IMA 2018-166 = pseudomeisserite-(NH4)

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Marco E. Ciriotti
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IMA 2018-166 = pseudomeisserite-(NH4)

Messaggio da Marco E. Ciriotti » mer 18 mar, 2020 9:53

Prossima pubblicazione.

Referenza:
▪ Kampf, A.R., Olds, T.A., Plášil, J., Nash, B.P., Marty, J. (2020): Pseudomeisserite-(NH4), a new mineral with a novel uranyl-sulfate linkage from the Blue Lizard mine, San Juan County, Utah, USA. Mineralogical Magazine, 84, (in press).

Abstract:
The new mineral pseudomeisserite-(NH4) (IMA2018-166), (NH4,K)2Na4[(UO2)2(SO4)5]·4H2O, 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, blödite, changoite, ferrinatrite, gypsum, ivsite, metavoltine, tamarugite. The streak is very pale yellow and the fluorescence is bright lime green under 405 nm ultraviolet light. Crystals are transparent with vitreous luster. The tenacity is brittle, the Mohs hardness is 2½, 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 α = 1.536(2), β = 1.559(2), γ = 1.565(2) (white light); 2V (meas.) = 53(1)°; dispersion is r > v, distinct; pleochroism: X = colourless, Y light yellow and Z pale yellow (X < Z < Y); optical orientation: Z = b, Y ^ c = 33° in obtuse β). Electron microprobe analyses (WDS mode) provided (NH4)1.49K0.60Na3.87U2.00S5.04O28H7.78. The five strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 12.69(76)(100), 6.83(84)(012,102), 6.01(100)(-202), 3.959(67)(-221,-214,-123) and 3.135(76)(-206,223,-116). Pseudomeisserite-(NH4) is monoclinic, P21/c, a = 13.1010(3), b = 10.0948(2), c = 19.4945(14) Å, β = 104.285(7)°, V = 2498.5(2) Å3 and Z = 4. The structural unit in thestructure (R1 = 0.0254 for 3837 I > 2I reflections) is a novel [(UO2)2(SO4)5]6– uranyl-sulfateband.
Marco E. Ciriotti

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