sedimentary
Sandstone (River Cobble)
Clastic sedimentary rock (primarily SiO2)
Hardness: 6-7 Mohs (if quartz-rich); Color: Tan, beige, gray with black lichen/organic staining; Luster: Dull, earthy; Structure: Clastic, fine-grained; Cleavage: None.
- Hardness
- 6-7 Mohs (if quartz-rich)
- Color
- Tan, beige, gray with black lichen/organic staining
- Luster
- Dull, earthy
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Physical properties
Hardness: 6-7 Mohs (if quartz-rich); Color: Tan, beige, gray with black lichen/organic staining; Luster: Dull, earthy; Structure: Clastic, fine-grained; Cleavage: None.
Formation & geological history
Formed from the accumulation and lithification of sand-sized mineral grains or rock fragments. This specific piece is a river cobble, rounded by water erosion through abrasion over thousands of years.
Uses & applications
Commonly used in landscaping, construction aggregates, and as a raw material for glass making. Tumbled specimens are used in garden decoration.
Geological facts
Sandstone makes up about 20-25% of all sedimentary rocks on Earth. The dark spots on this specimen are most likely organic growth (lichens) or manganese oxide staining acquired during weathering.
Field identification & locations
Identified by its gritty 'sandpaper' feel and rounded shape indicating transport in water. Found globally in riverbeds, beaches, and ancient sedimentary basins. Collectors often look for fossil inclusions within sandstone matrices.
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