Pavel Škácha

Mathesiusite, K5(UO2)4(SO4)4(VO5)(H2O)4, a new uranyl vanadate-sulfate from Jáchymov, Czech Republic

Abstract 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-SO4 mineral. 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, SO3 18.04, V2O5 4.30, UO3 61.46, 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 [dobs in 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 SO4 tetrahedra. Each SO4 shares 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.

Crystal structure of lead uranyl carbonate mineral widenmannite: Precession electron-diffraction and synchrotron powder-diffraction study

Abstract The crystal structure of the lead uranyl-carbonate mineral widenmannite has been solved from precession electron-diffraction data and refined using both electron-diffraction data and synchrotron powder-diffraction data. Widenmannite is orthorhombic, Pmmn, with a = 4.9744(9), b = 9.3816(16), c = 8.9539(15) Å, and V = 417.86(12) Å3. The structure was solved by charge-flipping and refined to an R1 = 0.1911 on the basis of 301 unique, observed reflections from electron diffraction data, and to Rp of 0.0253 and RF of 0.0164 from X-ray powder data. The idealized structure formula of widenmannite is Pb2(OH)2[(UO2)(CO3)2], Z = 2. However, both data sets suggest that the widenmmanite structure is not that simple. There are two symmetrically independent, partly occupied U sites. The substitution mechanism can be written as U(1)O2 + Pb(OH)2 ↔ U(2)O2. When the U(2) site is occupied, the U(1) O2 group is absent, the two OH groups are substituted by O2- and one Pb2+-vacancy. The chemical formula of the real structure should be written as Pb2-x(OH)2-2x[(UO2)(CO3)2], where x is the probability of the substitution U(2) → U(1). The probability of occurrence of U(2) refines to x = 0.074(15) from the powder-diffraction data and to x = 0.176(4) from the electron-diffraction data. There is one Pb site (nearly fully occupied), which is coordinated by 11 anions (up to the distance of 3.5 Å), including O and OH-. The shorter Pb-O bonds form a sheet structure, which is linked by the weaker bonds to the uranyl-carbonate chains to form a three-dimensional framework structure.

Hakite from Příbram, Czech Republic: compositional variability, crystal structure and the role in Se mineralization

Abstract Hakite, ideally Cu10Hg2Sb4Se13, is a Se-dominant member of the tetrahedrite group occurring at only a few localities in the World. A new occurrence of this mineral in the Pribram uranium and base-metal ore district, Central Bohemia, Czechia, is reported in this paper. Hakite was found to be locally abundant and was identified in several samples with Se mineralization. Three chemically distinct types of hakite were distinguished based on electron microprobe study, Hg-rich hakite (hakite sensu stricto), Zn-rich hakite and Cd-rich hakite. Hg-hakite dominates among the samples studied. Its average empirical formula based on 29 apfu (n = 54) is (Cu5.61Ag0.39)∑6.00Cu400(Hg1.61Zn0.20Cu0.19Cd0.15Fe0.04)∑2.19(Sb3.85As0.28)∑4.13(Se11.55S1.14)∑12.69. Less common is the Zn-hakite, (Cu5.80Ag0.20)∑6.00Cu4.00(Zn1.33Hg0.42Cd0.22Cu0.18Fe0.01)∑2.16(Sb3.85 As0.26)∑4.11(Se10.92S1.81)∑12.73(n = 22), and rare Cd-hakite has an empirical formula (n = 7) of (Cu5.84 Ag0.16)∑6.00Cu4.00(Cd1.27Zn0.60Cu0.10Hg0.07Fe0.02)∑2.06(Sb4.00As0.19)∑4.19(Se12.14S0.61)∑12.75. The refined unit cell of Hg-hakite from Příbram, obtained from powder X-ray diffraction data, is a = 10.8783(3) Å with V= 1287.3(1) Å3 (Z= 4, for the cubic space group I4̅3m). Structure refinement from the precession electron diffraction data collected on the transmission electron microscope (R = 24.4% for 424 observed reflections), confirmed that hakite is isostructural with tetrahedrite. The evolution of hydrothermal fluids, from which Se mineralization formed, suggests a distinct enrichment in sulfur and depletion in selenium over the time span of crystallization.

Widenmannite, a rare uranyl lead carbonate: occurrence, formation and characterization

Abstract The rare uranyl lead carbonate widenmannite, Pb2(UO2)(CO3)3, was found at the Jánská vein, Příbram, Czech Republic, where two generations occur in several morphological types and mineral associations in hydrothermal veins. Alpha spectroscopy shows that these two generations have different ages, >220,000 and 118±12 y. ICP-MS analysis indicates that both widenmannites have a dominance of non-radiogenic Pb which originates from weathered galena. The older widenmannite I forms fine-grained, grey to beige aggregates in the highly altered supergene part of the hydrothermal ore vein in association with pyromorphite, cerussite and goethite. The younger widenmannite II occurs as white, yellow or greenish-yellow thin tabular crystals up to 0.5 mm long in association with cerussite, anglesite, limonite, kasolite and an unnamed Pb-U-O phase. Thermal analysis suggests that widenmannite decomposes in several steps, with Pb uranate as the final product. Infrared and Raman spectroscopy confirm the presence of non-equivalent (CO3)2- groups, bidentately coordinated in uranyl hexagonal polyhedra, forming the well known uranyl tricarbonate complex. Infrared spectroscopy shows conclusively that widenmannite does not contain molecular H2O.

Klajite, MnCu4(AsO4)2(AsO3OH)2(H2O)10, from Jáchymov (Czech Republic): the second world occurrence

Abstract Klajite, MnCu4(AsO4)2(AsO3OH)2(H2O)10, the Mn-Cu-bearing member of the lindackerite group, was found in Jáchymov, Czech Republic, as the second world occurrence. It is associated with ondrušite and other arsenate minerals growing on the quartz gangue with disseminated primary sulfides, namely tennantite and chalcopyrite. Electron-microprobe data showed klajite aggregates to be chemically inhomogeneous at larger scales, varying from Mn-Ca-rich to Cu-rich domains. The chemical composition of the the Mn-rich parts of aggregates can be expressed by the empirical formula (Mn0.46Ca0.22Cu0.07Mg0.02)∑0.77(Cu3.82Mg0.14Ca0.03Zn0.01)∑4.00(As1.94Si0.06)∑2.00O8[AsO2.73(OH)1.27]2(H2O)10 (mean of seven representative spots; calculated on the basis of As + Si + P = 4 a.p.f.u. (atoms per formula unit) and 10 H2O from ideal stoichiometry), showing a slight cationic deficiency at the key Me-site. According to single-crystal X-ray diffraction, klajite from Jáchymov is triclinic, P1̄ , with a = 6.4298(8), b = 7.9716(8), c = 10.707(2) Å , α= 85.737(12)°, β = 80.994(13)°, γ = 84.982(10)°, and V = 538.85(14) Å3, Z = 1. The crystal structure was refined to R1 = 0.0628 for 1034 unique observed reflections (with Iobs > 3σ(I)), confirming that klajite (Mn-Cu member) and ondrušite (Ca-Cu member) are isostructural. The current data-set allowed determination of the positions of several hydrogen atoms. Discussion on hydrogen bonding networks in the structure of klajite as well as detailed bond-valence analysis are provided.

Hloušekite, (Ni,Co)Cu4(AsO4)2(AsO3OH)2(H2O)9, a new member of the lindackerite supergroup from Jáchymov, Czech Republic

Abstract Hloušekite, (Ni,Co)Cu4(AsO4)2(AsO3OH)2(H2O)9, is a new supergene arsenate mineral from the Geister vein (Rovnost mine), Jáchymov (St Joachimsthal), Western Bohemia, Czech Republic. It was found along with veselovskýite, pradetite, lavendulan, arsenolite, babánekite and gypsum on the surface of strongly altered ore fragments containing dominant tennantite and chalcopyrite. Hloušekite forms thin, lath-like crystals, locally elongated reaching up to 3 mm across. It is transparent, has a pale green colour with vitreous lustre, has a greyish-white streak and it is very brittle with an uneven fracture. It does not fluoresce under shortwave or longwave ultraviolet radiation. Cleavage on {010} is perfect; the Mohs hardness is 2-3. The calculated density is 3.295 g cm-3. Hloušekite is optically biaxial with α′ = 1.653(2) and γ′ = 1.73. The estimated optical orientation is γ′ vs. elongation (c) = 14(1)°. In larger grains it is weakly to moderately pleochroic (α = colourless, β = pale green to green). Hloušekite is triclinic, space group P1̅, a = 6.4010(6), b = 8.0041(6), c = 10.3969(14) Å, α = 85.824(8), β = 79.873(9), γ = 84.655(7)° and V = 521.23(10) Å3, with Z = 1, a:b:c = 0.800:1:1.299. The eight strongest lines in the powder X-ray diffraction (XRD) pattern [d in Å (I)(hkl)] are 10.211(100)(001), 7.974(9)(010), 3.984(6)(020), 3.656(5)(11̅2), 3.631(5)(02̅1), 3.241(5)(022), 3.145(5)(200) and 3.006(5)(210). Chemical analysis by electron microprobe yielded MgO 0.20, FeO 0.10, NiO 5.79, CoO 1.80, CuO 29.53, ZnO 0.66, Al2O3 0.14, P2O5 0.11, As2O5 45.01, H2O 17.71 (calc.), for a total of 101.05 wt.%. The resulting empirical formula, calculated by stoichiometry (9H2O + 2OH), obtained from the crystal structure, is (Ni0.79Co0.25)Σ1.04(Cu3.78Zn0.08Mg0.05Al0.03Fe0.01)S3.95 (AsO4)1.98(PO4)0.02(AsO3OH)2.00(H2O)9.00. The ideal endmember formula , NiCu4(AsO4)2(AsO3OH)2(H2O)9.00, requires NiO 7.23, CuO 30.81, As2O5 44.51, H2O 17.45, total 100.00 wt.%. The crystal structure of hloušekite was solved by charge flipping from single-crystal XRD data and refined to R1 = 0.0599 for 1441 reflections with [Iobs > 3σ(I)]. Hloušekite is a new member of the lindackerite group (also including lindackerite, pradetite and veselovský ite) of the lindackerite supergroup. The ondrušite group of the lindackerite supergroup includes ondrušite, chudobaite, geigerite and klajite. The establishment of these two groups reflects the difference between the crystal structures of their members, mainly in the coordination environment of the Me cations.