Nollmotzite, Mg[UV(UVIO2)2O4F3]·4H2O, the first natural uranium oxide containing fluorine

Abstract

Nollmotzite (IMA2017-100), Mg[UV(UVIO2)2F3O4](H2O)4, is a new uranium oxide fluoride mineral found in the Clara mine, Black Forest Mountains, Germany. Electron microprobe analysis provided the empirical formula (Mg1.06Cu0.02)Σ1.08[UV(UVIO2)2O3.85F3.15][(H2O)3.69(OH)0.31]Σ4.00based on three U and 15 O + F atoms per formula unit. Nollmotzite is monoclinic, space groupCm, witha= 7.1015 (12) Å,b= 11.7489 (17) Å,c= 8.1954 (14) Å, β = 98.087 (14)°,V= 676.98 (19) Å3andZ= 2. The crystal structure [twinned by reticular merohedry; refined toR= 0.0369 with GoF = 1.09 for 1527 unique observed reflections,I> 3σ(I)] is based upon [UV(UVIO2)2F3O4]2–sheets of β-U3O8topology and contains an interlayer with MgF2(H2O)4octahedra. Adjacent sheets are linked through F–Mg–F bonds, as well asviahydrogen bonds. The presence of fluorine and pentavalent uranium in the structure of nollmotzite has potentially important implications for the safe disposal of nuclear waste.