sedimentary
Ferruginous Sandstone
Arenite with Hematite/Limonite cement (SiO2 + Fe2O3)
Hardness: 6-7 (Mohs); Color: Reddish-brown, rust, or tan with grey layers; Luster: Dull/Earthy; Crystal structure: Granular (clastic); Cleavage: None; Specific Gravity: 2.6-3.0.
- Hardness
- 6-7 (Mohs)
- Color
- Reddish-brown, rust, or tan with grey layers
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Reddish-brown, rust, or tan with grey layers; Luster: Dull/Earthy; Crystal structure: Granular (clastic); Cleavage: None; Specific Gravity: 2.6-3.0.
Formation & geological history
Formed from the deposition of sand-sized quartz grains in river, beach, or desert environments. The red coloration occurs during diagenesis as iron-rich groundwater precipitates iron oxides (like hematite) between grains.
Uses & applications
Commonly used as a building stone or flagstone in construction due to its durability. High-iron varieties have historically been used as a minor source of iron ore.
Geological facts
The red color is essentially 'rust' on a geological scale. In the United States, this rock is famous for creating the landscape of the Red Rocks Amphitheatre and the Grand Canyon.
Field identification & locations
Identify by its 'sandpaper' feel and the distinctive reddish staining that doesn't wash off. Often found in continental shelf deposits and interior basins globally.
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