Alteration (fresh water) products (palagonite and zeolites) of a 12, 000–28, 000 year old basaltic glass from Hanauma Bay, Hawaii, were examined by electron microprobe analysis, scanning electron microscopy, and X-ray diffraction analysis. The palagonite, 0 to 300 microns thick, is depleted in Si, Al, Ca, Na, and K and enriched in Ti and Fe. Ca-rich zeolites are associated with palagonite that is slightly more depleted in Ca; all samples contain zeolites and low Al-palagonite. The rate of palagonitization (0.002–0.005 volume percent/year) is less than the experimentally predicted rate for basalt glasses due to the episodic presence of the percolating groundwater. The Si/AI ratio of the zeolites decreases with increasing pH of the groundwater as it passes through the vertical section. Zeolite paragenesis is (first to last): analcime (NaAlSi2O 6·H2O), phillipsite [(1/2 Ca, Na, K)(Al3Si5O16).6H2O], chabazite (CaAl2SiO16.6H2O).