sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (Fe2O3 + SiO2)
Hardness: 5-7. Color: Alternating bands of silver to black (iron oxides) and red, white, or grey (chert/quartz). Luster: Metallic to dull. Crystal structure: Cryptocrystalline. Cleavage: None.
- Hardness
- 5-7
- Luster
- Metallic to dull
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Physical properties
Hardness: 5-7. Color: Alternating bands of silver to black (iron oxides) and red, white, or grey (chert/quartz). Luster: Metallic to dull. Crystal structure: Cryptocrystalline. Cleavage: None.
Formation & geological history
Chemical precipitation in ancient oceans as a result of oxygen release by early photosynthetic organisms (cyanobacteria) reacting with dissolved iron. Most formed during the Precambrian era, between 2.4 and 1.8 billion years ago.
Uses & applications
Primary global source of iron ore for steel production. High-quality specimens are used for lapidary work (cabochons) and as educational/collector specimens.
Geological facts
These formations are evidence of the 'Great Oxidation Event,' a pivotal moment in Earth's history when oxygen first began to accumulate in the atmosphere and oceans.
Field identification & locations
Identify by its distinct banding and high density (it feels heavy for its size). Common in ancient 'shield' regions like the Lake Superior area (USA/Canada), Australia, and Brazil. Collectors look for sharp, high-contrast banding.
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