sedimentary
Banded Iron Formation (Jaspillite)
Banded Iron Formation (BIF)
Hardness: 6.5-7 (Mohs); Color: Alternating red (jasper) and silver-gray (hematite/magnetite) bands; Luster: Dull to metallic; Structure: Microcrystalline quartz and iron oxide layers; Specific Gravity: 3.0-5.0.
- Hardness
- 6
- Luster
- Dull to metallic
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Alternating red (jasper) and silver-gray (hematite/magnetite) bands; Luster: Dull to metallic; Structure: Microcrystalline quartz and iron oxide layers; Specific Gravity: 3.0-5.0.
Formation & geological history
Formed in Precambrian seas (2.4 to 1.8 billion years ago) during the Great Oxidation Event, where rhythmic precipitation of iron oxides and silica occurred in marine basins due to fluctuating oxygen levels from early photosynthesis.
Uses & applications
Primary global source of iron ore for steel production; also used as a decorative stone for lapidary work, jewelry (cabochons), and as museum-quality geological specimens.
Geological facts
These rocks represent the transition of Earth's atmosphere from oxygen-poor to oxygen-rich; they are among the oldest known rocks on Earth and provided the iron for the modern industrial world.
Field identification & locations
Identified by heavy weight, distinct red/gray banding, and magnetism if magnetite is present. Common locations include the Lake Superior region (USA), Western Australia, Brazil, and South Africa.
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