Large Gorgeous Archaean Banded Iron from Wisconsin
"The Rusting of the Earth"

This banded iron fossil easily warrants our Museum Fossil accolade based on both aesthetics and its huge mass. This late Archaean, Wisconsin banded iron is from a region near the great lakes which comprises one of the largest banded iron formations on earth. Theory holds that banded iron layers were formed in sea water as the result of oxygen released by photosynthetic cyanobacteria combining with dissolved iron in Earth's oceans The insoluble iron oxides precipitated out forming a thin layer sea floor, and which later formed shale or chert. Banding is believed to have been caused by cyclic variations in available oxygen. Early Earth had huge amounts of iron dissolved in acidic seas. Oxygen from photosynthetic organism metabolism rapidly and continually used up the dissolved iron, forming massive banded iron formation in the Archaean ERA before 2500 million years ago, a process that markedly slowed after about 1800 million years ago.

The specimen has been hand-polished to a glassine finish on one side with fine carbide and diamond abrasive, a very labor-intensive job. Most Banded iron from the Jackson County iron formation is black with some calcite crystals (for example). This specimen, however, came from the piece exhibiting an array of beautiful colors as readily seen in the pictures; alas, it was a small piece and there is no more.