| Summary: | 博士 === 國立臺灣大學 === 地質科學研究所 === 91 === The experiments were carried out with synthetic glasses of the systems of Na2OAl2O3nSiO2, CaOAl2O3nSiO2, xNa2O(1-x)CaOAl2O3nSiO2 and xNa2O(1-x)K2OAl2O36SiO2 in alkaline solutions of NaOH, KOH, Na2CO3, NH4OH, NaOH (+) NaCl and NaOH (+) KOH under the conditions of temperatures from 110℃ to 210℃ and autogeneous pressures in the autoclaves. Synthetic products were examined by using an X-ray powder diffractometer, scanning electron microscope, electron microprobe and energy dispersive spectrometer.
The minerals synthesized include zeolites of natural occurrences, i.e., thomsonite, gismondine, amicite, garronite, gobbinsite, analcime, phillipsite, merlinoite, chabazite and mordenite; some synthetic zeolites, and feldspars. Chemical analyses indicate that compositions of synthetic zeolites are profoundly influenced by those of initial glasses, especially the SiO2/Al2O3 ratios and cations. Besides, Na+ and K+ relating with those in glasses and liquids media can influence zeolites synthesized as well, such as CO32- preventing the formation of Ca-zeolites. In addition, each zeolite is synthesized at different range of temperatures, for example, the high temperature phases include thomsonite, garronite and analcime; the medium-high temperature ones include merlinoite and mordenite; the medium-low temperature ones include gobbinsite, phillipsite and gismondine; and the low temperature ones include chabazite and amicite.
Based on chemical compositions, the synthetic zeolites can be grouped into low silica (SiO2/Al2O3 = 2~4), medium silica (SiO2/Al2O3 = 4~8) and high silica (SiO2/Al2O3 = 10) ones. The firs group includes thomsonite, gismondine, amicite, gobbinsite and garronite; second one includes analcime, phillipsite, merlinoite and chabazite; and mordenite is the last group. Thomsonite, gismondine and garronite are chiefly composed of Ca with certain amount of Na, and garronite generally has a wider Na content; amicite often has an equal amount of Na and K; gobbinsite and analcime are mainly composed of Na with a little amount of Ca; phillipsite is essentially composed of Na and K with various amount of Ca; merlinoite generally has higher K content than Na; chabazite is also mainly composed of K with less amount of Na.
The experimental results and natural observations suggest that thomsonite, gismondine and amicite can usually be found in ultrabasic and basic rocks; garronite and gobbinsite in basic to intermediate rocks; the wide-spread zeolites including analcime, phillipsite, merlinoite and chabazite in basic to acid rocks; merlinoite in high-potassium rocks; and mordenite in acid rocks. Besides, the Ca-zeolites including thomsonite, gismondine and garronite are favored in fresh water environments; and the sodic gobbinsite and amicite is suitable in saline lake and sea water. Moreover, analcime often occurs in the inner zone of saline lake deposits, while phillipsite in the marginal zone. Philllipsite is usually favored in deep-sea environments.
|
|---|
