Archaean Banded Iron from Wyoming
"Evidence of the the Rusting of the Earth"

Name: Banded Iron

Geological Time: Archaean (2.87 billion years old)

Size: 8.3 by 6.5 inches

Fossil Site: Goldman Meadows Formation, Atlantic City Iron Mine, South Pass, Wyoming

Banded IronThese stromatolites are banded iron from the rusting of the earth. Unusual for banded iron is the intricate wavy laminae structure resulting domal growth. Coming from the Goldman Meadows Formation in Wyoming it Archaean in age, when life on earth was highly diverse, but all microbes.

This banded iron is metasediment (sediment that has undergone metamorphism) and has a high content of magnetite (Fe3O4), a natural magnet, and yielding the midnight black coloration; minute crystalline forms of other mineral-based compounds are also present.

The very large specimen has been hand-polished to a glassine finish on one side with fine carbide and diamond abrasive, a very labor-intensive job. The pictures comparing front and back reveals the value of this form of polishing in revealing the fine structure of the laminae.

Click to enlarge

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