X-ray diffraction data are obtained on polycrystalline samples of zircon ( ZrSiO₄) and almandine (Fe₃Al₂Si₃O₁₂) from 100 to 300 K using x-ray diffraction beam line at Elettra synchrotron source. The observed thermal expansions in zircon and almandine, which differ by a factor of 2–3, are found to be in good agreement with the predictions from our  lattice-dynamical calculations. The calculations also enabled a mi-croscopic interpretation of the available experimental data.