Meitnerite, (NH4)(UO2)(SO4)(OH)•2H2O, a new uranyl-sulfate mineral with a sheet structure

Meitnerite (IMA2017-065), (NH4)(UO2)(SO4)(OH)center dot 2H(2)O, is a new mineral from the Green Lizard mine in Red Canyon, San Juan County, Utah, USA, where it occurs as a secondary alteration phase. It occurs on partially recrystallized quartz grains in association with beshtauite and gypsum. Meitnerite occurs as intergrowths of tabular crystals, flattened on {0 1 (1) over bar}, up to about 80 mu m in diameter and 30 mu m thick. The mineral is slightly greenish yellow and transparent with a vitreous lustre and very pale yellow streak. It exhibits greenish-white fluorescence in 405 nm light. Crystals are brittle with irregular fracture, and a perfect cleavage on {0 1 (1) over bar}. The Mohs' hardness is ca. 2. The calculated density is 3.320 g.cm(-3). At room temperature, the mineral is slowly soluble in H2O and very rapidly soluble in dilute HCl. Optically, meitnerite is biaxial (-), with alpha = 1.568(2), beta = 1.589(2), gamma = 1.607(2) (white light); 2V = 84(1)degrees. The dispersion is r > v, moderate, The optical orientation is X (boolean AND) b = 26 degrees, Y (boolean AND) a = 15 degrees, Z (boolean AND) c = 53 degrees. The pleochroism is X nearly colourless, Z pale green yellow, Y light green yellow; X < Z < Y. Electron-microprobe analyses gave the empirical formula (NH4)(1.01)Na-0.07(U0.97O2)(S1.03O4)[(OH)(0.93)O-0.07]center dot 2H(2)O, based on 9 O apfu. Meitnerite is triclinic, P (1) over bar, a = 6.7964(2), b = 8.0738(3), c = 9.2997(7) angstrom, alpha = 113.284(8), beta = 99.065(7), gamma = 105.289(7)degrees, V = 431.96(5) angstrom(3) and Z = 2. The crystal structure, refined to R-1 = 0.013 for 1871 observed reflections [I > 2 sigma I], contains uranyl sulfate sheets based on the phosphuranylite anion topology. The interlayer region contains an NH4+ group and two H2O groups.