sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (Fe2O3 + SiO2)
Hardness: 5.5-7 (Mohs scale); Color: Reddish-brown, dark grey, or silver-black bands; Luster: Sub-metallic to earthy; Structure: Distinct laminated or layered bedding; Specific Gravity: 3.0-5.0
- Hardness
- 5
- Color
- Reddish-brown, dark grey, or silver-black bands
- Luster
- Sub-metallic to earthy
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Physical properties
Hardness: 5.5-7 (Mohs scale); Color: Reddish-brown, dark grey, or silver-black bands; Luster: Sub-metallic to earthy; Structure: Distinct laminated or layered bedding; Specific Gravity: 3.0-5.0
Formation & geological history
Formed in ancient seawater billions of years ago (mostly Archean and Proterozoic eons) when oxygen produced by cyanobacteria reacted with dissolved iron, causing it to precipitate as iron oxides on the ocean floor.
Uses & applications
Primary global source of iron ore for steel production; occasionally used for ornamental stones, lapidary work (when jasper-rich), and geological study.
Geological facts
BIFs provide some of the best evidence for the Great Oxidation Event, representing a massive shift in Earth's atmospheric chemistry roughly 2.4 billion years ago.
Field identification & locations
Identify by distinctive alternating layers of iron minerals (hematite/magnetite) and silica (chert/jasper). Commonly found in Western Australia, Brazil, and the Lake Superior region of North America.
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