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The Bohemian Massif hosts significant hydrothermal U-deposits associated with shear zones in the high-grade metamorphic basement. But there is a lack of evidence of a genetic link between mineralization and U-fertile igneous rocks. This contribution provides constraints on the major U source of the vein-type U-deposits, the timing of ore formation and the metallogenetic model. The anomalous trace element signatures of the low-temperature hydrothermal deposits (high Zr, Y, Nb, Ti, ∑REE) and their close spatial relation with ultrapotassic rocks of the durbachite series point to a HFSE and REE enriched source rock. The durbachites have high U content (13.4–21.5 ppm) mainly stored in magmatic uraninite and other refractory minerals (e.g., thorite, zircon, allanite) that became metamict over a time interval sufficient to release U from their crystal structure, as suggested by the time gap between emplacement of the durbachites (EMP uraninite U–Pb age ~ 338 Ma) and hydrothermal activity (SIMS uranium ore U–Pb age ~ 270 Ma). Airborne radiometric data show highly variable Th/U ratios (1.5–6.0), likely reflecting a combination between (1) crystallization of magmatic uraninite, (2) hydrothermal alteration, and (3) leaching and mobilization of U along NW–SE-trending fault zones, manifested by elevated Th/U values in the radiometric map. The presence of rare magmatic uraninite in durbachites suggests almost complete uraninite dissolution; EMP imaging coupled with LA-ICP-MS analyses of refractory accessory phases revealed extensive mobilization of U together with HFSE and REE, providing direct evidence for metal leaching via fluid-driven alteration of radiation-damaged U-rich minerals. The large-scale HFSE and REE mobilization, demonstrated by the unusual trace element signatures of the U-deposits, was likely caused by low-temperature (270–300 °C), highly alkaline aqueous solutions containing F-, P-, and K-dominated complexing ligands. The first SIMS U–Pb age of 270.8 ± 7.5 Ma obtained so far for U-mineralization from the Bohemian Massif revealed a main Permian U mineralizing event, related to crustal extension, exhumation of the crystalline basement, and basin formation, as recorded by U–Pb apatite dates (280–290 Ma) and AFT thermal history models of the durbachites. The Permo-Carboniferous sedimentary cover probably represented a source of oxidized basinal brines infiltrating the basement-hosted durbachite plutons and triggering massive metal leaching. The interaction between basin-derived brines and durbachites resulted in significant modification of the chemical composition of the hydrothermal system (K and F release during biotite chloritization, P liberation through monazite alteration), leading to the formation of ore-bearing fluids responsible for the metallogenesis of the basement-hosted unconformity-related U-deposits in shear zones in the Bohemian Massif.

Znucalite is a zinc uranyl-carbonate mineral that was until recently only partially characterized with a formula originally given as Zn12Ca(UO2)(CO3)3(OH)22·4H2O, with an unknown crystal structure and ambiguous symmetry determinations. We have reinvestigated this mineral using three-dimensional electron diffraction (3D ED) and powder X-ray diffraction and revealed for the first time its structural details. Znucalite is unambiguously monoclinic, P21/m, with a= 10.722(2) Å, b= 6.259(1) Å, c= 25.355(1) Å, β = 101.13(1)°, and V= 1669.54(9) Å3. The structure refinement of the 3D ED data using the dynamical approach (Robs= 0.1594 for 3579 observed reflections and 244 parameters) provided the following structure model. Znucalite possesses a layered structure, with a [Zn10(OH)14(CO3)2] double sheet (with Zn2+both in octahedra and tetrahedra), which is connected to a thick interlayer that hosts U6+, Ca2+, and H2O molecules. The linkage between structural units and the interlayer occurs via the vertices of ZnO4tetrahedra protruding from the sheet. In the interlayer, differences in ordering between U and Ca take place and likely cause the difficulties encountered during the attempts to solve the structure. The refined structural formula of znucalite, Zn10Ca0.828[UO2]0.828[CO3]4(OH)15.312(H2O)5.484, corresponds well to the composition obtained from the electron-microprobe analyses, (Zn9.84Al0.16)Σ10.00Ca0.83(UO2)0.80[(CO3)3.96(SO4)0.04]Σ4.00(OH)15.42(H2O)5.48. Raman spectroscopy evidenced the presence of several non-equivalent CO3groups, as well as OH and H2O. The U-O bond lengths obtained from the stretching frequencies of UO22+$\begin{array}{} \displaystyle {\rm UO_{2}^{2+}} \end{array}$vibrations are in line with the structural model. A discussion on the environmental importance of znucalite is appended, based on geochemical calculations with an estimate of the solubility product for this mineral.

A hydrothermal quartz vein with REE-U-Au mineralization in the Zimná Voda (Gemeric Unit, Western Carpathians, Slovakia) is associated with contact metamorphism between Permian granites and host phyllites and metaquartzites. It contains unique REE minerals of the monazite and xenotime groups. Monazite-(Ce), monazite-(Nd), monazite-(Sm), and Gd-dominant monazite [“monazite-(Gd)”], along with xenotime-(Y) to Gd-dominant xenotime [“xenotime-(Gd)”] and Gd-rich hingganite-(Y) show heterogeneous compositions and reflect a strong fractionation trend toward the enrichment of MREE (Sm to Dy), particularly Gd. Here, the gadolinium abundance reported in “monazite-(Gd)” (≤23.4 wt% Gd2O3) and Gd-rich xenotime-(Y) to “xenotime-(Gd)” (≤28.7 wt% Gd2O3) and accompanied by Gd-rich hingganite-(Y) (≤15.8 wt% Gd2O3), is among the highest Gd concentrations ever reported in natural minerals. The Gd-richest compositions show the following formulas: (Gd0.31Sm0.24Nd0.15Ce0.10La0.05Dy0.03Y0.03...)0.98PO4[“monazite-(Gd)”], (Gd0.36Y0.32Dy0.13Sm0.08Tb0.05...)0.98(P0.96As0.04)1.00O4[“xenotime-(Gd)”] and (Y0.71Gd0.43Dy0.23Sm0.22Tb0.06Er0.04Nd0.06...Ca0.06)1.96(◻0.87Fe0.132+)1.00(Be1.82B0.18)2.00(Si1.90As0.10)2.00O8(OH1.70O0.30)2.00${{({{\square }_{0.87}}\,\text{Fe}_{0.13}^{2+})}_{1.00}}{{(\text{B}{{\text{e}}_{1.82}}\,{{\text{B}}_{0.18}})}_{2.00}}\,{{(\text{S}{{\text{i}}_{1.90}}\text{A}{{\text{s}}_{0.10}})}_{2.00}}\,\,{{\text{O}}_{8}}{{(\text{O}{{\text{H}}_{1.70}}\,{{\text{O}}_{0.30}})}_{2.00}}$[hingganite-(Y)]. The MREE-rich monazites, xenotimes, and hingganite-(Y) precipitated in response to the alteration of primary uraninite, brannerite, and fluorapatite by low-temperature hydrothermal fluids of heterogeneous compositions on a microscale. These are responsible for the strong enrichment of individual MREE, especially Gd in the secondary minerals. This is accompanied by the advancing development of the W-type tetrad effect on REE through monazite species. The substantial incorporation of Gd into both REE-selective monazite and xenotime structures that are accompanied by LREE vs. HREE segregation indicates the possibility of differently sized REE3+miscibility in REEPO4solid solutions, as well as the stabilization of the Gd-rich orthophosphate structure by substitution of the remaining A-site cations with smaller HREE+Y in the xenotime-type, and/or larger LREE in the monazite-type structure.

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 three-dimensional 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(W60.98+Fe30.26+◻0.75)O4.7(OH)2.5(H2O)1.75](H2O)1.67(average of 8 points calculated on the basis of 2U apfu; 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+Fe30.25+◻0.75O4.75(OH)1.5(H2O)1.75]0.25–is composed of UO7polyhedra linked by (W,Fe)O5polyhedra 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-U3O8type of sheets.

Gungerite, TlAs5Sb4S13, is a new mineral from the Vorontsovskoye gold deposit in Northern Urals. It occurs in limestone breccias composed of calcite and dolomite and cemented by orpiment, pyrite, realgar, stibnite, and minor baryte and quartz. It belongs to the latest phases among sulfosalts (chiefly Tl-As-Sb ones) present in the ore. The empirical formula (based on the sum of all atoms = 23 pfu) is Tl0.99As5.29Sb3.77S12.95. The Raman spectrum exhibits bands corresponding to As-S and Sb-S stretching vibrations, and a band at 263 cm−1that is assigned to As–As stretching vibrations. Gungerite is bright orange with an orange streak, greasy luster, and perfect cleavage on {010}. It is translucent in thin fragments. The calculated density is 4.173 g/cm3. In reflected light, the mineral is yellowish-white with very weak bireflectance. In crossed polars, it is distinctly anisotropic but anisotropy efects are masked by strong internal reflections of bright orange color. Gungerite is orthorhombic, with the space group Pbcn. Unit-cell parameters determined from the single-crystal X-ray difraction data are as follows: a= 20.1958(3) Å, b= 11.5258(2) Å, c= 20.1430(2) Å, and V= 4688.74(12) Å3(Z= 8). The crystal structure consists of doughnut-shaped (As,Sb)-S clusters, which have van der Waals contacts to most of the surroundings, and are connected to them only by sparse cation-sulfur bonds. These clusters are formed by a chelating mirror-symmetrical group, which is “stacked” on, around, and along rods of the TlS9coordination polyhedra; these rods are oriented parallel to [010]. An individual doughnut-shaped cluster with a central TlS9polyhedron half-inserted into it contains one As–As bond 2.449 Å long. The polar Tl rods form a chessboard arrangement with occasional stacking errors leading to twinning on (101). The large and complex structure of gungerite shows remote similarities to that of gillulyite and the rod-like structure of lorándite.

Particularly interesting chemical variability in the U4+phosphate mineral vyacheslavite from Menzenschwand (Germany) has been discovered and investigated by means of electron-diffraction and micro-chemical methods. Suggested variability comprises the elevated contents of calcium and rare-earth elements (REEs or Ln). 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 Lnhave been discovered, characterized by the contents up to 11 wt% of Y2O3and ~4.5 wt% of Ln2O3. In addition to the above-mentioned substitution mechanism, substitution involving Y and Lncan be expressed as U4++ OH–→ REE3++ H2O. Although 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 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.

Celleriite, □(Mn22+Al)Al6(Si6O18)(BO3)3(OH)3(OH),$\square \,\left( \text{Mn}_{2}^{2+}\text{Al} \right)\text{A}{{\text{l}}_{6}}\left( \text{S}{{\text{i}}_{6}}{{\text{O}}_{18}} \right){{\left( \text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}}(\text{OH}),$is a new mineral of the tourmaline supergroup. It was discovered in the Rosina pegmatite, San Piero in Campo, Elba Island, Italy (holotype specimen), and in the Pikárec pegmatite, western Moravia, Czech Republic (co-type specimen). Celleriite in hand specimen is violet to gray-blue (holotype) and dark brownish-green (co-type) with a vitreous luster, conchoidal fracture, and white streak. Celleriite has a Mohs hardness of ~7 and a calculated density of 3.13 and 3.14 g/cm3for holotype and its co-type, respectively. In plane-polarized light in thin section, celleriite is pleochroic (O = pale violet and E = light gray-blue in holotype; O = pale green and E = colorless in co-type) and uniaxial negative. Celleriite has trigonal symmetry: space group R3m, Z= 3, a= 15.9518(4) and 15.9332(3) Å, c= 7.1579(2) and 7.13086(15) Å, V= 1577.38(9) and 1567.76(6) Å3for holotype and co-type, respectively (data from single-crystal X‑ray diffraction). The crystal structure of the holotype specimen was refined to R1 = 2.89% using 1696 unique reflections collected with MoKα X‑ray intensity data. Structural, chemical, and spectroscopic analyses resulted in the formulas: x(□0.58Na0.42)∑1.00Y(Mn1.392+Fe0.162+Mg0.01Al1.14Fe0.013.0Li0.28T0.01)Σ3.00ZAl6[T(Si5.99Al0.01)Σ6.00O18](BO3)3(OH)3w[(OH)0.65F0.03O0.32]Σ1.00(forholotype)$\begin{align}& \,\,\,\,{{\,}^{\text{x}}}{{\left( {{\square }_{0.58}}\text{N}{{\text{a}}_{0.42}} \right)}_{\sum 1.00}}\text{Y}{{\left( \text{Mn}_{1.39}^{2+}\text{Fe}_{0.16}^{2+}\text{M}{{\text{g}}_{0.01}}\text{A}{{\text{l}}_{1.14}}\text{Fe}_{0.01}^{3.0}\text{L}{{\text{i}}_{0.28}}~{{\text{T}}_{0.01}} \right)}_{\Sigma 3.00}}^{\text{Z}}\text{A}{{\text{l}}_{6}}\left[ {{~}^{\text{T}}}{{\left( \text{S}{{\text{i}}_{5.99}}\text{A}{{\text{l}}_{0.01}} \right)}_{\Sigma 6.00}}{{\text{O}}_{18}} \right]{{\left( \text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}} \\ & ^{\text{w}}{{\left[ {{(\text{OH})}_{0.65}}~{{\text{F}}_{0.03}}{{\text{O}}_{0.32}} \right]}_{\Sigma 1.00}}\,\text{(for}\,\text{holotype)} \\ \end{align}$andX(□0.51Na0.49)Σ1.00Y(Mn0.902+Fe0502+Al1.36Fe0043+Li0.17Zn0.04)Σ3.00ZAl6[T(Si5.75B0.25)Σ6.00O18](BO3)3(OH)3w[(OH)0.35F0.17O0.48]∑1.00(forco-type)$\begin{align}& \,\,\,\,\,{{\,}^{\text{X}}}{{\left( {{\square }_{0.51}}\text{N}{{\text{a}}_{0.49}} \right)}_{\Sigma 1.00}}^{\text{Y}}{{\left( \text{Mn}_{0.90}^{2+}\text{Fe}_{050}^{2+}\text{A}{{\text{l}}_{1.36}}\text{Fe}_{004}^{3+}\text{L}{{\text{i}}_{0.17}}\text{Z}{{\text{n}}_{0.04}} \right)}_{\Sigma 3.00}}^{\text{Z}}\text{A}{{\text{l}}_{6}}\left[ ^{\text{T}}{{\left( \text{S}{{\text{i}}_{5.75}}~{{\text{B}}_{0.25}} \right)}_{\Sigma 6.00}}{{\text{O}}_{18}} \right]{{\left( \text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}} \\ & ^{\text{w}}{{\left[ {{(\text{OH})}_{0.35}}~{{\text{F}}_{0.17}}{{\text{O}}_{0.48}} \right]}_{\sum 1.00}}\text{(for}\,\text{co-type)} \\ \end{align}$

The very first description of zirconolite, originally called polymignyte, discovered in alkaline pegmatites within the Larvik Plutonic Complex (LPC), Norway, was published almost 200 yr ago. We studied zirconolite from three occurrences located in this region using modern techniques—X‑ray powder diffraction (XRPD) upon thermal annealing of initially radiation-damaged mineral, electron probe microanalysis, and Mössbauer spectroscopy. The initial XRPD pattern lacked any sharp diffraction maxima, as the accumulated radiation dose exceeded a critical value of ca. 1016α-decays/mg. Annealing at 400–800 °C induced recrystallization to a transitional, cubic phase interpreted to have a disordered, defect fluorite structure [space group Fm3m; unit-cell parameters: a= 5.1047(4) Å, V= 133.02(2) Å3], with its XRPD pattern being very similar to that of cubic ZrO2. Rietveld analysis of the XRPD pattern obtained after a phase transition at 900 °C shows a mixture of -3O[wt. fraction of ca. 60%, space group Cmca, unit-cell parameters: a= 7.2664(8) Å, b= 14.1877(15) Å, c= 10.1472(12) Å, V= 1046.1(2) Å3], and -3T[wt. fraction of ca. 40%, space group P3121, unit-cell parameters: a= 7.2766(6) Å, c= 17.0627(15) Å, V= 752.42(11) Å3] zirconolite polytypes. However, the crystal habits of zirconolite from the LPC show a distinct orthorhombic symmetry. Although their chemical compositions are far from the ideal zirconolite composition and a large number of elements are involved in high concentrations [up to ca. 17 wt% REE2O3, ≤7 wt% ACTO2, ≤18 wt% Me25+O5, ≤9 wt% Me2+O + Me23+O3, Fe3+/(Fe3++Fe2+) ≈ 0.2, where ACT = Th + U, Me5+= Nb ± Ta, Me2+= Fe2+± Mg, Me3+≈ Fe3+], the compositional variability is relatively limited. To quantitatively describe the two distinct compositional trends observed, we introduced a concept called “edgemembers,” so that mixing is approximated to occur between two terminal compositions situated at two edges of the zirconolite composition space. These marginal compositions were determined from observed compositional trends, i.e., heterovalent substitution of Me5+for Ti in octahedral sites and ACT enrichment associated with increasing Ti/Me5+ratio. This approach provides general substitution vectors for both, Håkestad-type mode (ACT + 3 Ti + Me3+= Ca + 3 Me5++ Me2+), and Stålaker-type mode (0.7 ACT + 0.5 REE + 0.9 Ti + 0.7 Me3++ 0.05 Zr = 1.2 Ca + 1.3 Me5++ 0.3 Me2++ 0.05 Mn). In terms of chemical composition, the studied zirconolite corresponds to recently approved zirconolite-related minerals stefanweissite (for Ca > REE) and nöggerathite (for REE > Ca). Based on a careful analysis of zirconolite composition space, we show that our observed Håkestad-type compositional trend, as well as a high number of published zirconolite compositions worldwide (with Me2++ Me3+sum of ca. 1 atom per 14 O), can be well approximated by a modified end-member set comprising Ca2Zr2Me25+TiMe2+O14, REE2Zr2Ti3Me2+O14, CaACTZr2Ti3Me2+O14, CaREEZr2Ti3Me3+O14, and Ca2Zr2Ti2Me5+Me3+O14without a need to involve the ideal zirconolite formula Ca2Zr2Ti4O14. The redefined composition space constrained by end-members from this set, together with ideal zirconolite, may be representative of the vast majority of more than 450 published zirconolite compositions worldwide with Me2++ Me3+totaling ≤1 atom per 14 O. The equation XMe3+= 2 – 2XREE*– 3XMe5+*provides an independent calculation of iron oxidation state or XMe3+= Me3+/(Me2++ Me3+) for this remarkable group of zirconolites, where XREE*is derived from XREE= REE/(REE + Ca) and XMe5+*from XMe5+= Me5+/(Me5++ Ti). Understanding the oxidation state of iron in zirconolite may be helpful to characterize redox conditions during its crystallization.

Gadolinite [REE2Fe2+Be2Si2O10] is a common mineral in certain types of rare element and rare earth element (REL-REE) pegmatites. Changes in pegmatite environment during and after gadolinite formation may be devised by studying its crystal-chemical properties and a thorough observation of microfeatures in the mineral matrix. Post-crystallization processes in pegmatite might trigger alteration mechanisms in gadolinite like in other REE-rich pegmatite minerals, whereby various late-magmatic or metasomatic events may affect mineral chemistry. Three gadolinite samples originating from various pegmatite occurrences in southern Norway offer an excellent opportunity in studying post-crystallization evolution of the pegmatites; by determining their crystallographic, chemical, and micro-textural features, imprints of the related processes in the pegmatites have been characterized in this study. Relevant mineral information was collected in recrystallization experiments of fully or slightly metamictized gadolinite samples and subsequent XRD analyses. Micro-Raman spectroscopy, electron microprobe analysis (EMPA), and scanning electron microscope–backscattered electron–energy-dispersive X-ray spectroscopy (SEM-BSE-EDS) analyses were employed to retrieve micro-chemical properties and related micro-textural features of the mineral matrix. With a reference to the gadolinite supergroup, a general alteration path can be envisaged outlining the pegmatite evolution and suggesting the occurrence of the secondary REE mineral phases: altered gadolinite domains prove Ca enrichment with a tendency toward the hingganite composition, while a slight fluorine increase and sporadic secondary fluorite occurrence imply a significant role of fluorine as a complexing agent in the dissolution-reprecipitation mechanism of metasomatic alteration in the mineral. Micro-Raman spectra show improved vibration statistics for the altered gadolinite domains, which could be linked to the substitution of rare earth elements (REE) by Ca and a possible increase of structural ordering within the gadolinite structure, being at the same time an indication of structural healing of metamictized domains by metasomatic processes. A study of microfeatures in the complex silicates like gadolinite proves to be an excellent tool to trace post-crystallization processes in a pegmatitic environment. With a slight redistribution of radionuclides during an alteration in gadolinite, a moderate precaution has to be taken when selecting gadolinite for U-Th-Pb dating.

Kroupaite (IMA 2017-031), 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, on the 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 importance of these phases for the safe disposal of nuclear waste.

Smamite, Ca2Sb(OH)4[H(AsO4)2]·6H2O, is a new mineral species from the Giftgrube mine, Rauenthal, Sainte-Marie-Aux-Mines ore-district, Haut-Rhin department, France. It is a supergene mineral found in quartz-carbonate gangue with disseminated to massive tennantite-tetrahedrite series minerals, native arsenic, Ni-Co arsenides, and supergene minerals picropharmacolite, fluckite, and pharmacolite. Smamite occurs as lenticular crystals growing in aggregates up to 0.5 mm across. The new mineral is whitish to colorless, transparent with vitreous luster and white streak; non-fluorescent under UV radiation. The Mohs hardness is ~3½; the tenacity is brittle, the fracture is curved, and there is no apparent cleavage. The measured density is 2.72(3) g/cm3; the calculated density is 2.709 g/cm3for the ideal formula. The mineral is insoluble in H2O and quickly soluble in dilute (10%) HCl at room temperature. Optically, smamite is biaxial (–), α = 1.556(1), β = 1.581(1), γ = 1.588(1) (white light). The 2V(meas) = 54(1)°; 2V(calc) = 55.1°. The dispersion is weak, r> v. Smamite is non-pleochroic. Electron microprobe analyses provided the empirical formula Ca2.03Sb0.97(OH)4[H1.10(As1.99Si0.01O4)2]·6H2O. Smamite is triclinic, P1¯$\overline{1}$, a= 5.8207(4), b= 8.0959(6), c= 8.21296(6) Å, α = 95.8343(7)°, β = 110.762(8)°, γ = 104.012(7)°, V= 402.57(5) Å3, and Z= 1. The structure (Robs= 0.027 for 1518 I>3σIreflections) is based upon {Ca2(H2O)6Sb(OH)4[H(AsO4)2]} infinite chains consisting of edge-sharing dimers of Ca(H2O)3O2(OH)2polyhedra that share edges with Sb(OH)4O2octahedra; adjacent chains are linked by H-bonds, including one strong, symmetrical H-bond with an O–H bond-length of ~1.23 Å. The name “smamite” is based on the acronym of the Sainte-Marie-aux-Mines district.

The new mineral species bohuslavite, Fe 4 3 + (PO4)3(SO4)(OH)(H2O)10·nH2O (5 = n = 14), has been discovered in the Buca della Vena baryte ± iron oxides ± pyrite ore deposit, Apuan Alps, Tuscany (Italy), and in the Horní Mesto deposit, northern Moravia (Czech Republic). It occurs as pinkish to lilac tabular {001} crystals, with a pseudohexagonal outline, up to 0.25 mm in size, forming globular aggregates up to 1 mm across. At both localities, it is associated with gypsum. Optically, bohuslavite is biaxial negative. Indices of refraction and 2V angles, measured with white light, are a = 1.537(2), ß = 1.567(1), ? = 1.568(1), 2V = 16(3)° and a = 1.550(2), ß = 1.579(2), ? = 1.579(1), 2V = 5–10° for the samples from Buca della Vena (BdV) and Horní Mesto (HM), respectively. Dispersion, with r > v, is slight in BdV sample and it was not observed in HM. In both cases, X ˜ c. No pleochroism was observed. Electron microprobe analyses gave (in wt% – mean of 10 spot analyses on each sample): SO3 10.92, P2O5 25.34, Al2O3 0.26, Fe2O3 40.70, H2O 35.96, total 113.18 (BdV), and SO3 9.32, P2O5 24.84, Al2O3 0.30, Fe2O3 36.63, H2O 32.49, total 103.58 (HM). The H2O contents were determined through thermo-gravimetric analyses. Mössbauer spectroscopy indicated that all iron occurs as Fe3+. Thus, the empirical formulae of bohuslavite, based on S(Fe,Al) = 4 atoms per formula unit (apfu), are (Fe3.96Al0.04)(PO4)2.77(SO4)1.06(OH)1.56(H2O)10·7.90H2O (BdV) and (Fe3.95Al0.05)(PO4)3.02(SO4)1.00(OH)0.94(H2O)10·5.08H2O (HM), ideally Fe 4 3 + (PO4)3(SO4)(OH)(H2O)10·nH2O. Bohuslavite is triclinic, space group P 1 ¯ , with a = 13.376(3), b = 13.338(3), c = 10.863(4) Å, a = 92.80(2), ß = 91.03(2), ? = 119.92(2)°, V = 1675.7(9) Å3, Z = 2 (sample BdV). The crystal structure was solved and refined to R 1 = 0.232 on the basis of 2177 unique reflections with F o > 4s (F o) and 208 refined parameters. Its crystal structure is based on {001} heteropolyhedral layers with composition [Fe4(PO4)3O(OH)(H2O)10]. These layers are decorated, on both sides, by SO4 groups. Additional H2O groups are hosted in the interlayers and in the [001] channels. The name bohuslavite honours the Czech mineralogist and geologist Bohuslav Fojt for his contributions to mineralogy and economic geology. A third occurrence of bohuslavite from the Jeremias Glück mine, Garnsdorf near Saalfeld, Thuringia (Germany), is briefly discussed.

Nowadays, there is an increasing demand for new small modular reactors (SMR) reactors with a wide range of applications, often classified as a new Generation-IV reactors. Unfortunately, there is no commercially operating nuclear reactor meeting the characteristics of Generation-IV reactors in its technical design and features. However, Generation-IV nuclear reactors are intensively developed worldwide, including the Czech Republic. To support research activities linked with the development of these reactors, an appropriate experimental environment and resources simulating conditions expected in Generation-IV reactors with graphite are needed This work builds on previous research and presents a special arrangement of the LR-0 reactor core with a double-row graphite reflector, on which the influence of graphite on the neutron field shaping and power distribution was experimentally and computationally verified. The main reason for this article is to investigate the effect of the graphite reflector, which will serve as a support for the development of neutron instrumentation for Generation-IV reactors and other support for Generation-IV research activities. The results confirm the conclusions of previous research and also provide a better knowledge of the double-row graphite reflector neutron field. The presented and tested LR-0 core arrangement is included in a set of experiments supporting the research of reactor cores with graphite reflectors.

Jahnsite-(MnMnZn) (IMA2017-113), Mn 2 2 + Zn 2 Fe 2 3 + ( PO 4 ) 4 ( OH ) 2 · 8 H 2 O , is a new member of the jahnsite group from the Herdade dos Pendões mine, Beja district, southwest Portugal. It formed in a highly altered gossan in association with Zn-bearing libethenite, quartz, rhodochrosite and santabarbaraite. It occurs in sub-parallel bundles of light golden brown prisms up to 0.3 mm long. Crystals are transparent with vitreous to silky lustre and white streak. The mineral is brittle with irregular, splintery fracture, good cleavage parallel to {001} and Mohs’ hardness of about 4. The measured density is 2.89(2) g cm-3. Optically, it is biaxial (+), with a = 1.655(2), ß = 1.662(2), ? = 1.673(2) (white light); 2V = 78(1)°; pleochroism: X nearly colourless, Y and Z beige; X < Y ˜ Z. Electron microprobe analyses gave the empirical formula ( Mn 0.71 2 + Na 0.15 Ca 0.10 ) S 0.96 Mn 1.00 2 + Zn 1.00 Mn 0.66 2 + Fe 0.21 2 + Mg 0 . 10 Fe 0.03 3 + S 2.00 ( Fe 1.99 3 + Al 0.01 ) S 2.00 ( P 1.01 O 4 ) 4 ( OH ) 2 · 8 H 2 O . Jahnsite-(MnMnZn) is monoclinic, P2/a, a = 15.222(6), b = 7.187(6), c = 10.028(5) Å, ß = 111.746(16)°, V = 1019.0(11) Å3 and Z = 2. The eight strongest lines in the X-ray powder diffraction pattern are [d obs/Å (I) (hkl)]: 9.25 (63) (001), 5.00 (40) (210, 21 1 ¯ ,111), 4.648 (33) (002), 3.509 (41) ( 40 2 ¯ ), 2.842 (100) (022), 1.9984 (37) (422, 42 4 ¯ ), 1.9506 (30) (024) and 1.5853 (33) (820, 82 4 ¯ ). The jahnsite group has now been officially established by the Commission on New Minerals, Nomenclature and Classification. The general formula for jahnsite-group minerals is XM1M22 M32(H2O)8(OH)2(PO4)4; the ionic radii for the cation sites generally increase as follows: M3 < M2 < M1 < X, and the M3 site determines whether the species belongs to the jahnsite subgroup (M3 = Fe3+) or the whiteite subgroup (M3 = Al). The subgroup name is generally used as the species root name to be followed by a suffix of the form -(XM1M2). Using this as a guide for the jahnsite described herein results in the following site assignments: X = Mn, M1 = Mn, M2 = Zn, and M3 = Fe; and the name jahnsite-(MnMnZn). Jahnsite-(MnMnZn).

Sakhaite, ca. Ca48Mg16(BO3)32(CO3)16(HCl,H2O)2, is a rare rock-forming borate-carbonate mineral typically occurring in high-temperature, low-pressure calcareous skarns. It forms a complete solid solution with harkerite, ca. Ca48Mg16[AlSi4(O,OH)16]4(BO3)16(CO3)16(HCl,H2O)2. The solid solution can be described with the general formula Ca48(Mg,Fe,Mn)16(CO3)16[AlaSi5−a(O,OH)16]y(BO3)32−4y(HCl,H2O)n$$\begin{array} {} {\rm{C}}{{\rm{a}}_{48}}{({\rm{Mg}},{\rm{Fe}},{\rm{Mn}})_{16}}{({\rm{C}}{{\rm{O}}_3})_{16}}{[{\rm{A}}{{\rm{l}}_a}{\rm{S}}{{\rm{i}}_{5 - a}}{({\rm{O}},{\rm{OH}})_{16}}]_y}{({\rm{B}}{{\rm{O}}_{\rm{3}}})_{32 - 4y}}{({\rm{HCl}},{{\rm{H}}_2}{\rm{O}})_n}\end{array} $$ where ymax= 8 and nmax= 16 – y. In this study, we examine samples of sakhaite and harkerite from four localities worldwide: Titovskoye deposit, Sakha Republic, Russia (type locality for sakhaite); Solongo B deposit, Buryatia Republic, Russia; Camas Malag, Skye, Scotland (type locality for harkerite); as well as a sakhaite-like mineral from the Kombat Mine, Tsumeb. The Si:B ratios of the samples ranged from that of end-member sakhaite (containing B only) to that of end-member harkerite (Si:B = 1:1), with several intermediate compositions. All samples were deficient in B relative to the ideal composition, implying significant substitution for borate groups. The Si:Al ratio of silicate-containing samples ranged from the ideal 4:1 to 4:1.5, implying substitution of Al at the Si site. The cubic unit-cell parameter was found to increase linearly with increasing Si content, except for the sakhaite-like mineral from Tsumeb. This mineral was found to have significant substitution of Pb for Ca (0.4–0.5 apfu) and was poor in Cl, which in most sakhaite and harkerite samples occupies the interstitial site surrounded by four borate groups. This interstitial site in the Tsumeb samples appears to be, instead, mainly occupied by H2O, which may qualify the mineral as a distinct species.

The uranyl mineral swamboite has been redefined to swamboite-(Nd) and its structure has been solved and refined as a commensurate structure in six-dimensional superspace. The structure is monoclinic, superspace group P21/m(a1,b1,g1)00(−a1,b1,g1)00 (a2,0,g2)0s, cell parameters a=6.6560(3), b=6.9881(5), c=8.8059(6), c=11.3361(16) Å, β=102.591(5)°, modulation wave-vectors q1=1/3 1/3 0; q2=−1/3 1/3 0; q3=1/2 0 1/2. The structure was refined from 8717 reflections to a final R=0.0610. The model includes modulation both of atomic positions and displacement parameters, as well as occupancy waves. The structure is based upon uranyl-silicate sheets of uranophane topology alternating with an interlayer of partly occupied Nd3+sites and H2O molecules. The strong (3+3) dimensional modulation of the structure originates from the distribution of the Nd-dominated sites and further accommodation of the suitable geometry within the sheets and charge distribution within the structure. The separation distances between the corresponding occupied Nd sites are rationals of the super-cell vectors corresponding to the modulation vectors of the structure. The case of swamboite-(Nd) is the first example of a modulated structure within the oxysalts of U6+.

Four distinct paragenetic, morphological and compositional types of milarite-group minerals were distinguished in the NYF pegmatite Velká skála, Písek district, Czech Republic (Moldanubian Zone). The simply zoned (Kfs, Plg, Ab, Qz > Bt > Ap > Tur) pegmatite dike, ~60 cm thick, is enclosed in durbachite (K, Mg-rich melasyenite). The milarite-group minerals include: yellowish, subhedral, prismatic grains of homogeneous milarite I (milarite s. s.); prismatic subparallel aggregates of white to grayish milarite II (zoned milarite s. s. to Sc-rich milarite, up to ~20 mol% of the oftedalite component) from small pockets; colorless hexagonal prismatic crystals of milarite III (milarite s. s.) lining open fractures and microscopicfillings in recrystallized K-feldspar locally associated with REE -bearing minerals (allanite, aeschynite, titanite); very rare milarite IV (milarite s. s. to agakhanovite) as prismatic crystals and thin overgrowths with complex oscillatory zoning, 200µm in size, on crystals of milarite II and milarite III. Their mineral assemblages, textures and compositions suggest primary (magmatic) for milarite I and hydrothermal origin for milarite II, III, and IV. The simplified compositional evolution in these milarites is: Al + Ca ?Be + Sc ?Be + Y,HREE ? Be + LREE. Milaritegroup minerals are the sole carriers of Be in the pegmatite, no relics or pseudomorphs after other Be-rich minerals were found; thus milarite is now established as an additional primary Be-rich mineral in granitic pegmatites. Mineral assemblages, chemical composition of minerals and close relation to the host durbachite suggest an NYF affinity of the Velká skála pegmatite as well as a close relation to euxenite-type pegmatites of the Trebíc Pluton. Milarite-group minerals from Velká Skála exhibit very similar compositional evolution to those found in the Heftetjern pegmatite, Tørdal, Norway.

The isotopic composition of lead (207Pb/206Pb, 208Pb/206Pb, and 210Pb) in a recently formed galena from burning heaps after coal mining in Radvanice, Markoušovice, and Rybníček, the Lower Silesian basin, Czech Republic, was studied in detail. 210Pb activity in galena varied from 135 ± 9 to 714 ± 22 Bq/g and calculated integral doses ranged from 2.21 × 1011to 6.11 × 1011α/g. The radioactivity of the galena causes micro-deformations in its crystal structure as indicated by the Williamson-Hall graphs, showing that the level of micro-strain depends on the length of time that galena samples were exposed to the radiation. However, the crystal structure of galena is affected very inhomogenously; according to TEM investigations there are domains of fully crystalline, polycrystalline, and fully metamict galena within one crystal. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to determine the isotopic composition of the studied galena. The stable isotope ratios of Pb varied for 207Pb/206Pb from 0.8402 to 0.8435 and for 208Pb/206Pb from 2.0663 to 2.0836. The average ratios 207Pb/206Pb = 0.8312 and 208Pb/206Pb = 2.0421 were obtained for coal from the same localities. These isotope ratios show that there is no isotopic fractionation taking place during the coal burning and subsequent galena crystallization from hot gases.

Polarized FTIR spectroscopic measurements of 11 natural wolframite single crystals from different occurrences revealed the common presence of structurally bound OH groups in their crystal lattice, with potential influence on the properties of thisse geologically and technologically important group of compounds. Despite differences in the appearance of the OH absorption pattern, dependent among other on the end-member ratio, two types of “intrinsic” OH defects could be discerned from detailed studies of the pleochroic behavior of the absorption bands both at 80 K and room temperature. The accompanying chemical analyses by the electron microprobe helped to clearly identify the substitution trend W6++ O2–↔ (Nb,Ta)5++ OH–as the prevailing hydrogen incorporation mechanism into wolframite. The assignment of the observed IR absorption phenomena to hydrous defects was confirmed by the results of deuteration experiments and the negligible contribution of included impurities to the FTIR spectra in the OH absorption region. The results obtained in this study of natural wolframite crystals can be used to detect and analyze hydrous defects in synthetic technologically important tungstates.

The new mineral plavnoite (IMA2015-059), ideally K0.8Mn 0.6[(UO2)2O2(SO 4)]·3.5H2 O, is a member of the zippeite group. It was found in the Plavno mine, in the eastern part of the Jáchymov ore district, Western Bohemia, Czech Republic, where it occurs as a supergene alteration phase formed by hydrationbn–oxidation weathering of uraninite in hydrothermal U-veins. It was found to be associated with marécottite, magnesiozippeite, blatonite and gypsum. The mineral occurs as reddish to reddish-orange thin blades, elongated on [0 0 1] and flattened on {0 1 0}, which are intergrown in globular aggregates up to 0.5 mm across. Crystals are transparent with a vitreous to silky lustre. The streak is pale orange. The mineral is non-fluorescent under both long- and short-wave ultraviolet (UV) radiation. The Mohs hardness is about 2. Crystals are brittle with perfect {0 1 0} cleavage and uneven fracture. The density calculated from the empirical formula is 4.926 g cm-3. Optically, plavnoite is biaxial (+), with a = 1.740(5), b = 1.770(5), g = 1.850 (5) (measured in white light). The measured 2 V is 64.6(4)°; the calculated 2 V is 65.3°. Dispersion could not be observed; no pleochroism was observed. Electron-microprobe analyses yielded the empirical formula (based on 2 U atoms per formula unit, apfu) K0.77 (Mn0.51 Zn0.04 Ni0.03 Mg0.02)S 0.60 [(UO2)2 O1.08 (OH)0.92 (SO4 )0.96 (SiO4)0.24 ](H2 O)3.50. Plavnoite is monoclinic, C 2/ c, a = 8.6254 (16), b = 14.258(3), c = 17.703(4) Å, b = 104.052(18)°, V = 2122.0(8) Å3 and Z = 8. The structure ( R 1 = 4.99 % for 989 reflections with I> 3 s [I]) contains UO7 pentagonal bipyramids and SO4 tetrahedra forming sheets of the well-known zippeite topology. The interlayer region contains infinite zig–zag chains of corner-sharing Mn2+; f6 octahedra (F = O, H2 O) with K-centred polyhedra. The K atom sits at the partially occupied, mixed K/O site, the non-shared corner of the Mn2 octahedron. The mineral is named after the type locality the Plavno mine.

Gauthierite, KPb[(UO2)7 O5 (OH)7]· 8H2 O, is a new uranyl-oxide hydroxy-hydrate mineral from the Shinkolobwe Mine, Democratic Republic of Congo, Africa. It occurs on a matrix of uraninite-bearing quartz gangue associated with soddyite and a minor metazeunerite–metatorbernite series mineral. It is a product of oxidation–hydration weathering of uraninite. Gauthierite is monoclinic, P 21 / c, with a = 29.844(2) Å, b = 14.5368(8) Å, c = 14.0406(7) Å, b = 103.708(6) °, V = 5917.8(6) Å3 and Z = 8. Prismatic crystals have pronounced lengthwise striations and reach about 1 mm in length. Gauthierite is yellowish orange with a light orange streak and vitreous lustre. The Mohs hardness is ~3 to 4. It is brittle with an uneven fracture and perfect cleavage on {0 1 0}. The calculated density based on the empirical formula is 5.437 g/cm3. Optically, gauthierite is biaxial (–), with a = 1.780(5), b = 1.815(5), g = 1.825(5) (white light), 2V meas. = 58(1)° dispersion is extreme (r >> v). The optical orientation is X = b, Y ˜ a*, Z ˜ c (or X = b, Y ^ a = 14° in obtuse ß); it is pleochroic with X very pale yellow, Y and Z orange-yellow; X >> Y ˜ Z. Electron microprobe analyses (average of 9) provided: K2 O 1.29, PbO 7.17, UO3 82.10, H2O 8.78 (structure), total 99.34 wt.%. The empirical formula (based on 34 O a. p. f. u.) is: K0.67 Pb0.78 U7 O34 H23.77. The ideal formula is KPb[(UO2)7 O5 (OH)7 ](H2 O)8, which requires K2 O 1.90, PbO 9.00, UO3 80.74, H2 O 8.35, total 100 wt.%. Raman and infrared spectral data confirm the presence of UO2 2+, OH and molecular H2 O. The eight strongest powder X-ray diffraction lines are [d obs in Å ( hkl) I rel ]: 7.28 (020,400) 49, 3.566 (040, 802, 204) 67, 3.192 (622, 224) 100, 2.541 ( 842, 244) 18, 2.043 (406) 14, 2.001 (662, –264, 14·2·0) 23, 1.962 (426, 146) 14, and 1.783 (12·0· 4, 10·4·6) 17. The crystal structure of gauthierite ( R = 0.0567 for 6997 reflections with [I> 3 s (I)]) contains uranyl-(hydroxo)-oxide sheets with a novel topology that is similar to that of vandendriesscheite, but with a unique chain sequence UDPDPDUPUP, P4 (UD)6. Adjacent sheets are linked through K+ and Pb2+ cations (the lone 6s2 pair on Pb atoms is stereoactive).

Radiation damage in minerals is caused by the α-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400–1000 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia [6.4 wt% Th, 23.1·1018α-decay events per gram (dpg)], Panda Hill/Tanzania (1.6 wt% Th, 1.6·1018dpg), and Blue River/Canada (10.5 wt% U, 115.4·1018dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28%, Blue River 85% and Miass 100% according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm−1are sensitive to radiation damage (M. T. Vandenborre, E. Husson, Comparison of the force field in various pyrochlore families. I. The A2B2O7oxides. J. Solid State Chem.1983, 50, 362, S. Moll, G. Sattonnay, L. Thomé, J. Jagielski, C. Decorse, P. Simon, I. Monnet, W. J. Weber, Irradiation damage in Gd2Ti2O7single crystals: Ballistic versus ionization processes. Phys. Rev.2011, 84, 64115.), the degree of local order was deduced from the ratio of the integrated intensities of the sum of the Raman bands between 605 and 680 cm−1divided by the sum of the integrated intensities of the bands between 810 and 860 cm−1. The most radiation damaged pyrochlore (Miass) shows an abrupt recovery of both, its short- (Raman) and long-range order (X-ray) between 800 and 850 K, while the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its initial state an amorphous X-ray diffraction pattern superimposed by weak Bragg-maxima that indicates the existence of ordered regions in a damaged matrix. In contrast to the other studied pyrochlores, Raman spectra of the Blue River sample show the appearance of local modes above 560 K between 700 and 800 cm−1resulting from its high content of U and Ta impurities. DSC measurements confirmed the observed structural recovery upon annealing. While the annealing-induced ordering of Panda Hill begins at a lower temperature (ca. 500 K) the recovery of the highly-damaged pyrochlore from Miass occurs at 800 K. The Blue-River pyrochlore shows a multi-step recovery which is similarly seen by XRD. Thermogravimetry showed a continuous mass loss on heating for all radiation-damaged pyrochlores (Panda Hill ca. 1%, Blue River ca. 1.5%, Miass ca. 2.9%).

The system B2O3-Al2O3-SiO2(BAS) includes two ternary phases occurring naturally, boromullite, Al9BSi2O19, and boralsilite, Al16B6Si2O37, as well as synthetic compounds structurally related to mullite. The new mineral vránaite, a third naturally occurring anhydrous ternary BAS phase, is found with albite and K-feldspar as a breakdown product of spodumene in the elbaite-subtype Manjaka granitic pegmatite, Sahatany Valley, Madagascar. Boralsilite also occurs in this association, although separately from vránaite; both minerals form rare aggregates of subparallel prisms up to 100 μm long. Optically, vránaite is biaxial (–), nα= 1.607(1), nβ= 1.634(1), nγ= 1.637(1) (white light), 2Vx(calc) = 36.4°, X≈ c; Y≈ a; Z= b. An averaged analysis by EMP and LA-ICP-MS (Li, Be) gives (wt%) SiO220.24, B2O311.73, Al2O364.77, BeO 1.03, MnO 0.01, FeO 0.13, Li2O 1.40, Sum 99.31. Raman spectroscopy in the 3000–4000 cm−1region rules out the presence of significant OH or H2O. Vránaite is monoclinic, space group I2/m, a= 10.3832(12), b= 5.6682(7), c= 10.8228(12) Å, β = 90.106(11)°; V= 636.97(13) Å3, Z= 1. In the structure [R1= 0.0416 for 550 Fo> 4σFo], chains of AlO6octahedra run parallel to [010] and are cross-linked by Si2O7disilicate groups, BO3triangles, and clusters of AlO4and two AlO5polyhedra. Two Al positions with fivefold coordination, Al4 and Al5, are too close to one another to be occupied simultaneously; their refined site-occupancy factors are 54% and 20% occupancy, respectively. Al5 is fivefold-coordinated Al when the Al9 site and both O9 sites are occupied, a situation giving a reasonable structure model as it explains why occupancies of the Al5 and O9 sites are almost equal. Bond valence calculations for the Al4 site suggest Li is likely to be sited here, whereas Be is most probably at the Al5 site. One of the nine O sites is only 20% occupied; this O9 site completes the coordination of the Al5 site and is located at the fourth corner of what could be a partially occupied BO4tetrahedron, in which case the B site is shifted out of the plane of the BO3triangle. However, this shift remains an inference as we have no evidence for a split position of the B atom. If all sites were filled (Al4 and Al5 to 50%), the formula becomes Al16B4Si4O38, close to Li1.08Be0.47Fe0.02Al14.65B3.89Si3.88O36.62calculated from the analyses assuming cations sum to 24. The compatibility index based on the Gladstone-Dale relationship is 0.001 (“superior”). Assemblages with vránaite and boralsilite are inferred to represent initial reaction products of a residual liquid rich in Li, Be, Na, K, and B during a pressure and chemical quench, but at low H2O activities due to early melt contamination by carbonate in the host rocks. The two BAS phases are interpreted to have crystallized metastably in lieu of dumortierite in accordance with Ostwald Step Rule, possibly first as “boron mullite,” then as monoclinic phases. The presence of such metastable phases is suggestive that pegmatites crystallize, at least partially, by disequilibrium processes, with significant undercooling, and at high viscosities, which limit diffusion rates.

Significant uranium mineralization represented by a typical assemblage of uranyl supergene minerals in a quartz-uraninite vein hosted in the exocontact zone of the Variscan-Tanvald granite was found at a new construction site in the municipality of Jablonec n. Nisou. Activities of 222Rn in soil gas reached 1 MBq/m3around two houses, with a maximum of 3.33 MBq/m3between them on a uranium ore lens outcrop. The uranium content reaches up to 291 ppm eU (3595 Bq/kg 226Ra), and it is possible to find many ‘hot’ pieces of uranium ore fragments with a high percentage of uranium in the Quaternary cover in this place. This unfavourable situation is a result of an improper spatial planning process. The constructor was given the permission to construct the building even though the construction site did not meet safety requirements and the geological survey had failed. Not only geological prospecting was underestimated, but also the radon risk assessment was undervalued.

Silicified Agathoxylon-type wood of Late Palaeozoic age was characterized by means of cathodoluminescence (CL) and LA-ICP-MS of the quartz mass, which was found to contain wakefieldite, characterized by electron-microprobe (EMP) analysis, Raman microspectroscopy and X-ray diffraction. Although former organic matter is almost absent, plant anatomy served as the template for the quartz mass texture. Two generations of quartz mass were distinguished; the large proportion of the silicified wood consisting of brownish a-quartz with a dark reddish CL emission, and the minor portion of whitish ‘leached’ wood with a short-lived (transient) blue CL. On the outer edge, a silicified texture of formerly slightly humified wood also emits a dark reddish CL. Likely the wood specimen has been fossilized and diagenetically altered in several steps. The marginal part had been humified (reductively degraded) before the initial stages of silicification. The LA-ICP-MS analyses revealed chemical differences in all three distinct parts. The quartz mass relatively enriched in REEs and As and giving the dark reddish CL is interpreted as a primary diagenetic mineral mass. Whitish zones relatively depleted in U and V, and enriched in Al, Li, Rb, Cu, and Sr producing the blue CL would then be a secondary diagenetic overprint. An EMP/WDS analysis identified As-rich xenotime-(Y) and a solid solution of wakefieldite–(Ce) and wakefieldite–(Y), which locally enclose individual silicified tracheids. Wakefieldite, identified in silicified plant tissue for the first time, was most likely formed as a secondary mineral during post-depositional diagenesis. The mineral diagenesis did not erase the original anatomy of the wood.

Rameauite is a rare supergene uranyl-oxide hydroxy-hydrate mineral that forms during hydration-oxidation weathering of uraninite. On the basis of single-crystal X-ray diffraction data collected on a microfocus source, rameauite is monoclinic, space group Cc, with a = 13.9458(19), b = 14.3105(19), c = 13.8959(18) Å, ß = 118.477(14)°, V = 2437.7(6) Å3 and Z = 4, with Dcalc = 5.467 g cm-3. The structure of rameauite (R = 0.060 for 1698 unique observed reflections) contains sheets of the ß-U3O8 topology, with both UO6 and UO7 bipyramids, which is similar to the sheets found in spriggite, ianthinite and wyartite. The sheets alternate with the interlayer, which contain K+, Ca2+ and H2O molecules. Interstitial cations are linked into infinite chains that extend along [10-1]. Adjacent sheets are linked through K–O, Ca–O and H-bonds. The structural formula of rameauite is K2Ca(H2 [3]O)1(H2 [5]O)4[(UO2)6O6(OH)4](H2 [4]O)1. The empirical formula obtained from the average of eight electron-microprobe analyses is (on the basis of 6 U p.f.u.) K1.87(Ca1.10Sr0.04)S1.14[(UO2)6O6(OH)4.15]·6H2O. The Raman spectrum is dominated by U–O and O–H vibrations. A discussion of related uranyl-oxide minerals is given.

Primary black thick-prismatic Al-rich schorl to rare fluor-schorl (TurP1), locally overgrown by brownish-green Li-rich fluor-schorl to fluor-elbaite (TurP2) from the Kracovice pegmatite (mixed NYF+LCT signature), was partly replaced by secondary Li-rich fluor-schorl to fluor-elbaite (TurS) plus the assemblage REE-bearing epidote-group mineral + chamosite. Primary Al-rich schorl (TurP1) shows high and variable contents of Sc (33-364 ppm) and Y+REE (40-458 ppm) with steep, LREEenriched REE pattern. Overgrowing (TurP2) and replacing (TurS) Li-rich fluor-schorl to fluor-elbaite is typically depleted in Sc (21-60 ppm) and Y+REE (3-47 ppm) with well-developed tetrad effect in the first (La-Nd) and the second (Sm-Gd) tetrads. Scandium- and REE-rich black tourmaline (TurP1) crystallized earlier from the melt, whereas crystallization of primary Li-rich fluor-schorl to fluor-elbaite (TurP2) most likely took place during late magmatic to early hydrothermal conditions. Both the secondary Li-rich fluor-schorl to fluor-elbaite (TurS) and the unusual assemblage of REE-bearing epidotegroup mineral + chamosite are likely coeval products of subsolidus reactions of the magmatic Al-rich schorl (TurP1) with evolved REE-poor, Li,F-rich, alkaline pegmatite-derived fluids. Well-crystalline REE-bearing epidote-group mineral (Y+REE = 0.42-0.60 apfu) confirmed by Raman spectroscopy has a steep, LREE-rich chondrite-normalized REE pattern with significant negative Eu anomaly and shows variable and high contents of Sc (≤3.3 wt% Sc2O3) and Sn (≤1.0 wt% SnO2). Substitution ScAl-1and minor vacancy in the octahedral sites are suggested in the REE-bearing epidote-group mineral.

Garnet and other rock-forming minerals from A-type granite dikes in the Pre-Variscan Brno Batholith were analyzed to determine relative contributions of individual minerals to whole-rock Y and REE budget and to assess incorporation mechanisms of these elements in garnet. Minor to accessory garnet (<2 vol%) is the essential reservoir for Y+REE in the Hlína granite accounting ∼84% Y and 61% REE of the total whole-rock budget. Zircon is another important carrier of REE with ∼13% Y and ∼11% REE. At least ∼21% REE and 1% Y were probably hosted by Th- and U-rich monazite that has been completely altered to a mixture of secondary REE-bearing phases. The contribution of major rockforming minerals (quartz and feldspars) is low (∼1% Y; 10% LREE; ∼1% HREE) excluding Eu, which is hosted predominantly by feldspars (∼90%). Minor to accessory muscovite and magnetite incorporate ∼1% Y and ∼2% REE of the whole-rock budget. Magmatic garnet Sps41-46Alm28-44And0-13Grs6-12Prp0-1is Y- and HREE-rich (up 1.54 wt% Y; up ∼1 wt% ΣREE), and the Y+REE enter the garnet structure via the menzerite-(Y) substitution. The Y and REE show complex zoning patterns and represent sensitive indicator of garnet evolution, in contrast to a homogeneous distribution of major divalent cations. General outward decrease of Y+REE is a common feature due to the strong partitioning of Y+HREE in the garnet relative to the other phases. REE underwent significant fractionation during growth of early garnet I; the YbN/NdN ratio generally decreases from the core to rim of garnet I. Higher Mn and Al, lower Ca, and Y+REE contents, as well as higher YbN/NdNratio and more negative Eu anomaly in garnet II overgrowths indicate its crystallization from a more evolved melt. Application of zircon saturation geothermometry provides upper temperature limit of 734 ± 14 °C for the closed-system crystallization. Mineral equilibria reveal that crystallization started at QFM + 1.2, and preferential sequestration of Fe3+ into garnet and magnetite was responsible for progressively reducing conditions. Equilibrium between magnetite, garnet, quartz, and plagioclase, representing the final crystallization stage of the granitic magma, occurred at 658-663 °C and QFM 0 to + 0.8, hence at undercooling of ∼75 °C.

We report the first occurrence of kumdykolite, a high-temperature analog of albite, in the European Variscan belt. It was discovered in an ultrahigh-pressure, diamond-bearing quartzofeldspathic granulite from the northern Bohemian Massif. It is associated with phlogopite and quartz in a multiphase solid inclusion within garnet, considered to represent a trapped fluid or melt phase. Micro-Raman analysis and mapping along with BSE revealed the presence of a sub-equant, elongated grain of kumdykolite reaching 20 mm in length. WDX analysis has shown that kumdykolite contains 2 wt% CaO, probably indicating significant miscibility with the Ca-end-member svyatoslavite. Similar to the case of microdiamond inclusions, the kumdykolite-bearing multiphase inclusion is located in the Ca- and Mg-rich central part of the garnet and thus must have been trapped at P > 4 GPa. The inclusion minerals, however, crystallized upon decompression and cooling during the exhumation. Kumdykolite preservation thus provides independent evidence for high temperature of the original trapped fluid, or melt, crystallization, and rapid cooling of the rocks. Our results imply that kumdykolite and other feldspar modifications stable at elevated pressures and temperatures may be common phases in quartzofeldspathic granulites and need to be searched for.

Mathesiusite, K5(UO2)4(SO4)4(VO5)(H2O)4, a new uranyl vanadate-sulfate mineral from Jáchymov, Western Bohemia, Czech Republic, occurs on fractures of gangue associated with adolfpateraite, schoepite, čejkaite, zippeite, gypsum, and a new unnamed K-UO2-SO4mineral. It is a secondary mineral formed during post-mining processes. Mathesiusite is tetragonal, space group P4/n, with the unit-cell dimensions a = 14.9704(10), c = 6.8170(5) Å, V = 1527.78(18) Å3, and Z = 2. Acicular aggregates of mathesiusite consist of prismatic crystals up to ~200 μm long and several micrometers thick. It is yellowish green with a greenish white streak and vitreous luster. The Mohs hardness is ~2. Mathesiusite is brittle with an uneven fracture and perfect cleavage on {110} and weaker on {001}. The calculated density based on the empirical formula is 4.02 g/cm3. Mathesiusite is colorless in fragments, uniaxial (-), with ω = 1.634(3) and ε = 1.597(3). Electron microprobe analyses (average of 7) provided: K2O 12.42, SO318.04, V2O54.30, UO361.46, H2O 3.90 (structure), total 100.12 (all in wt%). The empirical formula (based on 33 O atoms pfu) is: K4.87(U0.99O2)4(S1.04O4)4(V0.87O5)(H2O)4. The eight strongest powder X-ray diffraction lines are [dobsin Å (hkl) Irel]: 10.64 (110) 76, 7.486 (200) 9, 6.856 (001) 100, 6.237 (101) 85, 4.742 (310) 37, 3.749 (400) 27, 3.296 (401) 9, and 2.9409 (510) 17. The crystal structure of mathesiusite was solved from single-crystal X-ray diffraction data and refined to R1= 0.0520 for 795 reflections with I > 3σ(I). It contains topologically unique heteropolyhedral sheets based on [(UO2)4(SO4)4(VO5)]5-clusters. These clusters arise from linkages between corner-sharing quartets of uranyl pentagonal bipyramids, which define a square-shaped void at the center that is occupied by V5+cations. Each pair of uranyl pentagonal bipyramids shares two vertices of SO4tetrahedra. Each SO4shares a third vertex with another cluster to form the sheets. The K+cations are located between the sheets, together with a single H2O group. The corrugated sheets are stacked perpendicular to c. These heteropolyhedral sheets are similar to those in the structures of synthetic uranyl chromates. Raman spectral data are presented confirming the presence of UO22+, SO4, and molecular H2O.

Darrellhenryite, Na(LiAl2)Al6(BO3)3Si6O18(OH)3O, a new member of the tourmaline supergroup (related to the alkali-subgroup 4), is a new Li-bearing tourmaline species, which is closely related to elbaite through the substitution YAlW0.5O1YLiW-0.5(OH)-1. It occurs in a complex (Li-bearing) petalite-subtype pegmatite with common lepidolite, Li-bearing tourmalines, and amblygonite at Nová Ves near Ceský Krumlov, southern Bohemia, Moldanubian Zone, Czech Republic. This zoned pegmatite dike cross-cuts a serpentinite body enclosed in leucocratic granulites. Pink darrellhenryite forms columnar crystals (sometimes in parallel arrangement) up to 3 cm long and up 2 cm thick, associated with albite (var. cleavelandite), minor quartz, K-feldspar, petalite, rare polylithionite, and locally rare pollucite. The optical properties and the single-crystal structure study (R1 = 0.019) of darrellhenryite are consistent with trigonal symmetry, w = 1.636(2), e = 1.619(2), birefringence: 0.017, space group R3m, a = 15.809(2), c = 7.089(1) Å, V = 1534.4(4) Å3, and Z = 3. The chemical analysis, in combination with the results from the single-crystal structure refinement, gives the formula X(Na0.58Ca0.01?0.41)1.00Y(Li1.05Al1.95)3.00ZAl6(BO3)3T(Si6O18)V(OH)3W(O0.66F0.34)1.00, which can be simplified to an ideal formula of Na(LiAl2) Al6(BO3)3Si6O18(OH)3O. The strongest lines of the powder pattern [d in Å (I, hkl)] are 4.180 (39, 211), 3.952 (54, 220), 3.431 (73, 012), 2.925 (100, 122), 2.555 (90, 051), 2.326 (42, 511), 2.029 (42, 223), 2.021 (42, 152), 1.901 (50, 342), 1.643 (49, 603). The density is Dmeas= 3.03(3) g/cm3, Dcalc= 3.038 g/ cm3. Darrellhenryite is considered to have crystallized in Li- and B-rich but F-moderate environments in complex pegmatites; no influence of higher activity of O on the darrellhenryite formation is implied from its mineral assemblage. The name is for Darrell J. Henry, Professor of Geology at the Louisiana State University, Baton Rouge, U.S.A., an expert on the mineralogy, petrology, crystal chemistry, and nomenclature of tourmaline-supergroup minerals.

The iron ore mineralizations at the Horní Benešov sulphidic deposit are located in the Devonian Šternberk-Horní Benešov Belt which is enveloped by the Lower Carboniferous flysch of the Culm Foreland Basin. The belt consists of metasedimentary and metavolcanic rocks. Horní Benešov is the only site in the Jeseníky Mountains, where the oxidic iron ores occur in close association with the sulphide orebodies of the VMS/SHMS type.

The crystal structure of cejkaite, Na4(UO2)(CO3)3, from the type locality, was determined for the first time by single-crystal X-ray diffraction. In contrast to the previously reported pseudohexagonal triclinic symmetry, the current data indicate cejkaite is monoclinic, triply twinned, and belongs to the space group Cc. Refined unit-cell parameters are a = 9.2919(8), b = 16.0991(11), c = 6.4436(3) Å, ß = 91.404(5)°, and V = 963.62(12) Å3. The monoclinic unit cell is also supported by the good fit to the powder diffraction data. The structure of cejkaite consists of uranyl tricarbonate clusters, forming sheets sub-parallel to (001) by sharing edges with (NaF) polyhedra. Sheets are interconnected through the uranyl O atoms and columns of (Na1F) polyhedra that share their trigonal faces. All Na atoms in the structure are in sixfold coordination . The structure refinement yielded Robs= 0.0424 for 1687 observed reflections [Iobs> 3s(I)] and 0.0538 for all 2016 unique reflections. Refinement and bondvalence analysis of the structure confirmed the previously proposed formula Na4(UO2)(CO3)3, Z = 4.

The previously published crystal structure study suggested that haiweeite is orthorhombic, Cmcm, with a = 7.125(1), b = 17.937(2), c = 18.342(2) Å, and V = 2344.3(7) Å3, and an ideal chemical formula Ca[(UO2)2Si5O12(OH)2]·3H2O, with Z = 4. Using single-crystal X-ray diffraction and electron microprobe analysis we re-examined haiweeite from the Teofilo Otoni, Minas Gerais, Brazil. Our diffraction experiment provided weak reflections responsible for doubling of the b cell parameter (for the current space-group settings), leading finally to the choice of a different space group. Haiweeite is thus orthorhombic, the space group Pbcn, with the unit-cell parameters a = 18.3000(5), b = 14.2331(3), c = 17.9192(5) Å, V = 4667.3(2) Å3, and an ideal formula Ca[(UO2)2(SiO3OH)2(Si3O6)]·6H2O (6.25 H2O inferred from the thermal analysis; 7.50 H2O from the structure model), with Z = 8. The structure refinement yielded R1= 0.0512 for 2498 observed reflections [Iobs> 3s(I)] and wR2= 0.1286 for all 6117 unique reflections. Structure solution confirmed by subsequent refinement provided a structure model with full occupancies for U, Si, and Ca atoms, contrasting to previous average structure model. Although the general topology of our structure resembles that reported previously, all Si and O sites in our structure are fully occupied, in contrast to the previous structure determination.

Abstract Oxy-schorl (IMA 2011-011), ideally Na(Fe22+Al)Al6Si6O18(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup, is described. In Zlatá Idka, Slovak Republic (type locality), fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming aggregates up to 3.5 cm thick were found in extensively metasomatically altered metarhyolite pyroclastics with Qtz+Ab+Ms. In Pribyslavice, Czech Republic (co-type locality), abundant brownish black subhedral, columnar crystals of oxy-schorl, up to 1 cm in size, arranged in thin layers, or irregular clusters up to 5 cm in diameter, occur in a foliated muscovite-tourmaline orthogneiss associated with Kfs+Ab+Qtz+Ms+Bt+Grt. Oxy-schorl from both localities has a Mohs hardness of 7 with no observable cleavage and parting. The measured and calculated densities are 3.17(2) and 3.208 g/cm3 (Zlatá Idka) and 3.19(1) and 3.198 g/cm3(Pribyslavice), respectively. In plane-polarized light, oxy-schorl is pleochroic; O = green to bluish-green, E = pale yellowish to nearly colorless (Zlatá Idka) and O = dark grayish-green, E = pale brown (Pribyslavice), uniaxial negative, ? = 1.663(2), e = 1.641(2) (Zlatá Idka) and ? = 1.662(2), e = 1.637(2) (Pribyslavice). Oxy-schorl is trigonal, space group R3m, Z = 3, a = 15.916(3) Å, c = 7.107(1) Å, V = 1559.1(4) Å3(Zlatá Idka) and a = 15.985(1) Å, c = 7.154(1) Å, V = 1583.1(2) Å3(Pribyslavice). The composition (average of 5 electron microprobe analyses from Zlatá Idka and 5 from Pribyslavice) is (in wt%): SiO233.85 (34.57), TiO2<0.05 (0.72), Al2O339.08 (33.55), Fe2O3not determined (0.61), FeO 11.59 (13.07), MnO <0.06 (0.10), MgO 0.04 (0.74), CaO 0.30 (0.09), Na2O 1.67 (1.76), K2O <0.02 (0.03), F 0.26 (0.56), Cl 0.01 (<0.01), B2O3(calc.) 10.39 (10.11), H2O (from the crystal-structure refinement) 2.92 (2.72), sum 99.29 (98.41) for Zlatá Idka and Pribyslavice (in parentheses). A combination of EMPA, Mössbauer spectroscopy, and crystal-structure refinement yields empirical formulas (Na0.591Ca0.103?0.306)S1.000(Al1.885Fe2+1.108Mn0.005Ti0.002)S3.000(Al5.428Mg0.572)S6.000(Si5.506Al0.494)S6.000O18 (BO3)3(OH)3(O0.625OH0.236F0.136Cl0.003)S1.000for Zlatá Idka, and (Na0.586Ca0.017K0.006?0.391)S1.000(Fe2+1.879Mn0.015Al1.013Ti0.093)S3.00(Al5.732Mg0.190Fe3+0.078)S6.000(Si5.944Al0.056)S6.000O18(BO3)3(OH)3(O0.579F0.307OH0.115)S1000for Pribyslavice. Oxy-schorl is derived from schorl end-member by the AlOFe-1(OH)-1 substitution. The studied crystals of oxy-schorl represent two distinct ordering mechanisms: disorder of R2+and R3+cations in octahedral sites and all O ordered in the W site (Zlatá Idka), and R2+and R3+cations ordered in the Y and Z sites and O disordered in the V and W sites (Pribyslavice).

The crystal structure of pseudojohannite from White Canyon, Utah, was solved by charge-flipping from single-crystal X-ray diffraction data and refined to an Robs= 0.0347, based on 2664 observed reflections. Pseudojohannite from White Canyon is triclinic, P1̄, with a = 8.6744(4), b = 8.8692(4), c = 10.0090(5) Å, α = 72.105(4)°, β = 70.544(4)°, γ = 76.035(4)°, and V = 682.61(5) Å3, with Z = 1 and chemical formula Cu3(OH)2[(UO2)4O4(SO4)2](H2O)12. The crystal structure of pseudojohannite is built up from sheets of zippeite topology that do not contain any OH groups; these sheets are identical to those found in zippeites containing Mg2+, Co2+, and Zn2+. The two Cu2+sites in pseudojohannite are [5]- and [6]-coordinated by H2O molecules and OH groups. The crystal structure of the pseudojohannite holotype specimen from Jáchymov was refined using Rietveld refinement of high-resolution powder diffraction data. Results indicate that the crystal structures of pseudojohannite from White Canyon and Jáchymov are identical.

The infrared (IR) spectra of gem-quality xenotime crystals containing considerable amounts of rare earth elements (REEs), are characterized by sharp and strongly pleochroic absorption bands in the 3650-3350 cm-1region. In contrast, the spectra of partially metamict samples are dominated by a broad band centered at around 3450 cm-1. Xenotime presents the interesting case of a nominally anhydrous mineral, where the OH stretching frequency region of weakly hydrogen-bonded OH groups is overlapped by absorption bands due to low-energetic f-f electron transitions of REEs, especially of dysprosium. In polarized spectra measured parallel to the c-axis, Dy shows a prominent sharp band at 3519 cm-1. The assignment of the REE bands is based on the polarized IR spectra of REE doped xenotime single crystals, which have been synthesized by the flux method. A single band at 3480 cm-1, strongly polarized perpendicular to the c-axis, is assigned to the stretching vibration of an OH group. Deuteration experiments performed at 950 °C prove the assignment of this band and the presence of additional structural OH groups, appearing at annealing temperatures above 500 °C. Models of the OH point defect incorporation into the crystal structure of xenotime can be derived on the basis of fully occupied cation sites and under the assumption of Y- and P-site vacancies. The water content of the gem-quality samples ranges from 5 to 10 wt ppm and for the partially metamict samples from 370 wt ppm to 1.7 wt% H2O.

Sejkoraite-(Y), the triclinic (Y1.98Dy0.24)Σ2.22H+0.34[(UO2)8O88O7OH(SO4)4](OH)(H2O)26, is a new member of the zippeite group from the Červená vein, Jáchymov (Street Joachimsthal) ore district, Western Bohemia, Czech Republic. It grows on altered surface of relics of primary minerals: uraninite, chalcopyrite, and tennantite, and is associated with pseudojohannite, rabejacite, uranopilite, zippeite, and gypsum. Sejkoraite-(Y) forms crystalline aggregates consisting of yellow-orange to orange crystals, rarely up to 1 mm in diameter. The crystals have a strong vitreous luster and a pale yellow-to-yellow streak. The crystals are very brittle with perfect {100} cleavage and uneven fracture. The Mohs hardness is about 2. The mineral is not fluorescent either in short- or long-wavelength UV radiation. Sejkoraite-(Y) is yellow, with no visible pleochroism, biaxial negative with α′ = 1.62(2), β′ = 1.662(3), γ′ = 1.73(1), 2Vcalc= 79°. The empirical chemical formula (mean of 8 electron microprobe point analyses) was calculated on the basis of 12 (S + U) atoms: (Y1.49Dy0.17Gd0.11Er0.07Yb0.05Sm0.02)Σ1.90H+0.54[(UO2)8.19O7OH(SO4)3.81](H2O)26.00. Sejkoraite-(Y) is triclinic, space group P1̄, a = 14.0743(6), b = 17.4174(7), c = 17.7062(8) Å, α = 75.933(4), β = 128.001(5), γ = 74.419(4)°, V = 2777.00(19) Å3, Z = 2, Dcalc= 4.04 g/cm3. The seven strongest reflections in the X-ray powder diffraction pattern are [dobs in Å (I) (hkl)]: 9.28 (100) (100), 4.64 (39) (200), 3.631 (6) (1̄42), 3.451 (13) (1̄44), 3.385 (10) (2̅4̅2), 3.292 (9) (044), 3.904(7) (300), 2.984 (10) (1̄4̅2). The crystal structure of sejkoraite-(Y) has been solved by the charge flipping method from single-crystal X-ray diffraction data and refined to Robs= 0.060 with GOFobs= 2.38, based on 6511 observed reflections. The crystal structure consists of uranyl sulfate sheets of zippeite anion topology, which alternate with an interlayer containing Y3+(H2O)n polyhedra and uncoordinated H2O groups. Two yttrium atoms are linked to the sheet directly via uranyl oxygen atom, and the remaining one is bonded by hydrogen bonds only. In the Raman and infrared spectrum of sejkoraite-(Y) there are dominating stretching vibrations of SO4tetrahedra (-1200-1100 cm-1), UO22+stretching vibrations (-900-800 cm-1), and O-H stretching (-3500-3200 cm-1) and H-O-H bending modes (-1640 cm-1). The new mineral is named to honor Jiří Sejkora, a Czech mineralogist of the National Museum in Prague.

A mineral assemblage involving grandidierite, ominelite, boralsilite, werdingite, dumortierite (locally Sb,Ti-rich), tourmaline, and corundum, along with the matrix minerals K-feldspar, quartz, and plagioclase, was found in a veinlet cutting leucocratic granulite at Horní Bory, Bory Granulite Massif, Moldanubian Zone of the Bohemian Massif. Zoned crystals of primary grandidierite to ominelite enclosed in quartz are locally overgrown by prismatic crystals of boralsilite and Fe-rich werdingite. Boralsilite also occurs as separate cross-shaped plumose aggregates with Fe-rich werdingite in quartz. Grandidierite is commonly rimmed by a narrow zone of secondary tourmaline or is partially replaced by the assemblage tourmaline + corundum ± hercynite. Grandidierite (XFe= 0.34-0.71) exhibits dominant FeMg-1substitution and elevated contents of Li (120-1890 ppm). Boralsilite formula ranges from Al15.97B6.20Si1.80O37to Al15.65B5.29Si2.71O37and the formula of werdingite ranges from (Fe,Mg)1.44Al14.61B4.00Si3.80O37to (Fe,Mg)1.22Al14.86B4.25Si3.55O37. Dumortierite and Sb,Ti-rich dumortierite occur as zoned crystals with zones poor in minor elements (≤0.12 apfu Fe+Mg) and zones enriched in Sb (≤0.46 apfu) and Ti (≤0.25 apfu). Secondary tourmaline (XFe= 0.44-0.75) of the schorlmagnesiofotite- foitite-olenite solid solution occurs as a replacement product of grandidierite, rarely boralsilite. Other accessory minerals in the veinlet include monazite-(Ce), ilmenite, rutile, ferberite, srilankite, löllingite, arsenopyrite, and apatite. Formation of the borosilicate-bearing veinlet post-dates the development of foliation in the host granulite and is related to the decompressional process. The assemblage most probably originated from a H2O-poor system at T ~ 750 °C and P ~ 6-8 kbar. Textural relations as well as geological position of the borosilicate veinlet suggest that it represents the earliest intrusion related to pegmatites in the Bory Granulite Massif. Younger granitic pegmatites in the area are characterized by high contents of B, Al, P, Fe, and minor concentrations of W, Ti, Zr, Sc, and Sb. All pegmatite types probably formed within a short time period of ~5 Ma.

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.