**1. Introduction**

Uranyl-oxide hydroxy-hydrate minerals are regarded to be the products of the first stages of uraninite alteration under oxidizing conditions [1–5]. Being formed as the result of the reaction of bedrock with aqueous fluids, these natural compounds obviously play an important, if not a key, role in the uranium transfer to the environment. In addition, uranyl-oxide hydroxy-hydrate phases can be regarded as the precursors of the formation of other secondary uranium-bearing minerals, under reaction with waters enriched by various cations (usually mono- and divalent) and oxyanions (CO3 2−, SO4 <sup>2</sup><sup>−</sup>, PO4 <sup>2</sup>−, etc.). The description of the new mineral species is rarely followed by the experiments, which could shed some light on the conditions of their genesis. Due to the complexity of uranyl-bearing complexes forming in aqueous solutions in the presence of a certain cation/oxyanion combination as a

function of pH, the exact formation mechanisms of uranyl minerals are not fully understood. In this study, we presented the results of uranyl sulfate synthesis experiments that might elucidate some of the formation behavior of natural uranyl sulfates.

Herein, we reported on the alteration experiment of the synthetic analog of uranyl-oxide hydroxy-hydrate mineral schoepite, [(UO2)8O2(OH)12](H2O)12 [6,7]. As the result, four different crystalline phases Cs[(UO2)(SO4)(OH)](H2O)0.25 (**1**), Cs3[(UO2)4(SO4)2O3(OH)](H2O)3 (**2**) [8], Cs6[(UO2)2(SO4)5] (H2O)3 (**3**), and Cs2[(UO2)(SO4)2] (**4**) were obtained, including three novel compounds. The obtained Cs uranyl sulfate compounds were analyzed using single-crystal X-ray diffraction (SC XRD), energy-dispersive X-ray analysis (EDX), as well as topological analysis and information-based structural complexity measures.
