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Redetermination of durangite, NaAl(AsO(4))F.

Downs GW, Yang BN, Thompson RM, Wenz MD, Andrade MB - Acta Crystallogr Sect E Struct Rep Online (2012)

Bottom Line: The Na(+) cation (site symmetry 2) occupies the inter-stitial sites and is coordinated by one F(-) and six O(2-) anions.The AlO(4)F(2) octa-hedron has symmetry -1; it is flattened, with the Al-F bond length [1.8457 (4) Å] shorter than the Al-O bond lengths [1.8913 (8) and 1.9002 (9) Å].Examination of the Raman spectra for arsenate minerals in the titanite group reveals that the position of the band originating from the As-O symmetric stretching vibrations shifts to lower wavenumbers from durangite, maxwellite [ideally NaFe(AsO(4))F], to tilasite [CaMg(AsO(4))F].

View Article: PubMed Central - HTML - PubMed

Affiliation: University High School, 421 N. Arcadia Avenue, Tucson, Arizona 85711-3032, USA.

ABSTRACT
The crystal structure of durangite, ideally NaAl(AsO(4))F (chemical name sodium aluminium arsenate fluoride), has been determined previously [Kokkoros (1938). Z. Kristallogr.99, 38-49] using Weissenberg film data without reporting displacement parameters of atoms or a reliability factor. This study reports the redetermination of the structure of durangite using single-crystal X-ray diffraction data from a natural sample with composition (Na(0.95)Li(0.05))(Al(0.91)Fe(3+) (0.07)Mn(3+) (0.02))(AsO(4))(F(0.73)(OH)(0.27)) from the type locality, the Barranca mine, Coneto de Comonfort, Durango, Mexico. Durangite is isostructural with minerals of the titanite group in the space group C2/c. Its structure is characterized by kinked chains of corner-sharing AlO(4)F(2) octa-hedra parallel to the c axis. These chains are cross-linked by isolated AsO(4) tetra-hedra, forming a three-dimensional framework. The Na(+) cation (site symmetry 2) occupies the inter-stitial sites and is coordinated by one F(-) and six O(2-) anions. The AlO(4)F(2) octa-hedron has symmetry -1; it is flattened, with the Al-F bond length [1.8457 (4) Å] shorter than the Al-O bond lengths [1.8913 (8) and 1.9002 (9) Å]. Examination of the Raman spectra for arsenate minerals in the titanite group reveals that the position of the band originating from the As-O symmetric stretching vibrations shifts to lower wavenumbers from durangite, maxwellite [ideally NaFe(AsO(4))F], to tilasite [CaMg(AsO(4))F].

No MeSH data available.


Related in: MedlinePlus

The Raman spectra of durangite, maxwellite, and tilasite. The spectra are shown with vertical offset for clarity.
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Fap2: The Raman spectra of durangite, maxwellite, and tilasite. The spectra are shown with vertical offset for clarity.


Redetermination of durangite, NaAl(AsO(4))F.

Downs GW, Yang BN, Thompson RM, Wenz MD, Andrade MB - Acta Crystallogr Sect E Struct Rep Online (2012)

The Raman spectra of durangite, maxwellite, and tilasite. The spectra are shown with vertical offset for clarity.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3515088&req=5

Fap2: The Raman spectra of durangite, maxwellite, and tilasite. The spectra are shown with vertical offset for clarity.
Bottom Line: The Na(+) cation (site symmetry 2) occupies the inter-stitial sites and is coordinated by one F(-) and six O(2-) anions.The AlO(4)F(2) octa-hedron has symmetry -1; it is flattened, with the Al-F bond length [1.8457 (4) Å] shorter than the Al-O bond lengths [1.8913 (8) and 1.9002 (9) Å].Examination of the Raman spectra for arsenate minerals in the titanite group reveals that the position of the band originating from the As-O symmetric stretching vibrations shifts to lower wavenumbers from durangite, maxwellite [ideally NaFe(AsO(4))F], to tilasite [CaMg(AsO(4))F].

View Article: PubMed Central - HTML - PubMed

Affiliation: University High School, 421 N. Arcadia Avenue, Tucson, Arizona 85711-3032, USA.

ABSTRACT
The crystal structure of durangite, ideally NaAl(AsO(4))F (chemical name sodium aluminium arsenate fluoride), has been determined previously [Kokkoros (1938). Z. Kristallogr.99, 38-49] using Weissenberg film data without reporting displacement parameters of atoms or a reliability factor. This study reports the redetermination of the structure of durangite using single-crystal X-ray diffraction data from a natural sample with composition (Na(0.95)Li(0.05))(Al(0.91)Fe(3+) (0.07)Mn(3+) (0.02))(AsO(4))(F(0.73)(OH)(0.27)) from the type locality, the Barranca mine, Coneto de Comonfort, Durango, Mexico. Durangite is isostructural with minerals of the titanite group in the space group C2/c. Its structure is characterized by kinked chains of corner-sharing AlO(4)F(2) octa-hedra parallel to the c axis. These chains are cross-linked by isolated AsO(4) tetra-hedra, forming a three-dimensional framework. The Na(+) cation (site symmetry 2) occupies the inter-stitial sites and is coordinated by one F(-) and six O(2-) anions. The AlO(4)F(2) octa-hedron has symmetry -1; it is flattened, with the Al-F bond length [1.8457 (4) Å] shorter than the Al-O bond lengths [1.8913 (8) and 1.9002 (9) Å]. Examination of the Raman spectra for arsenate minerals in the titanite group reveals that the position of the band originating from the As-O symmetric stretching vibrations shifts to lower wavenumbers from durangite, maxwellite [ideally NaFe(AsO(4))F], to tilasite [CaMg(AsO(4))F].

No MeSH data available.


Related in: MedlinePlus