sedimentary
Siltstone
Siltstone (primarily composed of quartz and clay minerals)
Hardness: 3-4 on Mohs scale; Color: typically buff, grey, or tan; Luster: dull/earthy; Texture: fine-grained (gritty against teeth)
- Hardness
- 3-4 on Mohs scale
- Color
- typically buff, grey, or tan
- Luster
- dull/earthy
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Physical properties
Hardness: 3-4 on Mohs scale; Color: typically buff, grey, or tan; Luster: dull/earthy; Texture: fine-grained (gritty against teeth)
Formation & geological history
Formed by the lithification of silt-sized particles deposited in low-energy environments like river floodplains, lagoons, or deep water basins. Accumulation can occur over millions of years.
Uses & applications
Used as low-grade fill in construction, occasionally for flagstones or decorative landscaping if well-indurated.
Geological facts
Siltstone is often confused with shale, but it lacks the fissility (layering that splits easily) found in shale. It feels grittier than claystone but smoother than sandstone.
Field identification & locations
Identified by its fine grain and lack of visible crystals; the 'teeth test' (nibbling on a piece) reveals a gritty texture compared to smooth clay. Found globally in sedimentary basins.
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