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@ARTICLE{Gatta:190043,
      author       = {Gatta, G. D. and Vignola, P. and Meven, M. and Rinaldi, R.},
      title        = {{N}eutron diffraction in gemology: {S}ingle-crystal
                      diffraction study of brazilianite,
                      {N}a{A}l$_{3}$({PO}$_{4}$)$_{2}$({OH})$_{4}$},
      journal      = {American mineralogist},
      volume       = {98},
      number       = {8-9},
      issn         = {0003-004X},
      address      = {Berlin},
      publisher    = {de @Gruyter},
      reportid     = {FZJ-2015-03002},
      pages        = {1624 - 1630},
      year         = {2013},
      abstract     = {The chemical composition and the crystal structure of a
                      gem-quality brazilianite from the Telírio pegmatite, near
                      Linópolis, Minas Gerais, Brazil, [NaAl3(PO4)2(OH)4, a =
                      11.2448(5) Å, b = 10.1539(6) Å, c = 7.1031(3) Å, β =
                      97.351(4)°, V = 804.36(7) Å3, space group P21/n, Z = 4],
                      have been reinvestigated by means of electron microprobe
                      analysis in wavelength-dispersive mode, single-crystal X-ray
                      and neutron diffraction. The chemical analysis shows that
                      brazilianite from Telírio Claim approaches almost ideal
                      composition. The neutron anisotropic structural refinement
                      was performed with final agreement index R1 = 0.0290 for 211
                      refined parameters and 2844 unique reflections with Fo >
                      4σ(Fo), the X-ray refinement led to R1 = 0.0325 for 169
                      refined parameters and 2430 unique reflections with Fo >
                      4σ(Fo). The building-block units of the brazilianite
                      structure consist of chains of edge-sharing AlO4(OH)2 and
                      AlO3(OH)3 octahedra. Chains are connected, via
                      corner-sharing, by P-tetrahedra to form a three-dimensional
                      framework, with Na atoms located in distorted cavities
                      running along [100]. Five independent H sites were located,
                      here labeled as H(1), H(2a), H(2b), H(3), and H(4). The
                      configuration of the OH groups, along with the complex
                      hydrogen-bonding scheme, are now well defined. The O-H
                      distances corrected for “riding motion” range between
                      ~0.992 and ~1.010 Å, the O···O distances between ~2.67
                      and ~2.93 Å, and the O-H···O angles between ~151° and
                      ~174°. The H(2a) and H(2b) are only ~1.37 Å apart and
                      mutually exclusive (both with site occupancy factor of
                      $50\%).$ The differences between the crystal structure of
                      brazilianite and wardite [ideally NaAl3(PO4)2(OH)4·2H2O]
                      are discussed. This work fulfills the need for accurate
                      crystal-chemical data for this gem mineral.},
      cin          = {JCNS (München) ; Jülich Centre for Neutron Science JCNS
                      (München) ; JCNS-FRM-II / JCNS-2 / PGI-4 / JARA-FIT},
      ddc          = {550},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)PGI-4-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {54G - JCNS (POF2-54G24) / NMI3 - Integrated Infrastructure
                      Initiative for Neutron Scattering and Muon Spectroscopy
                      (226507)},
      pid          = {G:(DE-HGF)POF2-54G24 / G:(EU-Grant)226507},
      experiment   = {EXP:(DE-MLZ)HEIDI-20140101},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000323584000030},
      doi          = {10.2138/am.2013.4476},
      url          = {https://juser.fz-juelich.de/record/190043},
}