Aegirine

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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.

  • Single-crystal X-ray diffraction and temperature dependent 57Fe Mössbauer spectroscopy on the hedenbergite-Aegirine (Ca,Na)(Fe2+,Fe3+)Si2O6 solid solution
    American Mineralogist, 2006
    Co-Authors: Günther J. Redhammer, Georg Amthauer, Georg Roth, Gerold Tippelt, Werner Lottermoser
    Abstract:

    Synthetic samples with different chemical compositions along the hedenbergite–Aegirine (CaFe 2+ Si 2 O 6 –NaFe 3+ Si 2 O 6 ) solid-solution series have been investigated by single-crystal X-ray diffraction and 57 Fe Mossbauer spectroscopy. All compounds show C 2 /c symmetry, both at 298 K and at low temperature (100 K). The structural changes within the hedenbergite–Aegirine series are dominated by the M1 site while the M2 site plays a minor role. Replacement of Fe 2+ by Fe 3+ increases the polyhedral distortion of the M1 site and causes an increased repulsion between neighboring M1 sites. The changes in M1-site geometry also induce distinct alterations within the kinking state of the tetrahedral chains, but the changes in tetrahedral bond lengths and angles are small. In addition to the single-crystal X-ray diffraction experiments, a large number of synthetic samples were investigated by 57 Fe Mossbauer spectroscopy at 298 K and, for three selected compositions, between 80 and 700 K. Here, substantial line broadening of the Fe 2+ resonance absorption was observed as an Aegirine component is substituted. Two different groups of local distortion environments were observed for Fe 2+ within the solid-solution series, which change relative proportions and numeric value of the quadrupole splitting as a function of chemistry and temperature. This line broadening cannot be ascribed to discrete next-nearest-neighbor (NNN) configurations of Ca and Na as has been done in the literature. Above ~250 K, additional resonance absorption appears in the spectra of samples with Aegirine components between 20 and 75 mol%. This absorption gains intensity with increasing temperature, while the 57 Fe hyperfine parameters approach values intermediate between Fe 2+ and Fe 3+ . This effect is ascribed to fast electron delocalization between Fe 2+ and Fe 3+ at elevated temperature.

  • single crystal x ray diffraction and temperature dependent 57fe mossbauer spectroscopy on the hedenbergite Aegirine ca na fe2 fe3 si2o6 solid solution
    American Mineralogist, 2006
    Co-Authors: Günther J. Redhammer, Georg Amthauer, Georg Roth, Gerold Tippelt, Werner Lottermoser
    Abstract:

    Synthetic samples with different chemical compositions along the hedenbergite–Aegirine (CaFe 2+ Si 2 O 6 –NaFe 3+ Si 2 O 6 ) solid-solution series have been investigated by single-crystal X-ray diffraction and 57 Fe Mossbauer spectroscopy. All compounds show C 2 /c symmetry, both at 298 K and at low temperature (100 K). The structural changes within the hedenbergite–Aegirine series are dominated by the M1 site while the M2 site plays a minor role. Replacement of Fe 2+ by Fe 3+ increases the polyhedral distortion of the M1 site and causes an increased repulsion between neighboring M1 sites. The changes in M1-site geometry also induce distinct alterations within the kinking state of the tetrahedral chains, but the changes in tetrahedral bond lengths and angles are small. In addition to the single-crystal X-ray diffraction experiments, a large number of synthetic samples were investigated by 57 Fe Mossbauer spectroscopy at 298 K and, for three selected compositions, between 80 and 700 K. Here, substantial line broadening of the Fe 2+ resonance absorption was observed as an Aegirine component is substituted. Two different groups of local distortion environments were observed for Fe 2+ within the solid-solution series, which change relative proportions and numeric value of the quadrupole splitting as a function of chemistry and temperature. This line broadening cannot be ascribed to discrete next-nearest-neighbor (NNN) configurations of Ca and Na as has been done in the literature. Above ~250 K, additional resonance absorption appears in the spectra of samples with Aegirine components between 20 and 75 mol%. This absorption gains intensity with increasing temperature, while the 57 Fe hyperfine parameters approach values intermediate between Fe 2+ and Fe 3+ . This effect is ascribed to fast electron delocalization between Fe 2+ and Fe 3+ at elevated temperature.

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, Marco Bruno, Fabrizio Nestola, 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, Marco Bruno, Fabrizio Nestola, 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, Tiziana Boffa Ballaran, Christian Liebske, 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.

  • the crystal structure of pyroxenes along the jadeite hedenbergite and jadeite Aegirine joins
    American Mineralogist, 2007
    Co-Authors: Fabrizio Nestola, Mario Tribaudino, Christian Liebske, Boffa T 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.

  • high pressure behaviour along the jadeite naalsi2o6 Aegirine nafesi2o6 solid solution up to 10 gpa
    Physics and Chemistry of Minerals, 2006
    Co-Authors: Marco Bruno, Fabrizio Nestola, Tiziana Boffa Ballaran, Christian Liebske, Mario Tribaudino
    Abstract:

    The volume variation as a function of pressure along the jadeite–Aegirine solid solution was determined at room temperature up to pressures between 6.5 and 9.7 GPa by single-crystal X-ray diffraction. The unit-cell volumes collected at room pressure for the different compositions indicate a slight deviation from linearity along the join. The pressure–volume data have been fitted using a third-order Birch-Murnaghan equation of state (BM3-EoS). The bulk modulus, KT0, varies from 134.0(7) GPa for pure jadeite to 116.1(5) GPa for pure Aegirine. Its evolution with composition along the join is not linear and can be described by the following second order polynomial: $$ K_{{T0}} = 116.2(5) + [0.25(3) \times ({\text{mol}}\% {\text{Jd}})] - [0.0008(3) \times ({\text{mol}}\% {\text{Jd}})^{2} ] $$ (1) The value of the first pressure derivative K′ is close to 4 for all the samples investigated and can be used in a BM3-EoS to determine the volume variations of these pyroxenes up to 7–10 GPa. Along the join the highest compressibility among the crystallographic directions is always observed along a, however, the compression along b is the most affected by compositional changes. The strain ellipsoid analysis indicates that the major compression occurs on the (0 1 0) plane along a direction at about 145° to the c axis (from c to a). The anisotropy of the compression increases with increasing the Aegirine component, as confirmed by the analysis of both the axial compressibility and the strain tensor.

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, Marco Bruno, Fabrizio Nestola, 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, Marco Bruno, Fabrizio Nestola, 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, Tiziana Boffa Ballaran, Christian Liebske, 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.

  • the crystal structure of pyroxenes along the jadeite hedenbergite and jadeite Aegirine joins
    American Mineralogist, 2007
    Co-Authors: Fabrizio Nestola, Mario Tribaudino, Christian Liebske, Boffa T 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.

  • 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.

Christian Liebske - 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, Marco Bruno, Fabrizio Nestola, 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, Marco Bruno, Fabrizio Nestola, 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, Tiziana Boffa Ballaran, Christian Liebske, 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.

  • the crystal structure of pyroxenes along the jadeite hedenbergite and jadeite Aegirine joins
    American Mineralogist, 2007
    Co-Authors: Fabrizio Nestola, Mario Tribaudino, Christian Liebske, Boffa T 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.

  • high pressure behaviour along the jadeite naalsi2o6 Aegirine nafesi2o6 solid solution up to 10 gpa
    Physics and Chemistry of Minerals, 2006
    Co-Authors: Marco Bruno, Fabrizio Nestola, Tiziana Boffa Ballaran, Christian Liebske, Mario Tribaudino
    Abstract:

    The volume variation as a function of pressure along the jadeite–Aegirine solid solution was determined at room temperature up to pressures between 6.5 and 9.7 GPa by single-crystal X-ray diffraction. The unit-cell volumes collected at room pressure for the different compositions indicate a slight deviation from linearity along the join. The pressure–volume data have been fitted using a third-order Birch-Murnaghan equation of state (BM3-EoS). The bulk modulus, KT0, varies from 134.0(7) GPa for pure jadeite to 116.1(5) GPa for pure Aegirine. Its evolution with composition along the join is not linear and can be described by the following second order polynomial: $$ K_{{T0}} = 116.2(5) + [0.25(3) \times ({\text{mol}}\% {\text{Jd}})] - [0.0008(3) \times ({\text{mol}}\% {\text{Jd}})^{2} ] $$ (1) The value of the first pressure derivative K′ is close to 4 for all the samples investigated and can be used in a BM3-EoS to determine the volume variations of these pyroxenes up to 7–10 GPa. Along the join the highest compressibility among the crystallographic directions is always observed along a, however, the compression along b is the most affected by compositional changes. The strain ellipsoid analysis indicates that the major compression occurs on the (0 1 0) plane along a direction at about 145° to the c axis (from c to a). The anisotropy of the compression increases with increasing the Aegirine component, as confirmed by the analysis of both the axial compressibility and the strain tensor.

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  • Alkali pyroxenes and amphiboles: a window on rare earth elements and other high field strength elements behavior through the magmatic-hydrothermal transition of peralkaline granitic systems
    Contributions to Mineralogy and Petrology, 2020
    Co-Authors: Cyrielle Bernard, Guillaume Estrade, Stefano Salvi, Didier Béziat, Martin Smith
    Abstract:

    Peralkaline granites and pegmatites are a prime repository of REE and HFSE, critical raw materials. Although it is accepted that magmatic processes are fundamental in concentrating these metals, the role of hydrothermal fluids in concentrating and fractionating these elements remains unclear. This paper investigates the global reproducibility of the magmatic-hydrothermal evolution of alkaline silica-saturated systems using alkali pyroxene and amphiboles from six alkaline complexes. These minerals contain significant amounts of REE and other HFSE, and pyroxene is stable throughout the magmatic and hydrothermal stages. Amphibole consists of mostly unzoned arfvedsonite, leakeite, and katophorite, while pyroxene is always Aegirine. Two types of Aegirine were defined. In all complexes, type-I Aegirine is zoned; its core is enriched in Ca, REE, Zr, Hf, Sc and Sn, and the rims in Na, Fe^3+ and contains secondary rare-metal bearing minerals and fluid inclusions. Type-II Aegirine replaces amphibole and is oscillatory zoned. We interpret the amphiboles and REE-rich cores of type-I Aegirine to have grown during the magmatic stage, whereas the rims of REE-poorer type-I and II Aegirine are formed during the hydrothermal stage. During magmatic crystallization, REE intake into amphiboles and pyroxene as well as LREE-HREE fractionation were favored by their crystallographic properties and by competition among them and other minerals. During subsequent hydrothermal stages, REE and other HFSE were remobilized, locally reconcentrated and fractionated in mineral pseudomorphs and secondary pyroxene. These observations point out the importance of studying rock-forming minerals such as pyroxenes and amphiboles to unravel geological events controlled by common processes globally.