The properties of CuSiF6 · 6H2O and Cu0.9Zn0.1SiF6 · 6H2O crystals were studied using X-Ray analysis and adiabatic calorimetry. The measurements cover the temperature range from 100 to 310 K. The enthalpy of transition for the phase transitions which occur at 300 K have been obtained and the crystal lattice parameters of the high-temperature phase of Cu0.9Zn0.1SiF6 · 6H2O have been determined. These