sedimentary
Banded Iron Formation (BIF) / Jaspilite
Banded Iron Formation (predominantly Hematite, Magnetite, and Quartz/Jasper)
Hardness: 5.5-7.0 (Mohs); Color: Alternating red/brown (jaspering) and silver/black/grey (iron oxides); Luster: Dull to sub-metallic; Structure: Finely laminated sedimentary layers; Cleavage: None.
- Hardness
- 5
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5.5-7.0 (Mohs); Color: Alternating red/brown (jaspering) and silver/black/grey (iron oxides); Luster: Dull to sub-metallic; Structure: Finely laminated sedimentary layers; Cleavage: None.
Formation & geological history
Formed in marine environments during the Precambrian era (mostly 2.4 to 1.8 billion years ago) when oxygen produced by cyanobacteria reacted with dissolved iron in the oceans, causing it to precipitate out as minerals on the sea floor.
Uses & applications
Primary global source of iron ore for steel production; also used as semi-precious ornamental stone, paperweights, and lapidary specimens due to its striking patterns.
Geological facts
BIFs provide geological evidence for the 'Great Oxidation Event', representing a time when Earth's atmosphere first became enriched with oxygen. Huge deposits exist in the Hamersley Range (Australia) and the Lake Superior region (USA/Canada).
Field identification & locations
Identify by the distinct, rhythmic dark and light colored banding; the dark bands are often weakly magnetic. Commonly found in ancient cratons; collectors should look for high-contrast banding and lack of heavy weathering.
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