Leydetite, Fe(UO_2)(SO_4)_2(H_2O)_(11) a new uranyl sulfate mineral from Mas d'Alary, Lodeve, France

摘要

Leydetite, monoclinic Fe(UO_2XSO_4)_2(H_2O)n (IMA 2012—065), is a new supergene uranyl sulfate from Mas d'Alary, Lodeve, Herault, France. It forms yellow to greenish, tabular, transparent to translucent crystals up to 2 mm in size. Crystals have a vitreous lustre. Leydetite has a perfect cleavage on (001). The streak is yellowish white. Mohs hardness is ~2. The mineral does not fluoresce under long- or short-wavelength UV radiation. Leydetite is colourless in transmitted light, non-pleochroic, biaxial, with a = 1.513(2), y = 1.522(2) (further optical properties could not be measured). The measured chemical composition of leydetite, FeO 9.28, MgO 0.37, A1_2O_3 0.26, CuO 0.14, UO_3 40.19, SO_3 21.91, SiO_2 0.18, H_2O 27.67, total 100 wt.%, leads to the empirical formula (based on 21 O a.p.f.u.), (Fe_(o.93)Mg_(o.o7)Al_(o.o4)Cu_(0.o1))E_(1.o5)(U_(1.01)O_2)(S_(1.96)Si_(o.o2))E_(1.98)O_8(H_20)_(11). Leydetite is monoclinic, space group Cllc, with a = 11.3203(3), b = 7.7293(2), c = 21.8145(8) A, (3 = 102.402(3)°, V= 1864.18(10) A3, Z= 4, andDcalo = 2.55 g cm"3. The six strongest reflections in the X-ray powder diffraction pattern are [d_9obs) in A (I) (hkt)]: 10.625 (100) (002), 6.277 (1) (111), 5.321 (66) (004), 3.549 (5) (006), 2.663 (4) (008), 2.131 (2) (0 0 10). The crystal structure has been refined from single-crystal X-ray diffraction data to R_1 = 0.0224 for 5211 observed reflections with [/ > 3σ(I)]. Leydetite possesses a sheet structure based upon the protasite anion topology. The sheet consists of UO_7 bipyramids, which share four of their equatorial vertices with SO_4 tetrahedra. Each SO_4 tetrahedron, in turn, shares two of its vertices with UO_7 bipyramids. The remaining unshared equatorial vertex of the bipyramid is occupied by H_2O, which extends hydrogen bonds within the sheet to one of a free vertex of the SO4 tetrahedron. Sheets are stacked perpendicular to the c direction. In the interlayer, Fe~(2+) ions and H_2O groups link to the sheets on either side via a network of hydrogen bonds. Leydetite is isostructural with the synthetic compound Mg(UO_2)(SO_4)_2(H_2O)_(11)- The name of the new mineral honours Jean Claude Leydet (born 1961), an amateur mineralogist from Brest (France), who discovered the new mineral.