction contrast fringe patterns observed by transmission electron microscopy in alexandrite (Al 2— x Cr x BeO 4 ), the chromium bearing variety of chrysoberyl. Evidence is presented that the fringe patterns are due to anti‐phase boundaries resulting from faults in the cation stacking within the same oxygen lattice. Models for the probable ionic configuration of such boundaries are proposed and discussed. It is shown that the diffraction contrast fringe patterns observed with different operating reflections are consistent with those expected from the proposed models.
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P. P. Phakey (1969) studied this question.
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