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Günther J. Redhammer – One of the best experts on this subject based on the ideXlab platform.

  • In situ high-pressure single-crystal X-ray study of Aegirine, NaFe3+Si2O6, and the role of M1 size in clinopyroxene compressibility
    American Mineralogist, 2008
    Co-Authors: Andrew C. Mccarthy, Robert T. Downs, Richard M. Thompson, Günther J. Redhammer

    Abstract:

    The crystal structure of a synthetic Aegirine crystal, NaFe 3+ Si 2 O 6 , was studied at room temperature, under hydrostatic conditions, over the pressure range 0–11.55 GPa using single-crystal X-ray diffraction. Unit-cell data were determined at 16 pressures, and intensity data were collected at eight of these pressures. A third-order Birch-Murnaghan equation of state fit to the P-V data from 0–11.55 GPa yielded K 0 = 117(1) GPa, K 0 ′ = 3.2(2), and V 0 = 429.40(9) A 3 . Aegirine, like the other Na-clinopyroxenes that have been examined at high pressure, exhibits strongly anisotropic compression, with unit strain axial ratios e 1 :e 2 :e 3 of 1.00:2.38:2.63. Silicate chains in Aegirine become more O-rotated with pressure, reducing ∠O3-O3-O3 from 174.1(1)° at ambient pressure to 165.5(5)° at 10.82 GPa. No evidence of a phase transition was observed over the studied pressure range. The relationship between M1 cation radius and bulk modulus is examined for 14 clinopyroxenes, and two distinct trends are identified in a plot of these values. The distinction between these trends can be explained by the presence or absence of antipathetic bonds around M2, a feature first described by McCarthy et al. (2008). Aegirine, with Fe 3+ , has nearly the same bulk modulus, within error, as hedenbergite, with Fe 2+ , despite the difference in M2 bonding topology, M2 (Fe) valence and ambient unit-cell volume. Several explanations for this apparent paradox are considered.

  • in situ high pressure single crystal x ray study of Aegirine nafe3 si2o6 and the role of m1 size in clinopyroxene compressibility
    American Mineralogist, 2008
    Co-Authors: Andrew C. Mccarthy, Robert T. Downs, Richard M. Thompson, Günther J. Redhammer

    Abstract:

    The crystal structure of a synthetic Aegirine crystal, NaFe 3+ Si 2 O 6 , was studied at room temperature, under hydrostatic conditions, over the pressure range 0–11.55 GPa using single-crystal X-ray diffraction. Unit-cell data were determined at 16 pressures, and intensity data were collected at eight of these pressures. A third-order Birch-Murnaghan equation of state fit to the P-V data from 0–11.55 GPa yielded K 0 = 117(1) GPa, K 0 ′ = 3.2(2), and V 0 = 429.40(9) A 3 . Aegirine, like the other Na-clinopyroxenes that have been examined at high pressure, exhibits strongly anisotropic compression, with unit strain axial ratios e 1 :e 2 :e 3 of 1.00:2.38:2.63. Silicate chains in Aegirine become more O-rotated with pressure, reducing ∠O3-O3-O3 from 174.1(1)° at ambient pressure to 165.5(5)° at 10.82 GPa. No evidence of a phase transition was observed over the studied pressure range. The relationship between M1 cation radius and bulk modulus is examined for 14 clinopyroxenes, and two distinct trends are identified in a plot of these values. The distinction between these trends can be explained by the presence or absence of antipathetic bonds around M2, a feature first described by McCarthy et al. (2008). Aegirine, with Fe 3+ , has nearly the same bulk modulus, within error, as hedenbergite, with Fe 2+ , despite the difference in M2 bonding topology, M2 (Fe) valence and ambient unit-cell volume. Several explanations for this apparent paradox are considered.

  • Crystal chemistry of Aegirine as an indicator of P-T conditions
    Mineralogical Magazine, 2007
    Co-Authors: L. Secco, Fabrizio Nestola, Günther J. Redhammer, Alessandro Guastoni, A. Dal Negro

    Abstract:

    One metamorphic and four magmatic Aegirines, together with two end-member Aegirines synthesized at atmospheric pressure and different temperatures, were investigated by single-crystal X-ray diffraction. The limited compositional differences allow the polyhedral volumes to be almost constant in all the Aegirines investigated ( V M 1 ≈ 11.0 A 3 ; V M 2 ≈ 26.3 A 3 ; V T ≈ 2.21 A 3 ). However, differences in polyhedral distortions are responsible for the cell-volume variations, reflected mainly in the change of a and β cell parameters. Cell volume is only partly related to the composition of these Aegirines: with increasing formation temperature, an increase in the unit-cell volume of ~1.2 A 3 is observed, while a significant contraction of the cell volume occurs during high-pressure formation. As the difference in cell volume between the two synthetic Aegirines is ascribed to the different conditions of synthesis temperature, the same interpretation could be adopted for the differences observed in natural Aegirines.

Marco Bruno – One of the best experts on this subject based on the ideXlab platform.

  • Thermal expansion along the NaAlSi_2O_6–NaFe^3+Si_2O_6 and NaAlSi_2O_6–CaFe^2+Si_2O_6 solid solutions
    Physics and Chemistry of Minerals, 2008
    Co-Authors: Mario Tribaudino, Fabrizio Nestola, Marco Bruno, Tiziana Boffa Ballaran, Christian Liebske

    Abstract:

    The high temperature volume and axial parameters for six C 2/ c clinopyroxenes along the NaAlSi_2O_6–NaFe^3+Si_2O_6 and NaAlSi_2O_6–CaFe^2+Si_2O_6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln( V / V _0) = α( T  −  T _0). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant between jadeite and Aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and Aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–Aegirine join instead the high-temperature and high-pressure strain are differently oriented.

  • Thermal expansion along the NaAlSi2O6-NaFe3+Si2O6 and NaAlSi2O6-CaFe2+Si2O6 solid solutions
    Physics and Chemistry of Minerals, 2008
    Co-Authors: Mario Tribaudino, Fabrizio Nestola, Marco Bruno, Tiziana Boffa Ballaran, Christian Liebske

    Abstract:

    The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V
    0) = α(T − T
    0). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant between jadeite and Aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and Aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–Aegirine join instead the high-temperature and high-pressure strain are differently oriented.

  • The crystal structure of pyroxenes along the jadeite–hedenbergite and jadeite–Aegirine joins
    American Mineralogist, 2007
    Co-Authors: Fabrizio Nestola, Mario Tribaudino, Christian Liebske, Tiziana Boffa Ballaran, Marco Bruno

    Abstract:

    The crystal-structures of seven synthetic pyroxenes along the jadeite–hedenbergite (Jd57Hd43, Jd26Hd74, JdHd100) and jadeite–Aegirine (Jd100Ae, Jd76Ae24, Jd35Ae65, JdAe100) joins were refined using data collected by means of single-crystal X-ray diffraction (space group C 2/ c , R 4σ between 2.2 and 3.4%).

    The M2 and M1 polyhedral volumes and bond lengths increase with increasing Aegirine and heden-bergite content, moreover the Ca for Na substitution along the jadeite–hedenbergite join changes the M2 coordination from 6 + 2 to 4 + 4, with remarkable tilting of the tetrahedral chains. The value of the displacement parameters follows the trend U eqM2 > U eqO2 > U eqO3 > U eqO1 > U eqM1 ≈ U eqT for all samples belonging to the jadeite–Aegirine join and for pure hedenbergite; in contrast,, for pyroxenes with intermediate compositions between hedenbergite and jadeite the trend is U eqO1 > U eqO2 > U eqM2 > U eqO3 > U eqM1 ≈ U eqT, with O1 and O2 having anomalously large displacement parameters, probably due to different local structural configuration around the cations with different size and charge.

    Cation substitution at the M1 site of Na-pyroxenes gives rise to a different structural deformation with respect of the double substitution at both the M1 and M2 sites in (Na,Ca)(M3+,M2+)Si2O6 pyroxenes as the rigid tetrahedral chains try to accommodate both the increasing size of the M1 site and the different coordination requirement of the M2 site.

Fabrizio Nestola – One of the best experts on this subject based on the ideXlab platform.

  • Thermal expansion along the NaAlSi_2O_6–NaFe^3+Si_2O_6 and NaAlSi_2O_6–CaFe^2+Si_2O_6 solid solutions
    Physics and Chemistry of Minerals, 2008
    Co-Authors: Mario Tribaudino, Fabrizio Nestola, Marco Bruno, Tiziana Boffa Ballaran, Christian Liebske

    Abstract:

    The high temperature volume and axial parameters for six C 2/ c clinopyroxenes along the NaAlSi_2O_6–NaFe^3+Si_2O_6 and NaAlSi_2O_6–CaFe^2+Si_2O_6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln( V / V _0) = α( T  −  T _0). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant between jadeite and Aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and Aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–Aegirine join instead the high-temperature and high-pressure strain are differently oriented.

  • Thermal expansion along the NaAlSi2O6-NaFe3+Si2O6 and NaAlSi2O6-CaFe2+Si2O6 solid solutions
    Physics and Chemistry of Minerals, 2008
    Co-Authors: Mario Tribaudino, Fabrizio Nestola, Marco Bruno, Tiziana Boffa Ballaran, Christian Liebske

    Abstract:

    The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V
    0) = α(T − T
    0). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant between jadeite and Aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and Aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–Aegirine join instead the high-temperature and high-pressure strain are differently oriented.

  • The crystal structure of pyroxenes along the jadeite–hedenbergite and jadeite–Aegirine joins
    American Mineralogist, 2007
    Co-Authors: Fabrizio Nestola, Mario Tribaudino, Christian Liebske, Tiziana Boffa Ballaran, Marco Bruno

    Abstract:

    The crystal-structures of seven synthetic pyroxenes along the jadeite–hedenbergite (Jd57Hd43, Jd26Hd74, JdHd100) and jadeite–Aegirine (Jd100Ae, Jd76Ae24, Jd35Ae65, JdAe100) joins were refined using data collected by means of single-crystal X-ray diffraction (space group C 2/ c , R 4σ between 2.2 and 3.4%).

    The M2 and M1 polyhedral volumes and bond lengths increase with increasing Aegirine and heden-bergite content, moreover the Ca for Na substitution along the jadeite–hedenbergite join changes the M2 coordination from 6 + 2 to 4 + 4, with remarkable tilting of the tetrahedral chains. The value of the displacement parameters follows the trend U eqM2 > U eqO2 > U eqO3 > U eqO1 > U eqM1 ≈ U eqT for all samples belonging to the jadeite–Aegirine join and for pure hedenbergite; in contrast,, for pyroxenes with intermediate compositions between hedenbergite and jadeite the trend is U eqO1 > U eqO2 > U eqM2 > U eqO3 > U eqM1 ≈ U eqT, with O1 and O2 having anomalously large displacement parameters, probably due to different local structural configuration around the cations with different size and charge.

    Cation substitution at the M1 site of Na-pyroxenes gives rise to a different structural deformation with respect of the double substitution at both the M1 and M2 sites in (Na,Ca)(M3+,M2+)Si2O6 pyroxenes as the rigid tetrahedral chains try to accommodate both the increasing size of the M1 site and the different coordination requirement of the M2 site.