sedimentary

Banded Iron Formation (BIF) / Chert

Banded Iron Formation (SiO2 with Fe2O3 / Fe3O4)

Hardness: 6.5 - 7 on Mohs scale. Color: Dark gray to black with reddish-brown or jasper-like iron bands. Luster: Sub-metallic to vitreous (glossy when wet/polished). Cleavage: None (conchoidal fracture). Specific Gravity: 3.0 - 5.0 depending on iron concentration.

Hardness: 6
Luster: Sub-metallic to vitreous (glossy when wet/polished)

Identified July 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in ancient marine environments Precambrian era (2.4 to 1.8 billion years ago) during the Great Oxidation Event, where dissolved iron precipitated with silica in alternating layers.

Uses & applications

Primary source of iron ore worldwide. Minor uses include lapidary arts, decorative stone cabochons, and educational geological specimens.

Geological facts

Banded Iron Formations record the oxygenation of Earth's atmosphere by early photosynthetic cyanobacteria, making them vital records of Earth's early biological and chemical evolution.

Field identification & locations

Identified by alternating layers of silica (chert/jasper) and metallic dark iron minerals (magnetite or hematite). Often weakly to strongly magnetic. Commonly found near ancient Precambrian shields such as the Lake Superior region.

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