Thomsonite

specimen number:
2062152

location:
Grand Marais, Minnesota, USA

description:
An attractive set of polished thomsonite. Classic Minnesota material. One good matrix example is present. The size provided is the size of the box shown in the picture and video.

Thomsonite from the Grand Marais area of Cook County, Minnesota, is found within the amygdaloidal cavities of the North Shore Volcanic Group, specifically the Precambrian basalts of the Midcontinent Rift System. Geologically, as gas bubbles in the cooling lava formed voids, hydrothermal fluids later deposited minerals, creating the unique radial, eye-like patterns and vibrant pink, white, and green colorations characteristic of this locality. Historically, the most famous deposits are found along a short stretch of Lake Superior shoreline known as Thomsonite Beach, just southwest of Grand Marais. Systematic collection and small-scale commercial surface mining began in the late 1800s and continued throughout the 20th century, with the material being widely used in regional jewelry and lapidary arts. While much of the original shoreline property is now privately owned or developed, it remains the definitive locality for gem-quality thomsonite, distinguished by its chatoyancy and complex concentric banding.

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