metamorphic
Banded Iron Formation (Metamorphosed Jasper/Siltstone)
Ferruginous Quartzite or Jasperoid Siltstone
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown (hematite-rich) with grey/white bands; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-3.2
- Hardness
- 6
- Color
- Reddish-brown (hematite-rich) with grey/white bands
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown (hematite-rich) with grey/white bands; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-3.2
Formation & geological history
Formed during the Precambrian era (over 2 billion years ago) through the rhythmic precipitation of iron oxides and silica in ancient ocean basins, subsequently subjected to regional metamorphism and stream tumbling.
Uses & applications
Used primarily as iron ore for steel production; also used as a tumble stone for collectors, lapidary work, and landscaping decoration.
Geological facts
Rocks like this are key evidence of the Great Oxidation Event, representing a time when Earth's atmosphere first became enriched with oxygen, leading to the precipitation of iron from the oceans.
Field identification & locations
Identify by its heavy weight (due to iron content), alternating color bands, and extreme hardness (cannot be scratched by a steel pocket knife). Commonly found in Precambrian shield areas like the Great Lakes region or Western Australia.
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