Powder diffraction is a technique used to identify crystalline substances in the solid state.
The parallel beam is aimed at the specimen which is in a powder, and it produces a diffraction pattern that is recorded on film or with a counter tube. Each substance has a unique and characteristic diffraction pattern, as a result of the atomic arrangement of that particular substance. The diffraction pattern is analogous to fingerprints on an individual person. Different substances have different atomic arrangements or crystal structures, therefore, no two chemically distinct substances give identical diffraction patterns. Identification can be made by comparing the pattern of an unknown substance with patterns of a known substance.