Synthesizing pure forsterite (Mg₂SiO₄) is challenging due to its strong dependence on heat treatment conditions. This study examined how the percentage of Mg₂SiO₄ phase formed during synthesis influences densification in subsequent sintering. Forsterite was synthesized via a solid-state reaction using MgO and SiO₂ in a non-stoichiometric ratio (MgO/SiO₂ = 2.05) to promote phase purity. The powder mixture was prepared by wet milling for 2 hours and then calcined at temperatures ranging from 1250°C to 1450°C for 2 hours to vary the Mg₂SiO₄ content. The resulting powders, along with an unmilled initial mixture, were compacted at 200 MPa and sintered at 1400–1500°C for 5 hours. XRD analysis confirmed that calcination at 1450°C produced pure forsterite, while lower temperatures resulted in intermediate phases. Despite differing initial phase compositions, all sintered samples ultimately transformed into pure Mg₂SiO₄. Higher initial forsterite content significantly improved densification, with the sample calcined at 1450°C (pure Mg₂SiO₄) achieving 95% of the theoretical density when sintered at 1500°C. These findings highlight the critical role of phase purity in optimizing forsterite ceramic processing.