sedimentary
Banded Iron Formation
Banded Iron Formation (BIF)
Hardness: 5.5-6.5 (Mohs); Color: Alternating bands of metallic silver/black and brick-red or brown; Luster: Sub-metallic to earthy; Crystal Structure: Trigonal (Hematite) and Cubic (Magnetite); Specific Gravity: 4.9-5.3
- Hardness
- 5
- Luster
- Sub-metallic to earthy
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Physical properties
Hardness: 5.5-6.5 (Mohs); Color: Alternating bands of metallic silver/black and brick-red or brown; Luster: Sub-metallic to earthy; Crystal Structure: Trigonal (Hematite) and Cubic (Magnetite); Specific Gravity: 4.9-5.3
Formation & geological history
Formed in Precambrian oceans (3.8 to 1.8 billion years ago) through the precipitation of iron oxides and silica as photosynthetic bacteria began oxygenating the Earth's atmosphere.
Uses & applications
Primary source of iron ore globally; also used for decorative carvings, cabochons in jewelry, and geological study.
Geological facts
BIFs provide some of the best evidence for the 'Great Oxidation Event'. They are the largest source of iron ore and helped build the modern world's industrial infrastructure.
Field identification & locations
Identify in the field by its distinct alternating stripes, high density, and strong magnetism in magnetite-heavy layers. They are common in ancient continental shields like those in Australia, Brazil, and Michigan/Minnesota in the US.
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