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Banded Iron
Banded Iron Huge slice of banded iron, cut and polished to a mirror-like finish. Slice measures 24" x 17.5" x 7/8" thick. Banded Iron Formations (BIF) are known from several locations around the world. It is a curious fact that all deposits of banded iron formed at the same time -- around 2 billion years ago. Several theories have been promoted to explain the alternating layers of reduced (dark bands) and oxidized (lighter bands) iron in BIFs. One of the most widely accepted theories centers on the role that photosynthesizing cyanobacteria would play by enriching the surrounding water with oxygen during a "bloom". During such a time, oxidized sediments would accumulate. When the bloom subsided, less oxygen was available and a more reduced form of oxygen accumulated. The end result is banded iron formation. The black parts of this polished slab are thin layers of dark, semi-metallic hematite, and the red layers are jasper, an iron-rich chert. The gray and bright golden areas are part of the same layers, made of tiger-eye quartz. It forms when quartz replaces the fibrous mineral crocidolite (also known as blue asbestos). The dark mineral flashes in golden highlights as you turn it in the light, an effect called chatoyancy. Stock #4053 |
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