Meitnerite (IMA2017-065), (NH4)(UO2)(SO4)(OH)·2H2O, 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¯}, up to about 80 µm in diameter and 30 µm 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¯}. 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 α = 1.568(2), β = 1.589(2), γ = 1.607(2) (white light); 2V = 84(1)°. The dispersion is r > v, moderate, The optical orientation is Xb = 26°, Ya = 15°, Zc = 53°. 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)1.01Na0.07(U0.97O2)(S1.03O4)[(OH)0.93O0.07]·2H2O, based on 9 O apfu. Meitnerite is triclinic, P−1, a = 6.7964(2), b = 8.0738(3), c = 9.2997(7) Å, α = 113.284(8), β = 99.065(7), γ = 105.289(7)°, V = 431.96(5) Å3 and Z = 2. The crystal structure, refined to R1 = 0.013 for 1871 observed reflections [I > 2σI], contains uranyl sulfate sheets based on the phosphuranylite anion topology. The interlayer region contains an NH4+ group and two H2O groups.

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