sedimentary
Banded Iron Formation
Banded Iron Formation (BIF)
Mohs hardness: 5.5 to 7. Color: Alternating bands of dark metallic silver/black (hematite/magnetite) and red, brown, or yellowish chert/jasper. Luster: Metallic to earthy or vitreous. Specific gravity: ~3.0 to 4.5.
- Hardness
- 5
- Luster
- Metallic to earthy or vitreous
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Physical properties
Mohs hardness: 5.5 to 7. Color: Alternating bands of dark metallic silver/black (hematite/magnetite) and red, brown, or yellowish chert/jasper. Luster: Metallic to earthy or vitreous. Specific gravity: ~3.0 to 4.5.
Formation & geological history
Formed in ancient marine environments during the Precambrian era (2.4 to 1.8 billion years ago) when oxygen released by photosynthetic cyanobacteria reacted with dissolved iron in oceanic waters, precipitating iron oxide minerals alongside silica.
Uses & applications
Primary global source of iron ore used for steel production; also used as an ornamental stone and lapidary material.
Geological facts
BIFs document the Great Oxidation Event, a critical turning point in Earth's atmospheric and evolutionary history.
Field identification & locations
Identified by distinct alternating dark magnetic/metallic and microcrystalline silica bands. Commonly found in Precambrian shield regions like Australia, Brazil, Canada, and Minnesota (USA).
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