Pseudomeisserite-(NH4), a new mineral with a novel uranyl-sulfate linkage from the Blue Lizard mine, San Juan County, Utah, USA

摘要

The new mineral pseudomeisserite-(NH4) (IMA2018-166), (NH4,K)(2)Na-4[(UO2)(2)(SO4)(5)]center dot 4H(2)O, was found in the Blue Lizard mine, San Juan County, Utah, USA, where it occurs as light yellow prisms in a secondary assemblage with belakovskiite, blodite, changoite, ferrinatrite, gypsum, ivsite, metavoltine and tamarugite. The streak is very pale yellow and the fluorescence is bright lime green under 405 nm ultraviolet light. Crystals are transparent with vitreous lustre. The tenacity is brittle, the Mohs hardness is 21/2, the fracture is curved or conchoidal and there is one perfect cleavage on {100}. The mineral is easily soluble in H2O and has a measured density of 3.22(2) g.cm(-3). Pseudomeisserite-(NH4) is optically biaxial (-) with alpha = 1.536(2), beta = 1.559(2) and gamma = 1.565(2) (white light); 2V(meas). = 53(1)degrees; dispersion is r > v, distinct; pleochroism: X colourless, Y light yellow and Z pale yellow (X < Z < Y); optical orientation: Z = b, Y boolean AND c = 33 degrees in obtuse beta). Electron microprobe analyses (WDS mode) provided (NH4)(1.49)K0.60Na3.87U2.00S5.04O28H7.78. The five strongest X-ray powder diffraction lines are [d(obs), angstrom(I)(hkl)]: 12.69(76)(100), 6.83(84)(012,102), 6.01(100)((2) over bar 02), 3.959(67)((2) over bar 21, (2) over bar 14, (1) over bar 23) and 3.135(76)((2) over bar 06,223, (1) over bar 16). Pseudomeisserite-(NH4) is monoclinic, P2(1)/c, a = 13.1010(3), b = 10.0948(2), c = 19.4945(14) angstrom, beta = 104.285(7)degrees, V = 2498.5(2) angstrom(3) and Z = 4. The structural unit in the structure (R-1 = 0.0254 for 3837 I > 2 sigma I reflections) is a novel [(UO2)(2)(SO4)(5)](6-) uranyl-sulfate band.