Quartz

specimen number:
2062335

location:
Great Sand Bay, Keweenaw Co., Michigan, USA

description:
A rounded attractive Lake Superior agate specimen. Collected in August 2000. This was collected by snorkel in Lake Superior.

Lake Superior agates are distinctive chalcedony gemstones characterized by rich red, orange, and iron-yellow banding, formed within the gas cavities of billion-year-old volcanic basalt. Geologically, these agates originated during the Keweenawan Rift event when silica-rich fluids deposited layers of microcrystalline quartz within vesicular lava flows, with trace amounts of oxidized iron providing the vibrant coloration. Over hundreds of millions of years, continental glaciers advanced across North America, eroding the host basalt and dispersing the highly durable quartz nodules southward throughout Minnesota, Wisconsin, Iowa, and Michigan. These stones are predominantly collected today as loose, water-worn pebbles along shorelines, gravel pits, and glacial till deposits throughout the upper Midwestern United States.

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