Data di Pubblicazione:
2004
Citazione:
Synthesis and crystal-chemistry of Na(NaMg Mg5Si8O22(OH)2, a P21/m amphibole / G. Iezzi, G.D. Ventura, R. Oberti, F. Cámara, F. Holtz. - In: AMERICAN MINERALOGIST. - ISSN 0003-004X. - 89:4(2004 Apr), pp. 640-646.
Abstract:
In the present work, we characterize the amphibole Na(NaMg)Mg5Si8O22(OH)2 synthesized at 0.4 GPa and 750, 800. and 850 °C, and 0.5 GPa, 900 °C. Experiments at 800 and 900 °C yielded crystals suitable for single-crystal data collection. Structure refinement shows that synthetic Na(NaMg)Mg5Si8O22(OH 2 has P21lm symmetry at room T. The two non-equivalent tetrahedral double-chains differ in their degree of stretching and kinking. The infrared spectrum of synthetic Na(NaMg Mg5Si8O22(OH)2 has two well-defined absorption bands at 3742 and 3715 cm-1 which can be assigned to O-H bands associated with the two independent anion sites (O3A and O3B) in the structure. The higher frequency band is assigned to the shorter O3B-H2 bond, and the lower frequency band is assigned to the longer O3A-H1 bond. The broader shape of the 3743 cm-1 band is consistent with a stronger interaction of the H2 atom with ANa, which is confirmed by structure refinement. Increasing T of synthesis causes a progressive departure from the ideal stoichiometry via the A□1BMg1ANa-1BNa-1 substitution, as confirmed by EMPA, structure refinement, and FTIR spectroscopy.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
SHORT-RANGE DISORDER; PHASE-TRANSITION; POTASSIUM-RICHTERITE; SOLID-SOLUTION; OH; TREMOLITE; EXCESS; SYSTEM; PARGASITE; PRESSURE
Elenco autori:
G. Iezzi, G.D. Ventura, R. Oberti, F. Cámara, F. Holtz
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