Advanced experimental techniques in geochemistry

Abstract

Has anyone wondered why clay is the most ubiquitous geomaterial in earth’s crust but we still are in need of developing more sophisticated methods and techniques to properly characterize it? The main reason is: it is not well defined; in fact, the variations in local clay structure and composition are virtually infinite. Geological origin descriptions provide an important foundation for clay models needed for interpretation of the experimental data collected on heterogeneous samples. Chemical analysis is the most essential step in mineral analysis; it usually follows structural analysis, in order to identify the major crystalline phases and impurities. Non-destructive techniques that are complementary to crystallography are electron microscopy and NMR spectroscopy for structure determination and study of dynamics. Some of the important methods in clay mineral identification are determination of coherent scattering domain size from XRD, Bertaut-Warren-Averbach analysis, counting layers on TEM lattice-fringe images, Pt-shadowing, and calculation of the average number of fundamental particles per MacEwan crystallite. A combination of the X-ray and neutron diffraction can be used for advanced model refinement, by utilizing a technique devised by Rietveld. Synchrotron radiation can be advantageous to laboratory sources. Several other advanced techniques are described in this chapter as well. Advances (including in situ analysis) in experimental methods go hand-in-hand with advances in conceptual understanding of the experimental observations.