Abstract: A high-pressure modification of NaAlSiO₄, with the calcium ferrite structure was synthesized at pressures higher than 24 GPa using a double-stage split-sphere type high-pressure apparatus. The unit cell dimensions are: a=10.1546(8), b=8.6642(8), c= 2.7385(4) Å, and V = 240.93(3) ų with the space group Pbnm. Calculated density is 3.916(1) g/cm³. The crystal structure was determined by the ordinary powder X-ray method. Both M1O₆ and M2O₆ octahedra run parallel to the c-axis, forming edge-shared double chains. The shared edges exhibit remarkable shortening (2.25–2.39 Å). Sodium atoms are located in the ‘tunnel’ formed by the linked double chains, being in eightfold co-ordination. The structure is very similar to that predicted by Dempsey and Strens (1976) with the aid of the DLS method. The possible instability of the calcium ferrite type of Mg₂SiO₄ is discussed.