25 October 2019

Friday fold: Identity of a BIF

Posted by Callan Bentley

Darrel Cowan steps up with the Friday fold again this week: this time it’s a polished slab, mounted on a wall indoors at the University of Washington’s Department of Earth & Space Sciences; an elegant and informative piece of d├ęcor:

…and with Darrel for scale:

It’s so reflective that glare is a bit of an issue in photographing it!

Here, I’ll zoom in on the un-glare-besmirched portion of the image:

Here’s another view:

Darrel wants your help, gentle and geologically-informed reader. He writes,

When we moved into our renovated building in 2006, the contractors had left spaces in the walls to mount six polished rock slabs. I found and chose the BIF and my brother and I gave it to the department. The slab is about 4 x 8 feet. The red layers are chert, and the gray, magnetite with possibly some hematite. The folds are awesome, and one can easily see the different behavior of the chert and magnetite. The wholesale slab merchant calls it “Iron Red” and claims it came from India, although they could not substantiate its origin.

BIFs are present in many Precambrian terranes. A colleague suspects the slab it “itabirite” from Brazil. Can anyone more positively identify the source?

Can you all help Darrel out with a positive ID on this beautiful BIF?

Thanks!