sedimentary
Banded Iron Formation / Hematite-Chert Matrix
Fe2O3 + SiO2 (Hematite and Microcrystalline Quartz)
Hardness: 5.5-7.0 on Mohs scale. Color: Dark brown, black, greyish to reddish tones. Luster: Sub-metallic to earthy. Structure: Fine-grained, microcrystalline, layered or massive. Cleavage: None.
- Hardness
- 5
- Color
- Dark brown, black, greyish to reddish tones
- Luster
- Sub-metallic to earthy
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Physical properties
Hardness: 5.5-7.0 on Mohs scale. Color: Dark brown, black, greyish to reddish tones. Luster: Sub-metallic to earthy. Structure: Fine-grained, microcrystalline, layered or massive. Cleavage: None.
Formation & geological history
Formed in ancient marine environments Precambrian era (over 1.8 to 3.8 billion years ago) through precipitation of iron oxides and silica as atmospheric oxygen levels rose.
Uses & applications
Major economic ore source for iron and steel production. Highly valued for geological study and lapidary/carving crafts.
Geological facts
Banded Iron Formations record the 'Great Oxidation Event', representing one of the most critical transitions in Earth's geological history.
Field identification & locations
Identified by high density/specific gravity, dark reddish-brown to black coloration, microcrystalline texture, and weak to moderate magnetism when magnetite is present. Commonly found in Western Australia, Minnesota (USA), and Brazil.
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