metamorphic
Banded iron formation (iron-rich metamorphic rock)
Banded iron formation (BIF), chiefly hematite/magnetite with chert or quartz (Fe₂O₃/Fe₃O₄ and SiO₂)
AI-generated identification · may be incorrectTypically fine- to medium-grained, with alternating reddish-brown iron-oxide and pale gray quartz/chert bands; metallic to earthy luster, hardness about 5.5–6.5, and no obvious cleavage. The dark areas may attract a magnet if magnetite-rich.
Identified More metamorphic →
Explore Banded iron formation (iron-rich metamorphic rock) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically fine- to medium-grained, with alternating reddish-brown iron-oxide and pale gray quartz/chert bands; metallic to earthy luster, hardness about 5.5–6.5, and no obvious cleavage. The dark areas may attract a magnet if magnetite-rich.
Formation & geological history
Chemical sedimentary layers formed mainly 3.8–1.8 billion years ago when dissolved oceanic iron precipitated with silica; later lithified and commonly metamorphosed. The specimen’s iron-rich banding and deformation are consistent with BIF, though exact identification from an image is approximate.
Uses & applications
Important iron ore when hematite- or magnetite-rich; also used as lapidary material, ornamental stone, and collectible rough.
Geological facts
BIF deposits record the rise of atmospheric oxygen and are major sources of the world’s iron. Red coloration generally reflects oxidized hematite or limonite.
Field identification & locations
Look for repeated magnetic dark bands alternating with hard pale quartz/chert, high density, and a reddish-brown streak; a magnet and streak test help distinguish it from jasper. Common in ancient shield regions such as Australia, Brazil, India, South Africa, Canada, and Ukraine.
More like this
