Authigenic zeolites in zeolitic palagonite tuffs on Oahu, Hawaii

Authigenic zeolites including phillipsite, gismondine, chabazite, gonnardite, natrolite, analcime and faujasite are the principal minerals in the cement of palagonitized alkali basalt and melilite nephelinite tuffs of the Honolulu Series on Oahu, Hawaii. The results of DTA, X-ray, chemical and electron microprobe analyses are given here. The authigenic zeolites are chemically similar to zeolites commonly found in the cavities of mafic lava flows. There is a regular succession of the zeolite formation: K zeolite CaXNa zeolites Na zeolites. This is explained by gradual change in composition of percolating groundwater through the tuff deposits during palagonitization. A sodium contribution by wind-blown salt from seawater and rainfall on the oceanic island probably causes the latter occurrence of Na zeolites in even the uppermost zeolitic tuffs in the semi-arid coastal area.