sedimentary
Red Sandstone
Arenite (primarily SiO2 with Fe2O3)
Hardness: 6-7 on Mohs scale (for grains); Color: Red, reddish-brown, or orange due to iron oxide; Luster: Dull to earthy; Crystal structure: Granular; Cleavage: None; Specific gravity: 2.2 - 2.8
- Hardness
- 6-7 on Mohs scale (for grains)
- Color
- Red, reddish-brown, or orange due to iron oxide
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 on Mohs scale (for grains); Color: Red, reddish-brown, or orange due to iron oxide; Luster: Dull to earthy; Crystal structure: Granular; Cleavage: None; Specific gravity: 2.2 - 2.8
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments, often in desert or river delta environments. The red color suggests deposition in an oxygen-rich terrestrial environment where iron minerals oxidized.
Uses & applications
Widely used as a building material, paving stone, and in the manufacturing of glass and grindstones. Finely crushed sandstone is also used in hydraulic fracturing and as an abrasive.
Geological facts
Red sandstone is famous for creating the iconic landscapes of the American Southwest, such as the Grand Canyon and Zion National Park. Some red sandstones, like the Old Red Sandstone, date back over 400 million years to the Devonian period.
Field identification & locations
Identify by its gritty, sandpaper-like feel and visible grains. It can be found globally in sedimentary basins. Collectors should look for unique cross-bedding patterns or fossils often preserved within the layers.
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