Crystal structure of a-CaSi₂O₅ synthesized at conditions of 1500°C and 10 GPa, has been solved and refined in centrosymmetric space group P1. The structure is closely related to that of titanite, CaTiSiO₅ and consists the square pyramid five-fold coordination of silicon by oxygen. The ionic radius for five-coordinated Si calculated from the bond distances is 0. 33 Å.