sedimentary

Banded Iron Formation

Banded Iron Formation (BIF)

AI-generated identification · may be incorrect

Hardness: 5.5-6.5 on Mohs scale; Color: Gray, black, and reddish-brown bands; Luster: Sub-metallic to dull; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0 depending on iron content.

Hardness: 5
Color: Gray, black, and reddish-brown bands
Luster: Sub-metallic to dull

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 5.5-6.5 on Mohs scale; Color: Gray, black, and reddish-brown bands; Luster: Sub-metallic to dull; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0 depending on iron content.

Formation & geological history

Formed in Precambrian oceans (largely between 2.4 and 1.8 billion years ago) when oxygen produced by cyanobacteria reacted with dissolved iron in seawater, causing it to precipitate as iron oxides on the seafloor.

Uses & applications

The primary global source of iron ore for steel production; also used as decorative stone and for geological study.

Geological facts

BIFs are the primary evidence for the 'Great Oxidation Event'. They are mostly found in very old Precambrian shields like those in Australia, Brazil, and the Lake Superior region.

Field identification & locations

Identify by characteristic alternating dark (magnetite/hematite) and light (chert/jasper) layers. Often magnetic or very heavy for its size. Common in the Mesabi Range of Minnesota and the Pilbara region of Western Australia.