Red-colored deposits occurring in the northwest and east of the Russian Plain lose their red color upon gleyzation under a stagnant water regime either because of dissolution of hematite particles or because of their dispersion and separation from the clay mineral surfaces. In clayey deposits with iron minerals presented mainly by fine crystals, processes induce the dissolution of hematite and goethite. In sandy deposits, gleyzation contributes to the dispersion of relatively coarse hematite grains in clay fraction and their separation from the clay mineral surfaces. Gley is more advanced in deposits with a higher degree of iron oxidogenesis, expressed as the Fe_d/Fe_t ratio.