sedimentary
Banded Iron Formation (Chert/Hematite)
Banded Iron Formation (BIF)
Color: alternating dark grey/black and brownish-red bands; Hardness: 6.5-7 Mohs; Luster: dull to sub-metallic; Structure: microcrystalline quartz (chert) and iron oxides; Specific gravity: approx. 3.0-5.0.
- Hardness
- 6
- Color
- alternating dark grey/black and brownish-red bands
- Luster
- dull to sub-metallic
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Physical properties
Color: alternating dark grey/black and brownish-red bands; Hardness: 6.5-7 Mohs; Luster: dull to sub-metallic; Structure: microcrystalline quartz (chert) and iron oxides; Specific gravity: approx. 3.0-5.0.
Formation & geological history
Formed in ancient seawater billions of years ago (typically 2.4 to 1.8 billion years) as a result of oxygen release by early cyanobacteria reacting with dissolved iron in the oceans.
Uses & applications
Primary global source of iron ore for steel production; used as architectural stone and in lapidary work for making cabochons or decorative items.
Geological facts
These rocks provide the most significant geological evidence for the Great Oxygenation Event, which transformed Earth's atmosphere to support aerobic life.
Field identification & locations
Identified by high density and characteristic alternating dark and light layers. Commonly found in ancient cratons like the Hamersley Range in Australia or the Lake Superior region in North America.
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