Crystal-structure of Seelite From Rabejac (france)

The crystal structure of seelite from Rabejac has been determined by X-ray diffraction and refined to R = 0.031 for 758 observed reflexions. Monoclinic system; space group C2/m with a = 18.194(3), b = 7.071(1), 6.670(1) Angstrom, beta = 99.70(1), V = 845.8(2) Angstrom(3), D-x = 3.71 (D-m = 3.70), Z = 2. Chemical formula : Mg[(UO2)(AsO3)(0.7)(AsO4)(0.3)](2).7H(2)O. The structure consists of layers similar to those of the seelite from Talmessi and those of the silicates of the uranophane structural group. Those layers are connected by octahedral Mg(H2O)(6) cations and by water molecules. The uranyl phosphate ranunculite is probably isostructural with seelite

Chemical-composition and Crystal-structure of Phosphuranylite, Ca(uo2)[(uo2)3(oh)2(po4)2]2.12h2o]

The crystal structure of phosphuranylite has been determined by X-ray diffraction and refined to R = 0.089 for 963 observed reflexions. The unit cell is orthorhombic, space group Bmmb (n-degrees 63), a = 15.835(7), b = 17.324(6), c = 13.724(4)angstrom, V = 3.765(2)angstrom3, Z = 4. Chemical formula : CaO.7UO3.2P2O5.14H2O with an U/P ratio = 7/4 instead of 6/4 or 8/4 as generally presumed. The structure consists of [(UO2)3(OH)2(PO4) 2]n2n- layers (type dumontite), parallel to (100), connected by Ca2+, UO2+ and H2O. The structure is compared with that of dewindtite. It is shown how two minerals whose formulae are rather different (replacement of 3PbO by 1CaO+1UO3+1H2O) can have similar structures, owing to subtle reorganizations

Structure of phuralumite

Al/sub 2/[(OH)/sub 2/(PO/sub 4/)/sub 2/(UO /sub 2/)/sub 3/]. (OH)/sub 4/.10H/sub 2/O (a mineral from Kobokobo, Kivu, Zaire) is monoclinic, with space group /b P/2 /sub 1///b a/, and lattice constants, /b a/=13.836 (6), /b b /=20.918 (6), /b c/=9.428 (3) A , beta =112.44 (3) degrees , /b Z/=4, /b V/=2522 A /sup 3/, /b D//sub m/=3.5, /b D//sub c/=3.52 Mg m/sup -3/. Structure type: phosphouranylite. The [(OH)/sub 2/(PO/sub 4/)/sub 2/(UO /sub 2/)/sub 3/]/sub n//sup 2n-/ layers are connected principally by Al/sub 4/O/sub 14/ groups, composed of two octahedra and two trigonal bipyramids sharing edges.Anglai

[New determination of the structure iron (II) chloride tetrahydrate]

The crystal structure of iron(II) chloride tetrahydrate has been redetermined with three-dimensional X-ray data from a Picker four-circle automatic diffractometer. The space group is /b P/2/sub 1///b c / with unit-cell parameters /b a/=5.885, /b b/=7.174, /b c/=8.505 A and beta =111.11 degrees . Bond distances within a group FeCl/sub 2/.4H/sub 2/O are Fe-Cl 2.53 and Fe-O 2.12 and 2.08 A.Francai