“This is a closeup photo of a typical polished banded iron formation. The darker layers are composed of hematite, and partially magnetite, while the red layers are composed of chert and shale. This particular piece is from one of the many iron mines in the area, and it is from the Hamersley iron formations, which formed about 2.4 billion years ago during the great oxygenation event. The hematite layers are thought to have formed when photosynthetic bacteria produced oxygen, which reacted with the large amounts of iron dissolved in the early ocean. Because iron oxides are insoluble, they fell to the bottom, and accumulated in layers. The layers of chert with no hematite or magnetite likely formed at night, when there was no light, and photosynthesis did not occur. I obtained this specimen from Classic Rocks and Gems.”

“Yellow fibrous "Tiger's Eye" (a mixture of Quartz and amphibole fibers) formed as fracture fillings in bands of dark grey Hematite-Magnetite, and red chert, which are part of a banded iron formation. I obtained this specimen from Classic Rocks and Gems.”