The crystal structure, crystal chemistry, and low-temperature structural evolution of natural thomsonite from Terzigno, Somma-Vesuvius volcanic complex, Naples Province, Italy, have been investigated by means of in situ single-crystal X-ray diffraction, electron microprobe analysis in the wavelength dispersive mode, and Raman spectroscopy. Six structure refinements have been obtained at different temperatures: 295.5, 248.0, 198.0, 148.0, 98.0, and 296.0 K (after the low-T experiments). The reflection conditions and the structure refinements prove that the crystal of thomsonite here investigated is orthorhombic with a = 13.0809(3), b = 13.0597(3), c = 6.6051(1) Å, V = 1128.37(14) Å3, and space group Pbmn, which differs from thomsonite from different localities reported in previ-ous studies (with a ∼ 13.1, b ∼ 13.06, c ∼ 13.2 Å, and space group Pncn). The refined bond distances suggest that the Si/Al-distribution in the tetrahedral framework is fully "disordered," giving rise to the halving of the c axis relative to that found in "ordered" thomsonites. The extra-framework population consists of: (1) one site about 50% occupied by Ca (labeled as "Ca"); (2) one site occupied by Na (∼70%) and Ca (∼30%) (labeled as "Na"); and (3) three water molecule sites ("W1," "W2," "W3"). The structure refinements allowed the location of all the proton sites, and the hydrogen-bonding scheme in the structure is provided. The low-temperature refinements show no significant change in the structure within the T-range investigated. The evolution of the unit-cell volume with T exhibits a continuous and linear trend, without any evident thermo-elastic anomaly, with thermal expansion coefficients αV = V -1· ∂V/∂T= 20(2) ·10-6 K -1 (between 98.0 and 295.5 K). A list with the principal Raman active modes is provided and a comparison with the vibrational modes previously found for "ordered" thomsonite is carried out.
Crystal-structure and low-temperature behavior of “disordered” thomsonite / G.D. Gatta, V. Kahlenberg, R. Kaindl, N. Rotiroti, P. Cappelletti, M. de’ Gennaro. - In: AMERICAN MINERALOGIST. - ISSN 0003-004X. - 95:4(2010 Apr), pp. 495-502.
|Titolo:||Crystal-structure and low-temperature behavior of “disordered” thomsonite|
GATTA, GIACOMO DIEGO (Primo)
|Parole Chiave:||Crystal chemistry; Low temperature; Single-crystal Raman spectroscopy; Single-crystal X-ray diffraction; Somma-Vesuvious; Thomsonite; Zeolite|
|Settore Scientifico Disciplinare:||Settore GEO/06 - Mineralogia|
Settore GEO/09 - Georisorse Miner.Appl.Mineral.-Petrogr.per l'amb.e i Beni Cul
|Data di pubblicazione:||apr-2010|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.2138/am.2010.3353|
|Appare nelle tipologie:||01 - Articolo su periodico|