International Union of Crystallography

The International Union of Crystallography (IUCr) is a member of the International Council for Science (ICSU) and exists to serve the world community of crystallographers.

It was founded 1948 with the help of Ralph Walter Graystone Wyckoff who served as Vice-president and President from 1951 to 1957.

The IUC notation is the notation for the symmetry group adopted by the International Union of Crystallography in 1952. It names the wallpaper groups with a 4 character name. First it has a P or C for primitive or centered groups. Groups are given a number 1, 2, 3, 4, or 6 for the highest order of symmetry. Groups can have one or two reflections, given as vertical mirrors first (horizontal reflection), and horizontal second (vertical reflection). A simple reflection is given an m (mirror), and a glide-reflection is given a g. Place holder 1 are given for an orthogonal direction with no reflections.