Kinetics and Mechanisms of Acid‐pH Weathering of Pyroxenes

Weathering of primary silicate minerals under acidic conditions occurs in contexts as varied acid mine drainage, volcanic environments, soils, stone monuments subjected to rain or Geological Carbon Storage (GCS). Considering the abundance pyroxenes on Earth crust, knowledge their weathering kinetics and mechanisms may help optimize carbonate yield GCS. Here we report experimental results from reaction clinopyroxenes augite diopside solutions. Dissolution at far-from-equilibrium formation etch pits where crack initiate propagate by stress corrosion pressure exerted swelling an amorphous, gel-like Si-rich phase, which precipitates despite undersaturation bulk solution whose is highly controlled heterogeneity mineral surface local transport mechanism. These are commonly localized within deep cracks, characterized a low fluid renewal high Si-concentrations can be reached locally, so that supersaturation with respect amorphous silica occur. Cracks most abundant case weathered flow-through experiments. This related its faster rate compared diopside, likely due higher iron content. Finally, magnesium hydrate (M-S-H) precursor forms, represents indirect evidence pH prevailing diopside-solution interface during dissolution.