Manganese redox cycling drives the epitaxial growth of dolomite on metastable kutnahorite templates

Daniel A. Petrash, Or M. Bialik , Yihang Fang, Maartje Hamers, Travis B. Meador, Tomaso R.R. Bontognali, Michael Boettcher, Oliver Plümper

Fine-crystalline, fabric-preserving dolostones in deep-time successions defy high-temperature burial models, implying an elusive low-temperature formation pathway hindered by the kinetic hydration barrier of Mg²⁺ and the thermodynamic miscibility gap separating calcite from ordered dolomite. Here, we demonstrate a kinetically facile route to self-assembling dolomite driven by the synergy of manganese redox cycling and carboxyl functionalization. Using a bio-inspired electrochemical reactor, we show that electrochemical valence-state modulation selectively regulates Mn2+ co-precipitation. Unlike inorganic controls where manganese is rapidly sequestered into non-templating phases, the functionalized system stabilizes reactive Mn(III) intermediates. This sustained redox cycling prevents irreversible oxide immobilization and templates the rapid nucleation of spheroidal magnesian-kutnohorite. Nanostructural characterization reveals a core-shell architecture where this metastable, isostructural precursor serves as a lattice-distorted scaffold, enabling the heteroepitaxial growth of substitutionally disordered dolomite cortices. Mechanistically, localized acidity from redox cycling triggers a "proton-driven cation pump," actively liberating Mg²⁺ from the functionalized hydrogel reservoir to the mineralization front. This electrochemical mechanism offers a unifying geological model that links the massive fabric-retentive dolostones of the Precambrian to ancient Mn-stratified oceans, while explaining the Phanerozoic scarcity of dolomite as a consequence of global oxygenation decoupling the manganese redox shuttle from shallow marine environments.