sedimentary
River Stone (composed of Siltstone/Basalt mixture)
Siltstone or microcrystalline Basalt pebble
Hardness: 5.5-6.5 (Mohs scale); Color: Dark grey to brown with iron oxidation staining; Luster: Dull to matte; Crystal structure: Aphanitic (not visible to naked eye); Cleavage: None visible due to water-worn shape; Specific Gravity: 2.6-3.0
- Hardness
- 5
- Color
- Dark grey to brown with iron oxidation staining
- Luster
- Dull to matte
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Physical properties
Hardness: 5.5-6.5 (Mohs scale); Color: Dark grey to brown with iron oxidation staining; Luster: Dull to matte; Crystal structure: Aphanitic (not visible to naked eye); Cleavage: None visible due to water-worn shape; Specific Gravity: 2.6-3.0
Formation & geological history
Formed either through the deposition and lithification of silt-sized particles or from the cooling of mafic lava, then tumbled and rounded by mechanical weathering in a river or coastal environment. Likely hundreds of millions of years old.
Uses & applications
Used primarily in landscaping, river rock drainage, decorative aquariums, and occasionally as raw material for stone carving or art.
Geological facts
The brown patches on the surface are likely iron-oxide staining (limonite or hematite) resulting from the oxidation of iron-bearing minerals as the rock weathered in a water-rich environment.
Field identification & locations
Identify in the field by its smooth, rounded edges and fine-grained texture. Commonly found in riverbeds, glacial tills, and beaches. Collectors search for unique shapes or those with interesting mineral veins.
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