sedimentary

Banded Iron Formation (BIF)

Banded Iron Formation (Oxide Facies)

Hardness: 5.5-7 (Mohs); Color: Alternating bands of silver-grey/black (magnetite/hematite) and red/brown/yellow (jasper/chert); Luster: Submetallic to earthy; Structure: Finely laminated layers; Specific Gravity: 3.0-5.3 depending on iron content.

Hardness: 5
Luster: Submetallic to earthy

Identified July 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in ancient ocean basins primarily during the Precambrian (2.4 to 1.8 billion years ago) through the precipitation of iron oxides from seawater, likely triggered by oxygen produced by early cyanobacteria.

Uses & applications

World's primary source of iron ore (steel industry). Also used as decorative stone, for lapidary work (Tiger Iron), and as geological teaching specimens.

Geological facts

BIFs are time capsules of the 'Great Oxidation Event' when Earth's atmosphere first began to accumulate oxygen. Some of the oldest known life forms (microfossils) have been found within chert layers of BIFs.

Field identification & locations

Identified by distinct alternating dark (iron-rich) and light/red (silica-rich) bands. Often magnetic. Found in ancient shield areas like Western Australia, Minnesota (USA), Brazil, and South Africa.

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