Browsing by Author "Grey, IE"
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- ItemBulachite, [Al6(AsO4)3(OH)9(H2O)4]⋅2H2O from Cap Garonne, France: crystal structure and formation from a higher hydrate(Cambridge University Press, 2020-06-30) Grey, IE; Yoruk, E; Kodjikian, S; Klein, H; Bougerol, C; Brand, HEA; Bordet, P; Mumme, WG; Favreau, G; Mills, SJBulachite specimens from Cap Garonne, France, comprise two intimately mixed hydrated aluminium arsenate minerals with the same Al:As ratio of 2:1 and with different water contents. The crystal structures of both minerals have been solved using data from low-dose electron diffraction tomography combined with synchrotron powder X-ray diffraction. One of the minerals has the same powder X-ray diffraction pattern (PXRD) as for published bulachite. It has orthorhombic symmetry, space group Pnma with unit-cell parameters a = 15.3994(3), b = 17.6598(3), c = 7.8083(1) Å and Z = 4, with the formula [Al6(AsO4)3(OH)9(H2O)4]·2H2O. The second mineral is a higher hydrate with composition [Al6(AsO4)3(OH)9(H2O)4]·8H2O. It has the same Pnma space group and unit-cell parameters a = 19.855(4), b = 17.6933(11) and c = 7.7799(5) Å i.e. almost the same b and c parameters but a much larger a parameter. The structures are based on polyhedral layers, parallel to (100), of composition [Al6(AsO4)3(OH)9(H2O)4] and with H-bonded H2O between the layers. The layers contain [001] spiral chains of edge-shared octahedra, decorated with corner connected AsO4 tetrahedra that are the same as in the mineral liskeardite. The spiral chains are joined together by octahedral edge-sharing to form layers parallel to (100). Synchrotron PXRD patterns collected at different temperatures during heating of the specimen show that the higher-hydrate mineral starts transforming to bulachite when heated to 50°C, and the transformation is complete between 75 and 100°C. © 2020 The Mineralogical Society of Great Britain and Ireland .
- ItemCrystal chemistry and formation mechanism of non-stoichiometric monoclinic K-jarosites(Mineralogical Society, 2013-04-01) Grey, IE; Scarlett, NVY; Brand, HEASyntheses in acidified hydrothermal (HT) solutions (1 N H2SO4 or stronger) produce monoclinic non-stoichiometric K-jarosites which contain Fe-site vacancies with long-range order. Syntheses in non-acidified HT solutions produce rhombohedral K-jarosites which contain relatively large numbers of Fe-site vacancies with no long-range order. Increasing the [Fe]/[K] ratio, reaction temperature and reaction time in non-acidified solutions promotes the formation of monoclinic jarosites which contain Fe-site vacancies with short-range order. A structural model including details of the ordering of the Fe-site vacancies was obtained by refinement of single-crystal synchrotron data from one of the HT synthesis products; this model was used to refine synchrotron powder X-ray diffraction data from products synthesized at different reaction times, temperatures and [Fe]/[K] ratios. Thermal and chemical analyses are consistent with a model for non-stoichiometry in which domains of stoichiometric jarosite are intergrown with butlerite-like iron-deficient domains with a composition [Fe-2(SO4)(2)(OH)(2)(H2O)(4)]. It was found that heterogeneous nucleation of monoclinic jarosite on Si disks is preceded by the formation of an oriented film of Maus's Salt, K5Fe3O(SO4)(6)center dot 10H(2)O, as a precursor phase, and that this transforms topotactically into oriented jarosite, which contains butlerite-like layers parallel to the disk surface. Structural models for the transformation of Maus's Salt into jarosite are proposed.© 2013, Mineralogical Society.
- ItemDehydration phase transitions in new aluminium arsenate minerals from the Penberthy Croft mine, Cornwall, UK(Cambridge University Press, 2016-12) Grey, IE; Brand, HEA; Betterton, JBettertonite, [Al6(AsO4)3(OH)9(H2O)5]•11H2O and penberthycroftite, [Al6(AsO4)3(OH)9(H2O)5].8H2O, two new minerals from the Penberthy Croft mine, Cornwall, have flexible layer structures based on corner-connected heteropolyhedral columns. Their response to dehydration on heating was studied using in situ synchrotron powder X-ray diffraction at temperatures in the range -53 to 157°C. The bettertonite sample transforms to penberthycroftite in a narrow temperature range of 67 to 97°C with a large (8%) contraction of the layer separation and a 6 Å sliding of adjacent layers relative to each other. Above 100°C a second phase transition occurs to a DL (displaced layer) phase, involving another 8% inter-layer contraction combined with a rotation of the columns. On heating the penberthycroftite sample the phase transition to the DL phase occurs at a lower temperature of ∼80°C. The DL phase is stable to a temperature of ∼120°C. At higher temperatures, increased rotation of the columns is accompanied by a progressive amorphization of the sample. Bettertonite, penberthycroftite and the DL phase exhibit negative thermal expansion (NTE) along all three axes with large NTE coefficients, of the order of-100 x 10 -6 °C-1. © 2016 The Mineralogical Society of Great Britain and Ireland
- ItemFormation of jarosite minerals in the presence of seed material(Universities Space Research Association, 2015-03-17) Brand, HEA; Scarlett, NVY; Grey, IEIntroduction: There has been a resurgence in interest in jarosite, (K,Na)Fe3(SO4)2(OH)6, and related minerals since their detection on Mars by the MER rover Opportunity [1]. In this context, the presence of jarosite has been recognised as a likely indicator of water at the surface of Mars in the past and it is hoped that study of their formation mechanisms will provide insight into the environmental history of Mars [2]. Jarosites are also of great importance to a range of mineral processing and research applications. For example: they are used in the removal of iron species from smelting processes; they form detrimentally in biometallurgical systems and they are present in acid mine drainage environments. Jarosites are also of considerable theoretical interest as model compounds for spin frustration in Kagomé-Heisenberg antiferromagnetic materials [3]. Knowledge of the formation mechanisms of jarosites is an indispensable prerequisite for understanding their occurrences, stabilities and potential environmental impacts both on Mars and Earth. We are engaged in a program of research to study the nucleation and crystal growth of jarosites under a variety of conditions. Here we report the results of in situ synchrotron powder diffraction experiments designed to follow the crystallisation and growth kinetics of jarosite minerals in the presence of seed materials. Figure 1 shows the structure of jarosite. Layers of blue corner sharing Fe octahedra are connected by yellow sulphate tetrahedra. Cations such as potassium or sodium can also be found in these interstitial layers (red). Jarosite is traditionally reported with rhombohedral symmetry [3]. However, we have synthesised monoclinic jarosite under certain preparative conditions [4].
- ItemGaleaclolusite, [Al6(AsO4)3(OH)9(H2O)4]⋅8H2O, a new bulachite-related mineral from Cap Garonne, France(Cambridge University Press, 2020-12-04) Grey, IE; Favreau, G; Mills, SJ; Mumme, WG; Bougerol, C; Brand, HEA; Kampf, AR; MacRae, CM; Shanks, FLGaleaclolusite, [Al6(AsO4)3(OH)9(H2O)4].8H2O, is a new secondary hydrated aluminium arsenate mineral from Cap Garonne, Var, France. It forms crusts and spheroids of white fibres up to 50 μm long by 0.4 μm wide and only 0.1 μm thick. The fibres are elongated along [001] and flattened on (100). The calculated density is 2.27 g.cm-3. Optically, galeaclolusite is biaxial with α = 1.550(5), β not determined, γ = 1.570(5) (white light) and partial orientation: Z = c (fibre axis). Electron microprobe analyses coupled with crystal structure refinement results gives an empirical formula based on 33 O atoms of Al5.72Si0.08As2.88O33H34.12. Galeaclolusite is orthorhombic, Pnma, with a = 19.855(4), b = 17.6933(11), c = 7.7799(5) A, V = 2733.0(7) Aand Z = 4. The crystal structure of galeaclolusite was established from its close relationship to bulachite and refined using synchrotron powder X-ray diffraction data. It is based on heteropolyhedral layers, parallel to (100), of composition Al6(AsO4)3(OH)9(H2O)4 and with H-bonded H2O between the layers. The layers contain [001] spiral chains of edge-shared octahedra, decorated with corner-connected AsO4 tetrahedra, that are the same as in the mineral liskeardite. © 2020. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland.
- ItemIn situ SAXS studies of the formation of sodium jarosite(Wiley-Blackwell, 2013-07-01) Brand, HEA; Scarlett, NVY; Grey, IE; Knott, RB; Kirby, NThis paper reports the results of time-resolved synchrotron small-angle scattering and powder diffraction experiments where natrojarosites were synthesized in situ in order to observe the species produced at the earliest stages of nucleation. The sample temperatures were 333, 353 and 368 K. These compounds were synthesized by co-precipitation from solution on the Small and Wide Angle Scattering and Powder Diffraction beamlines at the Australian Synchrotron. Scattering data were collected continuously throughout the syntheses. The results presented here show that the first particles to form in solution appear to be amorphous and nucleate on the walls of the reaction vessel. Crucially, there is a single nucleation event which forms particles with an elliptical disc morphology which then grow uniformly before natrojarosite crystallization is observed in complementary powder diffraction data. This nucleation event may represent the key to controlling the growth of jarosites in industrial and environmental settings. © 2013, Wiley-Blackwell.
- ItemIn situ studies into the formation kinetics of potassium jarosite(Wiley Blackwell, 2012-06-01) Brand, HEA; Scarlett, NVY; Grey, IEThis paper reports the results of time-resolved synchrotron powder diffraction and small-angle scattering experiments designed to investigate the kinetics of formation of potassium jarosite by co-precipitation at 353, 368 and 393 K. Only jarosite was produced in these syntheses, and the particles that formed nucleated on the walls of the capillary reaction vessels with a disc-like shape. Relative Rietveld scale factors indicating jarosite abundance have been used as the basis for kinetic modelling of the nucleation and growth stages using a modified form of the Avrami kinetic equation. The results show that jarosite forms by a single nucleation event followed by two distinct stages of growth, each characterized by a different Avrami exponent. The value of this exponent is initially between 1 and 2, and then reduces to around 1. This suggests that jarosite growth after nucleation is controlled by effects at the solution-boundary interface, with the first stage best described by two-dimensional growth which transitions to one-dimensional growth later in the reaction. An activation energy of 89 kJ mol(-1) was estimated for the first stage of growth, in good agreement with previous work. © 2012, Wiley-Blackwell.
- ItemIn situ synchrotron diffraction studies on the formation kinetics of jarosites(Wiley Blackwell, 2013-03-01) Scarlett, NVY; Grey, IE; Brand, HEAThis paper reports the results of time-resolved synchrotron powder diffraction experiments where jarosites with different K/H3O, K/Na and Na/H3O ratios were synthesized in situ at temperatures of 353, 368 and 393 K in order to observe the effect on kinetics and species produced. The Na/H3O sample formed monoclinic jarosite at all three temperatures, whereas the K/H3O and K/Na samples formed as rhombohedral jarosites at 353 K, and as mixtures of rhombohedral and monoclinic jarosites at the higher temperatures. The relative amount of the monoclinic phase increased with increase in temperature. Unit-cell parameter changes with reaction time could be explained by changes in iron stoichiometry (samples become more stoichiometric with time) together with changes in K/H3O and Na/H3O ratios. The reaction kinetics have been fitted using a two-stage Avrami model, with two different Avrami exponents corresponding to initial two-dimensional growth followed by one-dimensional diffusion-controlled growth. Activation energies for the initial growth stage were calculated to be in the range 90-126 kJ mol(-1). © 2013, Wiley-Blackwell.
- ItemNew type of cubic-stacked layer structure in anthoinite, AlWO3(OH)(3)(Mineralogical Society of America, 2010-04) Grey, IE; Madsen, IC; Mills, SJ; Hatert, F; Peterson, VK; Bastow, TJAnthoinite, AlWO3(OH)3, from the Mt. Misobo Mine, Democratic Republic of the Congo, has triclinic symmetry with cell parameters a = 8.196(1) Å, b = 9.187(1) Å, c = 11.316(1) Å, = 92.82(1)°, β = 94.08(1)°, = 90.23(1)°, space group ґI, Z = 8. The structure was solved by applying ab initio structure solution methods (Reverse Monte Carlo/Simulated Annealing) to both X-ray and neutron powder diffraction data and was refined using the Rietveld method. The structure is built up of two types of M4(O,OH)16 planar tetrameric clusters of edge-sharing octahedra, one containing predominantly Al and the other predominantly W. The Al-rich and W-rich clusters interconnect via corner sharing to form stepped layers parallel to (001). The layers are held together by strong hydrogen bonding. The structure can be described as a rocksalt derivative structure, with the close-packed anion layers parallel to (012), and with Al and W atoms ordered into one third of the octahedral sites within the cubic close-packed anion lattice. The structure is complicated by partial disorder between Al and W in the tetrameric clusters and associated disorder in the H atom sites. Infrared and 27Al MAS NMR results are also presented for anthoinite. © 2010, Mineralogical Society of America
- ItemThe rockbridgeite group approved and a new member, ferrorockbridgeite, (Fe2+,Mn2+)2(Fe3+)3(PO4)3(OH)4(H2O), described from the Hagendorf Süd pegmatite, Oberpfalz, Bavaria(Schweizerbart Science Publishers, 2019-06-06) Grey, IE; Kampf, AR; Keck, E; Cashion, JD; MacRae, CM; Gozukara, Y; Peterson, VK; Shanks, FLThe rockbridgeite group has been officially established by the IMA Commission on New Minerals, Nomenclature and Classification. The general formula is based on the structure and is A 2 B 3(PO4)3(OH, H2O)5, where A = the octahedrally coordinated M2 site, in which divalent cations are ordered, and B = the octahedrally coordinated M1 + M3 sites, which contain predominantly Fe3+, with trace Al. The different rockbridgeite-group minerals are distinguished by the occupancy of the A site. The ideal formula for rockbridgeite is F e 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 , that for frondelite is Mn 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 and that for plimerite is Z n 2 Fe 3 3 + P O 4 3 OH 4 ( H 2 O ) . In order to preserve the identity of frondelite and rockbridgeite within the structure-based formalism, these species correspond to mid-series compositions. We describe here the new end-member, ferrorockbridgeite, with dominant Fe2+ in the A site, from the Hagendorf Süd pegmatite mine, Oberpfalz, Bavaria. Electron microprobe analyses, coupled with Mössbauer spectroscopy, gives the empirical formula Fe 1.33 2 + Mn 0.52 2 + Zn 0.03 Ca 0.05 Fe 3.03 3 + Al 0.01 P 2.97 H 6.17 O 17 . The simplified formula is F e 2 + , M n 2 + 2 F e 3 3 + P O 4 3 OH 4 ( H 2 O ) . Ferrorockbridgeite is orthorhombic, space group Bbmm, with a = 13.9880(4), b = 16.9026(5), c = 5.1816(1) Å, V = 1225.1 Å3 and Z = 4. The six strongest lines in the X-ray powder diffraction pattern are [d meas/Å (I) (hkl)]: 4.853 (26) (101), 3.615 (24) (240), 3.465 (33) (301), 3.424 (39) (410), 3.205 (100) (321) and 1.603 (24) (642). Optically, ferrorockbridgeite is biaxial (–) with α = 1.763(3), β = 1.781(calc), γ = 1.797(3) (white light) and 2V (meas.) = 87(1)° from extinction data. The optical orientation is X = c, Y = a , Z = b. The pleochroism is X = blue green, Y = olive green, Z = yellow brown; X ≈ Y > Z. The rockbridgeite group has been officially established by the IMA Commission on New Minerals, Nomenclature and Classification. The general formula is based on the structure and is A 2 B 3(PO4)3(OH, H2O)5, where A = the octahedrally coordinated M2 site, in which divalent cations are ordered, and B = the octahedrally coordinated M1 + M3 sites, which contain predominantly Fe3+, with trace Al. The different rockbridgeite-group minerals are distinguished by the occupancy of the A site. The ideal formula for rockbridgeite is F e 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 , that for frondelite is Mn 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 and that for plimerite is Z n 2 Fe 3 3 + P O 4 3 OH 4 ( H 2 O ) . In order to preserve the identity of frondelite and rockbridgeite within the structure-based formalism, these species correspond to mid-series compositions. We describe here the new end-member, ferrorockbridgeite, with dominant Fe2+ in the A site, from the Hagendorf Süd pegmatite mine, Oberpfalz, Bavaria. Electron microprobe analyses, coupled with Mössbauer spectroscopy, gives the empirical formula Fe 1.33 2 + Mn 0.52 2 + Zn 0.03 Ca 0.05 Fe 3.03 3 + Al 0.01 P 2.97 H 6.17 O 17 . The simplified formula is F e 2 + , M n 2 + 2 F e 3 3 + P O 4 3 OH 4 ( H 2 O ) . Ferrorockbridgeite is orthorhombic, space group Bbmm, with a = 13.9880(4), b = 16.9026(5), c = 5.1816(1) Å, V = 1225.1 Å3 and Z = 4. The six strongest lines in the X-ray powder diffraction pattern are [d meas/Å (I) (hkl)]: 4.853 (26) (101), 3.615 (24) (240), 3.465 (33) (301), 3.424 (39) (410), 3.205 (100) (321) and 1.603 (24) (642). Optically, ferrorockbridgeite is biaxial (–) with α = 1.763(3), β = 1.781(calc), γ = 1.797(3) (white light) and 2V (meas.) = 87(1)° from extinction data. The optical orientation is X = c, Y = a , Z = b. The pleochroism is X = blue green, Y = olive green, Z = yellow brown; X ≈ Y > Z. The rockbridgeite group has been officially established by the IMA Commission on New Minerals, Nomenclature and Classification. The general formula is based on the structure and is A 2 B 3(PO4)3(OH, H2O)5, where A = the octahedrally coordinated M2 site, in which divalent cations are ordered, and B = the octahedrally coordinated M1 + M3 sites, which contain predominantly Fe3+, with trace Al. The different rockbridgeite-group minerals are distinguished by the occupancy of the A site. The ideal formula for rockbridgeite is F e 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 , that for frondelite is Mn 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 and that for plimerite is Z n 2 Fe 3 3 + P O 4 3 OH 4 ( H 2 O ) . In order to preserve the identity of frondelite and rockbridgeite within the structure-based formalism, these species correspond to mid-series compositions. We describe here the new end-member, ferrorockbridgeite, with dominant Fe2+ in the A site, from the Hagendorf Süd pegmatite mine, Oberpfalz, Bavaria. Electron microprobe analyses, coupled with Mössbauer spectroscopy, gives the empirical formula Fe 1.33 2 + Mn 0.52 2 + Zn 0.03 Ca 0.05 Fe 3.03 3 + Al 0.01 P 2.97 H 6.17 O 17 . The simplified formula is F e 2 + , M n 2 + 2 F e 3 3 + P O 4 3 OH 4 ( H 2 O ) . Ferrorockbridgeite is orthorhombic, space group Bbmm, with a = 13.9880(4), b = 16.9026(5), c = 5.1816(1) Å, V = 1225.1 Å3 and Z = 4. The six strongest lines in the X-ray powder diffraction pattern are [d meas/Å (I) (hkl)]: 4.853 (26) (101), 3.615 (24) (240), 3.465 (33) (301), 3.424 (39) (410), 3.205 (100) (321) and 1.603 (24) (642). Optically, ferrorockbridgeite is biaxial (–) with α = 1.763(3), β = 1.781(calc), γ = 1.797(3) (white light) and 2V (meas.) = 87(1)° from extinction data. The optical orientation is X = c, Y = a , Z = b. The pleochroism is X = blue green, Y = olive green, Z = yellow brown; X ≈ Y > Z. © 2018 E. Schweizerbart’sche Verlagsbuchhandlung
- ItemUltra-flexible framework breathing in response to dehydration in liskeardite, [(Al,Fe)16(AsO4)9(OH)21(H2O)11]·26H2O, a natural open-framework compound(Elsevier, 2015-05-02) Grey, IE; Brand, HEA; Rumsey, MS; Gozukara, YDehydration of the natural open-framework compound, liskeardite, [(Al,Fe)16(AsO4)9(OH)21(H2O)11]·26H2O, is accompanied by a change in the sign of the thermal expansion from positive to negative above room temperature, and at ~100 °C the structure undergoes a dramatic 2D contraction by co-operative rotation of heteropolyhedral columns that constitute the framework walls. Monoclinic liskeardite, I112 with a≈b≈24.7 Å, c ≈7.8 Å and β≈90° is transformed to a tetragonal phase, I-4 with a≈20.6 Å, c ≈7.7 Å. The associated 30% decrease in volume is unprecedented in inorganic microporous compounds. The flexibility of the contraction is related to the double-hinged nature of the column rotations about [001]. Octahedra in adjacent columns are interconnected by corner-sharing with the two pairs of anions forming opposing edges of AsO4 tetrahedra, so a double-hinged rotation mechanism operates. Thermal analysis and mass spectroscopic results for liskeardite show that the phase transition at ~100 °C is related to removal of the channel water. The tetragonal phase shows exceptionally large NTE behaviour. Over the temperature range 148–178 the NTE along a and b is close to linear with a magnitude of the order of −900×10−6 °C−1. The contraction along the channel direction is smaller but still appreciable at −200×10−6 °C−1. © 2015 Elsevier Inc.