sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (Magnetite/Hematite Chert)
Hardness: 6.5-7 (on Mohs scale); Color: Metallic gray to black with rusty orange/red oxidation; Luster: Sub-metallic to dull; Crystal structure: Microcrystalline; Cleavage: None; Specific Gravity: High (4.9-5.3).
- Hardness
- 6
- Color
- Metallic gray to black with rusty orange/red oxidation
- Luster
- Sub-metallic to dull
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Physical properties
Hardness: 6.5-7 (on Mohs scale); Color: Metallic gray to black with rusty orange/red oxidation; Luster: Sub-metallic to dull; Crystal structure: Microcrystalline; Cleavage: None; Specific Gravity: High (4.9-5.3).
Formation & geological history
Formed in Precambrian marine environments (mostly 2.4 to 1.8 billion years ago) through the precipitation of iron oxides and silica during the Great Oxygenation Event.
Uses & applications
The primary global source of iron ore for steel production; also used as a decorative stone or lapidary material when aesthetically banded (e.g., Tiger Iron).
Geological facts
These rocks provide evidence for the evolution of photosynthesis as they formed when oxygen released by cyanobacteria reacted with dissolved iron in the ancient oceans.
Field identification & locations
Identify by its high density (heavy for its size), distinct alternating layers or grooves, and magnetic properties if magnet-rich. It is commonly found in ancient cratons like the Lake Superior region and Western Australia.
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