File:Slate (Biwabik Iron-Formation, Paleoproterozoic, ~1.878 Ga; Thunderbird Mine, Mesabi Iron Range, Minnesota, USA) 4 (33824259464).jpg
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Slate from the Precambrian of Minnesota, USA. This rock is from a Minnesota iron mine that is targeting banded iron formations, or BIFs, which are unusual, dense, marine sedimentary rocks consisting of alternating layers of iron-rich oxides and iron-rich silicates. Most BIFs are Proterozoic in age, although some are Late Archean. They do not form in today's oceans - they're an example of an “extinct” rock type. Many specific varieties of iron formation are known. The most attractive type is jaspilite, which is a reddish & silvery gray banded rock consisting of hematite, red chert (“jasper”), and specular hematite or magnetite. Most BIFs have been subjected to one or more orogenic (mountain-building) events, resulting in folding and/or metamorphism. BIFs are known from around the world, but some of the most famous & extensive deposits are found in the vicinity of North America’s Lake Superior Basin. Many BIFs have economic concentrations of iron and are mined as iron ores. Stratigraphy: lower slaty member, Biwabik Iron-Formation, middle Animikie Group, upper Paleoproterozoic, ~1.878 Ga Locality: Thunderbird Mine/Auburn Mine - open-pit mine complex on the western side of Rt. 53, south of the town of Virginia & north of the town of Eveleth, Mesabi Iron Range, central St. Louis County, northeastern Minnesota, USA |
| Date | |
| Source | Slate (Biwabik Iron-Formation, Paleoproterozoic, ~1.878 Ga; Thunderbird Mine, Mesabi Iron Range, Minnesota, USA) 4 |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/33824259464 (archive). It was reviewed on 22 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 05:55, 22 October 2019 | | 2,454 × 2,394 (3.49 MB) | Rudolphous (talk | contribs) | Transferred from Flickr via #flickr2commons |
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