sedimentary

Banded Iron Formation (BIF) / Ironstone

Ferruginous sedimentary rock (Fe2O3 + SiO2)

Hardness: 5-7 (Mohs scale); Color: Metallic grey, rust red, and ochre yellow; Luster: Sub-metallic to earthy; Crystal Structure: Cryptocrystalline to microcrystalline; Cleavage: None; Specific Gravity: 3.5 - 5.0 (dense)

Hardness: 5-7 (Mohs scale)
Color: Metallic grey, rust red, and ochre yellow
Luster: Sub-metallic to earthy

Identified June 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in ancient oceans between 3.8 and 1.8 billion years ago (Precambrian) through the precipitation of iron oxides and silica as photosynthesis by cyanobacteria began oxygenating Earth's atmosphere.

Uses & applications

Primary source of iron ore for the global steel industry; polished specimens are used for decorative lapidary work and carvings.

Geological facts

These formations represent the 'Great Oxidation Event' and are some of the oldest known geological records of life on Earth. Significant deposits like the Hamersley Range in Australia or the Mesabi Range in the US drive the global economy.

Field identification & locations

Identify in the field by its distinct alternating stripes, high density, and strong magnetism in some layers. Commonly found in Western Australia, Canada, Brazil, and the Lake Superior region.

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