日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Natural zeolites have been reported from a large part of the earth's surface. Most of them occur in Mesozoic and Cenozoic rocks, while they are rate in Paleozoic and Precambrian ones. The northshore of L. Superior is a classic locality of Precambrian zeolites. Recently, the writer surveyed mode of occurrence and distribution of these zeolites. He found seven zeolites such as laumontite, heulandite, stilbite-stellerite, thomsonite, epistilbite, mordenite and analcime. They mainly occur in veins, vugs or interstices of lava flows in the Keweenawan Group (middle Proterozoic). They are probably of hydrothermal origin.