sedimentary
Siltstone
Siltstone (primarily SiO2, Al2O3)
Hardness: 6-7 on Mohs scale; Color: Gray, brown, or earthy; Luster: Dull/Matte; Structure: Clastic, fine-grained; Cleavage: None (conchoidal fracture possible)
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, brown, or earthy
- Luster
- Dull/Matte
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, brown, or earthy; Luster: Dull/Matte; Structure: Clastic, fine-grained; Cleavage: None (conchoidal fracture possible)
Formation & geological history
Formed from the accumulation and lithification of silt-sized particles (clay and quartz) in low-energy environments like river floodplains, lakes, or deep marine basins.
Uses & applications
Commonly used in construction as fill material or road base; sometimes used for decorative landscaping or as paving stones if durable enough.
Geological facts
Siltstones are intermediate between sandstone and shale. They lack the fissility (layering that splits easily) of shale but have much finer grains than typical sandstone.
Field identification & locations
Identify by its gritty feel on the teeth (finer than sand but coarser than clay) and horizontal sedimentary laminations. Often found in riverbeds and coastal areas.
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