Amurselite, a new uranyl selenite from the Burro Mine, San Miguel County, Colorado, USA

Amurselite (IMA2024-062), (NH (sub 4) ) (sub 2) [(UO (sub 2) ) (sub 5) (SeO (sub 3) ) (sub 3) O (sub 2) (OH) (sub 2) (H (sub 2) O)].8H (sub 2) O, is a new mineral discovered at the Burro mine, Slick Rock district, San Miguel County, Colorado, USA. It was found in a secondary efflorescent assemblage on asphaltite in association with gypsum, natrozippeite, quartz, and a potentially new lithium-uranyl-selenite mineral. Amurselite occurs as yellow prisms or blades. The streak is pale yellow, the luster is vitreous, the Mohs hardness is about 2, the tenacity is brittle, the fracture is irregular or stepped and the cleavages are perfect on {100} and fair on {010}. The mineral fluoresces weak green in 405 nm illumination. It is optically biaxial (-) with alpha = 1.580(5), beta = 1.720(5), gamma = 1.725(5) (white light); 2V = 18(3) degrees ; optical orientation: X^a nearly equal 20 degrees , Y^b nearly equal 44 degrees ; pleochroism: X colorless, Y and Z yellow; X < Y nearly equal Z. The calculated density is 4.178 g/cm (super 3) for the empirical formula. Electron probe microanalysis provided the empirical formula (NH (sub 4) ) (sub 1.87) Na (sub 0.07) K (sub 0.06) U (super 6+) (sub 5) Se (super 4+) (sub 2.98) O (sub 32) H (sub 20.07) . Amurselite is triclinic, space group , a = 8.598(3), b = 9.088(3), c = 11.071(4) Aa, alpha = 83.644(7), beta = 68.776(7), gamma = 79.940(8) degrees , V = 792.9(4) Aa (super 3) , and Z = 1. In the crystal structure (R (sub 1) = 0.0505 for 1210 I > 2sigma I reflections), UO (sub 7) and UO (sub 8) polyhedra link by sharing equatorial edges to form chains, which are cross-linked by SeO (sub 3) (super 2-) groups to form sheets. The interlayer region contains NH (sub 4) and H (sub 2) O.