IMA 2017-001 = greenlizardite

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Marco E. Ciriotti
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IMA 2017-001 = greenlizardite

Messaggio da Marco E. Ciriotti » mer 09 ago, 2017 6:23

Prossima pubblicazione.

▪ Kampf, A.R., Plášil, J., Nash, B.P., Marty, J. (2017): Greenlizardite, (NH4)Na(UO2)2(SO4)2(OH)2·4H2O, a new mineral with phosphuranylite type uranyl sulfate sheets from Red Canyon, San Juan County, Utah, USA. Mineralogical Magazine, 81, (in press).

The new mineral greenlizardite (IMA2017-001), (NH4)Na(UO2)2(SO4)2(OH)2·4H2O, 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 boussingaultite, dickite and NH4- rich zippeite. It forms as light green-yellow blades up to about 0.3 mm in length. The mineral is vitreous, transparent with a white streak. It fluoresces greenish-blue in 405 nm light. Mohs hardness is about 2. Crystals are brittle with irregular fracture and two cleavages: perfect {001} and good {2-10}. Greenlizardite is easily soluble in room-temperature H2O. The calculated density is 3.469 g cm-3. Optically, it is biaxial (+) with α = 1.559(1), β = 1.582(1), γ = 1.608(1) (measured in white light). The measured 2V is 88(1)°; the calculated 2V is 87.8°. Dispersion is moderate, r < v. Pleochroism is X very pale yellow green, Y pale yellow green, Z light yellow green; X < Y < Z. The optical orientation is X ≈ c, Y ≈ a, Z ≈ 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)0.98Na1.00U1.96S2.04O18.00H10.02. Greenlizardite is triclinic, P-1, a = 6.83617(17), b = 9.5127(3), c = 13.8979(10) Å, α = 98.636(7), β = 93.713(7), γ = 110.102(8)°, V = 832.49(8) Å3 and Z = 2. The crystal structure (R1 = 2.39% for 2542 I > 2σI) 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.
Marco E. Ciriotti

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