Centre of Inversion on Sixfold Screw Axis (63 / m)

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The symbol above shows a six-three 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 six-three screw axis, hence the written symbol "63 / 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 sixfold inversion axis (-6) 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.

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