Crystallography and X-ray Diffraction
X-ray diffraction is the definitive method for identifying minerals and other crystalline materials. X-rays are diffracted by the regular three-dimensional arrangements of atoms in crystals, and the resulting diffraction patterns are recorded by an imaging plate or other detector. A diffraction pattern is diagnostic for a particular material, and can be used as a “fingerprint” for its identification. The diffraction patterns are compared against those in a computerized database to find a match. Additionally, X-ray diffraction can be used to determine unit-cell parameters and other structural details, and for quantitative analyses of mixtures of minerals and other crystalline phases.
The primary X-ray diffraction instrument in the Department of Mineral Sciences is a Rigaku D/MAX Rapid microdiffractometer with an imaging plate detector. Diffraction data can be collected from powdered samples, aggregates, or single crystals. Typically a tiny amount of powder (a few milligrams) or a single crystal or fragment(s) are glued to the tip of a thin glass fiber, and then exposed to an X-ray beam for 5-10 minutes. Diffraction patterns can also be collected from gems, archeological artifacts, and art pieces.
In addition to the more routine applications described above, the Rigaku X-ray diffractometer is a critical tool for several research projects being carried out by scientists in the Department of Mineral Sciences. For example, Jeffrey Post uses powder X-ray diffraction to investigate how minerals in soils and sediments react with various metals and other potentially harmful chemical pollutants, and Cara Santelli characterizes minerals formed by interactions of fungi and microbes with metal-bearing solutions. X-ray diffraction is used to identify minerals and other crystalline phases and to study their atomic structures. Our is outfitted with an imaging plate detector for research and for rapid identification of small powder or single crystal mineral samples.
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