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Crystallography and mineralogy of Uranium

Goal: To determine crystal structures of uranium minerals and compounds and to hunt for new uranium minerals.

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Jakub Plasil
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The new mineral chenowethite, Mg(H2O)6[(UO2)2(SO4)2(OH)2]·5H2O, was found in efflorescence crusts on tunnel walls at the Blue Lizard, Green Lizard and Markey uranium mines in Red Canyon, San Juan County, Utah, USA. The crystals are long, thin blades up to about 0.5 mm long, occurring in irregular sprays and subparallel groups. Chenowethite is pale green yellow. It has white streak, vitreous to silky luster, brittle tenacity, splintery and stepped fracture and two cleavages: {010} perfect and {001} good. It has a hardness (Mohs) of about 2 and is nonfluorescent in both long- and short-wave ultraviolet illumination. The density is 3.05(2) g/cm3. Optically, crystals are biaxial (−) with α = 1.530(2), β = 1.553(2) and γ = 1.565(2) (white light). The 2V is 72(2)° and dispersion is r > v (slight). The optical orientation is X = b, Y = a, Z = c and the mineral exhibits weak pleochroism in shades of pale green yellow: X < Y < Z. The Raman spectrum is consistent with the presence of UO22+, SO42− and OH–/H2O. The empirical formula from electron microprobe analysis and arranged in accordance with the structure is (Mg0.71Fe2+0.09Co0.05Ni0.04)∑0.89(H2O)6[(UO2)2(SO4)2(OH)2]·[(H2O)4.78(NH4)0.22]∑5.00. Chenowethite is orthorhombic, space group Cmcm; the unit-cell parameters are a = 6.951(2), b = 19.053(6), c = 16.372(5) Å, V = 2168.19(7) Å3 and Z = 4. The crystal structure of chenowethite (R1 = 0.0396 for 912 I > 2σI reflections) contains [(UO2)2(SO4)2(OH)2]2− sheets that are topologically equivalent to those in deliensite, feynmanite, greenlizardite, johannite, meitnerite and plášilite.
Jakub Plasil
added a research item
IMA No. 2022-054 Pendevilleite-(Y) Mg2Y3Al(UO2)2(CO3)7(OH)6(H2O)16 Pnv-Y Kamoto East Cu-Co deposit, Kolwezi mining district, Lualaba, Democratic Republic of the Congo (10°43’08.8” S, 25°25’04.7” E) Jakub Plášil*, Gwladys Steciuk, Radek Škoda, Simon Philippo and Mael Guennou *E-mail: plasil@fzu.cz New structure type Triclinic: P�1; structure determined a = 11.9534(6), b = 13.499(2), c = 16.239(1) Å, α = 107.183(5), β = 92.532(5), γ = 110.127(5)° 15.3(100), 11.44(23), 10.26(33), 8.35(32), 8.04(28), 7.16(21), 6.84(17), 6.35(28) Type material is deposited in the collections of the Musée d’Histoire Naturelle, Rue Münster 25, Luxembourg 2160, Luxembourg, catalogue number VP230 How to cite: Plášil, J., Steciuk, G., Škoda, R., Philippo, S. and Guennou, M. (2022) Pendevilleite-(Y), IMA 2022-054. CNMNC Newsletter 69; Mineralogical Magazine, 86, https:// doi.org/10.1180/mgm.2022.115.
Francisco Colmenero
added a research item
Due to the high solubility of uranyl sulfate and selenite minerals, the investigation involving the determination of the crystal structures and physical properties of these minerals is essential in actinide environmental chemistry for the simulation of uranium migration from uraninite deposits and nuclear waste repositories. However, the determination of the complete crystal structures of the uranyl sulfate minerals johannite (Cu(UO) (SO) (OH) · 8H O) and pseudojohannite (Cu (UO) (SO) O (OH) · 12H O) and the uranyl selenite mineral derriksite (Cu [((UO)(SeO) (OH) ]) has not been feasible so far. In this work, the crystal structures of these minerals, including the positions of the hydrogen atoms, are determined using first principles solid-state methods based on periodic density functional theory using plane wave basis sets and pseudo-potentials. The lattice parameters and associated geometrical variables as well as the corresponding X-ray diffraction patterns derived from the computed crystal structures are in excellent agreement with their experimental counterparts, derived from the corresponding experimental structures lacking the hydrogen atom positions. The complete crystal structure of derriksite is also determined by refinement from X-ray diffraction data, the resulting structure being consistent with the computed one. The knowledge of the positions of H atoms is of fundamental importance not only because they define the corresponding hydrogen bond networks holding together the atoms in the structures, but also because it allows for the efficient, inexpensive and safe determination of the physical properties using first principles methods. This feature is particularly important in the case of uranium-containing minerals due to their radiotoxicity, complicating the handling of the samples and experimental measurements. In this work, from the computed crystal structures, the elasticity tensors of these minerals are computed using the finite displacement method and a rich set of elastic properties including the bulk, Young's and shear moduli, the Poisson's ratio, ductility, anisotropy and hardness indices and bulk modulus derivatives with respect to pressure derivatives are determined.
Jakub Plasil
added a research item
The new mineral scenicite (IMA2021-057), [(UO2)(H2O)2(SO4)]2·3H2O, was found in the Green Lizard, Giveaway-Simplot, Markey and Scenic mines, White Canyon district, San Juan County, Utah, USA, where it occurs as a secondary phase on granular quartz matrix in association with various combinations of deliensite, gypsum, natrozippeite, rietveldite and shumwayite. Scenicite crystals are transparent, light green-yellow, poorly formed blades or prisms, up to 0.1 mm in length. The mineral has white streak and vitreous lustre. It exhibits https://doi.org/10.1180/mgm.2022.53 Published online by Cambridge University Press 2 bright greenish-white fluorescence (405 nm laser). It is brittle with irregular, curved fracture and a Mohs hardness of ~2. It has an excellent {100} and good {001} cleavages. The calculated density is 3.497 g cm-3. Optically, the mineral is biaxial (-) with α = 1.556(2), β = 1.573(2), γ = 1.576(2) (white light); 2V = 45(3)°; extreme r < v dispersion; orientation: X = c, Y = a, Z = b; pleochroism: X and Y colourless, Z light green-yellow; X = Y < Z. The Raman spectrum exhibits bands consistent with UO 2 2+ , SO 4 2-and O-H. Electron microprobe analysis provided the empirical formula U 1.996 S 2.005 O 19 H 13.997. The five strongest X-ray powder diffraction lines are [d obs Å(I)(hkl)]: 7.69(70)(201), 5.63(100)(111), 4.92(84)(202,310), 4.80(93)(401) and 3.398(55)(020,120,511,601). Scenicite is orthorhombic, Pca2 1 , a = 21.2144(15), b = 6.8188(3) c = 11.2554(6), V = 1628.18(16) Å 3 and Z = 4. In the structure of scenicite (R 1 = 0.0365 for 1259 I > 2I), linkages of pentagonal bipyramids and tetrahedra form an infinite neutral [(UO 2)(SO 4)(H 2 O) 2 ] chain. The structure of shumwayite contains topologically identical chains.
Jakub Plasil
added 2 research items
Oldsite (IMA2021–075), ideally K2Fe2+[(UO2)(SO4)2]2(H2O)8, is a new uranyl sulfate mineral found on specimens from the North Mesa Mine group, Temple Mountain, San Rafael district, Emery County, Utah, USA. It is a secondary mineral occurring with alum-(K), halotrichite, metavoltine, quartz, römerite, stanleyite, sulfur, szomolnokite, and mathesiusite. It forms rectangular blades flattened on {010} and elongated on [001], reaching about 0.3 mm in length. Crystals are yellow in color, transparent with a vitreous luster; the streak is very pale yellow. The mineral is nonfluorescent. Cleavage is excellent on {100}, and perfect on {010}; the Mohs hardness is about 2. Crystals are brittle with irregular, splintery fracture. The density measured by flotation in a mixture of methylene iodide and toluene is 3.31 g·cm–3; the calculated density is 3.298 g·cm–3 for the empirical formula and 3.330 g·cm–3 for the ideal formula. Oldsite is biaxial (+), with α = 1.552(2), β = 1.556(2), γ = 1.588(2) (measured in white light). The 2V measured directly on a spindle stage is 37(1)°; the calculated 2V is 39.6°. Dispersion is r < v, moderate. The optical orientation is X = b, Y = a, Z = c. The mineral is nonpleochroic. The empirical formula of oldsite (on the basis of 28 O apfu) is K1.93(Fe2+0.53Zn0.31V3+0.09Mg0.08)Σ1.02[(U0.98O2)(S1.01O4)2]2(H2O)8. The Raman spectrum is dominated by the vibrations of SO42– and UO22+ units. Oldsite is orthorhombic, Pmn21, a = 12.893(3), b = 8.276(2), c = 11.239(2) Å, V = 1199.2(5) Å3 and Z = 2. The five strongest powder X-ray diffraction lines are [dobs, Å (I, %) (hkl) ]: 8.29 (59) (010), 6.47 (82) (200), 5.10 (62) (210), 4.65 (100) (012, 211), 3.332 (55) (022, 221). The crystal structure of oldsite was refined from single-crystal X-ray data to R = 0.0258 for 2676 independent observed reflections, with Iobs > 3σ(I). Oldsite is an Fe2+ analog of svornostite; its crystal structure is based upon infinite chains of uranyl-sulfate polyhedra, which comprises pentagonal UO7 bipyramids sharing four of their equatorial vertices with sulfate tetrahedra such that each tetrahedron is linked to two uranyl bipyramids to form an infinite chain (the free, non-linking equatorial vertex of the uranyl bipyramid is an H2O group). The broader discussion on the origin and composition of uranyl sulfate minerals is made. The new mineral name honors American mineralogist, Dr. Travis A. Olds for his contribution to uranium mineralogy.
Through the combination of low-temperature hydrothermal synthesis and room-temperature evaporation, a synthetic phase similar in composition and crystal structure to the Earth’s most complex mineral, ewingite, was obtained. The crystal structures of both natural and synthetic compounds are based on supertetrahedral uranyl-carbonate nanoclusters that are arranged according to the cubic body-centered lattice principle. The structure and composition of the uranyl carbonate nanocluster were refined using the data on synthetic material. Although the stability of natural ewingite is higher (according to visual observation and experimental studies), the synthetic phase can be regarded as a primary and/or metastable reaction product which further re-crystallizes into a more stable form under environmental conditions.
Jakub Plasil
added a research item
Gurzhiite, ideally Al(UO2)(SO4)2F·10H2O, is a new uranyl sulfate mineral from the Bykogorskoe U deposit, Northern Caucasus, Russia. It occurs as fine-grained aggregates forming veinlets up to 50 cm long in cracks of the brecciated rock. Gurzhiite aggregates are composed of small bladed crystals up to 0.1 mm across. Associated minerals include khademite and quartz. Gurzhiite is pale yellow in crystals, lemon yellow in aggregates, transparent with vitreous lustre and white streak. It is brittle and has an irregular fracture. Cleavage is good on {001}. The new mineral exhibits a bright yellow-green fluorescence under both longwave and shortwave UV radiation. Mohs hardness is ~2. Dmeas = 2.52(3) g/cm 3 , Dcalc = 2.605 g/cm 3. The mineral is biaxial https://doi.org/10.1180/mgm.2022.34 Published online by Cambridge University Press (-) with α = 1.528(3), β = 1.538(2), γ = 1.544(3) (589 nm); 2Vmeas= 80(10), 2Vcalc = 75.1. The empirical formula calculated on the basis of 21(O + F) apfu is Al0.92Zn0.05Fe 3+ 0.03Na0.03U0.95S2.00O9.85F0.99 · 10.16H2O. Gurzhiite is triclinic, space group P-1, a = 7.193(2), b = 11.760(2), c = 11.792(2) Å, α = 67.20(3), β = 107.76(3), γ = 89.99(3)°, V = 867.7(4) Å 3 and Z = 2. The five strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 10.24(100)(001); 5.40(14)(-1-11); 5.11(54)(002); 3.405(11)(-211); 3.065(11)(-1-13). The crystal structure of gurzhiite is based upon uranyl-sulfate chains of the same type as have been found e.g., in. bobcookite or svornostite. Between the chains are two types of Al-octahedra-Al1(H2O)6 and Al2F2(H2O)4. The entire structure is held by a complex network of H-bonds. The new mineral honors Russian mineralogist and crystallographer Dr. Vladislav V. Gurzhiy in recognition for his contributions to uranium mineralogy and crystallography.
Jakub Plasil
added a research item
Weathering of ore minerals proceeds through initial transient products to many crystalline secondary minerals. However, the initial products are usually poorly characterized or overlooked because of their extremely small particle size, poor crystallinity, and chemical variability. Here, we document the strength of the precession-assisted three-dimensional (3D) electron diffraction in the characterization of such nanocrystalline phases in a case study on uraninite-sulfide weathering in Jaćhymov (Czech Republic). The glassy, yellow-to-green near-amorphous coatings on the ore fragments contain at least two phases. 3D electron diffraction identified K 0.268 [(U 6+ O 2) 2 O(OH) 2.25 ](H 2 O) 0.676 as the dominant phase, yet unknown from nature, with fourmarierite topology of its uranyl sheets. The minor phase was characterized as K-rich fourmarierite, but its crystallinity was too low for complete structure refinement. Glassy and brownish coatings occur on samples that are not rich in uraninite. They are mainly composed of schwertmannite, i.e., iron oxides with structural sulfate and, in the case of our material, with a substantial amount of adsorbed uranium. This material contains up to 17 wt % of UO 3,total and 0.5−1.4 wt % of CuO according to the WDS study. Surprisingly, X-ray photoelectron spectroscopy showed that the adsorbed uranium is a mixture of U(IV) and U(VI), the reduced species formed most probably during Fe(II) oxidation to Fe(III) and coeval precipitation of schwertmannite. Hence, here, uraninite weathering produces initial nanocrystalline phases with fourmarierite-sheet topology. In the abundance of iron, schwertmannite forms instead and adsorbs much uranium, both tetra-and hexavalent. This study demonstrates the power of 3D electron diffraction techniques, such as precession electron diffraction tomography, to study the alteration nanosized phases. Such nanocrystalline phases and minerals should be expected in each weathering system and may impart significant control over the fate of metals and metalloids in such systems.
Jakub Plasil
added a research item
A synthetic analogue of the mineral natroboltwoodite was obtained unprecedently during a dissolution experiment with the mineral yttrialite-(Y), at a temperature of 200 °C, pressure ∼1.5 MPa, and strongly alkaline conditions. Natroboltwoodite formed along with analcime and aegirine. Single crystals of natroboltwoodite obtained allowed us to reveal its crystal structure for the first time. It differs from the other known uranyl silicate structures in the size of its respective unit-cell volume. The increased size of the structure corresponds to the positional and occupational disorder among one of the Si-tetrahedrally coordinated sites. On the basis of structural complexity parameters, a comparison involving both known synthetic and naturally occurring uranyl silicates is provided and discussed.
Jakub Plasil
added a research item
The new mineral paramarkeyite (IMA2020–024), Ca2(UO2)(CO3)3·5H2O, was found in the Markey mine, San Juan County, Utah, USA, where it occurs as a secondary phase on gypsum-coated asphaltum in association with andersonite, calcite, gypsum and natromarkeyite. Paramarkeyite crystals are transparent, pale green-yellow, striated tablets, up to 0.11 mm across. The mineral has white streak and vitreous lustre. It exhibits moderate bluish white fluorescence (405 nm laser). It is very brittle with irregular, curved fracture and a Mohs hardness of 2½. It has an excellent {100} cleavage and probably two good cleavages on {010} and {001}. The measured density is 2.91(2) g cm–3. Optically, the mineral is biaxial (–) with α = 1.550(2), β = 1.556(2), γ = 1.558(2) (white light); 2V = 60(2)°; strong r > v dispersion; orientation: Y = b; nonpleochroic. The Raman spectrum exhibits bands consistent with UO22+, CO32– and O–H. Electron microprobe analysis provided the empirical formula (Ca1.83Na0.20Sr0.03)∑2.05(UO2)(CO3)3·5H2O (+0.07 H). Paramarkeyite is monoclinic, P21/n, a = 17.9507(7), b = 18.1030(8), c = 18.3688(13) Å, β = 108.029(8)°, V = 5676.1(6) Å3 and Z = 16. The structure of paramarkeyite (R1 = 0.0647 for 6657 I > 2I) contains uranyl tricarbonate clusters that are linked by Ca–O polyhedra to form heteropolyhedral layers. The structure of paramarkeyite is very similar to those of markeyite, natromarkeyite and pseudomarkeyite.
Jakub Plasil
added a research item
In this work, the structures of chemically related uranyl-oxide minerals agrinierite and rameauite have been revisited and some corrections to the available structure data are provided. Both structures were found to be twinned. The two minerals are chemically similar, and though their structures differ considerably, their unit-cell metrics are similar. Agrinierite was found to be twinned by metric merohedry (diffraction type I), whereas the structure of rameauite is twinned by reticular merohedry (diffraction type II). The twinning of the monoclinic unit cells (true cells) leads to pseudo-orthorhombic or pseudo-tetragonal supercells in the single-crystal diffraction patterns of both minerals. According to the new data and refinement, agrinierite is monoclinic (space group Cm ), with a = 14.069 (3), b = 14.220 (3), c = 13.967 (3) Å, β = 120.24 (12)° and V = 2414.2 (12) Å ³ ( Z = 2). The twinning can be expressed as a mirror in (101) (apart from the inversion twin), which leads to a supercell with a = 14.121, b = 14.276, c = 24.221 Å and V = 2 × 2441 Å ³ , which is F centered. The new structure refinement converged to R = 3.54% for 6545 unique observed reflections with I > 3σ( I ) and GOF = 1.07. Rameauite is also monoclinic (space group Cc ), with a = 13.947 (3), b = 14.300 (3), c = 13.888 (3) Å, β = 118.50 (3)° and V = 2434.3 (11) Å ³ ( Z = 2). The twinning can be expressed as a mirror in ( 1 01) (apart from the inversion twin), which leads to a supercell with a = 14.223, b = 14.300, c = 23.921 Å and V = 2 × 2434 Å ³ , which is C centered. The new structure refinement of rameauite converged to R = 4.23% for 2344 unique observed reflections with I > 3σ( I ) and GOF = 1.48. The current investigation documented how peculiar twinning can be, not only for this group of minerals, and how care must be taken in handling the data biased by twinning.
Jakub Plasil
added a research item
Uranotungstite is an uranyl-tungstate mineral that was until recently only partially characterized with a formula originally given as (Fe2+,Ba,Pb)(UO2)2(WO4)(OH)4·12H2O and an unknown crystal structure. This mineral has been reinvestigated by electron microprobe analysis coupled with 3D electron diffraction. According to the electron microprobe data, the holotype material from the Menzenschwand uranium deposit (Black Forest, Germany) has the empirical formula (Ba0.35Pb0.27)Σ0.62¬[(U6+O2)2-(W6+0.98Fe3+0.26□0.75)O4.7(OH)2.5(H2O)1.75](H2O)1.67 (average of 8 points calculated on the basis of 2 U apfu; the H2O content derived from the structure). According to the precession-assisted 3D ED data, holotype uranotungstite from Menzenschwand is monoclinic, P21/m, with a = 6.318(5) Å, b = 7.388(9) Å, c = 13.71(4) Å, β = 99.04(13)° and V = 632(2) Å3 (Z = 2). The structure refinement of the 3D ED data using the dynamical approach (Robs = 0.0846 for 3287 independent observed reflections) provided a structure model composed of heteropolyhedral sheets. A β-U3O8-type sheet of idealized composition [(UO2)2W6+Fe0.253+□0.75O4.75(OH)1.5(H2O)1.75]0.25– is composed of UO7 polyhedra linked by (W,Fe)O5 polyhedra in which the W:Fe ratio is variable as well as the bulk occupancy of this site; the W site may also host a minor proportion of Cu, Mg, or V. In uranotungstite, the interlayer spaces between adjacent U-W-O sheets host water on one side and, on the other side, a partially occupied cation site mostly occupied by Ba and, to a lesser extent, Pb, as well as a partially occupied H2O site. This work is the first structural description of a natural uranyl-tungstate mineral and confirms the great structural and chemical flexibility of β-U3O8 type of sheets.
Jakub Plasil
added a research item
Nitscheite (IMA2020-078), (NH4)2[(UO2)2(SO4)3(H2O)2]·3H2O, is a new mineral species from the Green Lizard mine, Red Canyon, San Juan County, Utah, U.S.A. It is a secondary phase found in association with chinleite-(Y), gypsum, pyrite, and Co-rich rietveldite. Nitscheite occurs in subparallel and divergent intergrowths of yellow prisms, up to about 0.3 mm in length. Crystals are elongated on [101] and exhibit the forms {100}, {010}, {001}, and {11-1}. The mineral is transparent with vitreous luster and very pale-yellow streak. It exhibits bright green fluorescence under a 405 nm laser. The Mohs hardness is ~2. The mineral has brittle tenacity, curved fracture, and one good cleavage on {010}. The measured density is 3.30(2) g·cm-3. The mineral is easily soluble in RT H2O. The mineral is optically biaxial (-), α = 1.560(2), β = 26 1.582(2), γ = 1.583(2) (white light); 2Vmeas = 17(1)°; no dispersion; orientation X = b, Z ≈ [101]; pleochroism X colourless, Y and Z yellow; X < Y ≈ Z. Electron microprobe analysis provided the empirical formula (NH4)1.99U2.00S3.00O21H10.01. Nitscheite is monoclinic, P21/n, a = 17.3982(4), b = 12.8552(3), c = 17.4054(12) Å, β = 96.649(7)°, V = 3866.7(3) Å 3 , and Z = 8. The structure (R1 = 0.0329 for 4547 I > 3sigma(I) reflections) contains [(UO2)2(SO4)3(H2O)2]2- uranyl-sulfate sheets, which are unique among minerals, with NH4 and H2O groups between the sheets.
Jakub Plasil
added a research item
Uranyl carbonates are one of the largest groups of secondary uranium(VI)-bearing natural phases being represented by 40 minerals approved by the International Mineralogical Association, overtaken only by uranyl phosphates and uranyl sulfates. Uranyl carbonate phases form during the direct alteration of primary U ores on contact with groundwaters enriched by CO2, thus playing an important role in the release of U to the environment. The presence of uranyl carbonate phases has also been detected on the surface of “lavas” that were formed during the Chernobyl accident. It is of interest that with all the importance and prevalence of these phases, about a quarter of approved minerals still have undetermined crystal structures, and the number of synthetic phases for which the structures were determined is significantly inferior to structurally characterized natural uranyl carbonates. In this work, we review the crystal chemistry of natural and synthetic uranyl carbonate phases. The majority of synthetic analogs of minerals were obtained from aqueous solutions at room temperature, which directly points to the absence of specific environmental conditions (increased P or T) for the formation of natural uranyl carbonates. Uranyl carbonates do not have excellent topological diversity and are mainly composed of finite clusters with rigid structures. Thus the structural architecture of uranyl carbonates is largely governed by the interstitial cations and the hydration state of the compounds. The information content is usually higher for minerals than for synthetic compounds of similar or close chemical composition, which likely points to the higher stability and preferred architectures of natural compounds.
Jakub Plasil
added a research item
Revisiting the structure of uranyl arsenate mineral hügelite provided some corrections to the available structural data. The previous twinning model (by reticular merohedry) in hügelite has been corrected. Twinning of the monoclinic unit cell [ a = 7.0189 (7) Å, b = 17.1374 (10) Å, c = 8.1310 (10) Å and β = 108.904 (10)°], which can be expressed as a mirror in [100], leads to a pseudo-orthorhombic unit cell ( a = 7.019 Å, b = 17.137 Å, c = 61.539 Å and β = 90.02°), which is eight times larger, with respect to the unit-cell volume, than a real cell. Moreover, the unit cell of chosen here and the unit cell given by the previous structure description both lead to the same supercell. A new structure refinement undertaken on an untwinned crystal of hügelite resulted in R = 4.82% for 12 864 reflections with I obs > 3σ( I ) and GOF = 1.12. The hydrogen-bonding scheme has been proposed for hügelite for the first time.
Jakub Plasil
added a research item
The new mineral uranoclite (IMA2020-074), (UO2)2(OH)2Cl2(H2O)4, was found in the Blue Lizard mine, San Juan County, Utah, USA, where it occurs as tightly intergrown aggregates of irregular yellow crystals in a secondary assemblage with gypsum. The streak is very pale yellow and the fluorescence is bright green-white under 405 nm ultraviolet light. Crystals are translucent with vitreous lustre. The tenacity is brittle, the Mohs hardness is about 1½, the fracture is irregular. The mineral is soluble in H2O and has a calculated density of 4.038 g·cm–3. Electron microprobe analyses provided (UO2)2(OH)2.19Cl1.81(H2O)4. The six strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 8.85(38)(002), 5.340(100)(200,110), 5.051(63)(-202), 4.421(83)(112,004,202), 3.781(38)(-212) and 3.586(57)(014,-204). Uranoclite is monoclinic, P21/n, a = 10.763(8), b = 6.156(8), c = 17.798(8) Å, β = 95.656(15)°, V = 1173.5(18) Å3 and Z = 4. The structure is the same as that of synthetic (UO2)2(OH)2Cl2(H2O) in which the structural unit is a dimer consisting of two pentagonal bipyramids that share an equatorial OH–OH edge. The dimers are linked to one another only by hydrogen bonding. This is the second known uranyl mineral containing essential Cl and the first in which Cl coordinates to U6+.
Jakub Plasil
added a research item
Particularly interesting chemical variability in the U 4+ phosphate mineral vyacheslavite from Menzenschwand (Germany) has been discovered and investigated by means of electron-diffraction and micro-chemical methods. Suggested variability comprises namely the elevated contents of calcium and rare-earth elements (REEs). Based on the crystal structure refinement from 3D electron diffraction data, the structural formula of Ca-rich vyacheslavite studied is U0.895Ca0.105PO4(OH)0.790(H2O)0.210. In general, such compositional variability involving Ca2+ can be expressed as U1–xCaxPO4(OH)1–2x(H2O)2x. Based on detailed electron-probe microanalysis, regions extremely enriched in Y and Ln have been discovered, characterized by the contents up to 11 wt. % of Y2O3 and ~4.5 wt. % of Ln2O3. In addition to the above-mentioned substitution mechanism, substitution involving Y and Ln can be expressed as U4+ + OH–→REE3+ + H2O. Though the structure refinement has not provided direct evidence of H2O in the studied nano-fragments of vyacheslavite, the presence of H2O and its substitution at OH– sites is a reasonable and necessary charge-balancing mechanism. One H atom site was located during structure refinements, however, an additional H-site is only partially occupied and thus was not revealed from the refinement despite of the high-quality data. Substitutional trends observed here suggest possible miscibility or structural relationship between vyacheslavite, rhabdophane and ningyoite that may depend strongly on OH/H2O content; considering that all crystallize under similar paragenetic conditions.
Jakub Plasil
added 3 research items
Seaborgite (IMA2019-087), LiNa6K2(UO2)(SO4)5(SO3OH)(H2O), is a new mineral species from the Blue Lizard mine, Red Canyon, San Juan County, Utah, U.S.A. It is a secondary phase found on gypsum in association with copiapite, ferrinatrite, ivsite, metavoltine, and römerite. Seaborgite occurs in sprays of light-yellow, long flattened prisms or blades, up to about 0.2 mm in length. Crystals are elongated on [100], flattened on {010}, and exhibit the forms {100}, {010}, {001}, and {10-1}. The mineral is transparent with vitreous luster and very pale-yellow streak. It exhibits bright lime-green fluorescence under a 405 nm laser. The Mohs hardness is ~2½. The mineral has brittle tenacity, curved or conchoidal fracture, and one good cleavage on {100}. The measured density is 2.97(2) g·cm-3. The mineral is immediately soluble in RT H2O. The mineral is optically biaxial (–), α = 1.505(2), β = 1.522(2), γ = 1.536(2) (white light); 2Vmeas = 85(1)°; moderate r < v dispersion; orientation X ^ a ≈ 10°; pleochroic X colourless, Y and Z light green-yellow; X < Y ≈ Z. Seaborgite EPMA and LA-ICP-MS analyses undermeasured Li, K, and Na. The empirical formula using Li, Na, and K based on the structure refinement is Li1.00Na5.81K2.19(UO2)(SO4)5(SO3OH)(H2O). Seaborgite is triclinic, P–1, a = 5.4511(4), b = 14.4870(12), c = 15.8735(15) Å, α = 76.295(5), β = 81.439(6), γ = 85.511(6)°, V = 1203.07(18) Å3, and Z = 2. The structure (R1 = 0.0377 for 1935 I > 2I) contains [(UO2)2(SO4)8]4– uranyl-sulfate clusters that are linked into a band by bridging LiO4 tetrahedra. The bands are linked through peripheral SO4 tetrahedra forming a thick heteropolyhedral layer. Channels within the layers contain a K site, while an additional K site, six Na sites, and an SO3OH group occupy the space between the heteropolyhedral layers.
A rare supergene uranyl phosphate mineral, phurcalite, was found on a few specimens originating from the dump material of the Eduard shaft, the Jáchymov ore district, Czech Republic. Phurcalite forms yellow to yellowish-orange perfect prismatic crystals, reaching up to 3 - 4 mm in cavities of vuggy quartz-dominated gangue. Phurcalite was found in the association with walpurgite, uranophane-α, and members of the metatorbernite-metazeunerite series. According to single-crystal X-ray data phurcalite is orthorhombic, space group Pbca, with a 17.3785(8), b 15.9864(6), c 13.5477(6) Å, and V 3763.8(3) Å3. Its crystal structure has been refined to R = 3.56 % for 3488 unique observed reflections [Iobs>3σ(I)] collected on a Rigaku SuperNova X-ray diffractometer with an Atlas S2 CCD detector and focused MoKα radiation. The results of the structure refinement are in line with the recently published structure refinement of phurcalite from Shinkolobwe (Africa). Nevertheless, in phurcalite from Jáchymov, the substitution of As for P takes place at greater extent. The structural formula obtained for the crystal from Jáchymov is Ca2[(UO2)3O2(PO4)1.753(AsO4)0.247]·7H2O, Z = 8, Dcalc. = 4.409 g/cm3.
The crystal structure of the rare supergene Pb2+-containing uranyl-oxide mineral wölsendorfite has been revisited employing the single-crystal X-ray diffraction. The new structure refinement provided deeper insight into the complex structure of this mineral, revealing additional H2O sites in the interlayer complex and confirming the entrance of the Ca2+ into the structure. Studied wölsendorfite is orthorhombic, space group Cmcm, with unit cell dimensions a = 14.1233(8) Å, b = 13.8196(9) Å, c = 55.7953(12) Å, V = 10890.0(10) Å3, and Z = 8. The structure has been refined to an agreement index (R) of 10.74% for 3815 reflections with I > 3σ(I) collected using a microfocus X-ray source from the microcrystal. In line with the previous structure determination, the refined structure contains U–O–OH sheets of the wölsendorfite topology and an interstitial complex comprising nine symmetrically unique Pb sites, occupied dominantly by Pb2+. Nevertheless, one of the sites seems to be plausible for hosting Ca2+. Its presence has been successfully modeled by the refinement and further supported by the crystal-chemical considerations. The structural formula of wölsendorfite crystal studied is Pb6.07Ca0.68[(UO2)14O18(OH)5]O0.5(H2O)12.6, with Z = 8, Dcalc. = 6.919 g·cm–3 (including theoretical 30.2 H atoms). The rather complex structure of wölsendorfite makes it the third most complex known uranyl-oxide hydroxy-hydrate mineral.
Jakub Plasil
added a research item
The new minerals natromarkeyite, Na 2 Ca 8 (UO 2) 4 (CO 3) 13 (H 2 O) 24 ⋅3H 2 O (IMA2018-152) and pseudomarkeyite, Ca 8 (UO 2) 4 (CO 3) 12 (H 2 O) 18 ⋅3H 2 O (IMA2018-114) were found in the Markey mine, San Juan County, Utah, USA, where they occur as secondary phases on asphaltum. Natromarkeyite properties are: untwinned blades and tablets to 0.2 mm, pale yellow green colour; transparent; white streak; bright bluish white fluorescence (405 nm laser); vitreous to pearly lustre; brittle; Mohs hardness 1½ to 2; irregular fracture; three cleavages ({001} perfect, {100} and {010} good); density = 2.70(2) g cm-3 ; biaxial (-) with α = 1.528(2), β = 1.532(2) and γ = 1.533(2); and pleochroism is X = pale green yellow, Y ≈ Z = light green yellow. Pseudomarkeyite properties are: twinned tapering blades and tablets to 1 mm; pale green yellow colour; transparent; white streak; bright bluish white fluorescence (405 nm laser); vitreous to pearly lustre; brittle; Mohs hardness ≈ 1; stepped fracture; three cleavages ({10 1} very easy, {010} good, {100} fair); density = 2.88(2) g cm-3 ; biaxial (-) with α = 1.549(2), β = 1.553(2) and γ = 1.557(2); and it is nonpleochroic. The Raman spectra of markeyite, natromar-keyite and pseudomarkeyite are very similar and exhibit bands consistent with UO 2 2+ , CO 3 2-and O-H. Electron microprobe analyses provided the empirical formula Na 2.01 Ca 7.97 Mg 0.03 Cu 2+ 0.05 (UO 2) 4 (CO 3) 13 (H 2 O) 24 ⋅3H 2 O (-0.11 H) for natromarkeyite and Ca 7.95 (UO 2) 4 (CO 3) 12 (H 2 O) 18 ⋅3H 2 O (+0.10 H) for pseudomarkeyite. Natromarkeyite is orthorhombic, Pmmn, a = 17.8820(13), b = 18.3030(4), c = 10.2249(3) Å, V = 3336.6(3) Å 3 and Z = 2. Pseudomarkeyite is monoclinic, P2 1 /m, a = 17.531(3), b = 18.555(3), c = 9.130(3) Å, β = 103.95(3)°, V = 2882.3(13) Å 3 and Z = 2. The structures of natromarkeyite (R 1 = 0.0202 for 2898 I > 2σI) and pseudomarkeyite (R 1 = 0.0787 for 2106 I > 2σI) contain uranyl tricarbonate clusters that are linked by (Ca/Na)-O polyhedra forming thick corrugated heteropolyhedral layers. Natromarkeyite is isostructural with markeyite; pseudomarkeyite has a very similar structure.
Francisco Colmenero
added a research item
The research involving the crystal structures and properties of uranyl carbonate minerals is essential in actinide environmental chemistry due to the fundamental role played by these minerals in the migration of actinides from uranium deposits and nuclear waste repositories and in the investigation of accidental site contaminations. In this work, the crystal structure, hydrogen bonding network, X-ray diffraction pattern and mechanical properties of six important uranyl carbonate minerals, roubaultite (Cu2[(UO2)3(CO3)2O2 (OH)2] · 4 H2O), fontanite (Ca[(UO2)3(CO3)2O2 ] · 6 H2O), sharpite (Ca[(UO2)3(CO3)4 ] · 3 H2O), widenmannite (Pb2[(UO2)(CO3)2(OH)2]), grimselite (K3Na[(UO2)(CO3)3 ] · H2O) and čejkaite (Na4 [(UO2)(CO3)3 ]), are investigated using first principles solid-state methods based in Density Functional Theory. The determination of the positions of the hydrogen atoms in the unit cells of fontanite, sharpite and grimselite minerals, defining the hydrogen bonding network in their crystal structures, has not been feasible so far due to the low quality of their experimental X-ray diffraction patterns. The full crystal structures of these minerals are obtained here and their hydrogen bonding networks are studied in detail. Furthermore, the experimental structures of roubaultite, widenmannite and čejkaite, obtained by refinement from X-ray diffraction data, are confirmed. In the six cases, the computed unit-cell parameters and the associated geometrical variables are in excellent agreement with the available experimental information. Furthermore, the X-ray diffraction patterns computed from the optimized structures are in satisfactory agreement with their experimental counterparts. The knowledge of the full crystal structures, being extraordinarily relevant for many scientific fields, is also extremely interesting because it opens the possibility of determining their physico-chemical properties using the first principles methodology. The measurement of these properties under safe conditions is very expensive and complicated due to the radiotoxicity of these minerals. In this paper, a large set of relevant mechanical properties of these minerals are determined including their bulk, shear and Young moduli, the Poisson's ratio, ductility, hardness and anisotropy indices and bulk modulus pressure derivatives. These properties have not been measured so far and, therefore, are predicted here. Four of these minerals, roubaultite, fontanite, sharpite and widemmannite, are highly anisotropic and exhibit negative mechanical phenomena under the effect of small external pressures.
Francisco Colmenero
added a research item
In this paper, the fundamental thermodynamic functions of six important uranyl carbonate minerals, roubaultite, fontanite, widenmannite, grimselite, čejkaite and bayleyite, are computed using first principles solid-state methods based on Periodic Density Functional Theory, from their energy-optimized crystal structures determined in previous works. These properties are obtained within a wide range of temperature (250-800 K) and are employed in order to derive the thermodynamic functions of formation of these minerals in terms of the elements. The resulting temperature-dependent functions of formation are merged with the thermodynamic functions of other prominent uranyl-containing minerals, also determined using theoretical methods, to determine a rich set of thermodynamic functions of reaction for a series of chemical reactions relating these mineral phases. The influence of the presence of hydrogen peroxide in many of these reactions is also investigated. These additional minerals include uranyl oxide hydrates, hydroxides, peroxides, silicates, sulfates and other uranyl carbonate mineral (rutherfordine) and, therefore, a detailed and wide-ranging view of the relative thermodynamic stability of uranyl minerals is afforded. Unexpectedly, the uranyl tricarbonate minerals, grimselite, čejkaite and bayleyite, are shown to be by far the most stable phases within the full range of temperature considered and under the presence and absence of hydrogen peroxide. Furthermore, the analysis of the solubility products of the considered uranyl carbonate minerals, obtained from the Gibbs free energies of the dissolution reactions, reveals that the widespread belief of the great solubility of these minerals is not supported. Except for roubaultite and widenmannite, all these minerals are sparingly soluble. As a consequence, the development of accurate temperature-dependent thermodynamic functions of an even larger number of uranyl carbonate minerals is mandatory for the simulation of the migration of uranium from nuclear waste repositories, uraninite deposits and uranium contaminated sites, as well as for the study of the paragenetic sequence of uranyl minerals arising from the oxidative dissolution processes occurring in uraninite ore deposits and corrosion of spent nuclear fuel.
Francisco Colmenero
added a research item
The determination of the full crystal structure of the uranyl sulfate mineral uranopilite, (UO2 )6 (SO4)O2(OH)6·14 H2O, including the positions of the hydrogen atoms within the corresponding unit cell, has not been feasible up to date due to the poor quality of its X-ray diffraction pattern. In this paper, the complete crystal structure of uranopilite is established for the first time by means of first principles solid-state calculations based in Density Functional Theory employing a large plane wave basis set and pseudopotential functions. The computed unit-cell parameters and structural data for the non-hydrogen atoms are in excellent agreement with the available experimental data. The computed X-ray diffraction pattern is also in satisfactory agreement with the experimental pattern. The infrared spectrum of uranopilite is collected from a natural crystal specimen originating in Jáchymov (Czech Republic) and computed employing Density Functional Perturbation Theory. The theoretical and experimental vibrational spectra are highly consistent. Therefore, a full assignment of the bands in the experimental infrared spectrum is performed using a normal mode analysis of the first principles vibrational results. One overtone and six combination bands are recognized in the infrared spectrum. The elasticity tensor and phonon spectra of uranopilite are computed from the optimized crystal structure and used to analyze its mechanical stability, to obtain a rich set of elastic properties and to derive its fundamental thermodynamic properties as a function of temperature. Uranopilite is shown to have a large mechanical anisotropy and to exhibit the negative Poisson’s ratio and negative linear compressibility phenomena. The calculated specific heat and entropy at 298.15 K are 179.6 and 209.0 J·K^(-1)·mol^(-1), respectively. The computed fundamental thermodynamic functions of uranopilite are employed to obtain its thermodynamic functions of formation in terms of the elements and the thermodynamic properties of a set of chemical reactions relating uranopilite with a representative group of secondary phases of spent nuclear fuel. From the reaction thermodynamic data, the relative stability of uranopilite with respect to these secondary phases is evaluated as a function of temperature and under different hydrogen peroxide concentrations. From the results, it follows that uranopilite has a very large thermodynamic stability under the presence of hydrogen peroxide. The high stability of uranopilite under this condition justify its early crystallization in the paragenetic sequence of secondary phases occurring when uranium dioxide is exposed to sulfur-rich solutions.
Jakub Plasil
added a research item
The determination of the full crystal structure of the uranyl sulfate mineral uranopilite, (UO2)6(SO4)O2(OH)6.14H2O, including the positions of the hydrogen atoms within the corresponding unit cell, has not been feasible to date due to the poor quality of its X-ray diffraction pattern. In this paper, the complete crystal structure of uranopilite is established for the first time by means of first principles solid-state calculations based in density functional theory employing a large plane wave basis set and pseudopotential functions. The computed unit-cell parameters and structural data for the non-hydrogen atoms are in excellent agreement with the available experimental data. The computed X-ray diffraction pattern is also in satisfactory agreement with the experimental pattern. The infrared spectrum of uranopilite is collected from a natural crystal specimen originating in Jáchymov (Czech Republic) and computed employing density functional perturbation theory. The theoretical and experimental vibrational spectra are highly consistent. Therefore, a full assignment of the bands in the experimental infrared spectrum is performed using a normal mode analysis of the first principles vibrational results. One overtone and six combination bands are recognized in the infrared spectrum. The elasticity tensor and phonon spectra of uranopilite are computed from the optimized crystal structure and used to analyze its mechanical stability, to obtain a rich set of elastic properties and to derive its fundamental thermodynamic properties as a function of temperature. Uranopilite is shown to have a large mechanical anisotropy and to exhibit the negative Poisson's ratio and negative linear compressibility phenomena. The calculated specific heat and entropy at 298.15 K are 179.6 and 209.0 J K -1 mol -1 , respectively. The computed fundamental thermodynamic functions of uranopilite are employed to obtain its thermodynamic functions of formation in terms of the elements and the thermodynamic properties of a set of chemical reactions relating uranopilite with a representative group of secondary phases of spent nuclear fuel. From the reaction thermodynamic data, the relative stability of uranopilite with respect to these secondary phases is evaluated as a function of temperature and under different hydrogen peroxide concentrations. From the results, it follows that uranopilite has a very large thermodynamic stability in the presence of hydrogen peroxide. The high stability of uranopilite under this condition justify its early crystallization in the paragenetic sequence of secondary phases occurring when uranium dioxide is exposed to sulfur-rich solutions.
Jakub Plasil
added a research item
The new minerals natromarkeyite (IMA2018-152), Na 2 Ca 8 (UO 2) 4 (CO 3) 13 (H 2 O) 24 ·3H 2 O, and pseudomarkeyite (IMA2018-114), Ca 8 (UO 2) 4 (CO 3) 12 (H 2 O) 18 ·3H 2 O, were found in the Markey mine, San Juan County, Utah, USA, where they occur as secondary phases on asphaltum. Natromarkeyite properties: untwinned blades and tablets to 0.2 mm, pale yellow-green colour; transparent; white streak; 2 bright bluish white fluorescence (405 nm laser); vitreous to pearly lustre; brittle; Mohs hardness 1½ to 2; irregular fracture; three cleavages ({001} perfect, {100} and {010} good); 2.70(2) g cm-3 density; biaxial (-) with α = 1.528(2), β = 1.532(2), γ = 1.533(2); pleochroism: X pale green yellow, Y ≈ Z light green yellow. Pseudomarkeyite properties: twinned tapering blades and tablets to 1 mm; pale green-yellow colour; transparent; white streak; bright bluish white fluorescence (405 nm laser); vitreous to pearly lustre; brittle; Mohs hardness ~1; stepped fracture; three cleavages ({10-1} very easy, {010} good, {100} fair); 2.88(2) g cm-3 density; biaxial (-) with α = 1.549(2), β = 1.553(2), γ = 1.557(2); nonpleochroic. The Raman spectra of markeyite, natromarkeyite and pseudomarkeyite are very similar and exhibit bands consistent with UO 2 2+ , CO 3 2-and O-H. Electron microprobe analyses provided the empirical formula Na 2.01 Ca 7.97 Mg 0.03 Cu 2+ 0.05 (UO 2) 4 (CO 3) 13 (H 2 O) 24 ·3H 2 O (-0.11 H) for natromarkeyite and Ca 7.95 (UO 2) 4 (CO 3) 12 (H 2 O) 18 ·3H 2 O (+0.10 H) for pseudomarkeyite. Natromarkeyite is orthorhombic, Pmmn, a = 17.8820(13), b = 18.3030(4), c = 10.2249(3) Å, V = 3336.6(3) Å^3 and Z = 2. Pseudomarkeyite is monoclinic, P2 1 /m, a = 17.531(3), b = 18.555(3), c = 9.130(3) Å, β = 103.95(3)°, V = 2882.3(13) Å^3 and Z = 2. The structures of natromarkeyite (R1 = 0.0202 for 2898 I > 2sigmaI) and pseudomarkeyite (R1 = 0.0787 for 2106 I > 2sigmaI) contain uranyl tricarbonate clusters that are linked by (Ca/Na)-O polyhedra forming thick corrugated heteropolyhedral layers. Natromarkeyite is isostructural with markeyite; pseudomarkeyite has a very similar structure.
Jakub Plasil
added a research item
The crystal structure of phurcalite, Ca 2 [(UO 2 ) 3 O 2 (PO 4 ) 2 ]·7H 2 O, orthorhombic, a = 17.3785 (9) Å, b = 15.9864 (8) Å, c = 13.5477 (10) Å, V = 3763.8 (4) Å ³ , space group Pbca , Z = 8 has been refined from single-crystal XRD data to R = 0.042 for 3182 unique [ I > 3σ( I )] reflections and the hydrogen-bonding scheme has been refined by theoretical calculations based on the TORQUE method. The phurcalite structure is layered, with uranyl phosphate sheets of the phosphuranylite topology which are linked by extensive hydrogen bonds across the interlayer occupied by Ca ²⁺ cations and H 2 O groups. In contrast to previous studies the approach here reveals five transformer H 2 O groups (compared to three expected by a previous study) and two non-transformer H 2 O groups. One of the transformer H 2 O groups is, nevertheless, not linked to any metal cation, which is a less frequent type of H 2 O bonding in solid state compounds and minerals. The structural formula of phurcalite has been therefore redefined as {Ca 2 (H 2[3] O) 5 (H 2[4] O) 2 }[(UO 2 ) 3 O 2 (PO 4 ) 2 ], Z = 8.
Jakub Plasil
added a research item
Calcurmolite is a rare supergene U mineral formed during the alteration-hydration weathering of uraninite and hypo-gene Mo minerals; its structure has remained unsolved owing to a lack of crystal material suitable for conventional structure analysis. Here, single-crystal precession electron-diffraction tomography shows the calcurmolite (Rabejac, France) structure to be modulated; it is triclinic, crystallizing in the super-space group P1(α00)0, with a = 3.938 Å, b = 11.26 Å, c = 14.195 Å, α = 84.4°, β = 112.5°, γ = 133.95° and has a modulation vector q = 0.4 a*. Due to the poor quality of diffraction data, only a kinematical refinement was undertaken, although final results were reasonable: R obs /R all = 0.3825/0.3834 for 3953/17442 observed/all reflections. The structure of calcurmolite is based upon the infinite uranyl-molybdate sheets with baumoite topology (U : Mo ratio = 1.5) and an interlayer of 6-coordinated Ca 2+ cations with interstitial H 2 O (ligands are apical uranyl O atoms and molecular H 2 O). Adjacent sheets are linked via Ca-O, as well as H-bonds. The structure formula, based on assumed occupancies in the supercell 5a × b × c, is Ca[(UO2)3(MoO4)2(OH)4 ](H2O)~5 .0 (for Z = 4).
Jakub Plasil
added a research item
Uroxite (IMA2018-100), [(UO2)2(C2O4)(OH)2(H2O)2]·H2O, and metauroxite (2019-030), (UO2)2(C2O4)(OH)2(H2O)2, are the first two uranyl-oxalate minerals. Uroxite was found in the Markey mine, Red Canyon, Utah, USA and in the Burro mine, Slick Rock district, Colorado, USA. Metauroxite was found only in the Burro mine. Both minerals are post-mining, secondary phases found in efflorescent crusts on mine walls. Uroxite occurs as light yellow, striated blades exhibiting moderate neon-green fluorescence, ca 2 Mohs hardness, good {101} and {010} cleavages, density(calc) = 4.187 g/cm3; optics: biaxial (–), α = 1.602(2), β = 1.660(2), γ = 1.680(2) (white light), 2Vmeas. = 59(1)°, moderate r > v dispersion, orientation Y = b, Z ^ a = 35° in obtuse β, nonpleochroic. Metauroxite occurs as light yellow crude blades and tablets exhibiting weak green-gray fluorescence, ca 2 Mohs hardness, good {001}cleavage, densitycalc = 4.403 g/cm3; approximate optics: α′ = 1.615(5), γ′ = 1.685(5). Electron probe microanalysis provided UO3 79.60, C2O3 10.02, H2O 10.03, total 99.65 wt.% for uroxite and UO3 82.66, C2O3 10.40, H2O 7.81, total 100.87 wt.% for metauroxite; C2O3 and H2O based on the structures. Uroxite is monoclinic, P21/c, a = 5.5698(2), b = 15.2877(6), c = 13.3724(9) Å, β = 94.015(7)°, V = 1135.86(10) Å3 and Z = 4. Metauroxite is triclinic, P–1, a = 5.5635(3), b = 6.1152(4), c = 7.8283(4) Å, α = 85.572(5), β = 89.340(4), γ = 82.468°, V = 263.25(3) Å3 and Z = 1. In the structure of uroxite (R1 = 0.0333 for 2081 I > 2I reflections), UO7 pentagonal bipyramids share corners forming [U4O24] tetramers, which are linked by C2O4 groups to form corrugated sheets. In the structure of metauroxite (R1 = 0.0648 for 1602 I > 2I reflections) UO7 pentagonal bipyramids share edges forming [U2O12] dimers, which are linked by C2O4 groups to form zig-zag chains.
Jakub Plasil
added a research item
Bayleyite is a highly hydrated uranyl tricarbonate mineral containing eighteen water molecules per formula unit. Due to this large water content, the correct description of its crystal structure is a great challenge for the first principles solid state methodology. In this work, the crystal structure, hydrogen bonding, mechanical properties and infrared spectrum of bayleyite, Mg2[UO2(CO3)3] · 18 H2O, have been investigated by means of Periodic Density Functional Theory methods using plane wave basis sets and pseudopotentials. The computed unit-cell parameters, interatomic distances, hydrogen bonding network geometry and the X-ray powder diffraction pattern of bayleyite reproduce successfully the experimental data, thus confirming the crystal structure determined from X-ray diffraction data. From the energy-optimized structure, the elastic properties and infrared spectrum have been determined using theoretical methods. The calculated elastic properties include the bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson ratio and the ductility, hardness and anisotropy indices. Bayleyite is shown to be a very isotropic ductile mineral possessing a bulk modulus of B ~28 GPa. The infrared spectrum of bayleyite is obtained experimentally from a natural mineral sample from the Jáchymov ore district, Czech Republic, and determined employing density functional perturbation theory. Since both spectra show a high degree of consistence, the bands in the observed spectrum are assigned using the theoretical methodology. The atomic vibrational motions localized in the uranyl tricarbonate units are described in detail, using appropriate normal coordinate analyses based on accurate vibrational computations, since the vibrational normal modes have not been hitherto studied for any uranyl tricarbonate mineral.
Jakub Plasil
added a research item
A detailed structural, spectroscopic, mechanical and thermodynamic characterization of the bismuth uranyl-oxide hydroxy-hydrate mineral uranosphaerite, Bi(UO2)O2OH, is obtained using the X-ray diffraction and infrared and Raman spectroscopic techniques and first principles solid-state methods based on density functional theory employing plane wave basis sets and pseudopotentials. The full crystal structure of uranosphaerite, including the positions of the hydrogen atoms within the corresponding unit cell, is determined by the first time from X-ray diffraction data taken from a natural crystal sample from Menzenschwand uranium deposit (Germany). The crystal structure obtained from X-ray diffraction is confirmed by using the first principles methodology. The computed structural parameters and X-ray diffraction pattern are in excellent agreement with their experimental counterparts. From the energy-optimized crystal structure, the mechanical and dynamical stability of uranosphaerite is studied and a rich set of mechanical properties are determined. Uranosphaerite is shown to display the negative Poisson's ratio phenomenon. The experimental infrared spectrum is recorded from a natural sample from Schneeberg (Germany) and the Raman spectrum is collected from two crystal samples from Hagendorf and Schneeberg localities (Germany). Both spectra are also determined using density functional perturbation theory and compared with the observed spectra. Since the computed and experimental spectra have a very high degree of consistence, the infrared and Raman bands are completely assigned using a normal coordinate analysis of the theoretical vibrational results. The spectral zone from 1000 to 3000 cm-1 in the infrared and Raman spectra is shown to be plagued of low intensity combination bands. Eleven and eight combination bands are identified in the infrared and Raman spectra, respectively. The fundamental thermodynamic functions of uranosphaerite are computed as a function of temperature using phonon calculations. The computed specific heat and entropy at 298.15 K are 147.7 and 180.4 J K-1 mol-1 respectively. The computed thermodynamic parameters are used to determine the corresponding thermodynamic properties of formation in terms of the elements as a function of temperature and the Gibbs free energies of reaction of a series of reactions involving uranosphaerite and a representative subset of the most important secondary phases of spent nuclear fuel. The relative stability of uranosphaerite with respect to these phases as a function of temperature and under different concentrations of hydrogen peroxide is reported.
Jakub Plasil
added a research item
Kroupaite (IMA2017-031), ideally KPb0.5[(UO2)8O4(OH)10]·10H2O, is a new uranyl-oxide hydroxyl-hydrate mineral found underground in the Svornost mine, Jáchymov, Czechia. Electron-probe microanalysis (WDS) provided the empirical formula (K1.28Na0.07)Σ1.35(Pb0.23Cu0.14Ca0.05Bi0.03Co0.02Al0.01)Σ0.48[(UO2)7.90(SO4)0.04O4.04(OH)10.00]·10H2O, basis of 40 O atoms apfu. Sheets in the crystal structure of kroupaite adopt the fourmarierite anion topology, and therefore kroupaite belongs to the schoepite-family of minerals with related structures differing in the interlayer composition and arrangement, and charge of the sheets. Uptake of dangerous radionuclides (90Sr or 135Cs) into the structure of kroupaite and other uranyl-oxide hydroxy-hydrate is evaluated based on crystal-chemical considerations and Voronoi-Dirichlet polyhedra measures. These calculations show the importancy of these phases for the safe disposal of nuclear waste.
Jakub Plasil
added a research item
The full crystal structure of the copper-uranyl tetrahydroxide mineral (vandenbrandeite), including the positions of the hydrogen atoms, is established by the first time from X-ray diffraction data taken from a natural crystal sample from the Musonoi Mine, Katanga Province, Democratic Republic of Congo. The structure is verified using first-principles solid-state methods. From the optimized structure, the mechanical and dynamical stability of vandenbrandeite is studied and a rich set of mechanical properties are determined. The Raman spectrum is recorded from the natural sample and determined theoretically. Since both spectra have a high-degree of consistence, all spectral bands are rigorously assigned using a theoretical normal-coordinate analysis. Two bands in the Raman spectra, located at 2327 and 1604 cm À1 , are recognized as overtones and a band at 1554 cm À1 is identified as a combination band. The fundamental thermodynamic functions of vandenbrandeite are computed as a function of temperature using phonon calculations. These properties, unknown so far, are key-parameters for the performance-assessment of geological repositories for storage of radioactive nuclear waste and for understanding the paragenetic sequence of minerals arising from the corrosion of uranium deposits. The thermodynamic functions are used here to determine the thermodynamic properties of formation of vandenbrandeite in terms of the elements and the Gibbs free-energies and reaction constants for a series of reactions involving vandenbrandeite and a representative subset of the most important secondary phases of spent nuclear fuel. Finally, from the thermodynamic data of these reactions, the relative stability of vandenbrandeite with respect to these phases as a function of temperature and in the presence of hydrogen peroxide is evaluated. Vandenbrandeite is shown to be highly stable under the simultaneous presence of water and hydrogen peroxide.
Jakub Plasil
added a research item
Comparison of the natural and synthetic phases allows an overview to be made and even an understanding of the crystal growth processes and mechanisms of the particular crystal structure formation. Thus, in this work, we review the crystal chemistry of the family of uranyl selenite compounds, paying special attention to the pathways of synthesis and topological analysis of the known crystal structures. Comparison of the isotypic natural and synthetic uranyl-bearing compounds suggests that uranyl selenite mineral formation requires heating, which most likely can be attributed to the radioactive decay. Structural complexity studies revealed that the majority of synthetic compounds have the topological symmetry of uranyl selenite building blocks equal to the structural symmetry, which means that the highest symmetry of uranyl complexes is preserved regardless of the interstitial filling of the structures. Whereas the real symmetry of U-Se complexes in the structures of minerals is lower than their topological symmetry, which means that interstitial cations and H2O molecules significantly affect the structural architecture of natural compounds. At the same time, structural complexity parameters for the whole structure are usually higher for the minerals than those for the synthetic compounds of a similar or close organization, which probably indicates the preferred existence of such natural-born architectures. In addition, the reexamination of the crystal structures of two uranyl selenite minerals guilleminite and demesmaekerite is reported. As a result of the single crystal X-ray diffraction analysis of demesmaekerite, Pb2Cu5[(UO2)2(SeO3)6(OH)6](H2O)2, the H atoms positions belonging to the interstitial H2O molecules were assigned. The refinement of the guilleminite crystal structure allowed the determination of an additional site arranged within the void of the interlayer space and occupied by an H2O molecule, which suggests the formula of guilleminite to be written as Ba[(UO2)3(SeO3)2O2](H2O)4 instead of Ba[(UO2)3(SeO3)2O2](H2O)3.
Jakub Plasil
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The crystal structure, elastic properties and Raman spectrum of the layered calcium uranyl silicate pentahydrate mineral uranophane-beta, Ca(UO2)2Si2O6(OH)2 · 5H2O, are studied by means of first-principles solid-state methods and compared with the corresponding information for the alpha polymorph. The availability of the energy optimized full crystal structure of uranophane-beta including the positions of the hydrogen atoms, made possible the computation of its elastic properties and Raman spectrum by using the theoretical methodology. An extended set of relevant mechanical data is reported. Uranophane-beta is shown to be a weak and ductile mineral and, consequenty, is mechanically very different from the alpha polymorph which is a hard and brittle material. Uranophane-beta exhibits the important negative Poisson's ratio (NPR) and the negative linear compressibility (NLC) phenomena. The experimental Raman spectrum of uranophane-beta is obtained from a natural mineral sample from pegmatite Perus, São Paulo, Brazil and compared with the spectrum determined theoretically. Since both spectra are in very good agreement, the theoretical methods are employed to assign the Raman spectrum. Three weak bands of the experimental spectrum of this mineral, located at the wavenumbers 2302, 2128 and 2042 cm −1 , are identified as combination bands. The Raman spectrum of uranophane-beta is also compared with that of the Alpha polymorph. While they are rather similar, the detailed analysis reveals a significant number of differences. Finally, the relative thermodynamic stability of the beta and Alpha polymorphs is evaluated. The alpha polymorph is more stable than the beta polymorph at zero pressure and temperature by −12.0 kJ/mol.
Jakub Plasil
added a research item
The hydrogen bonding in the structure of the lead uranyl-oxide mineral sayrite has been refined and described directly from XRD data for the first time. Sayrite is monoclinic, a = 10.6925(4), b = 6.9593(2), c = 13.6035(5) Å, β = 107.680(3), with V = 964.46(6) Å ³ , and Z = 2, space group P 2 1 / n . The structure has been refined to an R = 2.34% based on 2252 unique [ I > 3σ I ] reflections. Sayrite possesses a layered structure with the uranyl-hydroxo-oxide sheets of the topology characterized by the topology symbol P 4 (UD) 8 R 5 . Between adjacent sheets, there are Pb ²⁺ cations and molecular H 2 O. All H 2 O groups in sayrite belong to non-transformer groups, which distribute bond-valence from equally from all the cationic parts of the structure to anions. The structural formula of sayrite is Pb 2 (H 2[4] O) 4 [(UO 2 ) 5 O 6 (OH) 2 ].
Jakub Plasil
added a research item
The crystal structure of the U(IV)-phosphate mineral vyacheslavite has been solved from precession electron diffraction tomography (PEDT) data from the natural nano-crystal and further refined using density-functional theory (DFT) calculations. Vyacheslavite is orthorhombic, with the space group Cmca, with a ≈ 6.96Å, b ≈ 9.07Å and c ≈ 12.27Å, V ≈ 775Å^3 (obtained from PEDT data at 100 K), Z = 8. Its structure is a complex heteropolyhedral framework consisting of sheets of UO7(OH) and PO4 polyhedra, running parallel to (001), interconnected by additional PO4 polyhedra. There is an (OH) group associated with the U(IV) polyhedron. The question of H2O presence within the small cavities of the framework has been addressed by the DFT calculations, which have proved that vyacheslavite does not contain any significant amount of H2O at room temperature.
Jakub Plasil
added a research item
The crystal structure, hydrogen bonding, mechanical properties and Raman spectrum of the lead uranyl silicate monohydrate mineral kasolite, Pb(UO2)(SiO4)H2O, are investigated by means of first-principles solid-state methods based on density functional theory using plane waves and pseudopotentials. The computed unit cell parameters, bond lengths and angles and X-ray powder pattern of kasolite are found to be in very good agreement with their experimental counterparts. The calculated hydrogen atom positions and associated hydrogen bond structure in the unit cell of kasolite confirmed the hydrogen bond scheme previously determined from X-ray diffraction data. The kasolite crystal structure is formed from uranyl silicate layers having the uranophane sheet anion-topology. The lead ions and water molecules are located in the interlayer space. Water molecules belong to the coordination structure of lead interlayer ions and reinforce the structure by hydrogen bonding between the uranyl silicate sheets. The hydrogen bonding in kasolite is strong and dual, that is, the water molecules are distributed in pairs, held together by two symmetrically related hydrogen bonds, one being directed from the first water molecule to the second one and the other from the second water molecule to the first one. As a result of the full structure determination of kasolite, the determination of its mechanical properties and Raman spectrum becomes possible using theoretical methods. The mechanical properties and mechanical stability of the structure of kasolite are studied using the finite deformation technique. The bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson ratio and the ductility, hardness and anisotropy indices are reported. Kasolite is a hard and brittle mineral possessing a large bulk modulus of the order of B~71 GPa. The structure is mechanically stable and very isotropic. The large mechanical isotropy of the structure is unexpected since layered structures are commonly very anisotropic and results from the strong dual hydrogen bonding among the uranyl silicate sheets. The experimental Raman spectrum of kasolite is recorded from a natural mineral sample from the Jánská vein, Příbram base metal ore district, Czech Republic, and determined by using density functional perturbation theory. The agreement is excellent and, therefore, the theoretical calculations are employed to assign the experimental spectrum. Besides, the theoretical results are used to guide the resolution into single components of the bands from the experimental spectrum. A large number of kasolite Raman bands are reassigned. Three bands of the experimental spectrum located at the wavenumbers 1015, 977 and 813 cm-1 , are identified as combination bands.
Jakub Plasil
added a research item
Baumoite, Ba0.5[(UO2)3O8Mo2(OH)3](H2O)~3, is a new mineral found near Radium Hill, South Australia, where it occurs in a granite matrix associated with baryte, metatorbernite, phurcalite and kaolinite. Baumoite forms thin crusts of yellow to orange–yellow tabular to prismatic crystals. The mineral is translucent with a vitreous lustre and pale yellow streak. Crystals are brittle, the fracture is uneven and show one excellent cleavage. The Mohs hardness is ~2½. The calculated density is 4.61 g/cm3. Optically, baumoite crystals are biaxial (–), with α = 1.716(4), β = 1.761(4), γ = 1.767(4) (white light); and 2Vcalc = 42.2°. Electron microprobe analyses gave the empirical formula Ba0.87Ca0.03Al0.04U2.97Mo2.02P0.03O22H11.99, based on 22 O atoms per formula unit. The eight strongest lines in the powder X-ray diffraction pattern are [dobs Å (I) (hkl)]: 9.175(39)(12 ), 7.450(100)(020), 3.554(20)(221), 3.365(31)(004, 202), 3.255(31)(123, 30 ), 3.209(28)(12 ), 3.067(33)(30, 222, 32 ) and 2.977(20)(142). Single-crystal X-ray studies (R1 = 5.85% for 1892 main reflections) indicate that baumoite is monoclinic, superspace group X2/m(a0g)0s with X = (0,½,0,½), with unit-cell parameters: a = 9.8337(3), b = 15.0436(5), c = 14.2055(6) Å, β = 108.978(3)°, V = 1987.25(13) Å3 and Z = 4. The crystal structure is twinned and incommensurately modulated and is based upon sheets of U6+ and Mo6+ polyhedra of unique topology. Four independent cationic sites partially occupied by Ba atoms are located between the sheets, together with H2O molecules.
Jakub Plasil
added a research item
The crystal structure of lead uranyl-oxide hydroxy-hydrate mineral curite, ideally Pb3(H2O)2[(UO2)4O4(OH)3]2, was studied by means of single-crystal X-ray diffraction and theoretical calculations in order to localize positions of hydrogen atoms in the structure. This study has demonstrated that hydrogen atoms can be localized successfully also in materials for which the conventional approach of structure analysis failed, here due to very high absorption of X-rays by the mineral matrix. The theoretical calculations, based on the Torque method, provide a robust, fast realspace method for determining H2O orientations from their rotational equilibrium condition. In line with previous results we found that curite is orthorhombic, with space group Pnma, unit-cell parameters a = 12.5510(10), b = 8.3760(4), c = 13.0107(9) A, V = 1367.78(16) A^3, and two formula units per unit cell. The structure (R1 = 3.58% for 1374 reflections with I > 3sI) contains uranyl-hydroxo-oxide sheets of the unique topology among uranyl oxide minerals and compounds and an interlayer space with Pb2+ cations and a single H2O molecule, which is coordinated to the Pb-site. Current results show that curite is slightly non-stoichiometric in Pb content (~3.02 Pb per unit cell, Z = 2); the charge-balance mechanism is via (OH) <-> O2 substitution within the sheets of uranyl polyhedra. Disproving earlier predictions, the current study shows that curite contains only one H2O group, with [4]-coordinated oxygen. The hydrogen bonding network maintains the bonding between the sheets in addition to Pb–O bonds; among them, a H-bond is crucial between the OH group on an apical OUranyl atom of an adjacent sheet that stabilizes the entire structure. The results show that the combination of experimental X-ray data and the Torque method can successfully reveal hydrogen bonding especially for complex crystal structures and materials where X-rays fail to provide unambiguous hydrogen positions.
Anthony R. Kampf
added 2 research items
Meyrowitzite, Ca(UO 2)(CO 3) 2 ·5H 2 O, is a new mineral species from the Markey mine, Red Canyon, San Juan County, Utah, U.S.A. It is a secondary phase found on calcite-veined asphaltum in association with gypsum, markeyite, and rozenite. Meyrowitzite occurs as blades up to about 0.2 mm in length, elongate on [010], flattened on {100}, and exhibiting the forms {100}, {001}, {101}, {110}, and {011}. The mineral is yellow and transparent with vitreous luster and very pale yellow streak. Fluorescence under a 405 nm laser is from weak greenish yellow to moderate greenish blue. The Mohs hardness is ca. 2, tenacity is brittle, fracture is irregular, and there is one perfect cleavage, {101}. The measured density is 2.70(2) g/cm 3. The mineral is optically biaxial (+) with α = 1.520(2), β = 1.528(2), and γ = 1.561(2) (white light). The 2V(meas) = 53.0(6)°; weak dispersion, r > v; optical orientation: Z = b, Y ^ a ≈ 19° in obtuse β; pleochroism pale yellow, X ≈ Y < Z. Electron microprobe analyses provided the empirical formula Ca 0.94 (U 1.00 O 2)(CO 3) 2 ·5(H 2.02 O) on the basis of U = 1 and O = 13 apfu, as indicated by the crystal structure determination. Meyrowitzite is monoclinic, P2 1 /n, a = 12.376(3), b = 16.0867(14), c = 20.1340(17) Å, β = 107.679(13)°, V = 3819.3(12) Å 3 , and Z = 12. The structure (R 1 = 0.055 for 3559 I o > 2σI) contains both UO 7 pentagonal bipyramids and UO 8 hexagonal bipyramids, the latter participating in uranyl tricarbonate clusters (UTC). The two kinds of bipyramids and the carbonate groups link to form a novel corrugated heteropolyhedral sheet. This is the first structural characterization of a uranyl-carbonate mineral with a U:C ratio of 1:2. Meyrowitzite is apparently dimorphous with zellerite.
Jakub Plasil
added a research item
Uranyl sulfates, including those occurring in Nature (∼40 known members), possess particularly interesting structures. They exhibit a great dimensional and topological diversity of structures: from those based upon clusters of polyhedra to layered structures. There is also a great variability in the type of linkages between U and S polyhedra. From the point of view of complexity of those structures (measured as the amount of Shannon information per unit cell), most of the natural uranyl sulfates are intermediate (300–500 bits per cell) to complex (500–1000 bits per cell) with some exceptions, which can be considered as very complex structures (>1000 bits per cell). These exceptions are minerals alwilkinsite-(Y) (1685.95 bits per cell), sejkoraite-(Y) (1859.72 bits per cell), and natrozippeite (2528.63 bits per cell). The complexity of these structures is due to an extensive hydrogen bonding network which is crucial for the stability of these mineral structures. The hydrogen bonds help to propagate the charge from the highly charged interlayer cations (such as Y ³⁺ ) or to link a high number of interlayer sites ( i.e. five independent Na sites in the monoclinic natrozippeite) occupied by monovalent cations (Na ⁺ ). The concept of informational ladder diagrams was applied to the structures of uranyl sulfates in order to quantify the particular contributions to the overall informational complexity and identifying the most contributing sources (topology, real symmetry, interlayer bonding).
Jakub Plasil
added a research item
Meyrowitzite, Ca(UO2)(CO3)2·5H2O, is a new mineral species from the Markey mine, Red Canyon, San Juan County, Utah, U.S.A. It is a secondary phase found on calcite-veined asphaltum in association with gypsum, markeyite, and rozenite. Meyrowitzite occurs as blades up to about 0.2 mm in length, elongate on [010], flattened on {100}, and exhibiting the forms {100}, {001}, {101}, {110}, and {011}. The mineral is yellow and transparent with vitreous luster and very pale yellow streak. Fluorescence is from weak greenish yellow to moderate greenish blue. The Mohs hardness is ca 2, tenacity is brittle, fracture is irregular, and there is one perfect cleavage, {-101}. The measured density is 2.70(2) g·cm-3. The mineral is optically biaxial (+) with α = 1.520(2), β = 1.528(2), and γ = 1.561(2) (white light). The 2V(meas.) = 53.0(6)°; weak dispersion, r > v; optical orientation: Z = b, Y ^ a ≈ 19° in obtuse β; pleochroism pale yellow, X ≈ Y < Z. Electron microprobe analyses provided the empirical formula Ca 0.94 (U 1.00 O 2)(CO 3) 2 ·5(H 2.02 O) on the basis of U = 1 and O = 13 apfu, as indicated by the crystal structure determination. Meyrowitzite is monoclinic, P2 1 /n, a = 31 12.376(3), b = 16.0867(14), c = 20.1340(17) Å, β = 107.679(13)°, V = 3819.3(12) Å 3 , and Z = 12. The structure (R 1 = 0.055 for 3559 I o > 2σI) contains both UO7 pentagonal bipyramids and UO8 hexagonal bipyramids, the later participating in uranyl tricarbonate clusters (UTC). The two kinds of bipyramids and the carbonate groups link to form a novel corrugated heteropolyhedral sheet. This is the first structural characterization of a uranyl-carbonate mineral with a U:C ratio of 1:2. Meyrowitzite is apparently dimorphous with zellerite.
Jakub Plasil
added 83 research items
This paper presents the existing and newly obtained information on supergene minerals of the Horní Slavkov uranium ore district. Mineralogical studies confirmed occurrences of the following minerals: anglesite, annabergite, arsenolite, autunite, carnotite, compreignacite, cuprosklodowskite, kaatialaite, liebigite, meta-autunite, metanováčekite, metatorbernite, mohrite, nováčekite, phosphuranylite, rutherfordine, schultenite, siderite, torbernite, uranophane, zeunerite, and unnamed phase UNK5. The present study did not confirm the presence of previously reported occurrences of bassetite soddyite, uranophane-β and uranospinite. Also presented is interpretation of formation of the icsupergene mineralization in this ore district.
Leydetite, monoclinic Fe(UO2)(SO4)2(H2O)11 (IMA 2012–065), is a new supergene uranyl sulfate from Mas d'Alary, Lodève, Hérault, France. It forms yellow to greenish, tabular, transparent to translucent crystals up to 2 mm in size. Crystals have a vitreous lustre. Leydetite has a perfect cleavage on (001). The streak is yellowish white. Mohs hardness is ~2. The mineral does not fluoresce under long- or short-wavelength UV radiation. Leydetite is colourless in transmitted light, non-pleochroic, biaxial, with α = 1.513(2), γ = 1.522(2) (further optical properties could not be measured). The measured chemical composition of leydetite, FeO 9.28, MgO 0.37, Al2O3 0.26, CuO 0.14, UO3 40.19, SO3 21.91, SiO2 0.18, H2O 27.67, total 100 wt.%, leads to the empirical formula (based on 21 O a.p.f.u.), (Fe0.93Mg0.07Al0.04Cu0.01)Σ1.05(U1.01O2)(S1.96Si0.02)Σ1.98O8(H2O)11. Leydetite is monoclinic, space group C2/c, with a = 11.3203(3), b = 7.7293(2), c = 21.8145(8) Å, β = 102.402(3)°, V = 1864.18(10) Å3, Z = 4, and Dcalc = 2.55 g cm−3. The six strongest reflections in the X-ray powder diffraction pattern are [dobs in Å (I) (hkl)]: 10.625 (100) (002), 6.277 (1) (1İ11), 5.321 (66) (004), 3.549 (5) (006), 2.663 (4) (008), 2.131 (2) (0 0 10). The crystal structure has been refined from single-crystal X-ray diffraction data to R1 = 0.0224 for 5211 observed reflections with [I > 3σ(I)]. Leydetite possesses a sheet structure based upon the protasite anion topology. The sheet consists of UO7 bipyramids, which share four of their equatorial vertices with SO4 tetrahedra. Each SO4 tetrahedron, in turn, shares two of its vertices with UO7 bipyramids. The remaining unshared equatorial vertex of the bipyramid is occupied by H2O, which extends hydrogen bonds within the sheet to one of a free vertex of the SO4 tetrahedron. Sheets are stacked perpendicular to the c direction. In the interlayer, Fe2+ ions and H2O groups link to the sheets on either side via a network of hydrogen bonds. Leydetite is isostructural with the synthetic compound Mg(UO2)(SO4)2(H2O)11. The name of the new mineral honours Jean Claude Leydet (born 1961), an amateur mineralogist from Brest (France), who discovered the new mineral.
Behounekite, orthorhombic U(SO4)(2)(H2O)(4), is the first natural sulphate of U4+. It was found in the Geschieber vein, Jachymov (St Joachimsthal) ore district, Western Bohemia, Czech Republic, crystallized on the altered surface of arsenic and associated with kaatialaite, arsenolite, claudetite, unnamed phase UM1997-20-AsO:HU and gypsum. Behounekite most commonly forms short-prismatic to tabular green crystals, rarely up to 0.5 mm long. The crystals have a strong vitreous lustre and a grey to greenish grey streak. They are brittle with an uneven fracture and have very good cleavage along 1100:. The Mohs hardness is about 2. The mineral is not fluorescent either in short- or long-wavelength UV radiation. Behounekite is moderately pleochroic, alpha similar to beta is pale emerald green and gamma is emerald green, and is optically biaxial (+) with alpha = 1.590(2), beta = 1.618(4), gamma = 1.659(2) (590 nm), 2V (calc.) = 81 degrees, birefringence 0.069. The empirical formula of behounekite (based on 12 0 atoms, from an average of five point analyses) is (U0.99Y0.03)(Sigma 1.02)(SO4)(1.97)(H2O)(4). The simplified formula is U(SO4)(2)(H2O)(4), which requires UO2 53.77, SO3 31.88, H2O 14.35, total 100.00 wt.%. Behounekite is. orthorhombic, space group Puma, a = 14.6464(3), b = 11.0786(3), c = 5.6910(14) angstrom, V = 923.43(4) angstrom(3), Z = 4, D-calc = 3.62 g cm(-3). The seven strongest diffraction peaks in the X-ray powder diffraction pattern are [d(obs) in angstrom (I) (hkl)]: 7.330 (100) (200), 6.112 (54) (210), 5.538 (21) (020), 4.787 (42) (111), 3.663 (17) (400), 3.478 (20) (410), 3.080 (41) (321). The crystal structure of behounekite has been solved by the charge-flipping method from single-crystal X-ray diffraction data and refined to R-1 = 2.10 % with a GOF = 1.51, based on 912 unique observed diffractions. The crystal structure consists of layers built up from [8]-coordinate uranium atoms and sulphate tetrahedra. The eight ligands include four oxygen atoms from the sulphate groups and four oxygen atoms from the H2O molecules. Each uranium coordination polyhedron is connected via sulphate tetrahedra with other uranium polyhedra and through hydrogen bonds to the apices of sulphate tetrahedra. The dominant features of the Raman and infrared spectra of behounekite are related to stretching vibrations of SO4 tetrahedra (similar to 1200-950 cm(-1)), O-H stretching modes (similar to 3400-3000 cm(-1)) and H-O-H bending modes (similar to 1650 cm(-1)). The mineral is named in honour of Frantisek Behounek, a well known Czech nuclear physicist.
Jakub Plasil
added a project goal
To determine crystal structures of uranium minerals and compounds and to hunt for new uranium minerals.