The crystal structure of alumoklyuchevskite,K<Subscript>3</Subscript>Cu<Subscript>3</Subscript>AlO<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript>

The crystal structure of the unstable mineral alumoklyuchevskite K₃Cu₃AlO₂(SO₄)₄ [monoclinic, I2, a = 18.772(7), b = 4.967(2), c = 18.468(7) Å, β = 101.66(1)°, V = 1686(1) Å] was refined to R ₁ = 0.131 for 2450 unique reflections with F ≥ 4σF _hkl. The structure is based on oxocentered tetrahedrons (OAlCu ₃ ⁷⁺ ) linked into chains via edges. Each chain is surrounded by SO₄ tetrahedrons forming a structural complex. Each complex is elongated along the b axis. This type of crystal structure was also found in other fumarole minerals of the Great Tolbachik Fissure Eruption (GTFE, Kamchatka Peninsula, Russia, 1975–1976), klyuchevskite, K₃Cu₃Fe³⁺O₂(SO₄)₄; and piypite, K₂Cu₂O(SO₄)₂.     

Crystal chemistry of selenates with mineral-like structures: VIII. Butlerite chains in the structure of K(UO<Subscript>2</Subscript>)(SeO<Subscript>4</Subscript>)(OH)(H<Subscript>2</Subscript>O)

A new potassium uranyl selenate compound K(UO₂)(SeO₄)(OH)(H₂O) has been synthesized for the first time using the technique of evaporation from water solution. Its crystal structure has been solved by direct methods (monoclinic, P2₁/c,a = 8.0413(9) Å, b = 8.0362(9) Å, c = 11.6032(14) Å, β = 106.925(2)°, V = 717.34(14) ų) and refined to R ₁ = 0.0319 (wR ₂ = 0.0824) for 1285 reflections with |F ₀| > 4σ _F . The structure consists of [(UO₂(SeO₄)(OH)(H₂O)]^? chains extending along axis b. In the chains, the uranyl pentagonal bipyramids are linked via bridged hydroxyl anions and tetrahedral oxoanions [SeO₄]^2?. Potassium ions are situated between these chains. No chains of that type have been observed in uranyl compounds earlier, but they had been detected in the structures of butlerite, parabutlerite, uklonskovite, fibroferrite, and a number of synthetic compounds.     

Crystal structures of the Rb- and Sr-exchanged forms of ivanyukite-Na-T

The Rb- and Sr-exchanged forms of ivanyukite have been obtained and structurally characterized. The chemical formulas derived from the electron microprobe data are as follows: the Rb-exchanged form (Na_0.10K_0.07Ca_0.15Sr_0.05Rb_1.81Ba_0.02)_{Σ = 2.20}[(Ti_3.65Nb_0.19Fe_0.05Mn_0.01)_{Σ = 3.90}O_2.07/(OH)_1.93(Si_2.98Al_0.02)_{Σ = 3.00} O₁₂] · 3.61H₂O; the Sr-exchanged form (K_0.03Sr_0.81Ca_0.04Ba_0.07)_{Σ = 0.95}[(Ti_3.74Nb_0.19Fe_0.03)_{Σ = 3.96}] [O_1.83/(OH)_2.17](Si_2.99Al_0.01)_{Σ = 3.00}O₁₂) · 7H₂O. The structures of the Rb- and Sr-exchanged forms of ivanyukite have been solved and refined using the least squares method. The structures are based on a mixed three-dimensional octahedral-tetrahedral framework of the pharmacosiderite type with channels occupied by Rb⁺ and Sr²⁺ cations and water molecules. The Rb⁺ cations in the Rb-exchanged form are 12-coordinated, whereas the Sr²⁺ cations in the Sr-exchanged form are 9- or 7-coordinated. The statistical investigation of the geometric parameters of the pharmacosiderite-type titanosilicates showed that symmetry changes are associated with the interactions of extraframework cations with the O atom of the Ti₄(O,OH)₄ clusters of the titanosilicate framework. The relationship between the unit-cell parameters in titanosilicates of the pharmacosiderite type and the structural geometric parameters of the titanosilicate framework has been proved by the use of multiple regression equations.     

Oxyphlogopite K(Mg,Ti,Fe)3[(Si,Al)4O10](O,F)2: A new mineral species of the mica group

Oxyphlogopite is a new mica-group mineral with the idealized formula K(Mg,Ti,Fe)₃[(Si,Al)₄O₁₀](O,F)₂. The holotype material came from a basalt quarry at Mount Rothenberg near Mendig at the Eifel volcanic complex in Rhineland-Palatinate, Germany. The mineral occurs as crystals up to 4 × 4 × 0.2 mm in size encrusting cavity walls in alkali basalt. The associated minerals are nepheline, plagioclase, sanidine, augite, diopside, and magnetite. Its color is dark brown, its streak is brown, and its luster is vitreous. D _meas = 3.06(1) g/cm³ (flotation in heavy liquids), and D _calc = 3.086 g/cm³. The IR spectrun does not contain bands of OH groups. Oxyphlogopite is biaxial (negative); α = 1.625(3), β = 1.668(1), and γ = 1.669(1); and 2V _meas = 16(2)° and 2V _calc = 17°. The dispersion is strong; r < ν. The pleochroism is medium; X > Y > Z (brown to dark brown). The chemical composition is as follows (electron microprobe, mean of 5 point analyses, wt %; the ranges are given in parentheses; the H₂O was determined using the Alimarin method; the Fe²⁺/Fe³⁺ was determined with X-ray emission spectroscopy): Na₂O 0.99 (0.89–1.12), K₂O 7.52 (7.44–7.58), MgO 14.65 (14.48–14.80), CaO 0.27 ((0.17–0.51), FeO 4.73, Fe₂O₃ 7.25 (the range of the total iron in the form of FeO is 11.09–11.38), Al₂O₃ 14.32 (14.06–14.64), Cr₂O₃ 0.60 (0.45–0.69), SiO₂ 34.41 (34.03–34.66), TiO₂ 12.93 (12.69–13.13), F 3.06 (2.59–3.44), H₂O 0.14; O=F₂ −1.29; 99/58 in total. The empirical formula is (K_0.72Na_0.14Ca_0.02)(Mg_1.64Ti_0.73Fe_0.30²⁺ Fe_0.27³⁺Cr_0.04)_Σ2.98(Si_2.59Al_1.27Fe_0.14³⁺ O₁₀) O_1.20F_0.73(OH)_0.07. The crystal structure was refined on a single crystal. Oxyphlogopite is monoclinic with space group C2/m; the unit-cell parameters are as follows: a = 5.3165(1), b = 9.2000(2), c = 10.0602(2) ?, β = 100.354(2)°. The presence of Ti results in the strong distortion of octahedron M(2). The strongest lines of the X-ray powder diffraction pattern [d, ? (I, %) [hkl]] are as follows: 9.91(32) [001], 4.53(11) 110], 3.300(100) [003], 3.090(12) [112], 1.895(21) [005], 1.659(12) [−135], 1.527(16) [−206, 060]. The type specimens of oxyphlogopite are deposited at the Fersman Mineralogical Museum in Moscow, Russia; the registration numbers are 3884/2 (holotype) and 3884/1 (cotype).     

The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, and review of mixed-ligand CuOmCln coordination geometries in minerals and inorganic compounds

The crystal structure of ilinskite, NaCu₅O₂(SeO₃)₂Cl₃, a rare copper selenite chloride from volcanic fumaroles of the Great fissure Tolbachik eruption (Kamchatka peninsula, Russia), has been solved by direct methods and refined to R ₁?=?0.044 on the basis of 2720 unique observed reflections. The mineral is orthorhombic, Pnma, a?=?17.769(7), b?=?6.448(3), c?=?10.522(4) Å, V?=?1205.6(8) ų, Z?=?4. The The CuO_mCl_n coordination polyhedra share edges to form tetramers that have 'additional' O1 and O2 atoms as centers. The O1Cu₄ and O2Cu₄ tetrahedra share common Cu atoms to form [O₂Cu₅]⁶⁺ sheets. The SeO₃ groups and Cl atoms are adjacent to the [O₂Cu₅]⁶⁺ sheets to form complex layers parallel to (100). The Na⁺ cations are located in between the layers. A review of mixed-ligand CuO_mCl_n coordination polyhedra in minerals and inorganic compounds is given. There are in total 26 stereochemically different mixed-ligand Cu-O-Cl coordinations.     

Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide Ores: Part VII. Solubility of synthetic analogs of erythrite and annabergite at 25°C

Understanding the mechanisms of arsenic’s behavior under near-surface conditions is one of the actual problems of contemporary mineralogy and geochemistry and is important for solving environmental problems. The aim of this study is to synthesize analogs of erythrite and annabergite and to investigate their solubility in water. These phases have been synthesized by the boiling-dry of aqueous solutions of cobalt and nickel nitrates mixed with sodium hydroarsenate alkalized with NaOH. The samples obtained have been identified with electron microprobe, X-ray diffraction, and IR spectroscopy. Solubility has been determined by the isothermal saturation method in ampoules at 25°C. The solubility has been calculated using the Geochemist’s Workbench (GMB 7.0) software package. The measured solubilities of erythrite and annabergite are 10^?35.76 and 10^?36.43, respectively. Eh-pH diagrams were calculated and plotted using the GMB 7.0 software package. The database comprises the thermodynamic parameters of 46 elements, 47 main particles, 48 redox pairs, 552 particles in solution, 624 solid phases, and 10 gases. The Eh-pH diagrams of the Ni-As-H₂O and Co-As-H₂O systems were plotted for the average contents of these elements in the acidic waters in the oxidation zones of sulfide deposits. The formation of erythrite and annabergite under near-surface conditions is discussed.     

Steklite, KAl(SO4)2: A finding at the Tolbachik Volcano, Kamchatka, Russia, validating its status as a mineral species and crystal structure

Steklite KAl(SO₄)₂ has been found in sublimates of the Yadovitaya (Poisonous) fumarole at the second cinder cone of the northern breach of the Great Fissure Tolbachik Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. Steklite was approved as a valid mineral species by the Commission on New Minerals, Nomenclature, and Mineral Classification of the International Mineralogical Association on June 2, 2011 (IMA no. 2011-041). The name steklite is left for this mineral, as it was named by Chesnokov et al. (1995) for its technogenic analog from a burnt dump of coal mine no. 47 at Kopeisk, the Southern Urals, Russia. It is named after the Russian word steklo, meaning glass, in allusion to the visual similarity of its lamellae to thin glass platelets. At Tolbachik, steklite is associated with alumoklyuchevskite, langbeinite, euchlorine, fedotovite, chalcocyanite, hematite, and lyonsite. It occurs as hexagonal or irregular-shaped lamellar crystals with the major form {001} reaching 30 μm in thickness and 0.2 mm (occasionally up to 1 mm) in width. The crystals are frequently split. They are combined into openwork aggregates or thin crusts up to 1.5 × 2.5 cm in area. Steklite is transparent and colorless, with vitreous luster. The cleavage is perfect, parallel to (001). The mineral is brittle. The Mohs’ hardness is 2.5. D _calc is 2.797 g/cm³. Steklite is optically uniaxial, (?), ω = 1.546(2), ? = 1.533(3). The chemical composition (wt %, electron-microprobe data) is as follows: 0.09 Na₂O, 18.12 K₂O, 0.08 CaO, 0.03 MnO, 2.02 Fe₂O₃, 18.18 Al₂O₃, 61.80 SO₃. The total is 100.37. The empirical formula calculated on the basis of eight O atoms is: (K_0.997Na_0.008Ca_0.004)_Σ1.009(Al_0.925Fe _0.066 ³⁺ Mg_0.003Mn_0.001)_Σ0.995S_2.01O₈. Steklite is trigonal, space group P321, a = 4.7281(3), c = 7.9936(5) Å, V = 154.76(17)ų, Z =1. The strongest reflections in the X-ray powder diffraction pattern (d, Å-I[hkl]) are: 8.02–34[001], 4.085–11[100], 3.649–100[011, 101], 2.861–51[012, 102], 2.660 - 19[003], 2.364–25[110], 2.267–14[111, 111, 103], 1.822–12[022, 202]. In the structure of steklite examined in microtwinned crystal with R = 0.0732, the SO₄ tetrahedral anions are shared-corners with distorted AlO₆ trigonal prisms to form _∞ ² [(Al, Fe) (SO₄)₂]^? layers coplanar to (001). The K⁺ cations are in the interlayer space. The type specimen of steklite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores: VI. Solubility of synthetic analogs of ahlfeldite and cobaltomenite at 25°C

The understanding of the mechanisms of the selenium behavior under near-surface conditions is an urgent problem of modern mineralogy and geochemistry, and is very important for solving environmental problems. The objective of this study is to synthesize analogs of ahlfeldite and cobaltomenite and to estimate their solubility in water. These analogs have been synthesized by mixing aqueous solutions of cobalt and nickel nitrates, respectively, and sodium selenite acidified with a solution of nitric acid. The obtained samples have been identified by X-ray diffraction and IR spectroscopy. The solubility has been determined by the isothermal saturation method in ampoules at 25°C, while the solubility products have been calculated using the Geochemist’s Workbench (GMB 7.0) software package. The solubility products of ahlfeldite and cobaltomenite are 10^?9.20 and 10^?9.44, respectively. The Eh-pH diagrams were calculated and plotted with the GMB 7.0 software package. The Eh-pH diagrams of the Ni-Se-H₂O and Co-Se-H₂O systems have been calculated for the average contents of these elements in underground water and their contents in acidic water of the oxidation zone of sulfide deposits. The formation of ahlfeldite and cobaltomenite under near-surface conditions is discussed.