sedimentary

Banded Iron Formation (BIF)

Banded Iron Formation (Magnetite-Hematite-Chert)

AI-generated identification · may be incorrect

Hardness: 5-7 (Mohs); Color: Dark gray to black bands with reddish-brown oxidation; Luster: Sub-metallic to dull; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0 (heavy due to iron content)

Hardness: 5-7 (Mohs)
Color: Dark gray to black bands with reddish-brown oxidation
Luster: Sub-metallic to dull

Identified May 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in Paleo-Proterozoic oceans (2.4 to 1.8 billion years ago) through the precipitation of iron and silica as atmospheric oxygen levels rose due to photosynthesis (The Great Oxygenation Event).

Uses & applications

Primary source of iron ore for steel production and industrial manufacturing globally. Smaller pieces are used as decorative lapidary material.

Geological facts

These formations provide the definitive evidence for the rise of life on Earth, as the iron only precipitated once ancient cyanobacteria started producing oxygen as a waste product.

Field identification & locations

Identify by its heavy weight, dark metallic bands, and magnetic properties if magnetite is present. Commonly found in ancient cratons like the Superior Upland, Western Australia, and Brazil.