sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (BIF)
Hardness: 5.5-6.5 (Mohs), Color: Alternating layers of silver-gray/black and red/brown/tan, Luster: Metallic to earthy, Crystal Structure: Trigonal (Hematite/Magnetite) and Hexagonal (Quartz), Specific Gravity: 3.0-5.3
- Hardness
- 5
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Physical properties
Hardness: 5.5-6.5 (Mohs), Color: Alternating layers of silver-gray/black and red/brown/tan, Luster: Metallic to earthy, Crystal Structure: Trigonal (Hematite/Magnetite) and Hexagonal (Quartz), Specific Gravity: 3.0-5.3
Formation & geological history
Formed in ancient marine environments during the Precambrian (3.8 to 1.8 billion years ago) through the precipitation of iron oxides and silica as photosynthesis increased oxygen in the oceans.
Uses & applications
Primary global source of iron ore for steel production; occasionally used as ornamental stone for paperweights or jewelry (Genesis stone).
Geological facts
These rocks represent a unique time in Earth's history called the 'Great Oxidation Event' when cyanobacteria first produced large amounts of oxygen.
Field identification & locations
Identify in the field by distinct high-contrast banding and high density (feels heavy for its size). It is often magnetic if magnetite-rich. Common in stable ancient continental crust like the Lake Superior region, Australia, and Brazil.
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