Precipitation of minerals is affected by water solubility within silicate melts, which typically exists as hydroxyl groups bound to Si or Group 1 and Group 2 cations in concentrations ranging from approximately 6-7 wt. %. Specifically, the equilibrium of water and dissolved oxygen yields hydroxides, where the K has been approximated between 0.1 and 0.3.
This inherent solubility is low yet varies greatly depending on the pressure of the system. Rhyolitic magmas have the highest solubility, ranging from approximately 0% at the surface to nearly 10% at 1100 °C and 5 kbar. Degassing occurs when hydrous magma is uplifted, gradually converting the dissolved water to aqueous phase. This aqueous phase is typically abundant in volatiles, metals (copper, lead, zinc, silver and gold), and Group 1 and Group 2 cations. Dependent on which cation the hydroxyl is bound to, it significantly impacts the properties of a volcanic eruption, particularly its explosiveness. During unusually high temperature and pressure conditions exceeding 374 °C and 218 bar, water enters a supercritical fluid state and becomes no longer a liquid or a gas.