Bobcookite, NaAl(UO₂)₂(SO₄)₄·18H₂O and wetherillite, Na₂Mg(UO₂)₂(SO₄)₄·18H₂O, two new uranyl sulfate minerals from the Blue Lizard mine, San Juan County, Utah, USA

Abstract

The new minerals bobcookite (IMA 2014-030), NaAl(UO2)2(SO4)4·18H2O and wetherillite (IMA 2014-044), Na2Mg(UO2)2(SO4)4·18H2O, were found in the Blue Lizard mine, San Juan County, Utah, USA, where they occur together as secondary alteration phases in association with boyleite, chalcanthite, dietrichite, gypsum, hexahydrite, johannite, pickeringite and rozenite.Bobcookite descriptive details: lime green to greenish-yellow massive veins and columnar crystals; transparent; vitreous lustre; bright greenish-white fluorescence; pale greenish yellow streak; hardness (Mohs) 2½; brittle; conchoidal fracture; no cleavage; moderately hygroscopic; easily soluble in cold H2O; densitycalc = 2.669 g cm–3. Optically, biaxial (–), α = 1.501(1), β = 1.523(1), γ = 1.536(1) (white light); 2Vmeas. = 78(1)°; 2Vcalc. = 74°; dispersion r < v, moderate. Pleochroism: X colourless, Y very pale yellow-green, Z pale yellow-green; X < Y < Z. EDS analyses yielded the empirical formula Na0.97Al1.09(U1.02O2)2(S0.98O4)4(H2O)18. Bobcookite is triclinic, P1, a = 7.7912(2), b = 10.5491(3), c = 11.2451(8) Å , α = 68.961(5), β = 70.909(5), γ = 87.139(6)°, V = 812.79(8) Å3 and Z = 1. The structure (R1 = 1.65% for 3580 Fo > 4σF) contains [(UO2)(SO4)2(H2O)] chains linked by NaO4(H2O)2 octahedra to form layers. Hydrogen bonds to insular Al(H2O)6 octahedra and isolated H2O groups hold the structure together. The mineral is named for Dr Robert (Bob) B. Cook of Auburn University, Alabama, USA.Wetherillite descriptive details: pale greenish-yellow blades; transparent; vitreous lustre; white streak; hardness (Mohs) 2; brittle; two cleavages, {101} perfect and {010} fair; conchoidal or curved fracture; easily soluble in cold H2O; densitycalc = 2.626 g cm–3. Optically, biaxial (+), α = 1.498(1), β = 1.508(1), γ = 1.519(1) (white light); 2Vmeas. = 88(1)°, 2Vcalc. = 87.9°; dispersion is r < v, distinct; optical orientation: Z = b, X ∧ a = 54° in obtuse β; pleochroism: X colourless, Y pale yellow-green, Z pale yellow-green; X < Y ≈ Z. EDS analyses yielded the empirical formula Na1.98(Mg0.58Zn0.24Cu0.11Fe0.092+)Σ1.02(U1.04O2)2(S0.98O4)4(H2O)18. Wetherillite is monoclinic, P21/c, a = 20.367(1), b = 6.8329(1), c = 12.903(3) Å, β = 107.879(10)°, V = 1709.0(5) Å3 and Z = 2. The structure (R1 = 1.39% for 3625 Fo > 4σF) contains [(UO2)(SO4)2(H2O)] sheets parallel to {100}. Edge-sharing chains of Na(H2O)5O polyhedra link adjacent uranyl sulfate sheets forming a weakly bonded three-layer sandwich. The sandwich layers are linked to one another by hydrogen bonds through insular Mg(H2O)6 octahedra and isolated H2O groups. The mineral is named for John Wetherill (1866–1944) and George W. Wetherill (1925–2006).

Organically Templated Layered Uranyl Molybdate [C3H9NH+]4[(UO2)3(MoO4)5] Structurally Based on Mineral-Related Modular Units

“…1.761 (12) Mo5-O26 1.702 (14) Mo4-O23 1.761 (11) Mo5-O24 1.765 (13) Mo4-O20 1.795 (11) Mo5-O13 1.767 (12) <Mo4-O> 1.755 <Mo5-O> 1.725…”

“…The same locality also bears bobcookite, NaAl(UO2)2(SO4)4•18H2O [12], fermiite, Na4(UO2)(SO4)3•3H2O, and oppenheimerite, Na2(UO2)(SO4)2•3H2O [13], whose structures are comprised of [(UO2)(SO4)2(H2O)] 2− chains (Figure 1с). This topology is common for synthetic uranyl sulfates, selenates, and chromates [14].…”

“…Therein, four out of five equatorial vertices of uranium polyhedra are occupied by oxygen atoms of sulfate tetrahedra while the fifth is occupied by a water molecule; all such vertices are similarly oriented in the layer plane. The layers in the structure of wetherillite, [12], differ in that the vertices occupied by water molecules exhibit two positions ( Figure 1i). Yet another layered arrangement is formed by vertex-sharing UO 6 (H 2 O) and SO 4 moieties (Figure 1j) in the structure of beshtauite, (NH 4 ) 2 (UO 2 )(SO 4 ) 2 •2H 2 O [27].…”

Synchrotron Diffraction Study of the Crystal Structure of Ca(UO2)6(SO4)2O2(OH)6·12H2O, a Natural Phase Related to Uranopilite

“…For instance, in the crystal structures of zippeite-group minerals, (UO 7 ) pentagonal bipyramids share edges to form infinite chains linked into [(UO 2 ) 2 (SO 4 )φ 2 ] sheets (φ = O 2− , (OH) − ) via (SO 4 ) tetrahedra [25]. The highest U:S ratios known so far are 8:1, which has been reported for jáchymovite, (UO 2 ) 8 (SO 4 )(OH) 14 •13H 2 O [30], and 6:1, which has been reported for both uranopilite, (UO 2 ) 6 (SO 4 )O 2 (OH) 6 •14H 2 O, and metauranopilite, (UO 2 ) 6 (SO 4 )(OH) 10 •5H 2 O (?) [31].…”

“…It would not be an exaggeration to say that, within the last few years, uranium mineralogy and crystal chemistry has witnessed a true renaissance due to the discoveries of exceptional suites of new uranium minerals in Jáchymov, Czech Republic [1][2][3][4][5][6] and San Juan County, Utah, USA [7][8][9][10][11][12][13][14][15][16][17][18][19]. The diversity of new natural uranyl sulfates is of particular interest [1- 5,[7][8][9][10][11][12][13][14][15]17,18,20,21], since most of them do not have direct synthetic analogues, and are therefore new to the synthetic inorganic chemistry as well. Most of the new uranium sulfates are the products of secondary low-temperature hydrothermal processes, which are often associated with the crystallization of very complex mineral species such as ewingite, Mg 8 Ca 8 (UO 2 ) 24 (CO 3 ) 30 O 4 (OH) 12 (H 2 O) 138 , which is the most structurally complex mineral known today [6].…”