Identification of crystalline substance and crystalline phases in a specimen is achieved by comparing the specimen diffraction spectrum with spectra of known crystalline substances. Xray diffraction data from a known substance are recorded as a powder diffraction file (PDF). Most PDFs are obtained with CuKα radiation. Standard diffraction data have been published by the ICDD, and they are updated and expanded from time to time. When we need to identify the crystal structure of a specimen that cannot be prepared as powder, matches of peak positions and relative intensities might be less than perfect. In this case, other information about the specimen such as chemical composition should be used to make a judgment.