sedimentary
Banded Iron Formation (Jaspilite)
Banded Iron Formation (BIF); predominantly Hematite (Fe2O3) and Magnetite (Fe3O4) with Chert/Jasper (SiO2)
Hardness: 5.5 to 7; Color: Alternating bands of silver-grey (hematite) and red/brown (jasper); Luster: Sub-metallic to dull; Structure: Microcrystalline and layered; Cleavage: None
- Hardness
- 5
- Luster
- Sub-metallic to dull
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Physical properties
Hardness: 5.5 to 7; Color: Alternating bands of silver-grey (hematite) and red/brown (jasper); Luster: Sub-metallic to dull; Structure: Microcrystalline and layered; Cleavage: None
Formation & geological history
Formed in Precambrian oceans between 2.4 and 1.8 billion years ago as photosynthetic organisms began producing oxygen, causing dissolved iron to precipitate out of seawater in seasonal layers.
Uses & applications
Primary global source of iron ore for steel production; also used as a decorative lapidary stone for cabochons and specimens.
Geological facts
These rocks provide geological evidence for the "Great Oxygenation Event," marking when Earth's atmosphere first became oxygen-rich.
Field identification & locations
Identify by distinct red and grey/black banding. It is heavy for its size due to high iron content. Commonly found in ancient shield areas like Minnesota (Mesabi Range), Australia, and Brazil.
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