sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (Taconite/Itabirite)
Hardness: 5.5-6.5 (Mohs scale); Color: Alternating bands of silver-grey (hematite/magnetite) and red/brown (jasper/chert); Luster: Metallic to dull; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0
- Hardness
- 5
- Luster
- Metallic to dull
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Physical properties
Hardness: 5.5-6.5 (Mohs scale); Color: Alternating bands of silver-grey (hematite/magnetite) and red/brown (jasper/chert); Luster: Metallic to dull; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0
Formation & geological history
Formed in Precambrian oceans between 2.4 and 1.8 billion years ago (Great Oxygenation Event) when dissolved iron precipitated as oxygen levels rose.
Uses & applications
Primary global source of iron ore for steel production; used in jewelry (as 'Tiger Iron' if metamorphosed) and as decorative lapidary material.
Geological facts
These rocks provide the most significant evidence for the rise of oxygen in Earth's early atmosphere. Without BIFs, the modern steel industry would not exist.
Field identification & locations
Identified by the distinct alternating layers of iron oxides and silica. Often magnetic if rich in magnetite. Commonly found in ancient shield areas like Minnesota, Western Australia, and Brazil.
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