sedimentary
Banded Iron Formation (BIF) / Iron Ore
Hematite-Magnetite BIF (Fe2O3 / Fe3O4 mixed with SiO2)
Hardness: 5-6 on Mohs scale; Color: Dark grey, steel black, to rusty brown with distinct layered banding; Luster: Metallic to sub-metallic; Crystal structure: Hexagonal/Trigonal (Hematite); Cleavage: None; Specific Gravity: 4.9-5.3.
- Hardness
- 5-6 on Mohs scale
- Luster
- Metallic to sub-metallic
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Physical properties
Hardness: 5-6 on Mohs scale; Color: Dark grey, steel black, to rusty brown with distinct layered banding; Luster: Metallic to sub-metallic; Crystal structure: Hexagonal/Trigonal (Hematite); Cleavage: None; Specific Gravity: 4.9-5.3.
Formation & geological history
Formed in ancient oceans during the Precambrian era (approx. 2.4 to 1.8 billion years ago) through the precipitation of iron and silica from seawater as oxygen levels rose, known as the Great Oxidation Event.
Uses & applications
Primary source of iron ore for the production of steel worldwide. Occasionally used for decorative purposes or as geological educational specimens.
Geological facts
These rocks provide the primary evidence for the Great Oxidation Event, representing the transition when the Earth's atmosphere and oceans first began to accumulate free oxygen.
Field identification & locations
Identified by high density, distinct dark/reddish layers, and magnetic response if magnetite is present. Found in major deposits in Western Australia, Brazil, and the Lake Superior region of North America.
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