We present the results of quantitative variable-temperature neutron powder diffraction experiments performed on the OSIRIS instrument at the ISIS facility on the pure silica zeolites chabazite and ITQ-4. Chabazite has been found to be one of the most strongly contracting materials known, with a linear expansion coefficient αv/3 varying from −0.5 × 10-6 to −16.7 × 10-6 K-1 over the temperature range 293−873 K. Full Rietveld refinement has been carried out using three different refinement strategies: free isotropic refinements, refinement using geometrical restraints, and a rigid body refinement. The free isotropic refinement was found to be the most successful. In agreement with previous studies on ZrW2O8 and Sc2(WO4)3 type materials, we suggest that changes in Si−O−Si interpolyhedral bond angles are the driving force for the contraction mechanism. ITQ-4 has also been found to contract over the temperature range 95−510 K, with αv/3 varying from −2.2 × 10-6 to −3.7 × 10-6 K-1 over this range.