DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Banded iron formation, polished surface. Banded iron formation (BIF) or banded ironstone is a rock formed from alternating layers of the minerals jasper (green and red), haematite (metallic) and tiger eye (orange). At greater than 3 billion years of age these are among the oldest rocks on Earth. They were laid down in shallow seas where primitive bacteria caused iron to be oxidised and precipitated. Subsequent deep burial of the rocks, and tectonic movements, have caused the rock to alter and deform. The lower layers in this sample have become twisted into peaks and troughs.
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