Hematite : Fe2O3, Magnetite : Fe2+Fe3+2O4, Chert

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Copyright © Alex Earl 2016
minID: X3H-FTL

Hematite : Fe2O3, Magnetite : Fe2+Fe3+2O4, Chert

Copyright © Alex Earl 2016  - This image is copyrighted. Unauthorized reproduction prohibited.
Field of View: 4 mm

This is a closeup photo of a typical polished banded iron formation. The darker layers are composed of hematite, and partially magnetite, while the red layers are composed of chert and shale.

This particular piece is from one of the many iron mines in the area, and it is from the Hamersley iron formations, which formed about 2.4 billion years ago during the great oxygenation event. The hematite layers are thought to have formed when photosynthetic bacteria produced oxygen, which reacted with the large amounts of iron dissolved in the early ocean. Because iron oxides are insoluble, they fell to the bottom, and accumulated in layers. The layers of chert with no hematite or magnetite likely formed at night, when there was no light, and photosynthesis did not occur.

I obtained this specimen from Classic Rocks and Gems.

This Photo was Mindat.org Photo of the Day - 20th Oct 2019

This photo has been shown 484 times
Photo added:21st Sep 2016
Dimensions:5920x3969px (23.50 megapixels)
Date/Time of Photo:20th Sep 2016 14:48:56
Camera:SONY ILCE-6000
Software:Snapseed 2.9.4232
Exposure time:2s
ISO speed:100

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