sedimentary
Banded Iron Formation / Jasper-Hematite Ore
Banded Iron Formation (BIF) containing Jasper (SiO2) and Hematite (Fe2O3)
Hardness: 6.5-7 (quartz fraction); Color: Red, yellow-orange, and grey bands; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline; Specific gravity: Approx 3.5-4.5.
- Hardness
- 6
- Color
- Red, yellow-orange, and grey bands
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.5-7 (quartz fraction); Color: Red, yellow-orange, and grey bands; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline; Specific gravity: Approx 3.5-4.5.
Formation & geological history
Formed in Precambrian oceans between 3.8 and 1.8 billion years ago. Created through the chemical precipitation of iron and silica as photosynthetic organisms produced oxygen, reacting with dissolved iron in the water.
Uses & applications
Major global source of iron ore for steel production. High-quality colorful specimens like the one pictured are used for lapidary work, jewelry, and decorative garden stones.
Geological facts
These rocks represent the 'Great Oxidation Event.' They record the transition of Earth's atmosphere from oxygen-poor to oxygen-rich, essentially acting as the planet's first rusting records.
Field identification & locations
Identify by distinct colorful banding (red jasper/yellow goethite/grey hematite) and high density. Commonly found in ancient cratons like the Superior Upland (USA), Western Australia, and Brazil.
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