• journal_title：Mineralogical Magazine
• Contributor：J. Plášil ; A. V. Kasatkin ; R. Škoda ; M. Novák ; A. Kallistová ; M. Dušek ; R. Skála ; K. Fejfarová ; J. Čejka ; N. Meisser ; H. Goethals ; V. Machovič ; L. Lapčák
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2013-06-01
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2013.077.4.03
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：77
• issue：4
• firstpage：429
• section：Articles

Leydetite, monoclinic Fe(UO₂)(SO₄)₂(H₂O)₁₁ (IMA 2012–065), is a new supergene uranyl sulfate from Mas d'Alary, Lodève, Hérault, 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 α = 1.513(2), γ = 1.522(2) (further optical properties could not be measured). The measured chemical composition of leydetite, FeO 9.28, MgO 0.37, Al₂O₃ 0.26, CuO 0.14, UO₃ 40.19, SO₃ 21.91, SiO₂ 0.18, H₂O 27.67, total 100 wt.%, leads to the empirical formula (based on 21 O a.p.f.u.), (Fe_0.93Mg_0.07Al_0.04Cu_0.01)_Σ1.05(U_1.01O₂)(S_1.96Si_0.02)_Σ1.98O₈(H₂O)₁₁. Leydetite is monoclinic, space group C2/c, with a = 11.3203(3), b = 7.7293(2), c = 21.8145(8) Å, β = 102.402(3)°, V = 1864.18(10) ų, Z = 4, and D_calc = 2.55 g cm⁻³. The six strongest reflections in the X-ray powder diffraction pattern are [d_obs in Å (I) (hkl)]: 10.625 (100) (002), 6.277 (1) (1İ11), 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 R₁ = 0.0224 for 5211 observed reflections with [I > 3σ(I)]. Leydetite possesses a sheet structure based upon the protasite anion topology. The sheet consists of UO₇ bipyramids, which share four of their equatorial vertices with SO₄ tetrahedra. Each SO₄ tetrahedron, in turn, shares two of its vertices with UO₇ bipyramids. The remaining unshared equatorial vertex of the bipyramid is occupied by H₂O, 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, Fe²⁺ ions and H₂O groups link to the sheets on either side via a network of hydrogen bonds. Leydetite is isostructural with the synthetic compound Mg(UO₂)(SO₄)₂(H₂O)₁₁. The name of the new mineral honours Jean Claude Leydet (born 1961), an amateur mineralogist from Brest (France), who discovered the new mineral.