• journal_title：American Mineralogist
• Contributor：Alberto Alberti ; Ilaria Parodi ; Giuseppe Cruciani ; Maria Chiara Dalconi ; Annalisa Martucci
• Publisher：Mineralogical Society of America
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2010.3419
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：95
• issue：11-12
• firstpage：1773
• section：Articles

The dehydration-rehydration process in gmelinite-Na |Na_7.27K_0.28Ca_0.15(H₂O)_21.85|[Al_7.71Si_17.24O₄₈]-GME, a natural zeolite that can be described as a parallel stacking of double six rings of tetrahedra in the AABB sequence, was studied by X-ray diffraction data. Its space group is P6₃/mmc with a = 13.764(1) and c = 10.078(1) Å cell parameters. Single-crystal data collections were performed at room conditions and at increasing temperatures, in a hot nitrogen stream, up to the fragmentation of the crystals, which occurs at a temperature as low as 100 °C, and afterward the crystal was cooled down to room conditions. X-ray powder diffraction data showed that gmelinite-Na transforms into a new structure with an AFI-type topology at about 300 °C. At room conditions, extraframework cations are located in two symmetrically independent positions, both of which are coordinated to either framework O atoms or water molecules. When the mineral is heated to 90 °C, about 40% of H₂O is lost, and one cation site splits over two positions, which are three-coordinated to the framework O atoms. The dehydration process is completely reversible over a period of hours. X-ray single-crystal data has highlighted that gmelinite-Na when quenched at 100 K displays remarkable modifications in its extraframework content, resulting in a strong disorder in its extraframework ions. As in the case of heating, the mineral restores its structural features when brought back to room temperature.