Minerals that make up rocks and soils are thrown out of equilibrium when the chemistry of their surroundings changes. Shifts in pH or the concentration of ions in water make minerals dissolve, grow, or react in other ways. These reactions are influenced by the arrangement of atoms at the interface—where minerals and water touch. Historically, it has been hard to study these structures while reactions are proceeding because the interface is constantly changing, limiting our understanding of how the structures control reaction speed.