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Nefedovite, Na5Ca4(PO4)4F, has been investigated by in situ high-temperature powder (30–690 °C) and single crystal (27–827 °C) X-ray diffraction and Raman spectroscopy. Nefedovite is tetragonal, space group I-4, a = 11.6560(2), c = 5.4062(2) Å, V = 734.50(2) Å3 (R1 = 0.0149). Nefedovite is a 1D antiperovskite, since its crystal structure contains chains of corner-sharing anion-centered [FCa4Na2]9+ octahedra. The chains are parallel to the c direction. Nefedovite is stable up to 727 °C and undergoes a displacive phase transition in the temperature range 277–327 °C. With increasing temperature, the PO4 tetrahedra in the crystal structure of nefedovite gradually rotate around the imaginary fourfold inversion axes aligning the O2…O3 edge parallel to [110], which ultimately leads to the appearance of the mirror plane perpendicular to the c direction and the change of space group from I-4 (82) to I4/m (87). The crystal structure of nefedovite expands strongly anisotropically with the direction of the maximum thermal expansion oriented perpendicular to the chains of anion-centered octahedra. The information-based structural complexity analysis demonstrates that both low- and high-temperature modifications of nefedovite are structurally simple with the IG,total value less than 100 bits per unit cell. The structural complexity decreases along the phase transition, which is typical for displacive phase transitions. [ABSTRACT FROM AUTHOR]

Behaviour of hingganite-(Y), Y2□Be2Si2O8(OH)2, on compression to 47 GPa has been studied by synchrotron-based in situ high-pressure single-crystal X-ray diffraction at room temperature in a diamond anvil cell. In the studied pressure range no obvious phase transitions have been observed. The compression of hingganite-(Y) crystal structure is anisotropic, with b axis showing the maximal compressibility. A fit of the experimental pressure–volume data by the Birch-Murnaghan third-order equation of state yielded the bulk modulus of 131(2) GPa and its pressure first derivative of 3.5(2). The difference between high-pressure behaviour of hingganite-(Y) and structurally related datolite is governed by the different chemical nature of interlayer cations. [ABSTRACT FROM AUTHOR]

Manaevite-(Ce), a new vesuvianite-group mineral has been investigated by means of electron microprobe, TGA and DSC and CHN analysis of H2O, powder X-ray diffraction, single-crystal X-ray structure analysis, 139La NMR, 57Fe Mössbauer spectroscopy, IR spectroscopy and optical measurements. Tetragonal unit-cell parameters are a = 15.9247(13) Å, c = 11.9661(10) Å, space group P4/nnc. The structure model was solved and refined to R1 = 3.35% for 1757 independent observed reflections with I > 4σ(I). Manaevite-(Ce) is the first vesuvianite-group mineral with the species-defining role of REE3+ at the X3 site. The mineral contains two different kinds of hydroxyl anions. The first type of hydroxyl groups is associated with the O10 and O11 sites as observed for other vesuvianite-group members. Another type of OH groups is due to the hydrogarnet substitution (H4O4)4‒ ↔ (SiO4) 4‒ associated with the Z1 and Z2 sites. The incorporation of REE3+ into the crystal structure of manaevite-(Ce) proceeds via the substitution schemes 2Ca2+ ↔ Th4+ + □ and 3Ca2+ ↔ 2REE3+ + □, which results in the formation of vacancies at the X3 site and the presence of H2O molecules. [ABSTRACT FROM AUTHOR]

Thermal behavior of three copper molybdates, lindgrenite, Cu3(MoO4)2(OH)2, szenicsite Cu3(MoO4)(OH)4, and cupromolybdite, Cu3O(MoO4)2, has been studied by high-temperature X-ray powder diffraction in the temperature range of 25–900 °C. The decomposition of lindgrenite and formation of cupromolybdite were observed at T > 325 °C according to the reaction: Cu3(MoO4)2(OH)2 → Cu3O(MoO4)2 + H2O. Szenicsite decomposes to cupromolybdite and tenorite at T > 350 °C according to the reaction: 2Cu3(MoO4)(OH)4 → Cu3O(MoO4)2 + 3CuO + 2H2↑. Cupromolybdite is stable up to 825 °C. The thermal expansion of lindgrenite, szenicsite and cupromolybdite is strongly anisotropic; the values of αmax/αmin are 5.6, 11.0 and 4.3, respectively. The maximal/minimal thermal expansion refers to the dominant direction of long/short Cu–O bonds owing to the distortion of CuO6 octahedral geometry due to the Jahn–Teller effect. For all three Cu molybdates, there are more or less aligned orientations of Jahn–Teller-distorted (CuO6) octahedra, which allows calculating the average 〈Cu–O〉 bond lengths along particular crystallographic directions. The 〈Cu–O〉 values observed are found to be in good correlation with the observed anisotropy of thermal expansion. The additional O2− anions in cupromolybdite act as coordination centers that form four strong Cu–O bonds each. These bonds propagate along the direction of the minimal thermal expansion, thus showing that the anion-centered structural motifs in cupromolybdite are the strongest after the Mo6+-centered (MoO4) tetrahedra. [ABSTRACT FROM AUTHOR]

Zuktamrurite, FeP2, is a new mineral, a natural iron diphosphide found in the pyrometamorphic rocks of the Hatrurim Formation, in the southern part of the Negev Desert, Israel and on the Transjordan Plateau, Jordan. The mineral occurs as irregular grains up to 50 µm in size associated with murashkoite, FeP, and barringerite, (Fe,Ni)2P. In reflected light, zuktamrurite is white with a distinct bluish tint. It is non-pleochroic but exhibits distinct anisotropy in bluish colours. Reflectance values for the IMA COM recommended wavelengths are [Rmax/Rmin, % (λ, nm)]: 50.40/47.20 (470); 49.16/46.23 (546); 48.97/46.16 (589); 49.40/46.40 (650). It is brittle. Electron microprobe analysis of the holotype specimen gave the following chemical composition (wt%, average of 5 points): Fe 40.23; Ni 7.97; P 51.70; total 99.90. The empirical formula calculated on the basis of 3 apfu is (Fe0.86Ni0.16)1.02P1.98 corresponding to FeP2. Zuktamrurite is orthorhombic, space group Pnnm, unit cell parameters refined from the single-crystal data: a 4.9276(6), b 5.6460(7), c 2.8174(4) Å, V 78.38(1) Å3, Z = 2. Dx = 5.003 g cm−3. The crystal structure was solved and refined to R1 = 0.0121 on the basis of 109 unique reflections with I > 2σ(I). The strongest lines of the powder X-ray diffraction pattern [(d, Å) (I, %) (hkl)]: 3.714 (54) (110); 2.820 (31) (020); 2.451 (100) (120, 101); 2.242 (55) (111); 1.760 (37) (211). The mineral is named for the Zuk-Tamrur cliff (Dead Sea) located nearby the type locality, the Halamish Wadi, southern Negev Desert, Israel. Zuktamrurite is the phosphide analogue of löllingite (loellingite), FeAs2. It is the most phosphorus-rich phosphide ever found in nature. [ABSTRACT FROM AUTHOR]

Philipsburgite, Cu5Zn((As,P)O4)2(OH)6·H2O, from the Middle Pit, Gold Hill Mine, Tooele Co., Utah, USA, was studied by single-crystal X-ray diffraction and scanning electron microscopy. The empirical formula of the studied sample is (Cu4.69Zn1.23)(As0.86P0.18O4)2(OH)5.61·H2O, which agrees well with the previous reports on the mineral. Philipsburgite is monoclinic, P21/c, a = 12.385(6), b = 9.261(4), c = 10.770(5) Å, β = 97.10(1)o, V = 1225.7(9) Å3 (at 100 K), and Z = 4. The crystal structure was refined to R1 = 0.046 for 2563 unique observed reflections with |Fo| ≥ 4σF. The crystal structure of philipsburgite is isotypic to that of kipushite and can be considered as a complex three-dimensional framework consisting of two types of layers stacked parallel to the a-axis. The A-type layer is formed by the edge-sharing Jahn-Teller-distorted Cuφ6 octahedra [φ = O2−, (OH)−, H2O]. Two adjacent octahedral layers are linked via (As2O4) tetrahedra. The B-type layer is built by corner-sharing (ZnO4) and (As1O4) tetrahedra and is formed by the four- and eight-membered tetrahedral rings. The A:B ratio of the A and B layers is equal to 2:1. The hydrogen bonding network in philipsburgite is rather complex and consists of two- and three-center hydrogen bonds. The As1 site accommodates ca. 18% of P and is a preferable position for the P substitution in philipsburgite. The observed selectivity of the As1 site for P may indicate that, for the intermediate compositions with the P:As ratios close to 1:1, there is a fully ordered species with P prevalent at the As1 site and As prevalent at the As2 site. The intermediate composition would, therefore, be Cu5Zn(AsO4)(PO4)(OH)6·H2O and such a mineral can be considered as a separate species, according to the rules of the International Mineralogical Association (IMA). Philipsburgite should be considered as structurally complex with the Shannon information contents of 4.954 bits/atom and 614.320 bits/cell. The obvious reason for the structural complexity of the mineral is its modularity, i.e., the presence of two structurally distinct modules, the octahedral-tetrahedral (A) and tetrahedral (B) layers. [ABSTRACT FROM AUTHOR]

Thermal behavior of three copper molybdates, lindgrenite, Cu3(MoO4)2(OH)2, szenicsite Cu3(MoO4)(OH)4, and cupromolybdite, Cu3O(MoO4)2, has been studied by high-temperature X-ray powder diffraction in the temperature range of 25–900 °C. The decomposition of lindgrenite and formation of cupromolybdite were observed at T > 325 °C according to the reaction: Cu3(MoO4)2(OH)2 → Cu3O(MoO4)2 + H2O. Szenicsite decomposes to cupromolybdite and tenorite at T > 350 °C according to the reaction: 2Cu3(MoO4)(OH)4 → Cu3O(MoO4)2 + 3CuO + 2H2↑. Cupromolybdite is stable up to 825 °C. The thermal expansion of lindgrenite, szenicsite and cupromolybdite is strongly anisotropic; the values of αmax/αmin are 5.6, 11.0 and 4.3, respectively. The maximal/minimal thermal expansion refers to the dominant direction of long/short Cu–O bonds owing to the distortion of CuO6 octahedral geometry due to the Jahn–Teller effect. For all three Cu molybdates, there are more or less aligned orientations of Jahn–Teller-distorted (CuO6) octahedra, which allows calculating the average 〈Cu–O〉 bond lengths along particular crystallographic directions. The 〈Cu–O〉 values observed are found to be in good correlation with the observed anisotropy of thermal expansion. The additional O2− anions in cupromolybdite act as coordination centers that form four strong Cu–O bonds each. These bonds propagate along the direction of the minimal thermal expansion, thus showing that the anion-centered structural motifs in cupromolybdite are the strongest after the Mo6+-centered (MoO4) tetrahedra. [ABSTRACT FROM AUTHOR]

Zuktamrurite, FeP2, is a new mineral, a natural iron diphosphide found in the pyrometamorphic rocks of the Hatrurim Formation, in the southern part of the Negev Desert, Israel and on the Transjordan Plateau, Jordan. The mineral occurs as irregular grains up to 50 µm in size associated with murashkoite, FeP, and barringerite, (Fe,Ni)2P. In reflected light, zuktamrurite is white with a distinct bluish tint. It is non-pleochroic but exhibits distinct anisotropy in bluish colours. Reflectance values for the IMA COM recommended wavelengths are [Rmax/Rmin, % (λ, nm)]: 50.40/47.20 (470); 49.16/46.23 (546); 48.97/46.16 (589); 49.40/46.40 (650). It is brittle. Electron microprobe analysis of the holotype specimen gave the following chemical composition (wt%, average of 5 points): Fe 40.23; Ni 7.97; P 51.70; total 99.90. The empirical formula calculated on the basis of 3 apfu is (Fe0.86Ni0.16)1.02P1.98 corresponding to FeP2. Zuktamrurite is orthorhombic, space group Pnnm, unit cell parameters refined from the single-crystal data: a 4.9276(6), b 5.6460(7), c 2.8174(4) Å, V 78.38(1) Å3, Z = 2. Dx = 5.003 g cm−3. The crystal structure was solved and refined to R1 = 0.0121 on the basis of 109 unique reflections with I > 2σ(I). The strongest lines of the powder X-ray diffraction pattern [(d, Å) (I, %) (hkl)]: 3.714 (54) (110); 2.820 (31) (020); 2.451 (100) (120, 101); 2.242 (55) (111); 1.760 (37) (211). The mineral is named for the Zuk-Tamrur cliff (Dead Sea) located nearby the type locality, the Halamish Wadi, southern Negev Desert, Israel. Zuktamrurite is the phosphide analogue of löllingite (loellingite), FeAs2. It is the most phosphorus-rich phosphide ever found in nature. [ABSTRACT FROM AUTHOR]