This paper reports a technique of quantitative micro-analysis of zeolite group minerals by electron-probe microanalyzer with an energy-dispersive spectrometer system. Natural analcite, laumontite, heulandite and stilbite were used as reference samples. To avoid radiation damages of zeolites, beam diameters of quantitative analysis for each zeolite are set as follows; analcite and laumontite can be analyzed by defocused beam with Ca. 5 microns in diameter, our laboratory routine analytical conditions, heulandite and stilbite have to be analyzed by scanning beam with 12.5 microns square or more.Heulandite and stilbite have the same anhydrous formula of CaAl_2Si_7O_(18); A water content of heulandite with ideal formula is 15.74 wt. percent and that of stilbite with ideal formula is 17.89 wt. percent. In analyzing these zeolites, total weight percent of anhydrous oxides sometimes falls between the values expected for two zeolites with ideal formula. As precision of analysis of the crystalline water for two zeolites, which were estimated by the difference between 100 and total weight percent of anhydrous oxides determined, is less than 2 wt. percent, the varying anhydrous total is considered real. Thus, the zeolites which have intermediate composition between heulandite and stilbite can not be identified by the present procedure.
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