sedimentary
Red Sandstone
Sandstone (lithic arenite / ferruginous sandstone)
Hardness: 6-7 Mohs (quartz-rich grains); Color: Red, reddish-brown, or terracotta; Luster: Dull/Earthy; Crystal Structure: Granular/Clastic; Specific Gravity: 2.2-2.8. Highly porous and sandpaper-like texture.
- Hardness
- 6-7 Mohs (quartz-rich grains)
- Color
- Red, reddish-brown, or terracotta
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 Mohs (quartz-rich grains); Color: Red, reddish-brown, or terracotta; Luster: Dull/Earthy; Crystal Structure: Granular/Clastic; Specific Gravity: 2.2-2.8. Highly porous and sandpaper-like texture.
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments, typically in desert, river, or coastal environments. The red color is caused by the presence of iron oxides (hematite) which coat the grains. Many red sandstones date back to the Triassic, Permian, or Devonian periods.
Uses & applications
Widely used as a building material (brownstone), in paving, landscaping, and as a natural filter in aquifers. It is also used by collectors and as a source of quartz for glassmaking.
Geological facts
The famous red cliffs of the Grand Canyon and the 'Red Rocks' of Colorado are primarily sandstone. It is often called 'Old Red Sandstone' when referring to the Devonian-aged layers in the North Atlantic region.
Field identification & locations
Identify by its gritty texture (feels like sandpaper) and visible sand grains. It does not react with acid unless it has a calcitic cement. Found globally in basins and mountainous regions where ancient sedimentary layers are exposed.
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