Form

Forme (Fr), Forma (It), 結晶形 (Ja)

For a point group P a form is a set of all symmetrically equivalent "elements", namely:

• in vector space, a crystal form or face form is a set of all symmetrically equivalent faces;
• in point space, a point form is a set of all symmetrically equivalent points.

The polyhedron or polygon of a point form is dual to the polyhedron of the corresponding face form, where "dual" means that they have the same number of edges but the number of faces and vertices is interchanged.

Forms in point groups correspond to crystallographic orbits in space groups.

See also

• Chapter 10 in the International Tables for Crystallography, Volume A