The crystal structure of beta-uranophane with the lattice constants a = 13.966(2), b = 15.443(4), c = 6.632(1) Å, β = 91.38°(2) has been refined. It shows that the space group is P21/a and that the basic structural features determined previously are correct. However, bond-strength sums, calculated using the refined interatomic distances, reveal that the apical oxygens of all SiO4 tetrahedra must be (OH)- ions and that the H bonds play as important a role as Ca in linking sheets that have the formula [(UO2)2(SiO3OH)2]2-. Hence the structural formula should be Ca(UO2)2(SiO3OH)2⋅5H2O instead of Ca(UO2)(UOOH)(SiO4)(SiO3OH)⋅4H2O as suggested earlier. Studies of the same mineral with dta, dtg, and infrared spectroscopy support this conclusion.

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