The 32
crystallographic point groups may be combined with the 14
Bravais lattices to give 230 possible
space groups. These are used in
crystallography to describe the arrangement of
symmetry elements in a crystal
Using X-ray diffraction the space group of a crystalline substance may be deduced from systematic absences in the diffraction pattern. These occur when destructive interference occurs between waves diffracted from different Miller planes, and the forbidden reflection will not be present.