DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Banded iron formation (BIF) refers to a rock type, formed by intense metamorphosis of sediment of very ancient age. These sediments were deposited in Pre Cambrian times, around 2 billion years ago, during a phase in the evolution of the earth known as 'the great oxygen event'. The polished chunk of this picture, actual width 30 cm, highlights the alternating bands of red jasper, black hematite and golden tiger-eye that make up this rock. The sharp folding of the layers is typical for BIF and an indication of the severe tectonic forces the rock was subjected to. This sample is from the iron mining districts of West Australia, the type area where BIF is widespread.
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