Banded Iron (BFI=Banded Iron Formation)

*from BIF of Wyoming
*51 x 38 x 4 mm.

Banded iron formations are thought to have formed in sea water as the result of oxygen production by photosynthetic cyanobacteria. The oxygen combined with dissolved iron in Earth's oceans to form insoluble iron oxides, which precipitated out, forming a thin layer on the ocean floor. Basically, this is really cool and OLD material dating back 3.7 billion years ago. Sorry for the camera shadow.