sedimentary

Banded Iron Formation (BIF)

Banded Iron Formation (Fe2O3 + SiO2)

AI-generated identification · may be incorrect

Hardness: 5.5-7 (Mohs scale); Color: Reddish-brown, dark grey, or silver-black bands; Luster: Sub-metallic to earthy; Structure: Distinct laminated or layered bedding; Specific Gravity: 3.0-5.0

Hardness: 5
Color: Reddish-brown, dark grey, or silver-black bands
Luster: Sub-metallic to earthy

Identified June 26, 2026More sedimentary →

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Physical properties

Hardness: 5.5-7 (Mohs scale); Color: Reddish-brown, dark grey, or silver-black bands; Luster: Sub-metallic to earthy; Structure: Distinct laminated or layered bedding; Specific Gravity: 3.0-5.0

Formation & geological history

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

Uses & applications

Primary global source of iron ore for steel production; occasionally used for ornamental stones, lapidary work (when jasper-rich), and geological study.

Geological facts

BIFs provide some of the best evidence for the Great Oxidation Event, representing a massive shift in Earth's atmospheric chemistry roughly 2.4 billion years ago.

Field identification & locations

Identify by distinctive alternating layers of iron minerals (hematite/magnetite) and silica (chert/jasper). Commonly found in Western Australia, Brazil, and the Lake Superior region of North America.