X-RAY POWDER DIFFRACTION METHODS ON CD-ROM

We have compiled and documented on a CD-ROM the methods used to perform X-ray powder diffraction at the USGS Center for Coastal and Marine Geology in Woods Hole, Massachusetts. Although optical microscopy can be readily used to identify sand and coarse silt-sized crystalline material, X-ray powder diffraction is still the most common technique used to study the characteristics of crystalline structure and to determine the mineralogy of finer grained sediments, especially clays. As a method, X-ray diffraction is rapid, non-destructive, requires only small amounts of material, and can be used to perform semi-quantitative analyses of poly- mineralic mixtures. The contents of this unique CD, which are supplied in HTML format and provide technical information that can be included in the metadata of individual data sets, are also useful for training and analytical planning. The CD is divided into four chapters: (1) an X-ray powder diffraction primer, which discusses theoretical principles and equipment geometry, provided with schematics and photographs to broaden the perspective and understanding of the user; (2) a methods manual that contains centrifugation software, tables and templates in several formats for converting measurements of degrees two theta to d-spacings, as well as illustrated preparatory, analytical, and interpretive procedures; (3) a discussions section on individual clay minerals that includes structure, paragenesis, bibliographies, and superimposed X-ray patterns of reference specimens showing their characteristic diffraction maxima and the effects of various treatments; and (4) a clay-mineral identification flow diagram presented in five formats.