Paddlewheelite, a New Uranyl Carbonate from the Jáchymov District, Bohemia, Czech Republic

Abstract

Paddlewheelite, MgCa 5 Cu 2 [(UO 2 )(CO 3 ) 3 ] 4 ·33H 2 O, is a new uranyl carbonate mineral found underground in the Svornost mine, Jáchymov District, Bohemia, Czech Republic, where it occurs as a secondary oxidation product of uraninite. The conditions leading to its crystallization are complex, likely requiring concomitant dissolution of uraninite, calcite, dolomite, chalcopyrite, and andersonite. Paddlewheelite is named after its distinctive structure, which consists of paddle-wheel clusters of uranyl tricarbonate units bound by square pyramidal copper "axles" and a cubic calcium cation "gearbox." Paddle wheels share edges with calcium polyhedra to form open sheets that are held together solely by hydrogen bonding interactions. The new mineral is monoclinic, Pc, a = 22.052(4), b = 17.118(3), c = 19.354(3) Å, β = 90.474(2) • , V = 7306(2) Å 3 and Z = 4. Paddlewheelite is the second-most structurally complex uranyl carbonate mineral known after ewingite and its structure may provide insights into the insufficiently described mineral voglite, as well as Cu-U-CO 3 equilibrium in general.the surface of used nuclear fuel exposed to groundwater. Uranyl carbonate minerals can record and be used to diagnose groundwater conditions at the moment of crystallization, allowing for more accurate safety assessments of U contaminated water transport and longer-term radionuclide release models for Ca-U-C systems. Here we describe the crystal-chemical and spectroscopic properties of the new Ca-Mg-Cu uranyl carbonate mineral paddlewheelite, whose structure contains several first known instances for uranyl minerals, including isolated square pyramidal copper polyhedra and calcium cations in cubic coordination. These two unique cation polyhedra bind to UTC units, forming an extraordinary paddlewheel motif arranged into an open-sheet topology that may provide several clues to understanding the structure and formation of the poorly described mineral voglite,The name paddlewheelite was chosen to reflect the unique structure of the mineral that resembles the paddlewheel of a steamboat. Four uranyl tricarbonate paddles are bound by two square pyramidal CuO 5 "axles" and a CaO 8 "gearbox" in cubic coordination. The new mineral and its name were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2017-098). The holotype specimen is deposited in the Natural History Museum of Los Angeles County, under catalogue number 66696. OccurrenceCrystals of paddlewheelite were collected underground from a bifurcation of the Prokop vein on the 5th level of the Svornost mine, Jáchymov District, Bohemia, Czech Republic. The Svornost mine (Einigkeit in German, Concord in English) is named for one of the six major ore clusters in the Jáchymov ore district. "Five-element" (Ni-Co-As-Ag-Bi, +/− U) mineralization was deposited there during episodic fracturing and space filling by metal-rich hydrothermal solutions. Further details regarding the geology and hydrothermal history of the J...

Structural, mechanical, spectroscopic and thermodynamic characterization of the copper-uranyl tetrahydroxide mineral vandenbrandeite

“…In particular, the copper-uranyl tetrahydroxide mineral (Cu(UO 2 )(OH) 4 ) vandenbrandeite, studied in this work, is one of the most important uranyl minerals containing copper. Other important uranyl and copper containing minerals are the uranyl silicate cuprosklodowskite, 71,72 the uranyl carbonates paddlewheelite 73 and voglite, 74 the uranyl vanadate sengierite, 75 the uranyl sulfates johannite, [76][77][78] and pseudojohannite, 79 the uranyl phosphates torbernite, metatorbernite 80 and ulrichite, 81,82 and the uranyl arsenates zeunerite and metazeunerite. 80 The knowledge of the structures of uranyl minerals [83][84][85] is crucial to evaluate the possible incorporation of ssion products and transuranic elements into their crystal structures.…”

“…While the crystal structures of the majority of the uranyl minerals are reasonably well-known, [71][72][73][74][75][76][77][78][79][80][81][82][83][84] the positions of the hydrogen atoms in their unit cells are unknown in many cases. The solution of this problem is currently being attempted by means of experimental X-ray diffraction techniques 72,[109][110][111][112] and rst-principles theoretical methods.…”

Structure Refinement and Thermal Stability Studies of the Uranyl Carbonate Mineral Andersonite, Na2Ca[(UO2)(CO3)3]·(5+x)H2O

“…Currently, there are almost 40 known uranyl carbonate mineral species. From the perspective of crystallography, this group of compounds is of considerable interest mainly due to the recent discoveries of the structurally highly complex minerals ewingite, Mg 8 Ca 8 (UO 2 ) 24 (CO 3 ) 30 O 4 (OH) 12 ·138(H 2 O) [9] and paddlewheelite, MgCa 5 Cu 2 (UO 2 ) 4 (CO 3 ) 12 ·33(H 2 O) [10]. However, members of this family are often challenging for research due to low crystallinity; crystal structures of about half of the uranyl carbonate minerals are still undetermined.…”

Natromarkeyite and pseudomarkeyite, two new calcium uranyl carbonate minerals from the Markey mine, San Juan County, Utah, USA

“…the Ca2–C5O 3 –C5O 3 –Ca2 linkages in markeyite). These three structures are nearly as complex as the suite of complex uranyl carbonate structures based upon ‘paddle-wheel’ units, which have I G,total >2000 bits/unit cell: braunerite, K 2 Ca(UO 2 )(CO 3 ) 3 ⋅6H 2 O (Plášil et al , 2016), línekite, K 2 Ca 3 [(UO 2 )(CO 3 ) 3 ] 2 ⋅7H 2 O (Plášil et al , 2017) and paddlewheelite, MgCa 5 Cu 2 (UO 2 ) 4 (CO 3 ) 12 ⋅33H 2 O (Olds et al , 2018). The most structurally complex uranyl carbonate mineral, ewingite, Mg 8 Ca 8 (UO 2 ) 24 (CO 3 ) 30 O 4 (OH) 12 ⋅180H 2 O (Olds et al , 2017b), is also the most structurally complex mineral known.…”

“…These are usually incorporated into heteropolyhedral sheets, such as in the minerals liebigite (Mereiter, 1982), grimselite (Plášil et al , 2012) and línekite (Plášil et al , 2017). There are also complex clusters, such as those in ewingite (Olds et al , 2017b) and paddlewheelite (Olds et al , 2018), which combine UTCs with other building units, such as the trimers of uranyl polyhedra in ewingite and the square–pyramidal copper polyhedra in paddlewheelite. Less commonly, the structural units in uranyl carbonate minerals are infinite sheets of uranyl polyhedra and carbonate triangles, such as in rutherfordine (Finch et al , 1999), fontanite (Hughes and Burns, 2003), sharpite (Plášil, 2018) and meyrowitzite (Kampf et al , 2019e), and sheets containing also lanthanide-centred polyhedra, such as in bijvoetite-(Y) and kamotoite-(Y) (Plášil and Petříček, 2017).…”