19 July 2019
Posted by Callan Bentley
A final Friday fold from Madison, Wisconsin: this one a slab of cut and polished banded iron formation from Australia:
What exquisitely beautiful rock!
Happy Friday!
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.
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I asked for a piece of BIF for Christmas last year from my 83 y/o mother, who never knows what to get me. She thinks I’m a little crazy sometimes, but I have everything I need, so I ask for small things I would like.
To me, banded iron is a fossil from the oxygenation of Earth’s atmosphere, a 2 Ga remnant of some Archean stromatolite in some long gone tropical sea, converting water and CO2 to hydrocarbon chains and releasing oxygen as a waste product. It’s a remnant from a time when the oceans were saturated with iron. It’s a relic from a different Earth. It’s an astounding thing, to me, to hold a piece of that in your hand. And equally astounding that we can understand it: how it formed, when it happened, why it exists, what created it.
I read on fossilmall.com that rocks like this are a form of stromatolites.
There can be stromatolites in BIF, and the source of free oxygen for BIFs is thought to be nearby shallow water stromatolite photosynthesis, but not all BIFs are stromatolites.