(A)Na(B)(NaMg)(C)Mg(5)Si(8)O(22)(OH,D)(2) amPhibole was hydrothermally synthesized at 850 degrees C and 0.3 GPa. SEM, EPMA, and X-ray powder-diffraction data showed the experimental product to consist of a high amphibole yield (90-95%), plus minor quartz and rare enstatite. Neutron powder-diffraction data were collected using a time-of-flight diffractometer at room T and at 8 K, respectively, and structure refinement was carried out using the Rietveld method. The space group of the amphibole is P2(1)/m at both temperatures, as confirmed by the presence of b-type reflections (h + k = 2n + 1). FTIR OH- and OD-stretching spectra at both room and low T (30 K) show two main absorptions, which are assigned to two non-equivalent OH groups in the structure, and a third lower-frequency band, assigned to A-site vacant environments (local cummingtonite environments). At room- and low-T, the cell parameters are (in A): a 9.7188(1) and 9.7016(2), b 17.9385(3) and 17.8953(4), c 5.2692(1) and 5.2574(1); beta (degrees) is 102.526(1) and 102.597(2). Cell volumes (A 3) are 896.78(2) at room T and 890.80(2) at 8 K, with a relative reduction of less than 1%. Accurate structural positions for the hydrogen atoms were obtained from diffraction data. The O5A-O6A-O5A and O5B-O6B-O5B angles, diagnostic of the A- and B-chains kinking along c, are 190.0 degrees and 159.2 degrees at 293 K and 193.8 degrees and 156.8 degrees at 8 K, respectively. The orientation of the thermoelastic strain ellipsoid was calculated and the principal unit-strain tensor components are reported. A comparison between the low-temperature data reported here and the high-temperature data for a similar amphibole composition, reported by Camara et al. (2003) up to 643 K, is discussed.
Iezzi, G., Gatta, G.D., Kockelmann, W., DELLA VENTURA, G., Rinaldi, R., Schfer, W., et al. (2005). Low-T neutron powder diffraction and synchrotron-radiation IR study of synthetic amphibole NaNaMgMg5Si8O22(OH)2. AMERICAN MINERALOGIST, 90, 695-700 [10.2138/am.2005.1764].
Low-T neutron powder diffraction and synchrotron-radiation IR study of synthetic amphibole NaNaMgMg5Si8O22(OH)2
DELLA VENTURA, Giancarlo;
2005-01-01
Abstract
(A)Na(B)(NaMg)(C)Mg(5)Si(8)O(22)(OH,D)(2) amPhibole was hydrothermally synthesized at 850 degrees C and 0.3 GPa. SEM, EPMA, and X-ray powder-diffraction data showed the experimental product to consist of a high amphibole yield (90-95%), plus minor quartz and rare enstatite. Neutron powder-diffraction data were collected using a time-of-flight diffractometer at room T and at 8 K, respectively, and structure refinement was carried out using the Rietveld method. The space group of the amphibole is P2(1)/m at both temperatures, as confirmed by the presence of b-type reflections (h + k = 2n + 1). FTIR OH- and OD-stretching spectra at both room and low T (30 K) show two main absorptions, which are assigned to two non-equivalent OH groups in the structure, and a third lower-frequency band, assigned to A-site vacant environments (local cummingtonite environments). At room- and low-T, the cell parameters are (in A): a 9.7188(1) and 9.7016(2), b 17.9385(3) and 17.8953(4), c 5.2692(1) and 5.2574(1); beta (degrees) is 102.526(1) and 102.597(2). Cell volumes (A 3) are 896.78(2) at room T and 890.80(2) at 8 K, with a relative reduction of less than 1%. Accurate structural positions for the hydrogen atoms were obtained from diffraction data. The O5A-O6A-O5A and O5B-O6B-O5B angles, diagnostic of the A- and B-chains kinking along c, are 190.0 degrees and 159.2 degrees at 293 K and 193.8 degrees and 156.8 degrees at 8 K, respectively. The orientation of the thermoelastic strain ellipsoid was calculated and the principal unit-strain tensor components are reported. A comparison between the low-temperature data reported here and the high-temperature data for a similar amphibole composition, reported by Camara et al. (2003) up to 643 K, is discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.