On the symmetry and crystal chemistry of britholite: new structural and microanalytical data (Articolo in rivista)

Type
Label
  • On the symmetry and crystal chemistry of britholite: new structural and microanalytical data (Articolo in rivista) (literal)
Anno
  • 2001-01-01T00:00:00+01:00 (literal)
Alternative label
  • OBERTI R.; OTTOLINI L.; DELLA VENTURA G.; PARODI G.C. (2001)
    On the symmetry and crystal chemistry of britholite: new structural and microanalytical data
    in The American mineralogist
    (literal)
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  • OBERTI R.; OTTOLINI L.; DELLA VENTURA G.; PARODI G.C. (literal)
Pagina inizio
  • 1066 (literal)
Pagina fine
  • 1075 (literal)
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  • This is another example of the very accurate results and of the sound crystal-chemical models that can be achieved when combining sophisticated analytical procedures, single-crystal structure refinement and infrared spectroscopy to the characterisation of complex mineral phases. Some of the results allow a better understanding of the structural changes with composition, and thus are relevant to all these studies which exploit either the properties of the apatite structure or its capability to incorporate REE or actinides. The American Mineralogist is the journal with the highest impact factor in mineralogy. (literal)
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  • 86 (literal)
Rivista
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  • Impact Factor 1,806 (literal)
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  • Combination of structural and micro-chemical (electron- and ion-probe analysis for intermediate Z and low and high-Z elements, respectively) analysis of two britholites samples gave the following compositions (Mn0.04Ca4.75REE4.37Th0.72U0.12)10.00(Si5.57P0.25B0.16)5.98O24 (OH0.23F1.77)2.00 and (Na0.98Ca2.01REE6.97)9.96 (Si5.07P0.75)5.82 O24 (OH0.53F1.47)2. Structure refinements indicate that the best approximation to the real symmetry is the P63 space group. In britholite, the lowering of symmetry with respect to the P63/m space group of apatite makes the O3 and O3a oxygen atoms no longer equivalent and allows a rotation of the tetrahedron of up to ~ 4° around the Si-O1 bond. Consequently, the O3a oxygen moves closer to the REE1a site, whereas the O3 oxygen moves farther from the REE1 site and closer to the REE2 site, which thus assumes a [7+1] coordination. The infrared spectrum of britholite shows a unique and very broad band in the OH-stretching region at 3437 cm-1, which is consistent with the ordering of trivalent REE cations at the REE2 site. A remarkable constancy in the unit-cell volume along the whole apatite-britholite compositional range is observed for values of the aggregate ionic radius at the REE sites shorter than 1.12 and longer than 1.15 Å, whereas large variations are observed for intermediate values; this behaviour suggests constraints due to the rigidity of the tetrahedral group, that is further enhanced at high symmetry. (literal)
Note
  • ISI Web of Science (WOS) (literal)
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  • R. Oberti a), L. Ottolini a), G. Della Ventura b) G.C. Parodi c). a) CNR-IGG Sezione di Pavia, via Ferrata 1, I-27100 Pavia, Italy, b) Dipartimento di Scienze della Terra, Università della Calabria, I-87030 Arcavacata di Rende, Italy, c) Laboratoire de Minéralogie, Museum National d’Histoire Naturelle, rue Buffon 61, F-75005 Paris, France (literal)
Titolo
  • On the symmetry and crystal chemistry of britholite: new structural and microanalytical data (literal)
Abstract
  • Combination of structural and micro-chemical (electron- and ion-probe analysis for intermediate Z and low and high-Z elements, respectively) analysis of two britholites samples gave the following compositions (Mn0.04Ca4.75REE4.37Th0.72U0.12)10.00(Si5.57P0.25B0.16)5.98O24 (OH0.23F1.77)2.00 and (Na0.98Ca2.01REE6.97)9.96 (Si5.07P0.75)5.82 O24 (OH0.53F1.47)2. Structure refinements indicate that the best approximation to the real symmetry is the P63 space group. In britholite, the lowering of symmetry with respect to the P63/m space group of apatite makes the O3 and O3a oxygen atoms no longer equivalent and allows a rotation of the tetrahedron of up to ~ 4° around the Si-O1 bond. Consequently, the O3a oxygen moves closer to the REE1a site, whereas the O3 oxygen moves farther from the REE1 site and closer to the REE2 site, which thus assumes a [7+1] coordination. The infrared spectrum of britholite shows a unique and very broad band in the OH-stretching region at 3437 cm-1, which is consistent with the ordering of trivalent REE cations at the REE2 site. A remarkable constancy in the unit-cell volume along the whole apatite-britholite compositional range is observed for values of the aggregate ionic radius at the REE sites shorter than 1.12 and longer than 1.15 Å, whereas large variations are observed for intermediate values; this behaviour suggests constraints due to the rigidity of the tetrahedral group, that is further enhanced at high symmetry. (literal)
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