Techniques used to characterize the H₂ potential of rock. Data from (a) scanning electron microscopy of a serpentininte (modified from Lévy et al., 2022), (b) Raman microspectroscopy on H₂-rich fluid inclusions (modified from Klein et al., 2019), (c) X-ray microtomography (acquired on a Zeiss Radia Versa 510, DMEX), and (d) Mössbauer spectroscopy of a BIF (modified from Geymond et al., 2023). Chry: chrysotile, Liz: lizardite, Mag: magnetite.