Abstract The phase equilibria in the SiO 2 ‐rich region of the Li 2 O‐, Na 2 O‐, and K 2 O‐SiO 2 systems at 1550°C to 1650°C were experimentally studied to determine accurate liquidus of SiO 2 in the systems. A classical equilibration/quenching method was used, and the equilibrated samples were analyzed by X‐ray diffraction (XRD) and electron probe microanalysis (EPMA). Samples were contained in sealed Pt crucibles and held at the target temperatures for 7–21 days to reach equilibrium condition. Sealed Pt crucibles were employed to avoid the volatile loss of alkali oxides during high temperature phase equilibration and hydration upon quenching. Accurate liquidus of SiO 2 in alkali‐silicate systems was determined for the first time, and the results were analyzed using the limiting slope rule in order to understand the dissolution behavior of alkali oxides in SiO 2 melt. It was confirmed that alkali oxide dissolves in SiO 2 melt by producing Li + , Na + , and K + cationic species rather than Li 2 2+ , Na 2 2+ and K 2 2+ species.