sedimentary
Banded Iron Formation (Chert)
Banded Iron Formation (BIF) with Jasper/Chert layers
Hardness: 6.5-7 (Mohs scale); Color: Red (Jasper), Black (Magnetite/Hematite), or Gray; Luster: Dull to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.9
- Hardness
- 6
- Color
- Red (Jasper), Black (Magnetite/Hematite), or Gray
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Red (Jasper), Black (Magnetite/Hematite), or Gray; Luster: Dull to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.9
Formation & geological history
Formed in ancient oceans between 3.8 and 1.8 billion years ago (Precambrian) through the precipitation of iron and silica due to oxygen produced by early cyanobacteria.
Uses & applications
Major source of iron ore globally; used in jewelry as Jasper; or as lapidary material for decorative carvings and cabochons.
Geological facts
Banded iron formations provide critical evidence for the 'Great Oxidation Event,' showing when oxygen first began to accumulate in Earth's atmosphere.
Field identification & locations
Identify by distinct banding of red and dark gray/black layers; often heavy for its size if iron content is high. Found in ancient cratonic areas like the Lake Superior region, Australia, and South Africa.
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