This work presents the results of a study of the phase (mineralogical) composition of clay from the Polyana field, Shebekinsky district, Belgorod region. To study the morphological and structural features of the mineral components that make up the specified clay, a set of methods of scanning and transmission microscopy, electron microdiffraction and energy dispersive analysis were used. Electron microscopic examination of Polyanskaya clay showed that it is composed of such minerals as: calcium and magnesium-iron form of montmorillonite, muscovite, low-temperature trigonal quartz, illite and ruthyl. More often than others, the preparations contain particles identified as montmorillonite, differing in structure without shaped edges and having a layered structure (layer thickness of about 1 nm). Particles of this mineral show a high tendency to aggregation, but at the same time they are quite easily split along the cleavage plane during dispersion, and therefore have a developed specific surface area, which determines good sorption characteristics.