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Thomsonite

Historical Information

Thomsonite is name after Dr. Thomas Thomson (1773-1852), the Scottish chemist and mineralogist who fist analyzed the material. The Ca modifier was added by the Zeolite Committee due to its Calcium content.

Thomsonite is the most colorful occurrence of this gem mineral is in Minnesota rocks. Pink and white Thomsonite, commonly forming radial patterns giving the appearance of little "bloodshot eyes”, occurs in vesicle fillings -- as Amygdule -- within the basaltic lava flows that outcrop along the North Shore, about 5 miles southwest of Grand Marais, near Good Harbor Bay.

These specimens may be collected from the beach sands or directly from the host basalt. Unfortunately, most good radial Thomsonite local cities are now closed to the public or are on private land. Other fibrous, sheaf-like Thomsonite may be found in the beach sands at Tofte, Minnesota. These specimens are of a white non-gem variety. A more or less structureless variety of Thomsonite exhibiting no apparent radial or fibrous pattern may be recovered -- along with agate -- on the beach at the Cook Lake County line. Also at this locality, white to pink amygdules, commonly flecked like bird's eggs, may be collected. Thomsonite is one of the hardest of the zeolites, having hardness greater than 5. Thomsonite nodules are oft en cut into attractive gem stones.