sedimentary
Sandstone (River Cobble)
Sandstone (primarily composed of silica, SiO2)
Hardness: 6-7 Mohs; Color: Tan to reddish-brown; Luster: Dull/Earthy; Crystal structure: Clastic/Granular; Cleavage: None; Specific Gravity: 2.2-2.8
- Hardness
- 6-7 Mohs
- Color
- Tan to reddish-brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Tan to reddish-brown; Luster: Dull/Earthy; Crystal structure: Clastic/Granular; 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 over millions of years, often in riverbeds or coastal environments. This specific piece was further shaped into a smooth cobble by water erosion.
Uses & applications
Commonly used in construction, as a building material, and for sharpening tools. Smooth river stones are popular in landscaping and decorative aquariums.
Geological facts
Sandstone acts as a natural filter in nature and is one of the most common sedimentary rocks on Earth. Old Red Sandstone deposits are famous for preserving early vertebrate fossils.
Field identification & locations
Identify in the field by its gritty, sandpaper-like texture and visible sedimentary layers. Found globally in riverbeds, deserts, and cliffs.
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