sedimentary
River Cobble (likely Siltstone or Sandstone)
Clastic Sedimentary Rock
Hardness: 3-7 Mohs; Color: Tan, grey, and brown with dark mineral staining; Luster: Dull to earthy; Structure: Fine-grained clastic; Cleavage: None, breaks irregularly.
- Hardness
- 3-7 Mohs
- Color
- Tan, grey, and brown with dark mineral staining
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-7 Mohs; Color: Tan, grey, and brown with dark mineral staining; Luster: Dull to earthy; Structure: Fine-grained clastic; Cleavage: None, breaks irregularly.
Formation & geological history
Formed through the lithification of silt and sand particles in ancient aquatic environments. These specific specimens were then rounded and polished by the mechanical action of river water over thousands of years.
Uses & applications
Used primarily in landscaping, decorative ground cover, construction aggregate, and as 'worry stones' or painting canvases for hobbyists.
Geological facts
The dark markings on the center rock are likely manganese or iron oxide dendrites or surface stains creating a pareidolia effect, resembling a face.
Field identification & locations
Found in riverbeds, glacial tills, and beaches. Identify in the field by their smooth, rounded edges and heavy weight compared to modern debris.
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