![Banded Iron Formation (BIF) / Tiger Iron (Ferruginous Chert (primarily Quartz [SiO2] and Hematite/Magnetite [Fe2O3/Fe3O4])) — metamorphic](https://media.rockidentification.com/19c0ce3b-be7c-47fb-b1d3-d6f891471113-compressed.jpg)
metamorphic
Banded Iron Formation (BIF) / Tiger Iron
Ferruginous Chert (primarily Quartz [SiO2] and Hematite/Magnetite [Fe2O3/Fe3O4])
Hardness: 6.5-7.0 (Mohs); Color: Alternating bands of silver-grey, red, brown, and yellow; Luster: Sub-metallic to vitreous; Crystal Structure: Microcrystalline; Specific Gravity: 3.3-5.3 depending on iron content.
- Hardness
- 6
- Color
- Alternating bands of silver-grey, red, brown, and yellow
- Luster
- Sub-metallic to vitreous
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Physical properties
Hardness: 6.5-7.0 (Mohs); Color: Alternating bands of silver-grey, red, brown, and yellow; Luster: Sub-metallic to vitreous; Crystal Structure: Microcrystalline; Specific Gravity: 3.3-5.3 depending on iron content.
Formation & geological history
Formed in Precambrian oceans between 1.8 and 3.0 billion years ago. Oxygen produced by early cyanobacteria reacted with dissolved iron, precipitating iron oxides into layers on the seafloor. Many specimens undergo low-grade metamorphism.
Uses & applications
Major source of iron ore globally; also used for lapidary work, jewelry (cabochons), and as ornamental display pieces. 'Tiger Iron' specifically is prized by collectors.
Geological facts
BIFs record the 'Great Oxygenation Event' of Earth's atmosphere. Without the biological production of oxygen by primitive life, these uniquely banded rocks would not exist.
Field identification & locations
Identified by distinct alternating layers of iron oxides and silica (chert/jasper). Often heavily magnetic if magnetite is present. Common locations include the Hamersley Range in Australia, the Lake Superior region in North America, and South Africa.
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