Threefold Axis (3)

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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.

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