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  • 1
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    Synthesis and structure of magnesium hydroxide fluoride, Mg(OH)F: a topological intermediate between brucite- and rutile-type structures (2012)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2012-02-01
    Description: Magnesium hydroxyfluoride, Mg(OH)F, has been synthesized by a subcritical hydrothermal route from a 1:1 molar mixture of brucite, Mg(OH)2, and sellaite, MgF2 with a rutile type structure, in excess water. Using a combination of synchrotron X-ray and time-of-flight neutron powder diffraction, the structure of Mg(OH)F has been solved in the diaspore space group Pnma with a = 10.116(3), b = 4.6888(10) and c = 3.0794(7) Å at ambient conditions. The most intense diffraction lines are [dobs (hkl) Iobs]: 2.291 (211) 10, 4.253 (101) 7, 1.747 (212) 7, 2.229 (401) 6 and 1.480 (610) (4) Å, with the largest d-spacing at 5.058 Å. Sharp infrared stretching bands are located at 3679 and 3645 cm -1, with a broader band at 3535 cm -1. The topology of the structure is intermediate between that of the OH and F endmembers, being derived through notional shearing nearly normal to the sheets of octahedra of the CdI2/Mg(OH)2-type structure. Further similar shearing at an interval ½a would lead to a Cd(OH)F-type structure, which is also related to the rutile structure type. The observations and model presented here indicate a close correlation between the structural properties of the endmembers and Mg(OH)F.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 2
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    Synthesis and structure of magnesium hydroxide fluoride, Mg(OH)F: a topological intermediate between brucite- and rutile-type structures (2012)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2012-02-01
    Description: Magnesium hydroxyfluoride, Mg(OH)F, has been synthesized by a subcritical hydrothermal route from a 1:1 molar mixture of brucite, Mg(OH)2, and sellaite, MgF2 with a rutile type structure, in excess water. Using a combination of synchrotron X-ray and time-of-flight neutron powder diffraction, the structure of Mg(OH)F has been solved in the diaspore space group Pnma with a = 10.116(3), b = 4.6888(10) and c = 3.0794(7) Å at ambient conditions. The most intense diffraction lines are [dobs (hkl) Iobs]: 2.291 (211) 10, 4.253 (101) 7, 1.747 (212) 7, 2.229 (401) 6 and 1.480 (610) (4) Å, with the largest d-spacing at 5.058 Å. Sharp infrared stretching bands are located at 3679 and 3645 cm -1, with a broader band at 3535 cm -1. The topology of the structure is intermediate between that of the OH and F endmembers, being derived through notional shearing nearly normal to the sheets of octahedra of the CdI2/Mg(OH)2-type structure. Further similar shearing at an interval ½a would lead to a Cd(OH)F-type structure, which is also related to the rutile structure type. The observations and model presented here indicate a close correlation between the structural properties of the endmembers and Mg(OH)F.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 3
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    Synthesis and structure of magnesium hydroxide fluoride, Mg(OH)F: a topological intermediate between brucite- and rutile-type structures (2012)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2012-02-01
    Description: Magnesium hydroxyfluoride, Mg(OH)F, has been synthesized by a subcritical hydrothermal route from a 1:1 molar mixture of brucite, Mg(OH)2, and sellaite, MgF2 with a rutile type structure, in excess water. Using a combination of synchrotron X-ray and time-of-flight neutron powder diffraction, the structure of Mg(OH)F has been solved in the diaspore space group Pnma with a = 10.116(3), b = 4.6888(10) and c = 3.0794(7) Å at ambient conditions. The most intense diffraction lines are [dobs (hkl) Iobs]: 2.291 (211) 10, 4.253 (101) 7, 1.747 (212) 7, 2.229 (401) 6 and 1.480 (610) (4) Å, with the largest d-spacing at 5.058 Å. Sharp infrared stretching bands are located at 3679 and 3645 cm -1, with a broader band at 3535 cm -1. The topology of the structure is intermediate between that of the OH and F endmembers, being derived through notional shearing nearly normal to the sheets of octahedra of the CdI2/Mg(OH)2-type structure. Further similar shearing at an interval ½a would lead to a Cd(OH)F-type structure, which is also related to the rutile structure type. The observations and model presented here indicate a close correlation between the structural properties of the endmembers and Mg(OH)F.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 4
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    The high-pressure monazite-to-scheelite transformation in CaSeO4 (2012)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2012-08-01
    Description: The high-pressure monazite–scheelite structure transition has been observed at P 〉4.57 GPa in CaSeO4 by synchrotron X-ray powder diffraction. It is a first-order transition with a 4.5% volume change and is severely hindered kinetically. Scheelite-type CaSeO4 remains to a maximum experimental pressure of 42.2 GPa and no (002) reflection, specifically indicative of a subgroup transition to a fergusonite-type structure, is observed. Scheelite-type CaSeO4 remains at ambient conditions, where the tetragonal unit cell has parameters of a = 5.04801(11) c = 11.6644(5) Å and V = 297.21(3) Å3 with Dcalc = 4.090 g cm−3. The diffraction pattern of the recovered material was refined in space group I41/a to Rp = 0.98%, wRp = 1.91%, GoF = 0.59, RFobs = 5.04%, wRFobs = 4.27%. The oxygen is located on the general 16f site at (0.2578(8) 0.3699(14) 0.5755(4)) and shares four identical bonds with Se (4a: ½ ½ ½) at 1.644(5) Å. The Ca (4b: 0, 0, ½) is eight-coordinated via O at 4 × 2.440(6) Å and 4 × 2.504(5) Å. This is further evidence of the dissimilarity of sulfate and selenate at high pressure and temperature conditions and the closer resemblance of the selenates to the orthophosphates, arsenates and vanadates, where this type of transition sequence has been described.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 5
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    Synthesis and structure of magnesium hydroxide fluoride, Mg(OH)F: a topological intermediate between brucite- and rutile-type structures (2012)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2012-02-01
    Description: Magnesium hydroxyfluoride, Mg(OH)F, has been synthesized by a subcritical hydrothermal route from a 1:1 molar mixture of brucite, Mg(OH)2, and sellaite, MgF2 with a rutile type structure, in excess water. Using a combination of synchrotron X-ray and time-of-flight neutron powder diffraction, the structure of Mg(OH)F has been solved in the diaspore space group Pnma with a = 10.116(3), b = 4.6888(10) and c = 3.0794(7) Å at ambient conditions. The most intense diffraction lines are [dobs (hkl) Iobs]: 2.291 (211) 10, 4.253 (101) 7, 1.747 (212) 7, 2.229 (401) 6 and 1.480 (610) (4) Å, with the largest d-spacing at 5.058 Å. Sharp infrared stretching bands are located at 3679 and 3645 cm–1, with a broader band at 3535 cm–1. The topology of the structure is intermediate between that of the OH and F endmembers, being derived through notional shearing nearly normal to the sheets of octahedra of the CdI2/Mg(OH)2-type structure. Further similar shearing at an interval 1/2a would lead to a Cd(OH)F-type structure, which is also related to the rutile structure type. The observations and model presented here indicate a close correlation between the structural properties of the endmembers and Mg(OH)F.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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  • 6
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    The high-pressure monazite-to-scheelite transformation in CaSeO4 (2012)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2012-08-01
    Description: The high-pressure monazite – scheelite structure transition has been observed at P 〉4.57 GPa in CaSeO4 by synchrotron X-ray powder diffraction. It is a first-order transition with a 4.5% volume change and is severely hindered kinetically. Scheelite-type CaSeO4 remains to a maximum experimental pressure of 42.2 GPa and no (002) reflection, specifically indicative of a subgroup transition to a fergusonite-type structure, is observed. Scheelite-type CaSeO4 remains at ambient conditions, where the tetragonal unit cell has parameters of a = 5.04801(11) c = 11.6644(5) Å and V = 297.21(3) Å3 with Dcalc = 4.090 g cm–3. The diffraction pattern of the recovered material was refined in space group I41/a to Rp = 0.98%, wRp = 1.91%, GoF = 0.59, RFobs = 5.04%, wRFobs = 4.27%. The oxygen is located on the general 16f site at (0.2578(8) 0.3699(14) 0.5755(4)) and shares four identical bonds with Se (4a: ½ ½ ½) at 1.644(5) Å. The Ca (4b: 0, 0, ½) is eight-coordinated via O at 4 × 2.440(6) Å and 4 × 2.504(5) Å. This is further evidence of the dissimilarity of sulfate and selenate at high pressure and temperature conditions and the closer resemblance of the selenates to the orthophosphates, arsenates and vanadates, where this type of transition sequence has been described.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
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  • 7
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    Monazite structure from dehydrated CaSeO4·2H2O (2010)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2010-02-01
    Description: The structure of the high-temperature form of CaSeO4, formed by dehydration of the gyspum-type structure dihydrate is presented. The material is equivalent to that described previously as a P212121 form, but is however, a monazite with unit cell a = 6.85661(16) Å, b = 7.04962(15) Å, c = 6.68817(15) Å and β = 104.2675(21)° in space group P121/n1. Also presented is evidence for two intermediate trigonal and pseudo-trigonal phases related to the structurally similar minerals rhabdophane, bassanite, and γ-CaSO4. This result permits closer comparisons between intermediate-temperature structures of the selenate with related sulphates, and orthophosphates with a view to extending structural stability via synthesis of solid-solutions.
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    Topics: Geosciences
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  • 8
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    Weathering products of andesitic rocks from Sulawesi, Indonesia (1984)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 1984-02-01
    Description: Mineralogical investigations of weathered andesitic bedrock and overburden on the valley flank of the Tondano river, Manado, Sulawesi, indicated that these had been subjected to different weathering conditions. The underlying andesite was completely altered to 7Å-halloysite and allophane. In the transported latosols of the overburden, 10Å- and 7Å-halloysites were found. The ratio of 10Å- to 7Å-halloysite increased linearly with depth in the profile. It is considered that weathering of the andesitic bedrock reflects a palaeoclimate with more strongly pronounced seasonal desiccation and lower annual rainfall. Neoformations by weathering of the overburden took place under the recent tropical climate.
    Print ISSN: 0009-8558
    Electronic ISSN: 1471-8030
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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  • 9
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    Mineralogy and genesis of the Pugu Hill kaolin deposit, Tanzania (1987)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 1987-12-01
    Description: According to field studies of the Pugu Hill kaolin deposit and mineralogical investigations (X-ray, SEM), two main types of Miocene sandstones are distinguished: (i) clayey-silty kaolinitic sandstones with stacks of idiomorphic pseudohexagonal kaolinite crystals; (ii) massive clayey-silty kaolinitic sandstones with irregular fabric of isolated kaolinite plates. The Precambrian metamorphic rocks of the Uluguru Mountains are a probable source for the kaolinitic sediments of the Pugu Hill Formation. Decomposition products of weathering profiles on meta-anorthosites are mainly 7Å- and 10Å-halloysite and gibbsite. It is suggested that the kaolinitic sandstones were deposited in a former delta. The first sandstone type is considered to have developed in situ from weathered arkosic sandstone, and the second represents channel deposits in an old river system (probably a Miocene predecessor of the Ruvu River) with kaolin transported from a hinterland and redeposited. The variable formation and fabric of the kaolinites in the Pugu Hill Formation are due to in situ weathering of transported primary minerals (fedspar), and to transported weathered material (with secondary halloysite).
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    Electronic ISSN: 1471-8030
    Topics: Geosciences
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