sedimentary

Banded Iron Formation (BIF)

Banded Iron Formation (predominantly Hematite Fe2O3 and Magnetite Fe3O4 with Chert SiO2)

Hardness: 5-7 (Mohs). Color: Alternating bands of silver-grey/black (iron oxides) and red/brown/yellow (chert or jasper). Luster: Metallic to dull. Crystal structure: Trigonal/Monoclinic. Specific gravity: 3.2-5.3.

Hardness: 5-7 (Mohs)
Luster: Metallic to dull

Identified July 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in ancient seawater during the Archean and Proterozoic eons (approx. 3.8 to 1.8 billion years ago) through the precipitation of iron and silica as oxygen levels rose due to photosynthesis by cyanobacteria.

Uses & applications

Primary global source of iron ore for steel production; also used as decorative stone, lapidary material (Tiger Iron), and educational geological specimens.

Geological facts

Banded Iron Formations record the 'Great Oxidation Event' when Earth's atmosphere first became oxygen-rich. They represent one of the most critical turning points in planetary history.

Field identification & locations

Identify by distinct, thin, contrasting layers of dark metallic minerals and lighter silicate bands. Often magnetic if magnetite is present. Found in Precambrian shields like Western Australia, Brazil, and the Lake Superior region.

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