Fig. 2: Reconstruction of the PXCT 3D electron density distribution after segmentation.

The panels highlight the different materials in (a) and (b). Most of the iron oxide grains have a major elongation axis between 80 and 600 nm (c) and an axial ratio (P1/P3) <2. In (d), the shape parameter (ϵ, revisit Equation (4)) is quite scattered, showing a well-distributed population of triaxial (ϵ ≈ 0), prolate (ϵ << 0) and oblate (ϵ >> 0) grains. The magenta dashed line represents the cumulative density distribution of the histograms.