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Electron diffraction patterns of gold, used for calibration purposes. The ring pattern (A) indicates that the material is polycrystalline and the spot pattern (B) indicates that it is a single crystal: amorphous materials give no regular pattern. The spacing of the rings gives information on crystalline structure and can be usefully applied to distinguish the various crystalline forms of silica (quartz, tridymite, cristobalite) for example.
(Courtesy of Dr M Wineberg, London, UK.)
