Kaolinite, dioctahedral 1M and 2M1 hydromicas, trioctahedral Ib and IIb chlorites, montmorillonite and mixed-layer phases from the terrigenous Carboniferous rocks of the Bolshoy Donbas at the southwestern border of the Russian Platform are described. Clay minerals form definite assemblages connected with the facies character and mineral composition of the rocks and with the intensity of post-sedimentary alteration. This post-sedimentary evolution of the terrigenous rocks is characterized by regional ranks of clay polytypes and clay isomorphous varieties, viz.:

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The persistence of mineral assemblages in definite PT intervals leads to the possibility of their use for characterizing post-sedimentary alteration stages.