Mineralogical studies of stagnated chernozems identified a number of features in comparison with modern zonal chernozems, and common features with some other soils. These features apply to the composition of primary and clay minerals, and also to the character of their distribution in soil profile. A characteristic feature of stagnated chernozems mineralogical composition that stimulated many of their specific properties is high content (40-70%) of clay minerals and, in this connection, low content of primary minerals. Nomenclature composition of minerals is the same as in zonal chernozems. Another distinctive feature of stagnated chernozems, in comparison with zonal ones, is the fact that they, as part of primary minerals, contain approximately twice less skeletal minerals (quartz and feldspar) and more – layered silicates, in particular, mica. Among clay minerals they are characterized by a higher content of smectite and illite, and by a shift of balance between these minerals in favor of illite. Besides, difference between stagnated and zonal chernozems is in irregularity of profile dynamics of primary and clay minerals. It indicates the presence of more or less explicit or implicit stratification of soil-forming rock, which reflects the complicated history of formation of these soils under repeated environments shifts of swamp-lake-alluvial sedimentation in the Late Pliocene. Heterogeneity of soilforming rock makes it difficult to diagnose these soils by pedogenic weathering of minerals as it is superimposed on the geological heterogeneity of rocks. In stagnated chernozems there are observed manifestations of clay properties. In some respects we can say that the process of destruction of primary aluminosilicates in stagnated chernozems advanced much further than in zonal chernozems, while the process of decomposition of clay minerals is inhibited. Their combination, apparently, leads to additional argillization of stagnated chernozems that extends to gleyed horizons. It's impossible to give unequivocal evidence of argillization in gley horizons of stagnated chernozems because of the heterogeneity of rocks, although probability of this process is high. The origin of gleyed horizons in these soils is explained by the specific smectite composition of swelling clays on which they are formed. Mineralogical composition of stagnated chernozems demonstrates genetic features common to other soils by habitus. Thus, high content of smectite and, especially, of illite shows an affinity of these ancient and modern alluvial compact soils. Another sign, exceptionally high contents of smectite, discovers kinship between stagnated chernozems and compact chernozems. Increased content of micas in composition of primary minerals of stagnated chernozems, and of illite - in clay minerals, indicates the natural enrichment of these soils by potassium-based minerals and therefore a high reserve of potassium. By mineralogical composition, as a source of mineral elements for plants, stagnated chernozems have higher potential fertility in comparison with zonal chernozems. Because of the long history of repeated changes in climate and soil-formation conditions throughout the Quaternary period stagnated chernozems contain relicts of past ages, which need to be considered and treated as soils of poligenetic series. Major genetic features: heavy-clayey composition, high content of smectite and of illite, exposure in dry season to formation of deep cracks and cemented lumps, and swelling during wet periods due to peculiar mineralogy - soil properties, directly related to the features of composition and properties of soil-forming rocks. Stagnated chernozems is bright example of the crucial role of the geological factors in formation of soil properties.