Lussierite, a new sodium uranyl sulfate mineral with bidentate UO (sub 7) -SO (sub 4) linkage from the Blue Lizard Mine, San Juan County, Utah, USA

The new mineral lussierite (IMA2018-101), Na (sub 10) [(UO (sub 2) )(SO (sub 4) ) (sub 4) ](SO (sub 4) ) (sub 2) (H (sub 2) O) (sub 3) , was found in the Blue Lizard mine, San Juan County, Utah, USA, where it occurs as pale green-yellow prisms or blades in a secondary assemblage with belakovskiite, ferrinatrite, halite, ivsite, metavoltine and thenardite. The streak is white and the fluorescence is bright cyan under 365 nm ultraviolet light. Crystals are transparent with vitreous lustre. The tenacity is brittle, the Mohs hardness is 2 1/2, the fracture is irregular and no cleavage was observed. The mineral is easily soluble in H (sub 2) O and has a measured density of 2.87(2) g cm (super -3) . Lussierite is optically biaxial (+), with alpha = 1.493(1), beta = 1.505(1) and gamma = 1.518(1) (white light); 2V (sub meas.) = 88(1) degrees ; dispersion is r > v, moderate; pleochroism: X = colourless, Y and Z = green yellow (X < Y nearly equal Z); optical orientation: X = b, Z (caret) a = 44 degrees in obtuse beta . Electron microprobe analyses (wavelength-dispersive spectroscopy mode) provided Na (sub 10) (U (sub 0.99) O (sub 2) )(S (sub 1.00) O (sub 4) ) (sub 6) .3H (sub 2) O (+0.06 H for charge balance). The five strongest X-ray powder diffraction lines are [d (sub obs) Aa(I)(hkl)]: 6.69(95)(4 11,130), 4.814(100)(150,002,060), 3.461(83)(171,202), 2.955(81)(113,330) and 2.882(74)(1 91,311,191,0.10.0). Lussierite is monoclinic, Cc, a = 9.3134(4), b = 28.7501(11), c = 9.6346(7) Aa, beta = 93.442(7) degrees , V = 2575.1(2) Aa3 and Z = 4. The structure (R (sub 1) = 0.0298 for 5202 I > 2sigma I) contains a [(UO (sub 2) )(SO (sub 4) ) (sub 4) ] (super 6-) uranyl sulfate cluster in which one SO (sub 4) tetrahedron shares an edge (bidentate linkage) with the UO (sub 7) pentagonal bipyramid. The uranyl sulfate clusters occur in layers and are linked through a complex network of bonds involving Na (super +) cations, isolated SO (sub 4) tetrahedra and isolated H (sub 2) O groups.