sedimentary
Banded Iron Formation (BIF) / Tiger Iron variety
Banded Iron Formation (predominantly Hematite, Magnetite, and Chert/Quartz - SiO2 + Fe2O3)
Hardness: 6.5-7.0 (Mohs); Color: Alternating bands of silver-grey, black, and red/brown; Luster: Sub-metallic to vitreous; Crystal Structure: Trigonal/Hexagonal systems; Cleavage: None; Opaque.
- Hardness
- 6
- Color
- Alternating bands of silver-grey, black, and red/brown
- Luster
- Sub-metallic to vitreous
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Physical properties
Hardness: 6.5-7.0 (Mohs); Color: Alternating bands of silver-grey, black, and red/brown; Luster: Sub-metallic to vitreous; Crystal Structure: Trigonal/Hexagonal systems; Cleavage: None; Opaque.
Formation & geological history
Formed in ancient shallow seas billions of years ago (mostly the Archean and Proterozoic eons) when oxygen produced by cyanobacteria reacted with dissolved iron in the water, precipitating it onto the seafloor in layers. Age: 1.8 to 3.5 billion years old.
Uses & applications
Primary global source of iron ore for steel production. Polished specimens like this are used in jewelry, lapidary arts, metaphysical ornaments, and as educational geological samples.
Geological facts
Banded iron formations are responsible for almost all of the iron we use today. They represent a massive 'snapshot' of Earth's atmosphere transitioning to an oxygen-rich environment, known as the Great Oxygenation Event.
Field identification & locations
Identify by distinct, alternating mineral bands and high density (feels heavy for its size). Common in Australia (Pilbara region), Brazil, South Africa, and the Lake Superior region of North America.
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