sedimentary

Weathered banded iron formation (iron-rich quartzite)

Banded iron formation (BIF), chiefly hematite/magnetite and microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Hardness about 6–7; metallic to earthy luster with rusty red-brown, gray, and silvery bands. Typically dense, fine-grained, and weakly to non-cleavable; iron oxides may be magnetic if magnetite-rich.

Identified August 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Chemical sediment precipitated from ancient iron-rich oceans, commonly between about 3.8 and 1.8 billion years ago, then compacted and metamorphosed into iron-rich chert or quartzite.

Uses & applications

Major source of iron ore for steelmaking; attractive polished pieces are used as decorative stone and mineral specimens. This rough fragment has modest collector value.

Geological facts

Alternating silica and iron-mineral layers are characteristic of BIF. Red-brown coloration usually reflects hematite or limonite weathering, while a magnet can detect magnetite-rich bands.

Field identification & locations

Common in Precambrian shield regions, especially Michigan and Minnesota, Western Australia, Brazil, South Africa, India, and Ukraine. Identify by dense layered texture, red streak or powder, and possible magnetism; a streak test and acid test help distinguish it from ordinary jasper.