sedimentary

Banded Iron Formation (BIF)

Banded Iron Formation containing Hematite (Fe2O3) and Jasper (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (chert/jasper layers) and 5.5-6.5 (iron layers); Color: Alternating red (jasper) and silver-grey to black (hematite/magnetite); Luster: Submetallic to dull; Structure: Fine-grained, distinctly layered or laminated.

Hardness: 6
Luster: Submetallic to dull

Identified June 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in ancient seawater during the Archean and Proterozoic eons (approx. 2.4 to 1.8 billion years ago) when oxygen produced by cyanobacteria reacted with dissolved iron, triggering the precipitation of iron oxides onto the ocean floor.

Uses & applications

Primary global source of iron ore for steel production; also used as a decorative stone, for cabochons in jewelry, and as a popular lapidary material known as 'Jaspilite'.

Geological facts

BIFs provide some of our best evidence for the 'Great Oxygenation Event' when the Earth's atmosphere first became enriched with oxygen. Most of the iron used in modern world infrastructure comes from these specific types of deposits.

Field identification & locations

Identified by high density (heavy weight), distinct alternating red and black/grey banding, and some layers may be weakly magnetic. Common in ancient shield areas like the Lake Superior region (USA/Canada), Australia, and Brazil.