Quartz

specimen number:
2062154

location:
Lake Superior region, Minnesota, USA

description:
An attractive example of what is known as a Lake Superior agate, this lightly polished on one surface.

Lake Superior agates are the official state gemstone of Minnesota and are found throughout the Lake Superior basin in North America. Geologically, these agates formed approximately 1.1 billion years ago within the gas bubbles, or vesicles, of basaltic lava flows associated with the Midcontinent Rift System. As silica-rich groundwater permeated these cavities, it deposited layers of quartz and chalcedony, often colored by iron impurities to create the characteristic bands of red, orange, and yellow. Historically, these gemstones were dispersed across the Midwest during the Pleistocene Epoch by massive glacial movements, specifically the Superior Lobe of the Laurentide Ice Sheet, which scoured the volcanic bedrock and deposited the agates in glacial till as far south as Iowa and Kansas. While they are not mined in a traditional industrial sense like copper or iron, commercial gravel pits and shoreline searching have been the primary methods of "operation" for collectors since the mid-19th century. Today, they are prized by lapidaries and collectors for their intricate "fortification" banding and their connection to the ancient volcanic history of the Great Lakes region.

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