<p>The solubility of phenakite (Be₂SiO₄) in granite melts was experimentally studied at temperatures of 1000 and 1100°C and pressures of 1 and 4 kbar in dry conditions and in the presence of 10 wt % H₂O. The starting materials were granite glasses with agpaitic coefficient of 1–2.5 and natural phenakite. It was found that the solubility of phenakite increases with increasing agpaitic index (Na + K)/Al of the melt, and the solubility of BeO in hydrous melts is higher than in dry ones. The solubility of phenakite also increases with pressure. The obtained experimental data were generalized with the previous data in the form of an equation describing the solubility of BeO in alkaline-granite melts coexisting with crystalline Be phases depending on the agpaitic index, temperature, and pressure. The results of the experiments and their generalizations support the model of Be concentration in alkaline hydrous melts—the products of differentiation of granite magmas.</p>