sedimentary
Red Sandstone (Old Red Sandstone)
Ferruginous Sandstone (SiO2 + Fe2O3)
Hardness: 6-7 on Mohs scale; Color: Red, reddish-brown, or pink; Luster: Dull to earthy; Crystal structure: Clastic (composed of mineral grains or rock fragments); Cleavage: None; Specific gravity: 2.2 - 2.8.
- Hardness
- 6-7 on Mohs scale
- Color
- Red, reddish-brown, or pink
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Red, reddish-brown, or pink; Luster: Dull to earthy; Crystal structure: Clastic (composed of mineral grains or rock fragments); Cleavage: None; Specific gravity: 2.2 - 2.8.
Formation & geological history
Formed from the lithification of sand-sized grains, primarily quartz and feldspar, in high-energy terrestrial environments like rivers and deltas. The red color is due to iron oxide (hematite) coating the grains. Much of the famous 'Old Red Sandstone' dates back to the Devonian Period (approx. 400 million years ago).
Uses & applications
Used extensively as building stone, flagstone for paving, and as an abrasive. In smaller, tumbled forms found on beaches, it is popular for decorative landscaping and amateur rock collecting.
Geological facts
Red sandstone is famous for preserving early vertebrate fossils and footprints. In the UK and parts of North America, it was the primary building material for many medieval cathedrals and castles due to its relative ease of carving.
Field identification & locations
Identify in the field by its distinct gritty texture (like sandpaper) and 'brick red' color that doesn't wash off. It is commonly found on coastlines in the UK (Scotland/Wales), the Southwestern US, and the Maritimes in Canada. Collectors look for pieces with interesting patterns or embedded fossils.
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