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.     

Batisivite,V<Subscript>8</Subscript>Ti<Subscript>6</Subscript>[Ba(Si<Subscript>2</Subscript>O)]O<Subscript>28</Subscript>, a new mineral species from the derbylite group

Batisivite has been found as an accessory mineral in the Cr-V-bearing quartz-diopside metamorphic rocks of the Slyudyanka Complex in the southern Baikal region, Russia. A new mineral was named after the major cations in its ideal formula (Ba, Ti, Si, V). Associated minerals are quartz, Cr-V-bearing diopside and tremolite; calcite; schreyerite; berdesinskiite; ankangite; V-bearing titanite; minerals of the chromite-coulsonite, eskolaite-karelianite, dravite-vanadiumdravite, and chernykhite-roscoelite series; uraninite; Cr-bearing goldmanite; albite; barite; zircon; and unnamed U-Ti-V-Cr phases. Batisivite occurs as anhedral grains up to 0.15–0.20 mm in size, without visible cleavage and parting. The new mineral is brittle, with conchoidal fracture. Observed by the naked eye, the mineral is black and opaque, with a black streak and resinous luster. Batisivite is white in reflected light. The microhardness (VHN) is 1220–1470 kg/mm² (load is 30 g), the mean value is 1330 kg/mm². The Mohs hardness is near 7. The calculated density is 4.62 g/cm³. The new mineral is weakly anisotropic and bireflected. The measured values of reflectance are as follows (λ, nm—R _max ^′ /R _min ^′ ): 440—17.5/17.0; 460—17.3/16.7; 480—17.1/16.5; 500—17.2/16.6; 520—17.3/16.7; 540—17.4/16.8; 560—17.5/16.8; 580—17.6/16.9; 600—17.7/17.1; 620—17.7/17.1; 640—17.8/17.1; 660—17.9/17.2; 680—18.0/17.3; 700—18.1/17.4. Batisivite is triclinic, space group P \(\overline 1\); the unit-cell dimensions are: a = 7.521(1) Å, b = 7.643(1) Å, c = 9.572(1) Å, α = 110.20°(1), β = 103.34°(1), γ = 98.28°(1), V = 487.14(7) ų, Z = 1. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %)(hkl)] are: 3.09(8)(12\(\overline 2\)); 2.84, 2.85(10)(021, 120); 2.64(8)(21\(\overline 3\)); 2.12(8)(31\(\overline 3\)); 1.785(8)(32\(\overline 4\)), 1.581(10)(24\(\overline 2\)); 1.432, 1.433(10)(322, 124). The chemical composition (electron microprobe, average of 237 point analyses, wt %) is: 0.26 Nb₂O₅, 6.16 SiO₂, 31.76 TiO₂, 1.81 Al₂O₃, 8.20 VO₂, 26.27 V₂O₃, 12.29 Cr₂O₃, 1.48 Fe₂O₃, 0.08 MgO, 11.42 BaO; the total is 99.73. The VO₂/V₂O₃ ratio has been calculated. The simplified empirical formula is (V _4.8 ³⁺ Cr_2.2V _0.7 ⁴⁺ Fe_0.3)_8.0(Ti_5.4V _0.6 ⁴⁺ )_6.0[Ba(Si_1.4Al_0.5O_0.9)]O₂₈. An alternative to the title formula could be a variety (with the diorthogroup Si₂O₇) V₈Ti₆[Ba(Si₂O₇)]O₂₂. Batisivite probably pertains to the V ₈ ³⁺ Ti ₆ ⁴⁺ [Ba(Si₂O)]O₂₈-Cr ₈ ³⁺ Ti ₆ ⁴⁺ [Ba(Si₂O)]O₂₈ solid solution series. The type material of batisivite has been deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Elastic behavior of vanadinite,Pb<Subscript>10</Subscript>(VO<Subscript>4</Subscript>)<Subscript>6</Subscript>Cl<Subscript>2</Subscript>, a microporous non-zeolitic mineral

The high-pressure behavior of a vanadinite (Pb₁₀(VO₄)₆Cl₂, a = b = 10.3254(5), c = 7.3450(4) Å, space group P6₃/m), a natural microporous mineral, has been investigated using in-situ HP-synchrotron X-ray powder diffraction up to 7.67 GPa with a diamond anvil cell under hydrostatic conditions. No phase transition has been observed within the pressure range investigated. Axial and volume isothermal Equations of State (EoS) of vanadinite were determined. Fitting the P–V data with a third-order Birch-Murnaghan (BM) EoS, using the data weighted by the uncertainties in P and V, we obtained: V ₀ = 681(1) Å³, K ₀ = 41(5) GPa, and K′ = 12.5(2.5). The evolution of the lattice constants with P shows a strong anisotropic compression pattern. The axial bulk moduli were calculated with a third-order “linearized” BM-EoS. The EoS parameters are: a ₀ = 10.3302(2) Å, K ₀(a) = 35(2) GPa and K′(a) = 10(1) for the a-axis; c ₀ = 7.3520(3) Å, K ₀(c) = 98(4) GPa, and K′(c) = 9(2) for the c-axis (K ₀(a):K ₀(c) = 1:2.80). Axial and volume Eulerian-finite strain (fe) at different normalized stress (Fe) were calculated. The weighted linear regression through the data points yields the following intercept values: Fe _a (0) = 35(2) GPa for the a-axis, Fe _c (0) = 98(4) GPa for the c-axis and Fe _V (0) = 45(2) GPa for the unit-cell volume. The slope of the regression lines gives rise to K′ values of 10(1) for the a-axis, 9(2) for the c-axis and 11(1) for the unit cell-volume. A comparison between the HP-elastic response of vanadinite and the iso-structural apatite is carried out. The possible reasons of the elastic anisotropy are discussed.     

Compressibility of strontium orthophosphate Sr<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> at high pressure

High pressure in situ synchrotron X-ray diffraction experiment of strontium orthophosphate Sr₃(PO₄)₂ has been carried out to 20.0 GPa at room temperature using multianvil apparatus. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields a volume of V ₀ = 498.0 ± 0.1 Å³, an isothermal bulk modulus of K _T  = 89.5 ± 1.7 GPa, and first pressure derivative of K _T ′ = 6.57 ± 0.34. If K _T ′ is fixed at 4, K _T is obtained as 104.4 ± 1.2 GPa. Analysis of axial compressible modulus shows that the a-axis (K _a  = 79.6 ± 3.2 GPa) is more compressible than the c-axis (K _c  = 116.4 ± 4.3 GPa). Based on the high pressure Raman spectroscopic results, the mode Grüneisen parameters are determined and the average mode Grüneisen parameter of PO₄ vibrations of Sr₃(PO₄)₂ is calculated to be 0.30(2).     

Hydroxylborite,Mg<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)(OH)<Subscript>3</Subscript>, a new mineral species and isomorphous series fluoborite-hydroxylborite

Hydroxylborite, a new mineral species, an analogue of fluoborite with OH > F, has been found at the Titovsky deposit (57°41′N, 125°22′E), the Chersky Range, Dogdo Basin, Sakha-Yakutia Republic, Russia. Prismatic crystals of the new mineral are dominated by the {10\(\overline 1 \)0} faces without distinct end forms and reach (1?1.5) × (0.1?0.2) mm in size. Radial aggregates of such crystals occur in the mineralized marble adjacent to the boron ore (suanite-kotoite-ludwigite). Calcite, dolomite, Mg-rich ludwigite, kotoite, szaibelyite, clinohumite, magnetite, serpentine, and chlorite are associated minerals. Hydroxylborite is transparent colorless, with a white streak and vitreous luster. The new mineral is brittle. The Mohs’ hardness is 3.5. The cleavage is imperfect on {0001}. The density measured with equilibration in heavy liquids is 2.89(1) g/cm³; the calculated density is 2.872 g/cm³. The wave numbers of the absorption bands in the IR spectrum of hydroxylborite are (cm^?1; sh is shoulder): 3668, 1233, 824, 742, 630sh, 555sh, 450sh, and 407. The new mineral is optically uniaxial, negative, ω = 1.566(1), and ε = 1.531(1). The chemical composition (electron microprobe, H₂O measured with the Penfield method, wt %) is 18.43 B₂O₃, 65.71 MgO, 10.23 F, 9.73 H₂O, 4.31-O = F₂, where the total is 99.79. The empirical formula calculated on the basis of 6 anions pfu is as follows: Mg_3.03B_0.98[(OH)_2.00F_1.00]O_3.00. Hydroxylborite is hexagonal, and the space group is P6₃/m. The unit-cell dimensions are: a = 8.912(8) Å, c = 3.112(4) Å, V = 214.05(26) ų, and Z = 2. The strongest reflections in the X-ray powder pattern [d, Å (I, %)(hkil)] are: 7.69(52)(01\(\overline 1 \)0), 4.45(82)(11\(\overline 2 \)0), 2.573(65)(03\(\overline 3 \)0), 2.422(100)(02\(\overline 2 \)1), and 2.128(60)(12\(\overline 3 \)1). The compatibility index 1 ? (K _p/K _c) is 0.038 (excellent) for the calculated density and 0.044 (good) for the measured density. The type material of hydroxylborite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow (inventory number 91968) and the Geological Museum of the All-Russia Institute of Mineral Resources, Moscow (inventory number M-1663).     

Oxyvanite,V<Subscript>3</Subscript>O<Subscript>5</Subscript>, a new mineral species and the oxyvanite-berdesinskiite V<Subscript>2</Subscript>TiO<Subscript>5</Subscript> series from metamorphic rocks of the Slyudyanka Complex,southern Baikal region

Oxyvanite has been identified as an accessory mineral in Cr-V-bearing quartz-diopside meta- morphic rocks of the Slyudyanka Complex in the southern Baikal region, Russia. The new mineral was named after constituents of its ideal formula (oxygen and vanadium). Quartz, Cr-V-bearing tremolite and micas, calcite, clinopyroxenes of the diopside-kosmochlor-natalyite series, Cr-bearing goldmanite, eskolaite-karelianite dravite-vanadiumdravite, V-bearing titanite, ilmenite, and rutile, berdesinskiite, schreyerite, plagioclase, scapolite, barite, zircon, and unnamed U-Ti-V-Cr phases are associated minerals. Oxyvanite occurs as anhedral grains up to 0.1–0.15 mm in size, without visible cleavage and parting. The new mineral is brittle, with conchoidal fracture. Observed by the naked eye, the mineral is black, with black streak and resinous luster. The microhardness (VHN) is 1064–1266 kg/mm² (load 30 g), and the mean value is 1180 kg/mm². The Mohs hardness is about 7.0–7.5. The calculated density is 4.66(2) g/cm³. The color of oxyvanite is pale cream in reflected light, without internal reflections. The measured reflectance in air is as follows (λ, nm-R, %): 440-17.8; 460-18; 480-18.2; 520-18.6; 520-18.6; 540-18.8; 560-18.9; 580-19; 600-19.1; 620-19.2; 640-19.3; 660-19.4; 680-19.5; 700-19.7. Oxyvanite is monoclinic, space group C2/c; the unit-cell dimensions are a = 10.03(2), b = 5.050(1), c = 7.000(1) Å, β = 111.14(1)°, V = 330.76(5)ų, Z = 4. The strongest reflections in the X-ray powder pattern [d, Å, (I in 5-number scale)(hkl)] are 3.28 (5) (20\(\bar 2\)); 2.88 (5) (11\(\bar 2\)); 2.65, (5) (310); 2.44 (5) (112); 1.717 (5) (42\(\bar 2\)); 1.633 (5) (31\(\bar 4\)); 1.446 (4) (33\(\bar 2\)); 1.379 (5) (422). The chemical composition (electron microprobe, average of six point analyses, wt %): 14.04 TiO₂, 73.13 V₂O₃ (53.97 V₂O_3calc, 21.25 VO_2calc), 10.76 Cr₂O₃, 0.04 Fe₂O₃, 0.01 Al₂O₃, 0.02 MgO, total is 100.03. The empirical formula is (V _1.70 ³⁺ Cr_0.30)_2.0(V _0.59 ⁴⁺ Ti_0.41)_1.0O₅. Oxyvanite is the end member of the oxyvanite-berdesinskiite series with homovalent isomorphic substitution of V⁴⁺ for Ti. The type material has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Crystal chemistry of selenates with mineral-like structures. III. Heteropolyhedral chains in the crystal structure of [Mg(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>(SeO<Subscript>4</Subscript>)]<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)

The crystal structure of a new compound [Mg(H₂O)₄(SeO₄)]₂(H₂O) (monoclinic, P2 ₁/a, a = 7.2549(12), b = 20.059(5), c = 10.3934(17) Å, β = 101.989(13), V = 1479.5(5) ų) has been solved by direct methods and refined to R ₁ = 0.059 for 2577 observed reflections with |F _hkl | ≥ 4σ|F _hkl |. The structure consists of [Mg(H₂O)₄(SeO₄)]⁰ chains formed by alternating corner-sharing Mg octahedrons and (SeO₄)^2? tetrahedrons. O atoms of Mg octahedrons that are shared with selenate tetrahedrons are in a trans orientation. The heteropoly-hedral octahedral-tetrahedral chains are parallel to the c axis and undulate within the (010) plane. The adjacent chains are linked by hydrogen bonds involving H₂O molecules not bound with M²⁺ cations.     

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.     

Barioferrite BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>: A new mineral species of the magnetoplumbite group from the Haturim Formation in Israel

A new mineral barioferrite—a natural analogue of synthetic barium ferrite Ba Fe ₁₂ ³⁺ O₁₉—has been identified in the central part of a metamorphosed barite nodule in the rock of the Haturim Formation (Mottled Zone) on the southern slope of Mount Ye’elim in Israel. The mineral is associated with barite, calcite, magnetite, and maghemite and occurs as tiny platy crystals up to 3 × 15 × 15 μm and their irregular aggregates. Barioferrite is black with streaks of brown, and its luster is submetallic. Its Calculated density is 5.31 g/cm³. The mineral is brittle; cleavage is absent. IR absorption bands (cm^?1) are observed at 635 (shoulder), 582, 544, 433, and 405 (shoulder). Barioferrite is characterized by ferrimagnetic behavior. Under a microscope in reflected light, barioferrite is grayish white with brownish red internal reflections, the pleochroism is weak (from gray-white on R _o to gray-white with a brown tint on R _e), and the bireflectance is weak with distinct anisotropy. The reflectance values of R _o/R _e, % (λ, nm) are 24.51/22.80 (470), 24.17/22.25 (546), 23.65/21.68 (589), and 22.67/20.85 (650). The chemical composition (electron microprobe, wt %; the ranges are given in parentheses) is BaO 13.13 (12.5–13.8), Fe₂O₃ 86.47 (85.5–87.5), and 99.60 in total. The empirical formula is Ba_0.95Fe _12.03 ³⁺ O₁₉. Barioferrite is hexagonal with space group P6₃/mmc, a = 5.875 (3) Å, c = 23.137 (19) Å, V = 691.6 (5) ų, and Z = 2. The strongest lines of the X-ray powder diffraction pattern [d, Å, (I, 5) (hkl)] are 2.938(46) (110), 2.770(100) (107), 2.624 (84) (114, 200), 2.420(44) (203), 2.225(40) (205), and 1.627(56) (304, 2.0.11). The holotype specimen of barioferrite is deposited at the Mineralogical Museum of St. Petersburg State University; its catalogue number is 1/19436.     

Equation of state of synthetic qandilite Mg<Subscript>2</Subscript>TiO<Subscript>4</Subscript> at ambient temperature

Using a diamond-anvil cell and synchrotron X-ray diffraction, the compressional behavior of a synthetic qandilite Mg_2.00(1)Ti_1.00(1)O₄ has been investigated up to about 14.9 GPa at 300 K. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yield an isothermal bulk modulus (K _T0) of 175(5) GPa, with its first derivative \(K_{T0}^{{\prime }}\) attaining 3.5(7). If \(K_{T0}^{{\prime }}\) is fixed as 4, the K _T0 value is 172(1) GPa. This value is substantially larger than the value of the adiabatic bulk modulus (K _S0) previously determined by an ultrasonic pulse echo method (152(7) GPa; Liebermann et al. in Geophys J Int 50:553–586, 1977), but in general agreement with the K _T0 empirically estimated on the basis of crystal chemical systematics (169 GPa; Hazen and Yang in Am Miner 84:1956–1960, 1999). Compared to the K _T0 values of the ulvöspinel (Fe₂TiO₄; ~148(4) GPa with \(K_{T0}^{{\prime }} = 4\)) and the ringwoodite solid solutions along the Mg₂SiO₄–Fe₂SiO₄ join, our finding suggests that the substitution of Mg²⁺ for Fe²⁺ on the T sites of the 4–2 spinels can have more significant effect on the K _T0 than that on the M sites.     

Crystal chemistry of selenates with mineral-like structures. IV. Crystal structure of Zn(SeO<Subscript>4</Subscript>)(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>, a new compound with a mixed framework of the variscite type

The crystal structure of a new compound Zn(SeO₄)(H₂O)₂ (orthorhombic, Pbca, a = 9.0411(13), b = 10.246(2), c = 10.3318(15) Å, V = 957.1(3) ų) has been solved by direct methods and refined to R ₁ = 0.033 on the basis of 1076 observed reflections with |F _hkl | ≥ 4σ|F _hkl |. The structure contains one independent Zn²⁺ cation coordinated by two water molecules and four oxygen atoms of selenate group. The only independent (SeO₄)^2? tetrahedral oxoanion is tetradentate, sharing its corners with four adjacent [Zn²⁺O₂(H₂O₄)]²⁺ octahedrons. The structure can be described as consisting of heteropolyhedral sheets parallel to the (001) plane and linked together into a three-dimensional network. The compound belongs to the variscite structure type and is the first structurally characterized selenate of this group.     

Minerals with Brackebuschite-Like Structures: A Novel Solid Solution System Involving Cr<Superscript>6+</Superscript> and V<Superscript>5+</Superscript>

A novel complex continuous system of solid solutions involving vauquelinite Pb₂Cu(CrO₄)(PO₄)(OH), bushmakinite Pb₂Al(VO₄)(PO₄)(OH), ferribushmakinite Pb2Fe³⁺(VO₄)(PO₄)(OH), and a phase with the endmember formula Pb₂Cu(VO₄)(PO₄)(H₂O) or Pb₂Cu(VO₄)(РО₃ОН)(ОН) is studied based on samples from the oxidation zone of the Berezovskoe, Trebiat, and Pervomaisko-Zverevsky deposits in the Urals, Russia. This is the first natural system in which chromate and vanadate anions show a wide range of substitutions and the most extensive solid solution system involving (CrO₄)^2– found in nature. The major couple substitution is Cr⁶⁺ + Cu²⁺ ? V⁵⁺ + M³⁺, where M = Fe, Al. The correlation coefficients calculated from 125 point analyses are: 0.96 between V and (Fe + Al), 0.96 between Cr and (Cu + Zn),–0.96 between V and (Cu + Zn),–0.97 between Cr and (Fe + Al), and–0.97 between (Fe + Al) and (Cu + Zn). The substitutions V⁵⁺ ? Cr⁶⁺ (correlation coefficient–0.98) and to a lesser extent P⁵⁺ ? As⁵⁺ (correlation coefficient–0.86) occur at two types of tetrahedral sites, whereas the metal–nonmetal/metalloid substitutions, i.e., V or Cr for P or As, are minor. The substitution Fe³⁺ ? Al³⁺ is also negligible in this solid solution system.     

Pressure induced phase transition in Pb<Subscript>6</Subscript>Bi<Subscript>2</Subscript>S<Subscript>9</Subscript>

The crystal structure of Pb₆Bi₂S₉ is investigated at pressures between 0 and 5.6 GPa with X-ray diffraction on single-crystals. The pressure is applied using diamond anvil cells. Heyrovskyite (Bbmm, a = 13.719(4) Å, b = 31.393(9) Å, c = 4.1319(10) Å, Z = 4) is the stable phase of Pb₆Bi₂S₉ at ambient conditions and is built from distorted moduli of PbS-archetype structure with a low stereochemical activity of the Pb²⁺ and Bi³⁺ lone electron pairs. Heyrovskyite is stable until at least 3.9 GPa and a first-order phase transition occurs between 3.9 and 4.8 GPa. A single-crystal is retained after the reversible phase transition despite an anisotropic contraction of the unit cell and a volume decrease of 4.2%. The crystal structure of the high pressure phase, β-Pb₆Bi₂S₉, is solved in Pna2 ₁ (a = 25.302(7) Å, b = 30.819(9) Å, c = 4.0640(13) Å, Z = 8) from synchrotron data at 5.06 GPa. This structure consists of two types of moduli with SnS/TlI-archetype structure in which the Pb and Bi lone pairs are strongly expressed. The mechanism of the phase transition is described in detail and the results are compared to the closely related phase transition in Pb₃Bi₂S₆ (lillianite).     

Crystal chemistry of selenates with mineral-like structures: VII. The structure of (H<Subscript>3</Subscript>O)[(UO<Subscript>2</Subscript>)(SeO<Subscript>4</Subscript>)(SeO<Subscript>2</Subscript>OH)] and some structural features of selenite-selenates

The crystal structure of a new compound, (H₃O)[(UO₂)(SeO₄)(SeO₂OH)] (monoclinic, P2₁/n, a = 8.6682(19), b = 10.6545(16), c = 9.846(2) Å, β = 97.881(17)°, V = 900.7(3) ų), was solved by direct methods and refined to R ₁ = 0.050. The structure contains two symmetrically different Se atoms. The Se1 site is coordinated by three O atoms as is characteristic of Se⁴⁺ cations. The Se2 site is coordinated by four O atoms and forms selenate anion SeO ₄ ^2? . The structure is based on selenite-selenate sheets [(UO₂)(SeO₄)(SeO₂OH)]^? linked by the interlayer H₃O^? ions. The sheets are parallel to (101). The structure is compared to that of schmiederite, Pb₂Cu₂(SeO₃)(SeO₄)(OH)₄.     

Ivsite,Na<Subscript>3</Subscript>H(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>, a new mineral from volcanic exhalations of fumaroles of the Fissure Tolbachik Eruption of the 50th Anniversary of the Institute of Volcanology and Seismology,Far East Branch,Russian Academy of Sciences

Fine-granular (<0.1 mm) flattened colorless transparent crystals of ivsite form white aggregates. The empirical formula (Na_2.793Cu_0.056)_2.849HS_2.016O₈ is close to the ideal Na₃H(SO₄)₂. The structure was refined up to R = 0.040. Ivsite has a monoclinic symmetry, P2₁/c, a = 8.655(1) Å, b = 9.652(1) Å, c = 9.147(1) Å, β = 108.76(1)°, V = 723.61(1) ų, Z = 4. Na atoms occur at six- and seven-fold sites (NaO₆ and NaO₇); S atoms, in isolated SO₄ tetrahedrons; these polyhedrons form a three-dimensional framework. The diagnostic lines of powder diffraction patterns (d[Å]–I–hkl) are 4.010–53–12-1, 3.949–87–012, 3.768–100–210, 3.610–21–20-2, 3.022–22–031, 2.891–42–22-2, 2.764–49–31-1, and 2.732–70–13-1.     

Synthesis,TEM characterization and thermal behaviour of LiNiSi<Subscript>2</Subscript>O<Subscript>6</Subscript> pyroxene

A pyroxene with composition LiNiSi₂O₆ was synthesized at T = 1,473 K and P = 2.0 GPa; the cell parameters at T = 298 K are a = 9.4169(6) Å, b = 8.4465(7) Å, c = 5.2464(3) Å, β = 110.534(6)°, V = 390.78(3) Å³. TEM examination of the LiNiSi₂O₆ pyroxene showed the presence of h + k odd reflections indicative of a primitive lattice, and of antiphase domains obtained by dark field imaging of the h + k odd reflections. A HT in situ investigation was performed by examining TEM selected area diffraction patterns collected at high temperature and synchrotron radiation powder diffraction. In HTTEM the LiNiSi₂O₆ was examined together with LiCrSi₂O₆ pyroxene. In LiCrSi₂O₆ the h + k odd critical reflections disappear at about 340 K; they are sharp up to the transition temperature and do not change their shape until they disappear. In LiNiSi₂O₆ the h + k odd reflections are present up to sample deterioration at 650 K. A high temperature synchrotron radiation powder diffraction investigation was performed on LiNiSi₂O₆ between 298 and 773 K. The analysis of critical reflections and of changes in cell parameters shows that the space group is P-centred up to the highest temperature. The comparative analysis of the thermal and spontaneous strain contributions in P2₁/c and C2/c pyroxenes indicates that the high temperature strain in P-LiNiSi₂O₆ is very similar to that due to thermal strain only in C2/c spodumene and that a spontaneous strain contribution related to pre-transition features is not apparent in LiNiSi₂O₆. A different high-temperature behaviour in LiNiSi₂O₆ with respect to other pyroxenes is suggested, possibly in relation with the presence of Jahn–Teller distortion of the M1 polyhedron centred by low-spin Ni³⁺.     

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.     

Bortnikovite,Pd<Subscript>4</Subscript>Cu<Subscript>3</Subscript>Zn,a new mineral species from the unique Konder placer deposit,Khabarovsk krai,Russia

Bortnikovite, a new mineral species that is an intermetallic compound of Pd, Cu, and Zn with the simplified formula Pd₄Cu₃Zn has been detected at the unique Konder placer deposit in the Ayan-Maya district, Khabarovsk krai. The primary source of this placer is a concentrically zoned alkaline ultramafic massif. The X-ray diffraction pattern is indexed on the assumption of a tetragonal unit cell: a = 6.00 ± 0.02 Å and c = 8.50 ± 0.03 Å, V = 306 ± 0.01 ų, Z = 3, probable space group P4/mmm. The calculated density is 11.16 g/cm³; the mean microhardness VHN is 368 kg/mm². In reflected light, the new mineral is white with a slight grayish beige tint; bireflectance, anisotropy, and internal reflections are not observed. The reflectance spectrum belongs to the concave group of the anomalous type. The measured values of reflectance are as follows: 56.9 (470 nm), 61.7 (546 nm), 63.4 (589 nm), and 65.4% (650 nm). The new mineral is intergrown with isoferroplatinum, titanite, perovskite, V-bearing magnetite, bornite, and chlorite. The origin of bortnikovite is related to the effect of alkaline fluid on ultramafic rocks. The new mineral is named in honor of Professor Nikolai Stefanovich Bortnikov, a prominent mineralogist and researcher of ore deposits and a corresponding member of the Russian Academy of Sciences. Bortnikovite is the first platinum group mineral that contains Zn as a major mineralforming element.     

Structural investigations of (Ca,Sr)ZrO<Subscript>3</Subscript> and Ca(Sn,Zr)O<Subscript>3</Subscript> perovskite compounds

(Ca _x ,Sr_1?x )ZrO₃ and Ca(Sn _y ,Zr_1-y )O₃ solid solutions were synthesized by solid-state reaction at high temperature before to be studied by powder X-ray diffraction and Raman Spectroscopy. Diffraction data allow the distortion of the ABO₃ perovskite structure to be investigated according to cations substitution on A and B-sites. It is shown that distortion, characterized by Φ, the tilt angle of BO₆ octahedra, slightly increases with decreasing y content in Ca(Sn _y ,Zr_1?y )O₃ compounds and strongly decreases with decreasing x content in (Ca _x ,Sr_1?x )ZrO₃ compounds. Such results are discussed in view of the relative A and B cation sizes. Raman data show that vibrational spectra are strongly affected by the cation substitution on A-site; the frequencies of most vibrational modes increase with increasing x content in (Ca _x ,Sr_1?x )ZrO₃ compounds, i.e. with the decreasing mean size of the A-cation; the upper shift is observed for the 358 cm^?1 mode (?ν/?r = ?60.1 cm^?1/Å). On the other hand, the cation substitution on B-sites, slightly affect the spectra; it is shown that in most cases, the frequency of vibrational modes increases with increasing y content in Ca(Sn _y ,Zr_1?y )O₃ compounds, i.e. with the decreasing mean size of the B-cation, but that two modes (287 and 358 cm^?1) behave differently: their frequencies decrease with the decreasing mean size of the B-cation, with a shift respectively equal to +314 and +162 cm^?1/Å. Such results could be used to predict the location of different elements such as trivalent cations or radwaste elements on A- or B-site, in the perovskite structure.