Abstract Possibility of study of structure of melts by research and measurement of physicochemical properties is presented in this paper. Density, surface tension and molar volume of synthetic melts in the system FeO-SiO2-Fe2O3 were measured. Conception of the melt structure is possible to describe on the basic of the result measurement of these properties with the comparison of the data of another authors. System FeO-SiO2-Fe2O3 may be considered as a solidified amorphous melt with specific noncrystallitic arrangement of atoms in the short distance. The local space heterogeneity is typical for this arrangement i.e. presence of various elements in the permanent amorphous clusters. Chemical compound of fayalite (2FeO.SiO2) is the basic part of the structure of these systems and in the melt is decomposed into Fe2+ cation and SiO44- anionic complex. The physicochemical properties of fayalite melts show the most important influence of ferrous and ferric oxides on the properties of the melts. Ferrous oxide is an oxygen donor in studied systems. According to decreasing of oxygen anions, the tetrahedral co-ordination of ferric complex is changed into octahedral. Presence of ferric-oxide and silicon-oxide complexes influences physical properties of fayalite melt. If these oxide systems are melted, the compounds are ionic decomposed on the cations (Fe2+ and FeO+), anionic complexes (SiO44-, FeO2-, Fe2O54-, SiFeO77-, FeO33- ect.) and clusters, which composition corresponds to presented chemical compounds (fayalite or magnetite).