sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation
Hardness: 5-7 (Mohs); Color: Alternating bands of dark (gray/black) and light (red/brown/tan); Luster: Earthy to metallic; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0
- Hardness
- 5-7 (Mohs)
- Luster
- Earthy to metallic
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Physical properties
Hardness: 5-7 (Mohs); Color: Alternating bands of dark (gray/black) and light (red/brown/tan); Luster: Earthy to metallic; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0
Formation & geological history
Formed in Precambrian marine environments (2.4 to 1.8 billion years ago) through the precipitation of iron and silica from ocean water, triggered by oxygen released by early photosynthetic bacteria.
Uses & applications
Primarily used as the world's major source of iron ore for steel production; also used as decorative stone or collector specimens.
Geological facts
These formations provide evidence for the 'Great Oxidation Event' when Earth's atmosphere first became enriched with oxygen. Many specimens contain the mineral Jasper (red) and Hematite or Magnetite (dark bands).
Field identification & locations
Identify by distinct rhythmic layering of iron-rich and silica-rich minerals. Often magnetic if it contains magnetite. Found in ancient shield regions like the Lake Superior area, Australia, and Brazil.
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