sedimentary

Banded Iron Formation

Banded Iron Formation (BIF)

Hardness (Mohs scale): 5.5 - 7; Color: Alternating red (chert/jasper) and black/silver (hematite/magnetite) bands; Luster: Variable, from earthy to metallic; Crystal structure: Trigonal or Isometric (mineral components); Cleavage: None/Conchoidal in chert layers; Specific Gravity: 3.0 - 5.3 depending on iron content.

Luster: Variable, from earthy to metallic

Identified June 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments billions of years ago (mostly Archean and Proterozoic eons, 3.8 to 1.8 billion years ago) through the precipitation of iron-oxide minerals due to the oxygenation of the oceans by early photosynthetic organisms.

Uses & applications

Primary global source of iron ore for steel production; used as decorative 'Tiger Iron' in jewelry when polished; studied as a record of early Earth atmospheric evolution.

Geological facts

BIFs provide some of the best evidence for the "Great Oxidation Event." The world's largest deposits are in the Hamersley Range of Western Australia and the Lake Superior region of North America.

Field identification & locations

Identify in the field by its distinct, often wavy, alternating color bands and high density. Highly magnetic if magnetite is present. Common in ancient shield areas (cratons).

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

sedimentary