The successful development of a number of branches of socialist industry, and first of all of metallurgical industry, depends to a large extent on the quality of refractory ceramic products. Modern metallurgy, which uses oxygen blast in blast furnaces and high-speed methods of steelmaking in open-hearth furnaces, needs new, more highly refractory materials than the current ones, whose melting temperature does not exceed 1800- 2000°. The given data (see article) emphasize the great urgency of the problem of new highly refractory materials. The main reason for the difficulties arising in the search for new highly refractory materials is the lack of state diagrams of oxide systems that make up refractory masses. The number of materials from which refractory masses are usually made is rather limited. Therefore, the study of the previously unstudied state diagram of the system MgO - Cr₂O₃ - ZrO₂ (melting point MgO - 2800 °, Cr₂O₃ - 2110 °, ZrO₂ - 2715 °) can have not only theoretical but also practical value in the search for new refractory materials with higher physical and chemical properties. Triple mixtures of magnesium oxide, chromium oxide and zirconium dioxide, whose compositions are located in the region of solid solutions, as not forming eutectics and therefore do not experience softening when heated up to melting temperatures (2200-2600 °), are new, practically important highly refractory materials.