The results of a detailed lithological and analytical study of glauconite grains extracted from marine argillaceous siltstones and sandstones of the Cenomanian Melovatskaya formation of the South East Russian Plate are released. The laboratory investigation of glauconite was conducted by optical and electron microscopy, X-Ray diffraction, IR-spectroscopy, chemical and thermal analysis. These results formed the basis for specific chemical characteristics and crystal structure determining and the crystal chemical formula calculations. The mechanism of formation of glauconite developed by À.Meunier & À.El Albani (2007) is updated. It is proposed that glauconite is formed by chemical diffusion of K+ and Fe+ ions through unconsolidated sediments inside the reductive microsystems around organic debris and Fe-Al smectite particles. The source of K ion was sea water. The Fe ions migrates from ferry-alumina-silica gel forming by ash paticles dissolution.
Key words: glauconite, illite, smectite, crystal-chemical formula, genesis, chemical diffusion, the Cenomanian, Russian Plate.