sedimentary
Red Sandstone (Siltstone Pebble)
Arenite / Siltstone with Iron Oxide (Fe2O3)
Hardness: 6-7 (Mohs scale); Color: Reddish-brown, maroon; Luster: Dull, earthy; Crystal structure: Clastic (grains); Cleavage: None; Specific gravity: 2.2 - 2.8
- Hardness
- 6-7 (Mohs scale)
- Color
- Reddish-brown, maroon
- Luster
- Dull, earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Reddish-brown, maroon; Luster: Dull, earthy; Crystal structure: Clastic (grains); Cleavage: None; Specific gravity: 2.2 - 2.8
Formation & geological history
Formed through the accumulation and cementation of mineral particles or rock fragments, typically in riverbeds, lakes, or desert environments. This specific color is due to the presence of hematite coating the grains.
Uses & applications
Used primarily in landscaping, decorative ground cover, and construction. Finer siltstones have also been used historically as sharpening stones or pigments.
Geological facts
The red color indicating iron oxidation is often associated with the 'Red Beds' of the Permian and Triassic periods. These rocks can store groundwater and petroleum in their pore spaces.
Field identification & locations
Identify by its gritty texture (feels like sandpaper) and its ability to leave a reddish streak if rubbed on a harder surface. Frequently found in riverbeds and arid regional outcrops.
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