Polymerization of aqueous silica in H2O-K2O solutions at 25-200 °C and 1 bar to 20 kbar

► SiO2-K2O-H2O system characterized via Raman spectroscopy at ambient and elevated PT. ► Polymerization promoted by increasing [SiO2] and decreasing P, T, and [K2O]/[SiO2]. ► Ab initio calculations suggest polymerization beyond monomer and dimer at high PT. ► Results confirm previous NMR characterization at ambient P. ► Results provide foundation for characterizing aqueous SiO2 in crust/mantle.