Over 600 million years ago, during the Keweenawan Period, lava flows produced thomsonite. When the lava solidified, trapped gases in the lava and cracks between the lava flows transformed into hollow pockets. These empty spaces filled up and consolidated over hundreds of thousands of years to create Thomsonite. The gemstone originated in this region along the North Shore due to a special mix of volcanic activity, certain chemicals, and minerals. The zeolite group of minerals, which contains more than 35 distinct known members, includes the mineral thomonite. One of the most uncommon zeolites is thompsonite. Like the majority of other minerals, it is found in the vesicles or bubbles of volcanic rock where it forms tight acicular radiating clusters and sphericules as well as some blockier crystals.