sedimentary

Banded iron formation (BIF)

Banded iron formation; chiefly hematite/magnetite and microcrystalline quartz (chert)

AI-generated identification · may be incorrect

Typically 5–7 Mohs; alternating metallic dark iron-oxide layers and pale gray-white chert layers, with earthy to submetallic luster and finely crystalline/granular texture. Dense, heavy, and commonly magnetic if magnetite-rich; no prominent cleavage.

Identified August 26, 2026More sedimentary →

Explore Banded iron formation (BIF) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Chemical sediment formed when dissolved iron precipitated with silica in ancient oceans, commonly between about 3.8 and 1.8 billion years ago, especially during the Precambrian Great Oxidation Event.

Uses & applications

Major iron ore when sufficiently iron-rich; also cut and polished for display, paperweights, and lapidary objects. Common specimens usually have modest collector value.

Geological facts

Its rhythmic banding records changing ocean chemistry and oxygen availability. Red-brown bands generally contain hematite, while black bands may contain magnetite or iron-rich silicates.

Field identification & locations

Identify it by persistent, wavy, parallel iron-rich and silica-rich bands, unusual heft, and possible magnetism; major occurrences include the Lake Superior region, Western Australia, Brazil, India, and South Africa. A magnet and streak test help distinguish magnetite-rich BIF from similar banded rocks.