Thomsonite

specimen number:
2351061

location:
Cook Co., Minnesota, USA

description:
Classic banded nodules of thomsonite, the largest measuring 3.5 x 1.5 cm in size, embedded up on a basalt matrix.

Thomsonite nodules from Cook County, Minnesota, form within amygdaloidal cavities of ancient Keweenawan-age basalt flows along the North Shore, where mineral-rich solutions filled gas bubbles in prehistoric lava. Discovered along the Lake Superior shoreline during the mid-19th century, these colorful stones became famous among collectors and lapidaries for their unique pink, white, and green concentric eye patterns. Collecting traditionally involved searching beach gravels or splitting basalt outcrops along the shore, though modern access is heavily restricted by private land ownership and decades of intensive searching.

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