sedimentary
Sandstone (Ferruginous)
Arenite (composed primarily of SiO2 with Fe2O3 cement)
Hardness: 6-7 (Mohs); Color: Reddish-brown to purple/maroon; Luster: Dull/Earthy; Texture: Fine to medium-grained; Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.2 - 2.8
- Hardness
- 6-7 (Mohs)
- Color
- Reddish-brown to purple/maroon
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Reddish-brown to purple/maroon; Luster: Dull/Earthy; Texture: Fine to medium-grained; Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.2 - 2.8
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments. The reddish hue indicates presence of iron oxide (hematite) during the lithification process. Formed in deserts, river beds, or ocean basins over millions of years.
Uses & applications
Used widely as a building and paving material, for grindstones, glass making (if high silica), and as a reservoir rock for oil and natural gas.
Geological facts
Red sandstones are often associated with arid 'Red Bed' environments and can preserve footprints or ripple marks from ancient environments. They are the primary material in famous landmarks like the Grand Canyon.
Field identification & locations
Identify in the field by its 'sandpaper' feel and visible grains that don't rub off like silt. It will not fizz with HCl (unlike limestone). Common in sedimentary basins worldwide.
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