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Rietveld Structure Refinement of the Kyanite Crystal from Negovanu (Sebeş-Lotru Series) Using X-ray Powder Diffraction Data
(Rafinarea Rietveld a structurii cristaline a distenului de la Negovanu (seria de Sebeş-Lotru) utiliznd date de difracţia razelor X pe pulberi)
Vol LXIII • No. 2/2011
Gheorghe Brănoiu, Octavian Georgescu
Universitatea Petrol-Gaze din Ploieşti, B-dul Bucureşti nr. 39, Ploieşti
e-mail: gbranoiu@yahoo.com

 Keywords   crystal structure, kyanite, X-ray powder diffraction, Rietveld refinement.

 Abstract
Kyanite is one of the three Al2SiO5 polymorphs, the other two being andalusite and sillimanite. The three aluminum silicate polymorphs (kyanite, sillimanite, and andalusite) are of major importance in metamorphic and experimental petrology because of their abundance in metamorphosed lutitic rocks and relatively simple chemistry.
The crystal structure of kyanite sampled from crystalline schists of Sebeş-Lotru Series (Negovanu, Cibin Mountains, Romania) from Getic nappe of Southern Carpathians has been refined using X-Ray powder diffraction data and the Rietveld method. The Rietveld refinements were carried out using the computer program Diffracplus TOPAS 4.1 (Bruker AXS GmbH). Pseudo-Voigt (pV) profile function was used for the fit of the peaks. Rietveld refinement using X-Ray powder diffraction data of kyanite sample in space group P-1 (No. 2), a=7.1491, b=7.8792, c=5.5912, α=89.75, β=101.16, γ=105.92, Z=4, confirm the basic kyanite structure.

 Rezumat
Distenul este una din cele trei faze polimorfe ale silicatului de aluminiu Al2SiO5, celelalte două fiind andaluzitul şi sillimanitul. Cele trei faze polimorfe ale silicatului de aluminiu Al2SiO5 prezintă o importanţă majoră n petrologia metamorfică şi experimentală datorită abundenţei lor n rocile lutitice metamorfozate şi a chimiei relativ simple.
Structura cristalină a unor cristale de disten prelevate din şisturile cristaline ale Seriei de Sebeş-Lotru (Negovanu, Munţii Cibinului) din Pnza Getică a Carpaţilor Meridionali a fost rafinată folosind difracţia de raze X pe pulberi şi metoda Rietveld. Rafinarea Rietveld a fost realizată cu ajutorul programului de calculator Diffracplus TOPAS 4.1 (Bruker AXS GmbH). Pentru potrivirea peakurilor a fost folosită funcţia pseudo-Voigt (pV). Rafinarea Rietveld utiliznd date de difracţie de raze X pe pulberi a eşantionului de disten n grupul spaţial P-1 (No. 2), a=7.1491, b=7.8792, c=5.5912, α=89.75, β=101.16, γ=105.92, Z=4, a confirmat structura de bază a distenului.



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