Recognizing the (false symmetry) triclinic (aP) to (true symmetry) centred monoclinic (mC) pathology

摘要

Some fifty-odd published examples of corrections from (false symmetry) triclinic to (true symmetry) centred monoclinic (aP to mC) are analysed to see whether the need for correction of symmetry should have been obvious to the original investigators. We conclude that about two-thirds of the examples were transparent in that special features of the dimensions of the reduced triclinic cell should have aroused the suspicions of the investigator. For the other third, calculation of the metric tensor would have indicated the possibility of symmetry higher than triclinic. However, it should always be remembered that the true symmetry of a crystal is revealed by intensity rather than by metric relationships, or by other techniques such as optical microscopy.