URANYL SULFATES: NEWS ON MINERALOGY, CRYSTAL CHEMISTRY AND OCCURRENCE

Uranyl sulfate minerals are typical and widespread products formed during hydration–oxidation weathering of primary uranium minerals under the low pH conditions, which result from the decomposition of associated (gangue) sulfide minerals. During last five years more than 20 new uranyl sulfate minerals have been disovered; this number represents a substantial portion (~20%) of all known uranyl minerals. The newly discovered minerals possesse less-frequently seen crystal structures or structures that have not been observed so far in Nature. The recognition of these new minerals and their structures helped us in understanding of mechanisms and constraints on their formation and occurrences. In general, increasing content of the molecular H₂O within the structural units of these minerals causes depolymerization from 2D→1D units (sheets→chains); while increasing SO₄ content causes lowering of dimensionality from chains to cluster units. These novel mineral structure topologies document that dimensionality and topology, in particular, are driven by conditions and the composition of fluids from which these minerals crystallized.