Fabrice Dal Bo

Strontiohurlbutite, SrBe2(PO4)2, a new mineral from Nanping No. 31 pegmatite, Fujian Province, Southeastern China

Abstract Strontiohurlbutite, ideally SrBe2(PO4)2, is a new member of hurlbutite group discovered in the Nanping No. 31 pegmatite, Fujian province, southeastern China. Crystals are mainly found in zones I, II, and IV; they are platy, subhedral-to-anhedral, with a length from 5 mm to 1.5 mm. Associated minerals mainly include quartz, muscovite, beryl, hurlbutite, hydroxylherderite, apatite-group minerals, and phenakite. Strontiohurlbutite crystals are light blue, translucent-to-transparent, and have vitreous luster. The Mohs hardness is about 6, and the tenacity is brittle. Optically, strontiohurlbutite is biaxial (-), α = 1.563(3), β = 1.569(2), γ = 1.572(3) (white light), 2Vmeas = 68.5(5)°, and exhibits weak dispersion, r > v. The optical orientation is X = b, Y ≈ c. Electron-microprobe and SIMS analyses (average of 16) give SrO 29.30, P2O5 51.05, CaO 0.91, BaO 0.64, and BeO 17.71 wt%; total 99.61 wt%. The empirical formula, based on 8 O apfu, is (Sr0.81Ca0.05Ba0.01)S0.87Be2.02P2.05O8. The stronger eight lines of the measured X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 3.554(100)(121); 3.355(51)(211); 3.073(38)(022); 2.542(67)(113); 2.230(42)(213); 2.215(87)(321); 2.046(54)(223); 1.714(32)(143). Strontiohurlbutite is monoclinic, space group P21/c; unit-cell parameters refined from single-crystal X-ray diffraction data are: α = 7.997(3), β = 8.979(2), γ = 8.420(7) Å, b = 90.18(6)°, V = 604.7(1) Å3 (Z = 4, calculated density = 3.101 g/cm3). The mineral is isostructural with hurlbutite, CaBe2(PO4)2, and with paracelsian, BaAl2Si2O8. The formation of strontiohurlbutite is related to the hydrothermal alteration of primary beryl by late Sr- and P-rich fluids.

Fe6.67(PO4)5.35(HPO4)0.65 and Fe6.23(PO4)4.45(HPO4)1.55: two new mixed-valence iron phosphates

Two new mixed-valence iron phosphates, namely heptairon pentaphosphate hydrogen phosphate, Fe(6.67)(PO(4))(5.35)(HPO(4))(0.65), and heptairon tetraphosphate bis(hydrogen phosphate), Fe(6.23)(PO(4))(4.45)(HPO(4))(1.55), have been synthesized hydrothermally at 973 K and 0.1 GPa. The structures are similar to that of Fe(II)(3)Fe(III)(4)(PO(4))(6) and are characterized by infinite chains of Fe polyhedra parallel to the [101] direction. These chains are formed by the Fe1O(6) and Fe2O(6) octahedra, alternating with the Fe4O(5) distorted pentagonal bipyramids, according to the stacking sequence ...Fe1-Fe1-Fe4-Fe2-Fe2.... The Fe3O(6) octahedra and PO(4) tetrahedra connect the chains together. Fe(II) is localized on the Fe3 and Fe4 sites, whereas Fe(III) is found in the Fe1 and Fe2 sites, according to bond-valence calculations. Refined site occupancies indicate the presence of vacancies on the Fe4 site, explained by the substitution mechanism Fe(II) + 2(PO(4)(3-)) = vacancies + 2(HPO(4)(2-)).

Li0.97FeII0.79FeIII0.15(PO4), a new oxidized triphylite-type phosphate

This paper reports a new partially oxidized triphylite-type phosphate (lithium iron phosphate), which has been synthesized hydrothermally at 973 K and 0.1 GPa. The structure is similar to that of natural triphylite, LiFe(PO(4)), and is characterized by two chains of edge-sharing octahedra parallel to the b axis. The weakly distorted M1 octahedra contain Li atoms, whereas the more strongly distorted M2 octahedra contain Fe(II) and Fe(III) atoms. Refined site occupancies and bond-valence analysis show the presence of Fe(III) and vacancies on the M2 site, mainly explained by the substitution mechanism 3 Fe(II) = 2 Fe(III) + vacancies.

Synthesis, IR spectroscopy and crystal structure of [(UO2)2{Be(H2O)2(PO4)2}]·(H2O), the first compound with a trimer beryllophosphate anion

Abstract The first uranyl beryllophosphate, [(UO2)2{Be(H2O)2(PO4)2}]·(H2O), has been synthesized under hydrothermal conditions at 200°C. The monoclinic unit-cell parameters are: a=9.3361(1), b=8.8545(4), c=9.6592(10) Å, β=93.211(1)°, V=797.21(6) Å3, space group P2/n, Z=2. The crystal structure has been solved by direct methods and refined to final R1=4.92% using 1294 I>3σ(I) reflections in the anisotropic approximation. The structure consists of sheets of UrO5 pentagonal bipyramids and PO4 tetrahedra. UrO5 bipyramids are linked by edge-sharing to form infinite chains. Adjacent chains of UrO5 bipyramids are connected by sharing alternating edges of uranyl bipyramids with PO4 tetrahedra. The resulting sheets are based on the well-known uranophane anion-topology. Be atoms are tetrahedrally coordinated by two oxygen atoms of PO4 tetrahedra and two water molecules in the interlayer space. One isolated water molecule also occurs in the interlayer space, where it is held in position by H bonds. The connection between the phosphorus and beryllium tetrahedra leads to formation of an unbranched trimer [BeP2O8(H2O)2]4− observed for the first time in inorganic oxysalts.

Mengxianminite (Ca2Sn2Mg3Al8[(BO3)(BeO4)O6]2) a new borate mineral from Xianghualing skarn, Hunan Province, China, with a highly unusual chemical combination (B + Be + Sn)

Abstract Mengxianminite, ideally Ca2Sn2Mg3Al8[(BO3)(BeO4)O6]2, is a new borate mineral from Xianghualing skam, Hunan Province, southern China. It occurs in the hsianghualite vein of Xianghualing skarn, associated with fluorite, phlogopite, hsianghualite, magnetite, dravite, magnesiotaaffeite-2N‘2S, and calcite. Mengxianminite forms subhedral to euhedral green crystals from 20 to 200 mm long, translucent to transparent, with a vitreous luster. The crystals show perfect cleavage on {100} and good cleavage on {010}, and do not fluoresce in long- or short-wave ultraviolet light. The estimated Mohs hardness is 8, and the tenacity is brittle with irregular fracture. The calculated density is 4.170 g/cm3. Optically, mengxianminite is biaxial (–), with α = 1.80(2), β = 1.83(2), γ = 1.84(2) (589 nm). The mean chemical composition of mengxianminite is Al2O3 40.00, SnO2 25.96, MgO 6.57, CaO 8.56, FeO 4.83, B2O3 6.53, BeO 4.37, ZnO 1.81, MnO 1.23, Na2O 1.13, TiO2 0.10, SiO2 0.04, sum 101.12 with a corresponding empirical formula calculated on the basis of 26 O atoms of (Ca1.64,Na0.39)Σ2.03(Sn1.85,Zn0.24)Σ2.09(Mg1.75, Fe0.72,Al0.42,Mn0.19,Ti0.01)Σ3.09Al8[(B1.01O3)(Be0.94O4)O6]2. (Be and B were measured by secondary ion mass spectrometry, average of six electron microprobe analyze points and in wt%.) The strongest eight lines of the powder XRD pattern [d in Å (I)(hkl)] are: 3.000 (35)(16.2.0); 2.931 (100)(17.1.1); 2.475 (29)(022); 2.430 (30)(13.3.1); 2.375 (100)(14.0.2/640); 2.028 (52)(21.3.1); 1.807 (35)(913); 1.530 (98)(14.6.0/15.3.3). Mengxianminite is orthorhombic, space group Fdd2; unit-cell parameters refined from single-crystal X-ray diffraction data are: a = 60.699(4), b = 9.914(1), c = 5.745(1) Å, V = 3457.4(4) Å3, and Z = 8. The structure of mengxianminite is characterized by the alternating O-T1-O-T2-O′-T2 layers stacked along the a axis, which are equal to two alternating modules: the module A (O-T1-O) corresponding to the spinel module with an additional O layer (AlO6 octahedra layer), and the module B (T2-O′-T2) showing the simplified formula CaSnAl(BeO4)(BO3), where SnO6 octahedra are isolated in the T2 layers, connected via BeO4 and CaO11 groups, and AlO6 edge-sharing octahedra in the O′ layer form chains running along the {011} or {011} direction, connected in the c direction by the BO3 triangular groups. Mengxianminite is the first borate mineral with both Sn and Be, likely crystallized under F-rich conditions at late stages of the Xianghualing skarn.

Structural variations of olivine-type phosphates : a good example of how minerals can inspire the development of new materials.

Phosphates of the triphylite-lithiophilite series [LiFePO4-LiMnPO4] occur in the geological context of granitic pegmatites, where they form masses that can reach several meters in diameter. During the oxidation processes affecting the pegmatites, these olivine-type phosphates progressively transform to ferrisicklerite– sicklerite [Li1-x(Fe ,Mn)(PO4)-Li1¬x(Mn 2+,Fe3+) (PO4)] and to heterosite-purpurite [(Fe 3+,Mn3+) (PO4)-(Mn ,Fe)(PO4)], according to the substitution mechanism Li+ + Fe2+ → [] + Fe3+. This oxidation mechanism was described by mineralogists in the 1940’s, based on petrographic observations of phosphates under the polarizing microscope and on chemical data [1,2]. In 1997, Padhi et al. [3] demonstrated the efficiency of triphylite-type phosphates as cathode material for Li-ion batteries. Such LiFePO4-based batteries are actually produced industrially, and are used as power sources for electric cars, laptops, or mobile phones. The crystal structure of minerals of the triphylite¬lithiophilite series (triphylite: a = 4.690, b = 10.286, c = 5.987 Å, Pbnm) is characterized by two types of octahedral sites: the M(1) octahedra occupied by Li, and the M(2) sites occupied by Fe and Mn. A natural sample from the Altai Mountains, China, was recently investigated by Hatert et al. [4], in order to understand the structural variations occurring during the oxidation of lithiophilite into sicklerite. Five single-crystals, corresponding to intermediate members of the lithiophilite-sicklerite series, were extracted from a thin section and are orthorhombic, space group Pbnm, with unit-cell parameters ranging from a = 4.736(1), b = 10.432(2), c = 6.088(1) Å (lithiophilite) to a = 4.765(1), b = 10.338(2), c = 6.060(1) Å (sicklerite). The structures show a topology identical to that of olivine-type phosphates, with Li occurring on the M(2) site and showing occupancy factors from 0.99 Li atoms per formula unit (p.f.u.) (lithiophilite) to 0.75 Li p.f.u. (sicklerite). Natrophilite, NaMnPO4, is another pegmatite phosphate with the olivine structure, in which the M(1) site is occupied by Na while the M(2) site contains the smaller divalent cations. Recently, the Fe-analogue of natrophilite was found at the Malpensata granitic pegmatite, Colico commune, Lecco province, north Italy [5]. This phosphate, Na(Fe2+,Mn2+) PO4, is orthorhombic, space group Pbnm, a =4.882(1)Å, b = 10.387(2)Å, c = 6.091(1) Å, V = 308.9(1)Å3, and Z = 4. The mineral shows the olivine structure, with M(1) occupied by Na and M(2) occupied by Fe and Mn. In order to elucidate the phase relations among lithiumiron phosphates, we decided to investigate the Li-Fe2+-Fe3+ (+PO4) system hydrothermally between 400 and 700°C, at 1 kbar pressure. These experiments first allowed to determine the stability fields of several phosphate assemblages. A black crystal of partially oxidized triphylite has been synthesized during these experiments, and its crystal structure has been solved in the Pnma space group (a = 10.306(4), b = 6,004(2), c = 4,69(1)Å, R1= 0.041). The structural data, electron-microprobe analysis, as well as the colour of this phosphate, indicate that this triphylite-type compound contains both Fe2+ and Fe3+; the insertion of Fe3+ in the structure is achieved through the substitution mechanism 3Fe2+ = 2Fe3+ + [] [6].