sedimentary

Banded Iron Formation (Jasper-Hematite)

Banded Iron Formation (BIF); composition primarily Hematite (Fe2O3) and Chalcedony/Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Steely grey-black (hematite) alternating with brick red (jasper/chert); Luster: Submetallic to dull; Crystal Structure: Cryptocrystalline; Specific Gravity: 3.5-5.3 depending on iron concentration.

Hardness: 6
Luster: Submetallic to dull

Identified March 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in Precambrian oceans (largely 2.4 to 1.8 billion years ago) through the precipitation of iron and silica during the 'Great Oxygenation Event' when oxygen produced by cyanobacteria reacted with dissolved iron in seawater.

Uses & applications

Primary global source of iron ore for steel production. Specific colorful specimens like this are used in lapidary work (cabochons), jewelry, and as educational geological samples.

Geological facts

BIFs are essential evidence for the evolution of photosynthesis; they record the era when Earth's atmosphere first became oxygen-rich, effectively 'rusting' the oceans.

Field identification & locations

Identify by the distinct alternating layers of red and black/grey. Hematite layers are often weakly magnetic or have a high density, while the red layers are scratch-resistant chert. Common in stable shield areas like the Lake Superior region (USA/Canada), Australia, and Brazil.

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

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Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

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