Analcime and montmorillonite were synthesized from naturally occurring Hawaiian tholeiitic glass and artificial seawater at 200 degrees C and 300 degrees C and 1 Kb over a period of 32 days. The Na/K ratio for the closed system was 12. Phillipsite and montmorillonite were synthesized at temperatures of 175 degrees C and 250 degrees C and 1 Kb with Na/K ratios for the closed system between 1 and 5. With Na/K = 0.5, no zeolites were formed. Scanning electron microscope photos show volcanic glass surfaces covered by layers and rosettes of montmorillonite, euhedral and subhedral zeolites, and palagonite-like spherules. The phillipsite crystals grow within the altering glass, whereas the analcime crystals grow on the glass surfaces as euhedral crystals and as interpenetrating crystals in circular groups. The textures observed in the experimental charges are remarkably similar to textures observed in naturally altered submarine basaltic glass and palagonite. Phillipsite, the most common authigenic marine zeolite, formed only if potassium was added to the experimental charge. This could correspond to glass altered in an environment open to a large potassium reservoir such as circulating seawater. In the experimental closed seawater system, analcime was formed. Analcime is found in rapidly deposited volcanic sandstones and breccias probably closed off from seawater circulation.

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