Journal article Open Access
Gatta, G. Diego; Vignola, Pietro; Meven, Martin; Rinaldi, Romano
<?xml version='1.0' encoding='utf-8'?> <resource xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://datacite.org/schema/kernel-4" xsi:schemaLocation="http://datacite.org/schema/kernel-4 http://schema.datacite.org/meta/kernel-4.1/metadata.xsd"> <identifier identifierType="URL">https://www.openaccessrepository.it/record/21900</identifier> <creators> <creator> <creatorName>Gatta, G. Diego</creatorName> <givenName>G. Diego</givenName> <familyName>Gatta</familyName> </creator> <creator> <creatorName>Vignola, Pietro</creatorName> <givenName>Pietro</givenName> <familyName>Vignola</familyName> </creator> <creator> <creatorName>Meven, Martin</creatorName> <givenName>Martin</givenName> <familyName>Meven</familyName> </creator> <creator> <creatorName>Rinaldi, Romano</creatorName> <givenName>Romano</givenName> <familyName>Rinaldi</familyName> </creator> </creators> <titles> <title>Neutron diffraction in gemology: Single-crystal diffraction study of brazilianite, NaAl3(PO4)(2)(OH)(4)</title> </titles> <publisher>INFN Open Access Repository</publisher> <publicationYear>2013</publicationYear> <subjects> <subject>FP7</subject> <subject>European Commission</subject> <subject>Research Infrastructures</subject> <subject>EC</subject> <subject>SP4-Capacities</subject> </subjects> <dates> <date dateType="Issued">2013-01-01</date> </dates> <language>en</language> <resourceType resourceTypeGeneral="Text">Journal article</resourceType> <alternateIdentifiers> <alternateIdentifier alternateIdentifierType="url">https://www.openaccessrepository.it/record/21900</alternateIdentifier> </alternateIdentifiers> <relatedIdentifiers> <relatedIdentifier relatedIdentifierType="DOI" relationType="IsIdenticalTo">10.2138/am.2013.4476</relatedIdentifier> <relatedIdentifier relatedIdentifierType="URL" relationType="IsPartOf">https://www.openaccessrepository.it/communities/itmirror</relatedIdentifier> </relatedIdentifiers> <rightsList> <rights rightsURI="info:eu-repo/semantics/openAccess">Open Access</rights> </rightsList> <descriptions> <description descriptionType="Abstract"><p>The chemical composition and the crystal structure of a gem-quality brazilianite from the Tel&iacute;rio pegmatite, near Lin&oacute;polis, Minas Gerais, Brazil, [NaAl3(PO4)2(OH)4, a = 11.2448(5) &Aring;, b = 10.1539(6) &Aring;, c = 7.1031(3) &Aring;, &beta; = 97.351(4)&deg;, V = 804.36(7) &Aring;3, 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 Tel&iacute;rio 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 &gt; 4&sigma;(Fo), the X-ray refinement led to R1 = 0.0325 for 169 refined parameters and 2430 unique reflections with Fo &gt; 4&sigma;(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 &quot;riding motion&quot; range between ~0.992 and ~1.010 &Aring;, the O&middot;&middot;&middot;O distances between ~2.67 and ~2.93 &Aring;, and the O-H&middot;&middot;&middot;O angles between ~151&deg; and ~174&deg;. The H(2a) and H(2b) are only ~1.37 &Aring; 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&middot;2H2O] are discussed. This work fulfills the need for accurate crystal-chemical data for this gem mineral.</p></description> <description descriptionType="Other">Funded by the European Union. Part of the European Commission FP7 Open Access pilot.</description> </descriptions> </resource>
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