sedimentary
Red Sandstone
Arenite (with Iron Oxide / Hematite cementation)
Hardness: 6-7 on Mohs scale (depending on silica content); Color: Reddish-brown, terracotta, or rust orange due to iron oxide; Luster: Dull/Earthy; Crystal structure: Clastic (composed of sand-sized grains); Cleavage: None (grains are cemented together); Specific gravity: 2.2–2.8.
- Hardness
- 6-7 on Mohs scale (depending on silica content)
- Color
- Reddish-brown, terracotta, or rust orange due to iron oxide
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale (depending on silica content); Color: Reddish-brown, terracotta, or rust orange due to iron oxide; Luster: Dull/Earthy; Crystal structure: Clastic (composed of sand-sized grains); Cleavage: None (grains are cemented together); Specific gravity: 2.2–2.8.
Formation & geological history
Formed by the accumulation and lithification of sand-sized mineral particles or rock fragments. The red color suggests deposition in an oxygen-rich environment (aerobic), often in desert dunes or river floodplains. Most red sandstones date from the Permian or Triassic periods (roughly 200–300 million years ago).
Uses & applications
Commonly used in construction for building facades, paving stones, and landscaping. It is also used as a source for glass sand or as a reservoir rock for oil, gas, and groundwater in geological formations.
Geological facts
Red sandstone is famous for creating the dramatic landscapes of the American Southwest, such as the Grand Canyon and Antelope Canyon. Old Red Sandstone is a significant geological unit that helped early geologists understand the Earth's history through stratigraphy.
Field identification & locations
Identify in the field by its gritty texture (feels like sandpaper) and distinct red/orange color that doesn't rub off. It is found globally, with major deposits in the Colorado Plateau (USA), Scotland, and central India. Collectors look for pieces with interesting patterns or cross-bedding indicating ancient wind patterns.
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