sedimentary
Ferruginous Sandstone
Arenite with Iron-Oxide cement (Fe2O3 · nH2O)
Hardness: 6-7 on Mohs scale; Color: Greyish-blue with rusty orange/brown staining; Luster: Dull, earthy; Crystal structure: Granular/Clastic; Cleavage: None (conchoidal to irregular fracture).
- Hardness
- 6-7 on Mohs scale
- Color
- Greyish-blue with rusty orange/brown staining
- Luster
- Dull, earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Greyish-blue with rusty orange/brown staining; Luster: Dull, earthy; Crystal structure: Granular/Clastic; Cleavage: None (conchoidal to irregular fracture).
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments. Often found in riverbeds or coastal environments where iron-rich groundwater precipitates oxides (like limonite or hematite) between grains.
Uses & applications
Used primarily as construction aggregate, building stone, or in landscaping. High-iron varieties were historically used as low-grade iron ore.
Geological facts
This specimen shows significant 'desert varnish' or oxidation staining. The pitting on the surface suggests chemical weathering where softer binder material has eroded out, leaving a more resistant silica/iron framework.
Field identification & locations
Identify by its gritty texture (feels like sandpaper) and distinct rust-colored staining. Common in sedimentary basins worldwide. For collectors, it represents the intersection of sedimentary geology and chemical weathering.
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