sedimentary

Banded Iron Formation (BIF) / Tiger Iron variety

Banded Iron Formation (predominantly Hematite, Magnetite, and Chert/Quartz - SiO2 + Fe2O3)

AI-generated identification · may be incorrect

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

Identified April 2, 2026More sedimentary →

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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.