Being a constituent of numerous minerals, magnesium silicates are of extraordinary interest for the Earth and planetary sciences, as well as for cosmology. At the same time, they have many industrial and technological applications, including those associated with the building industry. Reliable data on the thermodynamic properties of magnesium silicates at high temperatures are necessary for the forecasting of various natural phenomena, optimization of technological parameters in a wide range of technological processes and production techniques, and for the development of novel ceramic and ceramic-metal materials, glasses, fluxes, slags and slag-forming mixtures. However, these data are at present almost entirely absent. Results from the direct measurement of thermodynamic characteristics for a magnesium-silicate melt have been reported by a single group only [1, 2]. However, these results do not agree with the data related to the phase diagram [3]. The description of the thermodynamic characteristics of intermediate phases is mainly based on low-temperature measurements and the extrapolation of temperature dependence for specific heats [4]. The present study is aimed at determining the thermodynamic properties of all phases existing in the MgO‐SiO 2 system within the wide temperature range 1571‐1873 K for the entire set of chemical compositions. The measurements were performed by the Knudsen mass-spectrometry method using the approach of [5], which was based on the generation of volatile reaction products formed as a result of the reduction of oxide components. When the MgO‐SiO 2 mixture interacts with the reducing agent R, which is, in this case, either the material of the effusion cell itself (R = Ta, Nb, Mo) or the purposefully added powders of these metals, the following chemical reactions occur: n MgO(solid, liquid) + R(solid)