X-Ray Diffraction Laboratory
The department houses a laboratory for study of minerals and crystalline substances using X-ray diffraction techniques. Because the wavelength of X-rays are similar to the spacing of atoms in crystals, X-rays are scattered by crystals in much the same way that a diffraction grating scatters light. Discrete angles and intensities of scattering correlate with the geometric pattern of atoms within a crystal. Examination of the pattern and intensities of scattering from a sample are used to interpret its crystal structure and to identify the mineral or crystalline compound constituting the sample.
Our X-ray diffraction facilities are used to identify minerals in specimens within the collections and crystalline substances in experimental syntheses from other laboratories. In addition, the facilities are used by the conservation lab and other departments to identify such things as pigments in paints, degradation products on artifacts, and minerals in fossils. The basic facility for this a Philips PW-1710 automated powder (Bragg-Brentano) diffractometer attached to a 2000 watt Cu X-ray source (photo on right) and controlled by a PC.
A Rigaku DMAX-Rapid Microdiffraction system (photo on left) was acquired as a shared facility with Earth & Environmental Sciences Dept. at Columbia University, Research Conservation Dept. at the Metropolitan Museum of Art and AMNH with NSF funding in 2004. It can perform microdiffraction on small samples (~100 microns) or on surfaces of small objects, as well as single crystal diffraction measurements. It is used routinely to assist in mineral identification of specimens in the mineral collection, mineral components of rocks being studied as part of research projects, phase identification and cell parameters from multianvil experiments, and study of pigments, coatings, and alterations on art and archaeological objects.
Diffraction labs are used under the direction of Curator George Harlow.