Crystallization of Uranyl Silicate Natroboltwoodite during an Experimental Dissolution of the Mineral Yttrialite-(Y): Crystal Structure and Raman Spectroscopy

A synthetic analogue
of the mineral natroboltwoodite was obtained
unprecedently during a dissolution experiment with the mineral yttrialite-(Y),
at a temperature of 200 °C, pressure ∼1.5 MPa, and strongly
alkaline conditions. Natroboltwoodite formed along with analcime and
aegirine. Single crystals of natroboltwoodite obtained allowed us
to reveal its crystal structure for the first time. It differs from
the other known uranyl silicate structures in the size of its respective
unit-cell volume. The increased size of the structure corresponds
to the positional and occupational disorder among one of the Si-tetrahedrally
coordinated sites. On the basis of structural complexity parameters,
a comparison involving both known synthetic and naturally occurring
uranyl silicates is provided and discussed.