Banded iron formation |
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Banded iron formationBiogenous sedimentary rock.Alternating layers of hematite (dark red) and ferrigenous chert (light red) Precambrian age (estimated about 1.8 billion years or older). Banded iron formation is associated with early photosynthetic bacteria in the ancient oceans. Current thought is that the photosynthetic micro released oxygen that reacted with dissolved iron in seawater. The alternating bands of silica (chert) and iron-oxide (hematite) may represent, slow annual or longer cycles of deposition in a deep abyssal plain evironment in the ancient ocean rocks, now exposed in the core of the Wind River Mountain of Wyoming. Banded iron formations have been found in ancient deposits all around the world (where they are mined for iron ore). Their occurrence was part of the process of the conversion of the atmosphere from CO2-rich (anoxic) to 02-rich over many hundred of millions of years in early to mid Precambrian time.This sample came from an abandoned taconite (iron ore) mine near Lander, Wyoming. |
| https://gotbooks.miracosta.edu/rocks/sedimentary/3.html | 2/2/2021 |