sedimentary

Banded Iron Formation (Polished)

Banded Iron Formation (BIF)

AI-generated identification · may be incorrect

Hardness: 5-7. Color: varying bands of gray, red, brown, black. Luster: dull to submetallic, vitreous where polished. Crystal structure: microcrystalline. Composition: alternating layers of iron oxides (magnetite or hematite) and chert (silica).

Hardness: 5-7
Color: varying bands of gray, red, brown, black
Luster: dull to submetallic, vitreous where polished

Identified September 19, 2026More sedimentary →

Explore Banded Iron Formation (Polished) 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

Precambrian in age, typically formed in ancient oceans as a chemical sediment when dissolved iron reacted with oxygen produced by early cyanobacteria.

Uses & applications

Major source of iron ore for steel making; polished specimens are used as decorative objects, bookends, and in lapidary arts.

Geological facts

Most of the Earth's iron ore is derived from Banded Iron Formations, which record the Great Oxidation Event in Earth's history over 2 billion years ago.

Field identification & locations

Identified by distinct alternating bands of iron-rich layers and silica-rich layers. Often magnetic if magnetite is present. Common locations include Western Australia, the Lake Superior region of North America, and South Africa.