The Na-rich zeolites from Boron, California

摘要

Unusually Na-rich zeolites have been found in cavities in blocks of basalt on the waste dump at the US Borax Mine at Boron, 135 km northeast of Los Angeles, California. The basalt underlies Miocene basin fill deposits, consisting of sand, shale, tuff, and Na-borate deposits. The zeolites show two generations of growth. Early gmelinite-Na is overgrown by later chabazite-Na, and early clinoptilolite-Na is overgrown by heulandite-Na. Other zeolites in these cavities are phillipsite-Na, analcime, Na-rich mordenite, and mazzite-Na. The occurrence of searlesite and borax, attests to the saturation of the basalt with a sodium borate solution at least at some stage. The extreme Na-rich compositions of all the zeolites strongly indicate cation exchange in Na-borate brine, while the overgrowth crystals may have grown in the brine.