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Author: Admin | 2025-04-28
At Soudan Underground Mine State Park. A similar, but much younger, formation (only 1.9 billion years old) occurs along the Mesabi Iron Range that extends from Grand Rapids to Babbitt. This iron formation formed by the same process, but its deposition also involved interplay among seawater, surface rainwater, volcanic activity, and some of the Earth's oldest life forms (cyanobacteria). When upgraded in iron content by industrial processing, rocks of the Mesabi range yield an important ore called taconite. Banded iron formation (or BIF) from the Precambrian of Minnesota. Photo courtesy of Amy Block. Hand sample of banded iron formation. Photo courtesy of Kevin Murphy. An example of taconite pebbles from iron ore processing. Photo courtesy of Kevin Murphy. QUARTZITE QuartziteNot long after mountains were uplifted across central Minnesota, sand began to accumulate in braided streams in southwestern Minnesota. These stream deposits of reddish quartz sand grains were eventually consolidated and slightly altered into a very hard rock called quartzite.The reddish to purple Sioux Quartzite is at the surface near Blue Mounds State Park and the Jeffers Petroglyphs in southwestern Minnesota. At Pipestone National Monument, a thin mudstone layer is sandwiched between thick layers of quartzite. This mudstone layer is pipestone (catlinite), and is spiritually significant to Native Americans, who have carved it for centuries. Hand sample of quartzite. Photo courtesy of Kevin Murphy. Outcropping of Sioux Quartzite from the Precambrian of Rock County, Minnesota. Photo courtesy of Mark A. Jirsa. BASALT BasaltAbout 1.1 billion years ago, the continent that had been building for billions of years began to split apart across what is now Minnesota. The "Midcontinent Rift" is where the crust began to separate to form a new ocean basin. The same process is currently underway between the African continent and Saudi Arabia. The rifting process stopped short of producing a new ocean basin in central North America, but the abundant dark red-brown basaltic rocks now exposed along Lake Superior's North Shore are a testament to the massive outpouring of lava through fractures or cracks along the rift. Gooseberry Falls State Park is an ideal place to explore these ancient lava flows. Basalt lava flow from the Precambrian of Minnesota. Photo courtesy of James St. John / CC BY (https://creativecommons.org/licenses/by/2.0). Hand sample of an amygdaloidal basalt. Photo courtesy of Kevin Murphy. GABBRO GabbroGabbro is a silica-poor and Fe-Mg-rich intrusive rock formed when molten rock is trapped beneath the land
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