sedimentary
Siltstone with Sandstone Bands
Siltstone (composed of Quartz and Clay minerals)
Hardness: 3-5 Mohs; Color: Gray, brownish-tan; Luster: Dull/Earthy; Texture: Fine-grained with visible layering; Cleavage: None (friable)
- Hardness
- 3-5 Mohs
- Color
- Gray, brownish-tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-5 Mohs; Color: Gray, brownish-tan; Luster: Dull/Earthy; Texture: Fine-grained with visible layering; Cleavage: None (friable)
Formation & geological history
Formed from the deposition and lithification of silt and fine sand in low-energy aquatic environments such as river floodplains, deltas, or lakes over millions of years.
Uses & applications
Primarily used as fill material in construction or as low-quality building stone; occasionally used for garden landscaping.
Geological facts
Siltstone is intermediate between sandstone and shale. If individual grains are too small to be seen with the naked eye but feel gritty against the teeth, it is likely siltstone.
Field identification & locations
Look for distinct layering or 'bedding' and a gritty feel. Commonly found in sedimentary basins and along riverbanks where ancient sea levels have shifted.
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