sedimentary
Banded Iron Formation (BIF) / Jasper-Magnetite
Banded Iron Formation (majorly Fe2O3/Fe3O4 + SiO2)
Hardness: 5.5 to 7 on Mohs scale; Color: Reddish-brown to black bands; Luster: Sub-metallic to dull; Crystal structure: Trigonal (Hematite) and Isometric (Magnetite); Cleavage: None; Specific Gravity: 3.0 to 5.3 (dense).
- Hardness
- 5
- Color
- Reddish-brown to black bands
- Luster
- Sub-metallic to dull
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Physical properties
Hardness: 5.5 to 7 on Mohs scale; Color: Reddish-brown to black bands; Luster: Sub-metallic to dull; Crystal structure: Trigonal (Hematite) and Isometric (Magnetite); Cleavage: None; Specific Gravity: 3.0 to 5.3 (dense).
Formation & geological history
Formed during the Archean and Proterozoic eons (roughly 2.4 to 1.8 billion years ago) through the precipitation of iron and silica from seawater as oxygen levels rose due to early photosynthesis.
Uses & applications
Primary global source of iron ore for steel production; also used as an ornamental stone and for lapidary work (cabochons and carvings).
Geological facts
These rocks represent the 'Great Oxidation Event' when Earth's atmosphere first received a significant amount of oxygen, causing dissolved iron in the oceans to 'rust' and settle in layers.
Field identification & locations
Identify in the field by alternating dark (iron-rich) and red/brown (silica-rich) bands; often slightly magnetic. Common in regions like the Lake Superior area (USA), Western Australia, and Brazil.
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