Cristobalite, a silica (SiO2) polymorph, is commonly observed in volcanic edifices and is hypothesized to form as a result of vapour-phase precipitation and devitrification of volcanic glass at conditions outside its supposed stability field. This study investigates the role of mineralizing agents (Al3+, Na+, and K+) in promoting metastable cristobalite formation at temperatures, pressures and chemical conditions relevant to volcanic domes. We synthesised four simplified rhyolitic glasses, controlling for Al3+, Na+, and K+ content. These glasses are ground to grain sizes of 60-90 µm and subsequently exposed to acidic and alkaline fluid conditions in externally heated, closed-system, stainless steel pressure vessels at 200°C and water vapor pressures of 1.5 MPa, for up to 11 weeks. Under acidic conditions, post-experiment fluid analyses by ICP-OES show a progressive increase in Si, Na, and K over 11 weeks, suggesting that these systems did not reach equilibrium. Under alkaline conditions, no clear trend in the concentration of these elements is observed. These data suggest that the dissolution of these elements from the glasses is more efficient under acidic conditions. Glass analyses by X-ray powder diffraction (XRPD) show that quartz (3.4 wt.%) and cristobalite (0.2 wt.%) formed under acidic conditions, while only quartz (1.4 wt.%) was detected under alkaline conditions over the same time period. Research is ongoing to quantify the composition of newly formed silica polymorphs and to compare these laboratory results to natural volcanic rocks.