sedimentary
Red Sandstone
Clastic sedimentary rock (primarily SiO2 with Fe2O3)
Hardness: 6-7 (Mohs scale); Color: Red, reddish-brown, or orange; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8.
- Hardness
- 6-7 (Mohs scale)
- Color
- Red, reddish-brown, or orange
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Red, reddish-brown, or orange; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8.
Formation & geological history
Formed through the accumulation and lithification of sand-sized mineral particles or rock fragments. The red color is due to the oxidation of iron-bearing minerals (hematite) coating the quartz grains. These often form in arid desert or river floodplain environments.
Uses & applications
Extensively used as a building material, paving stone, and in decorative landscaping. In industry, it can be crushed for use in concrete or glass manufacturing if high in silica.
Geological facts
Famous structures built from red sandstone include the Red Fort in India and many iconic buildings in the American Southwest (Sedona, AZ). It is a primary indicator of terrestrial deposition during eras like the Permian and Triassic.
Field identification & locations
Identify by its gritty, sandpaper-like texture and its tendency to rub off slightly when scratched. It is commonly found in the Colorado Plateau (USA), Scotland, and Northern England. For collectors, look for cross-bedding patterns or fossil inclusions.
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