Stunning Archaean Banded Iron from Australia

Polished Banded Iron Stromatolites

Geological Time: Archaean (2.7 billion years old)

Size: Banded iron is 9.5 inches across widest diagonal, and .5 inches thick

Fossil Site: Marra Mamba Formation, Hammersley Ranges, Western Australia

Code: 12038

Price: Sold

Archaean Tiger Eye Banded IronWhile not always recognized as such, Banded Iron Formations (BIFs) are another form of stromatolites. BIFs are massive, laterally extensive and globally distributed chemical sediment deposits that consist primarily of Fe-bearing minerals (iron oxides) and silica. Iron can occur naturally in two states. Reduced, or ferric iron is soluble in water. Archaean oceans were rich in ferric iron that was released from Earth's interior. In the presence of oxygen, however, the iron becomes oxidized and precipitates out as a solid. Earth's BIFs are the result of oxygen released by photosynthetic organisms combining with dissolved iron in Earth's oceans to form insoluble iron oxides -- this is known as "the great rusting of the earth". Banding results from cyclicality in oxygen production. Earth started out with vast amounts of iron dissolved in the world's seas. BIFs in the geologic record date from about 3.8 billion years ago in Greenland to about 1.8 billion years ago with a maximum abundance at some 2.5 billion years ago, with another large reoccurrence in Neoproterozoic time (from about 0.8 and 0.6 billion years ago. Interestingly, it has been estimated that the amount of oxygen locked in earth's BIFs is some 10 times the amount contained in the atmosphere.

Some of the most famous banded iron comes from the Western Australia, and locally goes by the monikers Tiger Iron and Tiger Eye. With fine polishing, the beauty is stunning testament to one of the most important events in geological history -- the Earth needed to first rust, so that the atmosphere could then be oxygenated, setting the stage for the appearance and evolution of all eukaryotic life. Among the so-called Tiger Irons, that from the Marra Mamba Formation is the most treasured, and is often used in the jewelry trade. At 2.7 billion years of age in the Archaean, it is also among the oldest. This Marra Mamba Tiger Eye comes from only two small deposits in the Hammersley Ranges of Western Australia.

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