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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 µm 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)Σ0.87Be2.02P2.05O8. 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: a = 7.997(3), b = 8.979(2), c = 8.420(7) Å, β = 90.18(6)°, V = 604.7(1) ų (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. [ABSTRACT FROM AUTHOR]

Karenwebberite, Na(Fe2+,Mn2+)PO4, belongs to the triphylite group of minerals and corresponds to the Fe-equivalent of natrophilite or to the Na-equivalent of triphylite. It occurs in the Malpensata pegmatite dike, Colico, Lecco Province, Italy. Karenwebberite is found as late-magmatic-stage exsolution lamellae up to 100 µm thick, hosted by graftonite and associated with Na-bearing ferrisicklerite and with a heterosite-like phase. Lamellae are pale green, with very pale grayish-green streak. The luster is greasy to vitreous, and lamellae are translucent (pale green) to opaque (dark green). Optically, the mineral is anisotropic, biaxial (+), α = 1.701(2), β = 1.708(2), γ = 1.717(2) (for λ = 589 nm), 2Vmeas = 87(4)°, 2Vcalc = 41°, Z = b. Pleochroism is moderate with X = dark gray, Y = brown, and Z = yellow. The mineral is brittle with a Mohs hardness of 4.5; in thin section it displays a perfect cleavage along {001} with an irregular fracture. Karenwebberite is non-fluorescent either under short-wave or long-wave ultraviolet light, and its calculated density is 3.65 g/cm³. The mean chemical composition, determined by the electron microprobe from 16 point analyses (wt%), is: P2O5 41.12, Fe2O3* 7.00, FeO* 25.82, MgO 0.23, ZnO 0.11, MnO 9.31, CaO 0.10, Na2O 14.66, total 98.41 (*: calculated values). The empirical formula, calculated on the basis of 1 P atom per formula unit from, is (Na0.817Ca0.003□0.180)Σ1.000 (Fe0.6222+Mn0.1512+Mg0.010Zn0.002)Σ1.013PO4. Karenwebberite is orthorhombic, space group Pbnm, a = 4.882(1), b = 10.387(2), c = 6.091(1) Å, V = 308.9(1) ų, and Z = 4. The mineral possesses the olivine structure, with the M1 octahedra occupied by Na, and the M2 octahedra occupied by Fe and Mn. The eight strongest lines in the X-ray powder pattern are [d in Å (intensities) (hkl)]: 5.16 (50) (020), 4.44 (90) (110), 3.93 (80) (021), 3.56 (90) (120), 3.04 (80) (002), 2.817 (100) (130), 2.559 (100) (131), and 1.657 (50) (061). The mineral is named in honor of Karen Louise Webber, Assistant Professor Research at the Mineralogy, Petrology and Pegmatology Research Group, Department of Earth and Environmental Sciences, University of New Orleans, Louisiana, U.S.A. [ABSTRACT FROM AUTHOR]

Single crystals of iron and manganese phosphate Fe 6.36Mn 0.64(PO 3(OH)) 4(PO 4) 2 was synthesized by hydrothermal method. The compound crystallizes in the Fe 7(PO 4) 6 structure type and is isotypic with the solid solution $$ {\text{M}}_{{7 - {\text{x}}}} {\text{M}}_{\text{x}}^{\prime} \left( {{\text{HPO}}_{4} } \right)_{4} \left( {{\text{PO}}_{4} } \right)_{2} $$ where M is Fe, Co, Mg, Mn. The compound is triclinic, P-1, a = 6.571(5), b = 7.993(3), c = 9.547(2) Ǻ, α = 103.97(1)°, β = 109.29(2)°, γ = 101.57(3)°. The structure is based on a three-dimensional framework of distorted edge-sharing MO 6 and MO 5 polyhedra, forming infinite chains, which are interlinked by corner-sharing with PO 4 tetrahedra. The formula unit is centrosymmetric, with all atoms in general positions except for one Fe atom, which has site symmetry −1. Graphical Abstract:: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In order to assess the geothermometric potential of the Na2(Mn2−2 x Fe1+2 x )(PO4)3 system ( x = 0–1), which represents the compositions of natural weakly oxidized alluaudites, we performed hydrothermal experiments between 400 and 800°C, at 1 kbar, under an oxygen fugacity ( f(O2)) controlled by the Ni–NiO (NNO), Fe2O3–Fe3O4 (HM), Cu2O–CuO (CT), and Fe–Fe3O4 (MI) buffers. When f(O2) is controlled by NNO, single-phase alluaudites crystallize at 400 and 500°C, whereas the association alluaudite + marićite appears between 500 and 700°C. The limit between these two fields corresponds to the maximum temperature that can be reached by alluaudites in granitic pegmatites, because marićite has never been observed in these geological environments. Because alluaudites are very sensitive to variations of oxygen fugacity, the field of hagendorfite, Na2MnFe2+Fe3+(PO4)3, has been positioned in the f(O2)– T diagram, and provides a tool that can be used to estimate the oxygen fugacity conditions that prevailed in granitic pegmatites during the crystallization of this phosphate. [ABSTRACT FROM AUTHOR]

Several compounds of the Na2(Mn1-xFex2+)2Fe3+(PO4)3 solid solution have been hydrothermally synthesized at 400 °C and 1 kbar; pure alluaudite-like compounds have been obtained for x = 0.00, 0.25, 0.50, 0.75, and 1.00. Rietveld refinements of the powder X-ray diffraction patterns indicate the presence of Na+ at the A1 and A2' sites, Mn2+ and Fe2+ at the M1 site, and Mn2+, Fe2+, and Fe3+ at the M2 site. The presence of small mounts of Na+ at the M1 site and Mn2+ at the A1 site indicates a partially disordered distribution of these cations. An excellent linear correlation has been established between the M1-M2 distance and the energy of the infrared band attributed to the M2+-O vibrations. The Mössbauer spectra, measured between 85 and 295 K, were analyzed in terms of a model which includes the next-nearest neighbor interactions at the M2 and M1 crystallographic sites. Fe2+ and Fe3+ isomer shifts are typical of the alluaudite structure and exhibit the expected second-order Doppler shift. The derived iron vibrating masses and Mössbauer lattice temperatures are within the range of values expected for iron cations in an octahedral environment. The Fe2+ and Fe3+ quadrupole splittings are typical of the alluaudite structure, and the temperature dependence of the Fe2+ quadrupole splitting was fit with the Ingalls model, which yielded a ground state orbital splitting of ca. 460 to 735 cm-1 for the Fe2+ sites. The isomer shifts and quadrupole splittings of Fe2+ at the M1 site are larger than those of Fe2+ at M2, indicating that the M1 site is both larger and more distorted than the M2 site. [ABSTRACT FROM AUTHOR]

Two new mixed-valence iron phosphates, namely heptairon pentaphosphate hydrogen phosphate, Fe6.67(PO4)5.35(HPO4)0.65, and heptairon tetraphosphate bis(hydrogen phosphate), Fe6.23(PO4)4.45(HPO4)1.55, have been synthesized hydrothermally at 973 K and 0.1 GPa. The structures are similar to that of FeII3FeIII4(PO4)6 and are characterized by infinite chains of Fe polyhedra parallel to the [101] direction. These chains are formed by the Fe1O6 and Fe2O6 octahedra, alternating with the Fe4O5 distorted pentagonal bipyramids, according to the stacking sequence ...Fe1-Fe1-Fe4-Fe2-Fe2.... The Fe3O6 octahedra and PO4 tetrahedra connect the chains together. FeII is localized on the Fe3 and Fe4 sites, whereas FeIII 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 FeII + 2(PO43−) = vacancies + 2(HPO42−). [ABSTRACT FROM AUTHOR]

The paper describing the new phosphate mineral correianevesite, recently published by Chukanov et al. (2014), clearly demonstrates the importance of pegmatite phosphates. For material scientists, these minerals are a source of new structure types; for petrologists, they constitute valuable tools necessary to accurately determine the temperature conditions prevailing during pegmatite differentiation processes. [ABSTRACT FROM AUTHOR]

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(PO4), 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 FeII and FeIII atoms. Refined site occupancies and bond-valence analysis show the presence of FeIII and vacancies on the M2 site, mainly explained by the substitution mechanism 3 FeII = 2 FeIII + vacancies. [ABSTRACT FROM AUTHOR]

The article examines the hydrothermal synthesis and crystal structure of the inorganic compound sodium manganese phosphate. It observes the similarity of the chemical composition and structure of the compound with the natural fillowite-type phosphates described as hexagonal packing of rods parallel to the c axis consisting of sequence of polyhedra and ordered vacancies. It identifies the location of manganese cations on octahedral sites, nitrogen on coordinated sites and phosphors atoms on tetrahedral sites. The bond-valence sums of the atoms are shown.

The first hydro­thermal synthesis of an Al-rich alluaudite-type compound, namely disodium dimanganese aluminium tris­(phosphate), which has been obtained at 1073 K and 0.1 GPa starting from the composition Na2Mn2Al(PO4)3, is reported. The crystal structure, which has been refined in the monoclinic C2/ c space group, is identical to that of natural alluaudite. The structure consists of kinked chains of edge-sharing M1 and M2 octa­hedra, which contain Mn2+ and Al3+ ions. The chains are stacked parallel to {101} and are connected in the b direction by the P1 and P2 tetra­hedra. These inter­connected chains produce channels parallel to c, which contain the large A1 and A2′ sites occupied by Na+ and Mn2+ ions. [ABSTRACT FROM AUTHOR]

Abstract Na 1.5 □ 0.5 Mn 1.5 Fe 1.5 (PO 4) 3 (where □ denotes vacancies) microrods were obtained through a solvothermal synthesis in ethylene glycol. The combination of the XRD, Mössbauer and magnetic analyses confirm that the sodium vacancies in the Na 1.5 □ 0.5 Mn 1.5 Fe 1.5 (PO 4) 3 structure are linked to the oxidation of Mn and Fe transition metals. The electrochemical tests have shown that Na 1.5 □ 0.5 Mn 1.5 Fe 1.5 (PO 4) 3 is a dual electrode material for Li-ion batteries. The electrochemical study in the potential range of 1.5–4.5 V indicate that such material can be used as 3 V cathode with specific capacities of 109, 97, and 80 mAh·g−1 at current densities of 5, 10, and 20 mA·g−1, respectively. When it is tested in the potential range of 0.03–3.0 V as negative electrode material, it delivers a reversible capacity of about 170 mAh·g−1 at 200 mA·g−1 current density during >100 cycles. Highlights • Pure Na 1.5 □ 0.5 Mn 1.5 Fe 1.5 (PO 4) 3 (NMFP), was prepared by solvothermal synthesis route. • Only Fe (III) was identified in NMFP by 57Fe Mössbauer spectroscopy measurements. • Vacancies in Na 1.5 □ 0.5 Mn 1.5 Fe 1.5 (PO 4) 3 enhance its electrochemical performance. • Na 1.5 □ 0.5 Mn 1.5 Fe 1.5 (PO 4) 3 shows good dual electrochemical performances. [ABSTRACT FROM AUTHOR]

An ammonium-bearing fluorapophyllite-(K) occurs as a late hydrothermal product in the outer endoskarn zone from Aleului Valley (N 46°37′04″, E 22°35′22″), located at the contact of the granodiorite laccolith from Pietroasa, of Upper Cretaceous age, with Anisian dolostones. Associated minerals are wollastonite, K feldspar, diopside, fluorapatite, talc, and pectolite. The chemical structural formula is [K0.985Na0.012(NH4)0.076]Σ=1.073(Ca4.009Mn0.001Fe2+0.003Mg0.002Ba0.001)Σ=4.016(Si7.953Al0.047) O20.029[F0.899(OH)0.101]·8.059H2O. The structure was successfully refined as tetragonal, space group P4/mnc, with cell parameters of a = 8.9685(1) Å and c = 15.7885(5) Å. The indices of refraction are ω = 1.534(1) and ε = 1.536(1). The calculated density is Dx = 2.381 g/cm3, in good agreement with the measured density, Dm = 2.379(4) g/cm3. The thermal analysis shows that the mineral completely dehydrates at up to 450 °C (endothermic effects at 330, 371, and 448 °C) and loses ammonium at 634 °C. In the infrared spectra, the multiplicity of the bands assumed to be silicate modes (1ν1 + 3ν3 + 2ν2 + 3ν4) agrees with the reduction in the symmetry of the SiO44− ion from Td to Cδ. Fluorapophyllite-(K) from Aleului Valley is of late hydrothermal origin and crystallized from F-rich fluids originating from the granodiorite intrusion, which mobilized K, Ca, and Si from the pre-existing feldspar. [ABSTRACT FROM AUTHOR]

Compounds of the Na2(Mn1-xMx2+)Fe2+Fe3+(PO4)3 (M2+ = Mg, Cd, Ca, Ni, Zn) alluaudite-type solid solutions were synthesized by hydrothermal techniques at 1 kbar, between 400 and 600 °C, and were investigated by X-ray powder diffraction and infrared spectroscopy. The site occupancy factors of the Na2(Mn1-xCdx)Fe2+Fe3+(PO4)3 compounds, obtained from the Rietveld refinements of the X-ray powder patterns, indicate that the replacement of Mn by Cd mainly takes place on the M1 site. Small amounts of Cd were also detected on the A1 site, compensated by small amounts of Na occurring on M1. The cationic distributions in the Na2(Mn1-xMgx)Fe2+Fe3+(PO4)3 solid solution show a partially disordered distribution of Fe and Mg over the M1 and M2 crystallographic sites. The unit-cell parameters increase significantly when Mn is replaced by Ca or Cd, and decrease significantly when it is replaced by Ni, Mg, or Zn. The infrared spectra show the displacement of two absorption band at ca. 405-445 cm-1 and 595-610 cm-1, which are assigned to the vibrations of the M2+ cations localized on the M1 and M2 sites, respectively. This assignment is confirmed by the excellent correlations between the average ionic radius of the cations occurring on the M sites, and the energy of the absorption band. [ABSTRACT FROM AUTHOR]

This paper reports the hydrothermal synthesis and crystal structure refinement of diiron(II) phosphate hydroxide, FeII2(PO4)(OH), obtained at 1063 K and 2.5 GPa. This phosphate is the synthetic analogue of the mineral wolfeite, and has a crystal structure topologically identical to those of minerals of the triplite–triploidite group. The complex framework contains edge- and corner-sharing FeO4(OH) and FeO4(OH)2 polyhedra, linked via corner-sharing to the PO4 tetrahedra (average P—O distances are between 1.537 and 1.544 Å). Four five-coordinated Fe sites are at the centers of distorted trigonal bipyramids (average Fe—O distances are between 2.070 and 2.105 Å), whereas the coordination environments of the remaining Fe sites are distorted octahedra (average Fe—O distances are between 2.146 and 2.180 Å). The Fe—O distances are similar to those observed in natural Mg-rich wolfeite, except for two Fe—O bond distances, which are significantly longer in synthetic Fe2+2(PO4)(OH). [ABSTRACT FROM AUTHOR]

This study of white pottery from the Merovingian and Carolingian periods traces the use of white clay resources in the Middle Meuse valley at the beginning of the Middle Ages. The petrographic study of 56 sherds, the chemical analysis of 40 samples, and XRD study of 12 of them coming from 4 sites reach the changes of the process between the two time periods, characterize the production of three Carolingian workshops, and consider the material supply in the mechanism of potters’ settlement. It appears that, between the Antiquity and the Modern period, the white kaolinitic material has always been exploited. The main technical changes between the Merovingian and the Carolingian periods are related to the specific selection of these clays that allow to produce white pottery and cooking wares with few inclusions. The Carolingian workshops used the material available in their environment that can be differentiated by chemistry and mineralogy. Finally, it appears that the selection of this particular type of clay also oriented the choice of the place where the potters settled or at least the longevity of some of the workshops. [ABSTRACT FROM AUTHOR]

Samples of calcium stannate perovskite (CaSnO3) doped with a variable Nd content were synthesized by solid-state reaction in the system (1 − x)CaSnO3 − xNd2O3. The synthesized compounds were characterized by means of electron microprobe, powder X-ray diffraction, single-crystal X-ray diffraction and µ-Raman spectroscopy. The incorporation of Nd in the CaSnO3Pbnm structure leads to the formation of a complex (Ca1 − 2x Nd2x)(Sn1 − xCax)O3 perovskite. The A sublattice contains a random distribution of Ca and Nd in the whole range of composition of this system. For x < 0.28, the structure is Pbnm with Ca and Sn randomly distributed in the B sublattice. For x > 0.28 a symmetry change occurs; the structure turns into rock salt type P21/n. In this latter case half of the octahedral sites are fully occupied by Sn and the other half is randomly occupied by Sn and Ca. For x = 0.28, both structures are present in the sample. The presence of a Raman two modes behavior of A1g symmetry located near 700 cm− 1 coupled with the continuous linear evolution of the lattice parameters with Nd incorporation supports the proposed substitution mechanism. [ABSTRACT FROM AUTHOR]

Na 2 Mn 1.5 Fe 1.5 (PO 4 ) 3 (NMFP) dandelion sphere-like particles were successfully synthesized via a hydrothermal route without addition of any templates or surfactants (laboratory and pilot scales). The hydrothermal reactor (pilot scale) is equipped with stirrer for continuous agitation of reagents during the reaction. The obtained materials were characterized by X-ray diffraction, Mössbauer spectroscopy and Scanning electron microscopy. Results show that Na 2 Mn 1.5 Fe 1.5 (PO 4 ) 3 samples obtained from the reaction performed at laboratory scale have hierarchical dandelion sphere-like morphology and the dandelions consist of micro-/nano-rods. On the other hand, we obtained the self-assembly nano-rods morphology for the particles prepared using hydrothermal reactor. On the basis of the experimental results, a growth mechanism of Na 2 Mn 1.5 Fe 1.5 (PO 4 ) 3 self-assembly and dandelion sphere-like particles was proposed. Temperature and time of hydrothermal reaction are found to be crucial parameters in controlling the growth of Na 2 Mn 1.5 Fe 1.5 (PO 4 ) 3 particles. In addition, investigation of the effect of continuous stirring during the hydrothermal reaction shows that the reaction time can be optimized to obtain Na 2 Mn 1.5 Fe 1.5 (PO 4 ) 3 with small particles size. The influence of stirring on the NMFP morphology has been clearly evidenced. Indeed, the stirring leads to homogeneous particles. Cycling studies have shown that the synthesized Na 2 Mn 1.5 Fe 1.5 (PO 4 ) 3 dandelions materials exhibit specific discharge capacities of about 62 and 57 mAh g − 1 equivalent to about 1.2 and 1.05 lithium ions de-intercalated at C/15 and C/10 current density respectively. [ABSTRACT FROM AUTHOR]

Phosphate minerals are key indicators for understanding the processes of diagenesis and mineralization in granitic systems. More importantly, these minerals provide constraints on the post-magmatic behaviour of Li in pegmatite systems that remain to be explored, although Li from early-crystallized Li phosphates is known to leach into hydrothermal fluids. In this study, we performed a detailed petrographic and compositional analysis of phosphate minerals from the Nanping No. 31 pegmatite in southeastern of China, which provides new evidence of Li circulation in granitic systems. Primary phosphate minerals evolved from xenotime and monazite to Mn-rich fluorapatite and then to triphylite and montebrasite, with large amounts of montebrasite in the intermediate zones of the pegmatite, reflecting the increasing activities of both Li and P in peraluminous granitic melts. Montebrasite experienced stages of both high-temperature (360–273 °C) and low-temperature (273–100 °C) hydrothermal alteration. The high-temperature hydrothermal alteration of montebrasite by Fe- and Mg-rich fluids resulted in the formation of a series of Fe-, Mg-bearing phosphates; the replacement of montebrasite under low-temperature alteration generated amounts of Ca-, Sr-, Ba-bearing phosphate minerals, muscovite and akdalaite (Al 2 O 3 ) 4 ·H 2 O. The formation of micro-networks of akdalaite from montebrasite indicate the low mobility of Al in hydrothermal fluids. A four-stage scenario of post-magmatic Li transport in the Nanping No. 31 pegmatite is proposed: (1) Li derived from the breakdown of primary montebrasite was locally recrystallized and produced secondary montebrasite (Mtb-1); (2) hydrothermal alteration by Fe- and Mg-bearing fluids leached Li from montebrasite to form secondary triphylite and simferite; (3) Li derived from the alteration of montebrasite by Sr-, Ca-rich fluids was involved in the formation of secondary palermoite and bertossaite; and (4) the replacement of secondary triphylite, montebrasite, palermoite and bertossaite by later phases (apatites, ludlamite, anapaite, augelite and fine-grained muscovite) reflect the leaching of Li back into hydrothermal fluids. The re-enrichment of Li during the post-magmatic stage most likely increased the solubility of Ta in the hydrothermal fluids of the granitic pegmatite. [ABSTRACT FROM AUTHOR]

The sodium-manganese-iron phosphate Na 2 Mn 1.5 Fe 1.5 (PO 4 ) 3 (NMFP) with alluaudite structure was obtained by a one-step hydrothermal synthesis route. The physical properties and structure of this material were obtained through XRD and Mössbauer analyses. X-ray diffraction Rietveld refinements confirm a cationic distribution of Na + and presence of vacancies in A(2)’, Na + and small amounts of Mn 2+ in A(1), Mn 2+ in M(1), 0.5 Mn 2+ and Fe cations (Mn 2+ ,Fe 2+ and Fe 3+ ) in M(2), leading to the structural formula Na 2 Mn(Mn 0.5 Fe 1.5 )(PO 4 ) 3 . The particles morphology was investigated by SEM. Several reactions with different hydrothermal reaction times were attempted to design a suitable synthesis protocol of NMFP compound. The time of reaction was varied from 6 to 48 h at 220 °C. The pure phase of NMFP particles was firstly obtained when the hydrothermal reaction of NMFP precursors mixture was maintained at 220 °C for 6 h. When the reaction time was increased from 6 to 12, 24 and 48 h, the dandelion structure was destroyed in favor of NMFP micro-rods. The combination of NMFP (NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H) structure refinement and Mössbauer characterizations shows that the increase of the reaction time leads to the progressive increment of Fe(III) and the decrease of the crystal size. The electrochemical tests indicated that NMFP is a 3 V sodium intercalating cathode. The comparison of the discharge capacity evolution of studied NMFP electrode materials at C/5 current density shows different capacities of 48, 40, 34 and 34 mA h g −1 for NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H respectively. Interestingly, all samples show excellent capacity retention of about 99% during 50 cycles. [ABSTRACT FROM AUTHOR]

• The Stavelot Massif (Belgium) displays manganese weathering crust deposits. • Cryptomelane and nsutite are the main weathering Mn-bearing minerals. • Mn-carbonates and phyllosilicates are the main precursors of the secondary Mn oxides. • At least four weathering phases are identified since late Oligocene to Pliocene. • The Ardenne uplift is interpreted as the main parameter controlling weathering processes. The occurrence of Ordovician Fe-Mn-rich sediments (Ottré Formation, Salm Group) in the Stavelot inlier (NE Ardenne, Rhenish Massif, Belgium) has drawn the attention of geoscientists for more than one century, as they contain natural "coticule" whetstones and numerous weathered Mn deposits. Two locations expose the Fe-Mn-bearing rocks: the Chevron area to the north is located at an altitude of 230–380 m, and the Salmchâteau at 480–570 m. The Mn-bearing sediments have undergone greenschist facies metamorphism in relation to the Caledonian and Variscan orogenesis, and more recently weathering processes, transforming the early mineral assemblages (mainly rhodochrosite and/or kutnohorite, spessartine, muscovite, chloritoïd, andalusite, hematite) into secondary Mn oxides,—hydroxides and—oxyhydroxides (cryptomelane, nsutite, lithiophorite, manganite, pyrolusite), clays (mainly kaolinite) and Fe oxides (goethite). In this paper, we investigate the weathering processes of these Mn-rich rocks by i) new mineralogical, petrographical and geochemical data, and ii) new 40Ar/39Ar geochronology of K-Mn oxides. Petrographical and geochemical data indicate that rhodochrosite (and/or kutnohorite) is the main source of Mn, from which Mn oxides have precipitated. Spessartine and other Mn-silicates have poorly contributed to the Mn mobilization. Pure Mn oxides, namely manganite, nsutite, and pyrolusite, successively replace rhodochrosite under increasing O 2 conditions due to the weathering fluids, while the formation of cryptomelane and then lithiophorite in veins is associated to the recombination of K+, Li+ and Al3+ released from the phyllosilicate matrix of the host slate, probably in relation with sligh pH changes. This multistage character of weathering processes is well identified in the Salmchâteau area, where weathering conditions are stronger than in the Chevron area because of the elevation. This also positions the Mn levels close to the roll front within the lower saprolite and the fissured horizon, respectivelly. Such differences in the weathering grade of these areas determined a weathering-type deposit in the Salmchâteau area and a carbonate-hosted sedimentary deposit in the Chevron area. Weathering deposits are accompanied by an enrichment in Mn and associated transition metals (As, Co, Cu, Ni). Dating of pure cryptomelane samples corroborate the multistage character of the ore and yield at least four weathering stages: Chattian (26.33 ± 0.17 Ma), Aquitanian (22.2 ± 0.6 and 20.0 ± 0.2 Ma), Serravalian-Tortonian (11.79 ± 0.10 to 10.12 ± 0.18 Ma) and Pliocene or younger (5.30 ± 0.76 and 4.11 ± 0.57 Ma). A relatively continuous weathering of the Massif since the late Oligocene, or older weathering phases, cannot be excluded as the upper part of the saprolite (and laterite) have been removed. As climatic conditions evolve from tropical to temperate by the Oligocene, the uplift of the Ardenne is probably the main factor triggering the development of weathering mantle, together with the increasing seasonality and high precipitation. These ages with others obtained in supergene ores of Western European massifs define a long-lasting weathering wave since the late Oligocene until the uppermost Neogene. The absence of older periods in the 40Ar/39Ar record of these deposits indicates that the upper part of the weathering mantle was recently stripped and limit their economic interest. [ABSTRACT FROM AUTHOR]