Greenlizardite, (NH4)Na(UO2)(2)(SO4)(2)(OH)(2)center dot 4H(2)O, a new mineral with phosphuranylite-type uranyl sulfate sheets from Red Canyon, San Juan County, Utah, USA

摘要

The new mineral greenlizardite (IMA2017-001), (NH4)Na(UO2)(2)(SO4)(2)(OH)(2)center dot 4H(2)O, was found in the Green Lizard mine, Red Canyon, San Juan County, Utah, USA, where it occurs as a secondary alteration phase. It is associated with ammoniozippeite, boussingaultite and dickite. It forms as light green-yellow blades up to similar to 0.3 mm long. The mineral is vitreous and transparent with a white streak. It fluoresces greenish blue in 405 nm light. Mohs hardness is similar to 2. Crystals are brittle with irregular fracture and two cleavages: perfect {001} and good {2 (1) over bar0}. Greenlizardite is easily soluble in room-temperature H2O. The calculated density is 3.469 g cm(3). Optically, it is biaxial (+) with alpha = 1.559(1), beta = 1.582(1) and gamma = 1.608 (1) (measured in white light). The measured 2V is 88(1)degrees; the calculated 2V is 87.8 degrees. Dispersion is moderate, r v. Pleochmism is X = very pale yellow green, Y = pale yellow green and Z = light yellow green; X Y Z. The optical orientation is X approximate to c, Y approximate to a and Z approximate to b*. The Raman spectrum exhibits bands attributable to both sulfate and uranyl groups. Electron probe microanalyses (with H2O based on the crystal structure) yielded (NH4)(0.98)Na1.00U1.96 S2.04O18.00H10.02. Greenlizardite is triclinic, P(1)over bar, a = 6.83617(17), b = 9.5127(3), c 13.8979(10) , alpha = 98.636(7), beta = 93.713(7), gamma = 110.102(8)degrees, V = 832.49(8) (3) and Z = 2. The crystal structure (R-1 = 2.39% for 2542 I 2 sigma I) contains edge-sharing dimers of UO7 pentagonal bipyramids. The dimers link by sharing corners with SO4 groups to form a [(UO2)(2)(SO4)(2)(OH)(2)](2) sheet based on the phosphuranylite anion topology. Zig-zag edge-sharing chains of NaO6 octahedra link adjacent [(UO2)(2)(SO4)(2)(OH)(2)](2) sheets, forming thick slabs. NH4 bonds to O atoms in adjacent slabs linking them together. H2O groups occupy channels in the slabs and space between the slabs.