Experimental investigation of the reaction: An-rich plagioclase + quartz + fluid = analcime-wairakitess
Authors
Liuza Galbarczyk-Gąsiorowska
Institute of Geochemistry, Mineralogy and Petrology of the University of Warsaw, Al. Żwirki i Wigury 93, PL-02-089 Warszawa
Ewa Słaby
Institute of Geochemistry, Mineralogy and Petrology of the University of Warsaw, Al. Żwirki i Wigury 93, PL-02-089 Warszawa
The reaction An-rich plagioclase + quartz + fluid = analcime (NaAlSi4O12 * 2H2O) - wairakite (CaAl2Si4O12 * 2H2O)[ss] (solid solution series) has been studied experimentally in the temperature range 350-200oC. Distilled water or 0.1 M NaHCO3 solution was used as fluid. All experiments have been performed under low silica activity. Due to the short duration of the experiments the reaction had not approached equilibrium and partly metastable phases were formed. Wairakite nucleated in the laumontite stability field in the system plagioclase-quartz-H2O. Higher sodium activites led to the formation of mixed analcime-wairakite crystals or analcime crystals. The mechanisms of zeolite formation seems to comprise topotaxial growth on the plagioclase surface caused by a dissolution-precipitation process. Some variations in the nucleation and growth kinetics were noticed which appear to be due to different physico-chemical conditions of zeolite formation
