Nature
1
This rock came from the lower part of the Upper Slaty Member-Biwabik Formation. It consists of thin wavy beds of magnetite, a magnetic black fine grained argillite, and irregular shaped pods or lenses of chert and silicate. It is about 2 billion years old. During the last glacial stage about 10 thousand years ago, it was plucked from an outcrop north of here.
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Hoyt Lakes, Minnesota · United States
