sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (BIF), SiO2 / Fe2O3
Hardness (6.5-7 Mohs), Colors (Red, brown, grey, black), Dull to sub-metallic luster, Rhombohedral microcrystalline structure, Specific gravity 3.5-5.0.
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Physical properties
Hardness (6.5-7 Mohs), Colors (Red, brown, grey, black), Dull to sub-metallic luster, Rhombohedral microcrystalline structure, Specific gravity 3.5-5.0.
Formation & geological history
Formed in marine environments during the Precambrian era (3.8 to 1.8 billion years ago) through the precipitation of iron and silica due to biological oxygen production.
Uses & applications
Primary source of iron ore for steel manufacturing. Polished specimens are used for lapidary work and collectors.
Geological facts
BIFs record the 'Great Oxidation Event' when photosynthetic bacteria first released oxygen into Earth's oceans and atmosphere.
Field identification & locations
Identify by alternating layers of red chert (jasper) and dark iron oxides like hematite or magnetite. Found in Western Australia, Brazil, and the Lake Superior region.
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