Centre of Inversion on Fourfold Screw Axis (42 / m)


The symbol above shows a four-two screw axis perpendicular to the plane of the screen, i.e parallel to Z, with a centre of inversion on the axis. This combination results when there is a mirror plane perpendicular to the four-two screw axis, hence the written symbol "42 / m".

A fractional value next to the symbol indicates the height of the inversion centre above the XY plane. The mirror plane is separated from the centre of inversion by 1/4 of the repeat distance in the lattice along the axis direction. Although not shown, a fourfold inversion axis (-4) is also present with its inversion point at the same height as the mirror plane, i.e. at 1/4 along the axis from the centre of inversion.

© Copyright 1995-2006.  Birkbeck College, University of London. Author(s): Jeremy Karl Cockcroft