The crystal structures of niobophyllite, K(2) Na Fe(7)(2+) (NbTi) (Si(4)O(12))(2) O(2) (OH)(4) O, kupletskite-(Cs), Cs(2) Na Mn(7) Ti(2) (Si(4)O(12))(2) O(2) (OH)(4) F, and Sn-rich astrophyllite, K(2) Na Fe(7)(2+) Ti(2) (Si(4)O(12))(2) O(2) (OH)(4) F, all members of the astrophyllite group, have been refined in space group P (1) over bar to R(1) values 5.96, 3.33 and 3.53% for 3576, 3490 and 3791 observed [F(o) > 4 sigma F] unique reflections measured with MoK alpha radiation on a Bruker AXS diffractometer with a CCD SMART APEX detector. The crystal structures of all three minerals are topologically identical to that of triclinic astrophyllite. The crystals used in the collection of the X-ray intensity data were analyzed by electron microprobe, Fe(3+) : (Fe(2+) + Fe(3+)) ratios were measured by Mossbauer spectroscopy, and Li was determined by laser-ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS). The empirical formulae were calculated on an anion basis, (O + OH + F) = 31 apfu: niobophyllite, (K(1.79)Cs(0.03))(Sigma 1.82) Na(1.01) (Fe(4.02)(2+) Mn(1.98) Fe(0.55)(3+))(Sigma 6.55) (Nb(1.46)Ti(0.55)Ta(0.01))(Sigma 2.02) [(Si(7.77)Al(0.20))(Sigma 7.97)O(24)]O(2.73) [(OH)(4.13)F(0.13)](Sigma 4.26); kupletskite-(Cs), (Cs(1.42)K(0.36)Ca(0.08)Pb(0.06)Na(0.05)Sr(0.02))(Sigma 1.99) (Na(0.73)Ca(0.27))(Sigma 1) (Mn(3.74) Fe(1.82)(2+)Li(0.68)Zn(0.50)Fe(0.13)(3+)Mg(0.11))(Sigma 6.99) (Ti(1.54)Nb(0.45)Zr(0.02))(Sigma 2.01) [(Si(7.90)Al(0.05))(Sigma 7.95)O(24)] O(2.03) [(OH)(4.26) F(0.71)](Sigma 4.97); Sn-rich astrophyllite, (K(1.70)Ca(0.04)Cs(0.03)Pb(0.01))(Sigma 1.78) (Na(0.96)Ca(0.04))(Sigma 1) (Fe(6.18)(2+)Mn(0.45)Fe(0.26)(3+)Ca(0.09)Zn(0.02))(Sigma 7) (Ti(0.74)Sn(0.62)Nb(0.44)Zr(0.16)Ta(0.02)Mg(0.02))(Sigma 2.00) [(Si(7.75)Al(0.16))(Sigma 7.91)O(24)] O(2) [(OH)(4.356)F(0.65)](Sigma 5.00); Z = 1. In Sn-rich astrophyllite, Sn(4+) replaces Ti(4+) at the D site, and there is a corresponding expansion of the D octahedron: < D-phi > = 1.979 angstrom, where phi represents O, F, OH. The discovery of Sn-rich astrophyllite indicates that there is potential for a new species in the astrophyllite group with Sn(4+) as the dominant cation at the D site. We have identified three distinct A sites, A(1), A(2) and A(3) with coordinations [13], [5] and [13], respectively, that are separated by <= 1.2 angstrom such that locally adjacent sites cannot both be occupied.

The crystal structures of niobophyllite, kupletskite-(Cs) and Sn-rich astrophyllite: revisions to the crystal chemistry of the astrophyllite-group minerals

CAMARA ARTIGAS, Fernando;
2010-01-01

Abstract

The crystal structures of niobophyllite, K(2) Na Fe(7)(2+) (NbTi) (Si(4)O(12))(2) O(2) (OH)(4) O, kupletskite-(Cs), Cs(2) Na Mn(7) Ti(2) (Si(4)O(12))(2) O(2) (OH)(4) F, and Sn-rich astrophyllite, K(2) Na Fe(7)(2+) Ti(2) (Si(4)O(12))(2) O(2) (OH)(4) F, all members of the astrophyllite group, have been refined in space group P (1) over bar to R(1) values 5.96, 3.33 and 3.53% for 3576, 3490 and 3791 observed [F(o) > 4 sigma F] unique reflections measured with MoK alpha radiation on a Bruker AXS diffractometer with a CCD SMART APEX detector. The crystal structures of all three minerals are topologically identical to that of triclinic astrophyllite. The crystals used in the collection of the X-ray intensity data were analyzed by electron microprobe, Fe(3+) : (Fe(2+) + Fe(3+)) ratios were measured by Mossbauer spectroscopy, and Li was determined by laser-ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS). The empirical formulae were calculated on an anion basis, (O + OH + F) = 31 apfu: niobophyllite, (K(1.79)Cs(0.03))(Sigma 1.82) Na(1.01) (Fe(4.02)(2+) Mn(1.98) Fe(0.55)(3+))(Sigma 6.55) (Nb(1.46)Ti(0.55)Ta(0.01))(Sigma 2.02) [(Si(7.77)Al(0.20))(Sigma 7.97)O(24)]O(2.73) [(OH)(4.13)F(0.13)](Sigma 4.26); kupletskite-(Cs), (Cs(1.42)K(0.36)Ca(0.08)Pb(0.06)Na(0.05)Sr(0.02))(Sigma 1.99) (Na(0.73)Ca(0.27))(Sigma 1) (Mn(3.74) Fe(1.82)(2+)Li(0.68)Zn(0.50)Fe(0.13)(3+)Mg(0.11))(Sigma 6.99) (Ti(1.54)Nb(0.45)Zr(0.02))(Sigma 2.01) [(Si(7.90)Al(0.05))(Sigma 7.95)O(24)] O(2.03) [(OH)(4.26) F(0.71)](Sigma 4.97); Sn-rich astrophyllite, (K(1.70)Ca(0.04)Cs(0.03)Pb(0.01))(Sigma 1.78) (Na(0.96)Ca(0.04))(Sigma 1) (Fe(6.18)(2+)Mn(0.45)Fe(0.26)(3+)Ca(0.09)Zn(0.02))(Sigma 7) (Ti(0.74)Sn(0.62)Nb(0.44)Zr(0.16)Ta(0.02)Mg(0.02))(Sigma 2.00) [(Si(7.75)Al(0.16))(Sigma 7.91)O(24)] O(2) [(OH)(4.356)F(0.65)](Sigma 5.00); Z = 1. In Sn-rich astrophyllite, Sn(4+) replaces Ti(4+) at the D site, and there is a corresponding expansion of the D octahedron: < D-phi > = 1.979 angstrom, where phi represents O, F, OH. The discovery of Sn-rich astrophyllite indicates that there is potential for a new species in the astrophyllite group with Sn(4+) as the dominant cation at the D site. We have identified three distinct A sites, A(1), A(2) and A(3) with coordinations [13], [5] and [13], respectively, that are separated by <= 1.2 angstrom such that locally adjacent sites cannot both be occupied.
2010
48
1
16
http://canmin.geoscienceworld.org/content/48/1/1.abstract.fr
niobophyllite; kupletskite-(Cs); Sn-rich astrophyllite; astrophyllite group; crystal structure; electron-microprobe analysis; Mössbauer spectroscopy
Cámara F; Sokolova E; Abdu Y; Hawthorne FC
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/79069
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