Characteristics of soil nanoparticles before and after the DCB extraction in the sample LB. a Bright-field images of ferrihydrite-clay mineral associations before the extraction showing ferrihydrite particles (indicated by arrows) distributed around and on the surface of large illite/smectite lamellae. b The high-resolution TEM image and its Fourier transform show randomly oriented ferrihydrite nanoparticles (Fhy) with a poorly oriented structure, dominated by 2.5 Å lattice spacing. c Bright-field images of the illite/smectite (Ilt/Sm) surface after the DCB extraction show the lack of ferrihydrite particles with high contrast. d The high-resolution TEM and its Fourier transform indicate a more ordered clay structure of illite/smectite mixed-layer species with considerable Fe content (as shown by EDS analysis). The illite/smectite particles may contain significant Fe concentrations even after the DCB extraction showing structural Fe in the smectite component (see EDS spectrum).