sedimentary

Banded iron formation fragment

BIF; hematite–magnetite–chert/quartz assemblage

AI-generated identification · may be incorrect

Dark metallic gray to rusty brown, with alternating iron-oxide and silica-rich bands; submetallic to earthy luster, granular microcrystalline texture, hardness about 5–6.5 (hematite/magnetite and quartz), and no obvious cleavage. The specimen appears weathered and broken, with oxidation producing orange-brown surfaces.

Identified September 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Chemical sedimentary rock deposited mainly in Precambrian oceans, especially about 3.8–1.8 billion years ago, when dissolved iron precipitated with silica during changes in ocean chemistry and oxygen levels. Later compaction and metamorphism commonly recrystallized the layers.

Uses & applications

Major global source of iron ore when enriched; also used as decorative stone, lapidary material, and geological specimens. This small rough fragment has modest commercial value.

Geological facts

Many BIFs record the transition from anoxic to oxygenated Earth and are associated with early microbial activity. Magnetite-rich pieces may attract a magnet, while hematite-rich pieces typically show a reddish-brown streak.

Field identification & locations

Common in iron ranges of Minnesota and Michigan, the Pilbara of Australia, South Africa, Brazil, India, and Ukraine. Look for thin rhythmic red-black-gray banding, high density, rusty weathering, and possible magnetism; the pictured fragment is consistent with iron-rich banded rock.