sedimentary

Banded Iron Formation (BIF)

Banded Iron Formation (SiO2 + Fe2O3)

AI-generated identification · may be incorrect

Hardness: 5.5-7 (mohs); Color: alternating layers of silver-gray metallic hematite/magnetite and red jasper/chert; Luster: metallic to dull; Crystal Structure: microcrystalline; Specific Gravity: 3.0-5.0

Hardness: 5
Luster: metallic to dull

Identified June 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in ancient seawater billions of years ago (Archean to Proterozoic eons) when oxygen produced by cyanobacteria reacted with dissolved iron, causing it to precipitate as iron oxide layers on the ocean floor.

Uses & applications

Primary global source of iron ore for steel production; also used as a decorative stone in lapidary work and as a collectible geological specimen.

Geological facts

These rocks provide the most significant evidence for the 'Great Oxygenation Event' in Earth's history, showing when life first began drastically altering the atmosphere.

Field identification & locations

Identify by its distinct high-density (weight), magnetic properties if magnetite-rich, and characteristic red and black/gray stripes. Commonly found in ancient cratons like the Superior Upland (Lake Superior region) and Western Australia.