Abstract
The alteration of zeolites in the system chabazite-(SiO2) -H2O was experimentally studied using conventional hydrothermal techniques. Chabazite was transformed into the following mineral phases with increased temperature in accordance with the quantity of free silica in the reaction system.
(A) Ca-harmotome+gonnasdite→wairakite→anorthite. (B) heulandite→wairakite+quartz. (C) heulandite→mordenite→wairakite+quartz.
Phase boundaries between chabazite and wairakite, and between chabazite and heulandite had a negative gradient under a pressure rangea bove 300 bars. The stability of chabazite shifted toward a high temperature region by about 40°C with the increase of free silica content in the reaction system. The formation of heulandite and mordenite from chabazite was accelerated under the condition with excess silica. Particularly, the presence of excess. silica promoted the production of mordenite remarkably. Geological significance of these experimental results is discussed in the present paper.
