Hydrothermal Conversion of Trachytic Glass to Zeolite. 3. Monocationic Model Glasses

Abstract

Abstract--Experiments on zeolitization were conducted on four synthetic monocationic glasses (Na, K, Ca, or Mg-rich glass) with Si/A1 molar ratios of 2.67, similar in acidity to many volcanic glasses of partially zeolitized Italian tufts. The products of the hydrothermal treatment at 100, 150, and 200~ of single glasses or glass mixtures with deionized H20 or monosaline solutions (NaC1, KC1, CaC12) were characterized by X-ray diffraction, thermal, microscopic and chemical analyses. Chemical analyses of mother liquors were also performed. Mineral assemblages, containing chabazite, phillipsite, analcime, and K-feldspar, very similar to those found in altered, volcaniclastic alkali-trachytic or trachytic glass deposits were produced. Potassium was essential to chabazite and phillipsite crystallization, although phillipsite was obtained also in Ca-Na mixed systems. Sodium was necessary for analcime formation. Calcium plays only a secondary role in zeolitization, and magnesium does not favor zeolite crystallization but promotes the formation of smectite. Glass composition determines the mineral assemblages obtained and hence in those commonly found in nature.

New insights into the crystal structure and crystal chemistry of the zeolite phillipsite

“…Variations in the extra-framework population results from factors such as post-formational exchange processes (de'Gennaro et al 1982), peculiar chemical composition of the precursor reacting glass, or chemical composition of the fluids interacting with this precursor (de'Gennaro et al 1999). In the light of these considerations, accurate structure refinements of chemically different specimens of phillipsite are highly desirable.…”

Zeolite Crystal Growth Generations During Diagenetic and Hydrothermal Processes- Case Study of Lacustrine Volcaniclastics, Abu Treifiya Area, Cairo-Suez Road, Egypt

“…Precipitation of smectite increased the alkalis (Na + and K + ) ions in the solution and raised the pH that led to the deposition of phillipsite alone or accompanying thomsonite in varieties with high contents of plagioclase (probable source of Ca 2+ ), the commonest zeolites after smectite. Formation of phillipsite in lacustrine environments requires low Si activity (Honnorez, 1981;de′ Gennaro, et al 1993de′ Gennaro, et al , 1999Johnson and Smellie, 2007). Phillipsite fibrous crystals rim glassy clasts, filling pore spaces and lining cavities creating a rather closed-system environment.…”

The “Tufo Giallo della Via Tiberina” (Sabatini Volcanic District, Central Italy): a complex system of lithification in a pyroclastic current deposit

“…The presence of analcime, not detected so far, in agreement with transformation of chabazite to analcime and adularia is evidence that this portion of the deposit was affected by higher temperatures. In this process analcime could represent an intermediate product of transformation between chabazite and a more evolved/stable phase (K-feldspar) (Langella et al 2001;de' Gennaro et al 1999).…”