sedimentary
Banded Iron Formation (BIF) / Iron Ore
Banded Iron Formation (composed primarily of Hematite (Fe2O3) and Magnetite (Fe3O4) with Quartz/Chert)
Hardness: 5-6 (Iron minerals) to 7 (Chert); Color: Reddish-brown, grey, black; Luster: Metallic to dull; Crystal structure: Microcrystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 4.5-5.3 (dense due to iron content).
- Hardness
- 5-6 (Iron minerals) to 7 (Chert)
- Color
- Reddish-brown, grey, black
- Luster
- Metallic to dull
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Physical properties
Hardness: 5-6 (Iron minerals) to 7 (Chert); Color: Reddish-brown, grey, black; Luster: Metallic to dull; Crystal structure: Microcrystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 4.5-5.3 (dense due to iron content).
Formation & geological history
Formed in ancient oceans during the Precambrian eon (approx. 2.4 to 1.8 billion years ago) through the precipitation of iron from seawater as oxygen levels rose, creating alternating layers of iron oxides and silica.
Uses & applications
The primary global source of iron ore used in the production of steel for construction, infrastructure, and machinery. Also used as a decorative stone when high-grade (Tiger Iron).
Geological facts
These rocks provide the most significant geological record of the 'Great Oxygenation Event' in Earth's history. They are among the oldest sedimentary rocks on the planet.
Field identification & locations
Identified by distinct layering, heavy weight/high density, and reddish-brown streaks; many specimens are magnetic. Commonly found in Western Australia, Brazil, Lake Superior region, and South Africa.
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