sedimentary
Siltstone River Rock
Siltstone (composed of silt-sized particles, silicate minerals)
Hardness: 3-6 Mohs; Color: Brown, tan, earthy tones; Luster: Dull or earthy; Structure: Clastic, fine-grained; Cleavage: Generally poor, can be fissile if clay content is high.
- Hardness
- 3-6 Mohs
- Color
- Brown, tan, earthy tones
- Luster
- Dull or earthy
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Physical properties
Hardness: 3-6 Mohs; Color: Brown, tan, earthy tones; Luster: Dull or earthy; Structure: Clastic, fine-grained; Cleavage: Generally poor, can be fissile if clay content is high.
Formation & geological history
Formed through the accumulation and cementation of silt particles in low-energy aquatic environments like river deltas, floodplains, or lakes. This specimen shows significant rounding due to fluvial (river) erosion over many years.
Uses & applications
Used primarily as low-grade construction fill, garden landscaping, or decorative river stones. Occasionally used in cement production.
Geological facts
Siltstone is the bridge between sandstone (coarser) and shale (finer). Large, elongated river stones like this were historically used as primitive grinding stones or anchors.
Field identification & locations
Identify by its gritty texture (finer than sandpaper but rougher than shale) and lack of visible crystalline structure. Found in riverbeds and ancient sedimentary basins worldwide.
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