sedimentary
Ferruginous Sandstone (Ironstone)
Clastic sedimentary rock (SiO2 with Fe2O3/FeO(OH) cement)
Hardness: 6-7 (on Mohs scale); Color: Rusty brown, reddish-brown, or dull gray; Luster: Dull/Earthy; Structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.0-3.0
- Hardness
- 6-7 (on Mohs scale)
- Color
- Rusty brown, reddish-brown, or dull gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (on Mohs scale); Color: Rusty brown, reddish-brown, or dull gray; Luster: Dull/Earthy; Structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.0-3.0
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments, where iron oxides (like hematite or limonite) act as the binding agent. Primarily formed in fluvial, deltaic, or shallow marine environments during various geological eras.
Uses & applications
Used locally as low-grade building stone, road fill, or aggregate. Historically used as a source of iron ore (limonite/hematite) in primitive smelting processes.
Geological facts
The reddish-brown staining is caused by the oxidation of iron minerals, essentially making the rock 'rusted.' This material is often what gives the 'Red Rocks' of the American Southwest their distinct color.
Field identification & locations
Identify in the field by its gritty, sandpaper-like texture and its tendency to leave an orange or reddish streak on a ceramic plate. It is common in riverbeds and eroded plateau regions globally.
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