sedimentary
Gravel/Common Siltstone
Siltstone (fine-grained siliciclastic sedimentary rock)
Hardness: 3-5 (Mohs); Color: Grey, greenish-grey; Luster: Dull/Earthy; Crystal structure: Clastic (microscopic grains); Cleavage: None/Irregular fracture; Specific gravity: approx. 2.6
- Hardness
- 3-5 (Mohs)
- Color
- Grey, greenish-grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-5 (Mohs); Color: Grey, greenish-grey; Luster: Dull/Earthy; Crystal structure: Clastic (microscopic grains); Cleavage: None/Irregular fracture; Specific gravity: approx. 2.6
Formation & geological history
Formed from the lithification of silt-sized particles deposited in low-energy environments like river floodplains, lagoons, or deep water. Often associated with geological ages spanning hundreds of millions of years.
Uses & applications
Primarily used as construction aggregate, road base material, or fill. Low value for jewelry or specimen collecting.
Geological facts
Siltstone is intermediate between sandstone and shale; it has smaller grains than sandstone but lacks the fissility (easy splitting) of shale.
Field identification & locations
Identify by its gritty feel on the teeth (compared to smooth shale) and lack of visible grains to the naked eye. Extremely common in sedimentary basins worldwide.
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