sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation containing Hematite (Fe2O3) and Magnetite (Fe3O4)
Hardness: 5-6 (Mohs scale); Color: Black, grey, and rusty red/brown/yellow; Luster: Sub-metallic to earthy; Structure: Finely laminated layers; Specific Gravity: 4.5 - 5.3.
- Hardness
- 5-6 (Mohs scale)
- Color
- Black, grey, and rusty red/brown/yellow
- Luster
- Sub-metallic to earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Black, grey, and rusty red/brown/yellow; Luster: Sub-metallic to earthy; Structure: Finely laminated layers; Specific Gravity: 4.5 - 5.3.
Formation & geological history
Formed in marine environments during the Precambrian Eon (approx. 2.4 to 1.8 billion years ago) through the precipitation of iron-rich and silica-rich minerals following the Great Oxygenation Event.
Uses & applications
Primary source of iron ore for steel production globally. Highly polished specimens are used as lapidary stones, decorative carvings, or education specimens.
Geological facts
BIFs are time capsules for the 'Great Oxidation Event.' They represent a period when photosynthetic organisms first began releasing oxygen into Earth's oceans, causing dissolved iron to rust and settle on the seafloor.
Field identification & locations
Identify in the field by its distinct alternating dark (iron) and lighter (silica/chert) stripes. It is often magnetic and heavy. Commonly found in Western Australia, Brazil, and the Lake Superior region of North America.
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