banded iron formation
Definition of banded iron formation
: a sedimentary deposit that consists of alternating thin layers of iron oxides (such as magnetite or hematite) and iron-poor minerals (such as shale or chert) That bedrock includes intriguing structures known as banded iron formations, which are believed to occur only with the help of living organisms. — Kenneth Chang, New York Times, 2 Dec. 2008 ◆Banded iron formations, which formed over a billion years ago, are often used today as a source of low-grade iron ore. —abbreviation BIF
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