“…Only the reduction in aqueous Cr(VI) to Cr(III) is well‐studied empirically and experimentally to date, with apparent fractionation factors ranging from −0.4 to −5.0 ‰ (Δ Cr(III)solid‐Cr(VI)aqueous ) depending on the reaction kinetics and electron acceptor involved in Cr(VI) reduction (e.g. Ellis, Johnson, & Bullen, ; Izbicki, Ball, Bullen, & Sutley, ; Schoenberg et al., ; Zink et al., ; Døssing, Dideriksen, Stipp, & Frei, ; Jamieson‐Hanes, Lentz, Amos, Ptacek, & Blowes, ; Scheiderich, Amini, Holmden, & Francois, ). By contrast, the limited number of available reports addressing the oxidation of Cr(III) to Cr(VI) by Mn oxides has shown isotopic fractionation in both directions, with a range of δ 53/52 Cr from −2.5 to +1.1 ‰ in generated Cr(VI) (Bain & Bullen, ; Zink et al., ; Joshi, Wang, Ellis, Johnson, & Bullen, ).…”