metamorphic
Banded Iron Formation (BIF) / Gneiss
Banded Iron Formation (BIF)
Hardness: 6-7 on Mohs scale; Color: Alternating bands of dark grey/black (magnetite/hematite) and reddish-brown, yellow, or white (chert/quartz/limonite); Luster: Sub-metallic to dull/earthy; Texture: Distinctly foliated/banded
- Hardness
- 6-7 on Mohs scale
- Luster
- Sub-metallic to dull/earthy
Identified More metamorphic →
Explore Banded Iron Formation (BIF) / Gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 on Mohs scale; Color: Alternating bands of dark grey/black (magnetite/hematite) and reddish-brown, yellow, or white (chert/quartz/limonite); Luster: Sub-metallic to dull/earthy; Texture: Distinctly foliated/banded
Formation & geological history
Formed during Precambrian times (typically 1.8 to 3.8 billion years ago) through the precipitation of iron and silica in ancient marine environments as photosynthesizing cyanobacteria introduced oxygen into Earth's oceans. Subsequent regional metamorphism compressed and banded the rock.
Uses & applications
Primary source of iron ore worldwide used in steel production. High-grade or distinctly banded specimens are collected by rockhounds and educational institutions as historic geological display pieces.
Geological facts
Banded Iron Formations record the Great Oxidation Event, representing the era when oxygen first began accumulating in Earth's atmosphere and oceans over two billion years ago. Most of Earth's iron reserves come from these ancient deposits.
Field identification & locations
Identified in the field by alternating metallic or dark iron-rich layers and siliceous chert or quartz layers, often showing rust-like limonite weathering. Common in Precambrian shield areas like Minnesota, Michigan, Western Australia, and South Africa.
More like this
