sedimentary
Red Sandstone (Old Red Sandstone Pebble)
Arenite with iron oxide (Fe2O3) cement
Hardness: 6-7 (Mohs); Color: Reddish-brown to pink due to hematite staining; Luster: Dull/Earthy; Crystal structure: Granular (clastic); Cleavage: None; Specific Gravity: 2.2-2.8
- Hardness
- 6-7 (Mohs)
- Color
- Reddish-brown to pink due to hematite staining
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Reddish-brown to pink due to hematite staining; 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 grains or rock fragments. The red color suggests deposition in an oxidizing terrestrial environment (desert or river floodplain) during the Devonian period (approx. 400 million years ago).
Uses & applications
Common industrial use in construction as aggregate, building stone, or masonry. Smooth beach pebbles are often used in decorative landscaping, zen gardens, or as aquarium substrate.
Geological facts
The 'Old Red Sandstone' is a famous geological unit in the North Atlantic region, described by early geologists like James Hutton to help establish the concept of deep geological time.
Field identification & locations
Identify by its gritty texture (feels like sandpaper) and its uniform red color that doesn't wash off. Commonly found on beaches and riverbeds in the UK, Northeastern US, and Canada. Collectors look for unique shapes weathered by water.
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