X-ray diffraction (XRD) is a technique in which a crystalline sample is exposed to X-ray radiation to determine its composition.  The sample diffracts X-rays into a pattern which is unique to each crystalline substance.  The diffracted X-rays are collected by scintillations counters, semiconductor (solid-state) detectors, charge coupled devices (CCD), or other detectors. The characteristic patterns acquired are then matched to diffraction pattern libraries for compound identification.  XRD is a technique capable of providing both qualitative and quantitative information about the crystalline compounds in a sample.  X-ray diffraction is widely used for elemental, chemical, and structural analysis.  It has found wide use in the fields of geochemistry, forensic science, pharmaceuticals, and archaeology. XRD instruments are available in both bench top and field-portable models.  It is a mature technique with commercial instruments available from a number of manufacturers.