Characterization of composition and structure of clay minerals in sandstone with ptychographic X-ray nanotomography

Three-dimensional analysis of microporous and fine-grained particles in natural stone is important for understanding their internal fluid flow processes and to allow their internal dynamics to be modeled. These processes are of great interest in oil, gas and groundwater studies, as well as for the weathering of natural building materials. For features above 1 μm methods such as X-ray micro-computed tomography (μ-CT) can provide non-destructive, quantitative analysis. Non-destructive 3D imaging at resolutions below 300-400 nm, however, has remained a challenge until recent developments at synchrotron beam lines. In this paper we visualize the microstructure of clay mineral samples extracted from two different sandstones at 3D spatial resolutions down to 45 nm, using ptychographic X-ray computed tomography (PXCT). Furthermore, the relative humidity of the environment during these experiments was controlled in order to assess its influence on the analyzed samples. Based on these high-quality images, we were able to acquire non-destructively quantitative 3D information on mineral content and distribution, porosity and connectivity of clay mineral clusters inside sandstone.