![Banded Iron Formation (BIF) (Banded Iron Formation (composed primarily of Hematite [Fe2O3], Magnetite [Fe3O4], and Chert [SiO2])) — sedimentary](https://media.rockidentification.com/7c63c176-59b7-4b4b-a3a5-c9e6107d1aac-compressed.jpg)
sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (composed primarily of Hematite [Fe2O3], Magnetite [Fe3O4], and Chert [SiO2])
Hardness: 5.5-7 (Mohs scale), Color: Alternating red (Jasper/Chert) and silver-black (Hematite/Magnetite) bands, Luster: Metallic to dull, Crystal structure: Trigonal/Hexagonal systems in constituent minerals, Specific gravity: 3.5-5.0 depending on iron content.
- Hardness
- 5
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Physical properties
Hardness: 5.5-7 (Mohs scale), Color: Alternating red (Jasper/Chert) and silver-black (Hematite/Magnetite) bands, Luster: Metallic to dull, Crystal structure: Trigonal/Hexagonal systems in constituent minerals, Specific gravity: 3.5-5.0 depending on iron content.
Formation & geological history
Formed in marine environments during the Precambrian Eon (mostly 2.4 to 1.8 billion years ago). These deposits resulted from the 'Great Oxygenation Event' where oxygen produced by early cyanobacteria reacted with dissolved iron in the oceans, precipitating out as iron oxides on the sea floor.
Uses & applications
Primary global source of iron ore for steel production. High-quality specimens with vivid red jasper are used as semi-precious gemstones or 'Genesis Stone' in jewelry and lapidary art.
Geological facts
BIFs are geological 'clocks' that record the moment Earth's atmosphere became oxygen-rich. They are no longer forming in modern oceans because the water is now too oxygenated to allow iron to dissolve in large quantities.
Field identification & locations
Identified by distinct alternating color bands (red and dark grey/black) and its unusually high weight (density) for its size. Often magnetic if magnetite is present. Common in ancient shield areas like Western Australia, Minnesota (USA), and South Africa.
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