sedimentary
Banded Iron Formation (BIF) / Ironstone Conglomerate
Ironstone (Hematite/Goethite rich sedimentary rock)
Hardness: 5-6 (variable); Color: reddish-brown to dark gray; Luster: earthy to sub-metallic; Crystal Structure: microcrystalline/amorphous; Cleavage: none; Specific Gravity: high (feels heavy for its size).
- Hardness
- 5-6 (variable)
- Color
- reddish-brown to dark gray
- Luster
- earthy to sub-metallic
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Physical properties
Hardness: 5-6 (variable); Color: reddish-brown to dark gray; Luster: earthy to sub-metallic; Crystal Structure: microcrystalline/amorphous; Cleavage: none; Specific Gravity: high (feels heavy for its size).
Formation & geological history
Formed in ancient sea floors through the precipitation of iron oxides (Hematite, Magnetite) and silica, often dating back 1.8 to 3.5 billion years during the Great Oxygenation Event.
Uses & applications
Primary source of iron ore globally for steel production. Small tumbled pieces are used in lapidary work or as collector specimens.
Geological facts
These rocks are some of the oldest evidence of life on Earth, as the iron was precipitated out of the ocean by the metabolic processes of early oxygen-producing cyanobacteria.
Field identification & locations
Identified in the field by its high density, brownish-red streak, and tendency to be found in ancient cratons. Locations include the Lake Superior region (USA), Western Australia, and Brazil.
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