sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (SiO2 + Fe2O3/Fe3O4)
Hardness: 6-7 (Mohs); Color: Alternating red (jasper) and silver-black/dark grey (hematite or magnetite); Luster: Dull to metallic; Structure: Microcrystalline; Cleavage: None; Specific Gravity: 3.0 to 5.0.
- Hardness
- 6-7 (Mohs)
- Luster
- Dull to metallic
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Physical properties
Hardness: 6-7 (Mohs); Color: Alternating red (jasper) and silver-black/dark grey (hematite or magnetite); Luster: Dull to metallic; Structure: Microcrystalline; Cleavage: None; Specific Gravity: 3.0 to 5.0.
Formation & geological history
Formed in Precambrian marine environments (2.4 to 1.8 billion years ago) through the precipitation of iron and silica during the 'Great Oxygenation Event'. The oxic bands represent periods of photosynthetic bacteria blooming.
Uses & applications
Primary global source of iron ore for steel production. High-quality specimens are used for decorative carvings, lapidary cabochons, and as educational geological samples.
Geological facts
BIFs are time capsules of Earth's early atmosphere. Famous locations include the Mesabi Range (USA), the Pilbara region (Australia), and the Barberton Greenstone Belt (South Africa).
Field identification & locations
Identify in the field by its distinct, colorful alternating stripes and high density/heaviness compared to other rocks. Often magnetic if it contains magnetite. Found in ancient shield areas of continents.
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