sedimentary
River Pebble (Graywacke/Sandstone)
Lithic Sandstone
Hardness: 6-7 on Mohs scale; Color: Dull gray to grayish-green with orange/brown iron oxidation; Luster: Matte; Crystal structure: Clastic (grainy texture); Cleavage: None
- Hardness
- 6-7 on Mohs scale
- Color
- Dull gray to grayish-green with orange/brown iron oxidation
- Luster
- Matte
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dull gray to grayish-green with orange/brown iron oxidation; Luster: Matte; Crystal structure: Clastic (grainy texture); Cleavage: None
Formation & geological history
Formed through the accumulation and lithification of sand, rock fragments, and clay minerals. The rounded shape indicates long-term transport and erosion in a river or lacustrine environment.
Uses & applications
Primarily used in construction as aggregate, landscaping, or as garden stones. Smooth pebbles are often used in decorative zen gardens or as painting stones.
Geological facts
The orange-brown staining on the surface is likely limonite or goethite, which forms when iron-bearing minerals inside the rock react with oxygen and water (rusting).
Field identification & locations
Commonly found in riverbeds, glacial deposits, and beaches. Identify it by its grainy texture, rounded edges, and lack of visible crystals or fossils.
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