Crystal structure and refined formula of garyansellite Mg<Subscript>2</Subscript>Fe<Superscript>3+</Superscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH) · 2H<Subscript>2</Subscript>O

Single-crystal study of the structure (R = 0.0268) was performed for garyansellite from Rapid Creek, Yukon, Canada. The mineral is orthorhombic, Pbna, a = 9.44738(18), b = 9.85976(19), c = 8.14154(18) Å, V = 758.38(3) ų, Z = 4. An idealized formula of garyansellite is Mg₂Fe³⁺(PO₄)₂(OH) · 2H₂O. Structurally the mineral is close to other members of the phosphoferrite–reddingite group. The structure contains layers of chains of M(2)O₄(OH)(H₂O) octahedra which share edges to form dimers and connected by common edges with isolated from each other M(1)O₄(H₂O)₂ octahedra. The neighboring chains are connected to the layer through the common vertices of M(2) octahedra and octaahedral layers are linked through PO₄ tetrahedra.     

Attikaite,Ca<Subscript>3</Subscript>Cu<Subscript>2</Subscript>Al<Subscript>2</Subscript>(AsO<Subscript>4</Subscript>)<Subscript>4</Subscript>(OH)<Subscript>4</Subscript> · 2H<Subscript>2</Subscript>O,a new mineral species

Attikaite, a new mineral species, has been found together with arsenocrandalite, arsenogoyazite, conichalcite, olivenite, philipsbornite, azurite, malachite, carminite, beudantite, goethite, quartz, and allophane at the Christina Mine No. 132, Kamareza, Lavrion District, Attiki Prefecture (Attika), Greece. The mineral is named after the type locality. It forms spheroidal segregations (up to 0.3 mm in diameter) consisting of thin flexible crystals up to 3 × 20 × 80 μm in size. Its color is light blue to greenish blue, with a pale blue streak. The Mohs’ hardness is 2 to 2.5. The cleavage is eminent mica-like parallel to {001}. The density is 3.2(2) g/cm³ (measured in heavy liquids) and 3.356 g/cm³ (calculated). The wave numbers of the absorption bands in the infrared spectrum of attikaite are (cm^?1; sh is shoulder; w is a weak band): 3525sh, 3425, 3180, 1642, 1120w, 1070w, 1035w, 900sh, 874, 833, 820, 690w, 645w, 600sh, 555, 486, 458, and 397. Attikaite is optically biaxial, negative, α = 1.642(2), β = γ = 1.644(2) (X = c) 2V _means = 10(8)°, and 2V _calc = 0°. The new mineral is microscopically colorless and nonpleochroic. The chemical composition (electron microprobe, average over 4 point analyses, wt %) is: 0.17 MgO, 17.48 CaO, 0.12 FeO, 16.28 CuO, 10.61 Al₂O₃, 0.89 P₂O₅, 45.45 As₂O₅, 1.39 SO₃, and H₂O (by difference) 7.61, where the total is 100.00. The empirical formula calculated on the basis of (O,OH,H₂O)₂₂ is: Ca_2.94Cu _1.93 ²⁺ Al_1.97Mg_0.04Fe _0.02 ²⁺ [(As_3.74S_0.16P_0.12)_Σ4.02O_16.08](OH)_3.87 · 2.05H₂ O. The simplified formula is Ca₃Cu₂Al₂(AsO₄)₄(OH)₄ · 2H₂O. Attikaite is orthorhombic, space group Pban, Pbam or Pba2; the unit-cell dimensions are a = 10.01(1), b = 8.199(5), c = 22.78(1) Å, V = 1870(3) ų, and Z = 4. In the result of the ignition of attikaite for 30 to 35 min at 128–140°, the H₂O bands in the IR spectrum disappear, while the OH-group band is not modified; the weight loss is 4.3%, which approximately corresponds to two H₂O molecules per formula; and parameter c decreases from 22.78 to 18.77 Å. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %)((hkl)] are: 22.8(100)(001), 11.36(60)(002), 5.01(90)(200), 3.38(5)(123, 205), 2.780(70)(026), 2.682(30)(126), 2.503(50)(400), 2.292(20)(404). The type material of attikaite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. The registration number is 3435/1.     

The formation and recombination kinetics of [Si<Stack><Subscript>4</Subscript><Superscript>5−</Superscript></Stack>] centers in zircon

The radiation sensitivity, time stability and optical sensitivity of [Si₄⁵⁻] paramagnetic centers in natural zircon crystals, particularly those from the Late Neopleistocenic tuff of the Elbrus Volcano, have been studied. Optical bleaching was shown to result in the recombination of [Si₄⁵⁻] centers, while the concentration of centers increases in the absence of light due to the internal radiation background. The data obtained show the infeasibility of using [Si₄⁵⁻] centers in zircons as paleodosimeters in conventional dating methods using electron paramagnetic resonance (EPR) spectroscopy. New specific techniques need to be developed for EPR dating of zircons.     

Parageorgbokiite, β-Cu<Subscript>5</Subscript>O<Subscript>2</Subscript>(SeO<Subscript>3</Subscript>)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>, a new mineral species from volcanic exhalations,Kamchatka Peninsula,Russia

Parageorgbokiite, β-Cu₅O₂(SeO₃)₂Cl₂, has been found at the second cinder cone of the Great Fissure Tolbachik Eruption, Kamchatka Peninsula, Russia. Ralstonite, tolbachite, melanothallite, chalcocyanite, euchlorine, Fe oxides, tenorite, native gold, sophiite, Na, Ca, and Mg sulfates, cotunnite, and some copper oxoselenites are associated minerals. The estimated temperature of the mineral formation is 400–625°C. The color is green, with a vitreous luster; the streak is light green. The mineral is brittle, with the Mohs hardness ranging from 3 to 4. Cleavage is not observed. The calculated density is 4.70 g/cm³. Parageorgbokiite is biaxial (+); α = 2.05(1), β = 2.05(1), and γ = 2.08(1); 2V _(meas.) is ～0³, and 2V _(calc.) = 0(5)°. The optical orientation is X = a; other details remain unclear. The mineral is pleochroic, from grass green on X and Y to yellowish green on Z. The empirical formula calculated on the basis of O + Cl = 10 is Cu_4.91Pb_0.02O_1.86(ScO₃)₂Cl_2.14. The simplified formula is Cu₅O₂(ScO₃)₂Cl₂. Parageorgbokiite pertains to a new structural type of inorganic compounds. Its name points out its dimorphism with georgbokiite, which was named in honor of G.B. Bokii, the prominent Russian crystal chemist (1909–2000).     

Ab initio calculations on the O<Subscript>2</Subscript><Superscript>3−</Superscript>-Y<Superscript>3+</Superscript> center in CaF<Subscript>2</Subscript> and SrF<Subscript>2</Subscript>: its electronic structure and hyperfine constants

The O₂ ^3?-Y³⁺ center in fluorite-type structures (CaF₂ and SrF₂) has been investigated at the density functional theory (DFT) level using the CRYSTAL06 code. Our calculations were performed by means of the hybrid B3PW method in which the Hartree–Fock exchange is mixed with the DFT exchange functional, using Becke’s three parameter method, combined with the non-local correlation functionals by Perdew and Wang. Our calculations confirm the stability and the molecular character of the O₂ ^3?-Y³⁺ center. The unpaired electron is shown to be almost exclusively localized on and equally distributed between the two oxygen atoms that are separated by a bond distance of 2.47 Å in CaF₂ and 2.57 Å in SrF₂. The calculated ¹⁷O and ¹⁹F hyperfine constants for of the O₂ ^3?-Y³⁺ center are in good agreement with their corresponding experimental values reported by previous electron paramagnetic resonance and electron nuclear double resonance studies, while discrepancies are notable for the ⁸⁹Y hyperfine constants.     

Mangazeite,Al<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)(OH)<Subscript>4</Subscript> · 3H<Subscript>2</Subscript>O,a new mineral species

Mangazeite, a new mineral species, has been found at the Mangazeya silver deposit (300 km east of the Lena River, 65°43′40″ N and 130°20′ E) in eastern Yakutia (Sakha Republic, Siberia, Russia). The new mineral was described from fractured, sericitized, and pyritized granodiorite adjacent to a quartz-arsenopyrite vein. Associated minerals are gypsum and chlorite. The new mineral occurs as radial fibrous segregations of thin lamellar crystals. The size of the fibers does not exceed 40 μm in length and 1 μm across. The mineral is white, with a white streak and a vitreous luster. Mangazeite is transparent in isolated grains. No fluorescence is observed. The Mohs hardness is 1–2. The calculated density is 2.15 g/cm³. The new mineral is biaxial; its optical character was not determined; α = 1.525(9), β was not measured, and γ = 1.545(9). The average chemical composition is as follows (wt %): Al₂O₃ 36.28, SO₃ 28.81, H₂O⁺ 34.35, total 99.44, H₂O^? 9.27. The H₂O^? content was neither included in the total nor used in formula calculation. The empirical formula is Al_1.99(SO₄)_1.01(OH)_3.94 · 3.37H₂O. The simplified formula is Al₂(SO₄)(OH)₄ · 3H₂O. The theoretical chemical composition calculated from this formula is (wt %) Al₂O₃ 37.47, SO₃ 29.42, H₂O 33.11, total 100.00. The new mineral is triclinic; the unit cell parameters refined from X-ray powder diffraction data are a = 8.286(5), b = 9.385(5), c = 11.35(1) Å, α = 96.1(1), β = 98.9(1), γ = 96.6(1)°, and Z = 4. The strongest lines in the X-ray powder diffraction pattern (d(I, %)) are 8.14(19), 7.59(49), 7.16(46), 4.258(100), 4.060(48), and 3.912(43). Mangazeite is supergene in origin and crystallized in a favorable aluminosilicate environment in the presence of sulfate ion due to pyrite oxidation.     

Middendorfite,K<Subscript>3</Subscript>Na<Subscript>2</Subscript>Mn<Subscript>5</Subscript>Si<Subscript>12</Subscript>(O,OH)<Subscript>36</Subscript> · 2H<Subscript>2</Subscript>O,a new mineral species from the Khibiny pluton,Kola Peninsula

Middendorfite, a new mineral species, has been found in a hydrothermal assemblage in Hilairite hyperperalkaline pegmatite at the Kirovsky Mine, Mount Kukisvumchorr apatite deposit, Khibiny alkaline pluton, Kola Peninsula, Russia. Microcline, sodalite, cancrisilite, aegirine, calcite, natrolite, fluorite, narsarsukite, labuntsovite-Mn, mangan-neptunite, and donnayite are associated minerals. Middendorfite occurs as rhombshaped lamellar and tabular crystals up to 0.1 × 0.2 × 0.4 mm in size, which are combined in worm-and fanlike segregations up to 1 mm in size. The color is dark to bright orange, with a yellowish streak and vitreous luster. The mineral is transparent. The cleavage (001) is perfect, micalike; the fracture is scaly; flakes are flexible but not elastic. The Mohs hardness is 3 to 3.5. Density is 2.60 g/cm³ (meas.) and 2.65 g/cm³ (calc.). Middendorfite is biaxial (?), α = 1.534, β = 1.562, and γ = 1.563; 2V (meas.) = 10°. The mineral is pleochroic strongly from yellowish to colorless on X through brown on Y and to deep brown on Z. Optical orientation: X = c. The chemical composition (electron microprobe, H₂O determined with Penfield method) is as follows (wt %): 4.55 Na₂O, 10.16 K₂O, 0.11 CaO, 0.18 MgO, 24.88 MnO, 0.68 FeO, 0.15 ZnO, 0.20 Al₂O₃, 50.87 SiO₂, 0.17 TiO₂, 0.23 F, 7.73 H₂O; ?O=F₂?0.10, total is 99.81. The empirical formula calculated on the basis of (Si,Al)₁₂(O,OH,F)₃₆ is K_3.04(Na_2.07Ca_0.03)_Σ2.10(Mn_4.95Fe_0.13Mg_0.06Ti_0.03Zn_0.03)_Σ5.20(Si_11.94Al_0.06)_Σ12O_27.57(OH)_8.26F_0.17 · 1.92H₂O. The simplified formula is K₃Na₂Mn₅Si₁₂(O,OH)₃₆ · 2H₂O. Middenforite is monoclinic, space group: P2₁/m or P2₁. The unit cell dimensions are a = 12.55, b = 5.721, c = 26.86 Å; β = 114.04°, V = 1761 ų, Z = 2. The strongest lines in the X-ray powder pattern [d, Å, (I)(hkl)] are: 12.28(100)(002), 4.31(81)(11\(\overline 4 \)), 3.555(62)(301, 212), 3.063(52)(008, 31\(\overline 6 \)), 2.840(90)(312, 021, 30\(\overline 9 \)), 2.634(88)(21\(\overline 9 \), 1.0.\(\overline 1 \)0, 12\(\overline 4 \)), 2.366(76)(22\(\overline 6 \), 3.1.\(\overline 1 \)0, 32\(\overline 3 \)), 2.109(54)(42–33, 42–44, 51\(\overline 9 \), 414), 1.669(64)(2.2.\(\overline 1 \)3, 3.2.\(\overline 1 \)3, 62\(\overline 3 \), 6.1.\(\overline 1 \)3), 1.614(56)(5.0.\(\overline 1 \)6, 137, 333, 71\(\overline 1 \)). The infrared spectrum is given. Middendorfite is a phyllosilicate related to bannisterite, parsenttensite, and the minerals of the ganophyllite and stilpnomelane groups. The new mineral is named in memory of A.F. von Middendorff (1815–1894), an outstanding scientist, who carried out the first mineralogical investigations in the Khibiny pluton. The type material of middenforite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Droninoite,Ni<Subscript>3</Subscript>Fe<Superscript>3+</Superscript>Cl(OH)<Subscript>8</Subscript> · 2H<Subscript>2</Subscript>O,a new hydrotalcite-group mineral species from the weathered Dronino meteorite

A new mineral, droninoite, was found in a fragment of a weathered Dronino iron meteorite (which fell near the village of Dronino, Kasimov district, Ryazan oblast, Russia) as dark green to brown fine-grained (the size of single grains is not larger than 1 μm) segregations up to 0.15 × 1 × 1 mm in size associated with taenite, violarite, troilite, chromite, goethite, lepidocrocite, nickelbischofite, and amorphous Fe³⁺ hydroxides. The mineral was named after its type locality. Aggregates of droninoite are earthy and soft; the Mohs hardness is 1–1.5. The calculated density is 2.857 g/cm³. Under a microscope, droninoite is dark gray-green and nonpleochroic. The mean (cooperative for fine-grained aggregate) refractive index is 1.72(1). The IR spectrum indicates the absence of S O ₄ ^2? and C O ₃ ^2? anions. Chemical composition (electron microprobe, partition of total iron into Fe²⁺ and Fe³⁺ made on the basis of the ratio (Ni + Fe²⁺): Fe³⁺ = 3: 1; water is calculated from the difference) is as follows, wt %: 36.45 NiO, 12.15 FeO, 17.55 Fe₂O₃, 23.78 H₂O, 13.01 Cl, ?O=Cl₂ ?2.94, total is 100.00. The empirical formula (Z = 6) is Ni_2.16Fe _0.75 ²⁺ Fe _0.97 ³⁺ Cl_1.62(OH)_7.10 · 2.28H₂O. The simplified formula is Ni₃Fe³⁺Cl(OH)₈ · 2H₂O. Droninoite is trigonal, space group R \(\bar 3\) m, R3m, or R32; a = 6.206(2), c = 46.184(18) Å; V = 1540.4(8) ų. The strong reflections in the X-ray powder diffraction pattern [d, Å (I, %) (hkl)] are 7.76(100)(006), 3.88(40)(0.0.12), 2.64(25)(202, 024), 2.32(20)(0.2.10), 1.965(0.2.16). The holotype specimen is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, registration number 3676/1.     

Avdoninite: New data,crystal structure and refined formula K<Subscript>2</Subscript>Cu<Subscript>5</Subscript>Cl<Subscript>8</Subscript>(OH)<Subscript>4</Subscript> · 2H<Subscript>2</Subscript>O

The paper reports new findings of avdoninite from deposits of active fumaroles in the Second Scoria Cone at the Northern Breach of the Great Fissure Tolbachik Eruption, Tolbachik Volcano, Kamchatka Peninsula, Russia. The crystal structure of the mineral has been determined for the first time, which has allowed reliable determination of its space group and unit cell dimensions, refinement of its formula K₂Cu₅-Cl₈(OH)₄ · 2H₂O, and correct indexing of its X-ray powder diffraction pattern. Avdoninite is monoclinic, space group P2₁/c, a = 11.592(2), b = 6.5509(11), c = 11.745(2) Å, β = 91.104(6)°, V = 891.8(3) ų, Z = 2. The crystal structure of this mineral has been determined on a single crystal R ₁ [F > 4σ (F)] = 0.063. It is based on sheets of copper–oxo-chloride complexes [Cu₅Cl₈(OH)₄]^2– parallel to (100). The K⁺ cation and H₂O molecules are interlayers.     

Thermal expansion of hydrated six-coordinate silicon in thaumasite,Ca<Subscript>3</Subscript>Si(OH)<Subscript>6</Subscript>(CO<Subscript>3</Subscript>)(SO<Subscript>4</Subscript>)·12H<Subscript>2</Subscript>O

Thaumasite, Ca₃Si(OH)₆(CO₃)(SO₄)12H₂O, occurs as a low-temperature secondary alteration phase in mafic igneous and metamorphic rocks, and is recognized as a product and indicator of sulfate attack in Portland cement. It is also the only mineral known to contain silicon in six-coordination with hydroxyl (OH)^? that is stable at ambient P–T conditions. Thermal expansion of the various components of this unusual structure has been determined from single-crystal X-ray structure refinements of natural thaumasite at 130 and 298 K. No phase transitions were observed over this temperature range. Cell parameters at room temperature are: a= 11.0538(6) Å, c=10.4111(8) Å and V=1101.67(10) ų, and were measured at intervals of about 50 K between 130 and 298 K, resulting in mean axial and volumetric coefficients of thermal expansion (×10^?5K^?1); α _a =1.7(1), α _c =2.1(2), and α _V =5.6(2). Although the unit cell and ^VIIICaO₈ polyhedra show significant positive thermal expansion over this temperature range, the silicate octahedron, sulfate tetrahedron, and carbonate group show zero or negative thermal expansion, with α _V (^VISiO₆) = ?0.6 ± 1.1, α _V (^IVSO₄)=?5.8 ± 1.4, and α _R (C–O)= 0.0 ± 1.8 (×10^?5 K^?1). Most of the thermal expansion is accommodated by lengthening of the R(O...O) hydrogen bond distances by on average 5σ, although the hydrogen bonds involving hydroxyl sites on ^VISi expand twice as much as those on molecular water, causing the [Ca₃Si(OH)₆(H₂O)₁₂]⁴⁺ columns to expand in diameter more than they move apart over this temperature range. The average Si–OH bond length of the six-coordinated Si atom 〈R(^VISi–OH)〉 in thaumasite is 1.783(1) Å, being about 0.02 Å (?20σ) shorter than ^VISi–OH in the dense hydrous magnesium silicate, phase D, MgSi₂H₂O₆.     

Structural characterization of high-pressure C–Na<Subscript>2</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript> by single-crystal diffraction and <Superscript>29</Superscript>Si MAS NMR

Single crystals of C–Na₂Si₂O₅ have been synthesized from the hydrothermal recrystallization of a glass. The title compound is monoclinic, space group P2₁/c with Z= 8 and unit-cell parameters a= 4.8521 (4)Å, b=23.9793(16)Å, c=8.1410(6)Å, β=90.15(1)° and V=947.2(2)ų. The structure has been determined by direct methods and belongs to the group of phyllosilicates. It is based on layers of tetrahedra with elliptically six-membered rings in chair conformation. The sequence of directedness within a single ring is UDUDUD. The sheets are parallel to (010) with linking sodium cations in five- and sixfold coordination. Concerning the shape and the conformation of the rings, C–Na₂Si₂O₅ is closely related to β-Na₂Si₂O₅. However, both structures differ in the stacking sequences of the layers. A possible explanation for the frequently observed polysynthetic twinning of phase C is presented. In the ²⁹Si MAS-NMR spectrum of C–Na₂Si₂O₅ four well-resolved lines of equal intensity are observed at ?86.0, ?86.3, ?87.4, and ?88.2?ppm. The narrow range of isotropic chemical shifts reflects the great similarity of the environments of the different Si sites. This lack of pronounced differences in geometry renders a reliable assignment of the resonance lines to the individual sites on the basis of known empiric correlations and geometrical features impossible.     

Electrical conductivity,thermopower and <Superscript>57</Superscript>Fe Mössbauer spectroscopy of aegirine (NaFeSi<Subscript>2</Subscript>O<Subscript>6</Subscript>)

DC and AC electrical conductivities were measured on samples of two different crystals of the mineral aegirine (NaFeSi₂O₆) parallel () and perpendicular () to the [001] direction of the clinopyroxene structure between 200 and 600 K. Impedance spectroscopy was applied (20 Hz–1 MHz) and the bulk DC conductivity _DC was determined by extrapolating AC data to zero frequency. In both directions, the log _DC – 1/T curves bend slightly. In the high- and low-temperature limits, differential activation energies were derived for measurements [001] of E_A 0.45 and 0.35 eV, respectively, and the numbers [001] are very similar. The value of _DC [001] with _DC(300 K) 2.0 × 10^{–6 –1}cm^–1 is by a factor of 2–10 above that measured [001], depending on temperature, which means anisotropic charge transport. Below 350 K, the AC conductivity () (/2=frequency) is enhanced relative to _DC for both directions with an increasing difference for rising frequencies on lowering the temperature. An approximate power law for () is noted at higher frequencies and low temperatures with () ^s, which is frequently observed on amorphous and disordered semiconductors. Scaling of () data is possible with reference to _DC, which results in a quasi-universal curve for different temperatures. An attempt was made to discuss DC and AC results in the light of theoretical models of hopping charge transport and of a possible Fe²⁺ Fe³⁺ electron hopping mechanism. The thermopower (Seebeck effect) in the temperature range 360 K < T <770 K is negative in both directions. There is a linear – 1/T relationship above 400 K with activation energy E 0.030 eV [001] and 0.070 eV [001]. ⁵⁷Fe Mössbauer spectroscopy was applied to detect Fe²⁺ in addition to the dominating concentration of Fe³⁺.     

Yegorovite,Na<Subscript>4</Subscript>[Si<Subscript>4</Subscript>O<Subscript>8</Subscript>(OH)<Subscript>4</Subscript>]·7H<Subscript>2</Subscript>O,a new mineral from the Lovozero alkaline pluton,Kola Peninsula

A new mineral, yegorovite, has been identified in the late hydrothermal, low-temperature assemblage of the Palitra hyperalkaline pegmatite at Mt. Kedykverpakhk, Lovozero alkaline pluton, Kola Peninsula, Russia. The mineral is intimately associated with revdite and megacyclite, earlier natrosilite, microcline, and villiaumite. Yegorovite occurs as coarse, usually split prismatic (up to 0.05 × 0.15 × 1 mm) or lamellar (up to 0.05 × 0.7 × 0.8 mm) crystals. Polysynthetic twins and parallel intergrowths are typical. Mineral individuals are combined in bunches or chaotic groups (up to 2 mm); radial-lamellar clusters are less frequent. Yegorovite is colorless, transparent with vitreous luster. Cleavage is perfect parallel to (010) and (001). Fracture is splintery; crystals are readily split into acicular fragments. The Mohs hardness is ～2. Density is 1.90(2) g/cm³ (meas) and 1.92 g/cm³ (calc). Yegorovite is biaxial (?), with α = 1.474(2), β = 1.479(2), and γ = 1.482(2), 2V _meas > 70°, 2V _calc = 75°. The optical orientation is X ∧ a ～ 15°, Y = c, Z = b. The IR spectrum is given. The chemical composition determined using an electron microprobe (H₂O determined from total deficiency) is (wt %): 23.28 Na₂O, 45.45 SiO₂, 31.27 H₂O_calc; the total is 100.00. The empirical formula is Na_3.98Si_4.01O_8.02(OH)_3.98 · 7.205H₂O. The idealized formula is Na₄[Si₄O₈(OH)₄] · 7H₂O. Yegorovite is monoclinic, space group P2₁/c. The unit-cell dimensions are a = 9.874, b= 12.398, c = 14.897 Å, β = 104.68°, V = 1764.3 ų, Z = 4. The strongest reflections in the X-ray powder pattern (d, Å (I, %)([hkl]) are 7.21(70)[002], 6.21(72)[012, 020], 4.696(44)[022], 4.003(49)[211], 3.734(46)[\(\bar 2\) 13], 3.116(100)[024, 040], 2.463(38)[\(\bar 4\)02, \(\bar 2\)43]. The crystal structure was studied by single-crystal method, R _hkl = 0.0745. Yegorovite is a representative of a new structural type. Its structure consists of single chains of Si tetrahedrons [Si₄O₈(OH)₄]∞ and sixfold polyhedrons of two types: [NaO(OH)₂(H₂O)₃] and [NaO(OH)(H₂O)₄] centered by Na. The mineral was named in memory of Yu. K. Yegorov-Tismenko (1938–2007), outstanding Russian crystallographer and crystallochemist. The type material of yegorovite has been deposited at the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.     

The solubility of Gd<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> and the hydrolysis of Gd<Superscript>3+</Superscript> in acidic solutions at 250°C and saturation vapor pressure

The solubility of Gd₂Ti₂O₇ ceramic in acidic solutions (HCl and HClO₄) was studied at 250°C and saturation vapor pressure within pH 2.5–5.2. The dissolution process occurs mainly via two reactions: 0.5 Gd₂Ti₂O_7(cr) + 3H⁺ = Gd³⁺ + TiO_2(cr) + 1.5 H₂O at pH < 3 and 0.5Gd₂Ti₂O₇(cr) + H⁺ + 0.5H₂O = Gd(OH) ₂ ⁺ TiO₂(cr) at pH 3–5. The thermodynamic equilibrium constants were calculated at the 0.95 confidence level as log K ₍₁₎ ^o = 4.12 ± 0.47; = ?0.97 ± 0.16 at 250°C. It was shown that Gd³⁺ undergoes hydrolysis in solutions with pH > 3, and the species Gd(OH) ₂ ⁺ dominates up to at least pH 5. At pH < 3, Gd occurs in solutions as Gd³⁺. The second constant of Gd³⁺ hydrolysis was determined at 250°C as K ^o = ?5.09 ± 0.5, and the thermodynamic characteristics of the initial Gd₂Ti₂O₇ solid phase were determined: S _298.15 ^o = 251.4 J/(mol K) and ΔfG _298.15 ^o = ?3630 ± 10 kJ/mol.     

Chemical and isotopic investigations (δ<Superscript>18</Superscript>O, δ<Superscript>2</Superscript>H, <Superscript>3</Superscript>H, <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr) to define groundwater processes occurring in a deep-seated landslide in flysch

Deep-seated landslides are complex systems. In many cases, multidisciplinary studies are necessary to unravel the key hydrological features that can influence their evolution in space and time. The deep-seated Berceto landslide, in the northern Apennines of Italy, has been investigated in order to define the origin and geochemical evolution of groundwater (GW), to identify the slope system hydrological boundary, and to highlight the GW flow paths, transit time and transfer modalities inside the landslide body. This research is based on a multidisciplinary approach that involves monitoring GW levels, obtaining analyses of water chemistry and stable and unstable isotopes (δ¹⁸O-δ²H, ³H, ⁸⁷Sr/⁸⁶Sr), performing soil leaching tests, geochemical modelling (PHREEQC), and principal component analysis (PCA). The results of δ¹⁸O-δ²H and ⁸⁷Sr/⁸⁶Sr analyses show that the source of GW recharge in the Berceto landslide is local rainwater, and external contributions from a local stream can be excluded. In the landslide body, two GW hydrotypes (Ca-HCO₃ and Na-HCO₃) are identified, and the results of PHREEQC and PCA confirm that the chemical features of the GW depend on water–rock interaction processes occurring inside the landslide. The ³H content suggests a recent origin for GW and appears to highlight mixing between shallow and deep GW aliquots. The ³H content and GW levels data confirm that shallow GW is mainly controlled by a mass transfer mechanism. The ³H analyses with GW levels also indicate that only deep GW is controlled by a pressure transfer mechanism, and this mechanism is likely the main influence on the landslide kinematics.     

Avdoninite,K<Subscript>2</Subscript>Cu<Subscript>5</Subscript>Cl<Subscript>8</Subscript>(OH)<Subscript>4</Subscript> · H<Subscript>2</Subscript>O,a new mineral species from volcanic exhalations and the technogenic zone at volcanic-hosted massive sulfide deposits

Avdoninite, a new mineral species, has been found together with euchlorite, paratacamite, atacamite, belloite, and langbeinite hosted in exhalation sediments of the Yadovitaya fumarole in the Second Cinder Cone at the Northern Breach of the Great Fissure Tolbachik Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. Avdoninite occurs as imperfect, short prismatic and thick tabular crystals up to 0.2 mm long, with (001) and (100) forms, crystal aggregates, and pseudomorphs (together with atacamite) after melanothallite observed. The new mineral is brittle, with the Mohs hardness 3 (for aggregates). Density is 3.03 g/cm³ (meas.) and 3.066 g/cm³ (calc.). Avdoninite is biaxial and optically neutral, with α = 1.669, β = 1.688, γ = 1.707, 2V = ?90°. Dispersion is not observed. Optical orientation: Y = c, X = b? Pleochroism is absent. The infrared spectrum suggests the presence of water molecules in avdoninite. Electron microprobe chemical analysis has given (wt %) K₂O 11.94 (±0.4), CuO 51.43 (±0.7), Cl 37.07 (±0.6), H₂O (determined by the Penfield method) 6.9, ?O=Cl₂ ?8.37, total 98.97. The empirical formula is K_1.96Cu_5.00Cl_8.09(OH)_3.87. · 1.03H₂O. Avdoninite is monoclinic, space group P2/m, P2, or Pm; a = 24.34(2) Å, b = 5.878(4) Å, c = 11.626(5) Å, β = 93.3(1)°, V = 1660.6(20) ų, Z = 4. The compatibility index is good: 1 ? K _p/K _c = 0.056 for D _calc and 0.044 for D _meas. The strongest lines in the X-ray powder diffraction pattern (d, Å (I, %) (hkl)) are 11.63(100)(001), 5.88(20)(010), 5.80(27)(002), 5.73(17)(\(\overline 1 \)02), 2.518(19)(21\(\overline 4 \)), 2.321(17)(005). Avdoninite is identical to a technogenic analogue previously described from the Blyava volcanic-hosted massive sulfide deposit, Orenburg oblast, Russia. The new mineral is named after Vladimir Nikolaevich Avdonin (born 1925), a senior researcher of the Ural Geological Museum of the Ural State Mining University. The type material of avdoninite from Kamchatka is deposited in the Mineralogical Museum of the Department of Mineralogy, St. Petersburg State University, St. Petersburg, Russia. The registration number is 19175.     

Nickelpicromerite,K<Subscript>2</Subscript>Ni(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>•6H<Subscript>2</Subscript>O,a new picromerite-group mineral from Slyudorudnik,South Urals,Russia

A new picromerite-group mineral, nickelpicromerite, K₂Ni(SO₄)₂?·?6H₂O (IMA 2012–053), was found at the Vein #169 of the Ufaley quartz deposit, near the town of Slyudorudnik, Kyshtym District, Chelyabinsk area, South Urals, Russia. It is a supergene mineral that occurs, with gypsum and goethite, in the fractures of slightly weathered actinolite-talc schist containing partially vermiculitized biotite and partially altered sulfides: pyrrhotite, pentlandite, millerite, pyrite and marcasite. Nickelpicromerite forms equant to short prismatic or tabular crystals up to 0.07 mm in size and anhedral grains up to 0.5 mm across, their clusters or crusts up to 1 mm. Nickelpicromerite is light greenish blue. Lustre is vitreous. Mohs hardness is 2–2½. Cleavage is distinct, parallel to {10–2}. D _meas is 2.20(2), D _calc is 2.22 g cm^?3. Nickelpicromerite is optically biaxial (+), α?=?1.486(2), β?=?1.489(2), γ?=?1.494(2), 2V_meas =75(10)°, 2V_calc =76°. The chemical composition (wt.%, electron-microprobe data) is: K₂O 20.93, MgO 0.38, FeO 0.07, NiO 16.76, SO₃ 37.20, H₂O (calc.) 24.66, total 100.00. The empirical formula, calculated based on 14 O, is: K_1.93Mg_0.04Ni_0.98S_2.02O_8.05(H₂O)_5.95. Nickelpicromerite is monoclinic, P2₁/c, a?=?6.1310(7), b?=?12.1863(14), c?=?9.0076(10) Å, β?=?105.045(2)°, V?=?649.9(1) ų, Z?=?2. Eight strongest reflections of the powder XRD pattern are [d,Å-I(hkl)]: 5.386–34(110); 4.312–46(002); 4.240–33(120); 4.085–100(012, 10–2); 3.685–85(031), 3.041–45(040, 112), 2.808–31(013, 20–2, 122), 2.368–34(13–3, 21–3, 033). Nickelpicromerite (single-crystal X-ray data, R?=?0.028) is isostructural to other picromerite-group minerals and synthetic Tutton’s salts. Its crystal structure consists of [Ni(H₂O)₆]²⁺ octahedra linked to (SO₄)^2? tetrahedra via hydrogen bonds. K⁺ cations are coordinated by eight anions. Nickelpicromerite is the product of alteration of primary sulfide minerals and the reaction of the acid Ni-sulfate solutions with biotite.     

Mineralogy,Mössbauer spectra and electrical conductivity of triphylite Li(Fe<Superscript>2+</Superscript>,Mn<Superscript>2+</Superscript>) PO<Subscript>4</Subscript>

The electrical conductivity of monocrystalline triphylite, Li(Fe²⁺,Mn²⁺)PO₄, with the orthorhombic olivine-type structure was measured parallel (∥) to the [010] direction and ∥ [001] (space group Pnma), between ～400 and ～700 K. Electrical measurements on triphylite are of technological interest because LiFePO₄ is a promising electrode material for rechargeable Li batteries. Triphylite was examined by electron microprobe, ICP atomic emission spectroscopy, X-ray diffraction, Mössbauer spectroscopy and microscopic analysis. The DC conductivity σ_DC was determined from AC impedance data (20 Hz–1 MHz) extrapolating to zero frequency. Triphylite shows σ_DC with activated behavior measured ∥ [010] between ～500 and ～700 K during the first heating up, with activation energy of E _A = 1.52 eV; on cooling E _A = 0.61 eV was found down to ～400 K and extrapolated σ_DC (295 K) ～10^?9 Ω^?1cm^?1; ∥ [001] E _A = 0.65 eV and extrapolated σ_DC(295 K) ～10^?9 to 10^?10 Ω^?1cm^?1, measured during the second heating cycle. The enhanced AC conductivity relative to σ_DC at lower temperatures indicates a hopping-type charge transport between localized levels. Conduction during the first heating up is ascribed to ionic Li⁺ hopping. DC polarization experiments showed conduction after the first heating up to be electronic related to lowered activation energy. Electronic conduction appears to be coupled with the presence of Li⁺ vacancies and Fe³⁺, formed by triphylite alteration. For comparison, σ_DC was measured on the synthetic compound LiMgPO₄ with olivine-type structure, where also an activated behavior of σ_DC with E _A ～1.45 eV was observed during heating and cooling due to ionic Li⁺ conduction; here no oxidation can occur associated with formation of trivalent cations.     

Elastic and thermoelastic properties of synthetic Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript> (åkermanite) and Ca<Subscript>2</Subscript>ZnSi<Subscript>2</Subscript>O<Subscript>7</Subscript> (hardystonite)

Elastic and thermoelastic constants of large single crystals of Ca₂MgSi₂O₇ and Ca₂ZnSi₂O₇ have been derived from ultrasonic resonance frequencies of plane-parallel plates and their shift upon variation of temperature, respectively. In addition, coefficients of thermal expansion and dielectric constants were determined. Both species possess quite similar properties. As observed in other isotypic magnesium and zinc compounds, the mean elastic stiffness and the deviation from the Cauchy relations are significantly larger in the zinc compound, due to a covalent contribution of the Zn–O bond. Positive thermoelastic constants T₄₄ and T₆₆ in Ca₂MgSi₂O₇ allow temperature-independent ultrasonic generators and oscillators to be manufactured.     

Nickeltalmessite,Ca<Subscript>2</Subscript>Ni(AsO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 2H<Subscript>2</Subscript>O,a new mineral species of the fairfieldite group,Bou Azzer,Morocco

Nickeltalmessite, Ca₂Ni(AsO₄)₂ · 2H₂O, a new mineral species of the fairfieldite group, has been found in association with annabergite, nickelaustinite, pecoraite, calcite, and a mineral of the chromite-manganochromite series from the dump of the Aït Ahmane Mine, Bou Azzer ore district, Morocco. The new mineral occurs as spheroidal aggregates consisting of split crystals up to 10 × 10 × 20 μm in size. Nickeltalmessite is apple green, with white streak and vitreous luster. The density measured by the volumetric method is 3.72(3) g/cm³; calculated density is 3.74 g/cm³. The new mineral is colorless under a microscope, biaxial, positive: α = 1.715(3), β = 1.720(5), γ = 1.753(3), 2V _meas = 80(10)°, 2V _calc = 60.4. Dispersion is not observed. The infrared spectrum is given. As a result of heating of the mineral in vacuum from 24° up to 500°C, weight loss was 8.03 wt %. The chemical composition (electron microprobe, wt %) is as follows: 25.92 CaO, 1.23 MgO, 1.08 CoO, 13.01 NiO, 52.09 As₂O₅; 7.8 H₂O (determined by the Penfield method); the total is 101.13. The empirical formula calculated on the basis of two AsO₄ groups is Ca_2.04(Ni_0.77Mg_0.13Co_0.06)_Σ0.96 (AsO₄)_2.00 · 1.91H₂O. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %) (hkl)] are: 5.05 (27) (001) (100), 3.57 (43) (011), 3.358 (58) (110), 3.202 (100) (020), 3.099 (64) (0\(\bar 2\)1), 2.813 (60), (\(\bar 1\)21), 2.772 (68) (2\(\bar 1\)0), 1.714 (39) (\(\bar 3\)31). The unit-cell dimensions of the triclinic lattice (space group P1 or P) determined from the X-ray powder data are: a = 5.858(7), b = 7.082(12), c = 5.567(6) Å, α = 97.20(4), β = 109.11(5), γ = 109.78(5)°, V = 198.04 ų, Z = 1. The mineral name emphasizes its chemical composition as a Ni-dominant analogue of talmessite. The type material of nickeltalmessite is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 3750/1.