Garnets, A 3 B 2 C 3 O 12 , are an important group of minerals and have potential uses in the safe immobilisation of high-level nuclear waste. They have been found naturally to incorporate Zr, Ti and Fe, three elements of interest in the safe storage of nuclear waste. Kimzeyite, Ca 3 (Zr,Ti) 2 (Si,Al,Fe) 3 O 12 , is a naturally occurring garnet that contains Zr in a high percentage$30 wt%. For such a material to be of potential immobilisation for nuclear waste the structure needs to be completely understood. Electron channelling studies have shown that the Zr/Ti cations are located on the Y-site, with the Al/Fe cations located on the Z-site. This work has investigated synthetic analogues of kimzeyite, Ca 3 (Zr,Hf) 2 (Al,Fe,Si) 3 O 12 , by neutron powder diffraction, using the C2 spectrometer at the Chalk River nuclear facility, coupled with 57 Fe Mo¨ssbauer spectroscopy. Such work has allowed the structure of the synthetic material to be determined along with the distribution of cations across the X (CN ¼ 8), Y (CN ¼ 6), and Z (CN ¼ 4) sites. Results have shown that it is possible to synthesise Ca 3 (Zr,Hf) 2 (Al,Fe,Si) 3 O 12 with a range of Al/Fe ratios containing Zr and Hf. The Mo¨ssbauer data has indicated the Fe is located on the Z site. The structural analyses show that the unit cell changes linearly as a function of composition, and analysis of the disorder indicates that the Zr, Hf reside on the Y site and the Al, Fe, and Si reside on the Z site.