sedimentary
Siltstone
Siltstone (Detrital Clastic Sedimentary Rock)
Hardness: 3-5 Mohs; Color: Tan, brown, or buff; Luster: Dull/Earthy; Texture: Fine-grained (more grit than clay, smoother than sandstone); Structure: Massive or bedded.
- Hardness
- 3-5 Mohs
- Color
- Tan, brown, or buff
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-5 Mohs; Color: Tan, brown, or buff; Luster: Dull/Earthy; Texture: Fine-grained (more grit than clay, smoother than sandstone); Structure: Massive or bedded.
Formation & geological history
Formed through the lithification of silt-sized particles deposited in low-energy environments such as river floodplains, lagoons, or deep-sea basins. These deposits are typically millions of years old, often dating from the Paleozoic or Mesozoic eras.
Uses & applications
Primarily used in the construction industry as fill material or road base. Some smooth, durable varieties are used as flagstones for landscaping or walkways.
Geological facts
Siltstone is intermediate between sandstone and shale. While it looks like shale, it lacks the 'fissility' or tendency to split into thin, flat sheets. It often preserves delicate ripple marks or trace fossils.
Field identification & locations
Identify in the field by its fine-grained texture that feels slightly gritty when rubbed against teeth but smoother than sandstone. It is globally common, found in almost any sedimentary basin.
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