sedimentary
Banded Iron Formation
Banded Iron Formation (BIF)
Hardness: 5-7 (Mohs scale); Color: alternating layers of silver-gray metallic (hematite/magnetite) and red, brown, or white (chert/jasper); Luster: metallic to earthy; Structure: layered; Specific gravity: 3.2-5.0
- Hardness
- 5-7 (Mohs scale)
- Luster
- metallic to earthy
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Physical properties
Hardness: 5-7 (Mohs scale); Color: alternating layers of silver-gray metallic (hematite/magnetite) and red, brown, or white (chert/jasper); Luster: metallic to earthy; Structure: layered; Specific gravity: 3.2-5.0
Formation & geological history
Formed in coastal marine environments during the Precambrian era (3.8 to 1.8 billion years ago) through the precipitation of iron from seawater as oxygen levels rose due to early photosynthesis.
Uses & applications
The primary source of iron ore for the global steel industry; polished slabs are used for decorative items and bookends.
Geological facts
These rocks represent the 'Great Oxygenation Event' in Earth's history. They are among the oldest recognizable sedimentary rocks on the planet.
Field identification & locations
Identified by its distinctive stripes and high density. It is strongly magnetic if it contains high concentrations of magnetite. Found in massive deposits in Australia, Brazil, South Africa, and the Lake Superior region.
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