Crystal structure of synthetic soddyite (UO2)2[SiO4](H2O)2

Synthesized are the monocrystals of uranyl silicate with the 2UO3xSiO2x2H2O formula and established is its identity with natural soddyite. In the synthesis α-UO3x 0.9H2O and SiO2 (amorphous) with the ratio UO3:SiO2=2:1 at the 300 deg C have been used. Parameters of rhombic elementary cell of uranyl silicate are: a=8.297(2), b=11.219(4), c=18.661(4)A. Atoms of U in synthesized soddyite are arranged in distorted pentagonal bipyramides. Soddyite structure is singled out from the row of laminated structures of minerals of uranophane group and presents a new structure crystallochemical type of uranyl silicates. Carcass character of soddyite structure explains the absence of perfect cleavage as to pynacoid in it, which is characteristic of minerals of uranophane group