Threefold Axis (3)


The symbol above shows a threefold axis perpendicular to the plane of the screen, i.e. parallel to Z. A threefold axis is equivalent to an anticlockwise rotation of 120° about a line. A threefold rotation about the c-axis, i.e. about the line 0,0,z, will have the corresponding symmetry operator -y,x-y,z. This axis has the written symbol "3".
In space group diagrams for cubic symmetry, all the threefold axes are inclined at an angle of 54.736° to the XY plane. The symbol for these is shown above, the dot indicating the exact position of intersection with the plane.

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