ALBERT

Description: Arseniosiderite and yukonite are among the important arsenate minerals occurring as secondary alteration products in relation to the oxidation of arsenopyrite and arsenian pyrite and as discrete grains in some gold ores, mine tailings, and contaminated soils. Characteristics of these Ca-Fe arsenate species are not well known and our understanding of the conditions promoting their formation and dissolution is limited. Long- and short-range structural characteristics and thermodynamic properties of the Ca-Fe arsenates forming in the Ca-Fe(III)-As(V)-NO 3 system were determined to better predict the mineralogical transformations taking place in neutralized sludge and tailings environments, and their influence on arsenic mobilization. Yukonite and arseniosiderite readily form from solutions with highly variable compositions at a wide pH range from slightly acidic to alkaline conditions. Calcium concentrations corresponding to molar Ca/(Ca+Fe+As) ratios as low as 0.1 appear to be adequate for their formation. Our experimental results confirm observations in natural settings and mine tailings where scorodite is progressively replaced by yukonite and arseniosiderite. The initial amorphous precipitates made of small oligomeric units of edge-sharing FeO 6 octahedra with bridging arsenate evolve to yukonite through the establishment of corner linkages between the FeO 6 chains. Yukonite represents a nanocrystalline precursor and Ca-deficient variety of arseniosiderite. Formation of arseniosiderite is kinetically controlled with faster development of crystallinity at neutral to slightly acidic pH and slower kinetics under alkaline conditions. Calorimetric measurements provided an enthalpy of formation value of –1950.3 ± 3.1 kJ/mol and standard entropy of 237.4 ± 4.4 J/(mol·K) for arseniosiderite [with composition Ca 0.663 Fe 1.093 (AsO 4 )(OH) 1.605 ·0.827H 2 O], the corresponding Gibbs free energy of formation is –1733 ± 3.4 kJ/mol. A rough estimate of the thermodynamic properties of yukonite is also provided. Arseniosiderite is a stable arsenate between pH 3.5 and 7.5 in solutions saturated with respect to soluble Ca minerals such as calcite, gypsum, anorthite, or Ca-montmorillonite. Arsenic release from mine wastes and contaminated soils can be effectively controlled by arseniosiderite and the conditions promoting its formation such as lime-treatment leading to gypsum saturation in ferric arsenate solutions would prove to be desirable for stabilizing arsenic in the form of arseniosiderite in mine wastes.

Description: The new minerals bobcookite (IMA 2014-030), NaAl(UO 2 ) 2 (SO 4 ) 4 ·18H 2 O and wetherillite (IMA 2014-044), Na 2 Mg(UO 2 ) 2 (SO 4 ) 4 ·18H 2 O, were found in the Blue Lizard mine, San Juan County, Utah, USA, where they occur together as secondary alteration phases in association with boyleite, chalcanthite, dietrichite, gypsum, hexahydrite, johannite, pickeringite and rozenite. Bobcookite descriptive details: lime green to greenish-yellow massive veins and columnar crystals; transparent; vitreous lustre; bright greenish-white fluorescence; pale greenish yellow streak; hardness (Mohs) 21/2; brittle; conchoidal fracture; no cleavage; moderately hygroscopic; easily soluble in cold H 2 O; density calc = 2.669 g cm –3 . Optically, biaxial (–), α = 1.501(1), β = 1.523(1), = 1.536(1) (white light); 2V meas. = 78(1)°; 2V calc. = 74°; dispersion r 〈 v , moderate. Pleochroism: X colourless, Y very pale yellow-green, Z pale yellow-green; X 〈 Y 〈 Z . EDS analyses yielded the empirical formula Na 0.97 Al 1.09 (U 1.02 O 2 ) 2 (S 0.98 O 4 ) 4 (H 2 O) 18 . Bobcookite is triclinic, P 1I, a = 7.7912(2), b = 10.5491(3), c = 11.2451(8) Å, α = 68.961(5), β = 70.909(5), = 87.139(6)°, V = 812.79(8) Å 3 and Z = 1. The structure ( R 1 = 1.65% for 3580 F o 〉 4 F ) contains [(UO 2 )(SO 4 ) 2 (H 2 O)] chains linked by NaO 4 (H 2 O) 2 octahedra to form layers. Hydrogen bonds to insular Al(H 2 O) 6 octahedra and isolated H 2 O groups hold the structure together. The mineral is named for Dr Robert (Bob) B. Cook of Auburn University, Alabama, USA. Wetherillite descriptive details: pale greenish-yellow blades; transparent; vitreous lustre; white streak; hardness (Mohs) 2; brittle; two cleavages, {101I} perfect and {010} fair; conchoidal or curved fracture; easily soluble in cold H 2 O; density calc = 2.626 g cm –3 . Optically, biaxial (+), α = 1.498(1), β = 1.508(1), = 1.519(1) (white light); 2V meas. = 88(1)°, 2V calc. = 87.9°; dispersion is r 〈 v , distinct; optical orientation: Z = b, X ^ a = 54° in obtuse β; pleochroism: X colourless, Y pale yellow-green, Z pale yellow-green; X 〈 Y Z . EDS analyses yielded the empirical formula Na 1.98 (Mg 0.58 Zn 0.24 Cu 0.11 $${\mathrm{Fe}}_{0.09}^{2+}$$ ) 1.02 (U 1.04 O 2 ) 2 (S 0.98 O 4 ) 4 (H 2 O) 18 . Wetherillite is monoclinic, P 2 1 / c, a = 20.367(1), b = 6.8329(1), c = 12.903(3) Å, β = 107.879(10)°, V = 1709.0(5) Å 3 and Z = 2. The structure ( R 1 = 1.39% for 3625 F o 〉 4 F ) contains [(UO 2 )(SO 4 ) 2 (H 2 O)] sheets parallel to {100}. Edge-sharing chains of Na(H 2 O) 5 O polyhedra link adjacent uranyl sulfate sheets forming a weakly bonded three-layer sandwich. The sandwich layers are linked to one another by hydrogen bonds through insular Mg(H 2 O) 6 octahedra and isolated H 2 O groups. The mineral is named for John Wetherill (1866–1944) and George W. Wetherill (1925–2006).

Description: A bstract This work presents the results of investigation of the primary minerals and their weathering products of two tailing ponds near the villages of Rudňany and Slovinky in eastern Slovakia. The tailings are near-neutral or slightly alkaline (pH = 7.2–8.8) because the acidity generated by the decomposition of the sulfides is efficiently neutralized by the abundant carbonate minerals. The most frequent primary gangue minerals are siderite, quartz, barite, and muscovite. The prevailing primary sulfide minerals in both tailing ponds are pyrite and chalcopyrite; less common are tetrahedrite and arsenopyrite. The most frequent secondary and tertiary ( i.e. , formed in the tailings, not in the oxidation zone of the deposits) minerals at both localities are iron oxides, either goethite or poorly crystalline hydrous ferric oxide. Other minerals (cuprite, malachite, delafossite; identified by X-ray microdiffraction or Raman spectroscopy) are minor or rare and occur only in Slovinky. The iron oxide minerals are enriched in a suite of elements, including Cu, Si, Ca, Zn, As, Mg, and Mn. The transformations of the poorly crystalline hydrous ferric oxide to goethite and maturation of goethite is controlled by both high-valence tetrahedral cations (Si, As, P) and lower-valence octahedral cations (Cu), as shown by the measurements of the size of coherently diffracting domains in goethite and the chemical composition of goethite. The iron oxide minerals, by virtue of their adsorption capacity, prevent separate minerals of many metals and metalloids (Cu, Ca, As, Sb) from nucleating and growing, and therefore control the entire neutral mine drainage (NMD) system. Geochemical modeling of the discharged waters shows that all common Cu and ferric arsenate minerals are strongly undersaturated, confirming the central role of iron oxide phases in the NMD system.

Description: 〈span〉〈div〉Abstract〈/div〉Samples of the pharmacosiderite group were synthesized either directly, from aqueous solutions at 160 °C, or by ion exchange over extended periods of time at 100 °C. In more than 200 experiments, no pure pharmacosiderite sample was obtained, and a protocol was developed to remove scorodite and arsenical iron oxides from the samples. In this way, K-, Na-, Ba-, and Sr-dominant pharmacosiderite samples were prepared. The chemical compositions of the two samples used for further experiments were Ba〈sub〉0.702〈/sub〉Fe〈sub〉4〈/sub〉[(AsO〈sub〉4〈/sub〉)〈sub〉0.953〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.047〈/sub〉]〈sub〉3〈/sub〉(OH)〈sub〉3.455〈/sub〉O〈sub〉0.545〈/sub〉·5.647H〈sub〉2〈/sub〉O and K〈sub〉1.086〈/sub〉Fe〈sub〉4〈/sub〉[(AsO〈sub〉4〈/sub〉)〈sub〉0.953〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.047〈/sub〉]〈sub〉3〈/sub〉 (OH)〈sub〉3.772〈/sub〉O〈sub〉0.228〈/sub〉·4.432H〈sub〉2〈/sub〉O. The Ba-dominant pharmacosiderite is tetragonal at room temperature, and the K-dominant pharmacosiderite is cubic. Upon heating, both samples lose zeolitic H〈sub〉2〈/sub〉O (shown by thermogravimetry), and this loss is accompanied by unit-cell contraction. In Ba-dominant pharmacosiderite, this loss also seems to be responsible for a symmetry change from tetragonal to cubic. The slight unit-cell contraction in Ba-dominant pharmacosiderite at 〈100 °C might be attributed to either negative thermal expansion or minor H〈sub〉2〈/sub〉O loss; our data cannot differentiate between these two possibilities. Both samples persisted in a crystalline state up to 320 °C (the highest temperature of the powder XRD experiment), showing that pharmacosiderite is able to tolerate almost complete removal of the zeolitic H〈sub〉2〈/sub〉O molecules. Low-temperature heat capacity measurements show a diffuse magnetic anomaly for K-dominant pharmacosiderite at ≈5 K and a sharp lambda transition for Ba-dominant pharmacosiderite at 15.2 K. The calculated standard entropy at 〈span〉T〈/span〉 = 298.15 is 816.9 ± 5.7 J/molK for K-dominant pharmacosiderite (molecular mass 824.2076 g/mol, see formula above) and 814.1 ± 5.5 J/molK for Ba-dominant pharmacosiderite (899.7194 g/mol).〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Samples of the pharmacosiderite group were synthesized either directly, from aqueous solutions at 160 °C, or by ion exchange over extended periods of time at 100 °C. In more than 200 experiments, no pure pharmacosiderite sample was obtained, and a protocol was developed to remove scorodite and arsenical iron oxides from the samples. In this way, K-, Na-, Ba-, and Sr-dominant pharmacosiderite samples were prepared. The chemical compositions of the two samples used for further experiments were Ba〈sub〉0.702〈/sub〉Fe〈sub〉4〈/sub〉[(AsO〈sub〉4〈/sub〉)〈sub〉0.953〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.047〈/sub〉]〈sub〉3〈/sub〉(OH)〈sub〉3.455〈/sub〉O〈sub〉0.545〈/sub〉·5.647H〈sub〉2〈/sub〉O and K〈sub〉1.086〈/sub〉Fe〈sub〉4〈/sub〉[(AsO〈sub〉4〈/sub〉)〈sub〉0.953〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.047〈/sub〉]〈sub〉3〈/sub〉 (OH)〈sub〉3.772〈/sub〉O〈sub〉0.228〈/sub〉·4.432H〈sub〉2〈/sub〉O. The Ba-dominant pharmacosiderite is tetragonal at room temperature, and the K-dominant pharmacosiderite is cubic. Upon heating, both samples lose zeolitic H〈sub〉2〈/sub〉O (shown by thermogravimetry), and this loss is accompanied by unit-cell contraction. In Ba-dominant pharmacosiderite, this loss also seems to be responsible for a symmetry change from tetragonal to cubic. The slight unit-cell contraction in Ba-dominant pharmacosiderite at 〈100 °C might be attributed to either negative thermal expansion or minor H〈sub〉2〈/sub〉O loss; our data cannot differentiate between these two possibilities. Both samples persisted in a crystalline state up to 320 °C (the highest temperature of the powder XRD experiment), showing that pharmacosiderite is able to tolerate almost complete removal of the zeolitic H〈sub〉2〈/sub〉O molecules. Low-temperature heat capacity measurements show a diffuse magnetic anomaly for K-dominant pharmacosiderite at ≈5 K and a sharp lambda transition for Ba-dominant pharmacosiderite at 15.2 K. The calculated standard entropy at 〈span〉T〈/span〉 = 298.15 is 816.9 ± 5.7 J/molK for K-dominant pharmacosiderite (molecular mass 824.2076 g/mol, see formula above) and 814.1 ± 5.5 J/molK for Ba-dominant pharmacosiderite (899.7194 g/mol).〈/span〉

Description: The thermodynamic properties of libethenite [Cu 2 (PO 4 )(OH)], olivenite [Cu 2 (AsO 4 )(OH)], pseudomalachite [Cu 5 (PO 4 ) 2 (OH) 4 ], cyanochroite [K 2 Cu(SO 4 ) 2 · 6H 2 O], kröhnkite [Na 2 Cu(SO 4 ) 2 · 2H 2 O], and devilline [CaCu 4 (SO 4 ) 2 (OH) 6 · 3H 2 O] were determined by a combination of acid-solution calorimetry (enthalpy of formation) and relaxation calorimetry (heat capacity and entropy). The calculated Gibbs free energies (in kJ · mol –1 ) for these phases are –1229.3 ± 4.5, –848.7 ± 4.8, –2837.9 ± 10.8, –3441.4 ± 3.9, –2442.3 ± 3.6, –3843.2 ± 8.4, respectively. The phases studied were characterized by powder X-ray diffraction, infrared and Raman spectroscopy, and electron microprobe, as needed. We have also determined the crystal structure of devilline by single-crystal X-ray diffraction. Both of the copper phosphates investigated, libethenite and pseudomalachite, have a stability fieldinthe pH–p space, but olivenite appears to be the only copper arsenate among those considered here (cornubite, clinoclase, euchroite) that has a stability field at T = 298.15 K and P = 1 bar. Chemical data from natural solid-solutions between libethenite–olivenite and pseudomalachite–cornwallite suggest that both solid solutions deviate slightly from ideality. The arsenic-rich members of these solutions tend to accept zinc in larger amounts. We have performed thermodynamic simulations showing that devilline crystallizes only when gypsum is nearby, which elevates the activity of Ca 2+ in the aqueous solutions.

Description: Stepite, tetragonal U(AsO 3 OH) 2 (H 2 O) 4 (IMA 2012-006), is the first natural arsenate of tetravalent uranium. It occurs in the Geschieber vein, Jáchymov ore district, Western Bohemia, Czech Republic, as emerald-green crystalline crusts on altered arsenic. Associated minerals include arsenolite, behounekite, claudetite, gypsum, kaatialaite, the new mineral vysokyite (IMA 2012-067) and a partially characterized phase with the formula $${\left({\mathrm{H}}_{3}\mathrm{O}\right)}_{2}^{+}$$ (UO 2 ) 2 (AsO 4 ) 2 ·6H 2 O. Stepite typically forms tabular crystals with prominent {001} and {010} faces, up to 0.6 mm in size. The crystals have a vitreous lustre and a grey to greenish grey streak. They are brittle with an uneven fracture and a very good cleavage on (001). Their Mohs hardness is about 2. Stepite is not fluorescent in either short-wave or long-wave ultraviolet light. It is biaxial (–) with refractive indices (at 590 nm) of α = 1.636(2), β = 1.667(3), = 1.672(2) and 2V obs 〈 ~5°, anomalous greyish to pale yellow interference colours, and no pleochroism. The composition is as follows: 0.12 Na 2 O, 50.19 UO 2 , 0.04 SiO 4 , 0.09 P 2 O 5 , 0.93 As 2 O 5 , 1.95 SO 3 , 16.41 H 2 O; total 107.90 wt.%, yielding an empirical formula (based on 12 O a.p.f.u.) of (U 1.01 Na 0.02 ) 1.03 [(AsO 3 OH) 1.82 (PO 3 OH) 0.04 (SO 4 ) 0.13 (SiO 4 ) 0.01 ] 2.00 ·4H 2 O. Stepite is tetragonal, crystallizing in space group I 4 1 / acd , with a = 10.9894(1), c = 32.9109(6) Å, V = 3974.5(1) Å 3 , Z = 16 and D calc = 3.90 g cm –3 . The six strongest peaks in the X-ray powder-diffraction pattern [ d obs in Å ( I ) ( hkl )] are as follows: 8.190(100)(004), 7.008(43)(112), 5.475(18)(200), 4.111(16)(008), 3.395(20)(312,217), 2.1543(25)(419). The crystal structure of stepite has been solved from single-crystal X-ray diffraction data by the charge-flipping method and refined to R 1 = 0.0353 based on 1434 unique observed reflections, and to wR 2 = 0.1488 for all 1523 unique reflections. The crystal structure of stepite consists of sheets perpendicular to [001], made up of eight-coordinate uranium atoms and hydroxyarsenate ‘tetrahedra’. The ligands surrounding the uranium atom consist of six oxygen atoms which belong to the hydroxyarsenate groups and two oxygen atoms which belong to interlayer H 2 O molecules. Each UO 8 polyhedron is connected to five other U polyhedra via six AsO 3 OH groups. Adjacent electroneutral sheets, of composition $${\left[{\mathrm{U}}^{4+}{\left({\mathrm{AsO}}_{3}\mathrm{OH}\right)}_{2}^{2-}\right]}^{0}$$ , are linked by hydrogen bonds involving H 2 O molecules in the interlayers and OH groups in the sheets. The new mineral is named in honour of Josef Step (1863–1926), a Czech mining engineer and ‘father’ of the world's first radioactive spa at Jáchymov.

Description: Behounekite, orthorhombic U(SO4)2(H2O)4, is the first natural sulphate of U4+. It was found in the Geschieber vein, Jáchymov (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 {100}. The Mohs hardness is about 2. The mineral is not fluorescent either in short- or long-wavelength UV radiation. Behounekite is moderately pleochroic, a~ß is pale emerald green and ? is emerald green, and is optically biaxial (+) with a = 1.590(2), ß = 1.618(4), ? = 1.659(2) (590 nm), 2V (calc.) = 81°, birefringence 0.069. The empirical formula of behounekite (based on 12 O atoms, from an average of five point analyses) is (U0.99Y0.03)S1.02(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 Pnma, a = 14.6464(3), b = 11.0786(3), c = 5.6910(14) Å, V = 923.43(4) Å3, Z = 4, Dcalc = 3.62 g cm-3. The seven strongest diffraction peaks in the X-ray powder diffraction pattern are [dobs in Å (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 R1 = 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 (~1200–950 cm-1), O–H stretching modes (~3400–3000 cm-1) and H–O–H bending modes (~1650 cm-1). The mineral is named in honour of František Behounek, a well known Czech nuclear physicist.

Description: Pyrite is one of the most common ore minerals in hydrothermal ores and a hallmark of many types of hydrothermal deposits, e.g. , mesothermal quartz veins with pyrite, arsenopyrite, and visible or invisible gold. In addition to any other mineralogical investigation, it is possible to examine and interpret the crystal size distribution (CSD) of the mineral which is under investigation. The conditions of mineral-forming processes can be diverse in terms of temperature, pressure, and compositional variables, but the CSD shapes are usually convergent and by far the most common CSD type is the lognormal distribution. In this study, we determined the CSD for pyrite crystals from mesothermal quartz-pyrite-arsenopyrite-stibnite-gold ores from the Nízke Tatry Mountains (Western Carpathians, Slovakia). A large number of crystals were measured manually from ore sections or from stereographic images. All samples show a crystal size spectrum from 2 μm up to 550 μm. We discovered that all CSDs show a lognormal or pseudo-lognormal shape with low logarithmic size variances (β 2 ). In order to understand the history of nucleation and growth of pyrite formed in hydrothermal milieus, we compared our measurements to simulations with different growth mechanisms using the GALOPER (Growth According to the Law of Proportionate Effect) program (after Eberl et al. 1998 ). From the shape of the distributions, the logarithmic mean (α) and β 2 , we inferred that the crystals grew in an open system with its associated growth mechanisms (surface-controlled growth and supply-controlled growth), since no evidence for ripening processes in the data or in the numerical simulations of our data could be found. Since ripening as a growth mechanism can be excluded, we have to assume that the growth of the pyrite crystals and so the formation of the whole ore body occurred on a relatively short geological time scale. This preliminary result opens more questions related to the emplacement, circulation, and supersaturation of hydrothermal fluids and to the formation of large ore bodies over short time scales.