Nanoscale imaging of shale fragments with coherent X-ray diffraction

Despite the abundance of shales in the Earth’s crust and their industrial and
environmental importance, their microscale physical properties are poorly
understood, owing to the presence of many structurally related mineral phases
and a porous network structure spanning several length scales. Here, the use of
coherent X-ray diffraction imaging (CXDI) to study the internal structure of
microscopic shale fragments is demonstrated. Simultaneous wide-angle X-ray
diffraction (WAXD) measurement facilitated the study of the mineralogy of the
shale microparticles. It was possible to identify pyrite nanocrystals as inclusions
in the quartz–clay matrix and the volume of closed unconnected pores was
estimated. The combined CXDI–WAXD analysis enabled the establishment of a
correlation between sample morphology and crystallite shape and size. The
results highlight the potential of the combined CXDI–WAXD approach as an
upcoming imaging modality for 3D nanoscale studies of shales and other
geological formations via serial measurements of microscopic fragments.