Lenses of phosphatic sandstone occurring in the Permian sediments of the Stitnik Formation contain intraclasts of microsphorite as well as minute apatite crystals in the matrix. The microsphorite is composed of pelmicritic and microsparitic aggregates of fluorapatite. The sandstone contains up to 18 weight percent P₂O₅. The phosphatic sandstone originated in an eutrophic lacustrine environment as a result of phosphorus concentration in lake sediment due to the iron redox cycling and the associated microbiological effects. Two contrasted depositional realms are suggested: 1. a shallow, lacustrine low-energy depositional regime in which adsorption and desorption of iron-bound phosphorus between oxygen-deficient bottom water and anoxic sediment led to the formation of microsphorite deposit; 2. a relatively high-energy depositional regime during which river deltas invaded the lacustrine environment and affected phosphorite reworking. Apatite crystals in the matrix are accompanied by Fe-dolomite, uraninite, U-Ti oxides, Ti oxides, framboidal pyrite, chlorites, muscovite and albite. Their formation reflects diagenetic to very low-grade metamorphic redistribution. A hydrothermal association of minerals represents sulphide mineralization occurring in quartz-carbonate veinlets.