sedimentary
Red Sandstone
Arenite (primarily Quartz with Hematite cement)
Hardness: 6-7 (Mohs); Color: Red, reddish-brown, or rust; Luster: Dull to earthy; Crystal Structure: Clastic texture (grainy); Cleavage: None; Specific Gravity: 2.2-2.8
- Hardness
- 6-7 (Mohs)
- Color
- Red, reddish-brown, or rust
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Red, reddish-brown, or rust; Luster: Dull to earthy; Crystal Structure: Clastic texture (grainy); 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. The red color indicates formation in an oxygen-rich environment where iron minerals oxidized (rusted), common in desert or river-floodplain settings.
Uses & applications
Used extensively as a building material, decorative stone in landscaping, and as a source of high-purity silica in industrial glass-making. Historical monuments are often carved from durable varieties.
Geological facts
Many of the world's most famous natural landscapes, such as the Grand Canyon in the USA and Petra in Jordan, are composed of red sandstone. It is often referred to as 'Old Red Sandstone' when dating back to the Devonian period.
Field identification & locations
Identify in the field by its gritty, sandpaper-like feel and visible grains. It will not react with acid unless it contains calcite cement. Look for bedding planes or cross-bedding layers.
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