sedimentary
Banded Iron Formation
Banded Iron Formation (BIF)
Hardness: 5.5-7 Mohs. Color: Alternating dark gray to black and red, reddish-brown, or dark brown bands. Luster: Submetallic to dull or silky. Structure: Laminated sedimentary bedding.
- Hardness
- 5
- Luster
- Submetallic to dull or silky
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Physical properties
Hardness: 5.5-7 Mohs. Color: Alternating dark gray to black and red, reddish-brown, or dark brown bands. Luster: Submetallic to dull or silky. Structure: Laminated sedimentary bedding.
Formation & geological history
Formed in Precambrian marine environments over 1.8 to 3.7 billion years ago as photosynthetic organisms released oxygen, causing dissolved iron in seawater to precipitate into alternating oxide and silica-rich layers.
Uses & applications
Primary global source of iron ore used for steel production; also used as an ornamental stone and popular specimen for rock and mineral collectors.
Geological facts
BIFs record the Great Oxidation Event, representing the fundamental transformation of Earth's early atmosphere and oceans through the rise of oxygen-producing cyanobacteria.
Field identification & locations
Identified by distinct alternating layers of dark iron oxides (hematite/magnetite) and quartz/jasper, often weakly to strongly magnetic. Commonly found in ancient Precambrian cratons such as Lake Superior region, Australia, and South Africa.
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