The pyrochlore type of MgZrSi2O7 was synthesized at 25 GPa and 1500 degrees C using a Kawai-type, multi-anvil apparatus. Powder X-ray diffraction and Rietveld analysis revealed that the phase assumed the pyrochlore structure (space group Fd (3) over barm, cubic) with the lattice parameter a = 9.2883(1) angstrom and the structural parameter x=0.4295(4). Chemical analysis by the electron probe microanalysis (EPMA) confirmed the stoichiometry of MgZrSi2O7. It was demonstrated that the eight-fold coordinated 16c site is randomly occupied by both Mg2+ and Zr4+ ions in a 1:1 ratio. The high ionic radius ratio R-A/R-B (where A and B denote Mg + Zr and Si, respectively) of 2.22 necessitates a relatively high pressure to stabilize the pyrochlore structure. (C) 2011 Elsevier B.V. All rights reserved.