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The Rietveld Structure Refinement of the Marcasite Crystals from Herja Ore Deposit Using X-ray Powder Diffraction Data
(Rafinarea Rietveld a structurii cristaline a marcasitei din zăcământul Herja utilizând date de difracţia razelor X pe pulberi)
Vol LXVI • No. 2/2014
Gheorghe Brănoiu, Octavian Georgescu
Universitatea Petrol-Gaze din Ploieşti, Bd. Bucureşti nr. 39, Ploieşti
e-mail: gbranoiu@yahoo.com

 Keywords   marcasite crystal structure, X-ray powder diffraction, Rietveld refinement, Herja ore deposit, Neogene volcanites, Gutai Mountains

 Abstract
The crystal structure of marcasite sampled from Herja ore deposit (Maramures region, Romania) has been refined using X-Ray powder diffraction data and the Rietveld method. Marcasite is the metastable dimorph of FeS2 crystallized in the orthorhombic system, and rapidly inverts to pyrite when is heated above 500C. Genetically, marcasite appears under low-temperature conditions, both in sedimentary rocks and in hydrothermal veins. The Rietveld refinements were carried out using the computer program Topas 4.1 (Bruker-AXS). Pseudo-Voigt (pV) profile function was used for the fit of the peaks. Rietveld refinement using X-Ray powder diffraction data of marcasite crystals in space group Pnnm (No.58), a=4.4339A, b=5.3887A, c=3.3620A (2-sigma=0.0037), Z=2, confirm the basic marcasite structure.

 Rezumat
Structura cristalină a cristalelor de marcasita prelevate din zacamantul Herja (regiunea Maramures, Romania) a fost rafinată folosind difracţia de raze X pe pulberi şi metoda Rietveld. Marcasita este o modificatie polimorfa metastabila a FeS2, cristalizata in sistemul rombic, si care trece rapid in pirita la temperaturi mai mari de 500C. Genetic, marcasita apare in conditii de temperatura joasa, atat in roci sedimentare cat si in filoane hidrotermale. Rafinarea Rietveld a fost realizată cu ajutorul programului de calculator TOPAS 4.1 (Bruker-AXS). Pentru potrivirea peakurilor a fost folosită funcţia pseudo-Voigt (pV). Rafinarea Rietveld utilizând date de difracţie de raze X pe pulberi a eşantionului de marcasita în grupul spaţial Pnnm (No.58), a=4.4339A, b=5.3887A, c=3.3620A (2-sigma=0.0037), Z=2, a confirmat structura de bază a marcasitei.



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