sedimentary
River Cobble (Sandstone)
Arenite (primarily SiO2)
Hardness: 6-7 Mohs; Color: Tan, brown, or grey with green algae staining; Luster: Dull to earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
- Hardness
- 6-7 Mohs
- Color
- Tan, brown, or grey with green algae staining
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Tan, brown, or grey with green algae staining; Luster: Dull to earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
Formation & geological history
Formed from the accumulation and cementation of mineral particles or rock fragments of sand size, typically in riverbeds, lakes, or oceans. This specific specimen has been rounded by fluvial (water) erosion.
Uses & applications
Primarily used in construction aggregate, landscaping, road base, and occasionally for architectural stone veneer if large enough and decorative.
Geological facts
Sandstone makes up about 20-25% of all sedimentary rocks on Earth. The green coloring on the surface is likely organic algae growth rather than mineral content, common in riparian environments.
Field identification & locations
Identify in the field by its gritty 'sandpaper' feel and visible grains. Commonly found in riverbeds, glacial tills, and outcrops. Check for layering (bedding planes) if the rock is broken.
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