X-ray diffraction (XRD) is the interaction between x-rays and the arrangement of atoms that make up the structure of crystalline materials. An X-ray diffractometer is an instrument that generates x-rays and directs them at a sample and then measures the resulting diffraction.
Although actually being diffracted, it is possible to think of the x-rays as being reflected off planes of atoms in the structure of the sample.
The instrument records these reflections and, through the application of Bragg's Law, allows the calculation of the d-spacing or distance between planes of atoms.
A single d-spacing value may be common to many materials, but the group of d-spacings for a material is representative of a particular structure unique to a given chemical substance. Thus the main application in geosciences is the identification of minerals.
Only a small amount of sample is required, although it must be powdered. All crystalline substances can be identified whether organic, inorganic, alloy, or man-made.
Students usually use XRD in conjunction with field and other lab studies of rocks and minerals in a specific area.
Outside of geosciences, chemists and physicists also make use of x-ray diffraction. Dr. Wilson in geosciences, Dr. Herzog in chemistry, and Dr. Inglefield in physics have involved students in the use of the instrument.