Results are provided for a mineral petrographic study of reaction with molten metals of refractory material grade PPM-85 produced by OAO Kombinat Magnezit. Features are revealed for the change in its phase and chemical composition and the wear mechanism is considered during operation in an open-hearth furnace. 6Results of mineral petrographic studies of magnesia materials used in the hearths of open-hearth furnaces make it possible to reveal features of the change in phase and chemical compositions of refractory mixes subjected to chemical corrosion during reaction with metallurgical melts in service. In this work the wear mechanism has been studied for the bottoms of open-hearth furnaces during service using magnesia powders grade PPM-85 produced by OAO Kombinat Magnezit for ramming them. Ankerhearth [1] and Jehearth [2] magnesia-dolomite mixes produced overseas have been studied previously.Material PPM-85 has been studied before and after operation in an open-hearth furnace bottom in OAO Chusovoi Metallurgical Plant. Optical and electron microscopy, local x-ray spectral (microprobe), silicate and x-ray phases analyses were used for this purpose. In order to study the reaction column forming in a refractory material of the hearth a procedure was used developed for metasomatic natural processes [3] and processes of magmatic displacement of rock by magmatic melts [4].The original mix PPM-85 (GOST 24682) based on fired magnesite is a light-gray powder with a predominant grain size of tenths of a millimeter (specimen M32); 20 -30% of the volume consists of a different size (up to 8 mm), together with aggregates of periclase grains, sintered into a dense firm mix and cemented with calcium silicates. According to x-ray phase analysis data samples of different fractions of the original mix consist of 84% periclase and 16% x-ray amorphous substance. The individual reflections are identified as belonging to tri-and bicalcium silicates. Silicate analysis was used to determine the empirical chemical composition of an average sample selected from material of different fractions (Table 1). This analysis rested upon comparison with data for the material composition after service. Local x-ray spectral analysis was used to study the phase and empirical chemical composition of coarse fragments with a size of 3 -5 mm (Tables 1 and 2).According to electron microscopy data periclase of the original material is aggregates of polygonal grains (Fig. 1a ) with a size of 0.5 -2.0 mm (predominantly a size of 0.1 mm) and it has a stable iron coefficient of 0.03. The binding mass in the form streaky strips with a width up to 0.1 mm consists of crystals of bicalcium silicate and skeletal strips, i.e. calcium titanate (perovskite), forming typical growths. Within the composition of bicalcium silicate 10 -12% Ca replaces Mg; in addition, within it there are permanently present admixtures of Ti, Al and Fe. Within the composition of perovskite phase 10% titanium is replaced by Al; in addition it contains admixtures of Si, Mg and Fe.It follows f...