sedimentary
Sandstone (River Cobble)
Clastic Sedimentary Rock (primarily Quartz with Feldspar)
Hardness: 6-7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Dull or earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
- Hardness
- 6-7 on Mohs scale
- Color
- Tan, beige, or yellowish-brown
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Dull or earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
Formation & geological history
Formed through the accumulation and cementation of mineral particles or rock fragments (clasts) of sand size. This specific smooth, rounded shape indicates it was transported by water in a river or coastal environment, causing mechanical weathering over thousands of years.
Uses & applications
Commonly used in landscaping (as decorative river rock), construction aggregates, and historically as a building stone or for grindstones.
Geological facts
Sandstone makes up about 10-20% of the Earth's sedimentary rocks. The rounded shape (cobble) suggests it is part of a high-energy fluvial system where rocks roll and bounce along the bottom.
Field identification & locations
Identify in the field by its 'gritty' feel like sandpaper and visible sand grains. Found globally in riverbeds, glacial deposits, and beaches. Collectors look for unique banding or fossils within the layers.
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