sedimentary

Ferruginous Sandstone (Ironstone)

Clastic sedimentary rock (SiO2 with Fe2O3/FeO(OH) cement)

AI-generated identification · may be incorrect

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

Identified March 2, 2026More sedimentary →

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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.